High Expression of Fas Ligand by Synovial Fluid-Derived γδ T Cells in Lyme Arthritis

γδ 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 γδ T cells. We observe that γδ T cells of the Vδ1 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 γδ 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 γδ T cells. In this capacity, certain γδ T cell subsets may serve as cytolytic sentinels at sites of inflammation, and perhaps at epithelial barriers.