Faculty Bibliography

Signaling through the T cell antigen receptor (TCR) is important for the homeostasis of naive and memory CD4(+) T cells. The significance of TCR signaling in regulatory T (Treg) cells has not been systematically addressed. Using an Ox40-cre allele that is prominently expressed in Treg cells, and a conditional null allele of the gene encoding p56(Lck), we have examined the importance of TCR signaling in Treg cells. Inactivation of p56(Lck) resulted in abnormal Treg homeostasis characterized by impaired turnover, preferential redistribution to the lymph nodes, loss of suppressive function, and striking changes in gene expression. Abnormal Treg cell homeostasis and function did not reflect the involvement of p56(Lck) in CD4 function because these effects were not observed when CD4 expression was inactivated by Ox40-cre.The results make clear multiple aspects of Treg cell homeostasis and phenotype that are dependent on a sustained capacity to signal through the TCR

Forkhead box P3 (FOXP3)(+)CD4(+)CD25(+) inducible regulatory T (iT reg) cells play an important role in immune tolerance and homeostasis. In this study, we show that the transforming growth factor-beta (TGF-beta) induces the expression of the Runt-related transcription factors RUNX1 and RUNX3 in CD4(+) T cells. This induction seems to be a prerequisite for the binding of RUNX1 and RUNX3 to three putative RUNX binding sites in the FOXP3 promoter. Inactivation of the gene encoding RUNX cofactor core-binding factor-beta (CBFbeta) in mice and small interfering RNA (siRNA)-mediated suppression of RUNX1 and RUNX3 in human T cells resulted in reduced expression of Foxp3. The in vivo conversion of naive CD4(+) T cells into Foxp3(+) iT reg cells was significantly decreased in adoptively transferred Cbfb(F/F) CD4-cre naive T cells into Rag2(-/-) mice. Both RUNX1 and RUNX3 siRNA silenced human T reg cells and Cbfb(F/F) CD4-cre mouse T reg cells showed diminished suppressive function in vitro. Circulating human CD4(+) CD25(high) CD127(-) T reg cells significantly expressed higher levels of RUNX3, FOXP3, and TGF-beta mRNA compared with CD4(+)CD25(-) cells. Furthermore, FOXP3 and RUNX3 were colocalized in human tonsil T reg cells. These data demonstrate Runx transcription factors as a molecular link in TGF-beta-induced Foxp3 expression in iT reg cell differentiation and function

Upon encountering antigen in the context of antigen presenting cells, naive CD4(+) T cells undergo differentiation into effector T helper (Th) cells, which can secrete high levels of cytokines and other immunomodulators to mediate host defense and tissue inflammation. During the past three years, the immunology field has witnessed an explosion of research advances in the biology of Th17 cells, the most recently described subset of T helper cells, which play crucial roles in host immunity and inflammation. Here we review emerging data on transcriptional regulatory networks that govern the differentiation program of Th17 cells, and focus on how the orphan nuclear receptor RORgammat coordinates this process in concert with diverse cytokine-induced transcription factors

BACKGROUND AND AIMS: IL-17-producing CD4(+) T-helper cells (Th17) contribute to chronic autoimmune inflammation in the brain, and levels of Th17-derived cytokines increase in patients with colitis, suggesting a role in pathogenesis. We analyzed the roles of Th17 cells and the transcription factor retinoic acid receptor-related organ receptor (ROR)gamma, which regulates Th17 differentiation, in chronic intestinal inflammation. METHODS: Using an adoptive transfer model of colitis, we compared the colitogenic potential of wild-type, interleukin-17A (IL-17A)-, IL-17F-, IL-22-, and RORgamma-deficient CD4(+)CD25(-) T cells in RAG1-null mice. RESULTS: Adoptive transfer of IL-17A-, IL-17F-, or IL-22-deficient T lymphocytes into RAG1-null mice caused severe colitis that was indistinguishable from that caused by wild-type cells. In contrast, transfer of RORgamma-null T cells failed to increase mucosal IL-17 cytokine levels and did not induce colitis. Treatment with IL-17A was able to restore colitis after transfer of RORgamma-null T cells, indicating a crucial role for Th17 cells in pathogenesis. Treatment of RAG1 mice that received IL-17F-null (but not wild-type) T cells with a neutralizing anti-IL-17A antibody significantly suppressed disease, indicating redundant biological effects of IL-17A and IL-17F. CONCLUSIONS: We have identified a crucial role of RORgamma-expressing Th17 cells in chronic intestinal inflammation. RORgamma controls IL-17A and IL-17F production, and these cytokines have a redundant but highly pathogenic role in gut inflammation. Reagents that target RORgamma or a combination of anti-IL-17A and anti-IL-17F might be developed as therapeutics for chronic colitis

The interleukin (IL) 17 family of cytokines has emerged to be critical for host defense as well as the pathogenesis of autoimmune and autoinflammatory disorders, and serves to link adaptive and innate responses. Recent studies have identified a new subset of T cells that selectively produce IL-17 (Th17 cells; Bettelli, E., T. Korn, and V.K. Kuchroo. 2007. Curr. Opin. Immunol. 19:652-657; Kolls, J.K., and A. Linden. 2004. Immunity. 21:467-476), but the regulation of IL-17 production by innate immune cells is less well understood. We report that in vitro stimulation with IL-23 induced IL-17 production by recombination activating gene (Rag) 2(-/-) splenocytes but not Rag2(-/-) common gamma chain(-/-) splenocytes. We found that a major source of IL-17 was CD4(+)CD3(-)NK1.1(-)CD11b(-)Gr1(-)CD11c(-)B220(-) cells, a phenotype that corresponds to lymphoid tissue inducer-like cells (LTi-like cells), which constitutively expressed the IL-23 receptor, aryl hydrocarbon receptor, and CCR6. In vivo challenge with the yeast cell wall product zymosan rapidly induced IL-17 production in these cells. Genetic deletion of signal transducer and activator of transcription 3 reduced but did not abrogate IL-17 production in LTi-like cells. Thus, it appears that splenic LTi-like cells are a rapid source of IL-17 and IL-22, which might contribute to dynamic organization of secondary lymphoid organ structure or host defense

Recent research has uncovered complex transcription factor networks that control the processes of T-cell development and differentiation. RUNX (runt-related transcription factor) proteins are among the many factors that have crucial roles in these networks. In this Review, we examine the mechanisms by which RUNX complexes act together with other transcription factors, such as Th-POK (T-helper-inducing POZ/Kruppel-like factor) and GATA-binding protein 3 (GATA3) in determining the CD4/CD8 lineage choice of developing thymocytes. In addition, we discuss evidence indicating that RUNX complexes are also involved in the differentiation of effector T-cell subsets and that the molecular mechanisms by which RUNX proteins regulate T-cell fate decisions are conserved between the thymus and periphery

Although retroviruses have been extensively studied for many years, basic questions about how retroviral infections are detected by the immune system and which innate pathways are required for the generation of immune responses remain unanswered. Defining these pathways and how they contribute to the anti-retroviral immune responses would assist in the development of more effective vaccines for retroviral pathogens such as HIV. We have investigated the roles played by CD11c(+) dendritic cells (DCs) and by Toll-like receptor (TLR) signaling pathways in the generation of an anti-retroviral immune response against a mouse retroviral pathogen, Friend murine leukemia virus (F-MLV). Specific deletion of DCs during F-MLV infection caused a significant increase in viral titers at 14 days post-infection, indicating the importance of DCs in immune control of the infection. Similarly, Myd88 knockout mice failed to control F-MLV, and sustained high viral titers (10(7) foci/spleen) for several months after infection. Strikingly, both DC-depleted mice and Myd88 knockout mice exhibited only a partial reduction of CD8(+) T cell responses, while the IgG antibody response to F-MLV was completely lost. Furthermore, passive transfer of immune serum from wild-type mice to Myd88 knockout mice rescued control of F-MLV. These results identify TLR signaling and CD11c(+) DCs as playing critical roles in the humoral response to retroviruses

IL-17-producing CD4(+) T helper (Th17) cells have recently been defined as a unique subset of proinflammatory helper cells whose development depends on signaling initiated by IL-6 and TGF-beta, autocrine activity of IL-21, activation of STAT3, and induction of the orphan nuclear receptor RORgammat. The maintenance, expansion, and further differentiation of the committed Th17 cells depend on IL-1beta and IL-23. IL-17 was originally found produced by circulating human CD45RO(+) memory T cells. A recent study found that human Th17 memory cells selectively express high levels of CCR6. In this study, we report that human peripheral blood and lymphoid tissue contain a significant number of CD4(+)FOXP3(+) T cells that express CCR6 and have the capacity to produce IL-17 upon activation. These cells coexpress FOXP3 and RORgammat transcription factors. The CD4(+)FOXP3(+)CCR6(+) IL-17-producing cells strongly inhibit the proliferation of CD4(+) responder T cells. CD4(+)CD25(high)-derived T-cell clones express FOXP3, RORgammat, and IL-17 and maintain their suppressive function via a cell-cell contact mechanism. We further show that human CD4(+)FOXP3(+)CCR6(-) regulatory T (Treg) cells differentiate into IL-17 producer cells upon T-cell receptor stimulation in the presence of IL-1beta, IL-2, IL-21, IL-23, and human serum. This, together with the finding that human thymus does not contain IL-17-producing Treg cells, suggests that the IL-17(+)FOXP3(+) Treg cells are generated in the periphery. IL-17-producing Treg cells may play critical roles in antimicrobial defense, while controlling autoimmunity and inflammation

The transcription factor Foxp3 has an indispensable role in establishing stable transcriptional and functional programs of regulatory T cells (T(reg) cells). Loss of Foxp3 expression in mature T(reg) cells results in a failure of suppressor function, yet the molecular mechanisms that ensure steady, heritable Foxp3 expression in the T(reg) cell lineage remain unknown. Using T(reg) cell-specific gene targeting, we found that complexes of the transcription factors Runx and CBFbeta were required for maintenance of Foxp3 mRNA and protein expression in T(reg) cells. Consequently, mice lacking CBFbetab exclusively in the T(reg) cell lineage had a moderate lymphoproliferative syndrome. Thus, Runx-CBFbeta complexes maintain stable high expression of Foxp3 and serve as an essential determinant of T(reg) cell lineage stability

The gastrointestinal tract of mammals is inhabited by hundreds of distinct species of commensal microorganisms that exist in a mutualistic relationship with the host. How commensal microbiota influence the host immune system is poorly understood. We show here that colonization of the small intestine of mice with a single commensal microbe, segmented filamentous bacterium (SFB), is sufficient to induce the appearance of CD4(+) T helper cells that produce IL-17 and IL-22 (Th17 cells) in the lamina propria. SFB adhere tightly to the surface of epithelial cells in the terminal ileum of mice with Th17 cells but are absent from mice that have few Th17 cells. Colonization with SFB was correlated with increased expression of genes associated with inflammation and antimicrobial defenses and resulted in enhanced resistance to the intestinal pathogen Citrobacter rodentium. Thus, manipulation of this commensal-regulated pathway may provide new opportunities for enhancing mucosal immunity and treating autoimmune disease