Interferon-γ and CXCL10 responses related to complaints in patients with Q fever fatigue syndrome.

Approximately 20% of patients with acute Q fever develop Q fever fatigue syndrome (QFS), a debilitating fatigue syndrome. This study further investigates the role of C. burnetii-specific IFNγ, but also IL-2, CXCL9, CXCL10, and CXLC11 production in QFS patients. C. burnetii-specific IFNy, IL-2, CXCL9, CXCL10, and CXCL11 production were tested in ex vivo stimulated whole blood of QFS patients who recovered from their complaints (n = 8), QFS patients with persisting complaints (n = 27), and asymptomatic Q fever seropositive controls (n = 10). With the exclusion of one outlier, stimulation with C. burnetii revealed significantly higher IFNy and CXCL10 production in QFS patients with persisting complaints (medians 288.0 and 176.0 pg/mL, respectively) than in QFS patients who recovered from their complaints (medians 93.0 and 85.5 pg/mL, respectively) (p = 0.041 and 0.045, respectively). No significant differences between groups were found for C. burnetii-specific IL-2, CXCL9, and CXCL11 production. These findings point towards a difference in cell-mediated immunity in QFS patients with persisting complaints compared to those who recovered from their complaints. Such a difference may aid to eventually diagnose QFS more objectively and might serve as an indicator of its underlying etiology.