HUMAN CD4-CELLS KILL ANTIGEN-PULSED TARGET T-CELLS BY INDUCTION OF APOPTOSIS( CYTOLYTIC T)

Stimulation of human CD4+ T cell clones with appropriate specific pept ides or with lectins in the absence of APC induces a substantial degre e of cell death. We have investigated the mechanisms of induction of t his cell death and show that it occurs by apoptosis, identified by mor phology and the characteristic pattern of DNA degradation. We also inv estigated whether this T cell death was a result of a suicide process activated in the T cell after ''inappropriate'' recognition of Ag on t he surface of another T cell clone (and in the absence of other access ory signals), or was due to a conventional lethal hit delivered by one cytolytic T cell to another ''target'' T cell. Our results strongly s uggest that peptide-induced cell death of human CD4+ CTL is due to act ive killing of Ag-presenting target T cells by effector T cells of the same clone. The cell death that is induced in the target T cell occur s via apoptosis that requires de novo RNA transcription and translatio n in the effector T cell.