Pieter Ruytinx1, Elien Luyten1, Ann-Sophie De Craemer2, Filip Van den Bosch3, Dirk Elewaut4 and Veerle Somers1, 1Biomedical Research Institute, Hasselt University, Department of Immunology and Infection, Diepenbeek, Belgium, 2Ghent University Hospital, Gent, Belgium, 3Department of Internal Medicine and Pediatrics, Ghent University and VIB Center for Inflammation Research, Ghent, Belgium, 4Ghent University and VIB Center for Inflammation Research, Ghent, Belgium
Background/Purpose: Diagnosis of axial spondyloarthritis (axSpA) is challenging and a specific laboratory diagnostic test is lacking. Previously, an axSpA cDNA phage display library, constructed from axSpA hip synovium, was screened to identify novel antibodies in early axSpA patients. This resulted in the identification of novel immunoglobulin G (IgG) and IgA antibodies to 4 Hasselt University (UH)-axSpA peptides (UH-axSpA-IgG 4, 8 and UH-axSpA-IgA 1,10), corresponding to non-physiological peptides and to a novel axSpA autoantigen, Double homeobox protein 4 (DUX4). Validation of antibody reactivity in plasma samples of early axSpA patients (disease duration < 5 years) from 2 independent cohorts revealed antibody reactivity against at least one of these 4 peptide targets in 21.1% of early axSpA patients (30/142). Here we aim to validate the diagnostic potential of these 4 antibodies in a third independent cohort of new onset axSpA patients and controls.
Methods: Using ELISA, presence of antibodies to the 4 peptides was determined in 187 serum samples of the Belgian Inflammatory Arthritis and Spondylitis (Be-Giant) cohort and 74 controls with chronic low back pain (CLBP) and 101 age and gender-matched healthy controls (HC) from the UH cohort.
Results: The presence of antibodies against the 4 UH-axSpA peptides was confirmed in the Be-Giant cohort. Antibody reactivity against this panel of 4 antigens was present in 13.4% of newly diagnosed axSpA patients (25/187) compared to 6.2% (4/65, p=0.1740) in CLBP. The positive likelihood ratio (LR+) for confirming axSpA using antibodies to these 4 peptides was 2.2, which is comparable to the currently used laboratory marker C-reactive protein (CRP) with a LR+ of 2.5. So far, no correlation between these antibodies and clinical disease characteristics could be identified.
Conclusion: The presence of antibodies to 4 UH-axSpA peptides was confirmed in the Be-Giant of newly diagnosed axSpA patients and could be of added value for axSpA diagnosis.
P. Ruytinx: None; E. Luyten: None; A. De Craemer: None; F. Van den Bosch: AbbVie, 2, 6, Amgen, 2, BMS, 6, Celgene, 6, Eli Lilly, 2, Galapagos, 2, Janssen, 2, 6, Merck, 2, 6, Novartis, 2, 6, Pfizer, 2, 6, UCB Pharma, 2, 6; D. Elewaut: AbbVie/Abbott, 6, Bristol-Myers Squibb(BMS), 5, Eli Lilly, 2, galapagos, 5, Janssen, 6; V. Somers: None.
