IFNA1 and systemic lupus erythematosus: In this retrospective longitudinal study, in order to determine the relationship of systemic IFN activity with clinical phenotypes, disease activity, and damage accrual in SLE, we measured serum IFN activity by WISH assay, a sensitive and quantitative bioassay for IFN [5, 22], and examined the link between serum IFN activity and 10 domains and their 21 individual items of the 2019 European League Against Rheumatism/American College of Rheumatology classification criteria for SLE (EULAR/ACR-2019 criteria) [23] in treatment-naive SLE patients.