Lectinophagocytosis of type 1 fimbriated (mannose-specific) Escherichia coli in the mouse peritoneum

Abstract

Bacteria can bind specifically to phagocytic cells via lectin-carbohydrate interactions and such binding is often followed by activation and degranulation of the phagocytes, as well as uptake and killing of the bacteria, a phenomenon designated lectinophagocytosis. Although extensively studied in vitro, no direct evidence for the occurrence of lectinophagocytosis in vivo has been available. To obtain such evidence, we injected type 1 fimbriated (mannose-specific) or nonfimbriated Escherichia coli into the peritoneal cavity of mice (10(7)-10(10) bacteria/animal) in the absence or presence of sugars and quantified the phagocytic activity by assaying the release of lysosomal N-acetyl-beta-D-glucosaminidase into the peritoneal fluid, up to 45 min after injection. Following injection of the type 1 fimbriated bacteria, significant release of the enzyme was observed which was time dependent and increased with the number of bacteria injected, whereas the nonfimbriated bacteria caused only little release. Methyl alpha-D-mannoside (50 mM), but not methyl alpha-D-galactoside or sucrose, inhibited the release by 60 to 100%. No release of N-acetyl-beta-D-glucosaminidase was induced by bacteria injected into a peritoneal cavity from which the macrophages had been removed. Our findings show that lectinophagocytosis can occur in vivo and may contribute to the host's defence against type 1 fimbriated bacteria.