Macrophage-dependent activation of antigen-specific T cells requires antigen and a soluble monokine.

Antigen-induced T cell proliferation requires T cell interaction with antigen in the context of MHC I region-compatible accessory cells. The resulting activation and proliferation of T cells involves the production and utilization of several lymphokines or interleukins. This report describes experiments wherein these events could be separated into two phases, T cell activation and T cell proliferation. The first phase was achieved by stimulating antigen-specific T cell lines with antigen-pulsed ultraviolet light-irradiated accessory cells. T cell proliferation (second phase) could then be initiated by the addition of a soluble lymphokine with the characteristics of interleukin 1 (IL 1). These effects were only observed with homologous antigen and accessory cells syngeneic to the T cells at the I-A and E/C subregion of the MHC. This report has two applications in the study of lymphocyte-lymphokine interactions. First, T cell recognition of antigen and antigen-induced T cell proliferation can be examined as physically separate events. Secondly, this system may be used as a specific and sensitive means of measuring the effects of IL 1 on T cells.