Systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD) are long-term autoimmune diseases in which the immune system attacks parts of the body. The abnormal immune reaction causes inflammation of and damage to various body parts and can affect joints, skin, kidneys, heart, lungs, blood vessels, and the brain. SLE and MCTD often affect young women, especially black and Hispanic women, and there is no known cure. Knowing more about SLE and MCTD will help in developing new and effective treatments. The purpose of this study is to characterize immune system abnormalities, genetic components, and disease progression in people with SLE and MCTD.

Systemic lupus erythematosus (SLE) is an autoimmune disease in which the immune system produces antibodies against the body's healthy cells and tissues. These antibodies, called autoantibodies, contribute to the inflammation of various parts of the body and can cause damage to organs and tissues. Mixed connective tissue disease (MCTD) is another autoimmune disease that overlaps in terms of signs and symptoms with three other connective tissue diseases, including SLE. In both SLE and MCTD, the immune system appears to be abnormally activated by small nuclear ribonucleoprotein (snRNP) autoantigens. Furthermore, lung tissue, in particular, appears to be affected by the immune response induced by snRNP autoantigens. The causes of SLE and MCTD remain unknown. However, it is likely that a combination of genetic, environmental, and possibly hormonal factors work together to cause the diseases. Past studies suggest that several different genes may be involved in determining a person's likelihood of developing SLE or MCTD, which tissues and organs are affected, and the severity of the disease. The purpose of this study is to characterize immune system abnormalities, genetic components, and disease progression in people with SLE and MCTD.

Participants will attend up to four study visits, at intervals of at least 3 months, over the course of this study. Each study visit will include questionnaires, a physical exam, and possibly blood and/or urine collection. At the end of the study period, participants may choose to continue or discontinue participation.

Inclusion Criteria:

• Patients with known rheumatic diseases including systemic lupus erythematosus, rheumatoid arthritis, connective tissue disease, undifferentiated connective tissue disease

Exclusion Criteria:

• Poor venous access, unstable medical problems or significant cardiopulmonary disease, anemia, leukopenia, thrombocytopenia, anticoagulation therapy, recent significant changes in medication or pregnacy. Patient cannot be taking large dose of corticosteroids (above 30mg per day) or cytotoxic drugs (cyclophosphamide, azathiprine, cyclosporine, methotrexate).

Systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), mixed connective tissue disease (MCTD) or undifferentiated connective tissue disease (UCTD)