The CD8 glycoprotein ‘co-receives’ antigen Selleck Carfilzomib by binding to an invariant region of the MHCI molecule and can enhance ligand recognition by up to 1 million-fold. In recent years, a number of structural and biophysical investigations have shed light on the role of the CD8 co-receptor during T-cell antigen recognition. Here, we provide a collated resource for these data, and discuss how the structural and biophysical parameters governing CD8 co-receptor function further our understanding of T-cell cross-reactivity and the productive engagement of low-affinity antigenic ligands. T-cell antigen recognition and subsequent T-cell activation are governed by the interaction between the T-cell

receptor (TCR) and peptide–major histocompatibility complex (pMHC) molecules.[1] In a unique bipartite recognition mechanism TCR–pMHC-mediated T-cell activation is enhanced through the activities of co-receptor molecules that bind independently from the TCR to an invariant region of the pMHC (Fig. 1). The CD8 co-receptor exists as an αα homodimer Osimertinib in vivo (Fig. 2a) on the

surface of many different cell types within the lymphoid system, including natural killer cells, γδ T cells[2] and intestinal intra-epithelial T lymphocytes[3]; it is also expressed in this form on certain dendritic cell subsets.[4] In the alternative αβ heterodimeric form (Fig. 2b), CD8 is found on ~ 90% of cytotoxic T lymphocytes.[5] The functional role of the CD8αα homodimer has not been formally identified, although filipin a regulatory role has been proposed in the case of intestinal intra-epithelial T lymphocytes.[6] In contrast, the CD8αβ co-receptor plays a major role in CD8+ T-cell activation by increasing antigen sensitivity[7, 8] and by stabilizing the TCR–pMHC class

I (pMHCI) interaction at the cell surface.[9-11] The pMHCI–CD8 interaction is central to these functional roles. CD8 acts as a co-receptor during T-cell antigen engagement.[8] The dominant molecular basis for this functional role in antigen recognition centres on the association of the CD8 α-chain with p56Lck, via two vicinal cysteines, which interact through a zinc chelate complex to produce a co-activation signal.[12, 13] This interaction leads to a signalling cascade that recruits ZAP-70 to the TCR–CD3 complex, leading to the amplification or enhancement of T-cell activation signals.[14, 15] The signalling role of the CD8 α-chain can be enhanced by palmitoylation of the CD8 β-chain at a membrane-proximal cysteine.[16] Palmitoylation at this site allows the recruitment of the tripartite TCR–CD3–CD8 signalling complex to detergent-insoluble membrane domains, or lipid rafts.[17, 18] Lipid rafts are made up of ordered microdomains, enriched with sphingolipids and cholesterol, that exclude molecules such as phosphatases (CD45) but recruit molecules that are critical for T-cell activation, such as p56Lck and the linker for activation of T cells.