IDO1 and arthritic joint disease: 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.