Arid2 promotes Follicular B-cell differentiation and antibody responses in vivo
SWI/SNF chromatin remodeling complexes, also known as BAF complexes, regulate gene expression during development and differentiation.  These complexes exist in distinct variants, including the polybromo-associated BAF (PBAF) complex, defined by the ARID2 core subunit. ARID2 is frequently mutated in B cell leukemias, but its role in normal B cell development remains unknown. Using conditional knockout mice, we show that Arid2 deletion impairs B cell differentiation in vivo. Mb1-Cre–mediated deletion, active in early progenitors, caused a marked reduction of splenic and circulating Follicular B cells, whereas CD19-Cre deletion produced a milder phenotype. These defects were not due to altered proliferation or survival but reflected impaired differentiation potential.  Transcriptomic profiling of isolated pro-B, pre-B, and Follicular B cells revealed that Arid2 loss disrupts stage-specific gene expression programs, with cumulative downregulation of B cell receptor signaling and altered lineage-specifying pathways.  Functionally, Arid2-deficient mice exhibited impaired germinal center expansion after immunization and reduced IgG antibody production. Together, these findings identify Arid2 as a critical regulator of B cell differentiation and maturation by coordinating transcriptional programs during early lymphopoiesis. Overall design: RNA sequencing performed on B cell progenitors harvested from the bone marrow and follicular B cells harvested from the spleen of the indicated genoetypes.  Cells were isolated by FACS and processed from RNA sequencing.