Macrophage-independent activation of helper T cells. I. Production of Interleukin 2.

Abstract Interleukin 2 is an antigen nonspecific soluble factor produced by concanavalin A-activated mouse spleen cells that stimulates a number of in vitro lymphocyte activation processes, including the induction of thymocyte proliferation. Using the thymocyte proliferation assay for Interleukin 2 (IL 2), we found that the production of IL 2 was absolutely dependent on the presence of both macrophages and T lymphocytes. Neither purified T lymphocytes (>95% Thy 1.2 positive, <0.2% esterase positive) nor purified splenic macrophages produced detectable IL 2 after stimulation with Con A. Stimulation of recombined macrophages and T lymphocytes resulted in the production of IL 2 in amounts equivalent to that produced by unfractionated spleen cells. By utilizing mechanisms capable of activating T lymphocytes in the absence of viable macrophages, the cell-of-origin of IL 2 was determined to be the T lymphocyte. Purified T lymphocytes produced large quantities of IL 2 when incubated with Con A and either: 1) a P388D1 macrophage cell line culture supernatant or 2) phorbol myristic acetate (4 to 20 ng/ml). In contrast, splenic macrophages stimulated with both Con A and phorbol myristic acetate did not produce detectable IL 2. Gel filtration of a culture supernatant from purified T lymphocytes stimulated with Con A and phorbol myristic acetate revealed the IL 2 to have the m.w. and additional biologic properties (helper activity for antibody synthesis and T lymphocyte growth promoting activity) characteristic of Interleukin 2 produced by unfractionated Con A-stimulated spleen cells.