The macrophage as a production site for hematopoietic regulator molecules: sensing and responding to normal and pathophysiological signals.

Several functional capacities of the macrophage enable it to act as an "administrator" cell for normal and pathophysiological hemopoietic regulation. Its capacity of sensing and responding to physiso-chemical, cellular and humoral signals indicates that it can regulate myelomonocytopoiesis and erythropoiesis. This occurs by modulating colony stimulating factor and erythropoietin production in response to lactoferrin and oxygen tension respectively. Detection of erythropoietin gene expression in macrophages, both in vitro and in vivo, implies that the macrophage is an "active" member of the hemopoietic cellular microenvironment. Since a subpopulation of macrophages is responsible for this function, a model is proposed in which other hemopoietic regulator molecules may be produced by distinct subpopulations of macrophages under steady-state conditions.