Frequent occurrence of anti-tRNAHis autoantibodies that recognize a conformational epitope in sera of patients with myositis

Abstract

OBJECTIVE: To investigate the incidence of autoantibodies directed to deproteinized transfer RNA(His) (tRNA(His)) in anti-Jo-1 positive myositis patients and to determine the major B cell epitope. METHODS: One hundred sixty-seven myositis sera were screened by immunoblotting and enzyme-linked immunosorbent assay for the presence of anti-Jo-1 antibody. Autoantibodies directed to deproteinized RNA were detected by immunoprecipitation. Ribonuclease cleavage experiments were performed to determine the tRNA(His)-specific features important for recognition. RESULTS: Approximately one-third of the anti-Jo-1 positive sera also contained autoantibodies recognizing tRNA(His). This recognition was independent of modified bases, but the presence of stabilizing Mg2+ ions appeared to be essential for efficient immunoprecipitation. Transfer RNA(His)-specific features in the anticodon loop were not protected from ribonuclease cleavage by bound antibodies, while protection of bases located in the D and T loops was observed. CONCLUSION: A significant number of anti-Jo-1 positive myositis sera contain anti-tRNA(His) activity. Formation of the major autoepitope on tRNA(His) is strongly dependent on proper folding of this molecule mediated by an interaction between D and T loops which is stabilized by either modified residues or Mg2+ ions.