Shigella flexneri serotype 2a and 3a O-specific polysaccharide (SF2a/3a O-SP)

The O-specific polysaccharide (O-SP) is the outermost carbohydrate component of the lipopolysaccharide (LPS) located on the surface of Gram-negative bacteria such as Shigella flexneri. In S. flexneri, the O-SP consists of a repeating pentasaccharide backbone, where specific modifications like acetylation or glucosylation define the various serotypes, including the clinically prevalent 2a and 3a (Citations: PubMed: 16412402, PubMed: 31601573). These polysaccharides are the primary targets of the host's humoral immune response during natural infection and are considered the most critical antigens for vaccine development (Citations: WHO, PubMed: 28838758). Because purified polysaccharides are often poorly immunogenic in children, they are typically conjugated to carrier proteins to induce a T-cell dependent immune response and long-lasting memory (Citations: PubMed: 35123144). Therapeutic strategies focusing on S. flexneri 2a and 3a O-SP aim to prevent shigellosis, a leading cause of global moderate-to-severe diarrhea and childhood mortality (Citations: Lancet: S0140-6736(18)31254-0).

Other names

Shigella flexneri O-antigenS. flexneri 2a O-polysaccharideS. flexneri 3a O-polysaccharideLipopolysaccharide O-side chainShigella flexneri O-SP

Induction of serotype-specific protective antibodies (IgG and secretory IgA) that facilitate opsonophagocytosis and complement-mediated killing of the bacteria.