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The levels of transcription factor Ets1 are high in resting B and T cells, but are downregulated by signaling through antigen receptors and Toll-like receptors (TLRs). Loss of Ets1 in mice leads to excessive immune cell activation and development of an autoimmune syndrome and reduced Ets1 expression has been observed in human PBMCs in the context of autoimmune diseases. In B cells, Ets1 serves to prevent premature activation and differentiation to antibody-secreting cells. Given these important roles for Ets1 in the immune response, stringent control of Ets1 gene expression levels is required for homeostasis. However, the genetic regulatory elements that control expression of the Ets1 gene remain relatively unknown. Here we identify a topologically-associating domain (TAD) in the chromatin of B cells that includes the mouse Ets1 gene locus and describe an interaction hub that extends over 100?kb upstream and into the gene body. Additionally, we compile epigenetic datasets to find several putative regulatory elements within the interaction hub by identifying regions of high DNA accessibility and enrichment of active enhancer histone marks. Using reporter constructs, we determine that DNA sequences within this interaction hub are sufficient to direct reporter gene expression in lymphoid tissues of transgenic mice. Further analysis indicates that the reporter construct drives faithful expression of the reporter gene in mouse B cells, but variegated expression in T cells, suggesting the existence of T cell regulatory elements outside this region. To investigate how the downregulation of Ets1 transcription is associated with alterations in the epigenetic landscape of stimulated B cells, we performed ATAC-seq in resting and BCR-stimulated primary B cells and identified four regions within and upstream of the Ets1 locus that undergo changes in chromatin accessibility that correlate to Ets1 gene expression. Interestingly, functional analysis of several putative Ets1 regulatory elements using luciferase constructs suggested a high level of functional redundancy. Taken together our studies reveal a complex network of regulatory elements and transcription factors that coordinate the B cell-specific expression of Ets1.

BackgroundCNS stromal cells, especially fibroblasts and endothelial cells, support leukocyte accumulation through upregulation of adhesion molecules and lymphoid chemokines. While chronically activated fibroblast networks can drive pathogenic immune cell aggregates known as tertiary lymphoid structures (TLS), early stromal cell activation during CNS infection can support anti-viral T cells. However, the cell types and factors driving early stromal cell activation is poorly explored.AimsA neurotropic murine coronavirus (mCoV) infection model was used to better characterize signals that promote fibroblast networks supporting accumulation of antiviral lymphocytes. Based on the early appearance of IgD+ B cells with unknown functions during several CNS infections, we probed their potential to activate stromal cells through lymphotoxin ¦Â (LT¦Â), a molecule critical in maintaining fibroblast-networks in lymphoid tissues as well as promoting TLS in autoimmunity and cancers.ResultsKinetic analysis of stromal cell activation in olfactory bulbs and brains revealed that upregulation of adhesion molecules and lymphoid chemokines Ccl19, Ccl21 and Cxcl13 closely tracked viral replication. Immunohistochemistry revealed that upregulation of the fibroblast marker podoplanin (PDPN) at meningeal and perivascular sites mirrored kinetics of RNA expression. Moreover, both B cells and T cells colocalized to areas of PDPN reactivity, supporting a potential role in regulating stromal cell activation. However, specific depletion of LT¦Â from B cells using Mb1-creERT2 x Lt¦Âfl/fl mice had no effect on T or B cell recruitment or viral replication. B cell depletion by anti-CD20 antibody also had no adverse effects. Surprisingly, LT¦ÂR agonism reduced viral control and parenchymal T cell localization despite increasing stromal cell lymphoid chemokines and PDPN. Additional assessment of direct stromal cell activation by the viral RNA mimic poly I:C showed induction of Pdpn and Ccl19 preceding Ltb.ConclusionsNeither B cell-derived LT¦Â or B cells are primary drivers of stromal cell activation networks in the CNS following mCoV infection. Although supplementary agonist mediated LT¦ÂR engagement confirmed a role for LT¦Â in enhancing PDPN and lymphoid chemokine expression, it impeded T cell migration to the CNS parenchyma and viral control. Our data overall indicate that stromal cells can integrate LT¦ÂR signals to tune their activation, but that LT¦Â is not necessarily essential and can even dysregulate protective antiviral T cell functions.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12974-025-03491-7.

Affinity maturation and differentiation of B cells in the germinal center (GC) are tightly controlled by epigenetically regulated transcription programs, but the underlying mechanisms are only partially understood. Here we show that Cfp1, an integral component of the histone methyltransferase complex Setd1A/B, is critically required for GC responses. Cfp1 deficiency in activated B cells greatly impairs GC formation with diminished proliferation, somatic hypermutation and affinity maturation. Mechanistically, Cfp1 deletion reduces H3K4me3 marks at a subset of cell cycle and GC-related genes and impairs their transcription. Importantly, Cfp1 promotes the expression of transcription factors MEF2B and OCA-B and the Bcl6 enhancer-promoter looping for its efficient induction. Accordingly, Cfp1-deficient GCB cells upregulate IRF4 and preferentially differentiate into plasmablasts. Furthermore, Cfp1 ablation upregulates a panel of pre-memory genes with elevated H3K4me3 and leads to markedly expanded memory B populations. In summary, our study reveals that Cfp1-safeguarded epigenetic regulation ensures proper dynamics of GCB cells for affinity maturation and prevents the pre-mature exit from GC as memory cells. Cellular differentiation decisions, such as fates of B cells following entry into the germinal centres, are governed by epigenetically and transcriptionally regulated paths for bifurcating cell fates. Here the authors show that CFP1 is a master epigenetic regulator of activated B cells and controls their hypermutation and affinity maturation via the histone methyltransferase complex Setd1A/B.