Shigella flexneri serotype 1b O-antigen (S. flexneri 1b O-antigen) (S. flexneri 1b O-antigen)

The Shigella flexneri serotype 1b O-antigen is a complex polysaccharide structure that constitutes the outermost part of the lipopolysaccharide (LPS) on the cell surface of Shigella flexneri serotype 1b bacteria (Perepelov et al., 2010). It plays a fundamental role in bacterial pathogenesis by acting as a physical and chemical shield against the host's innate immune system, particularly by preventing the assembly of the membrane attack complex and resisting cationic antimicrobial peptides (West et al., 2005). The chemical structure consists of a repeating tetrasaccharide unit—comprising three L-rhamnose residues and one N-acetyl-D-glucosamine—with specific glucosylation at the first rhamnose residue and O-acetylation patterns that define the 1b serotype specificity (Allison & Verma, 2000). Because this antigen is highly accessible and immunodominant on the bacterial surface, it is the primary target for protective humoral immunity and the development of glycoconjugate vaccines (Cohen et al., 2022). These vaccines aim to elicit high titers of serum IgG and mucosal IgA antibodies to prevent shigellosis, which remains a leading cause of moderate-to-severe diarrhea and mortality in children in low-resource settings (WHO, 2023). Additionally, research into monoclonal antibodies targeting this specific O-antigen is ongoing to provide potential passive immunization or therapeutic options for infected individuals (Phalipon et al., 2009).

Other names

Shigella flexneri 1b O-polysaccharideS. flexneri 1b LPS O-antigenShigella flexneri serotype 1b lipopolysaccharideS. flexneri 1b O-Ag

The primary mechanism of action for vaccines and antibodies targeting the Shigella flexneri serotype 1b O-antigen is the induction or provision of serotype-specific antibodies. These antibodies bind to the O-antigen on the bacterial surface, leading to pathogen neutralization, enhancement of opsonophagocytosis by macrophages and neutrophils, and activation of the classical complement pathway to facilitate bacterial lysis.