Shigella flexneri serotype 3a O-antigen (SF3a O-antigen)

The Shigella flexneri serotype 3a O-antigen is a complex polysaccharide structure that constitutes the outermost domain of the lipopolysaccharide (LPS) on the surface of Shigella flexneri, a major causative agent of bacillary dysentery (Perepelov et al., 2010). The O-antigen consists of a repeating tetrasaccharide unit composed of three L-rhamnose residues and one N-acetyl-D-glucosamine residue, with serotype 3a specifically defined by O-acetylation at the 2-position of both the rhamnose III (Type III antigen) and rhamnose I (Group 6 antigen) residues (Sun et al., 2012). This surface-exposed molecule is essential for bacterial survival within the host, providing a barrier against complement-mediated killing and facilitating the invasion of intestinal epithelial cells (Mani et al., 2016). As a primary target of the host's adaptive immune system, the SF3a O-antigen is the focus of vaccine development, particularly for synthetic glycoconjugate vaccines that link the O-polysaccharide to a carrier protein to induce long-lasting, T-cell dependent immunity (Cohen et al., 2022). Therapeutic strategies also include the development of serotype-specific monoclonal antibodies that can neutralize the pathogen or enhance opsonophagocytosis (Phalipon et al., 2008). However, the high degree of antigenic variation among Shigella serotypes remains a significant challenge, as immunity to the 3a O-antigen typically does not provide cross-protection against other common serotypes like 2a or 6.

Other names

Shigella flexneri 3a O-polysaccharideS. flexneri 3a LPS O-side chainShigella flexneri serotype 3a lipopolysaccharide

Induction of serotype-specific bactericidal and opsonophagocytic antibodies that target the bacterial surface to facilitate pathogen clearance.