Action of a polysaccharide fraction ofHaemophilus influenzae lipopolysaccharide on macrophage: Implication of receptor for mannosyl-polysaccharides

Abstract

A polysaccharide fraction (PS) was separated by mild hydrolysis fromHaemophilus influenzae lipopolysaccharide. This preparation contained glucosyl, 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 ≅ 10⁶) and an association of aggregated units (fraction B; MW ≅ 10⁴). 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.