This research will be conducted nationwide in patients with autoimmune gastritis, focusing on their clinical characteristics, possible risk factors, and multi-omics analysis. Changes in gastrointestinal microbiota, host and microbial metabolism, gene transcription and biomarkers of autoimmune gastritis will be explored to provide evidence for further precise therapy of the disease.

Autoimmune gastritis is a chronic progressive disease that may develop into gastric cancer. However, on account of its low morbidity, atypical clinical and endoscopic manifestation, demanding technique for detection of serological markers, the diagnosis and treatment of this disease remains challenging. Therefore, there's inadequate studies focusing on its pathogenesis, metabolism, gene transcription, microbiota etc. In recent years, multi-omics analysis provides clinicians with depth and breadth understandings of diseases. This research, as well, aims at enhancing clinicians' knowledge of autoimmune gastritis to reduce the occurrence of neuroendocrine tumors, gastric cancer, pernicious anemia and other complications.

Inclusion Criteria:

• Aged 35-75 years.
• Type A atrophic gastritis: Underwent gastroscopy in hospitals mentioned above. Gastroscopy and histopathology showed no significant atrophy of antrum mucosa, but significant atrophy of the body or fundus mucosa, accompanied by positive blood and/or gastric fluid anti-parietal cell antibodies and/or anti-internal factor antibodies. No obvious tumor, deep ulcer, severe bile reflux, severe erosion, or active bleeding. Type B atrophic gastritis: Underwent gastroscopy in hospitals mentioned above. Gastroscopy and histopathological examination showed multifocal atrophy of gastric mucosa, mainly antrum involved. No obvious tumor, ulcer, moderate to severe bile reflux, moderate to severe erosion, multiple polyps (≥2) , or active bleeding. Chronic non-atrophic gastritis: Underwent gastroscopy in hospitals mentioned above. Gastroscopy and histopathology showed chronic inflammation of gastric mucosa with infiltration of lymphocytes and plasma cells, and no intrinsic glandular reduction. No obvious tumor, ulcer, moderate to severe bile reflux, moderate to severe erosion, multiple polyps (≥2) , or active bleeding.
• Underwent colonoscopy within the past 5 years, and no obvious abnormalities such as inflammation, polyps, tumor, or ulcer were observed.
• Have the cognitive level to understand the questionnaire and cooperate voluntarily.

Exclusion Criteria:

• Aged <35 years or>75 years.
• Histopathology indicated dysplasia.
• Long-term use of PPIs or H2-blockers for more than 3 months in the past 1 year. With a history of Helicobacter pylori eradication within the past 2 months.
• Use of antibiotics, nonsteroidal anti-inflammatory drugs, probiotics, steroids, or immunosuppressants for more than 2 weeks within the past 2 months.
• Severe constipation or diarrhea within the past 3 months, or notable changes in bowel habits within the past 3 months.
• History of tumor, organ transplantation, or severe parasitic disease, other diseases of digestive system (such as inflammatory bowel disease, cirrhosis, pancreatitis, etc.), or serious infection.
• History of severe trauma, major operation, extensive burn, cerebral vascular accident, severe organ failure (cardiac, hepatic, renal insufficiency, etc.), shock or sepsis within the past 6 months.
• History of gastrointestinal surgery.
• History of gastrointestinal bleeding, ileus, perforation.
• Chronic metabolic, infectious, or endocrine diseases (such as hypertension, diabetes, hyperlipidemia, hyperuricemia, hyperpurine) that are not well controlled, whether or not treated with medications.
• Vegetarians or had significant changes in eating habits within the past 3 months.

Chinese people