Abstract:

Objective：To analyze effect on the CD154-CD40 signaling pathway and Th1/Th2 polarization by deficient inducible co-stimulator (ICOS)-ICOS ligand (ICOSL) signaling in mice infected with Schistosoma japonicum. Methods:ICOSL knockout (ICOSL-KO) mice and wild-type C57BL/6J mice were used as experimental Schistosomiasis model infected with Schistosoma japonicum. The expressions of CD154 and CD40 on splenocytes and on inflammatory cells around granulomatous infiltration of liver in mice infected with Schistosoma japonicum were analyzed by flow cytometry,immunohistochemical staining, respectively, on the day before infection (0 week)and at the end of 4, 7, 12, 16 and 20 weeks post-infection. The splenocytes of the mice were stimulated with soluble egg antigen(SEA) for 72 hours, then the concentrations of interferon gamma(IFN-γ) and interleukin-4 (IL-4) in the culture supernatants were measured by sandwich enzyme-linked immunosorbent assay (ELISA) kits. The levels of SEA-specific antibodies of IgG and IgG1 and IgG2a were measured in the mice sera by ELISA. The granulomatous pathology in the mice liver was dynamically observed by hematoxylin and eosin (HE) staining.Results:Compared with the wild-type C57BL/6J mice, the expressions of CD154 on CD4+ T splenocytes ［(18.62±4.76)% vs.(27.91±3.94)%, (22.44±4.67)% vs.(40.86±5.21)%, (25.50±6.81)% vs.(43.81±8.41)%, (20.22±5.28)% vs.(40.95±7.34)%, (17.87±4.59)% vs.(33.16±6.31)%, all P<0.01］ and of CD40 on CD19+ B splenocytes ［(19.43±3.26)% vs.(24.37±3.59)%, (23.00±4.47)% vs.(31.80±5.86)%, (24.46±5.01)% vs.(35.85±5.32)%, (23.42±4.69)% vs.(33.30±6.14)%, (22.85±3.78)% vs.(30.88±5.94)%, all P<0.05］ in the ICOSL-KO mice significantly decreased at the end of 4, 7, 12, 16 and 20 weeks post-infection. Moreover, the expressions of CD154［(0.319±0.066) vs.(0.488±0.086), (0.389±0.067) vs.(0.596±0.082), (0.378±0.064) vs.(0.543±0.072), (0.348±0.069) vs.(0.523±0.076), all P<0.01］ and CD40［ (0.398±0.066) vs.(0.546±0.079), (0.461±0.085) vs.(0.618±0.076), (0.453±0.087) vs.(0.587±0.074), (0.449±0.065) vs.(0.565±0.082), all P<0.05］ on inflammatory cells around granulomatous infiltration in liver from the ICOSL-KO mice were significantly lower than those of the wild-type C57BL/6J mice at the end of 7, 12, 16 and 20 weeks post-infection. The levels of IFN-γ of the ICOSL-KO mice were significantly higher than those of the wild-type C57BL/6J mice at the end of 4, 7, 12, 16 and 20 weeks post-infection (P<0.05). However, the levels of IL-4 of the ICOSL-KO mice were significantly lower than those of the wildtype mice (P<0.05). Compared with the wildtype C57BL/6J mice, the levels of SEAspecific antibodies of IgG and IgG1 and IgG2a in the sera of the ICOSL-KO mice significantly decreased (P<0.01). Moreover, The Th2 differentiation index of the ICOSL-KO mice was significantly lower than that of the wild-type mice in post-infection (P<0.01). Also, the ratio of IgG1/IgG2a of the ICOSL-KO mice were significantly lower than that of the wild-type mice at the end of 7, 12 and 16 weeks post-infection (P<0.05). And the vo-lume of liver egg granulomas of the ICOSL-KO mice was significantly smaller than that of the wild-type mice (P<0.01).Conclusion: These findings suggest that there is obvious down-regulation in the expressions of CD154 and CD40 and impairment of Th2 immune response in the ICOSL-KO mice infected with Schistosoma japonicum, accompanying with notedly reduced hepatic granulomatous pathology. The ICOS-ICOSL signaling has a regulatory effect on CD154-CD40 signaling pathway, and may play an important role in the hepatic egg granuloma formation of Schistosomiasis.

Key words: Inducible T-cell co-stimulator protein, CD40 ligand, Th1-Th2 balance, Schistosoma japonicum, Mice, knockout