Endotoxin and macrophage-migration inhibition

Endotoxin inhibits the in vitro migration of macrophages. Macrophages which have been stimulated by intraperitoneal oil (Marcol) are more sensitive to the endotoxin than are nonstimulated, normal macrophages. Other factors appear to affect the sensitivity of macrophages and there is great variation between individual animals. This effect is not due to toxicity since the macrophages remain viable. Furthermore, it can be reversed by the addition of polymyxin B. This action appears to be a direct effect on macrophages since it is still evident with viable, enriched populations. The action of endotoxin can be potentiated by exposure of macrophages to lymphocyte supernatants containing migration-inhibition factor. The action is not potentiated by periodate treatment. In this situation the two effects are additive. It is suggested that some of the variability in the migration-inhibition factor assay might be due to contaminating endotoxin. Endotoxin has been found to contaminate most biological materials. The degree of contamination might well influence the level of activation of the macrophage, and thus the responsiveness to migration-inhibition factor. This work supports the concept that the macrophage needs to be at a certain level of activation to respond to migration-inhibition factor. It is clear that the presence of contaminating endotoxin needs to be considered, and prevented, in all work on migration-inhibition factor.