Early events during primary activation of T cells: antigen receptor cross-linking and interleukin 1 initiate proliferative response of human T cells.

To study early events during primary activation of human T cells, a simple method was developed which simultaneously allows positive selection of T cells from peripheral blood lymphocytes (PBL) and their polyclonal, antigen receptor-mediated stimulation with anti-T3 monoclonal antibodies. In the absence of accessory cells, T cells activated with matrix-bound OKT3 express high levels of the Tac antigen within 15 h and produce interleukin 2 (IL2). Tac expression was further enhanced by addition of exogenous IL2. However, under these conditions purified T cells were unable to mount a proliferative response, whereas unfractionated PBL proliferated already after 24 h of culture. This unresponsiveness of purified T cells could be overcome by either re-addition of low numbers of autologous accessory cells or semipurified human IL1. As IL1 had no significant effect on Tac expression of T3-stimulated T cells, we conclude from these data that IL1 exerts in addition to its influence on IL2 production an effect, which allows antigen receptor-triggered T cells to enter the cell cycle.