Immunochemical properties of Vi antigen from Salmonella typhi Ty2: presence of two antigenic determinants.

Antigen Vi of Salmonella typhi was found to have at least two antigenic determinants. In one of them, O-acetyl moiety played a dominant role. The second antigenic determinant did not involve O-acetyl residues, but both carboxyl and N-acetyl groups were necessary for the antigen-antibody reaction. These results were obtained by performing serological tests with antigen Vi, with its structural analog, polygalacturonic acid, and with the derivatives of both polysaccharides.