Identification and characterization of polyclonal αβ-T cells with dendritic cell properties

An efficient immune response requires coordination between innate and adaptive immunity, which act through cells different in origin and function. Here we report the identification of thymus-derived αβ-T-cell receptor+ cells that express CD11c and major histocompatibility complex class II, and require FLT3 ligand for development (T(DC)). T(DC) express genes heretofore found uniquely in T cells or dendritic cells, as well as a distinctive signature of cytotoxicity-related genes. Unlike other innate T-cell subsets, T(DC) have a polyclonal T-cell receptor repertoire and respond to cognate antigens. However, they differ from conventional T cells in that they do not require help from antigen-presenting cells, respond to Toll-like receptor-mediated stimulation by producing interleukin-12 and process and present antigen. The physiological relevance of T(DC), found in mice and humans, is still under investigation, but the fact that they combine key features of T and dendritic cells suggests that they provide a bridge between the innate and adaptive immune systems.