CD74 and spondyloarthropathy: 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].