CD5 Transgenic Mice

Abstract

CD5 is a glycoprotein expressed on all mature T cells [1], a small but distinct subset of B lymphocytes (referred to as Bla cells) [2], some mouse B cell lymphomas and most human chronic lymphocytic leukemias (CLL) [3,4]. Both human and mouse CD5 genes have been cloned. The mouse CD5 cDNA encodes a protein consisting of 471 amino acids which, within the carboxyl terminus, has one potential tyrosine and two potential threonine phosphorylation sites. The sequence surrounding this tyrosine residue is similar to the sequence surrounding the tyrosine autophosphorylation site encoded by the protooncogene c-src and the oncogenes yes and fgr which are conserved in both mouse and human CD5 [5]. As an accessory molecule, CD5 has been shown to be coupled to the TCR/CD3 complex on T cells [6]. Crosslinking of CD5 with anti-CD5 antibody suggests that CD5 may function as a co-stimulatory molecule to augment and sustain T cell proliferation induced by interleukins, lectins, anti-CD3 and alloantigens [8,9]. Both murine and human CD72 have been identified as a ligand for CD5 [10,11]. Recently, CD5 on B cells has also been shown to be associated with the B cell antigen receptor (BCR) complex and serves as a substrate for BCR-induced tyrosine kinase activity [13]. Despite these findings the function of CD5 on B cells is not well understood though it seems probable that CD5-CD72 interactions may play-a-role in B-B cell as well as in T-B cell interactions.