Studies of kynurenine supplementation, or inhibition of kynurenine production with the IDO1 inhibitor 1-methyl-tryptophan (1-MT) have shown conflicting effects on arthritis severity: 1-MT treatment ameliorates disease in the K/BxN (67) murine model but exacerbates disease in the CIA model (68). This evidence concerns the gene IDO1 and arthritic joint disease.