Granulomatous response to Coxiella burnetii, the agent of Q fever: Activation of type I interferon-related genes

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 and beads coated with C. burnetii, using BCG extracts as controls. A microarray analysis showed dramatic changes in gene expression in granuloma cells compared with peripheral blood mononuclear cells. About 60% of modulated genes were common to C. burnetii and BCG granulomas including M1-related genes. C. burnetii granulomas also expressed a specific transcriptional profile that was essentially enriched in genes associated with type I interferon response (IFI44, IFI44L, IFI6, OAS1, OAS2, OAS3, ISG15, IFIT1, IFITM2, IFITM3, MX1 and MX2). Real-time RT-PCR confirmed that C. burnetii especially increased the expression of interferon-stimulated genes in granulomas generated from controls or Q fever patients. Our results showed that granuloma formation is associated with a core of transcriptional response, but that the granulomatous response to C. burnetii is characterized by the activation of type I interferon-related genes, conferring a new role for type I interferon response in the control of C. burnetii infection. Human Peripheral Blood Mononuclear Cells (PBMC) were co-cultured with beads coated with Mycobacterium bovis strain Bacille Calmette Guerin (BCG) extracts or Coxiella burnetii (C.burnetii) extracts for 8 days and PBMC at day 0 were used as controls. For each condition ( unstimulated, BCG and C.burnetii), each microarray is a replicate of the same biological sample.