Immunobiological properties of a mixture of antigens from experimental protective protein-containing fractions isolated by different methods from the Streptococcus oralis strain

Background. Previously, the main pathogenicity factors of closely related strains of Mitis group streptococci of different virulence, including Streptococcus pneumoniae and Streptococcus oralis, were determined. Differences in the protein composition of protein-containing fractions (PCF) with a molecular weight of 30–100 kDa isolated from them using Amicon®Ultra filters (Millipore, Ireland) were established. It was of interest to obtain PCF by gel filtration (PCF-C) and the determination of the possibility of its use in the development of an antipneumococcal drug.

Aim. Comparison of the immunobiological properties of PCF from the S. oralis strain isolated by different methods and a study of the protective activity of a mixture of antigens of the Mitis group of streptococci.

Materials and methods. PCF-C was prepared by exclusion chromatography on a Toyopearl HW-55 column. Surface protein-containing antigens of S. oralis were assessed by protein content using the Lowry method and electrophoretic characteristics using the Laemmli method. The protective activity was studied in experiments on active protection of BALB / c mice with two intraperitoneal injections (with an interval of 14 days) of three preparations: PCF and PCF-C (50 μg protein / mouse) and a mixture of PCF-C + recombinant atoxic pneumolysin (raPly) (25 μg protein / mouse). Immunized mice were intranasally infected with a virulent strain of S. pneumoniae serotype 3 No. 10196. The level of specific immunoglobulin G (IgG) antibodies was determined in the hyperimmune sera of mice using solid-phase enzyme-linked immunosorbent assay. Statistical processing of the results was performed using parametric and nonparametric comparison methods.

Results. A comparative analysis of the PCF-C and PCF series established their protective activity against the virulent strain of S. pneumoniae; both preparations induced the production of specific IgG antibodies, did not differ in protein yield and were non-toxic. The protective activity of the PCF-C + raPly mixture was established.

Conclusion. The feasibility of using a surface protein-containing antigen of S. oralis obtained using size-exclusion chromatography, including as part of a two-component experimental preparation in a mixture with raPly not sorbed on aluminum hydroxide, is demonstrated.