Development and Differentiation of Macrophages and Related Cells: Historical Review and Current Concepts.

Abstract

In murine, macrophages and their related cells are classified into monocyte-derived macrophages, resident macrophages, Ly-1(CD5)-positive macrophages, and dendritic cells. Monocyte-derived macrophages are terminal cells of the mononuclear phagocyte system, differentiate from monocytes which develop via promonocytes from monoblasts in bone marrow, and possess no proliferative capacity under a normal steady state. Monocytic cells first develop in hepatic hematopoiesis in ontogeny and are produced in bone marrow after birth. Monocytes first appear in peripheral blood in the late stage of ontogeny and are constantly produced in the bone marrow throughout adult life. Resident macrophages have a proliferative potential, can be sustained by self-renewal, and are suggested to be derived from colony forming unit-granulocyte/macrophages (CFU-GM) or earlier precursor cells, bypassing the stage of promonocytes and monocytes. In ontogeny, the resident macrophages differentiate from primitive/fetal macrophages which develop in blood islands of the yolk sac. The primitive/fetal macrophages precede the development of monocytic cell series, are distributed into embryonic tissues after the combination of the vitelline vessels to the fetal cardiovascular system, and are circulating in peripheral blood in the early stage of ontogeny. Ly-1-positive macrophages are a minor population residing in the peritoneal cavity, develop in the milky spots, and are suggested to be derived from precursor cells common to those of Ly-1 B cells. Dendritic cells are classified into two major groups; B cell-associated dendritic cells (follicular dendritic cells) and T cell-associated dendritic cells (Langerhans cells, interdigitating cells, veiled cells).