Pertactin Is Required for Bordetella Species To Resist Neutrophil-Mediated Clearance

Pertactin (PRN) is an autotransporter protein produced by all members of the Bordetella bronchiseptica cluster, which includes B. pertussis, B. parapertussis, and B. bronchiseptica. It is a primary component of acellular pertussis vaccines, and anti-PRN antibody titers correlate with protection. In vitro studies have suggested that PRN functions as an adhesin and that an RGD motif located in the center of the passenger domain is important for this function. Two regions of PRN that contain sequence repeats (region 1 [R1] and R2) show polymorphisms among strains and have been implicated in vaccine-driven evolution. We investigated the role of PRN in pathogenesis using B. bronchiseptica and natural-host animal models. A Δprn mutant did not differ from wild-type B. bronchiseptica in its ability to adhere to epithelial and macrophage-like cells in vitro or to establish respiratory infection in rats but was cleared much faster than wild-type bacteria in a mouse lung inflammation model. Unlike wild-type B. bronchiseptica, the Δprn mutant was unable to cause a lethal infection in SCID-Bg mice, but, like wild-type bacteria, it was lethal for neutropenic mice. These results suggest that PRN plays a critical role in allowing Bordetella to resist neutrophil-mediated clearance. Mutants producing PRN proteins in which the RGD motif was replaced with RGE or in which R1 and R2 were deleted were indistinguishable from wild-type bacteria in all assays, suggesting that these sequences do not contribute to PRN function

Contribution of Bordetella Filamentous Hemagglutinin and Adenylate Cyclase Toxin to Suppression and Evasion of Interleukin-17-Mediated Inflammation

ABSTRACT Bordetella pertussis and Bordetella bronchiseptica establish respiratory infections with notorious efficiency. Our previous studies showed that the fhaB genes of B. pertussis and B. bronchiseptica , which encode filamentous hemagglutinin (FHA), are functionally interchangeable and provided evidence that FHA-deficient B. bronchiseptica induces more inflammation in the lungs of mice than wild-type B. bronchiseptica . We show here that the robust inflammatory response to FHA-deficient B. bronchiseptica is characterized by the early and sustained influx of interleukin-17 (IL-17)-positive neutrophils and macrophages and, at 72 h postinoculation, IL-17-positive CD4 + T cells, suggesting that FHA allows the bacteria to suppress the development of an IL-17-mediated inflammatory response. We also show that the cyaA genes of B. pertussis and B. bronchiseptica , which encode adenylate cyclase toxin (ACT), are functionally interchangeable and that ACT, specifically its catalytic activity, is required for B. bronchiseptica to resist phagocytic clearance but is neither required for nor inhibitory of the induction of inflammation if bacteria are present in numbers sufficient to persist during the first 3 days postinoculation. Incubation of bone marrow-derived macrophages with a Δ cyaA strain caused decreased production of IL-1β and increased production of tumor necrosis factor alpha (TNF-α) and IL-12, while incubation with a Δ cyaA Δ fhaB strain caused increased production of IL-23. These data suggest that FHA and ACT both contribute to suppress the recruitment of neutrophils and the development of an IL-17-mediated immune response. To our knowledge, this is the first demonstration of a microbial pathogen suppressing IL-17-mediated inflammation in vivo as a strategy to evade innate immunity

Contribution of Bordetella Filamentous Hemagglutinin and Adenylate Cyclase Toxin to Suppression and Evasion of Interleukin-17-Mediated Inflammation

Bordetella pertussis and Bordetella bronchiseptica establish respiratory infections with notorious efficiency. Our previous studies showed that the fhaB genes of B. pertussis and B. bronchiseptica, which encode filamentous hemagglutinin (FHA), are functionally interchangeable and provided evidence that FHA-deficient B. bronchiseptica induces more inflammation in the lungs of mice than wild-type B. bronchiseptica. We show here that the robust inflammatory response to FHA-deficient B. bronchiseptica is characterized by the early and sustained influx of interleukin-17 (IL-17)-positive neutrophils and macrophages and, at 72 h postinoculation, IL-17-positive CD4(+) T cells, suggesting that FHA allows the bacteria to suppress the development of an IL-17-mediated inflammatory response. We also show that the cyaA genes of B. pertussis and B. bronchiseptica, which encode adenylate cyclase toxin (ACT), are functionally interchangeable and that ACT, specifically its catalytic activity, is required for B. bronchiseptica to resist phagocytic clearance but is neither required for nor inhibitory of the induction of inflammation if bacteria are present in numbers sufficient to persist during the first 3 days postinoculation. Incubation of bone marrow-derived macrophages with a ΔcyaA strain caused decreased production of IL-1β and increased production of tumor necrosis factor alpha (TNF-α) and IL-12, while incubation with a ΔcyaA ΔfhaB strain caused increased production of IL-23. These data suggest that FHA and ACT both contribute to suppress the recruitment of neutrophils and the development of an IL-17-mediated immune response. To our knowledge, this is the first demonstration of a microbial pathogen suppressing IL-17-mediated inflammation in vivo as a strategy to evade innate immunity

A Novel Sensor Kinase Is Required for Bordetella bronchiseptica To Colonize the Lower Respiratory Tract▿

Bacterial virulence is influenced by the activity of two-component regulator systems (TCSs), which consist of membrane-bound sensor kinases that allow bacteria to sense the external environment and cytoplasmic, DNA-binding response regulator proteins that control appropriate gene expression. Respiratory pathogens of the Bordetella genus require the well-studied TCS BvgAS to control the expression of many genes required for colonization of the mammalian respiratory tract. Here we describe the identification of a novel gene in Bordetella bronchiseptica, plrS, the product of which shares sequence homology to several NtrY-family sensor kinases and is required for B. bronchiseptica to colonize and persist in the lower, but not upper, respiratory tract in rats and mice. The plrS gene is located immediately 5′ to and presumably cotranscribed with a gene encoding a putative response regulator, supporting the idea that PlrS and the product of the downstream gene may compose a TCS. Consistent with this hypothesis, the PlrS-dependent colonization phenotype requires a conserved histidine that serves as the site of autophosphorylation in other sensor kinases, and in strains lacking plrS, the production and/or cellular localization of several immune-recognized proteins is altered in comparison to that in the wild-type strain. Because plrS is required for colonization and persistence only in the lower respiratory tract, a site where innate and adaptive immune mechanisms actively target infectious agents, we hypothesize that its role may be to allow Bordetella to resist the host immune response

Bordetella filamentous hemagglutinin plays a critical role in immunomodulation, suggesting a mechanism for host specificity

Bordetella pertussis, the causative agent of the acute childhood respiratory disease whooping cough, is a human-adapted variant of Bordetella bronchiseptica, which displays a broad host range and typically causes chronic, asymptomatic infections. These pathogens express a similar but not identical surface-exposed and secreted protein called filamentous hemagglutinin (FHA) that has been proposed to function as both a primary adhesin and an immunomodulator. To test the hypothesis that FHA plays an important role in determining host specificity and/or the propensity to cause acute versus chronic disease, we constructed a B. bronchiseptica strain expressing FHA from B. pertussis (FHA(Bp)) and compared it with wild-type B. bronchiseptica in several natural-host infection models. FHA(Bp) was able to substitute for FHA from B. bronchiseptica (FHA(Bb)) with regard to its ability to mediate adherence to several epithelial and macrophage-like cell lines in vitro, but it was unable to substitute for FHA(Bb) in vivo. Specifically, FHA(Bb), but not FHA(Bp), allowed B. bronchiseptica to colonize the lower respiratory tracts of rats, to modulate the inflammatory response in the lungs of immunocompetent mice, resulting in decreased lung damage and increased bacterial persistence, to induce a robust anti-Bordetella antibody response in these immunocompetent mice, and to overcome innate immunity and cause a lethal infection in immunodeficient mice. These results indicate a critical role for FHA in B. bronchiseptica-mediated immunomodulation, and they suggest a role for FHA in host specificity

Bordetella pertussis pathogenesis: current and future challenges

Pertussis, or whooping cough, has recently reemerged as a major public health threat despite high levels of vaccination against the etiological agent, Bordetella pertussis. In this Review, we describe the pathogenesis of this disease, with a focus on recent mechanistic insights into virulence factor function. We also discuss the changing epidemiology of pertussis and the challenges of vaccine development. Despite decades of research, many aspects of B. pertussis physiology and pathogenesis remain poorly understood. We highlight knowledge gaps that must be addressed to develop improved vaccines and therapeutic strategies