Monocyt

Monocyt, also spelled monocyt or monocytic cell in some languages, refers to a type of leukocyte (white blood cell) in the vertebrate immune system. Monocytes circulate in the bloodstream and are one of the principal cells of the mononuclear phagocyte system. When they migrate into tissues, they differentiate into macrophages or dendritic cells, where they contribute to phagocytosis, antigen presentation, and cytokine production.

Origin and lifespan: Monocytes develop in the bone marrow from myeloid precursors in response to growth factors such as CSF-1 (M-CSF) and GM-CSF. In humans they spend about one to three days in blood before entering tissues, where they may persist for weeks to months as macrophages or dendritic cells.

Subtypes: In humans, monocytes are commonly classified into classical (CD14++ CD16-), non-classical (CD14+ CD16++), and intermediate (CD14++ CD16+). Classical monocytes are primarily phagocytic and inflammatory; non-classical monocytes patrol the vasculature and respond to viral infections and tissue damage.

Clinical relevance: Abnormal monocyte counts can indicate disease. Monocytosis occurs in chronic inflammatory states, tuberculosis, several autoimmune diseases, and some myelodysplastic syndromes; monocytopenia can accompany bone marrow suppression. Acute monocytic leukemia (a form of acute myeloid leukemia, sometimes denoted AML-M5) involves proliferation of monoblasts and monocytes.

Notes: The term monocyt is used variably across languages; in English, monocyte is the standard term. In the central nervous system, resident microglia originate mainly from embryonic precursors, but circulating monocytes can replenish macrophage populations under certain conditions.