Role of SWEF proteins in ABC differentiation

Age/autoimmune-associated B cells (ABCs) are a T-bet dependent B cell subset, which accumulates prematurely in autoimmune settings. The molecular pathways that regulate ABCs in autoimmunity are largely unknown. The SWEF proteins include SWAP-70 and DEF6, a newly identified SLE risk variant. SWEF-deficient mice (double knock-out=DKO) develop a lupus like syndrome, which is accompanied by a marked expansion of ABCs. The accumulation of ABCs in DKO mice provided us with a unique opportunity to gain new insights into the molecular features that characterize the ABCs that prematurely expand in autoimmune conditions. Splenic Follicular B cells (FoB, B220+CD19+CD23+CD11c-CD11b-) and ABCs (B220+CD19+CD11c+CD11b+) were FACS sorted from >20 weeks old WT or DKO female mice and RNA-seq was employed to compare the transcriptome of DKO ABCs to that of FoB cells derived from either WT or DKO mice. Here we show that loss of SWEF proteins leads to altered gene expression in B cells independently of their differentiation state. In addition, a subset of genes was uniquely regulated in ABCs from DKO mice as compared to FoB cells from either WT or DKO mice. Ananlysis of the ATAC-seq experiment show that the ABCs that expand aberrantly in the DKO autoimmune setting exhibit a unique chromatin landscape and ABC-specific accessible loci displayed enrichment in AP-1/BATF, IRF, and T-bet binding motifs. Together our findings suggest that absence of SWEF proteins affects several key processes in ABCs. In particular, we observed alterations in a number of pathways involved in the control of cellular proliferation and inflammation, a finding that may play a crucial role in the premature accumulation of ABCs in DKOs and could distinguish them from non-autoimmune ABCs. 1. Examination of Follicular B cells transcriptome in B cells isolated from WT or DEF6-/-SWAP70-/- (DKO) mice. 2. Examination of Follicular B cells and ABC transcriptome in DEF6-/-SWAP70-/- (DKO) mice. 3. Analysis of chromatin landscape in Follicular B cells and ABC cells from DEF6-/-SWAP70-/- (DKO) mice by ATAC-seq