Abstract
OBJECTIVES: The plague, which is an infectious disease caused by Yersinia pestis, still threatens many populations in several countries. The worldwide increase in human plague cases and the potential use of the bacteria as a biological weapon reinforce the need to study the immunity that is induced by potential vaccine candidates. To determine the immunogenicity of antigenic preparations based on the F1 protein and the total extract from Y. pestis, we assessed the role of these antigens in inducing an immune response. METHODS: The immunogenicity of antigenic preparations based on the Y. pestis (YP) total extract and the Y. pestis fraction 1 capsular antigen protein (F1) was determined in Swiss-Webster mice immunized with 40μg or 20μg for each preparation. Immunophenotyping was performed by flow cytometry. RESULTS: Animals immunized with the YP total extract did not elicit detectable anti-F1 antibodies (Ab) in the hemaglutination/inhibition (HA/HI) test. Animals immunized with 40μg or 20μg of the F1 protein produced anti-F1 Abs, with titres ranging from 1/16 to 1/8132. The average of CD3(+)-CD4(+) and CD3(+)-CD8(+) T cells did not differ significantly between the groups. Neither YP total extract nor F1 protein induced a significant expression of IFN-γ and IL-10 in CD4(+) T lymphocytes. In addition, F1 failed to induce IFN-γ expression in CD8(+) T cells, unlike the YP total extract. CONCLUSION: The results showed that F1 protein is not an immunogenic T cell antigen, although the YP total extract (40μg dose) favoured CD8(+) T cell-mediated cellular immunity.