Differential stimulatory and inhibitory effects of interleukin 4 on granulocytic and monocytic colony formation in human bone marrow cultures.

Both stimulatory and inhibitory effects of interleukin (IL) 4 on myelopoiesis have been described. In this paper we further define the specificity of these effects. IL-4 was added to cultures of bone marrow cells in which colony formation was stimulated with several colony-stimulating factors (CSFs): monocyte CSF (M-CSF), granulocyte CSF (G-CSF), IL-3, IL-5 and conditioned medium from phytohemagglutinin-stimulated peripheral blood cells (PHA-CM). Inhibition of monocytic colony formation by IL-4 was observed in cultures that were stimulated with IL-3 or with PHA-CM, similar to the inhibition in M-CSF- or GM-CSF-stimulated cultures. The enhancement of granulocytic colony formation by IL-4 was restricted to G-CSF-induced colony growth. No enhancement was observed in cultures that were stimulated with IL-5 or with PHA-CM from which the G-CSF was neutralized by anti-G-CSF antibodies. Both the inhibiting and enhancing effects of IL-4 were preserved in cultures that were stimulated with concentrations of CSF that exceeded more than tenfold the plateau concentrations. Enhancement of granulocytic and inhibition of monocytic colony formation by IL-4 occurred simultaneously in cultures stimulated with PHA-CM or with a combination of G-CSF and M-CSF. In summary, we show that the inhibiting effect of IL-4 on monocytic colony formation is independent of the growth factor used, whereas the stimulatory effect of IL-4 on granulocytic colony formation is restricted to G-CSF-induced cultures. Simultaneous occurrence of both effects results in preferential growth of granulocytes.