Alternatively activated mononuclear phagocytes from the skin site of infection and the impact of IL-4Rα signaling on CD4+T cell survival in draining lymph nodes after repeated exposure to Schistosoma mansoni cercariae

In areas endemic for schistosomiasis, repeated exposure to infective cercariae is a frequent occurrence, and repeated exposure of murine skin to Schistosoma mansoni resulted in CD4+ T cells becoming hypo-responsive. Here potential contributory mechanisms were investigated. In the skin infection site, three mononuclear phagocyte populations were identified (tissue macrophages, dendritic cells, and macrophages) which exhibited up-regulation of genes associated with alternative activation, in particular the gene encoding RELMα. However, in repeatedly infected mice deficient in RELMα, there was no change in the abundance of mononuclear phagocytes in the skin, and CD4+ cells in the skin draining lymph nodes remained hypo-responsive. In mice deficient for IL-4Rα, required for alternative activation, levels of dermal regulatory IL-10 were reduced and there was an increase in the abundance of antigen presenting MHC-IIhigh cells, which was accompanied by increased numbers of CD4+ T cells. Although the absence of IL-4Rα did not translate into increased CD4+ cell responsiveness, they exhibited lower expression of Fas/FasL, resulting in decreased apoptosis/cell death and increased cell viability. This study highlights a mechanism through which IL-4Rα may regulate the immune system through the induction of IL-10 and regulation of Fas/FasL mediated cell death. Mice were infected 1x or 4x with S. mansoni cercariae via the pinnae. Pinnae were harvested 4 days after the final infection and the DEC obtained after an overnight culture in vitro. Cells were then stained with F4/80 APC and MHC-II PE and four different populations sorted (using the MoFlo or the Astrios) based on their expression profiles. Several mice (12-18) from each group were pooled to generate each replicate.