Protective properties of certain external proteins of group B streptococci

: On the basis of genes, which control synthesis of externally localized proteins of group B streptococci (bac and scaAB), recombinant polypeptides P6 and ScaAB were obtained. Data on protective activity of these polypeptides during experimental infection of immunized mice as well as in opsonophagocytic test on cultivated peritoneal macrophages are presented. It has been shown that protective effect of specific antibodies to P6 was dependent from intensity of immune response. Titer of specific IgG to P6 equal 1:25000 was protective for mice during challenge with LD50. During sublethal challenge level of humoral immunity determined both rate of microorganism elimination and degree of decrease of concentration of streptococci in the spleen. Recombinant polypeptide ScaAB also had marked protective activity and protective titer ScaAB-specific IgG was significantly lower compared with the first polypeptide (1:1600). It has been established that both types of antibodies have opsonizing activity against different strains of group B streptococci. Opsonizing properties of antibodies to P6 were restricted to Bac protein-producing streptococci whereas specificity of antibodies to ScaAB was not restricted by type and group borders. Opsonization of both group B and group A streptococci was revealed. It has been established that protective efficacy mediated by antibodies was dependent not only from their opsonizing characteristics but also from availability of protein antigens, which under certain conditions can be shielded by capsular polysaccharide. It has been assumed that vaccine preparation developed on the basis of polypeptides P6 and ScaAB is promising for further research.