Monoclonal Antibodies Against two Discrete Determinants on Vi Capsular Polysaccharide

Abstract

Vi is a linear homopolymer of 1,4 N-acetyl galactosaminuronic acid. It is present in S. typhi and some other members of Enterobacteriaceae. Vi antigen of S. typhi has been associated with the virulence of the organism and a vaccine based upon this antigen has been found to confer immunity against typhoid. In this paper, we report production and characterization of four hybrid cell clones secreting monoclonal antibodies against Vi capsular polysaccharide. Binding analysis using different derivatives of Vi showed that three monoclonal antibodies reacted with the antigenic determinant constituted by O-acetyl group and one recognised the epitope constituted by N-acetyl and carboxyl groups together. All the antibodies bound to Vi positive strains of S. typhi and did not show any significant reactivity with Vi negative strains of S. typhi, S. paratyphi A, S. paratyphi B and E. coli. Besides their utility in studying the sub-specificity of antibodies produced after vaccination with Vi, these antibodies would be helpful in the diagnosis of typhoid fever.

Bacterial polysaccharides as major surface antigens: interest in O-acetyl substitutions

“…108 The contribution of the 3-O-acetyl group to a Vi immunodominant epitope was 45 revealed in the 1980s by use of sera, 109 or monoclonal antibodies. 110 Structural analysis involving chemical modifications of the Vi antigen supported these findings. Partial base-or acid-mediated de-O-acetylation of the native Vi CPS from 65% to 45% could increase immunogenicity slightly.…”

Unique lipid anchor attaches Vi antigen capsule to the surface of Salmonella enterica serovar Typhi

“…The inability of VexE activity to influence lipid A biosynthesis is perhaps not surprising, given the regulation of the essential Raetz pathway process. The LpxA reaction equilibrium favors the reverse reaction, and the first committed step of lipid A biosynthesis (LpxC) is tightly regulated (15,16,20), so pathway flow is regulated according to lipid A requirement. We pursued the possibility that ΔvexE Vi antigen possesses a single acyl chain (the product of LpxA) at its reducing terminus.…”

Vi polysaccharide ofSalmonella typhitargets the prohibitin family of molecules in intestinal epithelial cells and suppresses early inflammatory responses

“…The binding of Vi to a human intestinal epithelial cell line, Caco-2, was analyzed by flow cytometry. Briefly, cells were incubated at 4°C with varying concentrations of Vi in PBS containing 1% BSA (PBS-BSA; 50 mM phosphate͞ 150 mM NaCl, pH 7.4), washed, and incubated with an anti-Vi monoclonal antibody [P2B1G2͞A9 (10 g͞ml PBS-BSA) (19)] or an isotype-matched control antibody for 1 h at 4°C. Cells were washed and mixed with FITC-labeled anti-mouse Ig antibody (The Jackson Laboratory) for 1 h at 4°C.…”