Bordetella pertussis filamentous hemagglutinin itself does not trigger anti-inflammatory interleukin-10 production by human dendritic cells.

Filamentous hemagglutinin (FHA) is an important adhesin of the whooping cough agent Bordetella pertussis and is contained in most acellular pertussis vaccines. Recently, FHA was proposed to exert an immunomodulatory activity through induction of tolerogenic IL-10 secretion from dendritic cells. We have re-evaluated the cytokine-inducing activity of FHA, placing specific emphasis on the role of the residual endotoxin contamination of FHA preparations. We show that endotoxin depletion did not affect the capacity of FHA to bind primary human monocyte-derived dendritic cells, while it abrogated the capacity of FHA to elicit TNF-α and IL-10 secretion and strongly reduced its capacity to trigger IL-6 production. The levels of cytokines induced by the different FHA preparations correlated with their residual contents of B. pertussis endotoxin. Moreover, FHA failed to trigger cytokine secretion in the presence of antibodies that block TLR2 and/or TLR4 signaling. The TLR2 signaling capacity appeared to be linked to the presence of endotoxin-associated components in FHA preparations and not to the FHA protein itself. These results show that the endotoxin-depleted FHA protein does not induce cytokine release from human dendritic cells.

The Bordetella pertussis type III secretion system tip complex protein Bsp22 is not a protective antigen and fails to elicit serum antibody responses during infection of humans and mice.

The type III secretion system (T3SS) of pathogenic bordetellae employs a self-associating tip complex protein Bsp22. This protein is immunogenic during infections by Bordetella bronchiseptica and could be used as a protective antigen to immunize mice against B. bronchiseptica challenge. Since low-passage clinical isolates of the human pathogen Bordetella pertussis produce a highly homologous Bsp22 protein (97% homology), we examined its vaccine and diagnostic potential. No Bsp22-specific antibodies were, however, detected in serum samples from 36 patients with clinically and serologically confirmed whooping cough disease (pertussis syndrome). Moreover, although the induction of Bsp22 secretion by the laboratory-adapted 18323 strain in the course of mice lung infection was observed, the B. pertussis 18323-infected mice did not mount any detectable serum antibody response against Bsp22. Furthermore, immunization with recombinant Bsp22 protein yielded induction of high Bsp22-specific serum antibody titers but did not protect mice against an intranasal challenge with B. pertussis 18323. Unlike for B. bronchiseptica, hence, the Bsp22 protein is nonimmunogenic, and/or the serum antibody response to it is suppressed, during B. pertussis infections of humans and mice.

Filamentous hemagglutinin of Bordetella pertussis: a key adhesin with immunomodulatory properties?

The filamentous hemagglutinin of pathogenic Bordetellae is a prototype of a large two-partner-system-secreted and ß-structure-rich bacterial adhesin. It exhibits several binding activities that may facilitate bacterial adherence to airway mucosa and host phagocytes in the initial phases of infection. Despite three decades of research on filamentous hemagglutinin, there remain many questions on its structure-function relationships, integrin interactions and possible immunomodulatory signaling capacity. Here we review the state of knowledge on this important virulence factor and acellular pertussis vaccine component. Specific emphasis is placed on outstanding questions that are yet to be answered.