PRODUCTION AND CHARACTERIZATION OF THE EXTRACELLULAR DOMAIN OF HUMAN CD7 ANTIGEN - FURTHER EVIDENCE THAT CD7 HAS A ROLE IN T-CELL SIGNALING

CD7 is a T cell-associated antigen which appears early in ontogeny and persists on circulating T cells. It appears to have a significant rol e in T cell development and function. The precise mechanism by which t his molecule mediates its effect is not known. In this paper, we expre ssed the extracellular domain of CD7 in the baculovirus system and use d this product to study the function CD7 might have in T cell activati on. The recombinant protein was found to be structurally similar to th e native CD7 and recognized by monoclonal and polyclonal antibodies to CD7. This protein inhibited T cell proliferation induced by anti-CD3/ anti-CD7 costimulation. It also inhibited the augmentation effect of a nti-CD7 on suboptimal PHA stimulation. However, it did not block T cel l proliferation induced by optimal doses of PHA, staphylococcal entert oxin A or B. Interestingly, the recombinant protein inhibited antigeni c- and alloantigenic-induced T cell proliferation. The latter finding strongly suggests that a ligand for CD7 exists and crosslinking CD7 by this ligand may be responsible for the costimulatory role it plays in T cell activation. (C) 1995 Academic Press, Inc.