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 is involved in the recognition of certain bacterial, self-CD1 molecule, and tumor antigens bound to MHC class I. The gamma/delta TCR associates with CD3 and is expressed on a subset of T cells found in the thymus, the intestinal epithelium, and the peripheral lymphoid tissues and peritoneum. Most gamma/delta T cells are CD4-/CD8-, some are CD8+. T cells expressing the gamma/delta TCR have been shown to play a role in oral tolerance, innate immune response for some tumor cells, and autoimmune disease. It has been reported that gamma/delta T cells also play a principal role in antigen presentation.