Role of Bordetella pertussis virulence factors in pathogenesis of whooping cough.

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1.The function of dermonecrotic toxin(DNT) as a cause of whooping coughTo establish a highly sensitive method detecting DNT, we attempted to generate antibody against polyaminated Rho GTPases, which are yielded by DNT action, and obtained serum from rabbits immunized with polyaminated Rho. The serum, however, showed higher antibody titer against intact Rho than polyaminated one. Then, we attempted to directly detect dermonecrotic toxin by ELISA method, using rabbit anti-DNT antibody. This method made it possible to detect DNT at a low concentration as little as 0.2 ng/ml. Using this method, we determined the concentrations of DNT in culture supernatants of 10 different strains of Bordetella pertussis and B.bronchiseptica. The amounts of DNT in the culture supernatants were found to increase in accordance with proliferation of the organisms and to reach to an average of 5.4 ng/ml and 2.0 ng/ml for B.pertussis and B.bronchiseptica, respectively. These results indicate that DNT is present … More at fully effective concentrations in the extrabacterial milieu and likely affect the tissues which are infected with Bordetella spp. In addition, in the course of searching for target cells in the upper respiratory tissues, we found that tracheal smooth muscle cells from pig are sensitive to DNT. Taken together, we speculate that an effective dose of DNT is liberated from the organisms in the infected trachea, reach to smooth muscle cells through the epithelium, and make them easily constrictive, leading to the paroxysmal cough in whooping cough.2.Pathophysiologic analysis of Bordetella infections in in vitro models.We examined alterations caused by Bordetella infection in various lines of cells derived from the tracheal epithelium and found that rat alveolar epithelial L2 cells showed a characteristic morphological change in response to experimental infection with B.pertussis but not with B.bronchiseptica, implying that L2 cells could be useful as an in vitro cellular model for B.pertussis infection. Less