Interleukin-13 and IgE production in rat experimental schistosomiasis

We have previously demonstrated in rat experimental schistosomiasis an upregulation of IL-4 expression at the mRNA and protein levels which could explain, at least in part, the increased IgE production observed during infection. Using this model, we have investigated the expression of IL-13 which is also involved in the induction of the IgE response. In the present study, we have shown a significant increase in IL-13 mRNA expression in spleen, liver and lungs following primary and secondary infection. IL-13 protein was detected by intracellular staining in spleen cells from infected rats, and in the supernatants of antigen-stimulated spleen cells. Furthermore, circulating levels of IL-13 were increased in sera from infected rats as compared to those from non-infected control animals. These findings show that, similarly to IL-4, IL-13 is upregulated and secreted during rat schistosomiasis, suggesting an involvement of both cytokines in IgE induction. In the in vivo experiments, only rats cotreated with neutralizing anti-IL-4 and anti-IL-13 antibodies showed significant decrease in the IgE levels. Moreover, administration of IL-13 enhanced total IgE levels. These results demonstrate the implication of IL-4 and IL-13 in vivo in IgE production, and provide a relevant animal model for a better understanding of the role of IL-4 and IL-13 in humans.