Coxiella burnetiiis an intracellular bacterial pathogen that causes human Q fever, an acute debilitating flu-like illness that can also present as chronic endocarditis. Disease typically occurs following inhalation of contaminated aerosols, resulting in an initial pulmonary infection. In human cells,C. burnetiigenerates a replication niche termed the parasitophorous vacuole (PV) by directing fusion with autophagosomes and lysosomes.C. burnetiirequires this lysosomal environment for replication and uses a Dot/Icm type IV secretion system to generate the large PV. However, we do not understand howC. burnetiievades the intracellular immune surveillance that triggers an inflammatory response. We recently characterized human alveolar macrophage (hAM) infectionin vitroand found that avirulentC. burnetiitriggers sustained interleukin-1β (IL-1β) production. Here, we evaluated infection ofex vivohuman lung tissue, defining a valuable approach for characterizingC. burnetiiinteractions with a human host. Within whole lung tissue,C. burnetiipreferentially replicated in hAMs. Additionally, IL-1β production correlated with formation of an apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC)-dependent inflammasome in response to infection. We also assessed potential activation of a human-specific noncanonical inflammasome and found that caspase-4 and caspase-5 are processed during infection. Interestingly, although inflammasome activation is closely linked to pyroptosis, lytic cell death did not occur followingC. burnetii-triggered inflammasome activation, indicating an atypical response after intracellular detection. Together, these studies provide a novel platform for studying the human innate immune response toC. burnetii.
Optical Screening of Novel Bacteria-specific Probes on Ex Vivo Human Lung Tissue by Confocal Laser Endomicroscopy