Development of an Ex Vivo Tissue Platform To Study the Human Lung Response to Coxiella burnetii

Abstract

cCoxiella burnetii is 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. burnetii generates a replication niche termed the parasitophorous vacuole (PV) by directing fusion with autophagosomes and lysosomes. C. burnetii requires this lysosomal environment for replication and uses a Dot/Icm type IV secretion system to generate the large PV. However, we do not understand how C. burnetii evades the intracellular immune surveillance that triggers an inflammatory response. We recently characterized human alveolar macrophage (hAM) infection in vitro and found that avirulent C. burnetii triggers sustained interleukin-1␤ (IL-1␤) production. Here, we evaluated infection of ex vivo human lung tissue, defining a valuable approach for characterizing C. burnetii interactions with a human host. Within whole lung tissue, C. burnetii preferentially replicated in hAMs. Additionally, IL-1␤ 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 following C. 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 to C. burnetii. Coxiella burnetii is a Gram-negative, obligate intracellular pathogen that causes Q fever in humans (1). Acute Q fever presents with flu-like symptoms; however, infection can persist and cause life-threatening endocarditis. C. burnetii is a category B select agent due to an aerosol mode of transmission, low infectious dose, and environmental stability (2). The pathogen has a unique intracellular lifestyle that requires replication within an acidic lysosome-like parasitophorous vacuole (PV) in macrophages (3). Using a Dot/Icm type IV secretion system (T4SS) to secrete bacterial proteins into the host cytoplasm (4, 5), C. burnetii hijacks the host cell to control signaling cascades and heterotypic fusion with endosomes, autophagosomes, and lysosomes to establish the PV (6). Although C. burnetii intracellular trafficking has been well characterized, understanding of the initial interactions between the pathogen and its human host is lacking. Although small animal models provide beneficial information about the host response to C. burnetii, they do not accurately mimic the human lung response to infection, presenting the need for improved systems. For example, mouse alveolar macrophages degrade C. burnetii (7), while the pathogen replicates e...

Coxiella burnetii Avirulent Nine Mile Phase II Induces Caspase-1-Dependent Pyroptosis in Murine Peritoneal B1a B Cells

“…In contrast to this observation, Cunha et al reported that NMII can inhibit caspase-1 activation in murine bone marrow-derived macrophages and the caspase-11-mediated noncanonical activation of the NLRP3 inflammasome induced by L. pneumophila (59). In addition, Graham et al found that although NMII induces IL-1␤ production in human alveolar macrophages and IL-1␤ production correlated with caspase-dependent inflammasome activation, no lytic cell death was observed (60). Thus, these studies suggest that avirulent NMII may process the ability to activate or inhibit the inflammasome on the basis of the infected cell types and the stage of infection.…”

Coxiella burnetii Employs the Dot/Icm Type IV Secretion System to Modulate Host NF-κB/RelA Activation

“…M2 cells typically have an IL-12 low , IL-23 low , IL-10 high phenotype with a variable capacity to produce inflammatory chemotactic cytokines (Benoit et al, 2008). Other prominent NF-κB-dependent cytokines induced by C. burnetii include TNF-α, IL-1β, IFN-γ, RANTES, MCP-1, SCYA3, SCYA4, and IL-8 (Raoult and Marrie, 1995; Ren et al, 2003; Meghari et al, 2005, 2006, 2008; Soraya Meghari et al, 2006; Benoit et al, 2008; Mahapatra et al, 2010; Amara et al, 2012; Schoffelen et al, 2014; Graham et al, 2016). In addition, C. burnetii regulates host apoptosis at the transcriptional level by altering expression of NF-κB-mediated cell survival-related genes ( cIAP2 and a1/bfl-1 ) (Voth et al, 2007).…”

Right on Q: Genetics begin to Unravel Coxiella Burnetii host cell Interactions

“…The primary target of Coxiella during natural infection is alveolar macrophages [32,[41][42][43]. The organism can subsequently disseminate to colonize and replicate in resident macrophages of different tissues and organs [44].…”