The development of simple, express, and at the same time sensitive and selective methods for diagnosing pseudotuberculosis remains an urgent task of practical public health. The effectiveness of the test systems largely depends on the activity and the specificity of a diagnostic pseudotuberculous sera. Achieving high sensitivity and specificity of diagnostic test systems largely depends on the presence of specific pseudotuberculous sera with a high antibody titer, which, in turn, is ensured by the proper selection of the animal producer, the physicochemical properties of the immunogen, its dose, multiplicity and duration. introduction and use of adjuvants. Currently, diagnostic serum for Yersinia pseudotuberculosis for an approximate agglutination test on a glass slides is produced in the Russian Federation (FSUE SPbNIIVS FMBA of RUSSIA). Obtaining of pseudotuberculous sera for a wider scope of their use, in particular, in the design of diagnostic immunobiological preparations and test systems for pseudotuberculosis, is relevant and in demand in healthcare practice. The purpose of this study was to obtain and characterize hyperimmune specific sera against cellfree antigenic fractions of the causative agent of pseudotuberculosis. Chinchilla rabbits were used as sera producers. Cell-free antigenic fractions (urea extract, outer membranes, and proteinlipopolysaccharide complex) obtained by treating Yersinia pseudotuberculosis 3704 O:1b strain cells with a 9 M urea solution followed by differential centrifugation were used as immunogens. The presence of specific antibodies in experimental pseudotuberculosis sera was determined in the test tube agglutination reaction, passive hemagglutination reaction and agarose gel double immunodiffusion test. The proposed schemes of immunization of rabbits with subcellular fractions of the pseudotuberculosis microbe make it possible to prepare hyperimmune sera with activity in the standard tubeagglutination test ≥1:1600, in the indirect hemagglutination test ≥1:3200. There was no crossreactivity of antibodies in the immunodiffusion test with heterologous, closely related antigenically microorganisms (Yersinia enterocolitica 628, Salmonella typhi 21, Shigella flexneri 1964). The most important antigenic material is concentrated in the surface structures of pathogens of bacterial infectious diseases, against which, during immunization of laboratory animals, specific antibodies are produced that can interact with antigenic epitopes of outer membrane proteins and O-specific side chains of lipopolysaccharide (O-antigen) exposed on the surface of the microorganism. The data obtained confirm the effectiveness of the use of surface cell-free antigenic fractions of the pathogen to produce highly active specific pseudotuberculosis sera, suitable for use as a source of specific antibodies in the design of diagnostic immunobiological preparations and test systems for pseudotuberculosis.

Zagoskina Tatiana Yuriyevna, Doctor of Sciences (Medicine), Head of Department, Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: t_y_z_@mail.ru

Markov Evgeniy Yurievich, Doctor of Sciences (Biology), Senior Research Scientist, Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: mark_evgenii@mail.ru

Аndreevskaya Nina Mikhailovna, Candidate of Sciences (Biology), Senior Research Scientist Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: andreevskayа45@mail.ru

Klimov Valeriy Timofeyevich, Candidate of Sciences (Medicine), Senior Research Scientist, Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: 41klimov@mail.ru

Nikolaev Valeriy Borisovich, Candidate of Sciences (Medicine), Senior Research Scientist, Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: eaverschinin@mail.ru

Kryukova Anna Vital’yevna, Junior Research Scientist, Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: anjakrukova@gmail.ru

Doroschenko Anton Aleksandrovich, Jnior Research Scientist, Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: yashik.genry@mail.ru

Dolgova Tatyana Mikhailovna, Research Scientist, Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: adm@chumin.irkutsk.ru

Kolesnikova Olga Borisovna, Candidate of Sciences (Biology), Senior Research Scientist, Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: 89500884440@mail.ru

Gavrilova Olga Viktorovna, Candidate of Sciences (Biology), Research Scientist, Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: adm@chumin.irkutsk.ru

Starikova Olga Andreevna, Candidate of Sciences (Biology), Junior Research Scientist, Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: o.starickova@yandex.ru

Vershinskaya Irina Borisovna, Junior Research Scientist, Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: adm@chumin.irkutsk.ru

Baertueva Inna Ivanovna, Junior Research Scientist, Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: adm@chumin.irkutsk.ru

Popova Julia Olegovna, Research Assistant, Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: adm@chumin.irkutsk.ru

Balakhonov Sergey Vladimirovich, Doctor of Sciences (Medicine), Professor, Director, Irkutsk Anti-Plague Research Institute of Siberia and Far East of Rospotrebnadzor, 78, Trilisser st., Irkutsk, 664047, Russian Federation, e-mail: balakhonov.irk@mail.ru

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Yersinia pseudotuberculosis, pseudotuberculosis microbe, subcellular fractions, immunization, diagnostic sera.

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