Methods: We immunized C57Bl/6 mice with 1 µg of OMPs with 1 µg dmLT. Control mice received OMPs or saline. Antibody and T cell responses were assessed by ELISA and flow cytometry, respectively. We then evaluated the protective efficacy of the vaccine in a lethal acute pneumonia model. Immunized mice were challenged with 7x106 CFU of P. aeruginosa via oropharyngeal aspiration into the lungs. Finally, we examined if memory CD4+ T cells were essential for protection by depleting immunized mice of vaccine-induced memory CD4+ T cells.
Results: Mice immunized with OMPs and dmLT had a significantly greater concentration of anti-pseudomonal IgG in the serum and lungs and a significantly greater proportion of CD4+ T cells in the lung producing IFN-γ or IL-17A than mice immunized with OMPs alone or saline. ID immunization provided significant protection against P. aeruginosa pneumonia, with 78% of immunized mice surviving compared to 100% mortality in saline immunized controls. Memory CD4+ T cell-depleted mice displayed reduced survival (40%) compared to non-depleted mice (80%), confirming that memory CD4 T+ cells contribute to OMP-dmLT vaccine-mediated protection.
Conclusion: These results demonstrate that ID vaccination against P. aeruginosa protects against acute lethal P. aeruginosa pneumonia by stimulating antigen-specific IgG and Th1- and Th17-type CD4+ memory T cells in the pulmonary milieu. ID immunization with dmLT may reduce the global morbidity and mortality caused by multidrug resistant respiratory pathogens.