Suppression of in-vitro antibody production by pokeweed mitogen-stimulated human bone-marrow mononuclear cells. Evidence for a soluble suppressor substance.

The spontaneous synthesis and secretion of immunoglobulin by human bone-marrow mononuclear cells (MNC) in vitro, as well as its suppression by the addition of pokeweed mitogen (PWM), were previously reported by this laboratory. In the present study we demonstrate that this suppression is mediated by a soluble substance elaborated by marrow MNC stimulated with PWM. Marrow MNC were pulsed for 1 hr with PWM, washed and recultured for 7 days in media without PWM. The culture supernatants were collected by centrifugation and filter sterilized before addition to fresh marrow MNC in the in vitro antibody synthesis assay. The 14-day assay culture supernatants were then subjected to a solid phase radioimmunoassay to determine the immunoglobulin content. The suppressor substance was non-specific as to immunoglobulin isotype and was not genetically restricted. Suppressor activity was diminished by heating the supernatants at 56 degrees for 1 hr. The activity could be elaborated by cells subjected to 1000 R or 2000 R before or after 1-hr incubation with PWM. While the addition of PWM anytime during the culture period would suppress IgA production at the level produced up to that time, the suppressor substance only suppressed IgA production when added during the first 4 days of culture. The addition of indomethacin had no effect on the suppressor activity indicating that the activity was not mediated by prostaglandin. Including human fibroblast interferon or hydrocortisone in the assay cultures had no effect on IgA production or its suppression by PWM. We concluded that the lectin-induced suppression was mediated by a marrow-derived suppressor substance (MDSS).