Effects of endotoxins from Bacteroides intermedius and Escherichia coli on human monocytes in vitro.

Endotoxins (lipopolysaccharides, LPSs) from the strictly anaerobic bacterium Bacteroides intermedius and from Escherichia coli were compared with respect to effects on human monocytes. Exposure of monocyte monolayer cultures to the structurally different endotoxins caused morphological changes, demonstrated by large rounded cells containing cytoplasmic granules with the B. intermedius LPS, and smaller cells with several cytoplasmic protrusions with the E. coli LPS after 10 days of culture. The B. intermedius LPS was, at some doses, able to induce an increased level of the lysosomal enzyme acid phosphatase and increased C3b-receptor-mediated phagocytosis, while other doses gave no effect or weak suppression compared to control cultures. The stimulatory effects were donor-dependent. The E. coli LPS had predominantly suppressive effects on acid phosphatase level and C3b phagocytosis. Both endotoxins resulted in enhanced expression of the activation related cell surface antigen, characterized by the mononuclear phagocyte specific monoclonal antibody 1D5. Biphasic dose-response relationships were observed, particularly pronounced with B. intermedius LPS, giving stimulation of enzyme activity with low (1 ng/ml) and high (0.5 microgram/ml) doses, and suppressed enzyme activity with intermediate doses (0.01-0.10 microgram/ml). The results imply that the effects of endotoxins on different aspects of human monocytes vary considerably; they also suggest that the balance between stimulatory and suppressive properties of a particular endotoxin may influence its net effect on mononuclear phagocyte functions.