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CD8a molecule
Symbol CD8A
Alt. Symbols CD8
Entrez 925
HUGO 1706
OMIM 186910
RefSeq NM_001768
UniProt P01732
Other data
Locus Chr. 2 p12
CD8b molecule
Symbol CD8B
Alt. Symbols CD8B1
Entrez 926
HUGO 1707
OMIM 186730
RefSeq NM_172099
UniProt P10966
Other data
Locus Chr. 2 p12

CD8 (cluster of differentiation 8) is a transmembrane glycoprotein which serves as a co-receptor for the T cell receptor (TCR). Like the TCR, CD8 binds to a major histocompatibility complex (MHC) molecule, but is specific for the class I MHC protein.[1] It is predominantly expressed on the surface of cytotoxic T cells, but can also be found on natural killer cells. To function, CD8 forms a dimer, consisting of a pair of CD8 chains. The most common form of CD8 is composed of an CD8-α and CD8-β chain, both members of the immunoglobulin superfamily with an immunoglobulin variable (IgV)-like extracellular domain connected to the membrane by a thin stalk, and an intracellular tail. Less common homodimers of the CD8-α chain are also expressed on some cells. The extracellular IgV-like domain of CD8-α interacts with to the α3 portion of the Class I MHC molecule.[2] This affinity keeps the T cell receptor of the cytotoxic T cell and the target cell bound closely together during antigen-specific activation. Cytotoxic T cells with CD8 surface protein are called CD8+ T cells.

File:CD8 receptor.PNG
Schematic representation of CD8 co-receptor


  1. Gao G, Jakobsen B (2000). "Molecular interactions of coreceptor CD8 and MHC class I: the molecular basis for functional coordination with the T-cell receptor". Immunol Today. 21 (12): 630–6. PMID 11114424. 
  2. Devine L, Sun J, Barr M, Kavathas P (1999). "Orientation of the Ig domains of CD8 alpha beta relative to MHC class I". J Immunol. 162 (2): 846–51. PMID 9916707.