The protective immunity induced by infection withWhooping cough caused by Bordetella pertussis is a serious disease in children. Commercial pertussis vaccines, which consist of killed B. pertussis cells or derived antigens, are very effective and have reduced the incidence of whooping cough very considerably. However, in addition to B. pertussis, Bordetella parapertussis also causes symptoms typical of whooping cough (22). The illness caused by B. parapertussis is sometimes as severe as that caused by B. pertussis (10). Outbreaks of infection by B. parapertussis have been reported in several countries (8,11,18). B. parapertussis is closely related to B. pertussis in terms of virulence and attachment factors, such as filamentous hemagglutinin (FHA), adenylate cyclase toxin, heat-labile toxin, and pertactin (PRN) (29). However, several reports suggest that pertussis vaccine has no or limited ability to protect against B. parapertussis (9, 13, 15, 27, 32). Stehr et al. reported that the efficacy of the acellular pertussis component diphtheria-tetanus-pertussis (DTP) vaccine and the whole-cell pertussis component DTP vaccine in children was 31% and Ϫ6%, respectively (27). Khelef et al. suggested that immunization with antigens derived from B. pertussis induce no protection against B. parapertussis in mice (13). These reports suggested that reciprocal protective immunity between the two species might not be induced. However, in these studies, subcutaneous or peritoneal injections were commonly used as methods of immunization. Mills et al. suggested that there might be a difference, in terms of the profiles of the protective immune response against B. pertussis, between the response after immunization by injection with vaccines and the response during convalescence after infection with B. pertussis (20). We postulated that immunization by natural infection of the two species might clarify the relationship between protection against B. pertussis and protection against B. parapertussis. To test our hypothesis, we infected mice by exposing them to an aerosol of B. pertussis or B. parapertussis. After mice had recovered, convalescent mice were investigated for protective responses against the two species of Bordetella, for levels of antigen-specific antibodies, and for splenocyte proliferation and cytokine secretion responses in vitro after stimulation by antigens.
MATERIALS AND METHODSMice. Specific-pathogen-free female dd-Y mice were obtained from Japan SLC (Hamamatsu, Japan). All mice were 3.5 weeks old at the start of experiments.Bacterial strains and culture conditions. The phase I strain of B. pertussis strain 18-323 and B. parapertussis strain 23054 were used in this study. Cells were grown on Bordet-Gengou (BG) agar supplemented with 20% (vol/vol) defibrinated horse blood at 37°C.Bacterial antigens. Killed whole-cell B. pertussis or B. parapertussis antigens were prepared as described below. B. pertussis or B. parapertussis was cultured on BG plates for 30 h at 37°C. Cells were harvested in phosphate-buffered sali...