Constitutive activation of the type I interferon pathway and the ex vivo effect of ruxolitinib on constitutive phosphorylation of STAT1. (A) IFNα protein concentration (healthy controls <10 fg/ml) measured in the serum from the patient before treatment with ruxolitinib. (B) IFN score (normal <2.466) of the patient before treatment with ruxolitinib reflecting increased expression of IFN-induced gene transcripts. (C and D) Increased constitutive phosphorylation of STAT1 (C) and STAT3 (D) in CD3+ lymphocytes from the patient compared to a healthy control. (E) IFNα protein concentration (healthy controls <10 fg/ml) measured in the serum from the patient before and during treatment with ruxolitinib. Black lines depict median values. (F) Peripheral blood mononuclear cells (PBMCs) were obtained from the patient before treatment and 4 h after the first ruxolitinib intake. The treatment is taken twice daily. STAT1 constitutive phosphorylation in CD3+ lymphocytes and monocytes was decreased after treatment, being comparable to a healthy control.