Macrophage fusion and multinucleated giant cell formation, surface morphology

Abstract

Crude supernatants from BCG sensitized lymphocytes incubated with BCG were capable of mediating the in vitro fusion of and subsequent multinucleated giant cell (MGC) formation of either alveolar or peritoneal macrophages obtained from normal rabbits. The crude supernatant fluids which contained a lymphokine termed Macrophage Fusion (MFF) mediated the fusion of over 88% of the macrophages present in the experimental system. MGC possesing several hundred nuclei per cell were commonly observed with dimensions of over 1.5 mm. Control supernatants in most instances did not induce cell fusion. The surfaces of BCG-induced multinucleated giant cells of alveolar macrophage origin were examined using the scanning electron microscope. The surface of many MGC which were spread out onto the plastic substrate possessed four distinct morphological areas: a central area with a dense array of membranous veils, a transitional area with few veils, a peripheral area composed of pits and ridges giving an undulating appearance, and terminal edges which were smooth or possessed filopodia. Occasionally an atypical morphology consisting of dendritic-like structures were present on small sites on the MGC surface. Frequently many alveolar macrophages possessing typical membranous veils were attached to the MGC surface. It was concluded that the surface morphology of multinucleated giant cells was similar to that of macrophages.