Interaction of Vi antigen with proteins

Whiteside, Roberta E. (Boston University School of Medicine, Boston, Mass.), and Edgar E. Baker. Interaction of Vi antigen with proteins. J. Bacteriol. 92:1597-1603. 1966.-Purified Vi antigen (Vi) mixed in equal amounts with bovine serum albumin (BSA) or human gamma globulin (HGG) at pH values above 4.7 formed a complex which was not precipitated by trichloroacetic acid or tungstic acid. At pH values below 4.7, the interaction between Vi and either BSA or HGG produced insoluble complexes except when excess Vi antigen was present. When sufficient Vi was present at the lower pH values, the soluble complex was not precipitated by trichloroacetic acid. Other acid polysaccharides tested did not form trichloroacetic acid-soluble complexes with BSA. When subjected to immunoelectrophoresis, the Vi-BSA complex migrated in agar at a rate different from that of either BSA or Vi alone. The complex reacted with both Vi and BSA antiserum. The addition of either BSA or Vi antiserum to a Vi-BSA complex resulted in dissociation of the complex and precipitation of either Vi or BSA, depending upon the antiserum used. Vi antigen mixed with purified O antigen from Salmonella typhosa formed a complex which migrated in agar at a rate different from that of either component alone when subjected to immunoelectrophoresis.