For patients with active proliferative IgG4-RD, we plan to conduct a 52-week prospective randomized controlled trial to compare the efficacy and safety of 5mg lenalidomide plus prednisone, 10mg lenalidomide plus prednisone, and prednisone alone, so as to find new treatment measures for patients with proliferative IgG4-RD.

Inclusion Criteria:

1. Patients aged between 18 and 75 years who meet the 2019 American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) classification criteria for IgG4-RD；
2. Patients with active disease: For patients with initial treatment or relapse after drug withdrawal, active disease is defined as having an IgG4-RD Response Index (RI) of at least 2 points in at least one organ at the time of screening; for those experiencing relapse while on treatment, active disease is defined as having an IgG4-RD RI of at least 3 points in at least one organ at the time of screening；
3. Patients with the clinical subtype of proliferative IgG4-RD；
4. Patients who have no plans for pregnancy within the next 18 months and who agree to use reliable contraceptive measures during the study period；

Exclusion Criteria:

1. IgG4-RD patients with only fibrotic features;
2. Absolute neutrophil count <1.5×10^9 /L or platelet count <100×10^9/L;
3. Creatinine clearance less than 60 ml/ min;
4. Liver function Child-Pugh grade B or above;
5. Chronic active infection requiring systemic treatment;
6. Diagnosed with malignant tumor in the past five years;
7. Patients with a history of thrombosis;
8. Using biological agents within six months;
9. Known to be allergic to lenalidomide or thalidomide;
10. Pregnant or lactating women;
11. Patients with any other medical conditions or for specific reasons judged by the investigator to be ineligible to participate in the study.