ANTIBODIES TO TWO NOVEL PEPTIDES IN NEW ONSET AXIAL SPONDYLOARTHRITIS

Background: Diagnosis of axial spondyloarthritis (axSpA) is challenging since clinical manifestations often overlap with other disorders and a specific laboratory test for diagnosis is lacking. Previously, we identified antibodies to 3 Hasselt University (UH)-axSpA peptides which could provide a novel tool for diagnosis of a subset of axSpA patients. Validation of antibody reactivity in plasma samples of early axSpA patients (disease duration < 5 years) from the UH and the Leuven Spondyloarthritis (Biologics) Cohort ((Bio)SPAR) cohorts revealed antibody reactivity against at least one of these 3 peptide targets in 14.2% of early axSpA patients (22/155) . Objectives: We aim to validate the diagnostic potential of the antibodies to these 3 peptides in a third independent cohort of new onset axSpA patients and controls. Methods: Using enzyme-linked immunosorbent assays (ELISA), presence of antibodies to the 3 peptides was determined in 188 serum samples of the Belgian Inflammatory Arthritis and Spondylitis (Be-Giant) cohort, 74 controls with nonspecific chronic low back pain (CLBP) and 112 age and gender-matched healthy controls from the UH cohort. Patients were classified as having axSpA according to the ASAS classification criteria and had a mean age of 32.7 years. We further investigated whether clinical and disease characteristics were correlated with antibody reactivity. Results: The presence of antibodies against 2 of the 3 UH-axSpA peptides was confirmed in the Be-Giant cohort. Antibody reactivity against 1 of the 2 UH-axSpA peptides was found in 11.2 % of newly diagnosed axSpA patients (21/188) compared to 3.6% (4/112, p=0.0290 ) in HC and 6.8% (5/74, p=0.3619 ) in CLBP. We did not detect a significant difference in age, sex, HLA–B27 status, enthesitis, symptom duration, treatment, Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), BathAnkylosing Spondylitis Functional Index (BASFI), erythrocyte sedimentation rate (ESR), or C-reactive protein (CRP) levels between axSpA patients with and those without antibody reactivity against these 2 UH-axSpA peptides. Conclusion: The presence of antibodies to 2 UH-axSpA peptides was confirmed in an independent cohort of newly diagnosed axSpA patients and could be of added value for discriminating axSpA patients from HC in the Be-Giant cohort. REFERENCES: [1]Quaden D, Vandormael P, Ruytinx P, Geusens P, Corten K, Vanhoof J, et al. Antibodies against three novel peptides in early axial spondyloarthritis patients from two independent cohorts. Arthritis & rheumatology (Hoboken, NJ). 2020. Disclosure of Interests: None declared Citation: , volume 81, supplement 1, year 2022, page 799Session: Spondyloarthritis - clinical aspects (other than treatment) (POSTERS only)