Session Type: Abstract Submissions (ACR)
Background/Purpose: The pathogenesis of axial spondyloarthritis (axSpA) is still unclear. Based on the strong association with HLA-B27 and ERAP-1, T cells are believed to play a major role but a role of B cells seems also possible. Autoantibodies have not been frequently found in axSpA but recently anti-CD74 antibodies with specificity to a class II-associated invariant chain peptide (CLIP) have been detected. We studied the prevalence of antibodies against CLIP (anti-CLIP-ABs) in patients with axSpA in comparison to controls and determine their sensitivity and specificity.
Methods: Sera of patients with axSpA and non-SpA were analyzed for IgG- antibodies against CD74 using an ELISA with specificity for CLIP, developed in cooperation with AESKU Diagnostics (Germany). A cut-off of ≥4 standard deviations of arbitrary units (AU) from the mean serum level was used to differentiate results. The laboratory workers were completely blinded for the clinical data.
Results: A total of 145 sera from 94 patients with axSpA and 51 with other diseases were analyzed. The patient demographics differed: axSpA patients were more often male and younger. The HLA-B27 status was available in 72 patients. Anti-CLIP-ABs were detected in 85.1% in axSpA but in only 7.8% in non-SpA patients (p£0.0001). Higher levels of anti-CLIP-ABs were found in axSpA vs. non-SpA: mean 14.5 vs. 0.8 AU (p£0.0001). The sensitivity of anti-CLIP-ABs for a diagnosis of axSpA was 85.1% and the specificity 92.2%, with a positive likelihood ratio (LR) of 10.8 and a negative LR of 0.08. The relative contribution of anti-CLIP-ABs and HLA-B27 was largely similar: 87.5% of the patients with axSpA were positive for both, but only 14.9% were anti-CLIP-negative while 23.6% were HLA-B27-negative.
Conclusion: Anti-CLIP antibodies were strongly associated with axSpA including AS. The LR for diagnosing AS was even higher than for HLA-B27. More studies using this promising new method in patients with non-radiographic axial SpA or peripheral SpA are needed to establish its usefulness in clinical practice.
N. T. Baerlecken,
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/high-prevalence-of-anti-cd-74-antibodies-with-specificity-for-the-class-ii-associated-invariant-chain-peptide-in-patients-with-axial-spondyloarthritis-but-not-in-controls/