Analysis of a novel RNA epitope recognized by sera in patients with rheumatic diseases using randomized RNA epitope library

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We defined a novel RNA epitope recognized by serum from a patient with Sjogren's syndrome (SjS) from a randomized RNA epitope library, and investigated the epitope reactivity of the anti-RNA antibodies in patients with various connective tissue diseases. Serum from SjS patient TS was used to select ligands from the library of RNA oligomers with a central region of 25 degenerate nucleotides. Bound RNA was recovered by reverse transcription, PCR amplification and subcloning. Sera from 32 of 61 patients with SS (52.4%) precipitated with one of the selected RNA (TS1・RNA ; CGAAAGUCCGAUCGGCGUAAUGCA), whereas sera from 8 of 41 patients with systemic lupus erythematosus (19.5%) and 3 of 25 patients with rheumatoid arthritis (12.0%) precipitated. Frequency of anti-SS-A antibodies was significantly higher in anti-TS1・RNA positive patients but there was no cross-reactivity between anti-SS-A and anti-TS1・RNA.The epitopes on this RNA were further analyzed by immunoprecipitation using mutants of TS1・RNA.The reaction of patient sera with the RNAs declined when any part of the TS1・RNA was mutated. This finding indicates that the selected TS1・RNA is a novel sequence-specific RNA epitope that binds specifically sera with MCTD and SjS.Then we attempted to study the clinical significance of antibodies to TS1・RNA.Whereas there was no significant correlation between anti-TS1・RNA and clinical features in SjS patients, anti-TS1・RNA antibodies significantly correlated with the laboratory findings such as anti-dsDNA, Sm and U1 RNP, and low serum level of complement in MCTD patients. In addition, the activities of renal involvement was significantly correlated with the titer of anti-TS1・RNA.These results suggested that anti-TS1・RNA antibody is a novel antibody against the sequence specific RNA in SiS and MCTD patients and may play certain roles associated with autoantibody-production and pathogenesis in MCTD.