A role for T cell helper factors in antibody responses to "T-independent" antigens.

Plaque-forming cell responses were assessed in unprimed mouse spleen cells after stimulation in vitro with SRBC or "T-independent" type 2 (DNP-Ficoll or DNP-liposomes) or type 1 (TNP-LPS or DNP-liposomes containing lipid A) antigens. Rigorously T cell depleted, Sephadex G-10 passed spleen cells were almost completely unresponsive to all these antigens. In every case, responsiveness could be restored by adding supernates from concanavalin A stimulated spleen cells (Con A SN). Experiments in which supernates containing interleukin 1 (IL-1) from the P388D1 cell line, interleukin 2 (IL-2), and a non-IL-2 T cell replacing factor (IL-X) were mixed showed that optimal responses to all the above antigens could only be obtained if both IL-2 and IL-X were present. IL-2 was the only factor that had any effect alone. IL-2 restored responsiveness to different degrees depending on the antigen. This ranged from about 3% (for SRBC) to about 70% (for TNP-LPS) of the optimal response. The P388D1 supernate enhanced responsiveness only if IL-2 and IL-X were present, and only with the T-independent type 2 antigens. These results demonstrate that at least some examples of both type 1 and 2 "T-independent" antigens actually require nonspecific factors one of which, IL-2, is clearly T cell derived, to stimulate antibody production by B cells.