Table 1.
Recognition and signaling pathways contributed to host cell–N. caninum crosstalk.
| Host Factors | Host Species | Parasite or Its Molecule | Impacts and Outcomes | References |
|---|---|---|---|---|
| TLR2 | Bovine trophoblast and caruncular cells | N. caninum tachyzoites (Nc-Spain7 and Nc-Spain1H) | Higher mRNA expression levels of TLR-2 were noticed in the trophoblast cell line infected with the low-virulence Nc-Spain1H. | [87] |
| TLR2 and MAPK | BMDM from C57BL/6 (WT) and TLR2−/− mice | N. caninum tachyzoites (Nc-1) | N. caninum extracellular vesicles significantly increased the production of IL-12p40, TNF-α, IL-1β, IL-6, and IFN-γ by WT-BMDMs than in TLR2−/− mouse BMDMs mediated by MAPK signaling pathway. | [88] |
| TLR2 and TLR4 | Mouse macrophages cell line and DCs from OF1 mice | NcGPI | NcGPI induced stimulation of TLR2 and TLR4 from HEK cells, and TNF-α, IL-1β and IL-12 secretion by macrophages and DCs. NcGPIs reduced expression of MHC molecules of class I on DCs. |
[89] |
| TLR2 | DCs and in vivo assays in BALB/c mice | NcPDI, NcROP2 NcROP40 (Nc-Spain7) | Vaccination of mice with cocktail antigen mixed with OprI; TLR2 adjuvant induced a Th1/Th2 immune response in adult mice and conferred protection in adult and offspring mice. In vitro, cocktail antigens stimulated secretion of TNF-α in DCs. |
[90] |
| TLR2 | Spleen cells from C57BL/6 mice and TLR2−/− mice and in vivo assay | NcCyp-entrapped with oligomannose-coated liposomes (Nc-1) | Immunized WT mice with NcCyp-OML showed high protection against N. caninum infection in comparison to TLR2−/− immunized mice. Spleen cells from immunized WT mice with NcCyp-OML showed higher IFN-γlevels than those of TLR2−/− mice. |
[91] |
| TLRs 2 and 9 | Bovine plasma | NcPF (Nc-1) | The vaccine formulated with TLRs 2 and 9 agonists improved the production of systemic IFN-γ and induced long-term recall B-cell responses. | [92] |
| TLR4 | Dog blood | N. caninum in naturally infected animals | In genotyped sample, one TLR4 SNP marker was recorded in seropositive dog samples for N. caninum. | [93] |
| TLR4- and IL-12Rβ2 | WT and 57BL/10ScCr mice lacking TLR4 and IL-12 receptors |
N. caninum tachyzoites (Nc-1) |
All C57BL/10ScCr mice but not WT were succumbed by 8 dpi. KO mice showed higher parasite burden in the internal organs than WT controls, which might be correlated with reduced IFN-γ and increased IL-4 expressions. |
[94] |
| TLR4- and IL-12Rβ2 | WT and 57BL/10ScCr mice lacking TLR4 and IL-12 receptors |
N. caninum tachyzoites (Nc-1) |
TLR4−/− and IL-12Rβ2−/− were succumbed after intragastric challenge with N. caninum tachyzoites. In contrast, WT-BALB/c mice challenged with parasites remained alive for at least 6 months. | [95] |
| TLR3 and TRIF | BMDM from WT and TLR3−/− and TRIF−/− mice | N. caninum tachyzoites (Nc-Liv and Nc-1) | Infection of macrophages from mice with targeted deletions in various innate sensing genes demonstrates that host responses to N. caninum are dependent on the TLR3 and the adapter protein TRIF. RNA from Neospora elicited TLR3-dependent type I IFN responses. |
[96] |
| TLR11 and ERK | Peritoneal macrophages from C57BL/6 mice | N. caninum tachyzoites (Nc-1) |
N. caninum infection rapidly activated MEK-ERK signaling via TLR11 in mouse peritoneal macrophages. N. caninum infection elevated IL-12p40 by macrophages, which was significantly reduced via inhibition of TLR11/MEK/ERK pathway. |
[97] |
| TLR3 and TRIF | BMDM from C57BL/6 and TLR3−/− and TRIF−/− | N. caninum tachyzoites (Nc-Liv) | TLR3−/− and TRIF−/− mice showed higher parasite burdens, increased inflammatory lesions, and reduced production of IL-12p40,TNF-α, IFN-γ, and NO. N. caninum tachyzoites and RNA recruited TLR3 to the PV and translocated IRF3 to the nucleus, and upregulated the expression of TRIF in murine macrophages. |
[98] |
| TLR3, 7 and 8, 9 | Bovine placenta and fetal spleen. | N. caninum tachyzoites (Nc-1) | mRNA expression levels of TLRs 3, 7, 8, and 9 were high in the spleen of fetuses from N. caninum-infected heifers, and in the placenta and maternal caruncle from infected heifers. | [99] |
| TLR3, 7, 8 and 9 | Fetal-maternal interface of cattle | Inactivated soluble whole antigens (Nc-6), and rNcSAG1, rNcHSP20 and rNcGRA7 (Nc-1) | Heifers immunized with inactivated soluble antigens and recombinant NcSAG1, NcHSP20 and NcGRA7 showed higher TLR7 and 8 expressions in caruncles than non-immunized heifers. | [100] |
| CCR5 | Peritoneal monocytes and BMDM from C57BL/6 and CCR5−/− | N. caninum tachyzoites excreted/secreted antigens (Nc-1) | Excreted/secreted antigens from N. caninum (NcESAs) attracted monocytes to the site of infection in both in vitro and in vivo. NcCyp in the NcESAs might work as chemokine-like proteins and NcESA-induced chemoattraction involved CCR5 contribution. |
[101] |
| CCR5 | Murine and bovine cells | NcCyp (Nc-1) | Recombinant protein of NcCyp induces the migration of murine and bovine cells in a CCR5-dependent manner | [102] |
| CCR5 | DC and NKT cells from C57BL/6 J and CCR5−/− mice and in vivo assays. | N. caninum tachyzoites (Nc-1) | In the N. caninum-infected CCR5−/− mice, increased mortality and neurological dysfunctions, poor migration of DCs and NKT cells to the site of infection were observed. Higher IFN-γ and CCL5 levels were associated with brain tissue damage of CCR5−/− mice during the infection, and a primary microglia culture from CCR5−/− mice showed lower IL-6 and IL-12 productions against N. caninum. |
[103] |
| NOD2 | BMDM and in vivo assay using C57BL/6, (NOD2−/−) mice | N. caninum tachyzoites (Nc-1) | Infection of macrophages with N. caninum increased expression of NOD2, and NOD2−/− macrophages decreased IL-6 and TNF-α, and increased production of arginase-1 and IL-10 In vivo, NOD2−/− mice reduced MAPK phosphorylation and IL-6 production, and decreased inflammation in organs with higher parasite burden, but mice were partially resistant to lethal doses of tachyzoites. |
[104] |
| Dectin-1 | BMDM, DCs and spleen homogenate from C57BL/6 and Dectin-1−/− | N. caninum tachyzoites (Nc-1) | Lacking Dectin-1 rescued 50% of the mice infected with N. caninum, and Dectin-1−/− mice presented a reduction in the parasite load during acute and chronic phases. In vitro, IL-12p40 increased in N. caninum infected macrophages, DC and spleen cells of Dectin-1−/− mice than WT. |
[105] |
| PPAR-γ | BALB/c mice | N. caninum tachyzoites (Nc-1) | In vitro study, N. caninum treated macrophages revealed promotion of M2-ploarized phenotype compared with the GW9662 (PPAR-γ inhibitor) group and RGZ (PPAR-γ agonist) group, through up-regulating the activity of PPAR-γ and inhibiting NF-κB activation. | [106] |
| NLRP3 inflammasome | Peritoneal macrophages from C57BL/6 and Nlrp3−/− mice | N. caninum tachyzoites (Nc-1) | Inflammasome activation-mediated caspase-1 processing and IL-1β cleavage in response to infection with N. caninum were observed and correlated with the time of infection and infective dose. | [107] |
| NLRP3 inflammasome | BMDM from C57BL/6 and Nlrp3−/− mice | N. caninum tachyzoites (Nc-1) | In vitro results showed that N. caninum infection of murine BMDMs activated the NLRP3 inflammasome, associated with the release of IL-1β and IL-18, cleavage of caspase-1, and induction of cell death. Infection of Nlrp3−/− and caspase-1/11−/− mice resulted in decreased production of IL-18 and reduced IFN-γ in serum. |
[108] |
| Inflammasome mediate-caspase-1 | Cattle macrophage cell line | N. caninum tachyzoites (Nc-1) | Inflammasome-mediated activation of caspase-1 occurs in N. caninum-infected bovine macrophages. Caspase-1-dependent cell death triggered in N. caninum-infected cells. |
[109] |
| NF-kB | 293T human cell lines | NcGRA6 (Nc-1) | 293T cells were transfected with the luciferase reporter plasmids and the expression vector of NcGRA6 gene encoding protein. Cells transfected with NcGRA6 gene strongly activated NF-kB. | [126] |
| MAPK, AKT, and NF-kB | Peritoneal macrophages from C57BL/6 mice | Nc14-3-3 (Nc-1) | Recombinant Nc14-3-3 activates the MAPK and AKT signaling pathways, associated with an increase of IL-6, IL-12p40, and TNF-α. Phosphorylated NF-kB/p65 was observed in peritoneal macrophages treated with rNc14-3-3. |
[127] |
| MyD88 | C57BL/6 and MyD88−/− mice | N. caninum tachyzoites (Nc-1) | Sub-lethal infection induced acute mortality of MyD88−/− mice. Higher parasite burden in MyD88−/− mice was associated with reduced IL-12 production by DCs, delayed IFN-γ responses by NKT, CD4+ and CD8+ T lymphocytes, and production of high levels of IL-10. |
[128] |
| TLR2/MyD88 | Various immune cells from C57BL/6 b, TLR2−/− and MyD88−/− and in vivo assay |
N. caninum soluble antigen and tachyzoite (Nc-1) | Peritoneal macrophages and BMDDC exposed to N. caninum-soluble antigens increased the expression of TLR2. In case of infection, CD4+ and CD8+, and IFN-γ:IL-10 ratio decreased, and parasite burden increased in TLR2−/− mice than WT mice. |
[129] |
| MAPK | BMDM from C57BL/6 and in vivo assay | N. caninum tachyzoites (Nc-1) | p38 phosphorylation wasinduced in macrophages stimulated by live tachyzoites and antigen extracts, while its inhibition increased IL-12p40production. In vivo blockade of p38 increased production of cytokines, enhanced survival against the infection. |
[130] |
| ERK 1/2- and p38 MAPK | Bovine neutrophils | N. caninum tachyzoites (Nc-1) | N. caninum tachyzoites triggered extracellular trap formation in bovine neutrophils via ERK 1/2-, or p38 MAPK-signaling pathway | [131] |
| ERK 1/2- and p38 MAPK | Bovine macrophage | N. caninum tachyzoites (Nc-1) | N. caninum tachyzoites induced bovine macrophage-derived extracellular trap-like structures, which may be mediated by an ERK 1/2- and p38 MAPK-pathway. | [132] |
| ERK 1/2- and p38 MAPK | Caprine monocytes | N. caninum tachyzoites (Nc-1) | N. caninum tachyzoites triggered extracellular trap formation in caprine monocytes by ERK 1/2-, or p38 MAPK-signaling pathway dependent manner. | [133] |
| ERK 1/2, and p38 MAPK | Canine neutrophils | N. caninum tachyzoites (Nc-1) | N. caninum tachyzoites strongly induced NETs formation in canine neutrophils ERK 1/2, and p38 MAPK signaling pathways. | [134] |
| PI3K | Caprine neutrophils | N. caninum tachyzoites (Nc-1) | The inhibition of PMN autophagy via inhibition of the PI3K mediated signaling pathway resulted in failure of tachyzoite-induced NETosis. | [135] |
| NFAT | 293T cells transfected with the luciferase reporter plasmids | NcGRA7 (Nc-1) | Infection with NcGRA7−/− parasites showed reduced virulence in mice. The levels of IFN-γ in the ascites fluid, CXCL10 expression in the peritoneal cells, and CCL2 expression in the spleen were lower 5 dpi with the NcGRA7−/− parasite than the parental strain. |
[126] |
| STAT3 | HFF cells and in vivo assay using BALB/c mice. | NcROP16 (Nc-1) | NcROP16 secretion in host cell phosphorylates STAT3, and pSTAT3 then migrates to the cell nucleus. Deletion of NcROP16 decreased parasite growth kinetics in vitro and reduced virulence in mice. |
[40] |
| JAK-STAT | Bovine monocytes | N. caninum tachyzoites (Nc-Liv) | Neonatal monocytes are more resistant to cellular invasion with N. caninum and the magnitude of the responses is related to significant changes in the JAK-STAT pathway. | [136] |
| l-arginine/NO | BALB/c and NO−/− mice | N. caninum tachyzoites (Nc-1) | Production of NO increased in cultures of macrophages treated with IFN-γ, and dose-dependent growth inhibition was observed. Blockade of l-arginine-dependent pathway, NG-monomethyl-l-arginine, reduced the inhibitory effects induced by IFN-γ. |
[137] |