Direct evidence that inflammatory multinucleate giant cells form by fusion.

Multinucleate giant cells (MGC) are believed to be formed by fusion of macrophages. In a chimaeric mouse composed of two histoincompatible strains each homozygous for one of the two isoenzymic forms of glucose-6-phosphate isomerase it was found that hybrid enzyme was produced in MGC-rich leucocytic exudates. This hybrid can only occur if nuclei of the two different strains reside within a common syncytial cytoplasm, demonstrating unequivocally that macrophage fusion occurred between cells of the two strains. Since the two strains were histoincompatible it appears that no strain specific recognition is necessary for fusion to occur.