• Data characterizing CD4 T cells and corresponding clinical data [ Time Frame: Every 3 months ] [ Designated as safety issue: No ]
  
• Phenotype measurement to include disease activity, disease severity, and functional status [ Time Frame: Every 3 months ] [ Designated as safety issue: No ]
  

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 at least four study visits, spaced 3 months apart, 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.