Modulation of lectinophagocytosis of Escherichia coli by variation of pH and temperature

Abstract The effect of variation of pH and temperature on the lectinophagocytosis of enteropathogenic Escherichia coli by polymorphonuclear leukocytes and macrophages elicited by thioglycolate medium was evaluated. The phagocytosis of enteropathogenic E. coli is dependent on pH, being maximal at pH 7.0 and reduced at pH 5.5 or 6.0. Mannan and mannose (as representative sugars that bind to phagocyte lectin receptors), are recognized by mannose receptors and reduced the phagocytic index at pH 7.0 (from 41.6±8.5 to 17.0±6.1) and at pH 6.0 (from 24.1±5.1 to 14.5±5.0), suggesting that mannose receptors, despite their reduced affinity for ligand at pH 6.0, also participate in phagocytosis of enteropathogenic E. coli. The inhibition of phagocytosis by anti-substance A antibody was also examined at pH 7.0 and at pH 6.0, decreasing (from 41.6±8.5 to 21.1±3.4) and (from 24.1±5.1 to 12.0±3.5), respectively. This antibody reduced the phagocytosis of enteropathogenic E. coli in phagocytic assays at 37 or 41°C. These results suggest that the acidic pH decreased the affinity of mannose receptors to ligands on the surface of E. coli and also affected the binding of lectin from E. coli to N-acetylgalactosamine on phagocytes.