Mononuclear phagocyte proliferation, maturation and function.

The mononuclear phagocytic system is a continuum of cells beginning with the bone marrow monoblast and promonocyte, through the monocyte to the larger tissue macrophages and multinucleate giant cells. This system of cells is widely distributed throughout the body in the blood and bone marrow; the pleural, peritoneal, and alveolar spaces; the lymph nodes, spleen, liver, and other parenchymal organs. The activity and composition of the cell varies with the level of maturation, changes in cellular environment, and with various cellular activities. The monocyte-macrophage group of cells plays an active role in defense reactions against certain microorganisms, and in the removal of dying cells and cell debris. They are an integral part of both the inductive phase of the immune response, and of cell-mediated immune reactions. In addition, they probably play a role in the defence against spontaneously arising tumours, in the control of granulopoiesis, and possibly in erythropoiesis.