Defining the human alveolar macrophage response to the Q fever agent, Coxiella burnetii.

摘要

Coxiella burnetii is the intracellular bacterial agent of human Q fever, an acute debilitating illness that can persist and cause life-threatening endocarditis. Effective Q fever treatments are limited, particularly regarding chronic Q fever. Human infection occurs via inhalation of contaminated aerosols, and C. burnetii infects and replicates within alveolar cells. Inside these cells, C. burnetii establishes a unique membrane bound replicative compartment termed the parasitophorous vacuole (PV). The PV is a harsh, degradative lysosome-like environment; however, C. burnetii requires this acidic environment to activate metabolism. To generate the PV, C. burnetii uses a type IV secretion system (T4SS) to secrete effector proteins into the host cytosol and hijack host trafficking. Numerous cell types have been used to study C. burnetii -host interactions; however, the most relevant cell type in vivo has not been studied. In this dissertation, we characterized a human alveolar macrophage (hAM) model of infection and extended these studies to intact human lung tissue. We characterized production of the pro- inflammatory cytokine IL-1beta in the hAM response to C. burnetii. Avirulent C. burnetii triggered formation of a NLRP3 inflammasome containing the adaptor molecule ASC and caspase-1 activation. Additionally, a novel human-specific, non-canonical inflammasome involving processed caspase-4 and caspase-5 was activated during infection. Interestingly, virulent C. burnetii actively inhibited the IL-1beta response. Although a form of cell death termed pyroptosis is typically a consequence of inflammasome activation, C. burnetii-infected cells did not undergo lytic death, suggesting IL-1beta is released from infected cells through an alternative mechanism.;To manipulate macrophages, C. burnetii uses T4SS-secreted proteins to control host processes. Here, we identified six novel C. burnetii plasmid-encoded T4SS effector proteins. Four of these effectors are found only on the QpDG plasmid found in Dugway isolates that do not cause severe disease in animal models, suggesting a role in either decreased virulence or immune evasion. In addition to plasmid-encoded effectors, we identified and characterized a pathotype specific effector, termed ElpA, that localized to the endoplasmic reticulum and disrupted host secretion. Together, our studies contribute greatly to our understanding of the human innate immune response to C. burnetii and effectors used to manipulate eukaryotic cells.