To gain mechanistic insight into the capacity of neutralizing anti-IFN-Abs to reduce downstream IFN-I signaling, we compared the IFN-I composite score,33 a cumulative measure of mRNA expression of four individual ISGs, MX1, MCL1, IRF9, and STAT1 (see STAR Methods), in patients with SLE with and without anti-IFN-Abs and controls. Here, IRF9 is linked to systemic lupus erythematosus.