INHIBITION OF LYMPHOCYTE-TRANSFORMATION RESPONSES TO PHYTOHEMAGGLUTININ BY NORMAL HUMAN-PLASMA

Marked variability in lymphocyte transformation responses to a suboptimal phytohemagglutinin concentration (0.1 μg/ml) was observed when peripheral blood mononuclear cells of normal subjects were cultured in media containing 15% autologous plasma. Low responses were related to the plasma and were caused by direct inhibition rather than an inability to support the response. This inhibitory activity varied greatly among different plasma specimens and was also found in human and animal serum. It appeared to be specific for suboptimal concentrations of phytohemagglutinin and could be overcome by increasing the mitogen concentration. The inhibitory activity was heat stable, was not dialyzable, and appeared to affect a very early stage of the response since a delay in addition of the inhibitory plasma reversed its effect. Our interpretation of these results is that human plasmas vary greatly with respect to their ability to bind phytohemagglutinin so that the addition of different plasmas to lymphocyte cultures stimulated by a limiting concentration of phytohemagglutinin results in marked variability of the results obtained. © 1979.