The antigen receptor on a human T cell line initiates activation by increasing cytoplasmic free calcium.

Abstract Monoclonal antibodies to the antigen receptor on T cells can mimic the effects of antigen by inducing cellular proliferation and the production of lymphokines (1). Such agonist antibodies provide one approach to studying the mechanism of receptor-mediated activation. In a previous paper we demonstrated that antibodies to T3 determinants increase cytoplasmic free calcium (Ca++i)2 in the human T cell line, Jurkat (2). Because T3 and the antigen-receptor may be physically associated, this observation suggests that the antigen-receptor itself might use an increase in Ca++i as an intracellular messenger for activation (3). In this report, we extend these studies and show that a monoclonal antibody to the antigen-receptor heterodimer elicits a prompt, sustained increase in Ca++i in Jurkat. Moreover, this increase in Ca++i appears to play a crucial role in antigen-receptor-mediated activation.