Leflunomide Treatment for IgG4-RD

Inclusion Criteria: * Males and females * Aged 18 to 70 years old with informed consent * All patients must meet the following diagnostic criteria of IgG4RD (2011): 1. swelling, sclerosing and inflammatory involvement of one or more organ, including sclerosing pancreatitis, sialadenitis (Mikulicz disease), sclerosing cholangitis, inflammatory pseudotumors, retroperitoneal or mediastinal fibrosis, interstitial nephritis, hypophysitis, sclerosing dacryoadenitis, inflammatory aortic aneurysm, lymphadenopathy, or other inflammatory conditions; 2. elevated serum IgG4 (\>1.35 g/L); 3. histopathologic features of fibrosis and/or lymphocytic and polyclonal plasma cell infiltration (and IgG4+ plasma cells on immunohistology when performed). Patients fulfill 1)+2)+3) are diagnosed as definite IgD4RD, 1)+2): possible IgG4RD; 1)+3): probable IgG4RD; 4. exclusion of other diseases. Exclusion Criteria: * Patients will not be included if meets any of the following criteria: 1. Patients who were diagnosed as other autoimmune diseases; 2. Patients who were diagnosed as malignant diseases; 3. Pregnant and lactating women； 4. Active infection: HIV, HCV, HBV, TB； 5. Serious organ function failure, expected life time less than 6 months. 6. Presenting with Mikulicz disease without other manifestations.