ACTIVATION OF HUMAN B-LYMPHOCYTES .9. MODULATION OF ANTIBODY-PRODUCTION BY PRODUCTS OF ACTIVATED MACROPHAGES

Abstract

Human monocytes, after in vitro activation by mixed lymphocyte culture (MLC) supernatants produce a monokine (MK) that enhances the plaque-forming cell (PFC) response of pokeweed mitogen (PWM)-stimulated human B [bone marrow-derived] lymphocytes. Technical conditions and kinetics of MK production were established. Irradiation of monocytes (5000 rad) does not abolish MK production but heat-killed cells are unable to release the factor. Highly T [thymus-derived] cell-depleted monocyte populations still produced the PFC-enhancing factor. The same MK has an inconsistent enhancing effect on the PFC responses of [Escherichia coli] lipopolysaccharide (LPS) and Nocardia water-soluble mitogen (NWSM)-stimulated B cells. Other macrophage activators such as LPS, phytohemagglutinin (PHA) and latex particles failed to induce consistently the liberation of the PFC-enhancing MK. The target cell for the MK activity on PWM-stimulated B cells appears to be the B lymphocyte itself. Soluble monocyte products can have substantial modulatory effects on human B cell function.