Objective. To investigate serum levels of IL-6 and soluble IL-6 receptor (sIL-6R) in patients with large-vessel vasculitis and their relationship with disease activity.

Methods. Sera were obtained from 33 Takayasu’s arteritis (TAK) patients and 14 giant cell arteritis (GCA) patients, and from 60 age-matched normal controls (NCs). Disease activity was assessed using 18F-FDG PET/CT and clinical indices including NIH/Kerr criteria and ITAS. Among TAK patients with active disease at baseline, clinical records and serum samples from 11 TAK patients were available for the longitudinal study. IL-6 and sIL-6R serum levels were evaluated using commercial ELISA kits. Results. IL-6 and sIL-6R serum levels were significantly higher in both GCA and TAK patients compared to NCs. IL-6 levels in TAK patients were significantly increased irrespective of disease phase, while a significant increase in sIL-6R concentrations was only found in TAK patients with active disease. Conversely, in GCA, IL-6 levels were significantly raised only in patients with active diseases, whereas sIL-6R levels appeared to be significantly higher irrespective of disease activity. Longitudinal analysis showed that levels of sIL-6R in TAK patients were significantly higher only at baseline, compared to NCs, whereas IL-6 levels were found to be significantly increased at each follow-up time point. Conclusion. These overall results might suggest a role for sIL-6R as a potential biomarker for disease activity in TAK patients, whereas in GCA, modifications of IL-6 might better identify patients with active disease.