Membrane phenomena accompanying erythrophagocytosis. A scanning electron microscope study

Mouse peritoneal macrophages phagocytose opsonized sheep red blood cells in two distinct ways. The unflattened macrophage with its highly folded plasma membrane envelops erythrocytes by multiple pseudopodia that are frequently of unequal size and have overlapping margins. The flat macrophage with a smooth surface, acquired as a result of spreading on an artificial substrate or from engulfing several erythrocytes, internalizes erythrocytes by a single cuplike or funnel-like pseudopod. Both patterns are observed in in situ and in vitro preparations of macrophages from A and C3H/HeN strain mice, that are normal, sensitized to sheep red blood cells, or treated with pyran. These membrane patterns are observed on macrophages engulfing erythrocytes that had been coated with antibody from A strain mice, or with rabbit antisheep erythrocyte antibody. The factor that appears to determine the membrane pattern is the number of discrete points of contact made by the erythrocyte as it attaches to the folded or smooth surface of a macrophage.