The IFN gene signature is a known feature of human SLE, although it does not correlate well with overall disease severity.26 Stratification of ISM‐high patients is possible using qPCR assays to monitor expression of three genes in peripheral blood,26 which in our stratification corresponded to C2 and C4 (Figures 2b and 4h–l). Here, C4A is linked to systemic lupus erythematosus.