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Bordetella Pertussis Antigens
Bordetella pertussis is a Gram-negative bacterium and the causative agent of pertussis, commonly known as whooping cough. The pathogen’s ability to colonize the host respiratory tract and elicit severe disease symptoms is attributed to the coordinated expression of several potent virulence factors, which also serve as primary antigens for diagnostic assay development and the components of modern acellular pertussis vaccines (aPV). The most critical antigens of B. pertussis are sophisticated proteins that manipulate host immune and cellular processes:
- Pertussis Toxin (PTX): This is one of the most significant toxins and a major protective antigen in vaccines. PTX is an AB5-type holotoxin composed of an enzymatically active A subunit (S1) and a pentameric binding B moiety. Its mechanism of action involves ADP-ribosylation of the α subunits of the Gi/Go family of heterotrimeric G proteins. This modification effectively inactivates Gi protein signaling pathways, leading to dysregulation of cellular cyclic AMP (cAMP) levels, which results in profound immunological effects, including lymphocytosis and suppression of innate immune responses. PTX is also known as Islet Activating Protein for its distinct pharmacological activity.
- Filamentous Hemagglutinin (FHA): FHA is a large, multifunctional adhesin protein that is both surface-associated and secreted by the bacterium. Its primary biological function is to mediate the initial adherence of B. pertussis to the ciliated epithelial cells lining the host’s respiratory tract, a crucial step for bacterial colonization. FHA is included in acellular vaccine formulations due to its high immunogenicity.
- Adenylate Cyclase Toxin (ACT) / CyaA: This is a potent RTX (Repeat-in-Toxin) cytotoxin that targets phagocytic cells (such as macrophages and neutrophils). ACT binds to the host cell receptor CR3 (CD11b/CD18). Upon entry into the cell cytosol, the toxin’s adenylate cyclase domain is activated by host calmodulin, leading to the massive, unregulated production of intracellular cAMP. This abrupt surge in cAMP levels effectively inhibits the phagocyte’s antimicrobial functions, enabling the bacteria to evade the host’s early innate immune response.
These bacterial toxins and adhesins are widely purified and used as recombinant proteins or native preparations for medical research, the standardization of diagnostic kits, and the quality control of pertussis vaccine production.
