Synthetic peptides in the diagnosis of systemic autoimmune diseases

Proteins recognized by antibodies from patients with autoimmune diseases have been intensively studied over the two past decades since cDNAs encoding autoantigens have become available. Identity of many of them has been defined, and specific structural motifs or post-translational modifications, which may be important to explain the generation of such antibodies during the autoimmune process, have been pointed out. Immunological analysis of sera from autoimmune patients with recombinant fragments and with short peptides has revealed the presence of dominant epitopes along proteins; some of them are targeted by antibodies from patients with specific diseases or disease subsets. Innovative technologies such as peptide arrays and biosensors as well as the exploitation of large peptides libraries have recently open up new perspectives. Peptides bearing natural modifications, peptide analogues, as well as mimotopes of protein or non-protein antigens (DNA, RNA, sugar) have been developed and might advantageously replace native antigens in routine immunoassays. Although numerous conformational epitopes have not yet been identified, and cannot be identified by the approaches classically used in epitope mapping studies, such peptides and peptide analogues may represent efficient probes to detect the presence of circulating autoantibodies in the serum of autoimmune patients and help for establishing specific and sensitive early diagnostic tests. They may also lead to the design of high-affinity ligands for purifying autoantibodies. These different aspects are discussed and epitope mapping studies of a number of autoantigens (e.g. histones, sn and hnRNP proteins and Ro proteins) are summarized.