FIG. 1.
Developmental sources of adult tissue macrophages. Adult tissue macrophages are derived either from embryonic macrophages that develop early in the embryonal yolk sac and proliferate in situ, or from blood monocytes that develop along a specific line of progenitors in the bone marrow. There is speculation about a lymphoid source of macrophages in the lymphoid organs (dotted arrow). HSC, hematopoietic stem cell; CMP, common myeloid progenitor; CLP, common lymphoid progenitor; MDP, monocyte/dendritic cell progenitor; CDP, common dendritic cell progenitor. For details, see text.