Immuno-suppressive effect of human macrophages. II. Influence of macrophages on the kinetics of DNA, RNA and protein synthesis in PHA-stimulated lymphocytes.

Human macrophages obtained by culturing blood monocytes in vitro for 8 days release a soluble factor(s) inhibiting DNA synthesis and cell proliferation in PHA-stimulated lymphocytes. Synthesis of RNA and protein was strongly inhibited in PHA-stimulated lymphocytes sedimented on macrophages, as well as in lymphocytes separeted from the macrophages by a membrane, thus demomatrating that inhibition of RNA and protein synthesis was also mediated by a soluble factor(s). The kinetics of the factor-mediated inhibition showed that RNA synthesis was readily inhibited, whereas there was a delay in the inhibition of protein synthesis, thus indicating that the inhibition of protein synthesis and cell proliferation is a result of a blocking effect on the nucleic acid synthesis. The kinetics of DNA and protein synthesis in lymphocytes relieved from macrophage-mediated inhibition indicate a cytostatic effect.