Antigen-specific, major histocompatibility complex-restricted recognition by classical T cells is mediated by a T cell receptor (TCR) consisting of a disulfide-linked αβ heterodimer. During the search for the genes encoding the α and β proteins, a third immunoglobulin-like gene, termed γ, was uncovered. Like the TCR α and β genes, the TCR γ gene consists of variable and constant segments that rearrange during T cell development in the thymus. Although the physiological role of TCR γ remains an enigma, much has been learned with the recent identification of the protein products of this gene family in both mice and humans. The γ chain is associated with a partner chain, termed δ. The γδ heterodimer is associated with an invariant T3 complex, very similar to that associated with the αβ heterodimer, and appears predominantly, if not exclusively, on cells with a CD4-, CD8- phenotype both in the thymus and in the periphery. TCR γδ is the first T3-associated receptor to appear during thymocyte development and defines a separate T cell lineage distinct from αβ-bearing cells. Although TCR αβ-bearing cells and TCR γδ-bearing cells follow parallel developmental pathways, the diversity of expressed γδ receptors is extremely limited relative to that of αβ receptors.
ASJC Scopus subject areas
- Molecular Biology