Regulation of myeloid phagocyte development and function by growth hormone: a review

Growth hormone (GH) has previously been implicated in T cell development and function, and here we review its efficacy in promoting development and function of myeloid cells. Evidence obtained from both in vitro and in vivo studies suggests that, in animals as well as in man, GH augments proliferation and differentiation of erythroid, megakaryocytic and myeloid progenitor cells. Mechanisms of hemopoietic actions probably involve induction of insulin-like growth factor-1, which is under GH control. Effects are mostly, though not exclusively, seen in GH deficiency states. Like other hemopoietic factors currently undergoing clinical trials for modulation of mature phagocyte function, GH is found in vitro and in vivo to stimulate potently monocyte migration and to prime neutrophils and macrophages for enhanced activation by second stimuli. Activation of neutrophils is mediated by GH action on the neutrophil prolactin receptors. The detailed mechanism of macrophage activation is currently unknown. GH action on myeloid phagocytes may help to explain protective effects of GH observed in experimental infection as well as its promotive effect on wound healing.