Objectives To study the role of interleukin 22 (IL-22) in rheumatoid arthritis (RA).
Methods IL-22 serum levels were measured in patients with early, treatment-naive RA (n=49) and in 45 age- and sex-matched healthy individuals as controls. Patients were assessed clinically and radiographically at baseline and followed up for 2 years. Correlations of IL-22 serum levels were sought with parameters of disease activity, serological markers, demographic factors and the incidence of erosions. IL-22 production by peripheral blood T cells was investigated by intracellular flow cytometry.
Results 24 of 49 patients with RA demonstrated elevated IL-22 levels compared with the range of healthy controls. At baseline, a high percentage of these patients (8/24, 33%) demonstrated bone erosions, whereas only one patient (4%) from the group with normal IL-22 had erosions. During the 2 years of follow-up, six additional patients with increased IL-22 at baseline developed erosions. In contrast, none of the patients in whom IL-22 levels were normal developed erosions despite similar treatment regimens. Multivariate regression analysis accounting for other parameters predictive for erosions, such as the presence of rheumatoid factor or anti-cyclic citrullinated peptide antibodies and disease activity, showed that elevated IL-22 baseline levels were independently and significantly associated with erosive RA. Cellular analysis demonstrated enhanced expression of IL-22 from CD4 T cells in RA.
Conclusion IL-22 is elevated in the serum of half of the patients with RA. Elevated serum IL-22 allows discrimination between patients with different radiographic progression and indicates a possible involvement of IL-22 in the pathophysiology of RA.
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JL and MS contributed equally to this work.
Funding This work was supported by the Deutsche Forschungsgemeinschaft, grants SK59/4-1, Schu 786/2-5, the Sonderforschungsbereich 571 (project D9), the Graduiertenkolleg 1202 (project E2) and by the FöFoLe programme of the medical faculty of LMU Munich.
Competing interests None.
Patient consent Obtained.
Ethics approval This study was conducted with the approval of the ethics committee University of Munich.
Provenance and peer review Not commissioned; externally peer reviewed.