Evidence for an intracellular niche for Bordetella pertussis in broncho-alveolar lavage cells of mice

Bordetella pertussis can attach, invade and survive intracellularly in human macrophages in vitro. To study the significance of this bacterial feature in vivo, we analyzed the presence of viable bacteria in broncho-alveolar lavage (BAL) cells of mice infected with B. pertussis. We found B. pertussis to be present in a viable state in BAL fluid cells until at least 19 days after infection, suggesting B. pertussis to be able to survive in those cells. This intracellular niche may play an important role in the pathogenesis of pertussis. Pertussis toxin and the RGD sequence of the virulence factor filamentous hemagglutinin (FHA) both play a role in the attachment of B. pertussis to human and mouse macrophages in vitro and we hypothesized these virulence factors to be required for invasion and subsequent intracellular survival of B. pertussis in macrophages in vivo. A B. pertussis double mutant, in which the FHA RGD motif was changed to RAD and the ptx genes were deleted, was also found in a viable state in BAL fluid cells, albeit at lower levels than the wild-type strain. In our model, uptake of B. pertussis by alveolar phagocytes in vivo is thus, at least in part, determined by the bacterial virulence factors FHA and pertussis toxin.