CD8A, also known as CD8 or T-cell surface glycoprotein CD8 alpha chain, is a crucial integral membrane glycoprotein predominantly found on cytotoxic T lymphocytes. It functions as a coreceptor, aiding the T-cell receptor (TCR) in recognizing antigens presented by antigen-presenting cells (APCs) in the context of MHC class I molecules. This interaction is vital for the activation of cytotoxic T-lymphocytes (CTLs), which can then identify and eliminate infected or tumor cells. CD8A can exist as a homodimer of two alpha chains or as a heterodimer with a beta chain, both forms sharing significant homology to immunoglobulin variable light chains. The protein is also involved in intracellular signaling pathways, leading to lymphokine production, motility, adhesion, and activation of CTLs. Additionally, CD8A has been implicated in various diseases and is classified as a disease-related gene.