Page 86 - Recognizing axial spondyloarthritis - Janneke de Winter

CHAPTER FIVE
Figure 1. Anti-CD74 IgA antibody levels measured in serum from participants in the SPondyloArthritis Caught Early (SPACE) cohort. Axial spondyloarthritis (axSpA) (diagnosis), participants in SPACE who were diagnosed with axSpA by a rheumatologist at baseline; CBP, patients with chronic back pain. One data point is outside the axis limits.
DISCUSSION
The results of our study suggest that 1) serum anti-CD74 IgG and IgA antibodies are elevated in patients with AS vs. healthy controls, 2) serum anti-CD74 IgG antibodies are not elevated in patients with early axSpA vs. CBP patients, 3) serum anti-CD74 IgA antibody levels are elevated in patients with early axSpA vs. CBP patients, but 4) serum anti-CD74 IgA antibodies have no diagnostic value in early back pain patients because of small numerical differences.
Previous studies showed that anti-CD74 IgG antibodies were present in 69% and 85% of patients with (mostly radiographic) axSpA (7,8) in comparison with 6% and 8% in control populations of non-axSpA, non-back pain individuals. Somewhat lower numbers were obtained in the current study when assessing patients with radiographic axSpA in the SPACE cohort, as 54.5% had anti-CD74 IgG antibodies (data not shown). However, our study revealed two novel pieces of information. First, the percentage of patients with non-radiographic axSpA being positive for anti-CD74 IgG antibodies was lower (43.9%), suggesting that either the antibodies may develop over time or that they are associated with radiographic sacroiliitis rather than with the diagnosis of axSpA per se. Second, the percentage of control patients having elevated anti-CD47 IgG antibodies (47.9%) was much
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