IRF1 and myositis disease: To verify that the IFNPS we identified is reflecting type I IFN– and not type II IFN–associated biology, we first measured the correlation between IFNPS and transcription of several components of IFN-γ–inducible gene signatures, IRF1, CXCL9, and SLAMF839,41, and found no correlation between the IFNPS and these genes in samples from patients with either SLE or myositis.