Major histocompatibility complex class II-dependent basophil-CD4(+) T cell interactions promote T(H)2 cytokine-dependent immunity

Dendritic cells can prime naïve CD4(+) T cells, however we demonstrate that DC-mediated priming is insufficient for the development of T(H)2 cell-dependent immunity. We identify basophils as a dominant cell population that coexpressed MHC class II and Il4 message following helminth infection. Basophilia was promoted by thymic stromal lymphopoietin (TSLP) and depletion of basophils impaired immunity to helminth infection. In vitro, basophils promoted antigen-specific CD4(+) T cell proliferation and IL-4 production and transfer of basophils augmented the expansion of helminth-responsive CD4(+) T cells in vivo. Collectively, these studies suggest that MHC class II-dependent interactions between basophils and CD4(+) T cells promote T(H)2 cytokine responses and immunity against helminth infection.