A group of systemic autoimmune diseases, including systemic lupus erythematosus (SLE),'scleroderma, Sjogren's syn-drome, dermatomyositis/polymyositis, and mixed connective tissue disease (MCTD), are characterized by a distinctive im-mune response which is manifested as the spontaneous pro-duction ofautoantibodies that react with intracellular proteins and nucleic acids (reviewed in reference 1). A finding thathas had an important impact on clinical medicine has been the demonstration that each ofthe diseases described above has its own individual set of autoantibodies, so that autoantibody profiles havebeen useful in differential diagnosis. In molecular and cell biology, autoantibodies have been used to clarify the molecular structure ofintracellular molecules and their role in the biological function of important intracellular processes. The interactions between clinical and basic sciences in this field of research have been especially active in the past decade and are a good example of bridges being built between these disciplines.

Most of the earlier studies on autoantibodiesfocused on those reactive with DNA and nucleoproteins, the latter now recognized as the histone components ofdeoxyribonucleoprotein. These studies demonstrated the important role of au-toantibody to DNA in the pathogenesis of tissue inflammation via immune complex formation (2, 3) and stimulated continued investigations into the relationship of autoantibodies with disease mechanisms. A nonhistone nuclear protein antigen called Sm was defined in 1966 by immunoprecipitation in agarose gel double diffusion analysis (4). The Sm antigen was shown to be a protein that was nuclear in location and anti-bodies were found to behighly specific for SLE. Shortly there-after, another nuclear antigen was identified with antibodies present in sera of patients with lupus and MCTD, and since immunological studies showed that integrity ofboth RNA and