O-antigen polysaccharide from Shigella sonnei (OAg (O-antigen))

O-antigen polysaccharide from Shigella sonnei is a high-molecular-weight carbohydrate chain comprising repeating units unique to S. sonnei, including 2-acetamido-2-deoxy-L-altruronic acid and 2-acetamido-2-deoxy-L-fucose[1][5][9]. It forms the O-specific region of the bacterial lipopolysaccharide (LPS) and, in S. sonnei, also exists as a capsule (group 4 capsule) attached to an alternative lipid anchor[4][5]. This antigen is the primary target for protective immune responses, particularly vaccine-induced anti-OAg antibodies, and is critical for evasion of host immunity, resistance to complement-mediated killing, and modulation of bacterial virulence[1][3][4][5][9]. The biosynthetic genes for the O-antigen are carried on the S. sonnei virulence plasmid (pSS), rather than the chromosome, and are highly similar to those in Plesiomonas shigelloides, reflecting recent horizontal gene transfer[2][5]. S. sonnei O-antigen is essential for pathogenesis and is a validated vaccine target, with several human monoclonal antibodies and OMV (outer membrane vesicle/GMMA) vaccines in clinical development[3][9].

Other names

S. sonnei O-antigenShigella sonnei OAgO-antigen capsule (sometimes referred to for the high-molecular-weight form)S. sonnei O-antigen polysaccharide

Antibody-mediated complement-dependent bactericidal activity[3][9]; Vaccine-induced immunity (production of anti-OAg IgG that can kill bacteria or prevent invasion/extracellular survival)[3][9]