Clinical Chemistry
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Clinical Chemistry 55: 946-954, 2009. First published March 5, 2009; 10.1373/clinchem.2008.115626
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(Clinical Chemistry. 2009;55:946-954.)
© 2009 American Association for Clinical Chemistry, Inc.

Proteomics and Protein Markers

Heterogeneous Nuclear Ribonucleoprotein H1, a Novel Nuclear Autoantigen

Karolien Van den Bergh1, Herbert Hooijkaas2, Daniel Blockmans3, René Westhovens4, Katrijn Op De Beéck1, Patrick Verschueren4, Diana Dufour2, Joop P. van de Merwe5, Monika Fijak6, Jörg Klug6, Georges Michiels1, Benoit Devogelaere7, Humbert De Smedt7, Rita Derua8, Etienne Waelkens8, Norbert Blanckaert1 and Xavier Bossuyt1,a

1 Laboratory Medicine, Immunology, University Hospitals Leuven, Belgium; 2 Department of Immunology, Erasmus MC, University Medical Center Rotterdam, the Netherlands; 3 General Internal Medicine, University Hospitals Leuven, Belgium; 4 Rheumatology, University Hospitals Leuven, Belgium; 5 Department of Immunology and Department of Internal Medicine, Erasmus Medical Center Rotterdam, the Netherlands; 6 Department of Anatomy and Cell Biology, Justus-Liebig-University of Giessen, Germany; 7 Department of Molecular Cell Biology (Laboratory of Molecular and Cellular Signalling), Catholic University of Leuven, Belgium; 8 Department of Molecular Cell Biology (Laboratory of Protein Phosphorylation and Proteomics) and Biomacs, Catholic University of Leuven, Belgium.

aAddress correspondence to this author at: Laboratory Medicine, Immunology, University Hospitals Leuven, Herestraat 49, B-3000 Leuven, Belgium. Fax 00 32 16 347042; e-mail xavier.bossuyt{at}uz.kuleuven.ac.be.

Background: Serum samples from patients with autoimmune connective tissue diseases that show a finely speckled antinuclear antibody (ANA) on indirect immune-fluorescence often have antibodies against unknown nuclear target antigens. To search for such autoantigens we applied a proteomic approach using sera from patients with a high ANA titer (≥640) and finely speckled fluorescence but in whom no antibodies to extractable nuclear antigens (ENA) could be identified.

Methods: Using an immunoproteomics approach we identified heterogeneous nuclear ribonucleoprotein H1 (hnRNP H1) as a novel nuclear target of autoantibody response.

Results: Recombinant rat hnRNP H1 reacted in Western blot analyses with 48% of 93 sera from patients with primary Sjögren syndrome and with 5.2% of 153 sera from patients with other connective tissue diseases (diseased controls). For comparison, the diagnostic sensitivity and specificity of anti–Sjögren syndrome A (SSA) antibodies for primary Sjögren syndrome in the same patient cohort were 88.2% and 76.3%, respectively. Interestingly, 5 of 11 primary Sjögren syndrome patients with no anti-SSA or anti-SSB antibodies had anti–hnRNP H1 antibodies. Anti–hnRNP H1 antibodies were preabsorbed by hnRNP H1, as demonstrated by indirect immunofluorescence. In an evaluation of the presence of anti–hnRNP H1 antibodies in 188 consecutive samples submitted to the clinical laboratory with positive ANA (titer ≥160), anti–hnRNP H1 antibodies were found in 3 of 7 (2 primary and 5 secondary) Sjögren syndrome patients and in 8.3% of the diseased controls.

Conclusions: HnRNP H1 is a newly discovered autoantigen that could become an additional diagnostic marker.






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Copyright © 2009 by the American Association for Clinical Chemistry.