Inhibition and potentiation of T lymphocyte response to mitogens. Studies using two mitogenic stimuli simultaneously

Rat thymocytes were stimulated with phytohaemagglutinin (PHA), Concanavalin A (Con A), pokeweed mitogen (PWM) and lipopolysaccharide (LPS) or with mixtures of two of these mitogens, added simultaneously to in vitro cultures. Four-five concentrations of first mitogen were matched with four-five concentrations of second mitogen, in all possible combinations. Synergistic effects were observed with LPS plus PHA and LPS plus PWM and inhibitory effects with PHA plus Con A and LPS plus Con A. The hypothesis is discussed that an inhibitory effects occurs when two mitogens react with identical or very similar receptors on the lymphocyte surface, while a synergistic effect is produced by two mitogens reacting with different receptors.