Salmonella Typhi antigen and Salmonella Paratyphi A antigen (specifically, O-antigen, Vi capsule, and relevant surface polysaccharides) (None widely standardized; typically referred to as O-antigen, Vi antigen (for Salmonella Typhi))

Salmonella Typhi and Salmonella Paratyphi A antigens refer to structurally distinct surface-associated polysaccharide molecules found in these pathogens, the most notable being the O-antigen (a component of lipopolysaccharide, LPS, found in both serovars), and, specifically for Salmonella Typhi, the Vi capsular antigen[1][6][7]. These molecules are major determinants for serotyping and bacterial virulence: the O-antigen enables escape from host immunity, while the Vi capsule in S. Typhi confers additional protection against complement deposition and phagocytosis[1][6][7]. The O-antigen is a repeating sugar unit polymer—the composition and decoration (acetylation, glucosylation) define serovar-specific immune recognition and cross-reactivity[4][6]. These antigens are the primary targets for licensed and experimental typhoid and paratyphoid vaccines, relevant for both diagnostics (biomarker antibodies) and therapeutics (development of conjugate vaccines and experimental serotherapies)[4][5][6][7]. Antigenic variation and genetic control (such as phase variation, specific glycosyltransferases) influence the efficacy of immune response and present a challenge for universal vaccine development[1][6][7].

Other names

Salmonella Typhi O-antigenSalmonella Typhi Vi antigenSalmonella Paratyphi A O-antigenO-antigenVi capsuleLipopolysaccharide (LPS) O-antigen

Induction of specific antibody responses leading to opsonization, complement activation, and direct bacterial killing by immune cells. Vaccine-induced immunity acts by producing anti-O-antigen and anti-Vi antibodies, promoting bacterial clearance. Modifications to O-antigen or capsule can result in immune evasion, reduced complement deposition, and decreased antibody binding (i.e., vaccine or sera escape).