Granulomatous response to Coxiella burnetii, the agent of Q fever: the lessons from gene expression analysis

Abstract

The formation of granulomas is associated with the resolution of Q fever, a zoonosis due to Coxiella burnetii; however the molecular mechanisms of granuloma formation remain poorly understood. We generated human granulomas with peripheral blood mononuclear cells (PBMCs) and beads coated with C. burnetii, using BCG extracts as controls. A microarray analysis showed dramatic changes in gene expression in granuloma cells of which more than 50% were commonly modulated genes in response to C. burnetii and BCG. They included M1-related genes and genes related to chemotaxis. The inhibition of the chemokines, CCL2 and CCL5, directly interfered with granuloma formation. C. burnetii granulomas also expressed a specific transcriptional profile that was essentially enriched in genes associated with type I interferon response. Our results showed that granuloma formation is associated with a core of transcriptional response based on inflammatory genes. The specific granulomatous response to C. burnetii is characterized by the activation of type 1 interferon pathway.

From Q Fever to Coxiella burnetii Infection: a Paradigm Change

“…Incubation of beads coated with C. burnetii phase I or II with mononuclear cells allowed us to investigate the mechanisms of granuloma formation in C. burnetii infection. First, phase II C. burnetii was less efficient than phase I microorganisms in inducing granuloma formation; second, monocytes were more critical than lymphocytes in granuloma formation; and third, granulomatous cells exhibited a transcriptional program that clustered with that of IFN-␥-stimulated macrophages, which are known to be a canonical model of microbicidal cells (255,256).…”

T-Bet Controls Susceptibility of Mice to Coxiella burnetii Infection

“…Our results highlight the formation of granulomas in a context of low-diffusion IFN-γ release suggesting a different mode of granuloma formation during C. burnetii infection. Using an in vitro model of granuloma formation, we previously reported that the transcriptional response of C. burnetii -generated granulomas was associated with a down-modulation of genes encoding for T-bet, including IFN-γ ( Faugaret et al, 2014 ). However, the essential role of IFN-γ in granuloma formation is well documented in tuberculosis infection ( Asano et al, 1993 ; Hogan et al, 2001 ).…”

Tumor Necrosis Factor-Alpha Antagonist Interferes With the Formation of Granulomatous Multinucleated Giant Cells: New Insights Into Mycobacterium tuberculosis Infection

“…Reverse transcription was performed as previously described (49). Quantitative PCR was carried out using Light Cycler Fast Start DNA master SYBR Green I kit (Roche) and the primers listed in Table 1 (31). Real-time PCR was performed as follows: initial denaturation at 95°C for 10 min, followed by 39 cycles of denaturation at 95°C for 15 s and an annealing/extending step at 60°C for 1 min.…”

“…Thus, in vitro models of granulomas have been developed by co-culturing peripheral blood mononuclear cells (PBMCs) and Sepharose beads coated with bacterial extracts from Mtb or M. bovis (16, 28, 29). Using this approach, we previously showed that monocytes migrate to the beads, maturate into macrophages which then polarize and fuse to form MGCs under the influence of lymphocytes (30, 31). In addition, we also showed that defective granuloma formation was associated with low TNF-α expression and monocytopenia in septic patients (32).…”