Lessons learned from allergen adsorption on engineered nanomaterials: bridging experimental insights and computational technologies

ABSTRACT

Allergic disease has increased over past decades, coinciding with the use of nanomaterials in medicine, industry, and environmental applications. This trend introduces new opportunities for human exposure to allergen–nanomaterial complexes through different routes like inhalation, ingestion, and dermal exposure. Such interactions have emerged as a determinant influencing immune response. Recent studies reveal that allergen adsorption onto nanomaterial surfaces varies with shape, particle size, surface chemistry, morphology, and agglomeration state. These surface interactions can modify allergen structure, epitope accessibility, and proteolytic stability, thereby reshaping the immune outcomes. Key considerations including dose, exposure route, and kinetics play an important role in determining physiological effects and pathological consequences. This special report provides a comprehensive overview of current research on allergen-nanomaterial interactions, summarizing known mechanisms, structural and immunological consequences, and critically assessing the challenges, gaps, and controversies. Understanding the impact of allergen-nanomaterial interactions on the human immune response demands a cross-disciplinary approach that integrates the complexities in nanotechnology and immunology. Advances in molecular toxicology employing new approach methodologies provide mechanistic insight which can support regulatory science and improve the acceptance of innovative therapeutic strategies in the field of nanomedicine. Allergen-nanomaterial interactions may serve as a model for best practice in this context.

GRAPHICAL ABSTRACT

1. Introduction

Allergic diseases, including asthma, allergic rhinitis, atopic dermatitis, food allergies, represent a growing global health burden, currently affecting approximately 10–30% of the world’s population, with a particularly pronounced prevalence among children over the past two decades [1,2]. Allergy arises when allergens trigger a so-called Th2-skewed immune response, which is characterized by a reaction dominated by T helper 2 (Th2) cells that promote antibody production and allergy-related inflammation through secretion of Th2 cytokines, including IL-4, IL-5, and IL-13. Th2 cytokines drive IgE production, mast-cell sensitization, eosinophil activation, and mucus hypersecretion, producing the characteristic inflammatory and hypersensitivity symptoms. The multifactorial etiology of allergies, including genetic predisposition, environmental exposure, and changing lifestyles, underscores the complexity of preventing and managing them in both developed and developing regions [3]. Recent analyses based on the Global Burden of Disease data have demonstrated that, despite regional and age-related variations, the overall prevalence of allergic diseases and their associated comorbidities remain remarkably high [4]. This growing burden not only poses significant physical and psychological challenges for affected individuals but also exerts sustained pressure on healthcare systems and socio-economic structures worldwide [5].

Over the past two decades, the rise of nanomaterials (NMs) in medicine, industry, and environmental applications has profoundly reshaped the landscape of material science and biotechnology [6–9]. Nanomaterials are intentionally designed with at least one dimension between 1 and 100 nanometers, but while most are engineered for specific applications, they can also occur incidentally in the environment (micro-/nano-plastics) [10]. They are classified by composition and structure as organic (carbon-based materials such as fullerenes, carbon nanotubes, polymeric and lipid-based nanoparticles) or inorganic (metal- and metalloid-based or magnetic nanoparticles, and semiconductor quantum dots) [11]. This rapid expansion has inevitably led to increasing human exposure to NMs through inhalation, ingestion, dermal contact, or diverse intentional administration routes in nanomedical applications, raising concerns regarding their potential interactions with biological macromolecules and the immune system. Upon entering biological fluids, NMs rapidly acquire a layer of adsorbed proteins, forming both a loosely bound “soft” corona and a more stable “hard” corona that dictates their biological identity and governs interactions with cells and tissues [12]. Physicochemical properties such as surface charge, hydrophobicity, curvature, porosity, crystallinity, and the presence of surface functional groups strongly influence protein adsorption behavior and the subsequent formation of the protein corona [13]. Allergens relevant to human sensitization are particularly sensitive to interactions with nanoscale surfaces. Such interactions may occur intentionally, for instance, during the design of NM-allergen complexes for therapeutic applications [14]. Importantly, in these intentional settings NMs are not designed to physically sequester or eliminate the allergen from biological environment, but rather to modulate their structural properties like allergen stability, epitope exposure, allergen uptake and immunogenicity in the context of allergen-specific immunotherapy (AIT) [15]. In contrast, unintentional interactions occur upon exogenous contact of allergens with NMs in the environment without therapeutic intent [16,17]. Well-documented examples include particulate matter-allergen complexes that may exacerbate allergic inflammation [18]. Notably, this adsorption of allergens can affect their intrinsic stability, aggregation propensity and susceptibility to conformational change. Recent studies have highlighted that allergen adsorption onto NM surfaces may alter epitope exposure, potentially enhancing recognition by antigen-presenting cells or shifting immune polarization [19–22]. In parallel, accumulating experimental evidence support the epithelial barrier hypothesis as a prominent etiologic origin for the rising prevalence of allergies and other chronic inflammatory diseases, implicating barrier dysfunction and multifactorial environmental exposure [23]. The pervasive presence of NMs and micro-/nano-plastics in everyday products (e.g., detergents, cosmetics) may further contribute to disease elicitation or exacerbation [24]. Currently, much work is being done on elucidating the transformation of plastics in the environment (e.g., through weathering), which may have consequences on the prevalence and severity of food allergy [25]. Hence, understanding allergen – NM interactions is highly relevant for the safe design and regulatory evaluation of NMs and can be very useful for the development of novel nanotechnology-based approaches for AIT, enabling precise delivery and immune modulation while reducing the risk of unintended sensitization [26,27]. Incorporating this knowledge into predictive models, particularly those based on Adverse Outcome Pathways (AOP) is crucial for predicting immunological risks and supporting “safe-by-design” innovation [28].

This special report provides an overview of recent advances in understanding allergen – NM interactions and their immunological consequences. Notably, most studies available to this date have used nanoparticles as models for studying allergen–NM interactions. We highlight experimental findings, computational approaches and theoretical models, identify current research challenges, knowledge gaps, and controversies, and outline future research perspectives for both research and regulatory evaluation in the context of NM immunotoxicology and allergy risk. Fundamentals of allergy and mechanistic insight in sensitization and effector functions can be found in specific review articles [14,17].

2. Current research status

Research on allergen–NM interactions has evolved from descriptive observations of protein adsorption to mechanistic studies that clarify the impact of these interactions on immunological pathways and therapeutic outcomes. Adsorption is a dynamic phenomenon that can induce conformational changes in allergens, modify epitope presentation, and regulate biological activity. These transformations significantly impact allergic sensitization, immune regulation, and the rational design of nanomaterial-based interventions [29]. Various analytical techniques have been established to characterize allergen adsorption onto nanomaterials, enabling detailed assessment of allergen identity, quantity, structural integrity, and functional properties are listed in Table 1. Computational methods have emerged as powerful tools to predict and interpret NM-biomolecule interactions. Physics‑based simulations and data‑driven models have been developed to predict adsorption mechanisms, binding energetics, and structural rearrangements of proteins/allergens at NM interfaces [25,44,47–49]. Importantly, such in silico approaches increasingly incorporate immunologically relevant readouts, thereby supporting and extending conclusions drawn from physicochemical characterization. Despite their promise, current modeling frameworks require further refinement to fully capture the complexity of these interactions. In particular, improved representation of chemical surface functionalization and its effects on protein corona formation kinetics, allergen conformation, and biological function remain a key challenge. These aspects are critical, as surface chemistry can dictate not only allergen-binding profiles but also downstream immunological consequences [50]. Moreover, environmentally induced surface modifications such as oxidative alterations resulting from exposure to pollutants like ozone or nitrogen oxides may further modify NM reactivity and allergen interactions, with potential implications for hazard assessment and therapeutic efficacy. Therefore, continued developments of these approaches will be essential for guiding safe by design nanomaterial development and for therapeutic development [49].

Table 1.

Overview of analytical approaches to elucidate the identity, structural state and functional consequences of allergen adsorption onto nanomaterial surfaces.

Analysis	Key techniques/Tools	Scientific purpose	References
Quantification of allergen adsorption	Protein assays (Bradford, Lowry, …), SDS-PAGE, ELISA-based allergen quantification, LC-MS/MS, isothermal titration calorimetry (ITC)	Determine the amount of allergen adsorbed, adsorption efficiency, and corona composition specificity. Confirmation of sample homogeneity and equivalence of natural vs. recombinant allergens.	[30–33]
Allergen corona composition and physicochemical profiling	SDS – PAGE, LC-MS/MS, Small-Angle X-ray Scattering (SAXS), modulation excitation synchrotron-SAXS (ME-SAXS)	Identification and quantification of adsorbed allergens. Elucidation of corona composition, structural organization and dynamic structural changes. Assessment of physicochemical properties following nanomaterial-protein interactions. Minimal bio-corona reporting standards (MIRIBEL, MINBE).	[31,34–38]
Structural and conformational assessment of adsorbed allergens	Circular Dichroism (CD) spectroscopy, Infrared (IR) spectroscopy, Intrinsic Fluorescence Spectroscopy	Determination of conformational rearrangements, folding stability, secondary/tertiary structure modifications and epitope accessibility upon adsorption to nanomaterial surfaces.	[39–41]
Immunological evaluation of allergen functionality	IgE-binding assays, Basophil Activation Test (BAT), T-cell proliferation assays	Assessment of allergenic functionality after adsorption. Evaluation of IgE reactivity, effector cell activation, and allergen-specific cellular immune responses.	[30,42,43]
Predictive and Mechanistic Modeling Tools	Molecular docking, molecular dynamics simulations, Adverse Outcome Pathway (AOP) Toolbox	In silico prediction of protein – NM interaction sites, corona formation tendencies, and mechanistic descriptors (hydrophobic surface fractions, interface characteristics, charge distribution). Description of transitions from hard to soft coronas.	[44–46]

2.1. Mechanism of allergen adsorption onto nanomaterials

The adsorption of allergen onto NM surface is governed by non-covalent interactions such as electrostatic forces, hydrophobic interactions, van-der-Waals interactions, and hydrogen bonding. The relative contribution of these forces depends on the physicochemical characteristics of both the allergen and NM, with surface charge and hydrophobicity being key determinants of allergen adsorption [51]. Many major allergens such as those in pollen and molds are acidic proteins with isoelectric points in the pH 4–6 range, which enhances their propensity to interact with positively charged NMs such as titanium dioxide nanoparticles (TiNPs). TiNPs have been shown to facilitate allergen adsorption and promote allergic sensitization [52]. Hydrophobic interactions also play a critical role, as allergens often present surface-exposed hydrophobic patches and cavities that accommodate small hydrophobic ligands [53]. Such ligands have been reported to influence the structural stability and immunogenicity of allergens, exemplified by the major cockroach allergen [54]. Since many nanoparticles exhibit hydrophobic surfaces, these features further promote allergen adsorption. Nanoparticle surface chemistry and size influence the packing and orientation of adsorbed proteins [55]. Studies on silica nanoparticles (SiNPs) have demonstrated that functionalization with carboxyl or amine groups, PEGylation, or introduction of mesoporous structure directly alter allergen-protein binding, and the dispersion state of NMs, whether appearing as discrete particles or agglomerates, influences allergen adsorption and subsequent immune responses [56]. Studies on SiNPs demonstrated that well-dispersed nanoparticles and micron-scale agglomerates elicited significantly different immunological outcomes when co-delivered with allergens [57]. Environmental factors including pH, ionic strength, allergen concentration, and the presence of competing biomolecules can also strongly influence allergen adsorption dynamics [58]. For instance, in gastrointestinal fluids, allergens encounter bile salts, digestive enzymes, and dietary proteins that compete for NM surface sites, leading to coronas distinct from those formed in serum. These variations can modify allergen conformation and epitope accessibility, ultimately shaping immune recognition [59]. Collectively, these findings demonstrate that allergen adsorption onto NM is a multifactorial process governed by intrinsic nanoparticle properties, allergen physicochemical characteristics and environmental conditions.

2.2. Structural and conformational consequences

A major focus of recent research has been on understanding how adsorption at the nano-bio interface alters structural integrity, conformation dynamics and functional domains of allergenic proteins. The hydrophobic surfaces of NMs can readily absorb allergens, triggering significant conformational changes [60]. Depending on the physicochemical properties of the NMs, adsorption may lead to stabilization, destabilization, or even refolding of allergen structures [25]. These interactions can profoundly influence the immunological behavior of allergens. For instance, non‑covalent adsorption of the major birch pollen allergen Bet v 1 to amorphous SiNPs has been shown to distort its native fold, particularly affecting α‑helical regions and thereby reducing overall conformational stability. Such perturbations in the 3D structure of allergens are closely linked to altered proteolytic susceptibility which in turn impacts antigen processing and presentation [30,60]. Similarly, binding of Bet v 1 to mesoporous SiNPs impacted the 3D fold of the allergen leading to partial unfolding [61]. In contrast to unfolding, some NMs particularly gold nanoparticles (AuNPs) can stabilize enzymatic or catalytically active domains within allergens, preserving or even enhancing their bioactivity. For example, adsorption of the major house dust mite (HDM) allergen Der p 1 to AuNPs was found to preserve or even enhance the allergen’s intrinsic protease activity, suggesting that NMs may stabilize functional domains [42]. Beyond unfolding or stabilization, adsorption can also promote secondary structure transitions, such as α‑helix–to–β‑sheet conversions, depending on the properties of NMs [62]. These structural modifications can expose or mask epitopes, directly influencing downstream immune recognition. Overall, adsorption-induced structural and conformational changes are key mechanisms through which NMs modulate allergen behavior, with direct consequences for epitope accessibility, proteolytic processing and immunogenicity.

2.3. Immunological consequences

Allergen adsorption onto NMs reshapes how the immune system perceives and processes these proteins. By changing allergen conformation, aggregation state, stability, or uptake pathways, NMs effectively create a new presentation format that can either amplify or dampen immune activation. These interactions have been reported to drive immune responses in opposing directions, i.e. enhanced sensitization and exacerbation of allergic inflammation in some contexts and tolerance induction or controlled immunomodulation in others. NMs can function as unintended adjuvants, enhancing sensitization. For example, polyethylene glycol-coated amorphous SiNPs co-administered intranasally with the hen egg-derived model allergen ovalbumin (OVA) in mice amplified airway inflammation, eosinophil infiltration and allergen-specific IgE, indicating a strong Th2-skewing adjuvant effect when compared with OVA alone [63]. Furthermore, intranasal administration of different SiNP formulation with OVA increased airway hyperresponsiveness, inflammatory cell infiltration and exacerbated airway disease [64]. Similar outcomes have been observed with agglomerated SiNPs delivered cutaneously alongside HDM allergens, which promote IgE-biased responses and increased anaphylaxis susceptibility [57]. Metallic NMs such as AuNPs complexing Der p 1 preserved or enhanced protease activity and disrupted epithelial barriers more effectively, increasing the likelihood of initiating sensitization [42]. Likewise, TiNPs have been shown to exacerbate airway allergic responses in OVA-sensitized mice, elevating inflammatory cell infiltration and allergen-specific antibody titers [52,65]. Collectively, these findings highlight the adjuvant-like properties of NMs in promoting allergic sensitization. Conversely, NMs can promote immune tolerance and serve as platforms for AIT. Hollow mesoporous SiNPs loaded with the HDM allergen Der f 2, for instance, have been shown to reduce airway inflammation, suppress allergen-specific IgE and enhance protective IgG isotypes in mouse models, which are hallmarks of successful AIT [52,66]. Similarly Bet v 1 adsorbed onto SiNPs enhanced the uptake of allergen by micropinocytosis, accelerated proteolytic processing and presentation which skews the immune response toward a Th1-dominated profile [30]. AuNPs conjugated with dendritic cell (DC)-targeting ligands have demonstrated efficient allergen delivery during sublingual immunotherapy, enhancing regulatory T-cell induction and shifting responses from allergic Th2 to tolerogenic Th1 profiles [67]. Carbohydrate-modified ceramic nanoparticles also demonstrated immunomodulatory potential, outperforming traditional adjuvants like alum by reducing IgE and histamine while boosting protective IgG responses [68]. However, in contrast to these tolerogenic outcomes, adsorption of the HDM allergen Der p 2 onto carbon nanotubes has been shown to exacerbate allergic lung disease, increasing airway inflammation and Th2-skewed responses [31]. Allergen adsorption onto NMs can either enhance allergic sensitization or promote immunological tolerance, depending on the NM and allergen properties, highlighting their dual potential as both risk factors and therapeutic platforms. Current research on allergen – NM adsorption has demonstrated that these interfaces are highly complex, influenced by particle characteristics, protein properties, and environmental factors that jointly shape structural and functional outcomes.

3. Remaining challenges, gaps, and controversies

3.1. From mechanistic studies to in vivo relevance

Advances in NM-based drug delivery have driven the development of sophisticated experimental systems and complementary in silico methodologies. Computational methodologies cover atomistic and molecular-level investigations of interacting entities (NM and proteins) using classical mechanics models [42,69,70]. Despite these advances, modeling and experimentally assessing the dynamic structural behavior of allergen-NM complexes on physiological barriers, as well as their capability to cross these barriers and engage tissue resident antigen-presenting cells (APCs), a prerequisite to finally elicit a Th2-skewed immune response, remains highly challenging. Although experimental evidence exists for systemic uptake of NMs upon inhalation and dermal exposure, and for remote organ effects, this area is still underexplored [71]. Even minor changes during the spatial NM-allergen translocation across epithelial barriers may affect the biological identity, immunological profile and allergenicity, in addition to structural modifications influenced by NM interaction. The physiochemical structure of immune barriers, i.e. sputum and mucus viscosity provided by carbohydrates and physical entanglement caused by heavily glycosylated mucin proteins, as well as specific clearance mechanisms affect NM mobility [72]. These factors determine effective dose and exposure kinetics during both allergy phases (sensitization and effector phase) and in desensitization regimens for allergy treatment [73–75]. Furthermore, in vivo studies in mice show that different allergen-dose regimens (repeated low dose or short-term high dose) results in differential Th2 activation and IgE/IgG1 antibody responses [76]. For these reasons and lack of effective experimental-dose determination, mechanistically informative in vitro studies, e.g., testing mast cell activation and release of inflammatory mediators, may rarely predict potential clinical outcomes. Standard in vitro assays investigate immune responses in a somewhat isolated mode and do not reflect the high complexity of an orchestrated interplay of many cell subsets, soluble mediators such as cytokines and chemokines, and the immune system’s spatially distributed functionality entailing local and remote effects in vivo [77]. To support the selection of consistent in vitro dose setting scenarios, dose bridging by in silico methods can help to translate an observed environmental or occupational exposure level to an appropriate effective dose for cell culture testing and analysis for immunological effects. Integrating experimental-computational workflows for dose finding is therefore essential for NM immunotoxicity testing, interpretation of results and significance assignment [78]. However, such a multi-step dose finding concept, starting with estimation of relevant in vivo exposure and extrapolating to an in vitro effective dose and corresponding nominal concentration needs to be routinely established for the investigation of gene regulation, cytokine expression and immune priming toward Th2 responses after allergen exposure [79].

3.2. Controversies in immunological impact

There is mounting evidence that allergen adsorption to NM may attenuate or contrarily foster allergenicity by a plethora of fine-tuned mechanisms within the cellular and humoral immunological network (Figure 1).

Figure 1.

Allergen-NM adsorption and specific effects on allergenicity. Epitope hiding (i) may be an effect of allergen-NM-favored spatial binding orientation. Conformational changes and partial unfolding can foster de novo epitopes (ii) or impair allergen recognition by established antigen-binding sites (iii). Allergen-NM complexes vs. allergen alone may engage dissimilar antigen-presenting cells (APCs) and impact uptake mechanisms, kinetics, and activation (iv). Different proteolytic processing of allergen into peptides by APCs (v) may change the resulting profile of peptides for MHC II loading and subsequent T helper cell activation via MHC II – peptide – TCR signaling (vi). Depicted effects can either enhance or attenuate allergenicity.

Immune responses begin with internalization of allergens by APCs through uptake mechanisms such as endocytosis, to enable trans-epithelial passage as a first step [80,81]. Subsequently, proteolytic cleavage of allergens to small peptides allows loading of MHC II molecules and presentation on the cell surface. The differentiation of mature naïve B cells to antibody-secreting plasma cells needs a costimulatory signal by specific T helper cells. This is mediated via allergen-derived peptides bound to MHC II and recognized by T cell receptor. Allergens alone vs. NM-bound result in different uptake mechanisms and kinetics and undergo different proteolytic cleavage and presentation, as stable hard corona formation changes the proteolytic resistance to degradation, due to the loss of the proteins’ integrity by partial unfolding, with new cleavage sites accessible to enzymatic degradation [16,60,61]. In consequence, a new peptide profile for MHC II loading may deprive or enhance T cell receptor-peptide-MHC II interactions, thus changing the quality of the subsequent T cell response [82].

Attenuation or induction of tolerance may be an effect due to IgE-epitope hiding after adsorption. The existence of favored allergen-binding sites to NM during protein corona formation, resulting in oriented binding may consequently render inaccessibility of the specific epitopes for IgE antibodies [61,83]. In line with the established principles of allergenicity, adsorption that hides the IgE binding epitopes prevents the activation of mature naïve B cells with high-affinity receptors, thereby blocking allergic sensitization. Similarly, during the effector phase, this mechanism also abrogates the IgE-mediated activation of the network of FcɛRII-bearing cells, such as mast cells, eosinophils, or macrophages. However, slow IgE consumption via the silent internalization of antigen-IgE-FcɛRI complex upon low-dose exposure to a specific antigen is one of several proposed mechanisms for early-stage desensitization and maintenance therapy for sustained tolerance, achieved by prolonged dosing [84–86]. Continued exposure to NM capable of specific allergen binding and concomitant epitope hiding may interfere with such low-dose desensitization regimens. As described previously, allergen-NM interactions can elicit conformational changes, modifying a protein’s three-dimensional structure, giving rise for a broad range of immunological implications, with potential impact on pathways and outcomes of IgE mediated allergy [60,61,87]. Such epitope alterations imply not only masking and impairment of IgE binding-sites but also confer the potential formation of de novo epitopes. Following this concept, allergen engineering, using chemical or genetical modifications or allergen carriers, depriving specific IgE binding regions and the capability to activate FcɛRII-expressing immune cells, has been explored extensively to engineer hypoallergenic proteins for AIT [88]. Hence, the allergen-NM interaction may offer new opportunities for such strategies or, conversely, provoke naïve B lymphocytes to recognize de novo epitopes. Subsequently, after genetic rearrangement and antibody class switch, secretion of either specific IgG or IgE antibodies by plasma cells will occur, with B cell priming and differentiation to plasma cells moderated by the specific contextual profile of cytokines determined by APCs and T helper cells [89]. Consistent with fundamental allergy mechanisms, IgG with affinity to the de novo epitopes of allergen-NM complexes may foster silent elimination by opsonization and antibody-dependent cellular phagocytosis [90]. In contrast, an IgE mediated Th2 response may establish allergic sensitization specific to the allergen-NM complex. Ultimately, the exposure dose (low, high) and kinetics (one time, repeated, or chronic) may finally determine the clinical outcome. Due to these complex experimental requirements, composed of allergens, NMs, the high complexity and spatial distribution of the immune system network, and the sensitivity of dynamic complexes formed to dosing effects, this field requires further studies utilizing closer to reality models. Such advanced experimental models may exploit co-culture techniques, organoids and 3D spheroids (with and without extracellular matrix) and organs-on-a-chip systems [91,92]. Furthermore, to bridge between in vitro cell cultures and in vivo animal models, ex vivo cultures may pave the way.

3.3. Sources of variability - allergen variants and nanomaterial types

Molecular variations can significantly alter folding patterns, surface charge distribution, epitope accessibility and immunogenicity. This is particularly critical when comparing recombinant and natural allergens. In this regard, several factors complicate the interpretation of experimental data and hinder the development of models for computational prediction of safety-related aspects. Compared with crude protein extracts, component-resolved analysis methods using highly purified allergens have improved the sensitivity of diagnostic testing [93]. However, purified proteins may form dimers or larger oligomers and polymers, which can, as well, lead to the masking of relevant B cell epitopes and alteration of IgE-binding capacity [94]. Proper folding of proteins into their native three-dimensional structures is essential for maintaining biological activity and allergenicity as conformational epitopes exist only when the protein is correctly folded [95]. Recombinant allergens produced in different expression systems (E. coli, P. pastoris, or plant-based platforms) may display distinct conformations or stability profiles compared with their native counterparts [96]. On the nanomaterial side, batch-to-batch variation in physicochemical properties, including particle size distribution, surface chemistry, charge, and degree of aggregation, can profoundly impact protein corona formation and allergen binding affinity. Such inconsistencies often arise from differences in synthesis routes, storage conditions, or surface functionalization protocols, and may result in divergent biological outcomes [97]. A critical and often underappreciated source of batch-to-batch variability is endotoxins, which can independently drive or amplify allergic inflammatory responses. Endotoxin may co-purify with the natural allergens and can vary between batches and the nanomaterials can carry or adsorb endotoxin [79]. These endotoxin contaminations have long been recognized as a potent driver of inflammatory responses and remain an active area of research [98,99]. Thus, appropriate controls and transparent reporting of endotoxin units (EU) are important for reproducibility and cross-study comparability. Within the context of physicochemical variability, particle size represents a key determinant of protein adsorption behavior. At constant mass concentration, smaller nanostructures exhibit a higher surface-to-volume ratio, thereby increasing the potential for particle-to-protein interactions and consequently the amount of protein that can be adsorbed. However, protein binding is not governed by surface area alone; particle size also influences the cooperative or competitive adsorption process that shapes the composition and relative abundance of proteins within the corona [97]. For example, the incubation of carboxyl-modified polystyrene nanoparticles with human plasma resulted in a higher relative abundance of immunoglobulins in the protein corona of larger particles [100]. These adsorbed proteins can either mediate or inhibit immune cell recognition of NMs. Regarding shape, human serum albumin shows a threefold higher affinity for spherical AuNPs than for branched AuNPs [101]. Moreover, the electrostatic charge of nanoparticles has been demonstrated to influence the composition of the protein corona, with albumin displaying a higher affinity for either negative or positive surface charge [102]. Consequently, reproducibility and cross-laboratory comparability remain major challenges in this field.

4. Conclusions

Allergen – NM interactions have emerged as a critical determinant of immunological outcomes in both environmental exposure and biomedical applications. Evidence from recent studies demonstrates that allergen adsorption onto NMs surfaces is highly selective and shaped by particle size, surface chemistry, morphology, and agglomeration state. These interactions can modify allergen structure, epitope accessibility, and proteolytic stability, thereby reshaping immune recognition and downstream Th2-driven responses. Importantly, dose, exposure route, and exposure kinetics strongly modulate these biological effects, often determining whether allergen-NM complexes enhance allergenic reactions, remain immunologically neutral, or induce tolerance. Despite substantial progress, major gaps remain, including the lack of standardized analytical pipelines, limited in vivo and chronic-exposure data, and insufficient predictive tools linking NM properties to allergenicity outcomes. Given that adsorption may increase sensitization risk in consumer or occupational settings, improved exposure-relevant models are urgently needed. At the same time, controlled allergen adsorption can be therapeutically harnessed, for example, in tolerogenic or hypoallergenic formulations. Future research should integrate mechanistic in vitro models, in silico dose-bridging approaches, and carefully designed in vivo studies to support safe-by-design NMs that minimize unintended allergen binding. Cross-disciplinary collaboration between nanotechnology, immunology, toxicology, and regulatory science will be essential to translate these insights into actionable safety frameworks and innovative therapeutic strategies.

5. Future perspectives

In the next 5–10 years, our understanding of allergen-nanomaterial interactions is likely to become far more precise, driven by advanced imaging, real-time corona analysis, and smarter computational models. As in vitro barrier systems and organ‑on‑chip technologies mature, researchers will be able to mimic human exposure conditions with greater accuracy, linking structural changes in allergens directly to immune outcomes. At the same time, safe‑by‑design nanomaterials will increasingly incorporate strategies to minimize unintended allergen binding, while intentionally engineered nanoplatforms may open new possibilities for more effective and personalized allergen immunotherapy. With environmental nanomaterials and microplastics gaining global attention, this field is poised to play a key role in shaping future regulatory frameworks and guiding innovations that protect both human health and therapeutic progress.

Funding Statement

The authors gratefully acknowledge financial support by the PINK and the PLANETS projects funded by European Union’s Horizon Europe Research and Innovation program [101137809 and 101177608, respectively]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Article highlights

• Rising allergy prevalence coincides with increased human exposure to engineered nanomaterials (NMs). The rapid expansion of NMs in medical, industrial, and environmental applications has created new opportunities for allergen-nanomaterial interactions across inhalation, dermal, and ingestion routes.

• Allergen adsorption onto NMs is governed by multiple physicochemical factors, including surface charge, hydrophobicity, size, morphology, porosity, and agglomeration state. These parameters collectively influence adsorption efficiency, binding orientation, and corona composition.

• Protein corona formation fundamentally alters allergen identity by changing structural stability, epitope accessibility, proteolytic susceptibility, and allergen processing by antigen‑presenting cells.

• Allergen–NM interactions can induce diverse conformational changes, ranging from partial unfolding and α‑helix/β‑sheet transitions to stabilization of active domains. These structural rearrangements may mask IgE-binding epitopes, expose neoepitopes, or modify T‑cell epitope processing.

• Immunological consequences of allergen-NM complexes are highly context‑dependent. Adsorption can enhance allergic sensitization and airway inflammation or, conversely, promote immune tolerance and support allergen immunotherapy when appropriately engineered.

• NMs may act as unintended adjuvants, amplifying Th2‑skewed responses, IgE production, epithelial barrier disruption, and inflammatory cell infiltration. These effects depend strongly on NM properties and exposure conditions.

• Therapeutic opportunities exist in leveraging allergen – NM interactions for controlled antigen delivery, enhanced allergen uptake, optimized proteolytic processing, and induction of regulatory or Th1-skewed responses in allergen-specific immunotherapy.

• Variability in both allergens and NMs complicates data interpretation. Differences between natural and recombinant allergens, batch-to-batch variation in NM synthesis, aggregation state and endotoxin contamination remain major challenges for comparability and reproducibility.

• Mechanistic in vitro assays alone cannot predict in vivo allergy outcomes, due to the complexity of barrier function, immune system compartmentalization, exposure-dose kinetics, and multi-cellular interactions. Dose bridging using integrated experimental-computational workflows is essential.

• Computational approaches such as molecular dynamics and docking offer mechanistic insight into adsorption energetics, surface-binding patterns, and structural transitions. However, improved modeling of surface functionalization and environmental transformations is still required.

• Advanced experimental models are needed to more accurately simulate allergen-NM interactions at physiological barriers.

• A multidisciplinary approach is vital for bridging nanotechnology, immunology, toxicology, and regulatory science. Harmonized analytical pipelines, exposure-relevant testing frameworks, and predictive models will be key to developing safe-by-design NMs and innovative therapeutic applications.

Author contribution

XC: conceptualization, writing original draft, LS contributed to visualization, MG: writing original draft, SH and NH: writing original draft, visualization, revision, MH: conceptualization, funding acquisition, revision, writing–review, and editing and LJ: conceptualization, writing original draft, revision, writing–review, and editing. All authors have reviewed and approved the manuscript.

Disclosure statement

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.