Beschreibung:
<jats:title>Abstract</jats:title><jats:p>Conditioned medium, obtained from mononuclear cells after activation with concanavalin A and phorbol myristate acetate, strongly stimulated the <jats:italic>in vitro</jats:italic> production of IgM by human mononuclear cells. Partial purification by gel filtration showed that this activity co‐eluted with interleukin 2 (IL2). 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 IL2‐producing Jurkat cell line as well as recombinant IL2 confirmed its capacity to induce IgM production. In the absence of T cells, IL2 could not activate Ig synthesis, suggesting an indirect effect of IL2 in the induction of the helper signals for B cells. Evidence is presented that partially purified conditioned medium contained another factor, distinct from IL2, with the capacity to differentiate human B lymphocytes in the absence of T cells into IgM‐producing cells.</jats:p>