Immunological Characteristics of Preclinical IBD

Prior treatment

• Previous or current diagnosis of microscopic colitis.
• Alteration in biomarkers in blood or stool will not constitute an exclusion criterion.
  • Patients from cohort B will be excluded if they fulfill any the following exclusion criteria:
  • \- Previous use of immunomodulators or biologics for any condition.
  • Patients from cohort C will be excluded if they fulfill any the following exclusion criteria:
• Previous use of immunomodulators or biologics for any condition.

Other

• Patients from cohort A will be excluded if they fulfill any the following exclusion criteria:
• Identification of any enteropathogen in the stool culture.
• Isolated findings of acute inflammatory infiltrate without signs of chronicity.
• Any gastrointestinal symptoms at baseline.

• Patients from cohort A will be included if they fulfill all the following inclusion criteria:
• Male or female ≥18 years of age at baseline.
• New diagnosis of IBD during a CRC screening colonoscopy, based on the criteria from the European Crohn's and Colitis Organization (33, 34).
• Presence of a chronic inflammatory infiltrate and histological diagnosis compatible with IBD.
• The patient must be asymptomatic at diagnosis and without previous symptoms suggestive of IBD.
• Time interval between the index colonoscopy and the baseline visit up to 3 months.
  • Patients from cohort B will be included if they fulfill all the following inclusion criteria:
• Male or female ≥18 years of age at baseline.
• Recent diagnosis of IBD, with \<3 months from symptoms onset.
• Time interval between the index colonoscopy and the baseline visit up to 3 months.
  • Patients from cohort C will be included if they fulfill all the following inclusion criteria:
• Male or female ≥18 years of age at baseline.
• No endoscopic signs of IBD after a complete ileo-colonoscopy within the CRC screening program.
• Time interval between the index colonoscopy and the baseline visit up to 3 months.