CD8 antigen (CD8 co-receptor) (CD8)

The CD8 antigen is a transmembrane glycoprotein expressed primarily on the surface of cytotoxic T lymphocytes. It functions as a critical co-receptor with the T-cell receptor (TCR), specifically recognizing antigens presented by major histocompatibility complex class I molecules on target cells. The molecule exists as either a homodimer of two alpha chains (CD8αα) or more commonly as a heterodimer composed of an alpha and beta chain (CD8αβ), both encoded by separate genes. The extracellular domain binds to the non-polymorphic α3 region of MHC class I molecules, stabilizing interactions between the TCR and its cognate peptide-MHC complex during immune surveillance. Upon engagement with MHC-I/antigen complexes, the intracellular tail associates with Lck kinase to initiate downstream signaling cascades that activate gene transcription necessary for effector functions such as target cell lysis. This makes CD8+ T cells essential mediators in adaptive immunity against viral infections and tumor cells. In clinical practice, anti-CD8 monoclonal antibodies are used both diagnostically—to identify cytotoxic lymphocytes—and experimentally/therapeutically—to modulate immune responses. Alterations in CD8 expression or function are implicated in various diseases including cancers, chronic infections, autoimmune disorders, and transplant rejection. As such, it serves not only as a biomarker but also represents an important therapeutic target for immunomodulation strategies.

Other names

Cluster of differentiation 8CD8 co-receptorCD8 alpha chain (CD8A)CD8 beta chain (CD8B)Cytotoxic T cell marker

Blockade or depletion of CD8+ T cells via anti-CD8 monoclonal antibodies for immunosuppression or research purposes. Modulation of immune responses by targeting the co-receptor function in engineered therapies such as chimeric antigen receptor (CAR) constructs.