Ulcerative colitis (UC) is a chronic disease characterized by acute episodes of bloody diarrhea with varying degrees of severity. The most feared event, acute severe UC, can lead to life-threatening and systemic complications. Little is known about the determinants of severity in UC. The investigators hypothesize that distinct severity phenotypes of UC arise from intricated host-microbiota mechanisms influencing repair mechanisms. Our first and main objective is to study the natural history of UC during a one-year time period in a cohort of patients.

Ulcerative colitis (UC) is a chronic inflammatory bowel disease characterized by acute episodes of varying-severity bloody diarrhea. Acute severe colitis poses systemic risks. In our pilot ITAC project, the investigators found a direct link between deep colonic ulcers and systemic inflammation in acute severe colitis, suggesting repair failure. Conversely, excessive repair in UC can lead to colorectal neoplasia, especially sessile serrated adenomas in remission cases.. The investigators plan to prospectively collect tissue and blood samples of patients with UC or non-UC patients with polyps undergoing endoscopy in the Gastroenterology unit or colectomy in the Abdominal surgery unit of CHU de Bordeaux. For all patients, additional biopsies will be collected for histology, microbiota characterization, transcriptomic profiling and cells phenotyping. Additional blood samples will be collected for immune cells phenotyping, genetic profiling, and multiplex cytokines measurement. Routine clinical, endoscopic and biological data will be collected using the Entrepot de Données de Santé of CHU de Bordeaux. The patients will be divided in groups based on the endoscopy phenotype: unactive disease, non-severe active disease, severe disease and on the presence of polyps. Patients without ulcerative colitis with polyps will be studied as a control group.clinical, endoscopic and biological data will be collected using the Entrepot de Données de Santé of CHU de Bordeaux. The patients will be divided in groups based on the endoscopy phenotype: unactive disease, non-severe active disease, severe disease and on the presence of polyps. Patients without ulcerative colitis with polyps will be studied as a control group.

• Inclusion criteria:

  • General Inclusion Criteria:

    • Patients covered by a social security system.
    • French-speaking patients.
    • Patients aged ≥18 years.
    • Patients who have provided free, informed, and written consent (no later than the inclusion day and before any research-related examination).

  • Specific Inclusion Criteria for the UC Group:

    • Patients diagnosed with ulcerative colitis (UC) according to the European Crohn's and Colitis Organisation (ECCO) guidelines.
    • Patients undergoing lower gastrointestinal endoscopy or rectocolic surgery.

  • Non-UC Patients with Polyps Group:

    • Patients undergoing colonoscopy with resection of hyperplastic polyps in the rectum, sessile serrated lesions, or adenomas >2 cm.

• Exclusion criteria:

  • Patients with perianal, ileal lesions, or endoscopic features of colonic lesions suggestive of Crohn's disease.
  • Pregnant or breastfeeding women.
  • Patients under legal protection or unable to provide informed consent.
  • Patients deprived of liberty by judicial or administrative decision, hospitalized without consent, or admitted to a healthcare or social institution for reasons unrelated to the study.