Title: Serological markers in autoimmune diseases
Other Titles: Serologische merkers bij autoimmuunziekten
Authors: Op De Beéck, Katrijn
Issue Date: 9-Dec-2011
Abstract: State of the artA hallmark of autoimmune diseases is the production of high-affinity autoantibodies. Autoantibodies may be very specific for certain diseases and can be used as an important tool for diagnosis. In clinical laboratories, serologic testing for autoantibodies is primarily applied to assist in confirming the diagnosis, to formulate appropriate management strategies and to evaluate disease activity.In systemic autoimmune disorders, autoimmune activity is widely spread throughout the body. Autoantibodies to intracellular antigens (ANA) are a common feature of systemic autoimmune disorders such as systemic lupus erythematosus, systemic sclerosis, polymyositis, mixed connective tissue disease, dermatomyositis, primary Sjögren’s syndrome or rheumatic arthritis. These autoantibodies are typically directed to sets of proteins associated with discrete supramolecular entities built up of either DNA or RNA and proteins, such as the nucleosome, the centromere, the spliceosome, the ribosome or other ribonucleoproteins. These autoantibodies are starting to be regarded as important tools to obtain deeper insight into the pathogenesis of autoimmune rheumatic diseases. In a routine setting, indirect immune fluorescence and solid phase assays are used for the detection of these autoantibodies. However, in approximately 25 % of the patients with a systemic rheumatic disease and a high ANA titer, the nature of the autoantigen remains unknown.In organ-specific disorders, the autoimmune process is directed mostly against one organ. Examples of immune-mediated organ-specific disorders include autoimmune hepatitis, primary sclerosing cholangitis, type I diabetes, autoimmune thyroiditis, and inflammatory bowel disease (IBD). The detection of serum autoantibodies has a central role in the diagnosis and classification of autoimmune liver diseases and their overlap syndromes. Although the sensitivity of individual markers is too low to defend their general application for diagnosing IBD, using a panel of markers may reach sensitivity values of approximately 80%. In this thesis, we used an immunoproteomics approach to examine the repertoire of autoantibodies and their targetantigens in autoimmune diseases. The aims of the study were:1. To characterize the reactive epitopes of hnRNP H1, a recently identified target antigen in Sjögren’s syndrome.2. To unravel the mosaic of autoantibodies to hnRNP’s in systemic rheumatic diseases, to develop techniques for detecting them, and to establish their clinical value. 3. To evaluate diagnostic performance of current available automated systems for the detection of antibodies to known antigens in systemic rheumatic diseases.4. To identify novel autoantigens in autoimmune hepatitis. 5. To evaluate the GP2-assay, a commercial assay for the detection of anti-GP2 antibodies, on a large well-characterised IBD population.Summary of the results1. Our data demonstrated that RRM 3 is the major site of autoimmune recognition of autoantibodies to hnRNP-H1. The reactivity to fragment 4 (that contains RRM3) was very similar to the pattern of reactivity observed with full length hnRNP-H1 as antigen.2. Antibodies to recombinant human hnRNP A1, B1, C1, E1, F, Gi, H1, I, K, and P2 were determined by Western blotting and by ELISA (for hnRNP B1, E1, F, and H1). We showed that several hnRNP’s are target antigens in Sjögren’s syndrome. The combined presence of antibodies to several hnRNP’s was strongly associated with connective tissue disease in general and Sjögren’s syndrome in particular. 3. We tested two solid phase assays that have recently become available for the specific detection of ANA (Bioplex 2200 ANA screen, Bio-Rad, and EliA test, Phadia). We found that in contrast with IIF which has a high sensitivity and a lower specificity, both solid phase assays displayed high specificity and lower sensitivity. At an equal specificity level, the sensitivity of solid phase assays is higher than IIF.4. As demonstrated by Terjung et al., we confirmed that patients with autoimmune hepatic disorders display reactivity to ß-tubulin isotype 5. Besides, we identified VIP36 as a novel target antigen of autantibodies in autoimmune gastrointestinal disorders.5. We demonstrated that the anti-GP2 ELISA was reproducible, had a good linearity, and showed minor interferences. Anti-GP2 antibodies were found in 20.7% of patients with CD, 9.3% of patients with UC, and 4% of controls. We furthermore showed that anti-GP2 antibodies were associated with the extracellular pancreatic staining on indirect immunofluorescence.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Experimental Laboratory Immunology
Laboratory of Clinical Bacteriology and Mycology

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