Action of a polysaccharide fraction of Haemophilus influenzae lipopolysaccharide on macrophage: implication of receptor for mannosyl-polysaccharides.

A polysaccharide fraction (PS) was separated by mild hydrolysis from Haemophilus influenzae lipopolysaccharide. This preparation contained glycosyl-galactosyl, rhamnosyl, glucosaminyl and mannosyl residues (molar ratio: 4-1-1-2-2). It was nontoxic and immunogenic and consisted of at least one stable molecular group (fraction A; MW approximately equal to 10(6)) and an association of aggregated units (fraction B;MW approximately equal to 10(4)). This study evaluated the capacity of phagocytosis and quantitative nitroblue-tetrazolium reduction of mouse macrophages in presence of these polysaccharide fractions. After a 24-h incubation period, PS and fraction A, at 1 mg/ml, increased both phagocytosis and reduction potential of mouse peritoneal macrophages by 100%. In contrast, 1-h incubation with PS or fraction A induced a decrease of 50% in phagocytosis but no modification of NBT reduction. An identical incubation with various sugars showed that only mannosyl polymers could significantly decrease this phagocytic process. As in the case of toxic lipopolysaccharides, macrophages responded to a nontoxic preparation obtained from an endotoxin. We confirmed the role of mannosyl residues in recognition of macrophage binding receptors. Moreover, we suggest that this mannose binding ability was dependent on dose, aggregation state and molecular weight of the preparation.U