A novel epitope on the C-terminus of SmD1 is recognized by the majority of sera from patients with systemic lupus erythematosus.
The SmD1 protein is a specific target for the autoantibody response in SLE. To further analyze this reactivity epitope, mapping was performed with cellulose-bound 13-mer peptides overlapping 10 amino acids (aa). In this initial approach, 4 out of 15 SLE sera recognized more than five overlapping peptides of the SmD1 C-terminus. Therefore, longer oligopeptides of up to 37 aa of this region were generated and probed for as antigens by ELISA. For the SmD1 aa 83-119 polypeptide, there was a striking increase of reactivity with 70.0% positive reactions out of 167 SLE sera. In contrast, 105 healthy control sera were negative, and only 8.3% of sera from patients with other inflammatory diseases (n = 267) exhibited a response, which was of low level only. The anti-SmD183-119 reactivity was significantly higher in anti-dsDNA antibody positive vs. negative sera (P < 0.001) and correlated with disease activity. Four of five human monoclonal anti-dsDNA antibodies also reacted with SmD183-119. The specificity for SmD1 was demonstrated by inhibition experiments and immunization of rabbits with SmD183-119 inducing SmD1-specific antibodies. In conclusion, the SmD183-119 peptide was demonstrated to be an important and highly specific target of the autoimmune response in SLE. The high sensitivity of this ELISA probably depends on a conformational epitope, which appears not to be accessible in the full-size SmD1 protein.
Department of Medicine, Rheumatology and Clinical Immunology, Institute of Medical Immunology, Charitié University Hospital, Humboldt University at Berlin, D-10177 Berlin, Germany.
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G
Riemekasten
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J
Marell
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Trebeljahr
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R
Klein
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Hausdorf
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Häupl
J
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Schneider-Mergener
G R
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Burmester
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Hiepe
D000595:Amino Acid Sequence; D000918:Antibody Specificity; D001323:Autoantibodies / Q000097:blood*; D001324:Autoantigens / Q000737:chemistry / Q000276:immunology*; D015551:Autoimmunity; D004247:DNA / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes; D006801:Humans; D015151:Immunoblotting; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry / Q000276:immunology; D010446:Peptide Fragments / Q000737:chemistry / Q000276:immunology*; D011487:Protein Conformation; D017411:Ribonucleoproteins, Small Nuclear; D012680:Sensitivity and Specificity; D055517:snRNP Core Proteins
D001323:Autoantibodies; D001324:Autoantigens; D000939:Epitopes; D009842:Oligopeptides; D010446:Peptide Fragments; D017411:Ribonucleoproteins, Small Nuclear; C526409:SNRPD1 protein, human; D055517:snRNP Core Proteins; D004247:DNA