Vi capsular polysaccharide antigen of Salmonella Typhi (Vi antigen)

The Vi capsular polysaccharide antigen of Salmonella Typhi is a surface-expressed, virulence-enhancing glycan unique to this pathogen. Structurally, it consists of nonstoichiometrically O-acetylated α-1,4-linked N-acetylgalactosaminuronic acid residues anchored to the bacterial outer membrane via a specialized lipid moiety. Its main biological function is to protect S. Typhi from host immune clearance mechanisms by inhibiting complement activation, blocking phagocytosis by neutrophils, suppressing inflammatory signaling in epithelial cells, and promoting macrophage uptake via binding to human immune receptors such as DC-SIGN. The Vi antigen is the cornerstone of current typhoid vaccines and is also used as a biomarker for immune response post-vaccination. Genetic variation in Vi biosynthesis can influence the virulence and vaccine coverage across regions. While highly effective as a vaccine antigen, challenges include low immunogenicity in certain populations and possible antigenic variation.

Other names

Vi antigenVi capsular antigenVi polysaccharideVi capsuleVirulence (Vi) capsular polysaccharide

Active induction of protective immune response via antibody production against Vi antigen (prevents Salmonella Typhi infection). Antibody-mediated enhancement of opsonization and clearance of Vi-capsulated bacteria.