Membrane Vesicles Derived from Bordetella bronchiseptica: Active Constituent of a New Vaccine against Infections Caused by This Pathogen

Bordetella bronchiseptica , a Gram-negative bacterium, causes chronic respiratory tract infections in a wide variety of mammalian hosts, including humans (albeit rarely). We recently designedBordetella pertussis andBordetella parapertussis experimental vaccines based on outer membrane vesicles (OMVs) derived from each pathogen, and we obtained protection against the respective infections in mice. Here, we demonstrated that OMVs derived from virulent-phaseB. bronchiseptica (OMVBbvir+ ) protected mice against sublethal infections with differentB. bronchiseptica strains, two isolated from farm animals and one isolated from a human patient. In all infections, we observed that theB. bronchiseptica loads were significantly reduced in the lungs of vaccinated animals; the lung-recovered CFU were decreased by ≥4 log units, compared with those detected in the lungs of nonimmunized animals (P < 0.001). In the OMVBbvir+ -immunized mice, we detected IgG antibody titers againstB. bronchiseptica whole-cell lysates, along with an immune serum having bacterial killing activity that both recognizedB. bronchiseptica lipopolysaccharides and polypeptides such as GroEL and outer membrane protein C (OMPc) and demonstrated an essential protective capacity againstB. bronchiseptica infection, as detected by passivein vivo transfer experiments. Stimulation of cultured splenocytes from immunized mice with OMVBbvir+ resulted in interleukin 5 (IL-5), gamma interferon (IFN-γ), and IL-17 production, indicating that the vesicles induced mixed Th2, Th1, and Th17 T-cell immune responses. We detected, by adoptive transfer assays, that spleen cells from OMVBbvir+ -immunized mice also contributed to the observed protection againstB. bronchiseptica infection. OMVs from avirulent-phaseB. bronchiseptica and the resulting induced immune sera were also able to protect mice againstB. bronchiseptica infection.IMPORTANCE Bordetella bronchiseptica , a Gram-negative bacterium, causes chronic respiratory tract infections in a wide variety of mammalian hosts, including humans (albeit rarely). Several vaccines aimed at preventingB. bronchiseptica infection have been developed and used, but a safe effective vaccine is still needed. The significance and relevance of our research lie in the characterization of the OMVs derived fromB. bronchiseptica as the source of a new experimental vaccine. We demonstrated here that our formulation based on OMVs derived from virulent-phaseB. bronchiseptica (OMVBbvir+ ) was effective against infections caused byB. bronchiseptica isolates obtained from different hosts (farm animals and a human patient).In vitro andin vivo characterization of humoral and cellular immune responses induced by the OMVBbvir+ vaccine enabled a better understanding of the mechanism of protection necessary to controlB. bronchiseptica infection. Here we also demonstrated that OMVs derived fromB. bronchiseptica in the avirulent phase and the corresponding induced humoral immune response were able to protect mice fromB. bronchiseptica infection. This realization provides the basis for the development of novel vaccines not only against the acute stages of the disease but also against stages of the disease or the infectious cycle in which avirulence factors could play a role.