Immunoglobulin production in cultures of pokeweed mitogen stimulated human peripheral blood mononuclear cells requires interaction of interleukin 2 with the B cells

Abstract

Immunoglobulin (Ig) production in cultures of pokeweed mitogen (PWM)-stimulated human peripheral blood mononuclear cells (PBMC) is dependent on the presence of T cells. The latter can be replaced by a crude supernatant of PWM-stimulated PBMC, a conditioned medium containing interleukin 2 (IL-2) and presumably other helper factors for B cells. The present study examines the role of IL-2 among these helper factors. Anti-Tac, a monoclonal antibody that blocks the human IL-2 receptor, was found to suppress PWM-induced Ig production in cultures of human PBMC. The inhibition by anti-Tac was at least partly exerted at the level of B cells. Indeed, Ig production in cultures of T-cell-depleted PBMC or highly enriched B-cell preparations supplemented with PWM-induced conditioned medium was also inhibited by anti-Tac (82 ± 13% inhibition of IgG and 83 ± 12% inhibition of IgM production). When IL-2 was removed from the PWM-induced conditioned medium by absortion with an IL-2-dependent murine cytotoxic T-cell line, CTLL, the conditioned medium was unable to support PWM-induced Ig production by T-cell-depleted PBMC. On the other hand, recombinant IL-2 alone at a concentration similar to that of IL-2 in the PWM-induced conditioned medium was not able to support Ig production by PWM-stimulated B cells. We conclude that IL-2 acts on PWM-activated B cells in conjunction with other helper factors to induce Ig production and that anti-Tac inhibits PWM-induced Ig production by blocking IL-2 receptors on activated B cells.