Abstract
Bordetella pertussis filamentous hemagglutinin (FHA) is a surface-associated and secreted protein that serves as a crucial adherence factor, and displays immunomodulatory activity in human peripheral blood mononuclear cells (PBMCs). In order to appreciate more fully the role of secreted FHA in pathogenesis, we analyzed FHA-induced changes in genome-wide transcript abundance in human PBMCs. Among the 683 known unique genes with greater than 3-fold change in transcript abundance following FHA treatment, 125 (18.3%) were identified as interferon (IFN)-regulated. Among the latter group were genes encoding several members of the IFN type I response, as well as 3 key components of the ISGylation pathway. Using real-time RT-PCR, we confirmed FHA-associated increases in transcript abundance for the genes encoding ubiquitin-like protein, ISG15, and its specific protease USP18. Western-blot analysis demonstrated the presence of both, free ISG15 and several ISGylated conjugates in FHA-stimulated PBMC lysates, but not in unstimulated cells. Intracellular FACS analysis provided evidence that monocytes and a natural killer-enriched cell population were the primary producers of ISG15 in PBMCs after FHA stimulation. Our data reveal previously-unrecognized effects of B. pertussis FHA on host IFN and ISGylation responses, and suggest previously-unsuspected mechanisms by which FHA may alter the outcome of the host-pathogen interaction.
Highlights
Bordetella pertussis is a human restricted pathogen and the causative agent of the acute respiratory disease, pertussis or whooping cough
This analysis was undertaken with four different filamentous hemagglutinin (FHA) preparations, purified from four different B. pertussis strains, in order to recognize conserved activities associated with this protein and avoid strain-specific biases
Prior to FHA preparation, all genes associated with pertussis toxin (PT) expression were deleted from the strains, so that PT copurification would be eliminated
Summary
Bordetella pertussis is a human restricted pathogen and the causative agent of the acute respiratory disease, pertussis or whooping cough. Despite the use of an effective vaccine since the 1940s, pertussis remains a major cause of childhood mortality worldwide and has re-emerged in some highly vaccinated populations [1,2]. B. pertussis is primarily an extracellular organism, but it may persist within leukocytes and epithelial cells [3,4]. The infection process is mediated by several virulence factors [5], most of which are tightly regulated by a twocomponent signal transduction system, BvgAS [6]. A key BvgAS-regulated virulence factor is filamentous hemagglutinin (FHA), which plays a crucial role in mediating adherence to eukaryotic cells [7].
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