Heterogeneity of TLR-induced responses in dendritic cells: from innate to adaptive immunity

Toll-like receptors (TLR) mediate recognition of several microbial products. Accumulating evidence indicates that TLR are capable of inducing distinct responses in dendritic cells and other antigen-presenting cells, and can direct T-helper cell differentiation in opposing directions. The generation of such varied responses is achieved through the selective utilization of adaptor molecules that link TLR to distinct signal transduction pathways. The ability of TLR to activate and guide innate and adaptive immunity has the potential to be exploited for practical application that may lead to the development of more successful immunotherapies and vaccination strategies. A review of recent literature, unpublished observations, and future challenges is presented here.