Page 79 - Recognizing axial spondyloarthritis - Janneke de Winter

ANTI-CD74 ANTIBODIES IN EARLY AXIAL SPA
BACKGROUND
Axial spondyloarthritis (axSpA) is a prevalent form of chronic inflammatory arthritis, affecting 0.5-1.5% of the Western population (1,2). Current biological disease markers in axSpA (human leukocyte antigen (HLA)-B27, C-reactive protein (CRP), sacroiliitis shown on radiograph or magnetic resonance imaging (MRI)) show insufficient diagnostic properties to rely on for making a diagnosis, impeding early diagnosis and treatment. Although the diagnostic delay decreased over the past years as a result of modern imaging techniques and more awareness for axSpA, the current diagnostic delay from five to ten years (3–6) prevents treatment in an early disease phase.
Two recent studies provided preliminary evidence that anti-CD74 antibodies were elevated in SpA (7,8). CD74, also known as the HLA class II γ-chain or invariant chain, is involved in the assembly of major histocompatibility complex II and in preventing premature peptide binding (9). The extracellular part has two different domains, thyroglobulin type-1 and class II-associated invariant chain peptide (CLIP). Binding of antibodies to CD74 may lead to activation of cells and production of proinflammatory cytokines such as tumour necrosis factor α (TNFα) (10). A first cross-sectional study showed that anti-CD74 IgG antibodies were present in 67% of the 216 tested patients with axSpA, compared to 6% of 285 non-SpA controls (blood donors or patients with diseases other than axSpA) (8). The second study showed that IgG anti-CD74 antibodies were detected in 85% of the 145 axSpA patients and in 8% of the 51 non-SpA patients (7).
Although indicating the potential importance of anti-CD74 IgG antibodies in axSpA, the role of anti-CD74 antibodies in a diagnostic setting is still not confirmed. Therefore, the aim of this study was to test the level and diagnostic value of anti-CD74 IgG and IgA antibodies in a ‘real life’ diagnostic setting using patients with axSpA and chronic back pain (CBP) patients from an early back pain cohort, the SPondyloArthritis Caught Early (SPACE) cohort,
METHODS
Exploratory cohort: patients with radiographic axSpA and healthy controls
Sera from patients with radiographic axSpA (ankylosing spondyloarthritis (AS)) were collected in the Academic Medical Center/University of Amsterdam (n=21) and the Medical University of Hannover (n=117). All AS patients were diagnosed by a rheumatologist with AS and fulfilled the modified New York (mNY) criteria for AS. Sera from healthy controls were collected in the Academic Medical Center/ University of Amsterdam (n=19) and the Medical University of Hannover (n=38). All AS patients and healthy controls gave their written informed consent and the studies were approved by the local ethics committees of the Academic Medical Center/University of Amsterdam and the Medical University of Hannover. Serum samples were stored for at least 6 months by -80°C.
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