Activation of the Classical Complement Pathway in Human Serum by a Small Oligosaccharide

Abstract

Abstract Two small oligosaccharides were hydrolyzed from a native polysaccharide by polysaccharidases indigenous to the venom of the tropical ant Pseudomyrmex sp. after incubation for 5 hr at 37°C. They were purified by passage through an ultrafiltration membrane (m.w. cut-off, 500 daltons), cation exchange chromatography at pH 3 to separate the oligosaccharides from peptides, and gel filtration chromatography. The highly purified oligosaccharides contained no amino acids and no polar or nonpolar lipids. The larger oligosaccharide had an estimated m.w. of 840 daltons, and the smaller 430 daltons. The larger species was a potent activator of C1 in normal human serum at 37°C, resulting in the consumption of its two natural substrates C4 and C2. It had no effect on the C1 INH, and its action was destroyed by treatment with sodium periodate. Analysis of both oligosaccharides by gas chromatography revealed five sugars: glucose, mannose, galactose, N-acetyl-glucosamine, and N-acetyl-galactosamine. Chemical analyses revealed the presence of reducing sugars in the larger species, but neither contained hexuronic acids. The latter were found in the native polysaccharide. The smaller oligosaccharide may be a monomer of the larger species. After electrophoresis on paper at pH 1.9, the 840-dalton oligosaccharide separated into two species: the first, which remained at the origin, contained reducing carbon atoms. The second migrated toward the cathode and contained no reducing sugars. Both species caused the consumption of C2 in human serum. The oligosaccharide(s) with a m.w. of 840 daltons is the smallest carbohydrate described that causes activation of the classical complement pathway.