Membrane vesicles derived from <i>Bordetella bronchiseptica</i>: active constituent of a new vaccine against infections caused by this pathogen

Abstract

<i>Bordetella bronchiseptica</i>, a Gram-negative bacterium, causes chronic respiratory tract infections in a wide variety of mammalian hosts, including humans (albeit rarely). We recently designed <i>Bordetella pertussis</i> and <i>Bordetella parapertussis</i> 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-phase <i>B. bronchiseptica</i> (OMVBbvir⁺) protected mice against sublethal infections with different <i>B. bronchiseptica</i> strains, two isolated from farm animals and one isolated from a human patient. In all infections, we observed that the <i>B. bronchiseptica</i> 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 against <i>B. bronchiseptica</i> whole-cell lysates, along with an immune serum having bacterial killing activity that both recognized <i>B. bronchiseptica</i> lipopolysaccharides and polypeptides such as GroEL and outer membrane protein C (OMPc) and demonstrated an essential protective capacity against <i>B. bronchiseptica</i> infection, as detected by passive in 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 against <i>B. bronchiseptica</i> infection. OMVs from avirulent-phase <i>B. bronchiseptica</i> and the resulting induced immune sera were also able to protect mice against <i>B. bronchiseptica</i> infection.