Emerging roles of granulocytes in B cell responses

Protective antibody responses require cognate interaction between B cells and T helper cells in the germinal center of lymphoid follicles. This interaction leads to the formation of plasma cells that secrete high-affinity antibodies of different classes with distinct effector functions. Growing evidence shows that B cells receive additional helper signals from a variety of cells of the innate immune system, including dendritic cells, macrophages, follicular dendritic cells and epithelial cells. Granulocytes are a fundamental component of the innate immune system, as they are the first leukocytes that infiltrate infection and inflammation sites in order to clear invading microbes and necrotic cells. Granulocytes utilize opsonizing antibodies to enhance their phagocytic and killer functions, but recent studies indicate that granulocytes also optimize antibody diversification and production. In this article, the mechanisms by which different subsets of granulocytes deliver helper signals to B cells and plasma cells are discussed.