Pathogenesis and Immune Reaction in C57BL/6 and CBA/N Mice Infected with Clonorchis sinensis

Abstract

To develop a mouse model for the early immune responses in clonorchiasis, the CBA/N mouse, in which Th1 and Th17 responses dominate, and the C57BL/6, in which the Th2 response is dominant were examined. Two different strains of mice were infected with Clonorchis sinensis metacercariae and analyzed 2, 4, and 8 weeks later. CBA/N mice infected with C. sinensis developed more severe gross and histopathological changes than C57BL/6 mice, including more pronounced inflammatory cell infiltration and hepatocyte necrosis in CBA/N mice, especially at 2 weeks post-infection. Additionally, serum biomarkers of liver injury (ALT and AST) were increased significantly in CBA/N mice after C. sinensis infection, compared with those in infected C57BL/6 mice. Proliferation of splenocytes and cytokine production of the splenocytes was analyzed after stimulation with crude C. sinensis antigen. The splenocytes from CBA/N mice were highly proliferative and the IL-17 level was increased. Additionally, an increased IL-4 level was sustained until 8 weeks post-infection in CBA/N mice. The serum levels of C. sinensis-specific IgG1 and IgG2a were increased in CBA/N mice, whereas IgE was increased in C57BL/6 mice. To directly ascertain the role of IL-17 in the development of C. sinensis-induced liver inflammation, IL-17-neutralizing mAb were treated after infected with C. sinensis. Because IL-17 production was increased from 2 weeks p.i., infected C57BL/6 and CBA/N mice were systemically administrated with anti-IL-17 or rat IgG2a isotype control and the mice were sacrificed on 2 weeks p.i. Anti-IL-17 mAb, but not the control mAb, significantly improved the liver histopathological appearance. Accordingly, anti-IL-17 mAb-treated mice displayed attenuated liver injury, as indicated by considerably decreased levels of serum ALT (from 284 ± 162.8 to 70 ± 16.4) and AST (from 215 ± 65.5 to 121 ± 18.6) in CBA/N mice. Intrahepatic lymphocytes and splenocytes were isolated from each mouse and counted. Their numbers were significantly decreased from C. sinensis-infected mice treated with IL-17-neutralizing mAb than the positive control both in CBA/N mice. In conclusion, the CBA/N mouse is a good animal model to study early immune response after infection with C. sinensis. The infected CBA/N mice stimulate differentiation of pathogenic Th17 cells as well as to produce humoral immunity by B cells. IL-17 is playing a key role for development of severe immunopathology of the liver in early stage of clonorchiasis.