Shigella flexneri 2a O-antigen lipopolysaccharide (SF2a-O-Ag)

Shigella flexneri 2a O-antigen lipopolysaccharide is a critical surface component and primary virulence factor of the Gram-negative bacterium Shigella flexneri serotype 2a, which is a major cause of bacillary dysentery worldwide. The O-antigen is the distal, highly variable carbohydrate portion of the lipopolysaccharide (LPS) that extends from the bacterial surface, serving as a shield against host innate immune defenses such as the complement system and cationic antimicrobial peptides (PMID: 21605044). It is composed of a repeating pentasaccharide unit whose specific glucosylation and acetylation patterns define the 2a serotype (PMID: 3122615). Because natural immunity to Shigella is largely directed against the O-antigen and is serotype-specific, this molecule is the focal point for vaccine design. Therapeutic strategies, such as conjugate vaccines (e.g., SF2a-TT or Flexyn2a), aim to elicit high titers of O-antigen-specific IgG and mucosal IgA antibodies to block bacterial invasion of the colonic epithelium (PMID: 28438871). Additionally, the O-antigen is a target for diagnostic assays and potential monoclonal antibody therapies intended to provide passive protection against infection.

Other names

S. flexneri 2a O-polysaccharideShigella flexneri 2a LPSO-specific polysaccharide of Shigella flexneri 2aSF2a O-Ag

Induction of serotype-specific bactericidal and neutralizing antibodies (IgG and IgA) that bind to the O-antigen, preventing bacterial attachment and invasion of the intestinal epithelium (PMID: 28438871).