Development of chronic allergic responses by dampening Bcl6-mediated suppressor activity in memory T helper 2 cells

Abstract

Mice deficient in the transcriptional repressor B-cell CLL/lymphoma 6 (Bcl6) exhibit similar T helper 2 (TH2) immune responses as patients with allergic diseases. However, the molecular mechanisms underlying Bcl6-directed regulation of TH2 cytokine genes remain unclear. We identified multiple Bcl6/STAT binding sites (BSs) in TH2 cytokine gene loci. We found that Bcl6 is modestly associated with the BSs, and it had no significant effect on cytokine production in newly differentiated TH2 cells. Contrarily, in memory TH2 (mTH2) cells derived from adaptively transferred TH2 effectors, Bcl6 outcompeted STAT5 for binding to TH2 cytokine gene loci, particularlyInterleukin4(Il4) loci, and attenuated GATA binding protein 3 (GATA3) binding to highly conserved intron enhancer regions in mTH2 cells. Bcl6 suppressed cytokine production epigenetically in mTH2 cells to negatively tune histone acetylation at TH2 cytokine gene loci, includingIl4loci. In addition, IL-33, a pro-TH2 cytokine, diminished Bcl6’s association with loci to which GATA3 recruitment was inversely augmented, resulting in altered IL-4, but not IL-5 and IL-13, production in mTH2 cells but no altered production in newly differentiated TH2 cells. Use of a murine asthma model that generates high levels of pro-TH2 cytokines, such as IL-33, suggested that the suppressive function of Bcl6 in mTH2 cells is abolished in severe asthma. These findings indicate a role of the interaction between TH2-promoting factors and Bcl6 in promoting appropriate IL-4 production in mTH2 cells and suggest that chronic allergic diseases involve the TH2-promoting factor-mediated functional breakdown of Bcl6, resulting in allergy exacerbation.

Thymic stromal lymphopoietin drives the development of IL-13 + Th2 cells

“…However, how these tissue-derived factors mediate their effect on the evolving Th2 response is not well understood. IL-33 was recently found to promote Th2 effector activity by suppressing BCL6 expression in Tfh cells, in turn de-repressing IL-4 transcription ( 12 ). This mechanism of action is compatible with the known expression of the IL-33 receptor ST2 on activated Th2 cells ( 13 ).…”

Allergic TH2 Response Governed by B-Cell Lymphoma 6 Function in Naturally Occurring Memory Phenotype CD4+ T Cells

“…Bcl6- transgenic (TG) mice with exogenous Bcl6 under Lck proximal promoter control ( 17 , 30 ), Bcl6 -KO mice ( 31 ), and highly conserved intron enhancer (hcIE)-KO mice on a BALB/c background (Japan SLC) were described previously ( 15 ). CNS2-green fluorescent protein (GFP)-TG mice were gifted by Dr. Masato Kubo ( 28 ).…”

“…In addition to primary TCR-mediated stimulation with OVA, stimulation with soluble anti-CD3 (2 µg/mL) and anti-CD28 mAbs (2 µg/mL) was employed for some experiments. For T H 1 or T H 2 polarization, cells were cultured in the presence of rIL-12 (100 U/mL)/anti-IL-4 mAb (5 µg/mL) or rIL-4 (1,000 U/mL)/anti-IL-12 mAb (10 µg/mL), as previously described ( 15 ). In some experiments, anti-IL-4 mAbs or anti-IFN-γ mAbs were added to the T H 0 condition cultures.…”

“…Bcl6-binding DNA sequences resemble STAT protein-bound motifs ( 10 ), indicating that Bcl6 may repress T H 2 cytokine expression by competitively inhibiting the binding of STAT factors to GAS sites in target genes ( 5 , 11 – 13 ), including T H 2 cytokine gene loci ( 14 ). We previously identified Bcl6/STAT-binding sequences (BSs) ( 15 ) in CNS1 (BS1), IL-4 promoter region (BS2), and DNase hypersensitive site 2 (HS2) (BS3, BS4) and HS3 (BS5, BS6) in intron two and the 3′ region of CNS2 (BS7) in the Il4 locus; BSIL5 sequences in the Il5 locus ( 14 ); and BSIL13 sequences in the Il13 locus. We, furthermore, reported that Bcl6 repressed Il4 and Il5 expression by binding to genomic DNA in naïve CD4 + T cell-derived memory (NAM) T H 2 cells ( 14 , 15 ), identifying Bcl6 as a critical regulator of T H 2 cytokine production in memory CD4 + T cells in addition to its role in the maintenance and survival of the cells ( 15 – 17 ).…”

“…We previously identified Bcl6/STAT-binding sequences (BSs) ( 15 ) in CNS1 (BS1), IL-4 promoter region (BS2), and DNase hypersensitive site 2 (HS2) (BS3, BS4) and HS3 (BS5, BS6) in intron two and the 3′ region of CNS2 (BS7) in the Il4 locus; BSIL5 sequences in the Il5 locus ( 14 ); and BSIL13 sequences in the Il13 locus. We, furthermore, reported that Bcl6 repressed Il4 and Il5 expression by binding to genomic DNA in naïve CD4 + T cell-derived memory (NAM) T H 2 cells ( 14 , 15 ), identifying Bcl6 as a critical regulator of T H 2 cytokine production in memory CD4 + T cells in addition to its role in the maintenance and survival of the cells ( 15 – 17 ). Conversely, T follicular helper (T FH ) cell differentiation may result from Bcl6-mediated suppression of the differentiation of other T H cell lineages in vivo ( 18 – 20 ).…”