Shigella lipopolysaccharide O-antigen (O-Ag, OAg, O-antigen)

The Shigella lipopolysaccharide O-antigen is a high-molecular-weight polysaccharide component of the bacterial outer membrane that serves as a major virulence factor and primary target for protective immunity.[1][2] Composed of repeating oligosaccharide units, the O-antigen exhibits remarkable structural diversity across different *Shigella* serotypes and regulates chain-length distribution in a species- and growth-dependent manner.[2][3] The O-antigen functions as a critical immune evasion mechanism by physically blocking antibody-mediated complement deposition at the bacterial surface and preventing phagocytic recognition, thereby enabling bacterial persistence during infection.[4] As the primary target of serotype-specific protective antibodies induced by natural infection, the O-antigen represents a validated vaccine target for shigellosis prevention.[1][9] Current therapeutic and vaccine strategies target the O-antigen using monoclonal antibodies and synthetic oligosaccharide conjugates designed to mimic the native antigen structure.[1][5] A candidate human monoclonal antibody (C-0302B17) demonstrates potent bactericidal activity and protection in animal models by facilitating complement-mediated killing and blocking bacterial invasion of epithelial cells.[5] The main challenge in O-antigen-based therapeutics is achieving broad protection across multiple serotypes while maintaining specificity, as protection shows strict serotype specificity determined by the repeat unit structure.[1]

Other names

O-antigen polysaccharideO-PS (O-antigen polysaccharide)Somatic antigenLipopolysaccharide O-antigen

Antibody-mediated bacterial killing through complement deposition Blockade of bacterial invasion of epithelial cells Enhancement of phagocytic engulfment Prevention of bacterial persistence in host tissues