CHARACTERIZATION OF A HUMAN MONOCLONAL IMMUNOGLOBULIN-M (IGM) ANTIBODY (IGM(BEN)) SPECIFIC FOR VI CAPSULAR POLYSACCHARIDE OF SALMONELLA-TYPHI

A search for human monoclonal antibodies to protective antigens of bac teria revealed an immunoglobulin M lambda chain [IgM(lambda); designat ed IgM(BEN)] reactive with the Vi capsular polysaccharide of Salmonell a typhi. Vi, a linear homopolymer of alpha(1-->4)GalApNAc that is O ac etylated at C-3, is a licensed vaccine for typhoid fever. Immunologic properties of IgM(BEN) were compared to those of burro globulin prepar ed by intravenous injections of S. typhi (B339-340). IgM(BEN) and B339 -340 yielded identical precipitin lines with Vi by double immunodiffus ion. IgM(BEN) and B339-340 produced similar precipitation results with Vi and its derivatives prepared by de-O-acetylation, carboxyl reducti on, and removal or replacement of the N-acetyl at C-2 with O-acetyl. B 339-340 yielded maximal precipitation with Vi (0.41 mg of antibody per ml with 1.4 mu g of Vi); next was carboxyl-reduced, O-acetylatecl Vi, which precipitated 0.325 mg of antibody per mi with 2.5 mu g of Vi. I gM(BEN) yielded maximal precipitation,vith de-O-acetylated, carboxyl-r educed Vi (similar to 11.0 mg of antibody per mi with similar to 1.3 m u g of antigen); next were de-O-acetylated Vi (9.89 mg/ml) and Vi (9.1 9 mg/ml). The precipitin curves and equivalence points of these three antigens were similar. Pneumococcus type 1, which contains GalApNAc, d id not precipitate with Vi or its derivatives. These slight difference s in specificity between IgM(BEN) and B339-340 were related to our pro posed structure of Vi. We plan to use IgM(BEN) as a reference for meas urement of vaccine-induced Vi antibodies.