STUDYING DEVELOPMENT OF POST-VACCINAL CELLULAR IMMUNITY AGAINST BRUCELLOSIS BY MEANS OF LYMPHOCYTE IN VITRO TESTS USING AN EXPERIMENTAL ANTIGENIC COMPLEX

Regulatory framework and methodological approaches to evaluation of immunological effects of vaccination against brucellosis are not established, and the degree of immunological post-vaccinal rearrangement is not yet developed. Due to leading role of cellular immunity in formation of immune protection against brucellosis, evaluation the cellular response in response to antigenic stimulation may be considered the most informative and objective approach to analysis of immune changes in the body during vaccination. In order to develop the most diagnostically informative methods for design of antigen-stimulation cell tests in vitro, a careful selection of a stimulating agent (antigen) is required, which should have a sufficient activating potential, thus providing specificity of reaction under in vitro conditions. The aim of the present study is to study the in vitro specific activity of a protein-polysaccharide antigenic complex from the Brucella abortus 19 BA strain (BrAg), and an opportunity of its application in order to assess the formation of post-vaccinal cellular immunity against brucellosis.

The study was performed with white laboratory mice (n = 50) immunized with the Brucella abortus 19 BA strain. The control group (n = 50) consisted of laboratory mice that received a sterile saline solution in a volume of 0.5 ml. Blood samples were taken from immunized and control animals before vaccination, and 7, 14, 21, and 30 days after immunization. By means of flow cytometry, the activation molecules CD25, CD69, MHC II and CD95, expressed on T lymphocytes (CD3⁺CD69⁺, CD3⁺CD25⁺, CD3⁺CD95⁺, CD3⁺MHC⁺) were determined. To observe the development of immunity, the intensity of expression of T lymphocyte activation markers was calculated using the stimulation quotient. BrAg was used for specific in vitro stimulation of T lymphocytes. The liquid brucellosis allergen (brucellin) was used as an antigen for comparison, when studying opportunity of BrAg usage for assessing the postvaccinal immunity development.

The following results were obtained: BrAg has pronounced specific activity, it did not cause non-specific in vitro reactions (activation) of T lymphocytes, thus enabling its application as a test antigen when evaluating development of adaptive vaccine immunity against brucella.

Experimental testing of brucellosis antigen for carrying out the in vitro antigen-stimulated cellular reactions, aiming for evaluation of post-vaccinal immunity development against brucellosis, showed that the usage of BrAg promotes increase in diagnostic sensitivity of cellular reactions under in vitro experimental conditions. The applied experimental antigen is a quite promising tool for development of laboratory algorithms for brucellosis diagnostics, and assessment of actual vaccination efficiency in cohorts previously vaccinated against brucellosis.

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