The capacity of macrophage components to inhibit anti‐macrophage serum activity

Anti‐macrophage serum (AMS) was shown to lose part of its activity after incubation with macrophages. Both the cytotoxic and phagocytic inhibition properties of AMS decreased significantly after 12 h incubation with macrophages. Free and/or AMS‐bound macrophage antigens were found to be shed from the cell surface into the culture medium during incubation of macrophages with AMS. Labeled macrophage components were demonstrated to bind specifically to AMS, suggesting that the loss of AMS activity was mainly due to the blocking of antimacrophage antibody combining sites by macrophage antigens.