there is high mortality rate of sepsis, 36% in 90-days of sepsis in China, and there is no effective treatment. Immunosuppression mediated by sepsis is an important cause of death in patients. Treg cells are important immunomodulatory cell. Treg's over-differentiation is involved in the development of sepsis induced immunosuppression. In sepsis patients, the expression of PD-1、CTLA-4 and TIGIT on Treg cell surface increased, and Treg cells with high expression of co-inhibitory molecules showed stronger immunosuppressive characteristics. MiR-155-5p is an unencoded RNA transcript from a proto-oncogene B cell integration cluster. In sepsis, the expression of miR-155 increased in peripheral blood and correlated with the patient's prognosis. Recent studies have shown that miR-155-5p promotes co-inhibitory molecules expressed on T cells in LCMV infected animal models. However, the relationship between the expression of peripheral blood miR-155-5p in sepsis patients and the expression of co-inhibitory molecules on Treg cell surface is not clear.

1. peripheral blood Treg cells and their surface PD-1、CTLA-4 and TIGIT levels in sepsis patients were measured by flowcytometry. SOFA score、APACHE II score were recorded
2. the level of miR-155-5p were measured by RT-qPCR in patients with sepsis on day 0-1 and day 3-5, and the correlation between the expression of the co-inhibitory molecules and miR-155-5p were evaluated

Inclusion Criteria:

• sepsis 3.0 diagnositic criteria are met. older than 18 years old. total course is less than 7 days. Informed consent is obatained.

Exclusion Criteria:

• pregnancy. patients with active malignant tumors. chronic hepatitis or HIV. patients under treatment with immunosuppressive drugs (except patients with glucocorticosteroid prednisone or equivalent dose<10 mg/d per day)

patients diagnosed with sepsis