The F1 and V subunit vaccine protects against plague in the absence of IL-4 driven immune responses

A subunit vaccine for plague utilising the F1 and V antigens of Yersinia pestis has been shown to be highly protective in a mouse model. Protection against aerosol and parenteral infection has been found to correlate with the production of large amounts of IgG1. In this study the effect of a genetic mutation in the immune system on protection was studied. IL-4T mice which are unable to synthesize the Th2 cytokine IL-4, and so should have reduced IgG1 responses, were utilised to determine whether an immune system biased towards the Th1 axis could mount an effective response to the vaccine. Antibody isotype profiles generated in IL-4T mice differed from the intact parent C57 BL/6 strain, although total IgG levels were similar between the two strains. Immune cell and serum transfers from IL-4T and C57 BL/6 mice to naive mu MT strain mice were performed and recipient mice challenged with virulent Y. pestis. mu MT were fully protected by passive transfer of antibody from either donor strain immunized with F1+V or with F1 only. However, protection was only partial in mu MT receiving IL-4T serum with specificity for the V antigen only. Actively immunized IL-4T mice mounted a vigorous response to the vaccine and were resistant to challenge. These results suggest that even in an altered immune system the F1 and V subunit vaccine is capable of eliciting a protective immune response.