Immuno-inductive and immuno-suppressive influence of human mononuclear phagocytes cultured in vitro.

DNA-synthesis, as measured by 3H thymidine incorporation, in immune lymphocytes from human blood stimulated in vitro with PPD was shown to require monocytes. No such requirement was demonstrated for PHA-induced DNA-synthesis under the same conditions. Initial packing of cells by centrifugation was beneficial for the cultures stimulated by antigen, but not for the cultures stimulated by lectin, thus indicating the necessity for contact between monocytes and lymphocytes for antigen stimulation. Monocytes and macrophages preincubated with PPD indced DNA-synthesis in lymphocytes. Monocytes were found to be least as capable of retaining and presenting antigen as macrophages, and autologous macrophages presented antigen more efficiently than allogeneic macrophages. DNA-synthesis in lymphocytes, induced by adding PPD or PHA to the culture medium, was inhibited by a large number of monocytes. Macrophages caused inhibition under the same conditions, even a small number. DNA-synthesis in lymphocytes induced by PPD-preincubated monocytes and macrophages increased with increasing ratio of mononuclear phagocytes to lymphocytes up to a certain value. A further increase in the ratio caused inhibition, thus indicating both an immunoinductive and an immuno-suppressive influence of mononuclear phagocytes.