Human Q fever is caused by the category B select agent and potential biological warfare pathogen, Coxiella burnetii. Acute Q fever presents with flu-like symptoms whereas chronic Q fever presents as severe endocarditis. After human inhalation, alveolar macrophages engulf the pathogen and C. burnetii travels through the phagolysosomal maturation pathway, forming a parasitophorous vacuole (PV) for bacterial replication using a type IV secretion system (T4SS). Though two disease-relevant platforms, primary human alveolar macrophages (hAMs) and human precision cut lung slices (hPCLS), were characterized, further understanding was needed to model host-pathogen interactions in the pulmonary environment. In Chapter III, we show alveolar macrophages are the preferred replication niche for C. burnetii, while PV expansion, bacterial replication, and the autophagy proteins microtubule-associated protein 1A/1B (LC3) and sequestosome-1 (SQSTM1/p62) localization differs between cell types. PV expansion and C. burnetii replication is suppressed in fibroblasts, but not hAMs, with the addition of surfactant protein D. Lastly, we demonstrate significant IL-8 production and a M1 to M2 phenotypic switch during C. burnetii infection in hAMs, suggesting dynamic macrophage responses to infection.

The Nrf2-Keap1 pathway is activated when cargo receptor p62 is phosphorylated and binds to kelch-like ECH-associated protein 1 (Keap1), activating nuclear erythroid 2-related factor 2 (Nrf2) to allow nuclear translocation and antioxidant gene transcription. In Chapter IV we show p62 localizes near the PV in hAMs in a T4SS-dependent manner via an unknown domain. siRNA results indicate p62 is not absolutely required for C. burnetii infection, suggesting a signaling role for the protein. Therefore, we focused on the Nrf2-Keap1 pathway and show C. burnetii infection activates Nrf2, causing nuclear translocation. In Chapter V, we show Nrf2 is activated in a T4SS-dependent manner. We optimized two chemical inhibitors of Nrf2, brusatol and K67, though K67 is the only inhibitor that impacts PV expansion and C. burnetii replication. Using K67, we investigate the effect of Nrf2 on oxidative stress, apoptosis, autophagy, differential gene expression, and altered cellular signaling during infection. Collectively, these studies enhance the understanding of C. burnetii infection of the alveolar region and the novel contribution of Nrf2-Keap1 signaling to this unique host-pathogen dynamic.