IRF7 controls spontaneous autoimmune germinal center and plasma cell checkpoints.

How IRF7 promotes autoimmune B cell responses and systemic autoimmunity is unclear. Analysis of spontaneous SLE-prone mice deficient in IRF7 uncovered the IRF7 role in regulating autoimmune germinal center (GC), plasma cell (PC), and autoantibody responses and disease. IRF7, however, was dispensable for foreign antigen-driven GC, PC, and antibody responses. Competitive bone marrow (BM) chimeras highlighted the importance of IRF7 in hematopoietic cells in spontaneous GC and PC differentiation. Single-cell RNAseq of SLE-prone B cells indicated IRF7-mediated B cell differentiation through GC and PC fates. Mechanistic studies revealed that IRF7 promoted B cell differentiation through GC and PC fates by regulating the transcriptome, translation, and metabolism of SLE-prone B cells. Mixed BM chimeras demonstrated a requirement for B cell-intrinsic IRF7 in IgG autoantibody production but not in the regulation of spontaneous GC and PC responses. Altogether, we delineate previously unknown B cell-intrinsic and -extrinsic mechanisms of IRF7-promoted spontaneous GC and PC responses, loss of tolerance, autoantibody production, and SLE development.