Autoantibodies against interleukin-1 receptor antagonist in Still’s disease in adult patients, data from a multicenter cohort study

Objectives Emerging evidence supports the presence of autoantibodies targeting interleukin-1 receptor antagonist (IL-1Ra), a regulator of IL-1 signaling, in adult-onset Still’s disease (AOSD). However, existing data are limited by small cohorts and potential confounding due to prior exposure to IL-1 inhibitors. This study aimed to develop a simple and reproducible indirect ELISA for detecting anti-IL-1Ra antibodies and to assess their frequency and immunological features in IL-1 inhibitor-naïve AOSD patients. Methods Serum samples from IL-1 inhibitor-naïve AOSD patients (n=46) and healthy controls (n=26) were analyzed using an indirect ELISA based on recombinant IL-1Ra (anakinra) as antigen. Specificity was confirmed by dot blot. Anti-IL-1Ra IgG were affinity-purified from a high-titer patient and characterized by ELISA and SDS-PAGE. Epitope mapping was performed using phage display peptide libraries, followed by sequence alignment and structural mapping onto native IL-1Ra. Results Anti-IL-1Ra antibody levels were significantly higher in AOSD patients than in healthy controls (p=0.003), with a greater proportion showing high titers (p