Characteristic epitope recognition pattern of autoantibodies against eukaryotic ribosomal protein L7 in systemic autoimmune diseases

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Abstract
Objective. To define the epitope-recognition pattern and the fine specificity of the autoantibody response to protein L7 in patients with rheumatic diseases. Methods. The epitope-recognition pattern was studied by enzyme-linked immunosorbent assay utilizing overlapping fragments of L7. The fine specificity was examined by binding inhibition and isoelectric focusing. Results. We observed a disease-specific epitope-recognition pattern of anti-L7 autoantibodies. There was one immunodominant epitope that was recognized by all anti-L7-positive sera from patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and systemic sclerosis (SSc). Additional recognition of minor epitopes was observed; it arises by intramolecular epitope spreading and was correlated with disease activity in SLE patients. SSc patients differed from SLE and RA patients in that their sera did not recognize certain minor epitopes. The major epitope was recognized by high-affinity autoantibodies of limited heterogeneity. Minor epitopes were recognized by heterogeneous low-affinity autoantibodies. Conclusion. The anti-L7 autoantibody response is oligoclonal. Additional B cell clones are activated by antigen during active phases of disease.