CD4+CD25+ regulatory T cells control the magnitude ofT‐dependent humoral immune responses to exogenous antigens

CD4+CD25+ T reg cells are critical for peripheral tolerance and prevention of autoimmunity. Here we show that CD4+CD25+ T reg also regulate the magnitude of humoral responses against a panel of T‐dependent antigens of foreign origin during both primary and secondary immune responses. Depletion of CD4+CD25+ T cells leads to increased antigen‐specific antibody production and affinity maturation but does not affect T‐independent B cell responses, suggesting that CD4+CD25+ T reg exert a feedback mechanism on non‐self antigen‐specific antibody secretion by dampening the T cell help for B cell activation. Moreover, we show that CD4+CD25+ T reg also suppress in vitro B cell immunoglobulin production by inhibiting CD4+CD25– T cell help delivery, and that blockade of TGF‐β activity abolishes this suppression.