CD4 and infection: Our finding that infected DCs are able to promote IL-10 expression in naïve CD4 T cells, coupled with the inability of infected DCs to stimulate both CD4 and CD8 T cell proliferation, introduces previously unrecognized roles for direct infection and exposure of DCs in triggering a cascade effect of IL-10 production in uninfected cells, both LCMV-specific and polyclonal.