Gamma-delta TCRs are composed of a gamma and delta chain, and they are found on a subset of T cells known as gamma-delta T cells. These cells are less common than alpha-beta T cells, and they play a distinct role in the immune response by recognizing antigens that are not presented by MHC molecules, such as lipid antigens found on the surface of certain cells. Gamma-delta T cells are also involved in the immune response to certain infections and tumors.