macrophage

views updated

macrophage A large phagocytic cell (see phagocyte) that can ingest pathogenic microorganisms (e.g. bacteria, protozoa) or cell debris and forms part of the body's immune system. Macrophages develop from precursor cells (promonocytes) in bone marrow, become wandering monocytes in the bloodstream, and then settle as mature macrophages in various tissues, including lymph nodes, connective tissues (as histiocytes), lungs (alveolar macrophages), lining of liver sinusoids (as Kupffer cells), skin (as Langerhans cells), and nervous tissues (microglia). The sinusoids of the spleen are lined with macrophages that remove worn-out red cells and platelets from the blood and destroy them. Phagocytic activity by macrophages is stimulated by macrophage-activating factor, a cytokine released by sensitized T cells. Tissue macrophages can also contribute to inflammation by secreting various cytokines. Collectively the macrophages make up the mononuclear phagocyte system.

More From encyclopedia.com