Anti-CD74 IgA autoantibodies in radiographic axial spondyloarthritis : a longitudinal Swedish study

• Published in: Rheumatology
• Main Authors: Do, Lan, Granåsen, Gabriel, Hellman, Urban, Lejon, Kristina, Geijer, Mats, Baraliakos, Xenofon, Witte, Torsten, Forsblad-d'Elia, Helena
• Format: Article in Journal/Newspaper
• Language: English
• Published: Umeå universitet, Reumatologi 2021
• Subjects: IgA anti-CD74; outcomes research; radiographic axial spondyloarthritis ankylosing spondylitis; Rheumatology and Autoimmunity; Reumatologi och inflammation; Northern Sweden
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-191231; https://doi.org/10.1093/rheumatology/keaa882

OBJECTIVES: Antibodies against anti-CD74 are related to axial spondyloarthritis (axSpA). The objectives were (i) to study IgA anti-CD74 in radiographic (r)-axSpA patients in the Backbone cohort and to calculate the sensitivity and specificity of anti-CD74, (ii) to study the fluctuation of IgA anti-CD74 levels in prospectively collected samples, and (iii) to explore the relation between IgA anti-CD74 and radiographic spinal changes. METHODS: IgA anti-CD74 was analysed by ELISA in 155 patients with r-axSpA and age- and sex-matched controls. BASDAI, ASDAS, BASFI and BASMI were assessed and spinal radiographs were scored for r-axSpA-related changes with mSASSS. Previously donated samples, before inclusion in the Backbone study, were identified in the Medical Biobank of Northern Sweden. RESULTS: A total of 155 patients comprising 69% men and 31% women, age [mean (s.d.)] 55.5 (11.4) years and 152 (98.1%) HLA-B27 positive, were included. The plasma level of IgA anti-CD74 was significantly higher in the patients [median (interquartile range), 12.9 (7.9-17.9) U/ml] compared with controls [10.9 (7.2-14.6) U/ml, P = 0.003]. IgA anti-CD74 was above the cut-off level of 20 U/ml in 36/155 (23.2%) patients and in 15/151 (9.9%) controls (P = 0.002). Multivariable logistic regression analyses revealed ≥1 syndesmophyte associated with IgA anti-CD74 (odds ratio 5.64; 95% CI: 1.02, 35.58; P = 0.048) adjusted for hsCRP, smoking, BMI, sex and age. No distinct pattern of IgA anti-CD74 over time was revealed. CONCLUSION: Plasma levels of IgA anti-CD74 were increased in r-axSpA and independently associated with radiographic spinal changes, which suggests that IgA anti-CD74 could play a role in the pathogenies of r-axSpA.