The influence of bacterial exotoxins and endotoxins on the phagocytic activity of human macrophages in culture

The effect of bacterial exotoxins and endotoxins on phagocytosis was tested on human macrophages in monolayer cultures by determining the rate of zymosan particle ingestion at different toxin concentrations and incubation times. The exotoxins tested were staphylococcal alpha-toxin and diphtheria toxin. The endotoxins used were lipopolysaccharides fromSalmonella typhi, Salmonella typhimurium, Shigella flexneri andSerratia marcescens. Phagocytosis was significantly impaired after prolonged incubation with diphtheria toxin whereas alpha-toxin was ineffective. Endotoxin-treated macrophages showed a wide range of phagocytic activity. Enhancement of phagocytosis was observed with a low concentration of endotoxin (1 µg/ml) fromS. typhi, S. typhimurium andS. flexneri. Higher concentrations (2.5 and 5 µg/ml) depressed phagocytosis to varying extents, except forS. typhi lipopolysaccharide, which did not induce a significant decrease in phagocytosis in comparison to the controls.