The lipopolysaccharide endotoxin of a Group C Neisseria meningitidis strain 1908 has been isolated by phenol-water extraction and further purified by differential ultracentrifugation of the water soluble lipopolysaccharide-nucleic acid complex. The lipopolysaccharide was found to contain 20% lipid (composed of cephalin, fatty acids and plasmalogen) with polysaccharide constituents identified as glucose, galactose, glucosamine and sialic acid. The endotoxin contained less than 1% protein, and less than 1% nucleic acid. Hemagglutination inhibition tests revealed that this meningococcal lipopolysaccharide was able to inhibit antibodies from agglutinating sheep erythrocytes sensitized with Group C specific capsular polysaccharide composed principally of units of sialic acid. The converse was not found, however. Analytical ultracentrifugation and the separation of lipopolysaccharide and of capsular polysaccharide by gel filtration provided evidence that the sialic acid formed an integral part of the biologically active lipopolysaccharide. “Crude” and “purified” lipids extracted from parent lipopolysaccharide failed to demonstrate lethal activity in high dosages in normal or pertussis-sensitized mice. They were found to be nonpyrogenic and nonpreparing for the local Shwartzman reaction in rabbits in comparison to the native lipopolysaccharide. In rather small dosages, however, they were capable of increasing nonspecific resistance in the mouse to a lethal E. coli infection.

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