Shigella sonnei phase I O-specific polysaccharide antigen (S. sonnei O-Ag)

The Shigella sonnei phase I O-specific polysaccharide antigen is the immunodominant surface component of the S. sonnei bacterium, which is the primary cause of shigellosis in industrialized and middle-income countries [4, 11]. It is a unique polysaccharide composed of repeating units of two uncommon amino sugars, 2-acetamido-2-deoxy-L-altruronic acid and 2-acetamido-2-deoxy-L-fucose, and is encoded on a large virulence plasmid (pINV) [1, 4]. This antigen plays a critical role in bacterial pathogenesis by protecting the organism from host innate immune defenses, such as complement-mediated lysis and phagocytosis [1, 4]. It also modulates the inflammatory response by inhibiting inflammasome activation and reducing pyroptosis in macrophages [6, 12]. Because immunity to Shigella is largely serotype-specific and directed against the O-antigen, this molecule is the central target for the development of various vaccine candidates [5, 15]. These candidates include glycoconjugates, bioconjugates, and generalized modules for membrane antigens (GMMA) [11, 15]. Clinical studies have demonstrated that serum IgG antibodies against this antigen correlate with protection, making it a vital biomarker for vaccine efficacy [9, 10]. The antigen is also identical to the O-antigen of Plesiomonas shigelloides O17, reflecting its horizontal acquisition [1, 14]. Overall, targeting this polysaccharide is a key strategy for global health interventions aimed at reducing the burden of diarrheal disease [10, 13].

Other names

Phase I O-antigenForm I O-polysaccharideS. sonnei O-antigenO-specific polysaccharideO-SPShigella sonnei O-antigen

Vaccines targeting this antigen induce the production of serotype-specific antibodies, primarily serum IgG and mucosal IgA, which mediate complement-dependent bacteriolysis and prevent bacterial invasion of the colonic epithelium [8, 11].