High expression of Fas ligand by synovial fluid-derived γδ T cells in Lyme arthritis

gammadelta T cells accumulate at epithelial barriers and at sites of inflammation in various infectious and autoimmune diseases, yet little is understood about the function of tissue-infiltrating gammadelta T cells. We observe that gammadelta T cells of the Vdelta1 subset accumulate in synovial fluid of human Lyme arthritis and are intensely cytolytic toward a wide array of target cells. Particularly striking is that the cytolytic activity is highly prolonged, lasting for at least 3 wk after stimulation of the gammadelta T cells with Borrelia burgdorferi. Cytolysis is largely Fas dependent and results from very high and prolonged expression of surface Fas ligand, which is transcriptionally regulated. This also manifests in a substantial level of self-induced apoptosis of the gammadelta T cells. In this capacity, certain gammadelta T cell subsets may serve as cytolytic sentinels at sites of inflammation, and perhaps at epithelial barriers.