Abstract: Objective To establish the ICOS transgenic mice schistosomiasis japonica model and to observe the immune response and immunopathology of the model. Methods The transgenic mice were infected with Schistosoma japonicum. Spleen cells and sera of mice were harvested at week 4， 6， and 8 after infection. The cytokines IFN-γ and IL-4 were measured in culture supernatans by ELISA. The serum IgG， IgG1 and IgG2a were measured by ELISA at different period of infection. Liver tissue sections were prepared with HE staining. Liver granuloma formation was observed under microscope. Results The expression level of IFN-γ showed no significant difference between ICOS transgenic mice and control， while that of IL-4 in ICOS transgenic mice was significantly up-regulated to 20.81±1.95 and 25.31±3.37 pg/ml at week 6 and 8 respectively （P<0.01）. The serum IgG and IgG1 in ICOS transgenic mice were also significantly higher than those in control. Th2 differentiation index and IgG1/IgG2a were used to evaluate the immune regulation balance of Th1/Th2， and results showed that Th2 response in ICOS transgenic mice was significantly stronger than that of the control. The egg granuloma response in ICOS transgenic mice was also significantly stronger than that in control（P<0.01）. The rate of egg granuloma enlargement was 24.48% and 26.37% at week 6 and 8 respectively. Conclusion The findings suggest that there is stronger Th2 type response in ICOS transgenic mice infected with Schistosoma japonicum and ICOS may play an important role in the egg granuloma formation of Schistosoma japonicum.

Key words: Schistosoma japonicum, Egg granuloma, Th1/Th2, ICOS transgenic mice