How pattern recognition receptor triggering influences T cell responses: a new look into the system

Signaling through pattern recognition receptors (PRRs) in antigen-presenting cells (APCs) is required for the induction of T cell responses. PRR triggering in APCs induces important cellular modifications that have profound effects on antigen internalization, processing, MHC loading and antigen presentation. Accumulating experimental evidence also suggests that the fate of T cell responses depends strongly on the type of PRR triggered and the timing of PRR signaling. Here, we discuss the beneficial effects of PRR stimulation in the context of priming naive T cells, the generation and maintenance of effector/memory T cells, and the induction or break of tolerance. We propose a new classification into opsonic, phagocytic and instructive PRRs based on the functional properties of the receptors.