Vi antigen and microbial adhesion factors. The detection of adhesins in commercial Vi antigen preparations

Enterobacterial Vi-antigen inhibit the Escherichia coli-induced agglutination of red blood cells of guinea pigs and other animals, which indicates that Vi-antigen contains the admixture of adhesion associated with type I pili. The amount of adhesion contained in Vi-antigen can be determined from the degree to which its hemagglutination-inhibiting effect is manifested.     

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.     

Adsorption of Vi antigen on human erythrocytes

The accumulation of Vi-antigen in the human body was studied with the use of such characteristic as the specific adsorption capacity of red blood cells. This parameter was shown to depend on the phenotype in the ABO blood group system. In cases of typhoid fever an increase in the adsorption capacity of red blood cells was observed at the acute period of the disease. These changes were particularly manifest in patients belonging to groups O and A. The authors suggest that the adsorption of the antigen on red blood cells has a definite kinetics related to the dynamics of the infectious process.