Cytostatic effect on tumour cells induced in human monocytes by mediators from BCG-stimulated lymphocytes and MLC

Human monocytes activated by mediators (lymphokines) from BCG-stimulated, sensitized lymphocytes (from BCG-vaccinated donors) were cytostatic to a human cell line. Mediators from allogeneic lymphocytes activated the cytostatic ability of monocytes to the same degree as mediators from autologous lymphocytes. Mediators from BCG-stimulated lymphocytes from tuberculin-negative donors not vaccinated with BCG, activated the monocytes only to a small extent. Culture of lymphocytes in a membrane chamber (MC) proximate to monocytes, or incubation of monocytes with filtered supernatants of lymphocyte cultures, were equally effective procedures for inducing cytostatic ability in monocytes. Supernatants of sensitized lymphocytes cultured on BCG for four hours did not activate the monocytes, while supernatants collected after 24 hours activated the cytostatic ability to the same extent as 72-hour supernatants. Supernatants of mixed lymphocyte cultures (MLC) collected after 24 hours did not activate the monocyte cytostatic ability at all. Forty-eight and 72-hour supernatants of MLC showed a small but increasing activity. There was no significant difference between BCG-stimulated lymphocytes and MLC in their maximum DNA synthesis or in the kinetics of their DNA synthesis. Thus, the DNA synthesis and secretion of lymphocyte mediators may be independent phenomena resulting from the same stimulus.