Mammals co-exist with resident microbial ecosystem that is composed of an incredible number and diversity of bacteria, viruses and fungi. Owing to direct contact between resident microbes and mucosal ...surfaces, both parties are in continuous and complex interactions resulting in important functional consequences. These interactions govern immune homeostasis, host response to infection, vaccination and cancer, as well as predisposition to metabolic, inflammatory and neurological disorders. Here, we discuss recent studies on direct and indirect effects of resident microbiota on regulatory T cells (T
regs
) and Th17 cells at the cellular and molecular level. We review mechanisms by which commensal microbes influence mucosa in the context of bioactive molecules derived from resident bacteria, immune senescence, chronic inflammation and cancer. Lastly, we discuss potential therapeutic applications of microbiota alterations and microbial derivatives, for improving resilience of mucosal immunity and combating immunopathology.
The effective priming of adaptive immune responses depends on the precise dispatching of lymphocytes and antigens into and within lymph nodes (LNs), which are strategically dispersed throughout the ...body. Over the past decade, a growing body of evidence has advanced our understanding of lymph node stromal cells (LNSCs) from viewing them as mere accessory cells to seeing them as critical cellular players for the modulation of adaptive immune responses. In this review, we summarize current advances on the pivotal roles that LNSCs play in orchestrating adaptive immune responses during homeostasis and infection, and highlight the imprinting of location-specific information by micro-environmental cues into LNSCs, thereby tailoring tissue-specific immune responses.
Human γδ T cells are potent cytotoxic effector cells, produce a variety of cytokines, and can acquire regulatory activity. Induction of FOXP3, the key transcription factor of regulatory T cells ...(Treg), by TGF-β in human Vγ9 Vδ2 T cells has been previously reported. Vitamin C is an antioxidant and acts as multiplier of DNA hydroxymethylation. Here we have investigated the effect of the more stable phospho-modified Vitamin C (pVC) on TGF-β-induced FOXP3 expression and the resulting regulatory activity of highly purified human Vγ9 Vδ2 T cells. pVC significantly increased the TGF-β-induced FOXP3 expression and stability and also increased the suppressive activity of Vγ9 Vδ2 T cells. Importantly, pVC induced hypomethylation of the Treg-specific demethylated region (TSDR) in the FOXP3 gene. Genome-wide methylation analysis by Reduced Representation Bisulfite Sequencing additionally revealed differentially methylated regions in several important genes upon pVC treatment of γδ T cells. While Vitamin C also enhances effector functions of Vγ9 Vδ2 T cells in the absence of TGF-β, our results demonstrate that pVC potently increases the suppressive activity and FOXP3 expression in TGF-β-treated Vγ9 Vδ2 T cells by epigenetic modification of the FOXP3 gene.
DNA methylation controls Foxp3 gene expression Polansky, Julia K; Kretschmer, Karsten; Freyer, Jennifer ...
European journal of immunology,
June 2008, Volume:
38, Issue:
6
Journal Article
Peer reviewed
Open access
Compelling evidence suggests that Foxp3-expressing CD25⁺CD4⁺ regulatory T cells (Treg) are generated within the thymus as a separate lineage. However, Foxp3⁺CD4⁺ Treg can also be generated de novo in ...a TGF-β-dependent process from naive T cells by TCR triggering. Recently, we have shown that naturally occurring, but not in vitro TGF-β-induced Foxp3⁺ Treg display stable Foxp3 expression that was associated with selective demethylation of an evolutionarily conserved element within the Foxp3 locus named TSDR (Treg-specific demethylated region). Here, we report that inhibition of DNA methylation by azacytidine, even in absence of exogenous TGF-β, not only promoted de novo induction of Foxp3 expression during priming, but also conferred stability of Foxp3 expression upon restimulation. Most notably, such stable Foxp3 expression was found only for cells displaying enhanced TSDR demethylation. In contrast, in vitro TSDR methylation diminished its transcriptional activity. Foxp3⁺ Treg generated in vivo by DEC-205-mediated targeting of agonist ligands to dendritic cells showed long-term survival in the absence of the inducing antigen and exhibited efficient TSDR demethylation. Together, our data suggest that TSDR is an important methylation-sensitive element regulating Foxp3 expression and demonstrate that epigenetic imprinting in this region is critical for establishment of a stable Treg lineage.Supporting Information for this article is available at www.wiley-vch.de/contents/jc_2040/2008/38105_s.pdf
Compelling evidence suggests that the transcription factor Foxp3 acts as a master switch governing the development and function of CD4(+) regulatory T cells (Tregs). However, whether transcriptional ...control of Foxp3 expression itself contributes to the development of a stable Treg lineage has thus far not been investigated. We here identified an evolutionarily conserved region within the foxp3 locus upstream of exon-1 possessing transcriptional activity. Bisulphite sequencing and chromatin immunoprecipitation revealed complete demethylation of CpG motifs as well as histone modifications within the conserved region in ex vivo isolated Foxp3(+)CD25(+)CD4(+) Tregs, but not in naïve CD25(-)CD4(+) T cells. Partial DNA demethylation is already found within developing Foxp3(+) thymocytes; however, Tregs induced by TGF-beta in vitro display only incomplete demethylation despite high Foxp3 expression. In contrast to natural Tregs, these TGF-beta-induced Foxp3(+) Tregs lose both Foxp3 expression and suppressive activity upon restimulation in the absence of TGF-beta. Our data suggest that expression of Foxp3 must be stabilized by epigenetic modification to allow the development of a permanent suppressor cell lineage, a finding of significant importance for therapeutic applications involving induction or transfer of Tregs and for the understanding of long-term cell lineage decisions.
Background Cross-sectional studies suggest that maternal exposure to farming decreases the risk of allergic diseases in offspring. The potential underlying immunologic mechanisms are not understood. ...Objective We sought to assess whether maternal farm exposure activates regulatory T (Treg) cells in cord blood, exerting TH 2-suppressive effects after microbial stimulation. Methods Eighty-four pregnant mothers were recruited before delivery. Detailed questionnaires (60 nonfarming and 22 farming mothers with 2 exclusions) assessed the farming exposures. Cord blood was stimulated with the microbial stimulus peptidoglycan (Ppg), the mitogen PHA, house dust mite extracts (Der p 1), and combinations. Treg cells (CD4+ CD25high cells; intracellular forkhead/winged-helix family transcriptional repressor p3 FOXP3 expression, FOXP3 levels, lymphocyte activation gene 3 mRNA expression, functional studies, and DNA methylation of the FOXP3 locus), proliferation, and TH 2/TH 1/TH 17 cytokines were examined. Results Cord blood Treg cell counts (both unstimulated and PHA stimulated) were increased with maternal farming exposures and associated with higher FOXP3 (Der p 1 + Ppg stimulation) and trendwise higher lymphocyte activation gene 3 (Ppg) expression. Furthermore, Treg cell function was more efficient with farming exposure (effector cell suppression, P = .004). In parallel, TH 2 cytokine (IL-5) levels were decreased and associated with decreased lymphoproliferation and increased IL-6 levels (Ppg stimulation, Der p 1 + Ppg stimulation, or both; P < .05). Maternal exposure to increasing numbers of farm animals and stables was discovered to exert distinct effects on Treg cells, TH 1/TH 2 cells, or both. Additionally, FOXP3 demethylation in offspring of mothers with farm milk exposure was increased ( P = .02). Conclusions Farm exposures during pregnancy increase the number and function of cord blood Treg cells associated with lower TH 2 cytokine secretion and lymphocyte proliferation on innate exposure. One fascinating speculation is that maternal farm exposure might reflect a natural model of immunotherapy, potentially including a selection of innate stimuli in addition to allergen, shaping a child's immune system at an early stage.
Th cells integrate signals from their microenvironment to acquire distinct specialization programs for efficient clearance of diverse pathogens or for immunotolerance. Ionic signals have recently ...been demonstrated to affect T cell polarization and function. Sodium chloride (NaCl) was proposed to accumulate in peripheral tissues upon dietary intake and to promote autoimmunity via the Th17 cell axis. Here, we demonstrate that high-NaCl conditions induced a stable, pathogen-specific, antiinflammatory Th17 cell fate in human T cells in vitro. The p38/MAPK pathway, involving NFAT5 and SGK1, regulated FoxP3 and IL-17A expression in high-NaCl conditions. The NaCl-induced acquisition of an antiinflammatory Th17 cell fate was confirmed in vivo in an experimental autoimmune encephalomyelitis (EAE) mouse model, which demonstrated strongly reduced disease symptoms upon transfer of T cells polarized in high-NaCl conditions. However, NaCl was coopted to promote murine and human Th17 cell pathogenicity, if T cell stimulation occurred in a proinflammatory and TGF-β-low cytokine microenvironment. Taken together, our findings reveal a context-dependent, dichotomous role for NaCl in shaping Th17 cell pathogenicity. NaCl might therefore prove beneficial for the treatment of chronic inflammatory diseases in combination with cytokine-blocking drugs.
Autoreactive Th1 and Th17 cells are believed to mediate the pathology of multiple sclerosis in the central nervous system (CNS). Their interaction with microglia and astrocytes in the CNS is crucial ...for the regulation of the neuroinflammation. Previously, we have shown that only Th1 but not Th17 effectors activate microglia. However, it is not clear which cells are targets of Th17 effectors in the CNS.
To understand the effects driven by Th17 cells in the CNS, we induced experimental autoimmune encephalomyelitis in wild-type mice and CD4
T cell-specific integrin α4-deficient mice where trafficking of Th1 cells into the CNS was affected. We compared microglial and astrocyte response in the brain and spinal cord of these mice. We further treated astrocytes with supernatants from highly pure Th1 and Th17 cultures and assessed the messenger RNA expression of neurotrophic factors, cytokines and chemokines, using real-time PCR. Data obtained was analyzed using the Kruskal-Wallis test.
We observed in α4-deficient mice weak microglial activation but comparable astrogliosis to that of wild-type mice in the regions of the brain populated with Th17 infiltrates, suggesting that Th17 cells target astrocytes and not microglia. In vitro, in response to supernatants from Th1 and Th17 cultures, astrocytes showed altered expression of neurotrophic factors, pro-inflammatory cytokines and chemokines. Furthermore, increased expression of chemokines in Th1- and Th17-treated astrocytes enhanced recruitment of microglia and transendothelial migration of Th17 cells in vitro.
Our results demonstrate the delicate interaction between T cell subsets and glial cells and how they communicate to mediate their effects. Effectors of Th1 act on both microglia and astrocytes whereas Th17 effectors preferentially target astrocytes to promote neuroinflammation.
Intestinal Foxp3
regulatory T cell (Treg) subsets are crucial players in tolerance to microbiota-derived and food-borne antigens, and compelling evidence suggests that the intestinal microbiota ...modulates their generation, functional specialization, and maintenance. Selected bacterial species and microbiota-derived metabolites, such as short-chain fatty acids (SCFAs), have been reported to promote Treg homeostasis in the intestinal lamina propria. Furthermore, gut-draining mesenteric lymph nodes (mLNs) are particularly efficient sites for the generation of peripherally induced Tregs (pTregs). Despite this knowledge, the direct role of the microbiota and their metabolites in the early stages of pTreg induction within mLNs is not fully elucidated. Here, using an adoptive transfer-based pTreg induction system, we demonstrate that neither transfer of a dysbiotic microbiota nor dietary SCFA supplementation modulated the pTreg induction capacity of mLNs. Even mice housed under germ-free (GF) conditions displayed equivalent pTreg induction within mLNs. Further molecular characterization of these de novo induced pTregs from mLNs by dissection of their transcriptomes and accessible chromatin regions revealed that the microbiota indeed has a limited impact and does not contribute to the initialization of the Treg-specific epigenetic landscape. Overall, our data suggest that the microbiota is dispensable for the early stages of pTreg induction within mLNs.
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