Primary Role for Toll-Like Receptor-Driven Tumor Necrosis Factor Rather than Cytosolic Immune Detection in Restricting Coxiella burnetii Phase II Replication within Mouse Macrophages

• DOI: 10.1128/iai.01536-15
• Publication Date: 2016-01-20T03:58:49Z
• Authors: William P. Bradley; Mark A. Boyer; Hieu T. Nguyen; L. Dillon Birdwell; Janet Yu; Juliana M. Ribeiro; Susan R. Weiss; Dario S. Zamboni; Craig R. Roy; Sunny Shin
• Keywords: Mice, Knockout; 0301 basic medicine; Tumor Necrosis Factor-alpha; Macrophages; p38 Mitogen-Activated Protein Kinases; Toll-Like Receptor 2; Mice, Inbred C57BL; Toll-Like Receptor 4; Adaptor Proteins, Vesicular Transport; Mice; 03 medical and health sciences; Cytosol; Gene Expression Regulation; Coxiella burnetii; Myeloid Differentiation Factor 88; Animals; Cells, Cultured

ABSTRACTCoxiella burnetiireplicates within permissive host cells by employing a Dot/Icm type IV secretion system (T4SS) to translocate effector proteins that direct the formation of a parasitophorous vacuole. C57BL/6 mouse macrophages restrict the intracellular replication of theC. burnetiiNine Mile phase II (NMII) strain. However, eliminating Toll-like receptor 2 (TLR2) permits bacterial replication, indicating that the restriction of bacterial replication is immune mediated. Here, we examined whether additional innate immune pathways are employed by C57BL/6 macrophages to sense and restrict NMII replication. In addition to the known role of TLR2 in detecting and restricting NMII infection, we found that TLR4 also contributes to cytokine responses but is not required to restrict bacterial replication. Furthermore, the TLR signaling adaptors MyD88 and Trif are required for cytokine responses and restricting bacterial replication. TheC. burnetiiNMII T4SS translocates bacterial products into C57BL/6 macrophages. However, there was little evidence of cytosolic immune sensing of NMII, as there was a lack of inflammasome activation, T4SS-dependent cytokine responses, and robust type I interferon (IFN) production, and these pathways were not required to restrict bacterial replication. Instead, endogenous tumor necrosis factor (TNF) produced upon TLR sensing ofC. burnetiiNMII was required to control bacterial replication. Therefore, our findings indicate a primary role for TNF produced upon immune detection ofC. burnetiiNMII by TLRs, rather than cytosolic PRRs, in enabling C57BL/6 macrophages to restrict bacterial replication.