Dual mechanism of protection by live attenuated Bordetella pertussis BPZE1 against Bordetella bronchiseptica in mice.

Bordetella bronchiseptica, a gram-negative bacterium, causes chronic respiratory tract infections in a wide variety of mammalian hosts, including man, and no human vaccine is currently available. Acellular pertussis vaccines protect poorly against B. bronchiseptica, although they contain cross-reactive antigens. We have recently developed Bordetella pertussis BPZE1, a novel, live attenuated pertussis vaccine, currently completing phase I clinical trials in humans, and found that it protects against both B. pertussis and Bordetella parapertussis in mice. Here, we show that a single nasal administration of BPZE1 protects mice against lethal infection with B. bronchiseptica. After challenge, the vaccinated animals displayed markedly reduced lung inflammation and tissue damage, decreased neutrophil infiltration and increased levels of CD4(+)CD25(+)FoxP3(+) regulatory T cells in the lungs compared to non-immunized mice. Depletion of these cells abolished BPZE1-induced protection, indicating that BPZE1 protects against lethal inflammation through the recruitment of regulatory T cells. In addition, the B. bronchiseptica load was significantly decreased in the vaccinated animals. Using passive transfer experiments, protection was found to be essentially cell mediated, and BPZE1-induced Th1 and Th17 T cells recognize whole B. bronchiseptica extracts, although the participation of antibodies in protection cannot be discounted. Thus, a single administration of BPZE1 can confer protection against B. bronchiseptica in mice by a dual mechanism.