CD8

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CD8 (cluster of differentiation 8) is a transmembrane glycoprotein that 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 a 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.

Schematic representation of CD8 co-receptor

[edit] References

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. doi:10.1016/S0167-5699(00)01750-3. 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. 

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