FIGURE 4.

The enzymatic activity of IDO1 is required for the protective effect of IFN-α in the sensitization, but not in the disease onset phase. AIA was induced in female mice with or without IFN-α treatment, as described in Materials and Methods. To inhibit the enzymatic activity of IDO1, 1-MT was administered either through drinking water or by surgical insertion of a 1-MT pellet (Supplemental Fig. 1B) at day −1 to day 28 or day 20–28 of AIA. (A) The level of arthritis expressed as severity score (mean ± SEM, n ≥ 7) from WT mice that received 1-MT or vehicle and with or without IFN-α treatment. (B) Representative histochemical slides of the knee joints from each group. (C) Splenocytes from WT mice at day 28 of AIA were restimulated ex vivo with 50 μg/ml mBSA for 72 h and pulsed with radioactive thymidine for the last 20 h. The incorporated radioactivity (cpm value) was determined by a beta counter. From the expressed values (mean cpm ± SEM, n ≥ 7), the radioactivity (cpm) of the corresponding mock (medium) stimulation was subtracted. (D) The level of arthritis expressed as severity score (mean ± SEM, n ≥ 7) from WT or IFNΑRKO mice with or without Kyn treatment (15 mg/kg mouse weight) during immunization of AIA. Comparison of arthritis severity score and cpm values for proliferation between groups was done by the Mann–Whitney U test (*p < 0.05, **p < 0.01).