Several studies in patients affected by CD and UC showed increased expression of IDO1 mRNA and protein in both the lamina propria and epithelium during active IBD compared to controls.23,24,54 These findings are consistent with those of Nikolaus et al3 who showed a significant increase in Kyn/Trp ratio in patients with active disease compare to inactive disease or healthy controls. The gene discussed is IDO1; the disease is inflammatory bowel disease.