Because proteinuria is most sensitive for early renal involvement and outcomes in SLE, we first compared tubulointerstitial (n = 32) and glomerular (n = 32) type I interferon mRNA expression levels available from transcriptome array datasets (IFNA1, IFNA2, IFNA4, IFNA5, IFNA6, IFNA7, IFNA8, IFNA10, IFNA13, IFNA14, IFNA16, IFNA17, and IFNA21), IFN-ω (IFNW1), and IFN-β (IFNB1) in lupus nephritis with proteinuria in lupus nephritis (Supplementary Tables S1–S3) [31,32,33,34]. The gene discussed is IFNA21; the disease is lupus nephritis.