ROLE OF CD3-GAMMA AND CD3-DELTA CYTOPLASMIC DOMAINS IN CYTOLYTIC T-LYMPHOCYTE FUNCTIONS AND TCR CD3 DOWN-MODULATION/

TCR engagement leads to down-modulation of TCR/CD3 complexes from the T cell surface. The importance of this effect in T cell physiology is unknown. Here, we characterized a CTL clone deficient in TCR/CD3 surfa ce expression that had lost both CD3 delta and CD3 gamma mRNA, allowin g us to address the role of these chains in the assembly, signaling, a nd dynamics of the TCR/CD3 complex. Expression of either CD3 delta or CD3 gamma alone failed to reconstitute surface expression of the TCR/C D3 complex, but reconstitution with a cytoplasmically truncated CD3 de lta (delta t) and a native (gamma) or cytoplasmically truncated (gamma t) human CD3 gamma led to reexpression of TCR/CD3 complexes in both c ases. This indicated that CD3 delta and CD3 gamma assume specific func tions in TCR/ CD3 assembly independently of their cytoplasmic domains. The delta t gamma t variant specifically killed target cells, express ed the IFN-gamma gene in response to Ag, and produced TNF-alpha in res ponse to anti-CD3 mAb, but it was affected in CD3 ligand-induced TCR/C D3 down-modulation. Both PMA- and CD3 ligand-induced TCR/CD3 down-modu lation were defective in the delta t gamma t variant, whereas the delt a t gamma variants were unaffected, and previously described delta gam ma t variants were affected only in PMA-induced down-modulation, Speci fic protein kinase C (PKC) inhibitors indicated that PMA- but not CD3 ligand-induced down-modulation was dependent on PKC activity. Thus, am ino acid sequences present in either the CD3 delta or CD3 gamma cytopl asmic domain control ligand-induced TCR/CD3 down-modulation, and neith er these sequences nor this property are required for cytolysis and IF N-gamma gene expression in response to Ag.