Background/Purpose:

Spondyloarthritis (SpA) is a common debilitating inflammatory disorder. The pathogenesis of axial spondyloarthritis (axSpA) including ankylosing spondylitis (AS), although known to be strongly associated with genes such as the human leukocyte antigen HLA-B27, is still largely unclear. Establishing the diagnosis is difficult, since abnormalities in conventional X-rays develop with a latency of several years and only HLA-B27 is used as a laboratory marker. Additionally, the presence of radiographic sacroiliitis is now essential for the diagnosis of SpA. Furthermore, to prevent destructive effects of the disease, early diagnosis and intervention in patients with SpA may be important. Therefore, the goal of our study was to evaluate antibodies to the human leukocyte antigen class II-associated invariant chain peptide (anti-CD74) as a diagnostic marker of SpA.

Methods:

Sera of SpA and non-SpA patients were analyzed for IgA and IgG antibodies against CD74 by ELISA. Sera for the ELISA were obtained from 117 patients with axial SpA. Sera of 38 blood donors served as controls. All donors provided informed consent for the study, which was approved by the local ethics committee (project number 4928).

Results:

We analyzed 155 sera from 117 SpA and 38 non-SpA patients. SpA patients were more often male and younger. HLA-B27 status was available in 112 patients. Anti-CD74 antibodies were detected in 85.1% of the SpA patients but only in 5% of the non-SpA patients (p≤0.0001). The detection of both IgG and IgA anti-CD74 antibodies for diagnosing SpA revealed a sensitivity of 77% and a specificity of 90%. Remarkably, IgA autoantibodies against CD74 alone had a sensitivity of 67% and a specificity of 95%, the likelihood ratio (LR) LR+ was 12.7 and LR- was 0.35. Moreover, IgA anti-CD74 antibodies were even more frequent in SpA patients with short disease duration and significantly correlate with more advanced radiological sacroiliitis and reduced spinal mobility.

Conclusion:

Anti-CD74 IgA antibodies were strongly associated with SpA. Antibodies against CD74 could provide an important additional tool for diagnosis of SpA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/autoantibodies-against-cd74-a-new-diagnostic-marker-for-spondyloarthritis-spa/