# Anti-CD74 IgA as a potential biomarker in axial spondyloarthritis: diagnostic utility and clinical implications

## TL;DR

This study explores anti-CD74 IgA as a potential biomarker for axial spondyloarthritis, showing it can help distinguish the condition from healthy individuals and other arthritic diseases.

## Contribution

The study introduces anti-CD74 IgA as a novel biomarker for axial spondyloarthritis with high specificity for healthy controls.

## Key findings

- Anti-CD74 IgA levels were significantly higher in axial spondyloarthritis patients compared to controls.
- The biomarker showed 96.67% specificity in distinguishing axSpA from healthy individuals.
- No significant correlation was found between anti-CD74 IgA and disease activity markers.

## Abstract

Axial spondyloarthritis (axSpA) is chronic autoimmune disease affecting axial skeleton. Recently autoantibodies against CD74 have been linked to the pathogenesis of axSpA.

Investigate the diagnostic value of anti-CD74 in Egyptian axSpA patients and their relation to disease activity.

This study included 30 axSpA patients and control groups, which included 30 patients with peripheral psoriatic arthritis, and 30 healthy volunteers. disease activity was assessed using ASDAS-CRP (Ankylosing Spondylitis Disease Activity Score) and BASDAI (bath ankylosing spondylitis disease activity index) for axSpA patients. Bath ankylosing spondylitis functional index (BASFI) was used for functional assessment and mobility was assessed using Bath Ankylosing Spondylitis Metrology Index (BASMI). ESR, CRP and serum anti-CD74 IgA were evaluated.

There was no significant difference between the three studied groups regarding sex, age, and BMI. The serum levels of anti-CD74 IgA antibodies were significantly higher in axSpA patients compared to control groups.73.3, 66.6 and 3.3% of the axSpA, Peripheral psoriatic arthritis and healthy group, respectively, were anti- CD74 IgA antibody positive. Its specificity was 96.67% compared to the healthy control group, and 33.3% specificity compared to the peripheral psoriatic arthritis group. There was no significant correlation between anti-CD74 IgA antibodies and age, sex, duration of the disease, acute phase reactant, ASDAS-CRP, BASDAI, BASFI, and BASMI.

IgA anti-CD74 may be a useful marker for identifying axSpA. Further research on patients with peripheral SpA is required to determine the practical benefits of this biomarker.

Key Points

• Patients with axSpA had a significantly greater serum level of IgA anti-CD74 than controls.

• IgA Anti-CD74 had excellent discriminatory power in distinguishing axSpA from healthy controls but fair discriminatory power in distinguishing axSpA from peripheral psoriatic arthritis.

• IgA anti-CD74 wasn’t correlated with acute phase reactant or disease activity.