The positive role of IDO2 in the development of inflammatory processes was further and elegantly demonstrated by means of a murine model of autoimmune arthritis, i.e., the KRN.g7 mice, genetically deficient for either the Ido1 or Ido2 gene, which revealed that IDO2, but not IDO1, is necessary for arthritis development. Here, IDO2 is linked to arthritic joint disease.