Salmonella O antigen-specific oligosaccharide-octyl conjugates activate complement via the alternative pathway at...

Artificial Salmonella serogroup B, D or Cl-specific glycolipids were prepared by covalently linking oligosaccharides corresponding to two O-antigen repeating units, obtained by phage enzyme hydrolysis of native O-antigenic polysaccharides, to octyl residues. Sheep erythrocytes coated with the artificial glycolipids were studied for their ability to consume C3, when incubated in C4- deficient guinea pig serum. Salmonella C1 (0-6,7) glycolipid-coated erythrocytes consumed C3 40% more efficiently than Salmonella D (0-9,12) glycolipid-coated erythrocytes, and 10-times more efficiently than Salmonella B (0-4,12) glycolipid-coated erythrocytes. These results resemble C3 consumption by Salmonella C1, D, and B cells and by sheep erythrocytes coated with purified lipopolysaccharides of these O-specificities. The results prove directly that in a particulate system C3 activation via the alternative pathway depends on the structural properties of the O-antigenic side chain. Structures as small as octasaccharides, or as two O-antigenic repeating units, are sufficient for triggering C3 activation, but the magnitude of activation depends on the nature of the monosaccharides. Apparently, neither the core oligosaccharide nor Lipid A of lipopolysaccharide are required for C3 activation via the alternative pathway.