肺结节患者及健康受试者纳入标准：排除标准

Patients with pulmonary nodules and healthy subjects: ① Those with a history of untreated infectious diseases; ② Those with a history of autoimmune diseases; ③ Those with concomitant respiratory infections, oral diseases, liver cirrhosis, chronic renal insufficiency, intestinal obstruction, esophageal diverticulum, non-ketotic hyperosmolar syndrome in diabetes, and diabetic ketoacidosis; ④ Those who have taken oral antibiotics in the past month, or used antibiotics or corticosteroids on the skin surface within the past 7 days; ⑤ Those with a history of long-term immunosuppressant use; ⑥ Those who have consumed yogurt in the past week; ⑦ Those with severe mental disorders (perceptual disorders, cognitive disorders, etc.); ⑧ Those with multiple blisters, abscesses, burns, ulcers, or wounds on the scalp, face, arms, forearms, or hands; ⑨ Those with extrapulmonary tumors in the chest.