Emerging functions of basophils in protective and allergic immune responses.

Basophils that were long thought to have a redundant role in mast cells in the effector response to allergens and parasites are now being recognized to have important roles in the regulation of adaptive immune responses. Recent data have revealed their role in the initiation of the T helper cell 2 (Th2)-mediated immune response. Not only do basophils guide the Th1-Th2 balance by providing an early source of crucial Th2-skewing cytokines, interleukin (IL)-4 and thymic stromal lymphopoietin, but recent findings have also illustrated their capacity to function as antigen-presenting cells. Thus, basophils activate and instruct naive CD4 T cells, and guide their development into Th2 cells. Not only do basophils directly interact with T cells, but new insights have illustrated that they may also directly guide antibody responses in both the primary and memory responses. These and other studies have illustrated the emerging role of basophils in the regulation of type 2 immunity.