Immune regulation by monocytes.

Monocytes emerging from the bone marrow are the progenitors of monocyte-derived macrophages. An essential function of monocytes is to seed tissues with sufficient macrophages to replace loss from infection and tissue damage. Recent work from diverse inflammatory and homeostatic settings has shown monocytes also possess direct protective and pathogenic activities. Thus, monocytes are not simply needed to generate macrophages, but instead contribute to the overall orchestration of immunity. Some recently described properties of monocytes are both surprising and mechanistically specific; for example, inflammatory monocytes are required for the efficacy of transferred activated cytotoxic T cells, but can have potent tissue damaging effects while patrolling monocytes are required for anti-tumor immunity in some cases, but in another example provokes resistance to chemotherapy and thereby aid tumor growth. This summary will therefore focus on new findings about the regulatory activities of monocytes themselves.