Faculty Bibliography

Developing alphabeta T cells choose between the helper and cytotoxic lineages, depending upon the specificity of their T cell receptors for MHC molecules. The expression of the CD4 co-receptor on helper cells and the CD8 co-receptor on cytotoxic cells is intimately linked to this decision, and their regulation at the transcriptional level has been the subject of intense study to better understand lineage choice. Indeed, as the fate of developing T cells is decided, the expression status of these genes is accordingly locked. Genetic models have revealed important transcriptional elements and the ability to manipulate these elements in the framework of development has added a new perspective on the temporal nature of their function and the epigenetic maintenance of gene expression. We examine here novel insights into epigenetic mechanisms that have arisen through the study of these genes.

The mammalian alimentary tract harbors hundreds of species of commensal microorganisms (microbiota) that intimately interact with the host and provide it with genetic, metabolic, and immunological attributes. Recent reports have indicated that the microbiota composition and its collective genomes (microbiome) are major factors in predetermining the type and robustness of mucosal immune responses. In this review, we discuss the recent advances in our understanding of host-microbiota interactions and their effect on the health and disease susceptibility of the host.

The commensal microbiota that inhabit different parts of the gastrointestinal (GI) tract have been shaped by coevolution with the host species. The symbiotic relationship of the hundreds of microbial species with the host requires a tuned response that prevents host damage, e.g., inflammation, while tolerating the presence of the potentially beneficial microbes. Recent studies have begun to shed light on immunological processes that participate in maintenance of homeostasis with the microbiota and on how disturbance of host immunity or the microbial ecosystem can result in disease-provoking dysbiosis. Our growing appreciation of this delicate host-microbe relationship promises to influence our understanding of inflammatory diseases and infection by microbial pathogens and to provide new therapeutic opportunities

Two groups have identified SAMHD1, a protein encoded by an Aicardi-Goutieres Syndrome susceptibility gene, as the factor that restricts infection of macrophages and dendritic cells with HIV-1. Here we discuss implications of this discovery for induction of antiviral protective immunity.

Micro-RNAs (miRNAs) are short (average 22 nucleotides) noncoding regulatory RNAs that inhibit gene expression by targeting complementary 3'-untranslated regions of protein-encoding mRNAs for translational repression or degradation. miRNAs play key roles in both the function and differentiation of many cell types. Drosha and Dicer, two RNAase III enzymes, function in a stepwise manner to generate a mature miRNA. Previous studies have shown that podocyte-specific deletion of Dicer during development results in proteinuric renal disease and collapsing glomerulopathy (CG); however, Dicer has functions other than the generation of miRNAs. Here we found that the podocyte-specific deletion of Drosha results in a similar phenotype to Dicer mutants, confirming that the Dicer mutant phenotype is due to the loss of miRNAs. Moreover, the inducible deletion of Drosha in 2- to 3-month-old mice (Tet-On system) resulted in CG. Thus, continuous generation of miRNAs are required for the normal function of mature podocytes and their loss leads to CG. Identifying these miRNAs may provide new insight into disease pathogenesis and novel therapeutic targets in various podocytopathies

Perturbations of the composition of the symbiotic intestinal microbiota can have profound consequences for host metabolism and immunity. In mice, segmented filamentous bacteria (SFB) direct the accumulation of potentially proinflammatory Th17 cells in the intestinal lamina propria. We present the genome sequence of SFB isolated from monocolonized mice, which classifies SFB phylogenetically as a unique member of Clostridiales with a highly reduced genome. Annotation analysis demonstrates that SFB depend on their environment for amino acids and essential nutrients and may utilize host and dietary glycans for carbon, nitrogen, and energy. Comparative analyses reveal that SFB are functionally related to members of the genus Clostridium and several pathogenic or commensal 'minimal' genera, including Finegoldia, Mycoplasma, Borrelia, and Phytoplasma. However, SFB are functionally distinct from all 1200 examined genomes, indicating a gene complement representing biology relatively unique to their role as a gut commensal closely tied to host metabolism and immunity

CD4 coreceptor expression is negatively regulated through activity of the Cd4 silencer in CD4(-)CD8(-) double-negative (DN) thymocytes and CD8(+) cytotoxic lineage T cells. Whereas Cd4 silencing is reversed during transition from DN to CD4(+)CD8(+) double-positive stages, it is maintained through heritable epigenetic processes following its establishment in mature CD8(+) T cells. We previously demonstrated that the Runx family of transcription factors is required for Cd4 silencing both in DN thymocytes and CD8(+) T cells. However, additional factors that cooperate with Runx proteins in the process of Cd4 silencing remain unknown. To identify collaborating factors, we used microarray and RNAi-based approaches and found the basic helix-loop-helix ZIP transcription factor AP4 to have an important role in Cd4 regulation. AP4 interacts with Runx1 in cells in which Cd4 is silenced, and is required for Cd4 silencing in immature DN thymocytes through binding to the proximal enhancer. Furthermore, although AP4-deficient CD8(+) T cells appeared to normally down-regulate CD4 expression, AP4 deficiency significantly increased the frequency of CD4-expressing effector/memory CD8(+) T cells in mice harboring point mutations in the Cd4 silencer. Our results suggest that AP4 contributes to Cd4 silencing both in DN and CD8(+) T cells by enforcing checkpoints for appropriate timing of CD4 expression and its epigenetic silencing

BACKGROUND & AIMS: Although T-helper (Th) 17 and Th1 cells are involved in pathogenesis of intestinal inflammation, their developmental pathways and sufficiency to promote disease are not known; nor are the roles of CD4(+)CD25(+) regulatory T (T(R)) cells in their development. METHODS: We performed adoptive transfer experiments to investigate the induction and suppression of colitis using naive CD4(+)CD45RB(high) T cells and/or CD4(+)CD25(+) T(R) cells that were obtained from retinoid-related orphan receptor gamma t (RORgammat) gfp/(+) or Ly5.1/Ly5.2 congenic mice. RESULTS: We observed 3 types of colitogenic CD4(+) Th1 cells (interleukin [IL]-17A(-)interferon [IFN]-gamma(+)): RORgammat(-) classical Th1 cells that differentiated directly from naive T cells; RORgammat(+) Th1-like cells; and RORgammat(-) alternative Th1 cells that were terminally differentiated from RORgammat(+) cells via Th17 (IL-17A(+)IFN-gamma(-)), Th17/Th1 (IL-17A(+)IFN-gamma(+)), or Th1-like (IL-17A(-)IFN-gamma(+)) cells. In this pathway, CD4(+)CD25(+) T(R) cells suppress the development of not only classical Th1 cells, but also alternative Th1 cells at the transition of Th17/Th1 into alternative Th1 cells, resulting in accumulation of Th17 and Th17/Th1 cells in mice in which the development of colitis was suppressed. Furthermore, T(R) cells regulated the established balance of Th17 and Th1 cells under colitic conditions to yield a high ratio of Th17 and Th17/Th1 cells to Th1 cells in noncolitic conditions. CONCLUSIONS: Th17 and Th17/Th1 cells become colitogenic alternative Th1 cells via Th17, Th17/Th1, and Th1-like cells, independently of classical Th1 cells. T(R) cells suppress this pathway, resulting in accumulation of Th17 and Th17/Th1 cells

CD4(+) T helper lymphocytes that express interleukin-17 (T(H)17 cells) have critical roles in mouse models of autoimmunity, and there is mounting evidence that they also influence inflammatory processes in humans. Genome-wide association studies in humans have linked genes involved in T(H)17 cell differentiation and function with susceptibility to Crohn's disease, rheumatoid arthritis and psoriasis. Thus, the pathway towards differentiation of T(H)17 cells and, perhaps, of related innate lymphoid cells with similar effector functions, is an attractive target for therapeutic applications. Mouse and human T(H)17 cells are distinguished by expression of the retinoic acid receptor-related orphan nuclear receptor RORgammat, which is required for induction of IL-17 transcription and for the manifestation of T(H)17-dependent autoimmune disease in mice. By performing a chemical screen with an insect cell-based reporter system, we identified the cardiac glycoside digoxin as a specific inhibitor of RORgammat transcriptional activity. Digoxin inhibited murine T(H)17 cell differentiation without affecting differentiation of other T cell lineages and was effective in delaying the onset and reducing the severity of autoimmune disease in mice. At high concentrations, digoxin is toxic for human cells, but non-toxic synthetic derivatives 20,22-dihydrodigoxin-21,23-diol and digoxin-21-salicylidene specifically inhibited induction of IL-17 in human CD4(+) T cells. Using these small-molecule compounds, we demonstrate that RORgammat is important for the maintenance of IL-17 expression in mouse and human effector T cells. These data indicate that derivatives of digoxin can be used as chemical templates for the development of RORgammat-targeted therapeutic agents that attenuate inflammatory lymphocyte function and autoimmune disease

T cell fate is associated with mutually exclusive expression of CD4 or CD8 in helper and cytotoxic T cells, respectively. How expression of one locus is temporally coordinated with repression of the other has been a long-standing enigma, though we know RUNX transcription factors activate the Cd8 locus, silence the Cd4 locus, and repress the Zbtb7b locus (encoding the transcription factor ThPOK), which is required for CD4 expression. Here we found that nuclear organization was altered by interplay among members of this transcription factor circuitry: RUNX binding mediated association of Cd4 and Cd8 whereas ThPOK binding kept the loci apart. Moreover, targeted deletions within Cd4 modulated CD8 expression and pericentromeric repositioning of Cd8. Communication between Cd4 and Cd8 thus appears to enable long-range epigenetic regulation to ensure that expression of one excludes the other in mature CD4 or CD8 single-positive (SP) cells