Inhibition of normal human macrophage progenitors by retinoic acid.

The effects of retinoic acid on the clonal growth in nutrient agar of neutrophil and macrophage progenitors from normal bone marrow and fetal liver were studied. The technique of whole plate fixation and staining with luxol fast blue and haematoxylin was employed to distinguish colonies and clusters into morphological groups. Retinoic acid at a concentration of 3 X 10(-7) M resulted in 97% inhibition of macrophage clonal growth and a mean increase in neutrophil clonal growth from bone marrow of 150 +/- 14%. These effects of retinoic acid were most obvious on bone marrow cluster forming cells. The inhibition of macrophage cluster growth was independent of exogenous colony stimulating factor. This dual action of retinoic acid is likely to be a direct effect on the progenitor cells since it is (1) independent of cell concentration, (2) not mediated by phagocytic cells or other bone marrow cells, and (3) was maximal in the first 2 d of incubation before the appearance of clusters.