FIGURE 3.

IDO1 expression is required for the protective effect of IFN-α. AIA was induced in female Ido1^−/− mice and their wild type littermates with or without 1000 U IFN-α as described in Materials and Methods. (A) The level of arthritis evaluated at day 28 of AIA is expressed as severity score (mean ± SEM, n ≥ 16) from Ido1^−/− mice and their WT littermates. (B) Representative histochemical slide of the knee joints from each group is presented. (C) Splenocytes from day 28 of AIA were restimulated ex vivo with 50 μg/ml of 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 ≥ 6), the radioactivity (cpm) of the corresponding mock (medium) stimulation was subtracted. Comparison of arthritis severity score and cpm values for proliferation between different treatment groups was done by the Mann–Whitney U test (*p < 0.05, **p < 0.01).