The invention relates to polypeptides reacting with rheumatism-associated autoantibodies. The invention moreover relates to a diagnostic agent comprising any of said polypeptides, to a diagnostic kit comprising said diagnostic agent and to a process for in vitro detection of rheumatic diseases. The invention furthermore relates to a medicament comprising any of said polypeptides and to the use of said polypeptides for preparing a medicament for the prophylaxis and/or treatment of rheumatic diseases.