Immune changes of Schistosoma japonicum infections in various rodent disease models.

Rodent models for Schistosoma japonicum infections have demonstrated that these animals possess a degree of resistance to schistosome infections that may be both T and B lymphocyte-mediated. However, their exact role is not well-defined and other immune mechanisms are likely to also play a role in protecting against infection. Immunosuppressed and immunocompetent reed voles (Microtus fortis, Mf), rats and mice (n=24/group) were infected with S. japonicum, and animals were sacrificed 42 days later under anesthesia. Neither worms nor eggs were observed in infected immunosuppressed Mf or rats, with the exception of one rat that presented with few eggs. In immunosuppressed mice, changes in the number and size of the worms were not significantly different compared to immunocompetent mice, but worm fecundity was affected. The size and number of granulomas in immunosuppressed animals was also reduced. Analysis of serum antibodies specific to schistosome adult worm antigen at 3 weeks post-infection demonstrated that the levels of antibodies in the sera of rats were significantly higher than in Mf and mice. In addition, Mf serum levels of IL-4 and IL-12 were significantly higher than levels observed in rats and mice. Antibodies and cytokines in the sera of Mf peaked 3 weeks post-infection and then began to decrease, while antibody responses in rats and mice increased gradually between weeks 3-7 post-infection. It is possible that T and B cells have a dual role in both mediating protection and exacerbating disease outcomes.