Characterization of serotype II polysaccharide antigen of group E streptococci using a monoclonal antibody

A Monoclonal antibody (MAb II-T) specific for serotypes II and V of Group E streptococci (GES) was prepared by fusing myeloma cells with spleen cells of mice immunized with whole cells of a serotype II strain. MAb II-T reacted in an enzyme immunoassay (EIA) with whole cells of both serotypes and reacted in gel diffusion test with autoclaved-saline extracts of serotypes II and V. The extract was purified by DEAE-Se-phadex A-25, followed by treatment with proteinase K, and further by chromatography with a Sephadex G-200 column. The purified polysaccharide (PS) antigen contained 98.6% carbohydrate and 1.4% protein, but no detectable phosphorus. In hapten inhibition tests using various sugars, D-mannosamine markedly inhibited the precipitin reaction. These results indicated that the antigenic determinant might have a structure similar to D-mannosamine.