Wheat germ agglutinin potentiates uptake of bacteria by murine peritoneal macrophages

Exposure of thioglycollate-elicited murine peritoneal macrophages to wheat germ agglutinin (WGA) increased markedly the uptake of six different bacteria, which have surface receptors for the lectin. Uptake of Staphylococcus aureus H was higher by 3-5-fold, of S. aureus 52A2 by 1.8-fold, of S. aureus 52A5 by 1.7-fold, of S. albus by 2.3-fold, of Shigella flexneri by 6-fold and of Micrococcus luteus by 6.5-fold. Klebsiella pneumoniae, devoid of receptors for WGA, was not phagocytosed following pretreatment of macrophages with the lectin. Pretreatment of the bacteria with the lectin also resulted, in most cases, in an increase in phagocytosis. Interaction of WGA with the macrophages and with the bacteria, as well as the potentiation of phagocytosis, was abolished by tri-N-acetylchitotriose, a saccharide that binds specifically to WGA, but not by monosaccharides which do not interact with this lectin. With non-elicited macrophages, enhancement of phagocytosis by WGA was less pronounced, probably because of the higher number of lectin-binding sites (5-fold) on the elicited cells. Peanut agglutinin and soybean agglutinin, that bind to macrophages but not to the bacteria studied, lack the ability to potentiate phagocytosis. Macrophage surface sugars thus appear to play an important role in phagocytosis by serving as receptors for lectins that form bridges between the macrophages and the microorganisms.