Increased Type I Interferon Activity with Concurrent Plasmablast Expansion Identifies Systemic Lupus Erythematosus Patients with Poor Outcomes

Recent evidence suggests that type I interferon (IFN) activity has prognostic relevance in systemic lupus erythematosus (SLE). This study investigated whether combining IFN activity with elevated peripheral blood plasmablast (PB) levels-another key feature of lupus pathophysiology-improves risk stratification for poor clinical outcomes. Clinical data were prospectively collected at a single lupus center. Flow cytometry was performed on freshly isolated peripheral blood mononuclear cells to investigate Sialic acid-binding Immunoglobulin-like Lectin 1 (SIGLEC-1) as a surrogate marker of IFN activity, alongside CD19⁺CD20^-CD27^highHLA-DR⁺ PB frequencies. A total of 1276 samples from 121 patients were analyzed. At baseline, 48.8% of patients exhibited high IFN activity, including 27.3% with concurrent elevation in IFN and PB activity and 21.5% with isolated IFN activity. Patients with simultaneous IFN and PB activity showed higher anti-dsDNA antibody levels, were less frequently in DORIS remission (24.2% vs. 50.0%) and required higher daily prednisolone dosages (6.3 vs. 2.0 mg) than those with isolated IFN activity. During a median follow-up of 4.5 years (range 0.8-6.6), these patients experienced more flares (132 vs. 54, OR 1.42), required longer to achieve remission (median 399 vs. 140 days), and had a higher median time-adjusted prednisolone dose (5.6 vs. 3.0 mg). Concurrent elevation in IFN and PB activity identifies SLE patients with a poorer prognosis compared to isolated IFN activity. These findings suggest that combined IFN and PB assessment may improve prognostic stratification and support personalized treatment strategies in SLE.