Promotive and inhibitory effects of macrophages on the mitogen-induced blastogenesis of lymphocytes: a flow-cytometric study.

The effect of various concentrations of rat-liver macrophages on the Con-A-induced blastogenesis of syngeneic spleen lymphocytes has been studied by means of flow-cytometric methods and by measurement of the uptake of 3H-thymidine. By measuring the distributions of cellular and nuclear volume and cellular DNA to characterize the progression of responding lymphocytes through the cell cycle, we have distinguished a promotive and an inhibitory effect of macrophages. The promotive effect is on the number of cells initiating blastogenesis and on their rate of progression through the cell cycle. The degree of promotion increased strongly with the concentration of macrophages even for concentrations that suppressed the incorporation of 3H-thymidine almost completely from about 30 h of culture. The inhibition observed for macrophage concentrations +/- 10% was a late effect causing stagnation of cell cycle and reduced viability only from about 24 h of culture.