| Pseudomonas aeruginosa is an important opportunistic pathogen causing infections in immunocompromised individuals. The goal of this study was to determine whether mucosal vaccination with an attenuated Salmonella strain expressing the O-antigen portion of the P. aeruginosa lipopolysaccharide would be more effective than systemic delivery for protection in a mouse acute pneumonia model. We found that IN vaccination provided complete and long-term protection, while oral delivery of this vaccine could only promote increased time to death, and intraperitoneal immunization did not result in increased survival. Interestingly, the level of protection correlated with the level of antibody reactivity observed in the lung. IN transfer of antisera from vaccine-, but not PBS-, or vector-, immunized mice to naive animals, either prophylactically or therapeutically, was protective to challenge doses ten times the 50% lethal dose for PA103. Adsorption of diluted vaccine antisera with PA103, but not an O-antigen deficient PA103 mutant, removed the protective effects of antisera, suggesting that serotype-specific O-antigen antibodies are responsible for protection. Experiments with immune deficient animals, including IgA-, IgG3-, and athymic mice, suggested that protection correlated to the presence of T-dependent P. aeruginosa -specific IgG antibodies. To determine if the in vivo mechanism of protection correlated with opsonophagocytosis-mediated mechanisms, we analyzed the efficacy of bacterial clearance in vaccinated animals deficient for complement (C), complement receptor 3 (CR3), and Fc gamma receptors (FcgammaRs). Depletion of C or the absence of FcgammaRs, but not CR3, resulted in impaired clearance of P. aeruginosa from the lung, suggesting a model of protection that involves IgG, C, and FcgammaRs. Further experiments revealed that IN immunization was capable of mediating protection to P. aeruginosa in corneal and burn infection models. Altogether, our results suggest that protection in the P. aeruginosa acute pneumonia model correlates to IgG-mediated opsonophagocytosis mechanisms in the respiratory tract and that the presence of O-antigen specific antibodies, in combination with innate host factors, is sufficient for protection. This work has major clinical significance and provides a solid foundation for the construction of an active or passive therapeutic vaccine product to prevent or treat P. aeruginosa infections. |
