CD8A

CD8A is the gene that encodes the alpha chain of the CD8 co-receptor, a transmembrane glycoprotein that participates in the immune response of cytotoxic T lymphocytes. The CD8 co-receptor can form either a heterodimer with the CD8 beta chain (CD8αβ) or, in some T cell subsets and tissues, a homodimer composed of two CD8α chains (CD8αα). The CD8A-encoded protein is expressed on most CD8+ T cells and on certain natural killer T cells, contributing to their recognition of antigen presented by MHC class I molecules.

Structure and interactions: The CD8α chain contains an extracellular immunoglobulin-like domain responsible for binding to the conserved α3 domain of MHC class I molecules. The cytoplasmic tail mediates signaling by recruiting the Src family tyrosine kinase Lck, which accompanies the T cell receptor upon antigen recognition. The extracellular domain, together with CD8β or CD8α, stabilizes the interaction between the T cell receptor and peptide–MHC class I complexes, thereby enhancing T cell activation.

Function: CD8A product acts as a co-receptor that lowers the overall threshold for TCR signaling during recognition of peptide antigens presented by MHC class I. This support is important for effective cytotoxic responses to infected or malignant cells and for thymic selection processes that shape the CD8+ T cell repertoire. The balance of CD8αβ versus CD8αα forms may influence signaling strength and cell fate in different contexts.

Genetics and expression: In humans, the CD8A gene is located on the genome as part of the CD8 locus and is expressed predominantly on cytotoxic T cells and related immune cell subsets. CD8A is widely used as a marker to identify CD8+ T cells in research and clinical immunophenotyping.