Effect of chronic infection with Schistosoma japonicum on multiple low-dose streptozotocin induced diabetes mellitus in mice

Objective To investigate the effect of chronic infection with Schistosoma japonicum on multiple low-dose streptozotocin (MLDSTZ) induced diabetes mellitus and its possible mechanism. Methods Nineteen male BALB/c mice were randomly divided into 3 groups: S. japonicum infection+MLDSTZ group (group A, n=7), MLDSTZ induced diabetes group (group B, n=6) and normal control group (group C, n=6). Each mouse of group A was infected with 25 cercaria, and then type 1 diabetes was induced by MLDSTZ injection in groups A and B 9 weeks post-infection. Blood glucose levels of mice from each group were observed dynamically. By 12 weeks post-infection, mice were executed and sera were collected, then their pancreases were removed to be scored on insulitis by HE staining. The IFN-γ and IL-4 levels in serum were measured by ELISA. Results Mice injected with STZ became gradually hyperglycemic. On days 21 and days 28 after first injection, the mean blood glucose levels of group A were significantly lower than that of group B (P0.05). There were only less than 40% of islets with lymphocytic infiltration in group A, whereas 80% of islets in group B were infiltrated by massive lymphocyte (P0.01). IL-4 levels in group A were significantly higher than that in group B (P0.01), IFN-γ levels in group B were higher than that in group A (P0.05) and group C (P0.01). Conclusion Chronic infection with S. japonicum has antagonistic effects on MLDSTZ mice, which may be related to immune deviation of Th1 to Th2.