![]() An antigen is a molecule capable of stimulating an immune response and is often produced by cancer cells, viruses, bacteria or intracellular signals. Most cytotoxic T cells express T-cell receptors (TCRs) that can recognize a specific antigen. Retrieved 11 January 2016.Antigen presentation stimulates T cells to become either "cytotoxic" CD8+ cells or "helper" CD4+ cells.Ī cytotoxic T cell (also known as T C, cytotoxic T lymphocyte, CTL, T-killer cell, cytolytic T cell, CD8 + T-cell or killer T cell) is a T lymphocyte (a type of white blood cell) that kills cancer cells, cells that are infected by intracellular pathogens (such as viruses or bacteria), or cells that are damaged in other ways. Archived from the original on 21 September 2015. ^ "CD8 alpha - Marker for cytotoxic T Lymphocytes"."Orientation of the Ig domains of CD8 alpha beta relative to MHC class I". ^ Devine L, Sun J, Barr M, Kavathas P (1999)."Crystal structure of a soluble form of the human T cell coreceptor CD8 at 2.6 A resolution". ^ a b PDB: 1cd8 Leahy DJ, Axel R, Hendrickson WA (March 1992).^ Leong AS, Cooper K, Leong FJ (2003)."Molecular interactions of coreceptor CD8 and MHC class I: the molecular basis for functional coordination with the T-cell receptor". 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. The cytoplasmic tails of the CD8 co-receptor interact with Lck (lymphocyte-specific protein tyrosine kinase). In addition to aiding with cytotoxic T cell antigen interactions the CD8 co-receptor also plays a role in T cell signaling. The flexible α 3 domain is located between residues 223 and 229 in the genome. This was discovered by doing mutational analyses. The main recognition site is a flexible loop at the α 3 domain of an MHC molecule. Cytotoxic T cells with CD8 surface protein are called CD8+ T cells. This affinity keeps the T cell receptor of the cytotoxic T cell and the target cell bound closely together during antigen-specific activation. The extracellular IgV-like domain of CD8-α interacts with the α 3 portion of the Class I MHC molecule. Schematic representation of the heterodimeric CD8 co-receptor Function 2% of the protein is wound into α-helices and 46% into β-sheets, with the remaining 52% of the molecules remaining in the loop portions. The structure was determined to have an immunoglobulin-like beta-sandwich folding and 114 amino acid residues. by X-ray Diffraction at a 2.6A resolution. The structure of the CD8 molecule was determined by Leahy, D.J., Axel, R., and Hendrickson, W.A. The molecular weight of each CD8 chain is about 34 kDa. Less-common homodimers of the CD8-α chain are also expressed on some cells. 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. To function, CD8 forms a dimer, consisting of a pair of CD8 chains. It is expressed in T cell lymphoblastic lymphoma and hypo-pigmented mycosis fungoides. The CD8 molecule is a marker for cytotoxic T cell population. 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. In humans, both genes are located on chromosome 2 in position 2p12. There are two isoforms of the protein, alpha and beta, each encoded by a different gene. Like the TCR, CD8 binds to a major histocompatibility complex (MHC) molecule, but is specific for the MHC class I protein. Along with the TCR, the CD8 co-receptor plays a role in T cell signaling and aiding with cytotoxic T cell- antigen interactions. Marker on immune cells Putative T-cell surface glycoprotein CD8ĬD8 ( cluster of differentiation 8) is a transmembrane glycoprotein that serves as a co-receptor for the T-cell receptor (TCR). ![]()
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