Macrophage

any mononuclear, actively phagocytic cell arising from monocytic stem cells in the bone marrow

Description
Macrophages are widely distributed and vary in morphology and motility; most are large, long-lived cells with nearly round nuclei and abundant endocytic vacuoles, lysosomes, and phagolysosomes. Phagocytic activity is typically mediated by serum recognition factors, including certain immunoglobulins and components of the complement system, but also may be nonspecific for some inert materials and bacteria, as in the case of alveolar macrophages. Macrophages also are involved in both, in the production of antibodies and in cell-mediated immune responses, participate in presenting antigens to lymphocytes, and secrete a variety of immunoregulatory molecules.