IL-2 is a pleiotropic cytokine which can regulate or stimulate the differentiation and function of CD4+, CD8+ and NK cells. An opened-labelled trial and a retrospective study have indicated the incidence of infection is lower in the treatment of low-dose IL-2 combined with corticosteroid and immunosuppressor. We are going to conduct a multi-center prospective observational study to verify the above results.

We are going to conduct a multi-center prospective observational study, and plan to enroll 500 SLE patients. Low-dose IL-2 is defined as 100IU IL-2 injected subcutaneously every other day for two weeks, followed by two-week break as one treatment cycle, and at least three weeks.There will be 250 patients in low-dose IL-2 group which treat with IL-2 combined with steroid and immunosuppressor. Non-IL-2 group is only treat with steroid and immunosuppressor. These patients are followed by every one month until get infected, otherwise, patients will be followed for two years. We focus on the type, positive microorganisms, grade and treatment of infection. Then, we will compare the differences of above parameters between these two groups.

Inclusion Criteria:

• SLE patients diagnosed by the ACR Criteria of 1987;
• Treated with low-dose IL-2, corticosteroid and immunosuppressor for SLE.
• Consent to participate in this study.
• Regular follow-up for at least 2 years.

Exclusion Criteria:

• Other autoimmune disease;
• Without treatment of low-dose IL-2, corticosteroid and immunosuppressor for SLE.
• Mental disorder without regular or specific treatment.

Depending on the incidence of infection in our retrospective study, Low-dose IL-2 group was 14.1%, non-IL-2 group was 25.2%. α was 0.05, β was 0.2, After the calculation of sample size, with the addition of about 20% patients for loss of follow-up, we plan to enroll 500 patients, and 250 patients in every groups equally.