Inclusion Criteria:  18 years old ≤ age ≤60 years old; SOFA score ≥2; Mechanical ventilation should be required for at least 24 hours when included in the study; Informed consent is obtained.  Exclusion Criteria:  Age < 18 years old or ≥ 60 years old; Previous solid organ or bone marrow transplantation; Autoimmune diseases (rheumatoid arthritis, systemic lupus erythematosus, etc.), or hematologic malignancies (leukemia and lymphoma, etc.); Received radiotherapy or chemotherapy within the past 30 days, or received immunosuppressant drugs (tripterygium wilfordii, mycophenolate mofetil, cyclophosphamide, FK506, etc.), or continuous treatment with prednisolone more than 10 mg/day (or equivalent doses of the other hormones); Unstable angina pectoris or myocardial infarction in the past six months; Acute brain injury (traumatic brain injury, subarachnoid hemorrhage, acute ischemic stroke, acute intracranial hemorrhage, acute intracranial infection, etc.); Poorly controlled hypertension and congestive heart failure; Increased intraocular or intracranial pressure; Chronic kidney disease, received continuous renal replacement therapy in the past 30 days, or acute renal failure requiring CRRT; Severe chronic liver disease (Child-Pugh class B or C); Alcohol dependence, mental illness or severe cognitive impairment; Pregnancy or lactation; Informed consent is not obtained.