Pathogenicity and virulence of PRRSV: From regulated cell death reprogramming landscape and immune subversion to precision vaccinology

ABSTRACT

PRRSV remains a major challenge because pathogenicity arises from the convergence of rapid viral evolution, immune evasion, and maladaptive host responses rather than from isolated virulence determinants. This review synthesizes evidence from molecular and cellular studies, arguing that recurrent recombination, lineage turnover, and antigenic diversification continuously reshape viral fitness, tissue tropism, and vaccine efficacy. PRRSV suppresses interferon‑driven antiviral programs while rewiring inflammatory signaling and intertwined lytic and non-lytic regulated cell death cascades. The virus induces a phenotypic convergence akin to PANoptosis, notably marked by hyper-inflammatory pyroptotic responses in macrophages, which in turn facilitates immune dysfunction, delays the development of protective immunity, and contributes to persistent infection. We assess emerging intervention strategies, including consensus antigen design, rational attenuation, and nonreplicating platforms such as mRNA and protein nanoparticles. This framework explores regulated cell death pathways as a basis for identifying diagnostic biomarkers and developing precision vaccines for PRRSV.

Introduction

PRRSV as a persistent veterinary challenge

Porcine reproductive and respiratory syndrome virus (PRRSV) remains a major threat to swine health and production and has imposed sustained economic losses on the global pig industry since its emergence in the late 1980s [1–4]. PRRSV is now endemic in most major swine‑producing regions and remains one of the most economically consequential infectious diseases in contemporary pig production. Clinically, infection is classically associated with reproductive failure in sows and respiratory disease in suckling, weaned, and growing pigs [3]. In breeding herds, manifestations include late‑term abortion, premature farrowing, stillbirth, mummified fetuses, weak‑born piglets, delayed return to estrus, and reduced reproductive performance, whereas young pigs commonly develop interstitial pneumonia and respiratory distress and show increased susceptibility to secondary bacterial infection [5]. Highly pathogenic PRRSV variants in Asia have caused severe outbreaks and production losses, making PRRSV a global issue [6]. In Europe, PRRSV-1 persists with notable clinical effects, while North America and parts of Asia struggle with PRRSV-2 due to its genetic diversity and rapid lineage changes, especially the resurgence of Lineage 1 [7–10]. PRRSV exerts a significant and extensively documented economic impact on various production systems. In breeding herds, the economic losses are primarily due to severe reproductive failures and a decrease in the number of weaned piglets. Conversely, in fattening herds, the losses are mainly associated with increased feed costs and elevated morbidity rates among growing pigs [11]. These findings reinforce the view that PRRSV remains a persistent veterinary challenge with major economic consequences for modern pig production.

The persistence and clinical severity of PRRSV are closely linked to its potent immunosuppressive capacity [12]. The virus undermines host innate immunity through multiple molecular mechanisms, among which Nsp5 directly targets STING to suppress the cGAS-STING-IFN antiviral axis [13]. This interaction prevents STING trafficking from the endoplasmic reticulum to the Golgi and interferes with STING’s recruitment of TBK1/IKKε/IRF3 complexes, effectively disabling the host antiviral response [14]. As a result, PRRSV-infected pigs become highly susceptible to co-infections with bacteria, viruses, and parasites, which aggravate disease and complicate clinical management [15]. The immunosuppression also reduces viral clearance and prolongs viremia, creating conditions that favor viral persistence within herds.

Disease severity under field conditions varies widely and is inherently multifactorial [16]. Certain molecular signatures, particularly deletions within the NSP2 hypervariable region, are associated with attenuation and lower viral replication, as exemplified by the reduced virulence of the TJ-F19 strain carrying a 120‑amino‑acid deletion [17]. Identical 30‑amino‑acid deletions in NSP2 can produce markedly different phenotypes. Some strains caused 60% mortality, whereas others were nonpathogenic [18]. Regional variations significantly influence the clinical manifestations of PRRSV infections. The persistent challenge posed by PRRS, despite extensive research efforts over several decades, can be attributed to the intricate interplay among viral, host, and environmental factors. This complexity has hindered the development of universally effective vaccines or antiviral therapies.

Scope of this review

PRRSV virulence emerges from the convergence of viral immune evasion and the strategic reprogramming of Regulated Cell Death (RCD) pathways. This review posits RCD reprogramming as the unifying axis of pathogenesis: by initiating lytic pyroptosis to trigger tissue damage (immunopathology) and subsequently leveraging apoptosis and ferroptosis to facilitate viral persistence and egress, the virus fundamentally subverts host homeostasis. We argue that these RCD-centric processes, which differ in kinetics between PRRSV-1 and PRRSV-2, drive the clinical manifestations of disease and necessitate a shift toward RCD-targeted therapeutic and prophylactic strategies. This review examines each of these dimensions, beginning with molecular mechanisms and progressing through cellular pathology to evolutionary dynamics and vaccinology.

At the molecular level, viral proteins reprogram host cellular processes to support replication. Nsp4 drives CRM1-dependent nuclear export of TRIM28, redirecting this nuclear restriction factor to promote autophagosome formation and viral replication [19]. PRRSV also modulates autophagic flux across infection stages. During early infection, the host regulator MALT1 preserves lysosomal homeostasis and supports autophagosome-lysosome fusion for efficient viral release. During late infection, MALT1 downregulation triggers lysosomal membrane permeabilization and incomplete autophagy that favors persistence [20].

Immune evasion is supported by metabolic reprogramming. PRRSV infection activates a lipid metabolic remodeling cascade that promotes lipid droplet accumulation and supports viral replication [21]. Mitochondrial dysfunction serves as a central hub in host–pathogen interactions. PRRSV-induced mitochondrial DNA release and oxidative stress drive NLRP3 inflammasome activation and IL-1β production in pulmonary macrophages [22]. These observations indicate that the RCD landscape in PRRSV infection extends beyond apoptosis. Early infection is characterized by pyroptotic and, in select models, necroptotic contributions. In virulent infection, CD163-positive PAM depletion and rising viral loads coincide with a shift toward extrinsic apoptosis and M2-like macrophage polarization [23]. The predominance of caspase-3-independent RCD pathways in early infection highlights the multifaceted nature of host cell death responses. RCD landscape analysis provides a provisional framework that links molecular and cellular mechanisms to pathogenesis and precision vaccine development. This approach underscores the manner in which viral adaptation under immune pressure modifies host responses. However, it also recognizes that the formal criteria for coordinated convergence of multi-pathway cell death have not yet been fully delineated in the context of PRRSV infection.

Evolutionary landscapes of virulence

Shifting lineages

The evolutionary dynamics of PRRSV-2 lineages are unlikely to be explained by neutral drift alone, because the repeated emergence and expansion of immune escape variants instead point to strong selective pressure. Current phylogenetic analyses, however, often oversimplify this complexity by treating geographic and temporal patterns as independent variables. Phylogenetic analysis of ORF5 sequences classified PRRSV 2 into 11 genetic lineages and 21 sublineages. The analysis also identified two previously unrecognized lineages in Thailand and South Korea and showed sustained Lineage 1 dominance in the United States for nearly two decades [24]. The evolutionary trajectory of PRRSV-2 was marked by rapid, dominant lineage displacements rather than steady co-evolution. Lineage 1 expanded globally under strong selective pressure rather than neutral genetic drift. The rapid resurgence of L1C.5 illustrates the pace of this epidemiological shift [24].

A pronounced shift occurred as Lineage 1 progressively replaced Lineage 8 as the dominant circulating strain in China. The proportion of Lineage 1 sequences rose from 0.49% in 2011 to 71.20% in 2020, while Lineage 8 declined from 84.95% to 21.91% [14,25,26]. This displacement suggests that Lineage 1 variants possess refined mechanisms for host-cell entry and innate immune evasion, granting them a competitive advantage in environments where the ancestral Lineage 8 strains were constrained by the selective pressure of existing herd immunity. Since 2013, this transition has been characterized by the emergence of NADC30-like strains as the predominant form, replacing the highly pathogenic PRRSV (HP-PRRSV) variants that had prevailed in earlier phases of the epidemic [27]. Field surveillance confirmed Lineage 1 dominance in 60% of samples and 61% of farm batches; sublineages 1.5 and 1.8 accounted for 5.4% and 54.6% of Lineage 1 sequences, respectively. By 2021, Lineage 1 prevalence reached 92.75%. After the African swine fever (ASF) outbreak, NADC30-like strains showed reduced interprovincial transmission, whereas NADC34-like strains displayed clear interprovincial spread and evidence of foreign importation [7].

Recombination serves as a potent evolutionary mechanism for PRRSV-2, facilitating the swift acquisition of antigenic diversity beyond the capabilities of standard genetic drift. Through the rearrangement of genomic segments, the virus produces mosaic variants capable of evading neutralizing antibody responses and innate immune checkpoints, such as those directed against the GP5-M complex. This process enables the virus to sustain a fitness advantage within vaccinated populations, where ancestral strains are quickly recognized and neutralized. PRRSV-AH1 was identified as a novel chimera with a NADC30-like backbone that incorporated sequences from CH-1a-like (lineage 8), JXA1-like (lineage 8), and QYYZ-like (lineage 3) strains through six breakpoints grouped into three functional regions, including insertions in ORF1 and ORF1b; this strain elicited intermediate febrile responses compared with classic NADC30-like and highly pathogenic JXA1 strains, suggesting enhanced virulence [27]. Likewise, discordant phylogenetic placements between ORF5 and whole-genome sequences in US isolates such as UIL21-0712 (L1C), USA-NE-26342–1 (L1H), and USA-OK-27915–12 (L1E) were attributed to recombination events affecting ORF2-ORF7, with UIL21-0712 showing an ORF5 largely derived from L1C while other genomic segments reflected contributions from L1A [28]. In China, complex recombination patterns occur among five major lineages (1.5, 1.8, 3, 5, and 8.7), with Lineage 1.8 emerging as the predominant strain (48.5% of positive samples). Recombination hotspots are consistently identified in the ORF2-ORF3 region and often involve vaccine-related strains such as HP-PRRSV JXA1 [29]. The first L1B PRRSV strain reported in China, HLJDZD55, was characterized as a recombinant containing a Chinese L1C major parental backbone and a United States L1B minor parental contribution, with a recombination breakpoint located in ORF2a at nucleotide 12,074 [22].

Substitution rate estimates supported the rapid expansion of sublineage 1.8 in China. Glycosylation patterns also varied substantially across sublineages, consistent with ongoing immune‑driven diversification [22]. In Japan, a major shift occurred from endemic Cluster III (Lineage 4) to vaccine-associated Cluster II (Lineage 5) and virulent Cluster IV/Lineage 1F strains. By 2018–2020, Clusters II and IV predominated nationwide, a change strongly linked to modified live virus (MLV) vaccination. This transition coincided with a decline in Cluster III prevalence from 71% in 2007–2008 to 7.8–12.1% and a reduction in nucleotide identity among Cluster III isolates from 95.7% to 91.2%, indicating ongoing genetic divergence [30]. The first detection of NADC34-like strains in Japan occurred in 2024; these strains shared 90.9–92.9% nucleotide identity with US reference strains and displayed characteristic RFLP patterns [30,31].

High genetic diversity in the United States was quantified through the analysis of more than 25,000 ORF5 sequences, from which 118 genetic variants were identified. A median of 48 active variants per year and an average of 19 newly emerging variants annually were documented. Variant designation was defined by the presence of at least five sequences, strong phylogenetic support with bootstrap values above 85, and more than 2% genetic distance from the nearest variant. The mean within variant distance was estimated at 2.4%, whereas the mean distance to the nearest variant was 4.9% [32]. Predictive modeling employing the local branching index (LBI) effectively anticipated the L1C-1–4-4 outbreak by detecting early signs of population expansion. This achievement emphasizes that these variants do not emerge randomly; rather, their prevalence is a clinical consequence of effective “immune navigation.” Variants possessing advantageous mutations, especially within GP5 antigenic epitopes, are preferentially selected for swift spatial proliferation. This underscores the direct connection between viral evolution and the inadequacy of host-population control strategies. Variants exhibiting a greater GP5 amino acid divergence from prevalent strains demonstrated a 14.5-fold increase in the likelihood of spatial expansion [33]. In China, recombination patterns have undergone a clear temporal transition, with Lineage 8 strains dominating earlier events and Lineage 1 NADC30‑like strains later becoming the major recombination partners of Lineage 3 strains. Spatial transmission analysis identified Guangdong and Henan provinces as major viral exchange hubs linking northern and southern regions, and highlighted Hubei, Shanxi, and Jiangsu as emerging viral aggregation sites.

Genomic determinants of pathogenicity

Although deletions in NSP2 are used to classify lineages, their ability to predict virulence remains disputed. Reports of identical deletions producing markedly different pathogenic outcomes highlight limitations of current genotype–phenotype models and argue for systems-level approaches that integrate multiple genetic determinants [34]. These deletions also reshape replication kinetics and cell tropism, as removal of amino acids 323 to 521 from the hypervariable region of the JXwn06 strain eliminated infectivity in PAMs but retained replication in MARC 145 cells [18]. Site‑directed mutagenesis identified critical residues at NSP2 positions 893 and 979 that substantially changed infection efficiency on PAMs, with mutations at these sites markedly altering in vitro replication profiles [10]. Conversely, animal studies suggest that the discontinuous 30‑amino‑acid deletion in HP PRRSV NSP2 at residues 481 and 533 to 561 is not in itself a determinant of increased virulence, because reciprocal NSP2 exchange in chimeric viruses did not produce consistent shifts in piglet pathogenicity [18]. Rather than acting alone, NSP2 contributes to pathogenicity through interactions with structural proteins. Nsp2TF deubiquitinates GP5 and M via its PLP2 domain, preventing their proteasomal degradation and promoting GP5-M dimer formation required for virion assembly [35].

Polymerase fidelity and replication complex components are key modulators of pathogenicity. Nonstructural protein 11 plays a pivotal role through its endoribonuclease activity by decreasing host HDAC2 protein levels without altering transcript abundance. This modulation diminishes the activity of interferon-stimulated antiviral effectors, including ISG15, ISG54, and ISG56, thus facilitating viral replication. The catalytic residues His129, His144, and Lys173 are essential for this effect [36]. Likewise, nsp12 acts as a multifunctional hub that promotes autophagy-dependent degradation of host restriction factors such as PSMA2, and its cytoplasmic colocalization supports a role in undermining cellular antiviral defenses [37]. Programmed ribosomal frameshifting enables temporal control of nonstructural protein stoichiometry, with frameshifting efficiency at the nsp2 site increasing during infection and with newly identified ORF1b subgenomic RNAs contributing to the fine regulation of nsp10 to nsp12 expression at later stages [38].

Structural glycoproteins, especially the GP5-M heterodimer, have central roles in determining cellular tropism and cytopathogenicity, whereas mutations within GP5 antigenic epitopes and functional domains can directly modulate viral entry and immune evasion [39]. Virulence‑associated substitutions at GP5 residues 13 and 151 are recurrent features of highly pathogenic strains, with JXA1 HP PRRSV retaining arginine at both positions, whereas most other lineages carry glutamine at residue 13 and lysine at residue 151 [34]. N-glycosylation sites at GP5 positions 35, 37, 38, 46, and 53 modulate pathogenicity, and the addition of an asparagine at position 35N or deletion at 46N facilitates immune evasion [39]. The stability of the GP5–M heterodimer is a key determinant of virion integrity, and mutations in M together with variation in the hypervariable regions of GP5 can reshape epitope orientation in ways that reduce antibody binding without necessarily altering the primary peptide sequence [40].

Recombination acts as a potent virulence catalyst under immune selection pressure, producing mosaic genomes through inter‑subgroup exchange. Whole-genome analyses have demonstrated a transition from straightforward intra-subgroup recombination to more intricate inter-subgroup recombination in Chinese PRRSV. Additionally, these analyses have identified recombination events between field strains, such as NVDC-FJ, and vaccine strains, including PRRSV1-CN-FJFQ-1-2023, which illustrate the phenomenon of immune-driven mosaic formation wherein immune selection pressures in vaccinated herds selectively fix novel chimeric genomes. This mosaicism is driven mechanically by RNA-dependent RNA polymerase template-switching during co-infection, allowing the virus to swap structural blocks like GP5 to evade neutralizing hyperimmune sera while preserving replication fitness through optimized nonstructural backbones [39]. Distinct pathogenicity profiles in recombinant viruses such as PRRSV2 CN G8 2018 and FJLIUY2017 appear to be linked to these specific combinations of nonstructural protein regions acquired during recombination, as FJLIUY2017 was associated with more severe disease following the incorporation of multiple highly pathogenic PRRSV‑derived regions and a specific NSP9 residue configuration, whereas PRRSV2 CN G8 2018 showed more moderate disease in association with a more limited recombination pattern and an alternative NSP9 residue combination [41]. The N1 strain illustrates the complexity of triple‑lineage recombination, with multiple breakpoints reshaping genomic regions spanning Nsp1 to Nsp4, Nsp7, Nsp9, Nsp12, ORF3 and ORF5, and with this mosaic architecture being associated with severe clinical manifestations and prolonged viremia [42]. Such recombination is likely driven by template switching mediated by the RNA‑dependent RNA polymerase encoded by nsp9 during viral replication, particularly in the generation of structural subgenomic mRNAs [43]. Consequently, the occurrence of multi-lineage co-infection in vaccinated herds seems to promote the emergence of novel recombinant strains exhibiting GP5 antigenic variation. This phenomenon potentially undermines vaccine cross-protection and reduces the efficacy of neutralization by hyperimmune sera developed against predominant vaccine strains [41].

Recombination and virulence emergence

Recombination is a key driver of virulence emergence in PRRSV, especially under the stronger immune selection pressure present in PRRSV-2 vaccinated herds, where field evolution produces mosaic genomes and only environmentally adapted variants persist under genetic and selective constraints (Table 1) [44]. Field genomic analyses detected multiple recombination events, including six among ninety selected PRRSV strains, with two occurring in Chinese PRRSV-1 strains [45]. Phylogenetic analysis indicated that NVDC NM1 was derived mainly from LNEU12 with a secondary contribution from BJEU06 1 2006, whereas HU18861 2016 originated primarily from JB15 E M17 JB with HU18755 2016 as the minor parental contributor, and all six recombinant strains clustered within or near the Amervac‑like spectrum [45]. It is noteworthy that certain recombinant PRRSVs demonstrated increased virulence compared to one or both of their parental strains. It is crucial to acknowledge that the phenotypic outcomes of recombination are highly contingent upon specific contexts. Notably, the replication kinetics observed in vitro frequently do not consistently align with the pathogenicity observed in vivo. This discrepancy underscores the limitation of extrapolating laboratory-based replication data to accurately evaluate the virulence of recombinant strains within natural host environments [45,46].

Table 1.

Evolutionary and genomic determinants that shape PRRSV virulence emergence.

Determinant	Evidence in manuscript	Mechanistic implication	Pathobiological consequence	Key caution
Lineage displacement	Selective replacement of Lineage 8 by Lineage 1 in China, with rapid turnover also noted in the United States and Japan.	Indicates recurrent selection on fitness, transmission, and antigenic phenotype.	Reshapes the epidemiological background and weakens stable genotype to phenotype inference.	Virulence should be viewed as a moving population property, not a fixed strain trait.
Recombination hotspots	Breakpoints cluster in ORF2 to ORF3 and selected nonstructural regions, especially nsp2-linked segments.	Template switching can reassemble entry, antigenic, and replication modules.	Generates mosaic strains with altered pathogenicity, tissue tropism, and immune escape.	Hotspot location is informative but does not predict phenotype on its own.
Vaccine related recombination	Field surveillance identifies mosaics containing vaccine related backbones or segments.	Co circulation under immune pressure increases opportunities for mosaic genome formation.	Can erode field protection and complicate interpretation of virulence emergence.	A vaccine like sequence alone does not prove reversion to virulence.
NSP2 context dependence	Similar NSP2 deletions or substitutions can produce discordant replication and virulence phenotypes.	NSP2 acts as a context-dependent virulence modulator shaped by genomic background and host setting.	Explains why single marker models perform poorly for virulence prediction.	Avoid treating NSP2 signatures as standalone virulence markers.
Replication complex factors	nsp11, nsp12, ribosomal frameshifting, and altered nonstructural protein stoichiometry are linked to replication efficiency and immune antagonism.	Replicase configuration shapes viral fitness and escape from host restriction.	Can promote persistence and indirectly amplify pathogenicity.	Nonstructural determinants deserve equal emphasis alongside envelope variation.
Structural glycoprotein variation	GP5 and the GP5 M heterodimer vary in glycosylation, epitope exposure, tropism, and antibody sensitivity.	Envelope remodeling alters receptor engagement and neutralization susceptibility.	Links antigenic drift to vaccine mismatch and biological divergence.	Envelope change is important but not sufficient alone to explain phenotype.
Predictive epidemiological metrics	Large ORF5 datasets, variant growth analyses, local branching index, and GP5 divergence are associated with spread.	Phylodynamic signals may identify rising variants before broad detection.	Improves surveillance based risk assessment of emergence and dissemination.	These metrics are probabilistic and require phenotypic validation.

Molecular strategies of immune evasion

Interferon antagonism

PRRSV evades innate immunity through a multilayered mechanism in which Nsp5‑mediated degradation of RLR signaling components appears to be a major axis, while Nsp1β and Nsp11 contribute additional suppression of antiviral signaling through complementary mechanisms [26]. The temporal coordination among these mechanisms, especially the switch from sensor suppression to blockade of downstream signaling, remains poorly understood. This kinetic blind spot mirrors a parallel ambiguity in host cell death subversion; specifically, the precise molecular trigger that orchestrates the metabolic and enzymatic shift from early anti-apoptotic preservation to late pro-apoptotic execution remains unmapped. Rather than a passive consequence of cellular exhaustion, this biphasic transition likely represents an actively regulated viral checkpoint, wherein a critical threshold of structural protein accumulation overrides early innate survival signaling to optimize viral egress. By targeting RIG‑I through complementary mechanisms that include promoting its K48‑linked ubiquitination and proteasomal degradation and disrupting the TRIM25–RIG‑I activation complex through ZCCHC3 hijacking [47], nonstructural protein 5 broadly suppresses RIG‑I‑like receptor signaling by promoting autophagy–lysosome‑dependent degradation of key signaling components, including RIG‑I, MDA5, MAVS, TBK1, IRF3, and IRF7. Nsp5 is localized to the endoplasmic reticulum, where it facilitates reticulophagy by interacting with the ER-phagy receptor FAM134B, consequently promoting the selective degradation of proteins involved in the RLR signaling pathway [26]. In addition, PRRSV Nsp4 cleaves mitochondrial antiviral signaling protein (MAVS), and Nsp11 suppresses interferon activation by cleaving MAVS mRNA via its endoribonuclease domain [48].

Beyond evading sensors, PRRSV blocks downstream interferon signaling pathways. Nsp1b impedes interferon-induced JAK/STAT signaling through the degradation of karyopherin-α1, which in turn obstructs the nuclear translocation of STAT1 and significantly diminishes the expression of interferon-stimulated genes (ISGs) [49]. Nsp11 disrupts interferon signaling by targeting interferon regulatory factor 9 (IRF9), but not STAT1 or STAT2, impairing the formation and nuclear translocation of the ISGF3 transcriptional complex [50]. During PRRSV infection, upregulated METTL3 promotes selective degradation of IKKε by enhancing K63‑linked ubiquitination and coupling IKKε to SQSTM1‑dependent selective autophagy, with this effect being strengthened through METTL3‑mediated m6A modification of SQSTM1 (Figure 1) [51].

Figure 1.

Multilayered PRRSV immune evasion mechanisms. (A) Schematic overview of major innate antiviral pathways in uninfected porcine alveolar macrophages. These pathways include RIG‑I-like receptor signaling, the cGAS–STING axis, and interferon‑dependent JAK–STAT signaling. (B) PRRSV‑infected cells show extensive disruption of host antiviral defense by viral proteins. Nsp5, Nsp4, Nsp1β, Nsp11, and GP2a target distinct but interconnected signaling nodes to weaken innate immune responses. (C) At the molecular level, Nsp5 promotes FAM134B‑dependent reticulophagy and drives degradation of RIG‑I-like receptor signaling components. Nsp4 cleaves MAVS and targets DHCR24. Nsp1β induces degradation of karyopherin α1 and prevents STAT1 nuclear translocation. Nsp11 targets IRF9 and promotes cleavage of MAVS mRNA. GP2a enhances RIG‑I ubiquitination and redirects the TRIM25–RIG‑I complex through ZCCHC3. (D) These immune evasion events are temporally coordinated. Early infection is characterized by suppression of viral sensing, whereas later stages are dominated by blockade of downstream interferon signaling.

Protease and deubiquitinase functions

PRRSV uses multiple protease-driven mechanisms to evade host immunity, and Nsp4 protease activity plays a central role in disrupting interferon signaling. Nsp4 specifically targets the FAD domain of DHCR24, leading to an upregulation of DHCR24 expression in vitro [52,53]. This interaction results in elevated cellular cholesterol levels and inhibits IRF3 phosphorylation in PK-15 and MARC-145 cell lines [52]. The investigations elucidating this mechanism were performed using immortalized cell lines (PK-15, MARC-145, and HEK293T); however, it remains untested whether Nsp4 influences DHCR24 modulation and cholesterol synthesis in primary porcine alveolar macrophages, which are the natural target cells of PRRSV. Site-directed mutagenesis resulting in the deletion of the DHCR24 FAD domain eliminated its ability to enhance cholesterol levels in transfected cells [52,53]. While this domain-level analysis offers mechanistic insights, it fails to definitively prove DHCR24 as a relevant virulence factor in vivo. This is due to two main reasons: primary macrophages regulate cholesterol differently than immortalized epithelial cells, and possible compensatory mechanisms in the host that might maintain cholesterol balance have not been assessed [52,53].

Host defense mechanisms counteract viral replication through targeted ubiquitination pathways. LGALS3BP recruits the Cullin3 E3 ubiquitin ligase via its BACK domain to mediate site‑specific ubiquitination of nsp12 at lysine 91 (K91), triggering proteasomal degradation of this viral RNA-dependent RNA polymerase [54]. This degradation pathway is proteasome dependent, as MG132 (a proteasome inhibitor) completely blocked degradation, whereas 3-MA (an autophagy inhibitor) did not [54]. The K91R mutation in nsp12 rendered the protein resistant to LGALS3BP‑mediated degradation. Domain analysis showed that this effect depended specifically on the BACK domain of LGALS3BP, whereas the SRCR and BTB domains were dispensable for nsp12 ubiquitination and the resulting suppression of viral subgenomic RNA synthesis [54]. Together, these results indicate the formation of a ternary complex of LGALS3BP, Cullin3, and nsp12 that directly impairs viral replication via the ubiquitin–proteasome system [54].

Evasion of cGAS-STING signaling

PRRSV employs multiple strategies to antagonize STING-centered innate immune signaling [13]. Although cGAS is classically activated by cytosolic DNA, the evidence presented here most directly supports interference at the level of STING rather than definitive disruption of canonical cGAS activation [55]. Recent data suggest that Nsp5 sequesters STING at the endoplasmic reticulum, inhibiting its trafficking to the Golgi apparatus and the formation of puncta. This sequestration subsequently impairs the recruitment of TBK1, IKKε, and IRF3, leading to a reduction in interferon production [13]. The failure to recover viable recombinant viruses lacking Nsp5 residues 36–47 or 58–67 suggests that these regions contribute both to immune antagonism and to viral fitness. Beyond directly targeting STING, PRRSV broadly suppresses downstream activation of interferon regulatory factors (IRFs) [56]. PRRSV employs a multi-layered defense system to suppress the interferon response, using proteins like NSP1β, NSP2, NSP11, and the nucleocapsid (N) to inhibit IRF3 activity. This redundancy, along with NSP7’s suppression of IRF7, ensures that any host DNA-sensing signals are intercepted at various points. This strategy effectively maintains an immunosuppressive environment, allowing the virus to persist despite host defenses [56]. PRRSV subverted innate immunity through disruption of upstream pathogen‑sensing pathways, with NSP4 and NSP11 suppressing RIG‑I and MDA5 signaling and NSP1α driving degradation of the transcriptional coactivator CBP, weakening IRF‑mediated interferon responses [57].

Viral nonstructural proteins exploit host post-translational modifications to undermine innate immunity (Table 2). The PLP2 domain of nsp2 uses deubiquitinating activity to abrogate NF-κB signaling, while nsp11 employs its endoribonuclease activity to cleave critical immune transcripts. In parallel, the nsp4 D185N mutant shows attenuated replication but induces higher type I interferon (IFN-I) responses than the wild-type virus. Structural analyses of nsp2 indicate that the abrogation of its deubiquitinating activity, while preserving wild-type replication kinetics, leads to an over tenfold elevation in IFN-B mRNA levels. Nevertheless, interpreting this transcriptional increase as a comprehensive restoration of host immunity requires caution. This augmentation signifies a localized alleviation of transcriptional repression rather than a complete functional reestablishment of the host antiviral response. Given that PRRSV employs a highly redundant array of independent immune antagonists, including nsp1β, nsp4, and nsp11, the downstream translation, signaling kinetics, and actual protective efficacy of this induced interferon remain significantly constrained, even when a single viral enzymatic site is disrupted [58]. These findings demonstrate the complex mechanisms by which PRRSV evades nucleic acid-sensing pathways, ultimately leading to the suppression of interferon responses.

Table 2.

PRRSV immune evasion modules, host targets, and downstream biological consequences.

Viral factor or module	Primary host target or pathway	Mechanistic action	Biological consequence	Interpretive note for the review
GP2a	RIG I activation complex including TRIM25 and ZCCHC3 related machinery	Promotes RIG I ubiquitination and disrupts productive sensor activation.	Suppresses upstream interferon induction and weakens early antiviral sensing.	Useful as an example of structural protein mediated innate antagonism, not only nonstructural protein-driven suppression.
nsp5 reticulophagy axis	RIG I, MDA5, MAVS, TBK1, IRF3, IRF7 through FAM134B-dependent ER phagy	Induces reticulophagy and drives autophagy lysosome-dependent degradation of multiple RLR pathway components.	Produces broad collapse of antiviral signaling and supports persistence.	This is the central immune evasion node in the manuscript and should appear as the anchor row.
nsp4 protease	MAVS and DHCR24-linked antiviral control	Cleaves MAVS and manipulates host lipid associated signaling through DHCR24, thereby suppressing IRF3 activation.	Blunts interferon production while favoring a cellular state that supports replication.	A comparative row can clarify that nsp4 acts through more than one host interface.
nsp11 endoribonuclease	MAVS mRNA, IRF9, and selected immune transcripts	Cleaves immune related transcripts and interferes with ISGF3 formation via IRF9 targeting.	Suppresses both induction and execution arms of the interferon response.	This dual role makes nsp11 particularly relevant to attenuation strategies discussed later.
nsp1β and related JAK STAT blockade	Karyopherin α1, STAT1 nuclear translocation, ISG expression	Destabilizes transport machinery needed for interferon activated transcriptional responses.	Reduces the cell’s ability to translate interferon exposure into an antiviral state.	This row helps distinguish sensor antagonism from downstream signaling blockade.
METTL3-driven host autophagy coupling	IKKε and SQSTM1 selective autophagy pathway	Enhances K63-linked ubiquitination and selective autophagic turnover of IKKε.	Further reduces interferon signaling through host factor co option rather than direct viral proteolysis.	This row elevates the review by integrating virus induced host remodeling into the immune evasion narrative.
STING centered antagonism	STING trafficking, Golgi translocation, TBK1, IKKε, IRF3 recruitment	Sequesters STING at the endoplasmic reticulum and prevents productive signalosome assembly.	Restrains DNA sensing associated antiviral outputs and reinforces broad innate paralysis.	The manuscript is appropriately cautious that evidence most strongly supports STING interference rather than canonical cGAS blockade per se.
PLP2 deubiquitinase activity of nsp2	NF-κB-linked signaling and post translational immune regulation	Removes activating ubiquitin signals needed for effective innate pathway propagation.	Dampens inflammatory and antiviral signaling while contributing to replication fitness.	This row is important because it connects enzymatic function to attenuation logic.
NSP7 and NSP1α associated transcriptional suppression	IRF7 and CBP related transcriptional control nodes	Suppresses transcriptional co activators and interferon regulatory factors needed for antiviral gene expression.	Expands immune evasion beyond one pathway into a layered network of transcriptional shutdown.	A table format prevents these contributors from being lost in the text.

Cell death reprogramming in PRRSV infection

Apoptotic switching

PRRSV infection is characterized by temporal reprogramming of apoptosis, in which early anti‑apoptotic activity preserves a permissive environment for viral replication, whereas later pro‑apoptotic induction supports viral dissemination [59]. In the initial phase of infection, PRRSV actively suppresses host-cell apoptosis to preserve a stable environment for replication. Experimental evidence shows that porcine IFI30 (GILT) has an anti-apoptotic effect in MARC-145 cells, significantly reducing apoptosis compared to controls after PRRSV exposure. IFI30, a lysosomal thiol reductase, aids antigen processing by reducing disulfide bonds in acidic compartments. The anti-apoptotic mechanism of IFI30 during PRRSV infection is not fully understood but may involve maintaining lysosomal membrane integrity or altering caspase activation thresholds. The impact of IFI30 is proviral, as it inhibits premature host-cell apoptosis, consequently prolonging the period available for viral replication. This is evidenced by increased apoptosis and reduced viral replication in IFI30 knockdown experiments in porcine ST cells. Thus, IFI30 promotes PRRSV propagation by suppressing apoptosis and prolonging cell viability, rather than directly enhancing viral transcription. Consistent with this model, IFI30 knockdown in porcine ST cells increased apoptosis to 25.48% compared with 11.46% in negative controls and concomitantly reduced viral replication, confirming that IFI30-mediated apoptosis suppression is functionally required for efficient PRRSV propagation during early infection (Figure 2(A)) [60].

Figure 2.

PRRSV reprograms apoptosis over time and induces RTC–dTGN NLRP3‑dependent pyroptosis in porcine alveolar macrophages. (A) During early infection, IFI30 restrains caspase activation and supports a replication‑permissive state. Loss of IFI30 increases apoptosis and promotes viral replication. During late or persistent infection, apoptosis shifts toward full execution and may facilitate viral release and spread. Soluble Fas reflects this temporal transition and is reduced in vaccinated piglets. (B) PRRSV induces pyroptosis through an RTC‑linked pathway. The viral replication–transcription complex forms on endoplasmic reticulum‑derived membranes with TMEM41B and intermediate filaments and promotes trans‑Golgi network fragmentation into dispersed vesicles that support NLRP3 clustering. PRRSV nsp2 enhances inflammasome assembly, leading to Caspase 1 activation, GSDMD cleavage, inflammatory mediator release, and lytic cell death. In vivo findings support this pathway, and disruption of TMEM41B or intermediate filaments suppresses these responses.

As infection progresses, PRRSV shifts toward pro-apoptotic execution, particularly during persistent phases. Clinical observations in unvaccinated piglets show elevated serum soluble Fas (sFas) levels, which indicate apoptotic suppression early in infection but shift to a pro-apoptotic state as viral load increases. A statistically significant positive correlation exists between PRRSV viral load and Fas levels (r = 0.639, p < 0.0001) [61]. This late‑stage pro-apoptotic shift is supported by age-dependent increases in sFas levels during persistent infection, implicating apoptosis in viral egress. In contrast to their unvaccinated counterparts, vaccinated piglets demonstrate reduced Fas expression. This is attributed to vaccine-derived antibodies, which limit infection and attenuate lymphocyte-mediated cytotoxicity, consequently modifying the apoptotic trajectory. The interaction between PRRSV and apoptotic pathways also affects innate immune regulation, since the virus disrupts cellular innate responses through mechanisms tied to apoptosis control. This biphasic control of apoptosis highlights the precise reprogramming of host cell death pathways by PRRSV, whereby early suppression preserves a permissive replication environment and later induction supports viral dissemination.

Pyroptotic inflammation

HP-PRRSV-2 infection strongly triggers pyroptosis, a type of inflammatory cell death marked by gasdermin D pore formation, cell swelling, membrane rupture, and the release of proinflammatory cytokines like IL-1β and IL-18 [62,63]. It is still unclear if this pyroptotic response is consistent across all PRRSV strains, including PRRSV-1, attenuated PRRSV-2 variants, and low-pathogenicity strains [64]. Inflammasome sensor proteins, such as NLRP3, are responsible for detecting cellular stressors and subsequently recruiting the adaptor protein ASC to activate caspase-1 [65]. Upon activation, caspase-1 cleaves pro-IL-1β and pro-IL-18 into their mature cytokine forms. Additionally, caspase-1 cleaves GSDMD, releasing its N-terminal pore-forming fragment (GSDMD-N) [66]. GSDMD-N pores promote the release of IL-1β, IL-18, and DAMPs, boosting inflammation [67].

HP-PRRSV-2 infection induces pyroptosis in both cell culture and in vivo. Infection of PAMs and MARC-145 cells with HP-PRRSV-2 produced GSDMD-mediated pyroptosis, as shown by lactate dehydrogenase (LDH) release, cell swelling, and secretion of mature IL-1β and HMGB1 [64]. This mechanism was supported in a controlled pig challenge study using a single HP-PRRSV-2 strain, in which lung tissues displayed strong caspase-1 activation, GSDMD cleavage, and elevated IL-1β in serum and bronchoalveolar lavage fluid [64]. These in vivo findings establish pyroptosis as a feature of HP-PRRSV-2 pathology, but they do not establish whether pyroptosis contributes to disease severity in infections with other PRRSV strains [64]. Mechanistically, infection with PRRSV-2 elicited pyroptosis in a manner dependent on both dose and time, with the viral nonstructural protein 2 (nsp2) identified as the principal factor driving the activation of the NLRP3 inflammasome [68]. Building on the earlier described nsp2-NLRP3 interaction, it was discovered that the TM domain of PRRSV-2 nsp2 directly binds to the NACHT domain of NLRP3, promoting inflammasome assembly. This IKKβ-dependent dTGN translocation pathway may be particularly relevant in virulent PRRSV-2 infection. However, direct comparative in vivo evidence across highly pathogenic strains, attenuated strains, and PRRSV-1 isolates remains limited [69].

The upstream trigger of this cascade is the PRRSV replication-transcription complex (RTC), which initiates disassembly of the trans-Golgi network (TGN) into dispersed vesicles (dTGN) [64]. The dTGN serves as a phosphatidylinositol-4-phosphate (PtdIns4P)-dependent scaffold that promotes NLRP3 aggregation into multiple puncta, leading to inflammasome activation. The formation of RTC relies on the host factor TMEM41B and is encircled by an intermediate filament network. Disruption of RTC assembly through TMEM41B knockdown or inhibition of intermediate filaments using withaferin A significantly diminishes GSDMD cleavage, LDH release, and IL-1β secretion. These findings support an RTC–dTGN–NLRP3 axis as a major contributor to PRRSV‑induced inflammatory cell death (Figure 2(B)). They also suggest that therapeutic targeting of inflammasome activation or RTC assembly warrants preclinical evaluation [64].

Ferroptotic vulnerability

PRRSV induces metabolic vulnerability in PAMs by promoting oxidative stress, depleting the glutathione antioxidant system, and increasing ferrous iron and lipid peroxidation [70,71]. This is a strategic metabolic shift, as the virus alters lipid metabolism by downregulating fatty acid synthase and activating PPARγ, leading to increased lipid droplet storage. This approach minimizes free fatty acid toxicity and provides the necessary lipid structures for viral envelope assembly, demonstrating how the virus leverages metabolic stress to enhance its life cycle [72,73]. This oxidative profile accompanies reduced expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and glutathione peroxidase 4 (GPX4) and increased expression of Kelch-like ECH-associated protein 1 (Keap1) and acyl-CoA synthetase long-chain family member 4 (ACSL4) during infection [72]. Although transferrin receptor 1 (TfR1) expression was assessed in infected cells, no significant differences were found among groups, suggesting that PRRSV-driven ferroptosis may not depend on TfR1-mediated iron uptake [72].

An unresolved but significant observation is that PRRSV infection causes lipid droplets (LDs) to accumulate in PAMs via YY1-mediated transcriptional changes. Inducing LDs with oleic acid reduced viral protein levels and titers, and PPARγ activation by rosiglitazone inhibited viral replication. This antiviral lipid buildup contrasts with the pro-ferroptotic oxidative environment, as LDs sequester polyunsaturated fatty acids, potentially reducing ferroptotic sensitivity. However, PRRSV-infected cells show increased ferroptotic vulnerability. It remains unclear if this is a host response overwhelmed by viral stress or if LDs and ferroptosis function separately or at different infection stages, warranting research [73]. The antiviral mechanism was substantiated by the activation of PPARγ through rosiglitazone, which inhibited viral replication. In contrast, the knockout of PPARγ enhanced viral replication, suggesting that redirecting lipid metabolism toward storage, as opposed to the production of free fatty acids, creates an environment that is unfavorable for viral propagation [73]. Resveratrol mitigated PRRSV-induced ferroptosis by reinstating Nrf2/GPX4 expression and inhibiting Keap1/ACSL4. Additionally, it regulated the interaction between autophagy and ferroptosis via the PI3K/Akt signaling pathway, consequently inhibiting viral replication [72] (Figure 3(A)).

Figure 3.

PRRSV coordinates ferroptosis, autophagic rewiring, and PANoptosis‑related cell death convergence in porcine alveolar macrophages. (A) PRRSV promotes ferroptotic vulnerability by suppressing the Nrf2–GPX4 antioxidant axis and increasing Keap1 and ACSL4, which drives reactive oxygen species accumulation, lipid peroxidation, and ferrous iron overload. In parallel, YY1 reshapes lipid metabolism through FASN suppression and PPARγ activation, leading to lipid droplet accumulation that restricts viral replication. Resveratrol partly reverses these changes and modulates the autophagy–ferroptosis axis through PI3K–Akt signaling. (B) PRRSV initiates autophagy but blocks its completion. Nsp4 promotes TRIM28‑dependent stabilization of the Vps34–Beclin1 complex and supports phagophore formation. Endoplasmic reticulum stress induces FAM134B and drives formation of double‑membrane vesicles that support viral RNA replication. Nsp10 and SNX1 then disrupt RAB7‑dependent trafficking, inhibit autophagosome–lysosome fusion, and protect viral particles from degradation. (C) PRRSV induces features of pyroptosis, apoptosis, and necroptosis, suggesting convergence into a PANoptosis‑related death program. This integration contributes to both antiviral restriction and inflammatory injury, although direct evidence for PRRSV‑induced PANoptosome assembly remains limited.

Autophagic rewiring

PRRSV infection actively rewires autophagic flux to create a cellular environment that favors viral replication while subverting host degradation pathways (Figure 3(B)) [20]. The virus induces endoplasmic reticulum (ER) stress and activates the unfolded protein response (UPR), which leads to upregulation of FAM134B and the formation of double-membrane vesicles (DMVs) that serve as essential replication platforms [74]. PRRSV strategically modulates autophagy at three distinct functional stages to facilitate its replication cycle. In the initial stage, PRRSV appropriates autophagic membranes to establish replication platforms. This process involves FAM134B-mediated fragmentation of the endoplasmic reticulum (ER) within double-membrane vesicles (DMVs), which enhances viral RNA synthesis. Additionally, free fatty acids derived from ER-associated autophagy are repurposed for the assembly of the viral envelope. In the second stage, PRRSV obstructs autophagic degradation through two complementary mechanisms to prevent the lysosomal degradation of viral components. Firstly, nonstructural protein 10 (Nsp10) disrupts the interaction between RAB7, a late endosomal trafficking GTPase, and its effector PLEKHM1, thereby impeding the delivery of autophagic cargo to lysosomes. Secondly, the SNX1 BAR domain competes with PLEKHM1 for binding to RAB7-GTP, further inhibiting microautophagic degradation. Collectively, these RAB7-targeting strategies ensure the protection of viral particles and replication machinery from lysosomal degradation. PRRSV doesn’t just block host degradation; it spatially compartmentalizes it. By allowing early autophagosome–lysosome fusion for lipid sourcing and later inducing lysosomal membrane permeabilization, the virus creates a replication niche, diverting the host’s degradation machinery to aid its release [19].

PRRSV exploits the initial phases of autophagy by manipulating cellular mechanisms. Specifically, the non-structural protein 4 (Nsp4) facilitates the CRM1-dependent translocation of the nuclear restriction factor TRIM28 to the cytoplasm. In the cytoplasmic environment, TRIM28 interacts with and stabilizes the Vps34-Beclin1 complex, which is crucial for the initiation of autophagosome formation. Functionally, Nsp4 transforms TRIM28 from a nuclear repressor into an activator of autophagy within the cytoplasm. The knockdown of TRIM28 results in impaired conversion of LC3-I to LC3-II and a subsequent reduction in autophagosome formation, thereby confirming that the initiation of autophagy induced by PRRSV is contingent upon this nuclear-to-cytoplasmic translocation [19].

Convergent regulated cell death pathways as a potential virulence axis

PANoptosis is defined as an integrated inflammatory cell death program coordinated by PANoptosome complexes that link pyroptosis, apoptosis, and necroptosis (Figure 3(C)) [75]. In the context of PRRSV infection, recent findings from independent studies suggest the involvement of pyroptosis, apoptosis, and, in certain models, necroptosis during severe disease manifestations. This raises the potential for convergence among regulated cell death pathways [76]. However, it remains experimentally undetermined whether these three modalities are concurrently activated within the same cellular or tissue environment, and whether such convergence is orchestrated by a PANoptosome-like complex [76]. The current evidence is insufficient to confirm PANoptosis in a strict mechanistic sense, as a PRRSV-associated PANoptosome and its molecular framework have not been directly demonstrated. This highlights the need for biochemical precision: detecting pyroptosis, apoptosis, and necroptosis biomarkers in cell populations doesn’t prove a single PANoptosome complex in individual cells. Without identifying the specific upstream sensor and biochemical connections during PRRSV infection, linking these outcomes to canonical PANoptosis is speculative. Thus, PRRSV might trigger a parallel, multi-pathway cell death process, potentially aiding viral restriction and causing inflammatory tissue damage.

Immune dysregulation and viral persistence

The persistence of the Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) within the host arises from an integrated failure of the immune system that prevents effective viral clearance. This failure is not a single defect but a cumulative cascade of dysregulation starting from the initial innate recognition and extending to the eventual adaptive response. The virus systematically inhibits innate interferon and cytokine pathways, consequently depriving dendritic cells of essential activation signals. This lack of activation prevents the subsequent upregulation of co-stimulatory molecules and IL-12, leading to poor priming of T cells. Consequently, the adaptive response remains weak and regulatory in nature, allowing the virus to establish persistent infection in lymphoid tissues while evading immune selection pressure. Understanding this failure cascade is essential for developing next-generation vaccines that must simultaneously restore DC function, enhance Th1 responses, and avoid the risks of antibody-dependent enhancement (Figure 4).

Figure 4.

PRRSV-mediated immune dysregulation and viral persistence through macrophage subversion, innate signaling suppression, and adaptive immune hyporesponsiveness. (A) PRRSV reshapes alveolar macrophage polarization in a context-dependent manner and consistently weakens antiviral competence. Although some experimental systems show an M1-like inflammatory profile, broader evidence supports immunoregulatory dysfunction linked to IL‑10, TGF‑β, β, and Arg‑1 and associated with viral persistence. (B) PRRSV antibody immune complexes engage Fcγ receptors and suppress RIG‑I and MDA5-dependent sensing, weakening MAVS, TBK1, and IRF3 signaling, reducing type I interferon production, and promoting viral persistence. (C) PRRSV is associated with adaptive immune hyporesponsiveness with regulatory bias. Effector T cells show reduced functional activity, whereas regulatory signatures become more prominent.

Macrophage dysfunction

Macrophage dysfunction serves as a cornerstone of PRRSV pathogenesis, as these cells are the primary targets for viral replication. By establishing a productive infection within macrophages, the virus directly compromises the cell’s ability to maintain homeostasis and communicate with other immune components. This infection limits the macrophage’s capacity to act as an effective effector cell, often diverting its function to support viral dissemination rather than viral clearance. Furthermore, the persistent infection of macrophages creates a reservoir that protects the virus from systemic immune surveillance and contributes to the chronic nature of the disease. This cellular impairment is exacerbated by the virus’s ability to manipulate macrophage cytokine production, shifting the environment from a pro-inflammatory state toward a more permissive, regulatory milieu that favors viral persistence [12,77].

T‑cell responses: delayed priming, regulatory bias, and impaired memory

The adaptive T-cell response to PRRSV is characterized by a significant delay and functional impairment that distinguishes it from other acute viral infections. While typical viral infections elicit robust T-cell responses within days, PRRSV infection displays a kinetic lag, creating a critical window during which the virus replicates largely unchecked by cell-mediated immunity. CD4+ T-cell responses are notably weak and skewed toward a Th2-biased profile, featuring elevated levels of IL-4 and IL-10 [78]. This imbalance is problematic because Th1 responses, which are driven by IFN-γ-producing CD4+ T cells, are required for effective macrophage activation and the subsequent priming of CD⁸⁺ T cells.

The emergence of these Th1 responses typically coincides with the transition from acute to persistent infection, suggesting that the timing of this priming is a bottleneck for protective immunity. Similarly, the CD⁸⁺ cytotoxic T lymphocyte response remains weak and delayed, with epitope-specific cells remaining at low frequencies for weeks post-infection. This weak response is attributed to a multifactorial failure, including insufficient type I interferon signaling, the depletion of antigen-presenting cells, and the viral antagonism of the immunoproteasome. Recent research suggests that the observed lack of T-cell activity is better described as a functional hyporesponsiveness driven by a regulatory bias rather than classic exhaustion [79]. This bias, marked by increased Treg cell signatures, suggests that therapies targeting Treg modulation may prove more effective than standard checkpoint blockade in restoring T-cell function.

Humoral immunity: delayed antibody responses, neutralization evasion, and antibody-dependent enhancement

Humoral immunity against PRRSV is significantly hampered by delayed antibody production and sophisticated mechanisms of viral evasion. Although binding antibodies are detected relatively early, neutralizing antibodies (NAbs) generally emerge only after 3 to 4 weeks and often remain at low titers throughout the infection. This dissociation between binding and neutralizing responses is a distinctive feature of the virus, largely driven by the architecture of the GP5 protein. The GP5 ectodomain presents a dominant non-neutralizing decoy epitope that effectively distracts the immune system, diverting the humoral repertoire away from the subdominant and shielded neutralizing epitopes [80,81].

This evasion strategy is complicated by the risk of Antibody-Dependent Enhancement (ADE), where sub-neutralizing concentrations of antibodies facilitate the uptake of the virus into macrophages via Fc receptors [82]. Because systemic IgG levels are poor predictors of protection, researchers are shifting focus toward mucosal IgA responses, which correlate more strongly with reduced viral shedding and transmission. However, most current injectable vaccines fail to induce substantial respiratory IgA, representing a significant gap in vaccine-induced immunity. The lack of a reliable immunological correlate of protection remains a major challenge, as neither NAb titers nor IFN-γ levels alone have proven sufficient to predict protective outcomes across diverse studies.

Dendritic cell impairment and the innate–adaptive disconnect

Dendritic cells represent the critical bridge between innate pathogen sensing and adaptive immune priming, yet PRRSV systematically disables these cells to evade detection [83,84]. Although the virus productively infects conventional dendritic cells, it modulates their phenotype rather than inducing massive viral replication, transforming them from immunostimulatory cells into tolerogenic or regulatory antigen-presenting cells. Infected dendritic cells exhibit downregulated co-stimulatory molecules and reduced MHC class II expression, which fundamentally impairs their capacity to activate naive CD4+ T cells.

This functional paralysis is compounded by the suppression of pro-inflammatory cytokines such as IL-12 and TNF-alpha, which are essential for driving effector T‑cell differentiation [85]. By suppressing the NF-κB and MAPK signaling pathways, the virus ensures that the innate immune system fails to provide the necessary instructions for a potent adaptive response. Furthermore, the virus alters proteasome composition and promotes autophagy, which may sequester viral antigens and limit their accessibility for presentation to T cells. Dendritic cell defects cause the innate immune system to detect the virus but fail to trigger an effective adaptive immune response, allowing the virus to survive in the host.

Host genetic determinants of PRRSV susceptibility and resistance

PRRSV pathogenesis is shaped by a dynamic interaction between viral immune evasion and host genetic variation. Susceptibility is not random, but differs among individuals, breeding populations, and experimental genetic backgrounds. Genomic studies have shown that viral load, growth performance, and immune traits after PRRSV challenge are moderately to substantially heritable, supporting the concept that host genetics contributes to disease outcome. These findings have shifted the field from descriptive comparisons among breeds toward a mechanistic framework in which viral entry factors, interferon‑inducible restriction pathways and polygenic immune regulation determine susceptibility, resilience and tolerance.

CD163 as an essential viral receptor and validated target for genetic resistance

PRRSV has a restricted tropism for cells of the monocyte and macrophage lineage. This tropism is largely governed by CD163, a macrophage scavenger receptor that is required for productive infection in susceptible porcine macrophages. Among host factors identified to date, CD163 is the most firmly validated determinant of PRRSV entry and represents the clearest example of receptor based genetic resistance.

The fifth scavenger receptor cysteine rich domain of CD163, known as SRCR5, is central to PRRSV susceptibility. Genome editing experiments have shown that complete CD163 disruption can protect pigs from PRRSV infection under experimental challenge conditions [86–88]. More refined editing strategies that remove or alter the SRCR5 domain have provided an especially important advance, because they preserve much of the physiological function of CD163 while blocking viral infection by tested PRRSV strains. These studies demonstrate that targeted receptor editing can uncouple antiviral resistance from broad loss of macrophage scavenger activity. Nevertheless, resistance should be interpreted within the limits of viral genotype, challenge model, and long‑term surveillance, because receptor usage and viral adaptation may vary among PRRSV lineages.

The WUR quantitative trait locus on SSC4 as a major genetic modifier

CD163 determines whether PRRSV can productively enter susceptible macrophages, but additional host loci influence the magnitude of infection and clinical outcomes. The most reproducible modifier is a quantitative trait locus on Sus scrofa chromosome 4. This region is tagged by the WUR10000125 single‑nucleotide polymorphism, located near the guanylate‑binding‑protein gene cluster. Experimental challenge studies have shown that pigs carrying the favorable B allele generally have lower viral loads and better weight gain than pigs homozygous for the unfavorable A allele.

The SSC4 locus does not confer sterilizing resistance. Instead, it modifies host response by reducing viral burden and improving tolerance to infection. This distinction is important for breeding and vaccinology. CD163 editing targets viral entry, whereas the WUR region influences the efficiency of antiviral control and disease resilience after infection has occurred.

Guanylate binding proteins from genetic markers to candidate mechanisms

The SSC4 locus contains several guanylate binding protein genes, which encode interferon inducible GTPases involved in innate defense against intracellular pathogens. Among these genes, GBP5 has emerged as a strong candidate for the functional basis of the WUR association [89,90]. A splice site mutation linked to the unfavorable haplotype can generate a truncated GBP5 protein, suggesting a plausible mechanism for impaired antiviral control.

However, this relationship should be presented as a strong candidate mechanism rather than a fully closed causal model. The GBP region is complex, and linkage disequilibrium among GBP genes may contribute to the observed phenotype. Functionally, guanylate binding proteins may restrict PRRSV through regulation of innate immune signaling, inflammasome related pathways, and intracellular antiviral states. Their effect is therefore best described as enhancing resistance or resilience rather than preventing infection. This distinction avoids overstating the role of GBP5 and better reflects the polygenic nature of PRRSV response.

Breed differences, broader genetic architecture and implications for breeding and vaccinology

Breed comparisons and genome-wide studies indicate that PRRSV susceptibility is controlled by a broader genetic architecture beyond CD163 and the SSC4 locus. Differences have been reported among Meishan, Large White, Duroc, Pietrain, Landrace, Yorkshire, Hampshire, and commercial crossbred populations, but these differences should not be generalized without considering viral strain, experimental design, age, immune status, and production background. Additional loci on other chromosomes have been associated with viral load, growth performance, reproductive traits, and antibody responses, indicating that PRRSV outcome is influenced by multiple host pathways.

These findings create two complementary opportunities. Marker-assisted and genomic selection can increase the frequency of favorable alleles such as the WUR B allele in breeding populations. Genome editing can create targeted resistance by modifying essential entry factors such as CD163 [91]. Both approaches should be integrated with vaccination, biosecurity, and viral surveillance rather than used as stand‑alone solutions.

For precision vaccinology, host genotype may help explain variation in vaccine responsiveness, viral shedding, and protection against heterologous challenge. Future immunization strategies may benefit from incorporating genetic markers of receptor usage, interferon responsiveness, and adaptive immune competence. Long-term implementation must also monitor animal fitness, macrophage biology, production traits, and the possible emergence of viral variants capable of bypassing host resistance mechanisms.

Toward precision vaccinology

Limits of current vaccines

A significant limitation of contemporary modified live virus (MLV) vaccines is their infrequent ability to provide sterilizing immunity against a wide range of field strains. As a result, vaccinated pigs may still experience transient viral replication, viremia, shedding, and incomplete heterologous protection. This residual susceptibility may sustain viral circulation and, in cases of co-infection, provide opportunities for recombination with field strains. However, it is an overstatement to assert that vaccination uniformly transforms pigs into potential viral sources [92]. Interpretation of vaccine‑derived virulence requires particular caution. Although sequence similarity to vaccine strains may indicate a vaccine‑like or vaccine‑derived origin, confirmation of true reversion to virulence depends on integrated genomic, epidemiological, and phenotypic evidence rather than near identity alone [93].

Recombination between MLV vaccines and circulating field strains undermines vaccine safety and efficacy. Some recombinant variants appear to acquire enhanced virulence relative to their parental strains. GM2, which arose from recombination between Ingelvac PRRS MLV and QYYZ‑like strains, showed increased replication in vivo, whereas FJWQ16, a recombinant associated with NADC30 and HP PRRS MLV, was likewise linked to substantial pathogenicity in pigs [46]. Antigenic divergence between the predominant circulating lineages, especially lineages 1.8 and 3, and current vaccine strains is evident from multidimensional scaling analysis and may contribute to reduced vaccine effectiveness. Computational models indicate that recombination involving vaccine‑related strains, particularly within the ORF2 and ORF3 hotspot, could give rise to viruses with novel antigenic properties or enhanced virulence [29]. Improper immunization practices, such as using multiple MLV vaccines on the same farm, increase the risk of pathogenic recombinants. This situation presents a dilemma in vaccine design: while deploying consensus immunogens or structure-guided antigens aims to produce broadly neutralizing antibodies, it also raises selection pressure. This heightened immune barrier fails to achieve sterilizing immunity and instead encourages viral RNA polymerase to switch templates. As a result, efforts to neutralize historical diversity through structural engineering may unintentionally lead to the emergence of highly virulent mosaic chimeras, showing that structural optimization must consider evolutionary ecology [94].

Vaccine‑driven selection pressure accelerates viral evolution, as shown by the rapid replacement of strain variant 1α with 1β within weeks despite robust vaccination. Sera from animals exposed to 1α exhibited significantly diminished neutralizing activity against 1β, with 43% of sows demonstrating no neutralization. This finding directly implicates amino acid alterations in nsp1α, GP2, GP3, and GP5, including the presence of an additional glycosylation site in GP5, as factors contributing to immune evasion [95]. This pressure also influences immune subversion pathways, as evidenced by antibody-dependent enhancement (ADE) suppressing RIG-I-mediated antiviral signaling through FcγRI activation during PRRSV infection. This process markedly suppresses the expression of RIG-I, TBK-1, IRF-3, STAT-1, and STAT-2 in porcine alveolar macrophages, consequently diminishing the production of essential antiviral effectors such as IFN-α, ISG15, ISG56, OAS1, OAS2, Mx1, and RSAD2 (Figure 5) [96].

Figure 5.

Molecular mechanisms of PRRSV vaccine failure and principles of precision vaccinology. (A) Modified live virus vaccines rarely induce sterilizing immunity against heterologous PRRSV strains. Residual replication, viremia, and shedding sustain viral circulation, favor co‑infection with field strains, and create conditions for recombination that can generate pathogenic mosaic variants such as GM2 and FJWQ16. Protection is weakened by antigenic mismatch with prevalent lineages, especially lineages 1.8 and 3, together with variation in nsp1α, GP2, GP3, and GP5 and increased glycan shielding of GP5. Antibody-dependent enhancement may suppress RIG‑I-driven antiviral signaling in porcine alveolar macrophages through FcγRI-linked pathways and reduce TBK1, IRF3, STAT1, STAT2, and downstream interferon-stimulated effectors. (B) Rational attenuation targets viral determinants that suppress innate immunity and amplify immunopathology, including nsp1, nsp2, nsp4, and nsp11. Editing these regions may restore interferon induction, preserve MAVS-dependent signaling, relieve JAK–STAT inhibition, and limit excessive regulated cell death while retaining immunogenicity. (C) Precision vaccine design integrates optimized antigen configuration with advanced delivery systems, including ORF2 to ORF6 consensus immunogens, GP5m redesign, ferritin display, polylactic acid nanoparticles, lipid nanoparticle-delivered mRNA or self-amplifying RNA, and chimeric platforms such as Cap DS. These approaches can broaden neutralizing activity, strengthen CD4-positive and CD8-positive IFNγ producing T-cell responses, and reduce viremia and lung injury, but differences in breadth, durability, and field performance indicate that antigen design, vaccine backbone, and delivery system must be matched with greater precision.

Consequently, contemporary modified live vaccines (MLVs) exhibit an asymmetric cross-protective profile against heterologous strains; while they frequently fail to induce complete sterilizing immunity or prevent subclinical replication and shedding due to significant viral genetic variability, they remain highly effective at reducing clinical severity, macro-lesions, and mortality. Commercial MLVs therefore remain clinically useful but translationally incomplete. They reduce macroscopic lesions and mortality, yet fail to block infection, viremia, or shedding against genetically diverse isolates. The GM2 and FJWQ16 recombinants illustrate this risk, showing that vaccine‑associated viruses can recombine with circulating field strains to generate progeny with increased in vivo replication or substantial pathogenicity under farm‑level immune pressure. This limitation is underscored by the extensive passaging necessary to develop attenuated strains, such as CON-P90, which maintain heterologous immunogenicity [97].

Antigen design for broad protection

Structure-guided antigen design has become a key strategy for developing broadly protective PRRSV vaccines by focusing on conserved epitopes in envelope proteins to counter viral immune evasion (Figure 5). A consensus sequence approach encoding all PRRSV2 envelope proteins (ORF2-6-CON) was derived from 30 representative Chinese isolates and shares >90% nucleotide identity across all four PRRSV2 lineages in China [98]. Upon integration into an avirulent infectious clone backbone, the resultant chimeric virus (rJS-ORF2-6-CON) elicited broadly neutralizing antibodies capable of neutralizing multiple PRRSV2 lineages and a PRRSV1 isolate. Furthermore, it demonstrated enhanced cross-protective efficacy against virulent NADC30-like challenge in comparison to commercial modified-live vaccines, as evidenced by significantly reduced viremia and the absence of clinical symptoms. Immunoinformatics-driven reverse vaccinology has also enabled systematic identification of conserved epitopes across global PRRSV strains and the design of multi-epitope candidates targeting structural proteins such as the GP5-M complex. One candidate, PRRSV-V-2, engineered with a β-defensin adjuvant and selected B-cell, helper T-lymphocyte (HTL), and cytotoxic T-lymphocyte (CTL) epitopes, demonstrated favorable physicochemical properties under in silico simulation and exhibited the strongest predicted binding affinity to swine Toll-like receptors TLR3 (−308.16 kJ/mol) and TLR8 (−263.17 kJ/mol) in molecular docking models. Crucially, while these computational models predict stable stabilization via hydrogen bonds and salt bridges, these docking scores represent idealized binding dynamics that await rigorous in vivo validation to confirm actual conformational stability and pattern-recognition receptor activation within the porcine immune system [99].

A separate multi-epitope construct, incorporating B-cell, CTL, and HTL epitopes derived from GP3 and GP5, was conjugated with a 50S ribosomal protein L7/L12 adjuvant. This construct demonstrated high-affinity binding to Toll-like receptor 3 (TLR-3) via interactions with eight specific amino acid residues and the formation of nineteen hydrophobic contacts. Furthermore, it elicited robust cellular and humoral immune responses, characterized by elevated production of interferon-gamma (IFN-γ), interleukin-2 (IL-2), and interleukin-12 (IL-12) [100]. To circumvent immune evasion caused by non-neutralizing decoy epitopes, strategic alterations to GP5 have demonstrated efficacy. Specifically, substituting the decoy epitope (amino acids 27–31) with the neutralizing GP5B epitope (amino acids 37–45), along with mutating glycosylation sites (N30, N34, N35, N51), resulted in the creation of a modified antigen (GP5m) that significantly increased the exposure of neutralizing antibodies [101]. Fusion of GP5m with H. pylori ferritin for nanoparticle assembly enhanced neutralizing antibody responses relative to the unmodified subunit vaccine and promoted a Th1‑biased cellular immune profile marked by increased CD4 positive IFN-γ positive and CD8 positive IFN-γ positive T lymphocytes [102].

Alternative antigen combinations have identified critical targets for broad protection. In primary PAMs, which serve as the natural host cells for the virus, the GP3, GP4, and M proteins have been identified as highly effective targets for neutralizing antibodies. In one experimental setting, combined GP3, GP4, and M antigen formulations conferred complete survival after a highly pathogenic PRRSV challenge and reduced lung pathology and viremia relative to selected comparator formulations. Whether this degree of protection generalizes across heterologous field strains remains unresolved [103]. For enhancement of cellular immunity, multi‑epitope constructs incorporating conserved CTL epitopes such as NSP9 TCE2 together with porcine Fc molecules improved antigen stability and supported sustained Th1 responses for an extended period after immunization despite a modest decrease in antigenicity [104].

Emerging mRNA lipid nanoparticle strategies suggest that antigen configuration may critically influence immunogenicity. Comparative observations indicate that co‑delivery of discrete GP5, M, and N antigens can outperform selected fusion designs, although robust evidence for durable heterologous protection in pigs remains limited [49]. Vaccines targeting T cells, exemplified by M-NSP5 fusions, elicited cross-reactive IFN-γ responses and polyfunctional T-cell activation, which mitigated lung pathology while exerting minimal impact on viral loads following heterologous challenge. This highlights the complementary roles of humoral and cellular immunity in achieving comprehensive protection [105].

Rational attenuation

Reverse genetics systems provide a powerful strategy for rationally attenuating PRRSV by enabling precise modifications of viral genomic regions that encode immune antagonists and virulence determinants [12]. While the engineering of “smart” MLVs through targeted deletions offers a theoretically cleaner safety profile, we must critically evaluate the stability of these phenotypes in the field. There is a persistent risk that rationally attenuated viruses may exhibit different replication kinetics or competitive fitness when subjected to the selective pressure of complex, multi-strain endemic environments. Furthermore, the assumption that an attenuated backbone will maintain its immunogenicity profile when challenged by rapidly evolving, highly virulent field isolates lacks extensive longitudinal field evidence. Thus, the transition from “smart” laboratory designs to field-effective vaccines requires a cautious, multi-phase validation process that accounts for both viral evolution and herd-level immune diversity.

Current challenges in PRRSV vaccinology emphasize the need to improve cross-protective immunity against genetically diverse field isolates and to attenuate MLVs to safety levels comparable to inactivated vaccines, and numerous full-length cDNA infectious clones for both genotype 1 and 2 viruses are now available to support these goals. PRRSV antagonizes host innate immunity via multiple nonstructural proteins that inhibit type I interferon (IFN) responses. Among nsp1, nsp2, nsp4, and nsp11, nsp1 produces the strongest suppression of IFN-β promoter activation. Nsp11 suppresses IFN-β activation by cleaving MAVS mRNA through its endoribonuclease domain and induces STAT2 degradation via the ubiquitin-proteasome pathway, while the pseudoknot region in the 3′ untranslated region triggers robust interferon-stimulated gene (ISG) expression in porcine alveolar macrophages [48,106]. These mechanisms define critical targets for rational attenuation, since removing such domains could restore protective IFN signaling without provoking excessive RCD.

Functional convergence in RCD manipulation across unrelated viruses: implications for PRRSV attenuation. Large DNA viruses (poxviruses and herpesviruses) encode dedicated RCD inhibitors – poxvirus vFLIPs that block caspase-8 oligomerization to suppress apoptosis, and herpesvirus M45 (via its RHIM domain) that disrupts RIP kinase signaling to suppress necroptosis [107]. PRRSV, despite its much smaller RNA genome and lack of sequence or structural homology to these DNA virus factors, achieves functionally similar RCD modulation through entirely different molecular mechanisms. Specifically: PRRSV Nsp2 suppresses apoptosis during early infection (functionally analogous to vFLIPs, though acting via the NLRP3 inflammasome axis rather than direct caspase-8 inhibition) [68]; PRRSV Nsp5 promotes FAM134B-dependent reticulophagy to degrade RLR signaling components [26], a strategy with no direct parallel in DNA viruses; and PRRSV GP2a promotes RIG-I degradation [47], functionally convergent with herpesvirus-mediated sensor disruption but mechanistically distinct.

The relevance of this cross-virus comparison for PRRSV vaccine design lies in a general principle, not a specific molecular recipe: viruses that invest genomic resources in RCD suppression can be rationally attenuated by disrupting these RCD-modulating functions, as demonstrated for poxviruses and herpesviruses [108]. For PRRSV, altering specific motifs like the nsp2 transmembrane domain, which triggers NLRP3, might reduce inflammation while maintaining enough replication for immune response. However, this approach has limitations: PRRSV’s smaller genome may not handle many deletions without losing replication ability; its molecular mechanisms differ and aren’t directly applicable; and identifying RCD-modulating domains that don’t affect PRRSV replication requires empirical research [108].

Complementary innovations in rational design encompass nanoparticle-based subunit vaccines that are engineered to present multiple PRRSV neutralizing epitopes, along with dendritic cell-binding peptides, to augment antigen presentation. The Cap-DS vaccine, engineered by replacing residues 85–88 of the PCV2 Cap protein with a PRRSV GP5B epitope linked to a dendritic cell binding peptide (DCBp) and incorporating the GP35 epitope at the C-terminus, elicited substantially elevated neutralizing antibody titers and resulted in an 80% survival rate among piglets challenged with highly pathogenic PRRSV. This outcome was achieved without inducing excessive inflammatory responses, as evidenced by minimal lung pathology and the absence of significant elevations in proinflammatory cytokines such as IL-6 and TNF-α [109]. This result demonstrates the feasibility of structure‑guided approaches to balance immune activation and safety in next-generation vaccine development.

Next‑generation vaccine platforms

Next-generation vaccine platforms for PRRSV seek to address the shortcomings of conventional vaccines by improving immunogenicity, safety, and the precision of immune targeting [110]. Nanoparticle-coupled formulations have shown, in preclinical studies, the potential to enhance antigen delivery to antigen-presenting cells and promote stronger Th1 and cytotoxic T-cell responses. Polylactic acid nanoparticles carrying inactivated PRRSV combined with heat-labile enterotoxin subunit B improved systemic and mucosal immunity in pigs [111]. Ferritin-based presentation of modified GP5 antigens improved neutralizing responses in a controlled porcine challenge study [88], demonstrating the immunological potential of self-assembling protein nanoparticles. However, ferritin is produced through recombinant expression in bacterial or yeast systems with purification requirements that increase production complexity and cost relative to conventional subunit or MLV production. Whether ferritin-based GP5 vaccines can be manufactured at a cost compatible with routine commercial piglet vaccination remains to be demonstrated [101]. These immunological and biosafety advantages must be weighed against substantial manufacturing and field-application constraints.

Messenger RNA (mRNA) and viral-vectored vaccines present numerous advantages, including expedited development timelines, adaptable antigen design, and the capacity to induce comprehensive humoral and cellular immune responses, all while mitigating the principal risks associated with conventional vaccine platforms [112]. Messenger RNA and self‑amplifying RNA platforms offer attractive design flexibility and the potential to induce combined humoral and cellular immune responses. The mRNA and self‑amplifying RNA candidates should therefore be regarded as adaptable but unproven translational platforms. Co‑delivered GP5, M and N antigens show that configuration can improve immunogenicity relative to selected fusion designs, but current porcine evidence has not established durable cross‑lineage protection, sterilizing control of shedding or consistent efficacy under farm conditions. Until antigen selection, delivery chemistry, dose interval and field stability are optimized in multi‑lineage herds, these candidates remain promising models rather than validated replacements for existing vaccines [113]. To minimize vaccine-field recombination and improve genetic stability, rational modification of recombination-prone regions or redesign of the vaccine backbone warrants investigation [46]. Integrating high-throughput sequencing with bioinformatic analysis is essential for detecting recombination events and for mapping breakpoints relative to transcription‑regulating sequences to guide safer vaccine design.

Conclusions and outlook

Rethinking PRRSV virulence

The traditional understanding of PRRSV virulence should be unified into a cohesive framework centered on RCD reprogramming. RCD serves as the key link between viral molecular factors such as Nsp2-induced pyroptosis, systemic immune issues like cytokine storms and macrophage damage, and clinical challenges such as vaccines failing to provide sterilizing immunity. The viral life cycle fundamentally follows an RCD-dependent trajectory, wherein the initial suppression of host cell death maintains the niche for replication. In contrast, the later induction of pyroptosis and ferroptosis facilitates tissue damage and viral egress. Future control strategies must transcend the targeting of specific viral proteins and instead concentrate on the RCD landscape, which acts as the principal regulator of PRRSV persistence and represents the primary obstacle to vaccine efficacy [23,64,72]. It is crucial to consider the significant context-dependent differences between PRRSV 1 and PRRSV 2. PRRSV infection induces GSDMD-mediated pyroptosis in PAMs both in vitro and in vivo, a process that differs from classical apoptosis pathways [64]. The physical association of viral replication machinery with inflammatory scaffolds, as exemplified by RTC-mediated trans-Golgi dispersal, establishes a direct functional connection between viral proliferation and significant host tissue damage [64]. Importantly, the formation of RTC is contingent upon the host factor TMEM41B and is encased within an intermediate filament network. This suggests that the viral replication complex itself, rather than solely viral RNA or structural proteins, is responsible for initiating this inflammatory cell-death cascade [64].

Multiple RCD pathways are activated during infection, adding complexity. Virulent PRRSV-1 strains induced necroptosis and pyroptosis within the first week post-infection and then predominantly triggered extrinsic apoptosis during the second week [23]. The initial prevalence of TUNEL-positive cells compared to cleaved caspase-3-positive cells indicates the potential involvement of caspase-3-independent regulated cell death mechanisms [23]. Notably, the Lena virulent strain preferentially activated caspase-8 rather than caspase-9 in lung tissues, indicating strong induction of the extrinsic apoptotic pathway via Fas/caspase-8 signaling [23]. The activation of multiple regulated cell death pathways thus has a dual role in PRRSV infection, potentially limiting viral spread through elimination of infected cells while concurrently exacerbating lung pathology through excessive inflammatory damage. The clinical implications of the interaction between RCD and immune evasion are exemplified by the emergence of variants capable of escaping neutralization in vaccinated populations. Variant 1β, which harbors multiple amino acid substitutions in nsp1α, GP2, GP3 and GP5, including an additional glycosylation site and deletion of a GP5 epitope, exhibits enhanced replication kinetics in porcine alveolar macrophages and generates higher early viral loads than variant 1α [95]. This fitness advantage was attributed to enhanced attachment to PAMs and diminished neutralization by sera from animals previously exposed to variant 1α. Notably, six out of fourteen sows exhibited a complete loss of neutralizing activity against variant 1β, despite maintaining high titers against variant 1α [95]. Phylogenetic analysis suggests that the 1β variant emerged through recombination among multiple 1α subvariants, each contributing unique advantageous mutations. This facilitated the swift replacement of 1α in partially immune herds and was associated with increased morbidity in nursery populations and elevated individual viral loads [95].

Future directions

Future research should transcend the prevailing paradigm, which is predominantly centered on optimization and incremental enhancements in antigen binding or delivery, to conduct a comprehensive “translational audit” of vaccine efficacy. Translational assessment should distinguish demonstrated benefit from unresolved risk across representative platforms. The consensus envelope chimera derived from 30 Chinese isolates reduced viremia and prevented clinical disease after NADC30 like challenge, and the GP3, GP4 and M formulation achieved complete survival in the cited challenge model, although protection across heterologous field strains remains unproven. GP5m ferritin and the PCV2 Cap‑based dendritic cell‑targeted construct improved neutralizing responses or survival, but manufacturing scalability, durability and herd‑level effectiveness remain unresolved, whereas mRNA platforms allow rapid antigen redesign but still lack definitive evidence of durable cross‑lineage protection under farm conditions. The recovery of GM2 and FJWQ16 recombinants further illustrates a failure mode in which incomplete protection and co‑circulation permit vaccine‑associated recombination and enhanced pathogenicity. We propose that future assessments of vaccine candidates should include longitudinal monitoring in heterogeneous, multi-parity herds to account for the interactions between maternal immunity, environmental stressors, and the RCD-reprogramming landscape characteristic of natural infection. Mucosal IgA remains a plausible correlate of improved protection. However, current field evidence more strongly supports associations with reduced viremia or lower transmission risk than with sterilizing immunity [114]. Integrating molecular epidemiology with farm biosecurity measures, animal movement control, and vaccination strategies is of equal importance, as sustainable control of PRRSV will rely on the combination of mechanistic immunology and effective transmission management practices.

Funding Statement

This work was supported by the project of Jiangsu Agri-animal Husbandry Vocational College, Grant No. NSF2026ZR04.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data sharing is not applicable to this article as no new data were created or analyzed in this study.