Inhibition of macrophage differentiation and function by cortisol

Neuroendocrine mechanisms are involved in modulation of the immune system, but the mode of action of the complex interplay between hormones and the immune system is only partially understood. This study examines the role of cortisol in monocyte differentiation and function, with regard to interleukin-1 beta (IL-1 beta) expression. The differentiation of the human histiocytic lymphoma cell line U 937 into macrophage-like cells by phorbol ester [phorbol myristate acetate (PMA)] is inhibited by cortisol. Some cells remain in suspension and continue to divide; others stop proliferation, but do not undergo full morphological differentiation. When cells are washed after 3 days to remove PMA and cortisol, all cells stop dividing and become fully differentiated. The PMA, therefore, commits the cells to differentiate even after its removal, while cortisol is only suppressive when present. Differentiated cells are shown to produce IL-1 beta mRNA when stimulated with lipopolysaccharide. This effect is inhibited by cortisol in a dose-dependent manner. After removal of cortisol, the least differentiated cells that remained in suspension were found to be overproducers of IL-1 beta mRNA after stimulation with lipopolysaccharide. This suggests that PMA induces a buildup of transcription-activating factors that were suppressed in the presence of cortisol. We conclude that the adrenal glucocorticoids that are elevated in acute stress conditions or major depression attenuate the differentiation and function of monocytes.