Avaliação da resposta imune humoral e celular em animais imunizados com antígenos de yersinia pestis

Abstract

The plague still poses a real threat in several continents and it has recently been defined by the World Health Organization as a re-emerging disease. The occurrence of human plague outbreaks in several countries and the possibility of illegitimate use of Yersinia pestis as a biological weapon reinforce the need to study the immunity induced by potential vaccine candidates having in mind the future use of these antigens in immunoprophylaxis of the plague. With this purpose, the immunogenicity of the antigenic preparations based on F1 protein and on the total extract from Y. pestis was investigated in order to verify the role of these antigens in inducing the production of antibodies, as well as in determining the phenotype of splenic T-lymphocytes and also the stimulation of the production of IFN- and IL-10 through the subpopulations of T CD4 and CD8 cells. In order to achieve this objective, female Swiss Webster mice were intramuscularly immunized with 40 g or 20 g of the purified F1 and total proteinextract from Y. pestis, given in two doses with a 21 day interval and one booster dose of 4 g or 2 g that was administered intravenously on the 42nd day after the primary immunization. On the 45th day, euthanasia of the animals was performed as well as the collection of blood and removal of the spleen. The titers of anti-F1 antibodiesinduced by different immunization schedules were evaluated in serum through the indirect hemagglutination test. Phenotypic analysis of subpopulations of splenic T cells and the detection of intracellular IFN- and IL-10 were performed by flow cytometry using monoclonal antibodies. Animals immunized with total extract from Y. pestis atdoses of 40g and 20 g didn´t show anti-F1 antibody in the test, in the same way as the control animals. On the other hand, animals immunized with the purified F1 antigen, both at a dose of 40 g as well as at a 20 g dose showed positive results with titers ranging from 1/16 to 1/8132. With respect to the phenotypic analysis, it was observed that the average of T CD3+-CD4+ cells and T CD3+-CD8+ do not significantly differ between the studied groups. As for the detection of cytokines, it was found that the total extract and the F1 antigen of Y. pestis do not induce significant expression of IFN- and IL-10 in CD4 T-lymphocytes. The F1 protein also does not induce IFN- expression on CD8 + T cells, unlike the total extract from Y. pestis. Overall, the results showed that the F1 protein, although an important inducer of humoral immune response, is not imunogenic T cell antigen even if the total extract from Y. pestis at dose of 40 g seems to favor cellular immunity mediated by T lymphocytes CD8.