T cell receptor (TCR) is a heterodimer consisting of an alpha and a beta chain (TCR alpha/beta) or a gamma and a delta chain (TCR gamma/delta). TCR gamma/delta belongs to the immunoglobulin superfamily, which is involved in the recognition of certain bacterial and tumor antigens bound to MHC class I. gamma/delta TCR associates with CD3 and is expressed on a T cell subset found in the thymus, the intestinal epithelium, and the peripheral lymphoid tissues and peritoneum. Most gamma/delta T cells are CD4-/CD8- although some are CD8+. T cells expressing the gamma/delta TCR have been shown to play a role in oral tolerance, tumor-associated tolerance, and autoimmune disease. It has been reported that gamma/delta T cells also play a principal role in antigen presentation.