Incubation of human macrophages with endotoxin resulted in significantly enhanced colony-stimulating activity (CSA) production by these cells. Preincubation of endotoxin with mature granulocytes abolished this stimulatory effect. The stimulatory effect of endotoxin on macrophage CSA production was not abolished, however, by preincubation with NaF-treated granulocytes, granulocyte membranes, or nonphagocytic cells (lymphocytes or erythrocytes). These data suggest that mature granulocytes may play a role in the modulation of CSA production and granulopoiesis by inactivation of stimulatory materials such as endotoxin.

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