Complement and autoantibody levels under anifrolumab therapy in SLE: implications for clinical practice

Introduction Anifrolumab (ANI), a type I interferon receptor antagonist, has demonstrated clinical efficacy in systemic lupus erythematosus (SLE). However, its effects on serological markers commonly used to assess disease activity in clinical practice remain uncertain. This study evaluated changes in complement and autoantibody levels in SLE patients treated with ANI under routine care conditions. Methods We performed a single-center retrospective analysis of SLE patients receiving ≥3 ANI infusions over a 12-month period. Clinical and serological data, including complement (C3c, C4), anti-double-stranded DNA (anti-dsDNA) antibodies, prednisone dose, and SLE Disease Activity Index 2000 (SLEDAI-2K) scores, were analyzed using mixed-effects modeling (REML). Correlations between changes in clinical SLEDAI-2K (excluding serological components) and serological markers were assessed. Results Thirteen patients (84.6% female, median age 53 years) were included. The median baseline SLEDAI-2K was 10, and 76.9% exhibited abnormal complement and/or anti-dsDNA levels. Over the treatment course (median 12 infusions), 76.9% of patients improved clinically, with a mean SLEDAI-2K reduction of 3.77 ± 2.78 points (p 0.001). Prednisone doses decreased in 38.5% of cases. Complement (C3c, p = 0.25; C4, p = 0.10) and anti-dsDNA levels (p = 0.12) remained largely unchanged. No correlations were observed between clinical SLEDAI-2K improvement and serological parameters. Discussion Anifrolumab therapy led to significant clinical improvement without corresponding serological changes, suggesting that traditional biomarkers may not adequately reflect therapeutic response. Monitoring under ANI should therefore emphasize clinical rather than serological parameters. These findings have implications for interpreting composite disease activity indices incorporating immunological markers in SLE management depending on the mechanism of action of a particular treatment.