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Proinflammatory and proapoptotic activities associated with Bordetella pertussis filamentous hemagglutinin
T Abramson1, H Kedem, D A Relman
1Department of Medicine, Stanford University School of Medicine, Stanford, California 94305, USA.
Abstract:
Filamentous hemagglutinin (FHA) is a dominant cell surface-associated Bordetella pertussis adhesin. Recognition that this protein is secreted in significant amounts and that bacterial adhesins may have other activities, prompted an assessment of FHA effects on human macrophages. Incubation of human macrophage-like U937 cells with preparations of FHA resulted in dose-dependent cytotoxicity, with death of 95% of treated cells after 24 h. Based on the use of four independent methods, death of these cells could be largely attributed to apoptosis. FHA-associated apoptosis was also observed in THP-1 macrophage-like cells, fresh human peripheral blood monocyte-derived macrophages (MDM), and BEAS-2B human bronchial epithelial cells. Infection of MDM with wild-type B. pertussis resulted in apoptosis within 6 h, while infection with an FHA-deficient derivative strain was only 50% as effective. FHA-associated cytotoxicity was preceded by host cell secretion of tumor necrosis factor alpha (TNF-alpha), a potential proapoptotic factor. However, pretreatment of cells with a neutralizing anti-TNF-alpha monoclonal antibody inhibited only 16% of the FHA-associated apoptosis. On the other hand, a blocking monoclonal antibody directed against TNF-alpha receptor 1 inhibited FHA-associated apoptosis by 47.7% (P = 0.0001), suggesting that this receptor may play a role in the death pathway activated by FHA. Our in vitro data indicate that secreted and cell-associated FHA elicits proinflammatory and proapoptotic responses in human monocyte-like cells, MDM, and bronchial epithelial cells and suggest a previously unrecognized role for this prominent virulence factor in the B. pertussis-host interaction.
Insights
Filamentous hemagglutinin (FHA) from Bordetella pertussis induces apoptosis in human macrophages and bronchial cells. This adhesin plays a significant role in the bacterium-host interaction, potentially via TNF-alpha receptor 1 signaling.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Filamentous hemagglutinin (FHA) is a key adhesin of Bordetella pertussis.
- FHA is known to be secreted and cell-associated, suggesting diverse roles.
- The potential cytotoxic effects of FHA on host immune cells were unexplored.
Purpose of the Study:
- To investigate the effects of FHA on human macrophages and other relevant cell types.
- To determine if FHA induces apoptosis and elucidate the underlying mechanisms.
- To explore the role of FHA in the interaction between B. pertussis and host cells.
Main Methods:
- Incubation of human macrophage-like cell lines (U937, THP-1) and primary cells (MDM) with FHA preparations.
- Assessment of cell viability and apoptosis using multiple independent methods.
- Infection of MDM with wild-type and FHA-deficient B. pertussis strains.
- Evaluation of the role of tumor necrosis factor alpha (TNF-alpha) and its receptor 1 (TNFR1) using neutralizing antibodies.
Main Results:
- FHA induced dose-dependent apoptosis in U937 cells (95% cell death), THP-1 cells, primary MDM, and BEAS-2B bronchial epithelial cells.
- Infection with wild-type B. pertussis caused faster apoptosis in MDM compared to FHA-deficient strains.
- FHA-induced apoptosis was partially inhibited by blocking TNFR1, but not by anti-TNF-alpha antibodies, indicating TNFR1 involvement.
Conclusions:
- Secreted and cell-associated FHA triggers pro-inflammatory and pro-apoptotic responses in human macrophages and bronchial epithelial cells.
- FHA represents a significant virulence factor contributing to B. pertussis pathogenesis.
- The findings suggest a novel role for FHA in modulating host cell death pathways, potentially via TNFR1.