TCR γ/δ (TCR gamma/delta) [H41]

T-cell receptor (TCR), a heterodimer composed of either α and β or γ and δ chains, recognizes foreign antigens and translates such recognition events into intracellular signals that elicit a change in the cell from a dormant to an activated state. TCR recognition of self-peptides has been linked to autoimmune disease. Mutant self-peptides have been associated with tumors. Most human T cells (95%) express the α/β or either CD4 or CD8 molecule (single positive, SP), while 2-5% express the γ/δ. However, a small number of T cells lack both CD4 and CD8 (double negative, DN). T helper cells express CD4 proteins and T cytotoxic cells display CD8. Increased percentages of α/β DN T cells have been identified in some autoimmune and immunodeficiency disorders. γ/δ T cells are primarily found within the epithelium. They show less TCR diversity and recognize antigens differently than α/β T cells. Subsets of γ/δ T cells have shown antitumor and immunoregulatory activity.