Assessment of the Diagnostic Significance of Rabbit Polyclonal Antibodies to Complex Antigens of Outer Membranes and Secreted Stress Proteins of Francisella tularensis

The widespread distribution of natural foci of tularemia on the territory of the Russian Federation necessitates the creation of new and improvement of existing methods of immunodiagnostics of the pathogen. To date, the search for Francisella tularensis antigens that could provide high sensitivity and specificity of diagnostic test systems developed on their basis remains an urgent task. At the same time, great hopes are placed on the surface structures of the cells of tularemia microbe (LPS and outer membrane proteins) and secreted stress proteins. The aim of the work was to evaluate the diagnostic value of rabbit polyclonal antibodies to complex antigens and secreted stress proteins of tularemia microbe. Materials and methods. The work used a vaccine strain, its acapsular derivative, 6 virulent strains of F. tularensis of different subspecies and biovars, as well as 10 strains of heterologous microorganisms. The diagnostic significance of the obtained sera was assessed using immunochemical and serological methods: enzyme immunoassay, immunoblotting, microagglutination reaction and indirect hemagglutination. Pure cultures of microorganisms and suspensions of organs from laboratory animals vaccinated with F. tularensis 15NIIEG and infected with F. tularensis 503/840 were used as samples. Results and discussion. Polyclonal antibodies to outer membrane antigens and secreted stress proteins of F. tularensis have been obtained. Their epitope orientation was determined using immunoblotting. The ability of the obtained polyclonal antibodies to enter into serological reactions with specific antigens of F. tularensis of different subspecies in immunological tests has been demonstrated. It has been found that these antibodies can be used to detect the pathogen in organ suspensions of vaccinated and infected laboratory animals. We have established that antibodies to complex antigens of F. tularensis, which in addition to the protein component include the carbohydrate component of the tularemia microbe cells, have the greatest diagnostic significance. Polyclonal antibodies to individual secreted stress proteins (Bfr and GroEL/GroES) are specific, but do not allow identifying the pathogen at its low concentration in the sample, which may be due to different intensities of expression of these antigens during the life of the microorganism.

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