CD8a

CD8a is the alpha chain of the CD8 co-receptor, expressed as alpha-alpha homodimers or alpha-beta heterodimers on cytotoxic T lymphocytes, NK cells, and thymocytes. Each chain carries one extracellular immunoglobulin-like domain that docks onto the α3 domain of MHC class I molecules, stabilizing TCR recognition and allowing Lck, associated with the CD8 cytoplasmic tail, to phosphorylate the TCR complex. In the thymus, CD8 expression marks the cytotoxic lineage during positive selection. Anti-CD8a antibodies are indispensable tools for identifying cytotoxic T cells in immunophenotyping and tissue staining, and CD8a is used to track antitumor CD8+ T cell responses in cancer immunotherapy monitoring.