Coxiella burnetii Blocks Intracellular Interleukin-17 Signaling in Macrophages

Abstract

is an obligate intracellular bacterium and the etiological agent of Q fever. Successful host cell infection requires the type IVB secretion system (T4BSS), which translocates bacterial effector proteins across the vacuole membrane into the host cytoplasm, where they manipulate a variety of cell processes. To identify host cell targets of T4BSS effector proteins, we determined the transcriptome of murine alveolar macrophages infected with a T4BSS effector mutant. We identified a set of inflammatory genes that are significantly upregulated in T4BSS mutant-infected cells compared to mock-infected cells or cells infected with wild-type (WT) bacteria, suggesting that T4BSS effector proteins downregulate the expression of these genes. In addition, the interleukin-17 (IL-17) signaling pathway was identified as one of the top pathways affected by the bacteria. While previous studies demonstrated that IL-17 plays a protective role against several pathogens, the role of IL-17 during infection is unknown. We found that IL-17 kills intracellular in a dose-dependent manner, with the T4BSS mutant exhibiting significantly more sensitivity to IL-17 than WT bacteria. In addition, quantitative PCR confirmed the increased expression of IL-17 downstream signaling genes in T4BSS mutant-infected cells compared to WT- or mock-infected cells, including the proinflammatory cytokine genes ,, and , the chemokine genes and , and the antimicrobial protein gene We further confirmed that the T4BSS downregulates macrophage CXCL2/macrophage inflammatory protein 2 and CCL5/RANTES protein levels following IL-17 stimulation. Together, these data suggest that downregulates IL-17 signaling in a T4BSS-dependent manner in order to escape the macrophage immune response.

Functional inhibition of acid sphingomyelinase disrupts infection by intracellular bacterial pathogens

“…To determine whether desipramine’s action on the pathogen was bacteriostatic or bactericidal, C. burnetii was allowed to infect HeLa cells and MH-S murine alveolar macrophages treated with desipramine or DMSO. Cells were harvested every 48 h to determine the number of viable bacteria using a colony-forming unit (CFU) assay ( Clemente et al, 2018 ). In control HeLa cells, a fourfold increase in bacterial load was observed, whereas the number of viable C. burnetii decreased over time in desipramine-treated cells ( Fig 6C ).…”

“…For C. burnetii infections, MH-S or HeLa cells were treated for 1 h with desipramine or DMSO and infected as previously described with mCherry-expressing small cell variants for 1 h ( Mulye et al, 2017 ; Clemente et al, 2018 ). Infection conditions were optimized for both cell type and vessel for less than one internalized bacterium per cell.…”

“…Viable C. burnetii were assayed using a CFU assay as previously described ( Clemente et al, 2018 ). Briefly, bacteria were recovered from infected cells using water lysis as described ( Mulye et al, 2017 ).…”

A tale of two fish: Comparative transcriptomics of resistant and susceptible steelhead following exposure to Ceratonova shasta highlights differences in parasite recognition

“…However, it has been shown that certain pathogens actively interfere with the host IL-17 pathway. The mucosal pathogen Candida albicans inhibits IL-17 production in human hosts, which is the primary pathway for elimination of the fungus [ 115 ], and the intracellular bacteria Coxiella burnetii blocks IL-17 signaling in human macrophages [ 116 ].…”

Frenemies within: An Endocarditis Case in Behçet’s Disease

“…In BD activation of neutrophils and NLRP3 inflammasome (nucleotide-binding domain, leucine-rich containing family, pyrin domain-containing 3) is seen [ 41 , 42 ]. Nevertheless, C. Burnetii inhibits the NLRP3 inflammasome and also IL-17, important in neutrophil recruitment in BD [ 40 , 43 , 44 , 45 ]. Of interest, a similar tolerance induction using a recombinant Cholera toxin B subunit (conjugated with a peptide derived from the HSP protein 60) was therapeutically tried in BD uveitis [ 46 ].…”