Lymphokine-mediated fusion and migration inhibition of alveolar macrophages

Guinea pigs were shown to produce a lymphokine termed macrophage fusion factor (MFF) which mediated the fusion of 70–80% of guinea pig or rabbit alveolar macrophages, but not guinea pig peritoneal macrophages. In the conventional migration inhibitory factor (MIF) assay, guinea pig aveolar macrophages were inhibited in their migration and large numbers of giant cells were present. There appeared to be a correlation between the titer of MFF and migration inhibition of alveolar macrophages but not with MIF titer as expressed on the peritoneal macrophage. Guinea pig MFF production was erratic and its absence from lymphokine supernatant fluids correlated with an absence of migration inhibitory activity for the alveolar macrophage. Guinea pig MIF production was more constant and high titers were invariably present. Rabbit crude lymphokine supernatant fluids containing MFF also inhibited the migration of their alveolar macrophages when measured at 24 and 48 hr during the MIF assay. Extensive numbers of giant cells were observed in the cell fan whenever migration inhibition was present. α-l-Fucose, which is known to block the receptor sites of MIF, failed to block giant cell formation in either the MFF or the MIF assay and also failed to block migration inhibition of the alveolar macrophages. The results suggest that lymphokines other than MIF can inhibit the migration of alveolar macrophages in the standard MIF assay and that the lymphokine responsible for migration inhibition and fusion of alveolar macrophages is the same lymphokine, MFF.