Interleukin 2 induces T cell-dependent IgM production in human B cells

Conditioned medium, obtained from mononuclear cells after activation with concanavalin A and phorbol myristate, strongly stimulated the in vitro production of IgM by human mononuclear cells. Partial purification by gel filtration showed that this activity co-eluted with interleukin 2 (IL 2). Via removal by adsorption and further purification by chromatofocusing techniques, it was demonstrated that the factor in this conditioned medium, responsible for the IgM production, was in fact IL 2. Experiments with purified IL 2 from the human IL 2-producing Jurkat cell line as well as recombinant IL 2 confirmed its capacity to induce IgM production. In the absence of T cells, IL 2 could not activate Ig synthesis, suggesting an indirect effect of IL 2 in the induction of the helper signals for B cells. Evidence is presented that partially purified conditioned medium contained another factor, distinct from IL 2, with the capacity to differentiate human B lymphocytes in the absence of T cells into IgM-producing cells.