CD40 stimulation leads to NF-B-mediated upregulation of IRF4 (13), which in turn represses transcription (61)

CD40 stimulation leads to NF-B-mediated upregulation of IRF4 (13), which in turn represses transcription (61). and OCT2, are critical for GC formation (15C18). Mice deficient in (encoding OCT2), (encoding OBF1) or both showed complete lack of GCs (19). The underlying molecular mechanism is not clear yet, and the target genes of OBF1/OCT2 in the context of the germinal center reaction are largely unknown, although Spi-B which itself is required for GCs (20, 21) has been identified as a downstream target of OBF1 (22). Moreover, in CD4+ T cells OBF1 and OCT1/OCT2 directly bind to the promoter region of and activate its transcription, thereby promoting the development of TFH cells (23). The putative role of these factors in regulating expression in early GC B cells remains to be investigated. BCL6 is a zinc finger TF that is essential for germinal center formation, as by CD19cre which deletes from early B cells onwards LEP leads to impaired GC formation (26). In contrast, once GCs have formed or initiated, IRF4 is no longer needed, as conditional knockout by C1cre which deletes in already formed GC cells has minimal effects on GC differentiation (27). These results suggest that IRF4 is required for the very early phase upon T-cell-dependent antigen stimulation. Additional evidence supporting this idea is the rapid upregulation of IRF4 following BCR stimulation (28). Moreover, IRF4 is involved in modulating the expression of BCL6 and OBF1, which both are key factors for GC initiation (3, 26). Taken together, IRF4 plays an important role in the early initiation phase of GC formation, possibly by regulating the induction of and (encoding the Bcl-xL protein) and several cell cycle related genes (34). Specific deletion of in B cells leads to reduced proliferation and increased cell apoptosis upon anti-IgM stimulation. However, the responses are normal in the case of LPS, CD40, IL4, BAFF and RP105 stimulations. By histological examination, reduced number of GC follicules are observed in the spleens of transcription by binding to the regulatory region 1 kb upstream of the gene transcription start site (35). Mutation of the MEF2B binding motif in the gene promoter abrogates transcription activity in cotransfection assays in 293T cells. Furthermore, knockdown of MEF2B protein by shRNAs leads to downregulation of BCL6 and upregulation of BCL6 target genes. These data suggest that MEF2B plays an important role in early GC formation by modulating expression (35, 36). BATF is a transcription factor of the AP-1 family, which is LY2940680 (Taladegib) involved in GC structure establishment and class switch recombination. and by C1cre leads to impaired GCs (39). GC development The dark zone and the light zone of the GC are organized by the expression of the chemokine receptors CXCR4 and CXCR5, respectively (40). Thus, one can expect that TFs critical for CXCR4 and CXCR5 expression will be important for GCs. GC dark zone The germinal LY2940680 (Taladegib) center LY2940680 (Taladegib) DZ is characterized LY2940680 (Taladegib) by an interconnected network of CXCL12 expressing reticular cells and compactly filled with rapidly proliferating centroblasts (41). FOXO1 is highly expressed in human and mouse GC B cells, and its expression is largely specific to DZ B cells (with also some expression in na?ve B cells) (42). Like in gene. By binding to the promoter region, FOXO1 and BCL6 maintain the germinal center DZ program (42). specifically in GC B cells leads to a significant decrease in the number of DZ B cells, and elevated cell apoptosis (44). Somatic hypermutation (SHM) SHM generates a wide repertoire of affinities toward specific antigens, and mainly takes place in the DZ (45), although some extrafollicular SHM has been reported in transgenic mice deficient in the ability to establish GCs (46). AID, encoded by the gene, is the enzyme responsible for SHM and class switch recombination (47, 48). AID deaminates cytidines in DNA (49C54), followed.