CD5[5] is a cluster of differentiation expressed on the surface of T cells (various species) and in a subset of murine B cells known as B-1a. The expression of this receptor in human B cells has been a controversial topic and to date there is no consensus regarding the role of this receptor as a marker of human B cells. B-1 cells have limited diversity of their B-cell receptor due to their lack of the enzyme terminal deoxynucleotidyl transferase (TdT) and are potentially self-reactive. CD5 serves to mitigate activating signals from the BCR so that the B-1 cells can only be activated by very strong stimuli (such as bacterial proteins) and not by normal tissue proteins. CD5 was used as a T-cell marker until monoclonal antibodies against CD3 were developed.
In humans, the gene is located on the long arm of chromosome 11. There is no confirmed ligand for CD5 but there is evidence that CD72, a C-type lectin, may be a ligand or that CD5 may be homophilic, binding CD5 on the surface of other cells.[6] CD5 includes a scavenger receptor cysteine-rich protein domain.
T cells express higher levels of CD5 than B cells. CD5 is upregulated on T cells upon strong activation. In the thymus, there is a correlation with CD5 expression and strength of the interaction of the T cell towards self-peptides.
Osman N, Ley SC, Crumpton MJ (1992). "Evidence for an association between the T cell receptor/CD3 antigen complex and the CD5 antigen in human T lymphocytes". Eur. J. Immunol. 22 (11): 2995–3000. doi:10.1002/eji.1830221135. PMID1385158. S2CID34625072.
Jones NH, Clabby ML, Dialynas DP, Huang HJ, Herzenberg LA, Strominger JL (1986). "Isolation of complementary DNA clones encoding the human lymphocyte glycoprotein T1/Leu-1". Nature. 323 (6086): 346–9. Bibcode:1986Natur.323..346J. doi:10.1038/323346a0. PMID3093892. S2CID4361866.
Lankester AC, van Schijndel GM, Cordell JL, van Noesel CJ, van Lier RA (1994). "CD5 is associated with the human B cell antigen receptor complex". Eur. J. Immunol. 24 (4): 812–6. doi:10.1002/eji.1830240406. PMID7512031. S2CID25093082.
Dianzani U, Bragardo M, Buonfiglio D, Redoglia V, Funaro A, Portoles P, Rojo J, Malavasi F, Pileri A (1995). "Modulation of CD4 lateral interaction with lymphocyte surface molecules induced by HIV-1 gp120". Eur. J. Immunol. 25 (5): 1306–11. doi:10.1002/eji.1830250526. PMID7539755. S2CID37717142.
Van de Velde H, Thielemans K (1996). "Native soluble CD5 delivers a costimulatory signal to resting human B lymphocytes". Cell. Immunol. 172 (1): 84–91. doi:10.1006/cimm.1996.0218. PMID8806810.
Dennehy KM, Broszeit R, Garnett D, Durrheim GA, Spruyt LL, Beyers AD (1997). "Thymocyte activation induces the association of phosphatidylinositol 3-kinase and pp120 with CD5". Eur. J. Immunol. 27 (3): 679–86. doi:10.1002/eji.1830270316. PMID9079809. S2CID41540340.
Gary-Gouy H, Lang V, Sarun S, Boumsell L, Bismuth G (1997). "In vivo association of CD5 with tyrosine-phosphorylated ZAP-70 and p21 phospho-zeta molecules in human CD3+ thymocytes". J. Immunol. 159 (8): 3739–47. doi:10.4049/jimmunol.159.8.3739. PMID9378960. S2CID42470132.
Mier-Aguilar CA, Vega-Baray B, Burgueño-Bucio E, Lozano F, García-Zepeda EA, Raman C, Soldevila G (2015). "Functional requirement of tyrosine residue 429 within CD5 cytoplasmic domain for regulation of T cell activation and survival". Biochem Biophys Res Commun. 466 (3): 381–7. doi:10.1016/j.bbrc.2015.09.033. PMID26363459.