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E16 Transcriptional regulation and role of the commensal microbiota in Th17 cell differentiation
Extended abstracts of the lectures disease development may therefore provide important novel insights into the complex pathophysiology of inflammation. As DNA methylation may be the most important flexible genomic parameter that can change genome function under an exogenous influence, it most likely provides the main link between the genetics of disease, and the environmental components that are widely acknowledged to play the decisive role in the aetiology of all inflammatory diseases in the focus of biomedical research today. New techniques have recently been developed which enable genome-wide methylation profiling. Reference(s) [1] Backdahl L, Bushell A, Beck S. Inflammatory signalling as mediator of epigenetic modulation in tissue-specific chronic inflammation. Int J Biochem Cell Biol, 2009; 41: 176 84. [2] Bjornsson HT, Fallin MD, Feinberg AP. An integrated epigenetic and genetic approach to common human disease. Trends Genet 2004; 20: 350 8. [3] Murrell A., Rakyan VK, Beck S. From genome to epigenome. Hum Mol Genet 2005; 14(Suppl 1): R3 10. [4] Issa JP. Epigenetic variation and human disease. J Nutr 2002; 132(8 Suppl): 2388S 2392S. [5] Ahuja N, Issa JP. Aging, methylation and cancer. Histol Histopathol 2000; 15: 835 42. [6] Esteller M. Aberrant DNA methylation as a cancerinducing mechanism. Annu Rev Pharmacol Toxicol 2005; 45: 629 56. [7] Eckhardt F, et al. Future potential of the Human Epigenome Project. Expert Rev Mol Diagn 2004; 4: 609 18.
Session 6
Adaptive immunity
E16 Transcriptional regulation and role of the commensal microbiota in Th17 cell differentiation D.R. Littman. Howard Hughes Medical Institute, Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY, USA IL-17-producing CD4+ T lymphocytes define a discrete lineage of pro-inflammatory T helper (Th) cells termed Th17 cells. While important for mucosal immunity, Th17 cells have also been implicated as major contributors to tissue inflammation and are thought to be involved in multiple human autoimmune diseases, including inflammatory bowel disease (IBD). Efforts to treat disease by modulating the development and effector activity of Th17 cells will necessitate a precise understanding of how these cells differentiate and function. In this regard, our group has identified the orphan nuclear receptor RORgt as a key transcription factor regulating Th17 cell development, being both required and sufficient for lineage induction. Although critical for Th17 cell differentiation, RORgt needs to function with other nuclear factors, namely STAT3, IRF-4, and BATF, that have also been demonstrated to be essential; and AHR and Runx-1, that contribute in a more restricted manner to Th17 cell differentiation. There is limited evidence suggesting that these factors function collaboratively in the transcription of lineage-associated genes, although the underlying mechanisms are unknown. The interaction of RORgt and other transcription factors with direct target genes is being examined using chromatin immunoprecipitation combined with whole transcriptome analysis of T cells from mice with mutations in the genes encoding the factors. This analysis promises to identify new targets for anti-Th17 therapy. In this context, we have developed small molecule inhibitors of RORgt activity that block Th17 cell differentiation and inhibit disease in mouse models for autoimmunity.
13 Th17 cells can be generated in vitro by culturing activated naïve CD4+ T cells in the presence of IL-6 and TGF-b. At higher concentrations of TGF-b, there is induction of the transcription factor Foxp3, and the cells acquire the suppressor function of Treg cells. This balance of Th17 and Treg phenotypes appears to be governed by the concentration of TGF-b and by an interaction of RORgt with Foxp3 [1]. Foxp3 inhibits the activity of RORgt, but this inhibition is overcome by STAT3 activation downstream of IL-6 and other inflammatory cytokines. The balance of Th17 and Treg cells is best visualized in vivo in the lamina propria of the small intestine, where the proportion and abundance of both types of cells is regulated by the composition of the commensal microbiota. For example, in germ-free mice, Th17 cells are absent, and the proportion of Treg cells among the CD4+ T cells is substantially increased [2]. We have identified a single bacterial species, segmented filamentous bacteria (SFB), as responsible for the accumulation of Th17 cells in the intestine [3] (Ivanov et al., 2009). Mice lacking SFB were found to have few Th17 cells and were more susceptible to colitis induced by Citrobacter rodentium than mice with SFB. There is also evidence that colonization with SFB correlates with increased susceptibility of mice to autoimmune disease, illustrating the importance of maintaining an appropriate commensal bacterial-regulated balance between effector T cells and Treg cells. The mechanism by which SFB, which bind tightly to ileal epithelium, elicits signals that result in Th17 accumulation (by polarization of Th0 cells or migration) is not yet known. However, this process does not appear to affect the number of other lamina propria lymphoid cells, including gd T cells, lymphoid tissue inducer (LTi) cells, and NK-like cells that also express IL-17 and/or IL-22. These cells are also dependent on RORgt for their differentiation, and they compensate for the absence of Th17 cells in germ-free mice to protect the animals from lethal damage induced by C. rodentium, at least in part through production of IL-22. Expression of IL-22 by these cells, as well as Th17 cells, is dependent on the ligand-regulated transcription factor AHR, in whose absence mice succumb to infection with this intestinal pathogen. How specific microbial products influence the differentiation of the lamina propria RORgt- and AHR-expressing lymphoid cells as well as Treg cells (many of which are induced to differentiate post-thymically) is an area that is increasingly recognized to be of central importance in pathogenesis of inflammatory diseases, particularly IBD. The implications of commensal microbe-induced signals for the development of future therapeutic strategies will be discussed. Reference(s) [1] Zhou L, Lopes JE, Chong MM, Ivanov II, Min R, Victora GD, Shen Y, Du J, Rubtsov YP, Rudensky AY, et al. TGFbeta-induced Foxp3 inhibits T(H)17 cell differentiation by antagonizing RORgammat function. Nature 2008; 453: 236 40. [2] Ivanov II, Frutos Rde L, Manel N, Yoshinaga K, Rifkin DB, Sartor RB, Finlay BB, Littman DR. Specific microbiota direct the differentiation of IL-17-producing T-helper cells in the mucosa of the small intestine. Cell Host Microbe 2008; 4: 337 49. [3] Ivanov II, Atarashi K, Manel N, Brodie EL, Shima T, Karaoz U, Wei D, Goldfarb KC, Santee CA, Lynch SV, et al. Induction of intestinal Th17 cells by segmented filamentous bacteria. Cell 2009; 139: 485 98.
Session 6
Adaptive immunity
E16 Transcriptional regulation and role of the commensal microbiota in Th17 cell differentiation D.R. Littman. Howard Hughes Medical Institute, Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY, USA IL-17-producing CD4+ T lymphocytes define a discrete lineage of pro-inflammatory T helper (Th) cells termed Th17 cells. While important for mucosal immunity, Th17 cells have also been implicated as major contributors to tissue inflammation and are thought to be involved in multiple human autoimmune diseases, including inflammatory bowel disease (IBD). Efforts to treat disease by modulating the development and effector activity of Th17 cells will necessitate a precise understanding of how these cells differentiate and function. In this regard, our group has identified the orphan nuclear receptor RORgt as a key transcription factor regulating Th17 cell development, being both required and sufficient for lineage induction. Although critical for Th17 cell differentiation, RORgt needs to function with other nuclear factors, namely STAT3, IRF-4, and BATF, that have also been demonstrated to be essential; and AHR and Runx-1, that contribute in a more restricted manner to Th17 cell differentiation. There is limited evidence suggesting that these factors function collaboratively in the transcription of lineage-associated genes, although the underlying mechanisms are unknown. The interaction of RORgt and other transcription factors with direct target genes is being examined using chromatin immunoprecipitation combined with whole transcriptome analysis of T cells from mice with mutations in the genes encoding the factors. This analysis promises to identify new targets for anti-Th17 therapy. In this context, we have developed small molecule inhibitors of RORgt activity that block Th17 cell differentiation and inhibit disease in mouse models for autoimmunity.
13 Th17 cells can be generated in vitro by culturing activated naïve CD4+ T cells in the presence of IL-6 and TGF-b. At higher concentrations of TGF-b, there is induction of the transcription factor Foxp3, and the cells acquire the suppressor function of Treg cells. This balance of Th17 and Treg phenotypes appears to be governed by the concentration of TGF-b and by an interaction of RORgt with Foxp3 [1]. Foxp3 inhibits the activity of RORgt, but this inhibition is overcome by STAT3 activation downstream of IL-6 and other inflammatory cytokines. The balance of Th17 and Treg cells is best visualized in vivo in the lamina propria of the small intestine, where the proportion and abundance of both types of cells is regulated by the composition of the commensal microbiota. For example, in germ-free mice, Th17 cells are absent, and the proportion of Treg cells among the CD4+ T cells is substantially increased [2]. We have identified a single bacterial species, segmented filamentous bacteria (SFB), as responsible for the accumulation of Th17 cells in the intestine [3] (Ivanov et al., 2009). Mice lacking SFB were found to have few Th17 cells and were more susceptible to colitis induced by Citrobacter rodentium than mice with SFB. There is also evidence that colonization with SFB correlates with increased susceptibility of mice to autoimmune disease, illustrating the importance of maintaining an appropriate commensal bacterial-regulated balance between effector T cells and Treg cells. The mechanism by which SFB, which bind tightly to ileal epithelium, elicits signals that result in Th17 accumulation (by polarization of Th0 cells or migration) is not yet known. However, this process does not appear to affect the number of other lamina propria lymphoid cells, including gd T cells, lymphoid tissue inducer (LTi) cells, and NK-like cells that also express IL-17 and/or IL-22. These cells are also dependent on RORgt for their differentiation, and they compensate for the absence of Th17 cells in germ-free mice to protect the animals from lethal damage induced by C. rodentium, at least in part through production of IL-22. Expression of IL-22 by these cells, as well as Th17 cells, is dependent on the ligand-regulated transcription factor AHR, in whose absence mice succumb to infection with this intestinal pathogen. How specific microbial products influence the differentiation of the lamina propria RORgt- and AHR-expressing lymphoid cells as well as Treg cells (many of which are induced to differentiate post-thymically) is an area that is increasingly recognized to be of central importance in pathogenesis of inflammatory diseases, particularly IBD. The implications of commensal microbe-induced signals for the development of future therapeutic strategies will be discussed. Reference(s) [1] Zhou L, Lopes JE, Chong MM, Ivanov II, Min R, Victora GD, Shen Y, Du J, Rubtsov YP, Rudensky AY, et al. TGFbeta-induced Foxp3 inhibits T(H)17 cell differentiation by antagonizing RORgammat function. Nature 2008; 453: 236 40. [2] Ivanov II, Frutos Rde L, Manel N, Yoshinaga K, Rifkin DB, Sartor RB, Finlay BB, Littman DR. Specific microbiota direct the differentiation of IL-17-producing T-helper cells in the mucosa of the small intestine. Cell Host Microbe 2008; 4: 337 49. [3] Ivanov II, Atarashi K, Manel N, Brodie EL, Shima T, Karaoz U, Wei D, Goldfarb KC, Santee CA, Lynch SV, et al. Induction of intestinal Th17 cells by segmented filamentous bacteria. Cell 2009; 139: 485 98.