Toll-like receptors (TLRs) detect microbial infection and have an essential role in the induction of immune responses^,,. TLRs can directly induce innate host defence responses, but the mechanisms of TLR-mediated control of adaptive immunity are not fully understood. Although TLR-induced dendritic cell maturation is required for activation of T-helper (T_H) cells, the role of TLRs in B-cell activation and antibody production in vivo is not yet known. Here we show that activation and differentiation of T_H cells is not sufficient for the induction of T-dependent B-cell responses. We find that, in addition to CD4⁺ T-cell help, generation of T-dependent antigen-specific antibody responses requires activation of TLRs in B cells.