Elevated numbers of SCART1⁺ γδ T cells in skin inflammation and inflammatory bowel disease

The members of the scavenger receptor cysteine-rich (SRCR) superfamily group B have diverse functions, including roles in the immune system. For years it has been known that the WC1 protein is expressed on the surface of bovine γδ T cells, and more recent studies indicate that WC1+ γδ T cells respond to stimulation with bacterial antigens by producing interferon-γ. The SRCR proteins CD5, CD6, Spα, CD163, and DMBT1/gp-340 are also involved in the immune response, since they are pattern recognition receptors capable of binding directly to bacterial and/or fungal components. Here, we investigate a novel murine SRCR protein named SCART1. The ectodomain and the full-length SCART1 were expressed in mammalian cells and used to raise monoclonal antibodies against the ectodomain for immunohistochemical and FACS analysis. Immunohistochemical analysis shows that SCART1 is expressed in a range of lymphoid organs and epithelial-rich tissues by a subset of T cells identified as being γδ T cells by FACS analysis. SCART1 was present in 86% of the γδ T cells and was not found in CD4+ or CD8+ T cells. The numbers of SCART1+ cells were elevated in two mouse models of human diseases: skin inflammation and inflammatory bowel disease. In the skin inflammation model, an 8.6-fold increase in SCART1+ cells was observed. Finally, recombinant SCART1 protein was found not to bind to selected bacterial or fungal components or to whole bacteria. Our results show that SCART1 is a novel γδ T cell marker and it is therefore likely that SCART1 plays a role in the immune response.