Triggering of the lethal hit in human cytotoxic T lymphocytes: a functional role for a 103-kDa T cell-specific activation antigen.

A monoclonal antibody (CB.1) is described that defines a new triggering signal for human cytotoxic T lymphocytes (CTL). The antibody precipitates a 103-kDa surface antigen from activated normal human T cells. The antigen is undetectable or present in only low amounts on resting T lymphocytes but its expression increases strongly after activation and proliferation on T4+ and T8+ T lymphocytes. Binding of antibody CB.1 to CTL results in triggering of the lethal hit. This induction of cytotoxicity is dependent on cross-linking of CTL and an Fc receptor-bearing target cell with CB.1 and requires Ca2+ like antigen-specific triggering. CB.1-induced triggering can be specifically inhibited by binding of antibodies to the T8 or T4 molecules on T8+ or T4+ CTL.