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The metabolic syndrome and diabetic conditions support atherosclerosis, but the exact mechanisms for accelerated atherogenesis remain unclear. Although the proinflammatory role of STAT4 in atherosclerosis and diet-induced insulin resistance (IR) was recently established, the impact of STAT4 on atherogenesis in conditions of IR is not known. In this study, we generated Stat4-/-Ldlr-/- mice that were fed a diabetogenic diet with added cholesterol (DDC). DDC-fed Stat4-/-Ldlr-/- mice demonstrated improved glucose tolerance, insulin sensitivity, and a 36% reduction in atherosclerosis compared with Ldlr-/- controls. Interestingly, we detected a reduction in T follicular helper (Tfh) cells and plasma B cells but a sharp elevation in CD8+ regulatory T cells (Tregs) in spleens and aortas of Stat4-/-Ldlr-/- mice compared with Ldlr-/- mice. Similarly, STAT4 deficiency supported CD8+ Treg differentiation in vitro. STAT4-deficient CD8+ Tregs suppressed Tfh cell and germinal center B cell development upon immunization with keyhole limpet hemocyanin, indicating an important role for STAT4 in CD8+ Treg functions in vivo. Furthermore, adoptive transfer of Stat4-/-Ldlr-/- CD8+ Tregs versus Ldlr-/- CD8+ Tregs resulted in a significant reduction in plaque burden and suppression of Tfh cell and germinal center B cells in DDC-fed Ldlr-/- recipients. STAT4 expression in macrophages (MΦs) also affected the Tfh/CD8+ Treg axis, because conditioned media from Stat4-/-Ldlr-/- MΦs supported CD8+ Treg differentiation, but not Tfh cell differentiation, in a TGF-β-dependent manner. These findings suggest a novel mechanism by which STAT4 supports atherosclerosis in IR Ldlr-/- mice via STAT4-dependent MΦs, as well as cell-intrinsic suppression of CD8+ Treg generation and functions and maintenance of Tfh cell generation and the accompanying humoral immune response. [ABSTRACT FROM AUTHOR]

In this study, we determined the role of IL-21R signaling in Mycobacterium tuberculosis infection, using IL-21R knockout (KO) mice. A total of 50% of M. tuberculosis H37Rv--infected IL-21R KO mice died in 6 mo compared with no deaths in infected wild type (WT) mice. M. tuberculosis--infected IL-21R KO mice had enhanced bacterial burden and reduced infiltration of Ag-specific T cells in lungs compared with M. tuberculosis--infected WT mice. Ag-specific T cells from the lungs of M. tuberculosis--infected IL-21R KO mice had increased expression of T cell inhibitory receptors, reduced expression of chemokine receptors, proliferated less, and produced less IFN-γ, compared with Ag-specific T cells from the lungs of M. tuberculosis--infected WT mice. T cells from M. tuberculosis--infected IL-21R KO mice were unable to induce optimal macrophage responses to M. tuberculosis. This may be due to a decrease in the Ag-specific T cell population. We also found that IL-21R signaling is associated with reduced expression of a transcriptional factor Eomesodermin and enhanced functional capacity of Ag-specific T cells of M. tuberculosis--infected mice. The sum of our findings suggests that IL-21R signaling is essential for the optimal control of M. tuberculosis infection. [ABSTRACT FROM AUTHOR]

Humoral immunity, including Ab switching and somatic hypermutation, is critically regulated by CD4+ T cells. T follicular helper (Tfh) cells have been recently shown to be a distinct T cell subset important in germinal center reactions. The transcriptional regulation of Tfh cell development and function has not been well understood. In this study, we report that C/EBPα, a basic region/leucine zipper transcription factor, is highly expressed in Tfh cells. Cebpa-deficient CD4+ T cells exhibit enhanced IFN-γ expression in vitro and in vivo. T cell–specific Cebpa knockout mice, although not defective in Tfh cell generation, produce significantly increased levels of IgG2a/b and IgG3 following immunization with a protein Ag. Moreover, C/EBPα binds to the Ifng gene and inhibits T-bet–driven Ifng transcription in a DNA binding–dependent manner. Our study thus demonstrates that C/EBPα restricts IFN-γ expression in T cells to allow proper class switching by B cells. [ABSTRACT FROM AUTHOR]

The metabolic syndrome and diabetic conditions support atherosclerosis, but the exact mechanisms for accelerated atherogenesis remain unclear. Although the proinflammatory role of STAT4 in atherosclerosis and diet-induced insulin resistance (IR) was recently established, the impact of STAT4 on atherogenesis in conditions of IR is not known. In this study, we generated Stat4 -/- Ldlr -/- mice that were fed a diabetogenic diet with added cholesterol (DDC). DDC-fed Stat4 -/- Ldlr -/- mice demonstrated improved glucose tolerance, insulin sensitivity, and a 36% reduction in atherosclerosis compared with Ldlr -/- controls. Interestingly, we detected a reduction in T follicular helper (Tfh) cells and plasma B cells but a sharp elevation in CD8 + regulatory T cells (Tregs) in spleens and aortas of Stat4 -/- Ldlr -/- mice compared with Ldlr -/- mice. Similarly, STAT4 deficiency supported CD8 + Treg differentiation in vitro. STAT4-deficient CD8 + Tregs suppressed Tfh cell and germinal center B cell development upon immunization with keyhole limpet hemocyanin, indicating an important role for STAT4 in CD8 + Treg functions in vivo. Furthermore, adoptive transfer of Stat4 -/- Ldlr -/- CD8 + Tregs versus Ldlr -/- CD8 + Tregs resulted in a significant reduction in plaque burden and suppression of Tfh cell and germinal center B cells in DDC-fed Ldlr -/- recipients. STAT4 expression in macrophages (MΦs) also affected the Tfh/CD8 + Treg axis, because conditioned media from Stat4 -/- Ldlr -/- MΦs supported CD8 + Treg differentiation, but not Tfh cell differentiation, in a TGF-β-dependent manner. These findings suggest a novel mechanism by which STAT4 supports atherosclerosis in IR Ldlr -/- mice via STAT4-dependent MΦs, as well as cell-intrinsic suppression of CD8 + Treg generation and functions and maintenance of Tfh cell generation and the accompanying humoral immune response., (Copyright © 2017 by The American Association of Immunologists, Inc.)

In this study, we determined the role of IL-21R signaling in Mycobacterium tuberculosis infection, using IL-21R knockout (KO) mice. A total of 50% of M. tuberculosis H37Rv - infected IL-21R KO mice died in 6 mo compared with no deaths in infected wild type (WT) mice. M. tuberculosis - infected IL-21R KO mice had enhanced bacterial burden and reduced infiltration of Ag-specific T cells in lungs compared with M. tuberculosis - infected WT mice. Ag-specific T cells from the lungs of M. tuberculosis - infected IL-21R KO mice had increased expression of T cell inhibitory receptors, reduced expression of chemokine receptors, proliferated less, and produced less IFN- γ, compared with Ag-specific T cells from the lungs of M. tuberculosis - infected WT mice. T cells from M. tuberculosis - infected IL-21R KO mice were unable to induce optimal macrophage responses to M. tuberculosis. This may be due to a decrease in the Ag-specific T cell population. We also found that IL-21R signaling is associated with reduced expression of a transcriptional factor Eomesodermin and enhanced functional capacity of Ag-specific T cells of M. tuberculosis - infected mice. The sum of our findings suggests that IL-21R signaling is essential for the optimal control of M. tuberculosis infection., (Copyright © 2017 by The American Association of Immunologists, Inc.)

Humoral immunity, including Ab switching and somatic hypermutation, is critically regulated by CD4(+) T cells. T follicular helper (Tfh) cells have been recently shown to be a distinct T cell subset important in germinal center reactions. The transcriptional regulation of Tfh cell development and function has not been well understood. In this study, we report that C/EBPα, a basic region/leucine zipper transcription factor, is highly expressed in Tfh cells. Cebpa-deficient CD4(+) T cells exhibit enhanced IFN-γ expression in vitro and in vivo. T cell-specific Cebpa knockout mice, although not defective in Tfh cell generation, produce significantly increased levels of IgG2a/b and IgG3 following immunization with a protein Ag. Moreover, C/EBPα binds to the Ifng gene and inhibits T-bet-driven Ifng transcription in a DNA binding-dependent manner. Our study thus demonstrates that C/EBPα restricts IFN-γ expression in T cells to allow proper class switching by B cells., (Copyright © 2014 by The American Association of Immunologists, Inc.)

T cell activation and tolerance are delicately regulated by costimulatory molecules. Although B and T lymphocyte attenuator (BTLA) has been shown as a negative regulator for T cell activation, its role in peripheral T cell tolerance induction in vivo has not been addressed. In this study, we generated a novel strain of BTLA-deficient mice and used three different models to characterize the function of BTLA in controlling T cell tolerance. In an oral tolerance model, BTLA-deficient mice were found resistant to the induction of T cell tolerance to an oral Ag. Moreover, compared with wild-type OT-II cells, BTLA(-/-) OT-II cells were less susceptible to tolerance induction by a high-dose OVA peptide administered i.v. Finally, BTLA(-/-) OT-I cells caused autoimmune diabetes in RIP-mOVA recipient mice. Our results thus demonstrate an important role for BTLA in the induction of peripheral tolerance of both CD4(+) and CD8(+) T cells in vivo.

Upon activation, naive CD4(+) T cells differentiate into effector Th cell subsets. The stability and plasticity of effector Th cells have not been well understood. In this study we used an IL-17F-red fluorescent protein reporter mouse to analyze the plasticity of Th17 cells in vitro and in vivo. We found that in vitro generated Th17 cells poorly maintained their differentiation program in vitro and could be reprogrammed into other T cell lineages. Moreover, upon transfer into lymphopenic hosts, Th17 cells rapidly lost their IL-17 expression and were converted into Th1 cells independently of IL-7 signaling. However, Th17 cells maintained their phenotypes well in normal animals, even in the absence of Ag and inflammation. These results, although suggesting the plasticity of Th17 cells, also indicate active maintenance of their program in vivo.

Th17 and regulatory T (Treg) cells play opposite roles in autoimmune diseases. However, the mechanisms underlying their proper migration to inflammatory tissues are unclear. In this study, we report that these two T cell subsets both express CCR6. CCR6 expression in Th17 cells is regulated by TGF-beta and requires two nuclear receptors, RORalpha and RORgamma. Th17 cells also express the CCR6 ligand CCL20, which is induced synergistically by TGF-beta and IL-6, which requires STAT3, RORgamma and IL-21. Th17 cells, by producing CCL20, promote migration of Th17 and Treg cells in vitro in a CCR6-dependent manner. Lack of CCR6 in Th17 cells reduces the severity of experimental autoimmune encephalomyelitis and Th17 and Treg recruitment into inflammatory tissues. Similarly, CCR6 on Treg cells is also important for their recruitment into inflammatory tissues. Our data indicate an important role of CCR6 in Treg and Th17 cell migration.

CD1d-restricted Valpha14(+) invariant NK T (iNKT) cells are a specialized alphabeta T cell subset that regulates both innate and adaptive immunity. Although costimulatory molecules are required for the activation of conventional T cells and for the development of Foxp3(+) T cells, their role in iNKT cell regulation is unclear. Here we report that mice deficient in CD80/CD86 and/or B7h exhibit severe defects in thymic iNKT cell maturation, associated with largely reduced iNKT cell number in the thymus and the periphery. We show that costimulation is necessary for the optimal expansion of postselected NK1.1(-) immature iNKT cells in the thymus and for the proper expression of the maturation markers T-bet and CD122. Surprisingly, costimulatory molecules on both hemopoietic and nonhematopoietic cells are required for iNKT cell development. Our results thus demonstrate a previously unknown function of costimulation in the intrathymic development of iNKT cells, distinct from that of conventional T cells and regulatory T cells.

T cell activation and differentiation is accompanied and mediated by transcriptional reprogramming. The NFATc1 transcription factor is strongly induced upon T cell activation and controls numerous genes involved in the T cell effector function. However, its regulation by physiological stimuli in primary T cells has not been well understood. We previously found that ICOS synergizes with TCR and CD28 to greatly enhance NFATc1 expression in primary T cells. In this study, we have examined the signaling mechanisms whereby costimulation regulates NFATc1 expression. We found that CD28 and ICOS regulate sustained PI3K activity in primary T cells, which is required for NFATc1 up-regulation. CD28 and ICOS costimulation, possibly through Itk, a Tec kinase downstream of the PI3K, enhanced phosphorylation of phospholipase C gamma1 and increased and sustained Ca(2+) flux in T cells. Costimulation of T cells potentiated transcription of the Nfatc1 gene P1 promoter in a PI3K-dependent manner. This work demonstrates an important role for costimulatory receptors in sustaining T cell activation programs leading to Nfatc1 gene transcription and has implications in our understanding of the immune response and tolerance.

ICOS, a CD28 family member expressed on activated CD4(+) and CD8(+) T cells, plays important roles in T cell activation and effector function. Here we studied the role of ICOS in graft-vs-host disease (GVHD) mediated by CD4(+) or CD8(+) T cells in allogeneic bone marrow transplantation. In comparison of wild-type and ICOS-deficient T cells, we found that recipients of ICOS(-/-) CD4(+) T cells exhibited significantly less GVHD morbidity and delayed mortality. ICOS(-/-) CD4(+) T cells had no defect in expansion, but expressed significantly less Fas ligand and produced significantly lower levels of IFN-gamma and TNF-alpha. Thus, ICOS(-/-) CD4(+) T cells were impaired in effector functions that lead to GVHD. In contrast, recipients of ICOS(-/-) CD8(+) T cells exhibited significantly enhanced GVHD morbidity and accelerated mortality. In the absence of ICOS signaling, either using ICOS-deficient donors or ICOS ligand-deficient recipients, the levels of expansion and Tc1 cytokine production of CD8(+) T cells were significantly increased. The level of expansion was inversely correlated with the level of apoptosis, suggesting that increased ability of ICOS(-/-) CD8(+) T cells to induce GVHD resulted from the enhanced survival and expansion of those cells. Our findings indicate that ICOS has paradoxical effects on the regulation of alloreactive CD4(+) and CD8(+) T cells in GVHD.