Cluster of differentiation 8 / CD8 , also known as Ly-2 or Leu-2, is a two chain and transmembrane glycoprotein which is expressed on the surface of circulating T-cells. Cluster of differentiation 8 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. There are two isoforms of the protein, alpha and beta, each encoded by a different gene. Cluster of differentiation 8 exists as both a heterodimer and a homodimer
Cluster of differentiation 8 was first discovered as a cell surface marker in mice and was used to distinguish between CD8+ Cytotoxic T lymphocytes (CTLs) and CD4+ Th cells. Cluster of differentiation 8 has been shown to be involved in CTL co-activation by increasing antigen sensitivity, and by stabilising the TCR/MHC interaction. In order to carry out these roles, the CD8 co-receptor binds to a distinct invariant region of the MHCI molecule, compared to the TCR, allowing the potential for tripartite (TCR/pMHC/CD8) complex formation.
Cluster of differentiation 8 is often described as a T-cell co-receptor because it has important role in T-cell signalling, to induce TCR mediated T-cell activation signals. cluster of differentiation 8 co-receptor is also important for that stabilisation of the interface between CD8+ T-cells and target cells, and activation of intestinal epithelial T lymphocytes. Therefore, CD8 has been the target of many therapeutic strategies designed to modulate T-cell responses during auto-immune reactions, allergy and organ transplant rejection.
Cluster of differentiation 8 in HIV infection:
Cluster of differentiation 8 play a crucial role in controlling HIV replication during the early phase of infection. HIV-specific CD8 T-cells are targeted at the dominant viral variant and their emergence is associated with a rapid fall in viral load before the development of an antibody response. Cluster of differentiation 8 antiviral factor that inhibits HIV replication, and may or may not directly kill CD4 T-cells.
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