CD8

The CD8 co-receptor is predominantly expressed on the surface of cytotoxic T cells, but can also be found on natural killer cells, cortical thymocytes, and dendritic cells. The CD8 molecule is a marker for cytotoxic T cell population. It is expressed in T cell lymphoblastic lymphoma and hypo-pigmented mycosis fungoides. ==Structure of the CD8 complexes==

The first crystal structure of the deglycosylated IgV domain of the CD8A molecule was published by Leahy, DJ, Axel, R, and Hendrickson, WA in 1992. Since then, crystal structures have been determined for over 20 different complexes containing CD8 molecules. ==Function==

The interaction of the extracellular IgV-like domains of CD8 with the α3 portion of the Class I MHC molecule increases affinity for the T cell receptor of the cytotoxic T cell and the target cell such that they bound closely together during antigen-specific activation. In addition, CD8 co-receptor also plays a role in T cell signaling. The cytoplasmic tail of the CD8 co-receptor bind Lck (lymphocyte-specific protein tyrosine kinase) via common Cys4-Zn finger. Once the T cell receptor binds its specific antigen Lck phosphorylates the cytoplasmic CD3 and ζ-chains of the TCR complex which initiates a cascade of phosphorylation eventually leading to activation of transcription factors like NFAT, NF-κB, and AP-1 which affect the expression of certain genes. ==References ==