Yijun Carrier

Reciprocal developmental pathways for the generation of pathogenic effector TH17 and regulatory T cells

On activation, T cells undergo distinct developmental pathways, attaining specialized properties and effector functions. T-helper (TH) cells are traditionally thought to differentiate into TH1 and TH2 cell subsets. TH1 cells are necessary to clear intracellular pathogens and TH2 cells are important for clearing extracellular organisms. Recently, a subset of interleukin (IL)-17-producing T (TH17) cells distinct from TH1 or TH2 cells has been described and shown to have a crucial role in the induction of autoimmune tissue injury. In contrast, CD4+CD25+Foxp3+ regulatory T (Treg) cells inhibit autoimmunity and protect against tissue injury. Transforming growth factor-β (TGF-β) is a critical differentiation factor for the generation of Treg cells. Here we show, using mice with a reporter introduced into the endogenous Foxp3 locus, that IL-6, an acute phase protein induced during inflammation, completely inhibits the generation of Foxp3+ Treg cells induced by TGF-β. We also demonstrate that IL-23 is not the differentiation factor for the generation of TH17 cells. Instead, IL-6 and TGF-β together induce the differentiation of pathogenic TH17 cells from naive T cells. Our data demonstrate a dichotomy in the generation of pathogenic (TH17) T cells that induce autoimmunity and regulatory (Foxp3+) T cells that inhibit autoimmune tissue injury.

A dominant function for interleukin 27 in generating interleukin 10-producing anti-inflammatory T cells

Regulatory T cells (Treg cells) expressing the transcription factor Foxp3 are key in maintaining the balance of immune homeostasis. However, distinct induced T regulatory type 1 (Tr1) cells that lack Foxp3 expression also regulate T cell function, mainly by producing the immunosuppressive cytokine interleukin 10 (IL-10). However, the factors required for the induction of IL-10-producing suppressive T cells are not fully understood. Here we demonstrate that dendritic cells modified by Treg cells induced the generation of IL-10-producing Tr1 cells. The differentiation of naive CD4+ T cells into IL-10-producing cells was mediated by IL-27 produced by the Treg cell–modified dendritic cells, and transforming growth factor-β amplified the generation of induced IL-10+ Tr1 cells by IL-27. Thus, IL-27 and transforming growth factor-β promote the generation of IL-10-producing Tr1 cells.

Th3 Cells in Peripheral Tolerance. I. Induction of Foxp3-Positive Regulatory T Cells by Th3 Cells Derived from TGF-β T Cell-Transgenic Mice

TGF-β has been shown to be critical in the generation of CD4+CD25+Foxp3+ regulatory T cells (Tregs). Because Th3 cells produce large amounts of TGF-β, we asked whether induction of Th3 cells in the periphery was a mechanism by which CD4+CD25+ Tregs were induced in the peripheral immune compartment. To address this issue, we generated a TGF-β1-transgenic (Tg) mouse in which TGF-β is linked to the IL-2 promoter and T cells transiently overexpress TGF-β upon TCR stimulation but produce little or no IL-2, IL-4, IL-10, IL-13, or IFN-γ. Naive TGF-β-Tg mice are phenotypically normal with comparable numbers of lymphocytes and thymic-derived Tregs. We found that repeated antigenic stimulation of pathogenic myelin oligodendrocyte glycoprotein (MOG)-specific CD4+CD25− T cells from TGF-β Tg mice crossed to MOG TCR-Tg mice induced Foxp3 expression in both CD25+ and CD25− populations. Both CD25 subsets were anergic and had potent suppressive properties in vitro and in vivo. Furthermore, adoptive transfer of these induced regulatory CD25+/− T cells suppressed experimental autoimmune encephalomyelitis when administrated before disease induction or during ongoing experimental autoimmune encephalomyelitis. The suppressive effect of TGF-β on T cell responses was due to the induction of Tregs and not to the direct inhibition of cell proliferation. The differentiation of Th3 cells in vitro was TGF-β dependent as anti-TGF-β abrogated their development. Thus, Ag-specific TGF-β-producing Th3 cells play a crucial role in inducing and maintaining peripheral tolerance by driving the differentiation of Ag-specific Foxp3+ regulatory cells in the periphery.

IL-22 Induces an Acute-Phase Response

IL-22 is made by a unique set of innate and adaptive immune cells, including the recently identified noncytolytic NK, lymphoid tissue-inducer, Th17, and Th22 cells. The direct effects of IL-22 are restricted to nonhematopoietic cells, its receptor expressed on the surface of only epithelial cells and some fibroblasts in various organs, including parenchymal tissue of the gut, lung, skin, and liver. Despite this cellular restriction on IL-22 activity, we demonstrate that IL-22 induces effects on systemic biochemical, cellular, and physiological parameters. By utilizing adenoviral-mediated delivery of IL-22 and systemic administration of IL-22 protein, we observed that IL-22 modulates factors involved in coagulation, including fibrinogen levels and platelet numbers, and cellular constituents of blood, such as neutrophil and RBC counts. Furthermore, we observed that IL-22 induces thymic atrophy, body weight loss, and renal proximal tubule metabolic activity. These cellular and physiological parameters are indicative of a systemic inflammatory state. We observed that IL-22 induces biochemical changes in the liver including induction of fibrinogen, CXCL1, and serum amyloid A that likely contribute to the reported cellular and physiological effects of IL-22. Based on these findings, we propose that downstream of its expression and impact in local tissue inflammation, circulating IL-22 can further induce changes in systemic physiology that is indicative of an acute-phase response.

Th3 Cells in Peripheral Tolerance. II. TGF-β-Transgenic Th3 Cells Rescue IL-2-Deficient Mice from Autoimmunity

We developed a transgenic (Tg) mouse that expresses TGF-β under control of the IL-2 promoter to investigate Th3 cell differentiation both in vitro and in vivo. We previously found that repetitive in vitro Ag stimulation results in constant expression of Foxp3 in TGF-β-Tg Th3 cells that acquire regulatory function independent of surface expression of CD25. To examine the differentiation and function of Th3 cells in vivo and to compare them with thymic-derived CD4+CD25+ regulatory T cells (Treg), we introduced the TGF-β transgene into T cells of IL-2-deficient (IL-2−/−) mice. We found that the induction, differentiation, and function of TGF-β-derived Foxp3+ Th3 cells were independent of IL-2, which differs from thymic Tregs. In an environment that lacks functional CD25+ thymic-derived Tregs, expression of the TGF-β transgene in IL-2−/− mice led to the induction of distinct CD25− regulatory cells in the periphery. These cells expressed Foxp3 and efficiently controlled hyperproliferation of T cells and rescued the IL-2−/− mouse from lethal autoimmunity. Unlike IL-2−/− animals, TGF-β/IL-2−/− mice had normal numbers of T cells, B cells, macrophages, and dendritic cells and did not have splenomegaly, lymphadenopathy, or inflammation in multiple organs. Accumulation of Foxp3+ cells over time, however, was dependent on IL-2. Our results suggest that TGF-β-derived Foxp3+CD25+/− Th3 regulatory cells represent a different cell lineage from thymic-derived CD25+ Tregs in the periphery but may play an important role in maintaining thymic Tregs in the peripheral immune compartment by secretion of TGF-β.

Deficiency of thrombospondin-1 reduces Th17 differentiation and attenuates experimental autoimmune encephalomyelitis.

Transforming growth factor beta (TGF-beta) plays a role both in the induction of Treg and in the differentiation of the IL-17-secreting T cells (Th17) which drive inflammation in experimental autoimmune encephalomyelitis (EAE). We investigated the role that thrombospondin-1 (TSP-1) dependent activation of TGF-beta played in the generation of an encephalitic Th17 response in EAE. Upon immunization with myelin oligodendrocyte glycoprotein peptide (MOG(35-55)), TSP-1 deficient (TSP-1(null)) mice and MOG(35-55) TCR transgenic mice that lack of TSP-1 (2D2 x TSP-1(null)) exhibited an attenuated form of EAE, and secreted lower levels of IL-17. Adoptive transfer of in vitro-activated 2D2 x TSP-1(null) T cells induced a milder form of EAE, independent of TSP-1 expression in the recipient mice. Furthermore, in vitro studies demonstrated that anti-CD3/anti-CD28 pre-activated CD4+ T cells transiently upregulated latent TGF-beta in a TSP-1 dependent way, and such activation of latent TGF-beta was required for the differentiation of Th17 cells. These results demonstrate that TSP-1 participates in the differentiation of Th17 cells through its ability to activate latent TGF-beta, and enhances the inflammatory response in EAE.

Impaired glutamate recycling and GluN2B-mediated neuronal calcium overload in mice lacking TGF-β1 in the CNS

Transforming growth factor β1 (TGF‐β1) is a pleiotropic cytokine expressed throughout the CNS. Previous studies demonstrated that TGF‐β1 contributes to maintain neuronal survival, but mechanistically this effect is not well understood. We generated a CNS‐specific TGF‐β1‐deficient mouse model to investigate the functional consequences of TGF‐β1‐deficiency in the adult mouse brain. We found that depletion of TGF‐β1 in the CNS resulted in a loss of the astrocyte glutamate transporter (GluT) proteins GLT‐1 (EAAT2) and GLAST (EAAT1) and decreased glutamate uptake in the mouse hippocampus. Treatment with TGF‐β1 induced the expression of GLAST and GLT‐1 in cultured astrocytes and enhanced astroglial glutamate uptake. Similar to GLT‐1‐deficient mice, CNS‐TGF‐β1‐deficient mice had reduced brain weight and neuronal loss in the CA1 hippocampal region. CNS‐TGF‐β1‐deficient mice showed GluN2B‐dependent aberrant synaptic plasticity in the CA1 area of the hippocampus similar to the glutamate transport inhibitor DL‐TBOA and these mice were highly sensitive to excitotoxic injury. In addition, hippocampal neurons from TGF‐β1‐deficient mice had elevated GluN2B‐mediated calcium signals in response to extrasynaptic glutamate receptor stimulation, whereas cells treated with TGF‐β1 exhibited reduced GluN2B‐mediated calcium signals. In summary, our study demonstrates a previously unrecognized function of TGF‐β1 in the CNS to control extracellular glutamate homeostasis and GluN2B‐mediated calcium responses in the mouse hippocampus.