A ROLE FOR CD5 IN TCR-MEDIATED SIGNAL-TRANSDUCTION AND THYMOCYTE SELECTION

CD5 is a transmembrane protein that is expressed on the surface of T c ells and a subset of B cells. The absence of CD5 rendered thymocytes h yperresponsive to stimulation through the T cell antigen receptor (TCR ) in vitro. Selection of T cells expressing three distinct transgenic TCRs was also abnormal in CD5-deficient mice. These observations indic ate that CD5 can influence the fate of developing thymocytes by acting as a negative regulator of TCR-mediated signal transduction.