A study of the avidity of Vi antibodies in typhoid fever patients and chronic carriers

: Avidity of Vi-antibodies was studied in the patients suffering from typhoid fever and chronic carriers in the indirect hemagglutination test (IHAT) by means of titration with erythrocytic diagnostic agents sensitized with various doses of the Vi-antigen. The minimal sensitizing dose still adequate for detection of the antibodies in the titre of 1 : 20 was accepted as the avidity index. By the avidity sign the antibody heterogeneity index was calculated as the ratio of the optimal sensitizing dose to the minimal sensitizing one. In comparison with the patients suffering from typhoid fever of at the acute period of the disease in chronic carriers Vi-antibodies were more avid, this being conditioned chiefly by the highly avid IgG-antibodies. During the acute period of the disease the avidity of Vi-antibodies elevated only against the antibodies of the IgG-class. An increase of heterogeneity by the same sign was noted with increase of the degree of the serum antibody avidity.