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

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Abstract
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 (IL 2). Tac expression was further enhanced by addition of exogenous IL 2. 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 IL 1. As IL 1 had no significant effect on Tac expression of T3‐stimulated T cells, we conclude from these data that IL 1 exerts in addition to its influence on IL 2 production an effect, which allows antigen receptor‐triggered T cells to enter the cell cycle.