a widely distributed collection of both free and fixed macrophages derived from bone marrow precursor cells by way of monocytes; their substantial phagocytic activity is mediated by immunoglobulin and the serum complement system. In both connective and lymphoid tissue, they may occur as free and fixed macrophages; in the sinusoids of the liver, as Kupffer cells; in the lung, as alveolar macrophages; and in the nervous system, as microglia. SYN: system of macrophages.
