Pathogenesis of Intestinal Behcet's Syndrome

Inclusion Criteria: Behcet's syndrome patients with intestinal involvement: * Attendance at Peking Union Medical College Hospital, fulfillment of one of the two diagnostic criteria for BS (1990 Criteria of International Study Group for Behcet's disease or 2014 International Criteria for Behçet's Disease), and well-documented medical records; * Age 20-65 years old; * Have evidence of GI involvement, including clinical manifestations, laboratory tests, endoscopy, imaging and pathology; * Signed written informed consent and willingness to cooperate. Behcet's syndrome patients with intestinal involvement: * Attendance at Peking Union Medical College Hospital, fulfillment of one of the two diagnostic criteria for BS (1990 Criteria of International Study Group for Behcet's disease or 2014 International Criteria for Behçet's Disease), and well-documented medical records; * Age 20-65 years old; * Have no evidence of GI involvement, including clinical manifestations, laboratory tests, endoscopy, imaging and pathology; * Signed written informed consent and willingness to cooperate. Inflammatory bowel disease patients: * Attended Peking Union Medical College Hospital and was diagnosed with Crohn's disease by a combination of clinical, imaging, and pathologic diagnosis; * Age 20-65 years old; * Signed written informed consent and willingness to cooperate. Health controls: * Healthy individuals aged 20-65 years; * Signed written informed consent and willingness to cooperate. Exclusion Criteria: * Other systemic diseases, such as autoimmune diseases, infectious diseases, malignant tumors, etc; * Patients with other intestinal diseases, such as intestinal tumors, intestinal tuberculosis, intestinal infections; * Patients with other oral diseases, such as cavity caries, oral abscesses, oral tumors, oral candidiasis, and dry mouth; * Patients taking antibiotics and probiotics within one month.