CD40/CD154 interactions are required for the optimal maturation of skin-derived APCs and the induction of helminth-specific IFN-gamma but not IL-4.

The mechanisms through which Schistosoma mansoni larvae induce Th1 rather than Th2 immune responses are not well understood. In this study, using CD154-/- mice exposed to radiation-attenuated S. mansoni larvae, we demonstrate roles for CD154/CD40 in the activation of skin-derived APCs and the development of Th1 cells in the skin-draining lymph nodes (sdLN). The presence of CD154 was important for optimal IL-12p40 and essential for Ag-specific IFN-gamma, but CD154 expression by wild-type CD4- cells was insufficient to rescue recall responses of CD4+ cells from CD154-/- mice. This defect is probably due to impaired CD40-dependent IL-12 production in vivo, because administration of anti-CD40 Ab, or rIL-12, restored IFN-gamma production by sdLN cells from CD154-/- mice. CD154 ligation of CD40 was not required for the migration of skin-derived APCs, but did have a limited role in their maturation (increased MHC II and CD86). Unexpectedly, although CD4 cells from CD154-/- mice were deficient in their ability to produce IFN-gamma, they produced significant amounts of IL-4 and IL-5 in the presence of skin-derived APCs from wild-type and CD154-/- mice. Thus, in contrast to IFN-gamma, the production of Th2-associated cytokines is (in this model) independent of CD154. We conclude that whereas the priming of Th1 responses soon after exposure to schistosome larvae is completely CD40/CD154 dependent, IL-4, IL-5, and IL-13 are independent of CD154, suggesting a dichotomy in the specific mechanisms that induce these cytokines by CD4+ cells in the sdLN.