Abstract
BackgroundAnti-CD74 IgG antibodies are reported to be elevated in patients with axial spondyloarthritis (axSpA). This study assessed the diagnostic value of anti-CD74 antibodies in patients with early axSpA.MethodsAnti-CD74 IgG and IgA antibodies were first measured in an exploratory cohort of patients with radiographic axSpA (138 patients with ankylosing spondyloarthritis (AS)) and 57 healthy controls and then were measured in patients with early axSpA (n = 274) and with non-SpA chronic back pain (CBP) (n = 319), participating in the spondyloarthritis caught early (SPACE) prospective cohort study of patients under 45 years old with early back pain (for ≥ 3 months, but ≤ 2 years).ResultsIn the exploratory cohort, anti-CD74 IgG antibodies were present in 79.7% of patients with AS vs. 43.9% of healthy controls (p < 0.001). Anti-CD74 IgA antibodies were present in 28.5% of patients with AS vs. 5.3% of healthy controls (p < 0.001). In the SPACE cohort, anti-CD74 IgG antibody levels were present in 46.4% of the patients with axSpA vs. 47.9% of the patients with CBP (p = 0.71). Anti-CD74 IgA antibodies were present in 54.7% of the patients with axSpA and 37.0% of the patients with CBP (p < 0.001). This resulted in a positive predictive value of 58.8% (compared to a prior probability of 46.2%) and a negative predictive value of 59.1% (compared to a prior probability of 53.8%). In a regression model, total serum IgA was associated with axSpA odds ratio (OR) 1.19, p < 0.001) whereas anti-CD74 IgA was not (OR) 1.01, p = 0.33). Furthermore, anti-CD74 IgA was associated with sacroiliitis on magnetic resonance imaging (MRI) (OR) = 2.50, p = 0.005) and heel enthesitis (OR) = 2.56, p = 0.002).ConclusionsAlbeit anti-CD74 IgA is elevated in patients with early axSpA, this elevation is not sufficiently specific to yield significant diagnostic value in patients under 45 years old presenting with early back pain.
Highlights
Anti-CD74 IgG antibodies are reported to be elevated in patients with axial spondyloarthritis
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 axial spondyloarthritis (axSpA) and patients with chronic back pain (CBP) from a cohort of patients with early back pain, the spondyloarthritis caught early (SPACE) cohort
Anti-CD74 IgA antibodies Because anti-CD74 IgG antibodies did not have diagnostic value in the SPACE cohort, we explored the level, prevalence and diagnostic value of anti-CD74 IgA antibodies, as earlier research shows that total serum IgA is elevated in axSpA [12, 16] and that IgA is produced at mucosal surfaces, including the gut, which may be inflamed in spondyloarthritis [17]
Summary
Anti-CD74 IgG antibodies are reported to be elevated in patients with axial spondyloarthritis (axSpA). CD74, known as the HLA class II γ-chain or invariant chain, de Winter et al Arthritis Research & Therapy (2018) 20:38 is involved in the assembly of major histocompatibility complex II and in preventing premature peptide binding [9]. The first cross-sectional study showed that antiCD74 IgG antibodies were present in 67% of the 216 tested patients with axSpA, compared to 6% of 285 nonSpA 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 patients with axSpA and in 8% of the 51 patients without SpA [7]
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