Fusion of macrophages following simultaneous attempted phagocytosis of glutaraldehyde-fixed red cells.

A model for the fusion of macrophages in areas of chronic inflammation in vivo has been presented which is derived from the associations of macrophage fusion in vivo and in vitro. It is suggested that in granulomata, where macrophages are closely packed in the presence of endocytogenic material, this material may on occasion attach simultaneously to more than one macrophage. Ensuing endosome margin formation may then lead to the endosome margins of one macrophage fusing with those of the other. By causing macrophages to phagocytose glutaraldehyde-fixed red blood cells in vitro under circumstances which more closely reflect in-vivo phagocytosis than the phagocytosis of the red cells by macrophages in a glass adherent monolayer, it has been shown that simultaneous attachment leads to macrophage fusion. It is suggested that giant cell formation in vivo in granulomata results from the process of simultaneous attempted endocytosis.