Selected properties of lipopolysaccharides possessing the mannan as O-specific polysaccharides of Gram-negative bacteria

Lipopolysaccharides of some Gram-negative bacteria from genera Citrobacter, Hafnia, Escherichia, Klebsiella, Salmonella, and Serratia have the O-specific polysaccharide moieties consisting of mannan. Mannose-rich lipopolysaccharides exhibit several characteristic immunological activities. Lipopolysaccharides possessing the mannose homopolymer are much more potent in activating the complement system than these with heteropolymer. The complement system can be activated by classical, lectin or alternative pathways. The lectin pathway plays significant role in first-line host defense. Mannose-binding protein (MBL), the main component of the lectin pathway, recognizes specific carbohydrate residues (mannose, N-acetylglucosamine) on the surface of microorganisms and promotes the killing of pathogens. Many bacterial strains are resistant to complement-dependent host defense, which is related with complicated structure of their outer membrane.