C3 and systemic lupus erythematosus: We performed a multivariable linear regression model with plasma log-NfL concentrations as the outcome, age as the adjusting variable, and the following exploratory variables: SLICC/ACR-DI ≥1, low complement C3, plasma creatinine, ongoing treatment with glucocorticoids, non-antimalarial DMARDs and anti-hypertensive treatment, and a history of anti-dsDNA-positivity or renal involvement according to SLICC Classification Criteria for SLE.