Combined Testing of anti-CD74 IgA and Anti-UH-axSpA Antibodies Increases the Diagnostic Potential for axSpA

Kurt de Vlam¹, Pieter Ruytinx², Elien luyten², Anouk Agten², Frank Vandenabeele² and Veerle somers², ¹Department of Rheumatology, UZ Leuven, and Department of Development and Regeneration, Skeletal Biology and Engineering Research Center, KU Leuven, Leuven, Belgium, ²Universiteit Hasselt, Hasselt, Belgium

Meeting: ACR Convergence 2024

Keywords: Autoantibody(ies), Biomarkers, spondyloarthritis, Spondyloarthropathies

Session Information

Date: Saturday, November 16, 2024

Title: SpA Including PsA – Diagnosis, Manifestations, & Outcomes Poster I

Session Type: Poster Session A

Session Time: 10:30AM-12:30PM

Background/Purpose: Diagnosis of axial spondyloarthritis (axSpA) is challenging and a specific laboratory diagnostic test is lacking. Previously, we identified novel immunoglobulin G (IgG) and IgA antibodies to 4 Hasselt University (UH)-axSpA antigens (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 axSpA patients from the Leuven spondyloarthritis biologics cohort (BIOSPAR) cohort revealed antibody reactivity against at least one of these 4 peptide targets in 15.9 % of axSpA patients (26/164). In addition, IgA antibodies against CD74, involved in the assembly of and the prevention of premature peptide-binding to major histocompatibility complex (MHC) class II has been shown in patients with axSpA.

Here we aim to determine the diagnostic potential of the anti-CD74 IgA antibodies in combination with previously determined IgG and IgA antibodies against the 4 UH-axSpA antigens.

Methods: Anti-CD74 IgA antibodies were measured using the AESKULISA SpA Detect Kit (AESKU Diagnostics, Wendelsheim, Germany) in axSpA patients from the BIOSPAR cohort and patients with chronic low back pain (CLBP) served as the control group. The cut-off of the ELISA was 20 U/ml.

Results: In the BIOSPAR cohort, anti-CD74 IgA antibodies were present in 29.3% of axSpA patients (48/164) versus no presence in the CLBP patients (0/58) (p< 0.0001). Additional testing for the presence of antibodies against the 4 UH-axSpA peptides further increased the antibody reactivity in 40.2 % of the patients (66/164) and only in 3.4% of the CLBP patients (2/58) (p< 0.0001). Interestingly, we found a significant increase in age, disease duration and Bath Ankylosing Spondylitis Functional Index (BASFI) in axSpA patients who tested positive for antibodies against at least one of the 4 UH-axSpA antigens or CD74 compared to seronegative patients.

Conclusion: Combined testing for antibody reactivity against the 4 novel UH-axSpA peptides and anti-CD74 results in improved diagnosis of axSpA. Including this set of antibody reactivities increases the post-test probability for axial spondyloarthritis considerably in patients with chronic back pain

Disclosures: K. de Vlam: AbbVie, 2, 6, Amgen, 2, 5, 6, Galapagos, 2, 6, Lilly, 2, 6, 12, Paid instructor, Novartis, 2, 6, Pfizer, 2, 6, UCB, 2, 6; P. Ruytinx: None; E. luyten: None; A. Agten: None; F. Vandenabeele: None; V. somers: None.

To cite this abstract in AMA style:

de Vlam K, Ruytinx P, luyten E, Agten A, Vandenabeele F, somers V. Combined Testing of anti-CD74 IgA and Anti-UH-axSpA Antibodies Increases the Diagnostic Potential for axSpA [abstract]. Arthritis Rheumatol. 2024; 76 (suppl 9). https://acrabstracts.org/abstract/combined-testing-of-anti-cd74-iga-and-anti-uh-axspa-antibodies-increases-the-diagnostic-potential-for-axspa/. Accessed .

ACR Meeting Abstracts - https://acrabstracts.org/abstract/combined-testing-of-anti-cd74-iga-and-anti-uh-axspa-antibodies-increases-the-diagnostic-potential-for-axspa/