Polyclonal hypergammaglobulinaemia is characterized by increased levels of immunoglobulins and is a common feature observed in various diseases such as autoimmune diseases, chronic infectious diseases or lymphoid hemopathy. Some autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis or Sjögren's syndrome are frequently associated with polyclonal hypergammaglobulinaemia. Recent data have suggested that the distribution of immunoglobulin isotypes in polyclonal hypergammaglobulinaemia may be disease-specific. However, isotype repartition in polyclonal hypergammaglobulinaemia remains poorly understood. The investigators will investigate the distribution of immunoglobulin isotype in patients with autoimmune disease and polyclonal hypergammaglobulinaemia. Moreover, the investigators will evaluate the isotype repartition as predictor of lymphoma or monoclonal gammopathy among patients with autoimmune diseases.