Species restriction in cytostatic activity of human and murine monocytes and macrophages.

The pattern of species restriction in cytostatic activity of human breast-milk macrophages (Mph) and murine starch-activated peritoneal exudate (PE) Mph was investigated. Human Mph had appreciable cytostatic activity only for human target cells and not for murine or avian target cells. In contrast, murine Mph were particularly cytostatic for target cells from heterologous species and not as cytostatic for other murine cells. This difference in the activity of murine Mph was more notable when freshly explanted fibroblasts were used as target cells than when the cytostasis of long-term tissue culture lines was measured. Experiments with peripheral blood monocytes from the two species indicated that this pattern of reactivity may be common to mononuclear phagocytes from other sources. Therefore, human Mph are preferentially cytostatic for target cells of self species; whereas, murine Mph are equally if not more cytostatic for target cells from other species.