CD8A, also known as T-cell surface glycoprotein CD8 alpha chain, is a protein encoded by the CD8A gene. It is a cell surface glycoprotein found on most cytotoxic T lymphocytes, mediating efficient cell-cell interactions within the immune system. The CD8 protein acts as a coreceptor with the T-cell receptor on T lymphocytes to recognize antigens displayed by antigen-presenting cells in the context of class I MHC molecules. The functional coreceptor can be either a homodimer composed of two alpha chains or a heterodimer composed of one alpha and one beta chain. CD8A has significant homology to the variable domain of immunoglobulin light chains. It plays an essential role in the immune response, enabling cytotoxic T lymphocytes to recognize and eliminate infected cells and tumor cells.