Innate immune functions of human gammadelta T cells.

gammadelta T cells expressing the Vgamma9Vdelta2 T cell receptor (TCR) account for 1-10% of CD3(+) peripheral blood T lymphocytes. Vgamma9Vdelta2 T cells use their TCR as a pattern recognition receptor to sense the presence of infection through specific recognition of intermediates of the microbial non-mevalonate pathway of isoprenoid biosynthesis. Such phosphoantigens rapidly and selectively activate human gammadelta T cells to produce proinflammatory cytokines, notably interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). In addition, human gammadelta T cells express certain Toll-like receptors (TLR) and directly respond to the corresponding ligands. We have demonstrated expression of TLR3 in Vgamma9Vdelta2 T cells and striking costimulatory effects of the ligand polyinosinic-polycytidylic acid (polyI:C) on TCR-stimulated IFN-gamma production. Gene expression studies by microarray analysis identified additional genes that were up-regulated by combined TCR- and TLR3 stimulation. We discuss these findings in the context of the suspected role of human Vgamma9Vdelta2 T cells as a link between innate and adaptive immune responses.