A method of attaching mouse RBCs to mouse macrophages is described. Both cell types were coated with rabbit anti-mouse macrophage F(ab')2, and cross-linkage of cells was effected with sheep F(ab')2 directed against rabbit F(ab')2. 98% of macrophages attached an average of 11 RBCs each. Attachment occurred at 37°C and was stable for at least 4 h. Less than 0.1% of macrophages ingested RBCs under these conditions.
Latex particles and opsonized pneumococci were ingested as avidly by RBC-coated macrophages as by native macrophages. Ingestion of these particles did not prompt ingestion of attached RBCs. When anti-RBC IgG was added, however, over 90% of macrophages ingested an average of six RBCs each. Thus, ingestion of one particle does not trigger generalized phagocytosis of all particles attached to the cell's plasma membrane, and the phagocytic stimulus is confined to the segment of the cell's plasma membrane immediately adjacent to the particle being ingested.