We have previously demonstrated in rat experimental schistosomiasis an upre
gulation of IL-4 expression at the mRNA and protein levels which could expl
ain, at least in part, the increased IgE production observed during infecti
on. 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, li
ver 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, circul
ating 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 secre
ted during rat schistosomiasis, suggesting an involvement of both cytokines
in IgE induction, In the in vivo experiments, only rats cotreated with neu
tralizing anti-IL-4 and anti-IL-13 antibodies showed significant decrease i
n the IgE levels, Moreover, administration of IL-13 enhanced total IgE leve
ls. 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 understand
ing of the role of IL-4 and IL-13 in humans.