Vi capsular polysaccharide (Salmonella Typhi) (Vi antigen)

The Vi capsular polysaccharide of Salmonella Typhi is a linear homopolymer of α-1,4-linked N-acetylgalactosaminuronic acid residues, variably O-acetylated at the C3 position, and anchored to the bacterial surface via a lipid-modified terminal N-acetylhexosamine. It forms a protective capsule that is a major virulence factor, enabling Salmonella Typhi to evade innate immunity by preventing complement deposition, neutrophil phagocytosis, and pro-inflammatory signaling in host tissues. The Vi antigen is the basis for licensed typhoid vaccines, which induce functional antibodies conferring protective immunity against typhoid fever. Vi expression is encoded by the viaB locus within Salmonella Pathogenicity Island 7 (SPI-7) and is regulated by a set of dedicated biosynthetic, export, and regulatory genes. The capsule’s interaction with human C-type lectin receptor DC-SIGN on macrophages contributes to host immune modulation, promoting uptake by macrophages while suppressing inflammation[1][2][3][4][5][6][7][8][9].

Other names

Vi antigenVi capsuleVi polysaccharideVi antigen capsuleTyphi Vi antigenTyV polysaccharideTyphi Vi polysaccharide

Elicitation of protective anti-Vi antibodies that block bacterial infection; Opsonization of Salmonella Typhi for immune clearance; Inhibition of Vi function through antibody-mediated neutralization