c-Rel gain in B cells dose-dependently drives germinal center reactions and autoantibody production in mice

Single nucleotide polymorphisms and locus amplification link the NF-?B transcription factor c-Rel to human autoimmune diseases and B cell lymphomas, respectively. However, the functional consequences of enhanced c-Rel levels remain enigmatic. Here, we overexpress c- Rel specifically in mouse B cells from BAC-transgenic gene loci and demonstrate that c-Rel protein levels linearly dictate expansion of germinal center (GC) B cells and isotype-switched plasma cells. c-Rel expression in B cells of otherwise c-Rel-deficient mice fully rescues terminal B cell differentiation, underscoring its critical B cell-intrinsic roles. Unexpectedly, in GC B cells transcription-independent regulation produces the highest c-Rel protein levels amongst B cell subsets. In c-Rel overexpressing GC B cells this causes enhanced nuclear translocation, a profoundly altered transcriptional program and increased proliferation. Finally, we provide the first link between c-Rel gain and autoimmunity by showing that c-Rel overexpression in B cells causes autoantibody production and renal immune complex deposition. Overall design: For RNA sequencing experiments 8 mice per genotype were immunized i.p. with SRBC. Desired splenocyte populations were pre-separated by MACS followed by flow-cytometry- based cell sort of 1000 cells per sample into 96-well-plates containing TCL buffer (Qiagen) (naïve B cells: pre-MACS IgD+CD43+, sort IgDhiIgMlo; GC B cells: pre-MACS IgD-CD43-, sort B220+IgD-CD38loCD95hiGL7+; PC: pre-MACS CD138+, sort B220loCD138+).