Requirement for T-cell apoptosis in the induction of peripheral transplantation tolerance.

The mechanisms of allograft tolerance have been classified as deletion, anergy, ignorance and suppression/regulation. Deletion has been implicated in central tolerance, whereas peripheral tolerance has generally been ascribed to clonal anergy and/or active immunoregulatory states. Here, we used two distinct systems to assess the requirement for T-cell deletion in peripheral tolerance induction. In mice transgenic for Bcl-xL, T cells were resistant to passive cell death through cytokine withdrawal, whereas T cells from interleukin-2-deficient mice did not undergo activation-induced cell death. Using either agents that block co-stimulatory pathways or the immunosuppressive drug rapamycin, which we have shown here blocks the proliferative component of interleukin-2 signaling but does not inhibit priming for activation-induced cell death, we found that mice with defective passive or active T-cell apoptotic pathways were resistant to induction of transplantation tolerance. Thus, deletion of activated T cells through activation-induced cell death or growth factor withdrawal seems necessary to achieve peripheral tolerance across major histocompatibility complex barriers.     

Thrombopoietin signal transduction: studies from cell lines and primary cells

Thrombopoietin (TPO) and its receptor Mpl support all of the developmental step necessary for megakaryocytopoiesis. In the past few years, the signaling pathways utilized by this member of the cytokine receptor family have been extensively studied, especially JAK/STAT, Ras/MAP kinase, Shc, and other adapter molecules. Many if not most of the secondary signaling pathways activated by thrombopoietin have also been identified upon binding of other hematopoietic growth factors to their cognate receptors, making the study of Mpl signaling representative of the field in general. However, identifying unique molecules or combinations of signals that direct megakaryocyte development has been an elusive goal and has led some investigators to conclude that there is little specificity during Mpl signal transduction. In this article we review the data regarding Mpl signaling with particular attention to the methods employed and critical interpretation of the data generated. Future studies will have to focus on primary bone marrow cells and intact animal models rather than transformed cell lines. Furthermore, it is likely that a comprehensive, integrative analysis of the many pathways activated by ligand binding will be necessary to understand the physiology of cytokine signaling.     

Interleukin-1 signaling in solid organ malignancies

As inflammation plays a critical role in the development and progression of cancer, therapeutic targeting of cytokine pathways involved in both tumorigenesis and dictating response to clinical treatments are of significant interest. Recent evidence has highlighted the importance of the pro-inflammatory cytokine interleukin-1 (IL-1) as a key mediator of tumor growth, metastatic disease spread, immunosuppression, and drug resistance in cancer. IL-1 promotes tumorigenesis through diverse mechanisms, including the activation of oncogenic signaling pathways directly in tumor cells and via orchestrating crosstalk between the cellular constituents of the tumor microenvironment (TME), thereby driving cancer growth. This review will provide an overview of IL-1 signaling and physiology and summarize the disparate mechanisms involving IL-1 in tumorigenesis and cancer progression. Additionally, clinical studies targeting IL-1 signaling in the management of solid organ tumors will be summarized herein.     

Human acute lymphoblastic leukemia (ALL) blasts as accessory cells during T-cell activation: differences between patients in costimulatory capacity affect proliferative responsiveness and cytokine release by activated T cells

The ability of acute lymphoblastic leukemia (ALL) blasts to mediate costimulatory signals during T-lymphocyte activation was investigated in an experimental model in which monoclonal T-cell populations were stimulated with standardized activation signals (anti-CD3 and anti-CD28 monoclonal antibodies; phytohemagglutinin, PHA). Leukemia cells from 12 consecutive ALL patients with high peripheral blood blast counts were studied. Proliferative T-cell responses were detected for a majority of these patients when irradiated leukemia blasts were used as accessory cells during activation. T-cell cytokine release was also observed for most patients when using nonirradiated ALL accessory cells. Low or undetectable cytokine levels were usually observed for CD8+ clones, whereas the CD4+ clones often showed a broad cytokine response with release of interleukin-2 (IL-2), IL-4, IL-10, IL-13 and interferon gamma(IFN-gamma) in the presence of the ALL accessory cells. ALL blasts were also able to function as allostimulatory cells for normal peripheral blood mononuclear responder cells. However, both T-cell proliferation and cytokine release showed a wide variation between ALL patients. The accessory cell function of ALL blasts showed no correlation with the release of immunomodulatory mediators (IL-2, IL-10, IL-15) or the expression of any single adhesion/costimulatory membrane molecule (CD54, CD58, CD80, CD86) by the blasts. We conclude that for a majority of patients, native ALL blasts can mediate costimulatory signals needed for accessory cell-dependent T-cell activation, but differences in costimulatory capacity between ALL patients affects both the proliferative responsiveness and cytokine release by activated T cells.     

Expression of γ-chain cytokine receptors on CD8+ T cells in HIV infection with a focus on IL-7Rα (CD127)

When interleukin-2 (IL-2) receptor γ-chain (γ(C))-sharing cytokine receptors on T cells bind their specific ligands (IL-2, -4, -7, -9, -15 or -21), they initiate a variety of cell signals that promote survival, differentiation or antiviral or antitumor cytolytic functions. Although expression of the γ(C) is constitutive across T-cell subsets, the varying expression of other receptor complex components can regulate cytokine signalling and function. Impaired γ(C) cytokine activity in HIV infection, and the role of γ(C) cytokines in CD8(+) T-cell function and homeostasis, implicates these molecules among potential contributors to the observed decline of cytolytic activity (CTL) in HIV disease. In particular, this review will be highlighting information about the IL-7 receptor (IL-7R) complex, which is composed of the γ(C) and the IL-7Rα (CD127) chains. There has been an abundance of HIV-related CD127 research and its important role in CD8(+) T-cell survival and function. The expression of CD127 undergoes dramatic changes throughout the course of T-cell responses in HIV infection. The expression of CD127 is significantly decreased in progressive HIV disease, whereas effective antiretroviral therapy results in its recovery. Observations of impaired IL-7 activity in HIV(+) individuals have suggested that CD127 has an important role in HIV immunopathogenesis. In addition, a soluble form of CD127 (sCD127) is upregulated in the plasma of HIV(+) individuals. Hence, CD127 is being increasingly considered as a marker of disease prognosis, and related information may provide insight into understanding the expression and role of other γ(C) receptors in HIV disease and contribute to the development of novel cytokine-based therapeutics.     

Immune-To-Brain Signaling: How Important are the Blood–Brain Barrier-independent Pathways?

A conceptual obstacle for understanding immune-to-brain signaling is the issue of the blood-brain barrier (BBB). In the last 30 years, several pathways have been investigated to address the question of how peripheral immune signals are transmitted into the brain. These pathways can be categorized into two types: BBB-dependent pathways and BBB-independent pathways. BBB-dependent pathways involve the BBB as a relay station or porous barrier, whereas BBB-independent pathways use neuronal routes that bypass the BBB. Recently, a complete BBB-dependent ascending pathway for immune-to-brain signaling has been described. Details of BBB-independent pathways are still under construction. In this review, I will summarize the current progress in unraveling immune-to-brain signaling pathways. In addition, I will provide a critical analysis of the literature to point to areas where our knowledge of the immunological afferent signaling to the central nervous system is still sorely lacking.     

Role of the intracellular domain of IL-7 receptor in T cell development

Signals from the IL-7R are uniquely required for T cell development and maintenance, despite the resemblance of IL-7R to other cytokine receptors and the apparent sharing of common signaling pathways. This unique requirement could either reflect unique expression of IL-7R or IL-7, or it could indicate that the IL-7R delivers unique signals. To determine whether the IL-7R provided unique signals, we exchanged its intracellular domain with that of other cytokine receptors: IL-4R, IL-9R, and prolactin receptor (PRLR). Chimeric receptors were used to reconstitute development of IL-7R(-/-) hemopoietic progenitors by transducing the receptors in retroviral vectors. Whereas IL-7R(-/-) thymocytes are arrested at the double-negative stage, IL-4R, IL-9R, or PRLR all imparted some progression to the double-positive stage. IL-4R and PRLR gave only small numbers of thymocytes, whereas IL-9R gave robust alphabeta T cell development and reconstitution of peripheral CD4 and CD8 cells, indicating that it can duplicate many of the functions of IL-7R. However, IL-9R failed to reconstitute rearrangement of the TCRgamma locus or development of gammadelta T cells. Thus, the IL-7R signals required in the alphabeta T cell lineage (such as survival and proliferation) are not unique to this receptor, whereas rearrangement of the TCRgamma locus may require a signal that is not shared by other receptors.     

Targeting T cell-specific costimulators and growth factors in a model of autoimmune hemolytic anemia

Although it is established that failure of regulatory mechanisms underlies many autoimmune diseases, the stimuli that activate autoreactive lymphocytes remain poorly understood. Defining these stimuli will lead to therapeutic strategies for autoimmune diseases. IL-2-deficient mice develop spontaneous autoimmunity, because of a deficiency of regulatory T cells, and on the BALB/c background, they rapidly die from autoimmune hemolytic anemia. To define the importance of costimulatory pathways in various components of this autoimmune disorder, we first intercrossed IL-2-deficient mice with mice lacking CD28 or CD40L. Elimination of CD28 reduced the activation of autoreactive T cells and lymphoproliferation as well as production of autoantibodies, whereas elimination of CD40L reduced autoantibody production without affecting T cell expansion and accumulation. To examine the role of IL-7, we blocked IL-7R signaling with neutralizing Abs. This treatment inhibited the production of autoantibodies and the development of autoimmune hemolytic anemia. Together, these data indicate that specific costimulatory and cytokine signals are critical for the spontaneous autoantibody-mediated disease that develops in IL-2-deficient mice.     

Augmented IL-7 signaling during viral infection drives greater expansion of effector T cells but does not enhance memory

IL-7 signals are crucial for the survival of naive and memory T cells, and the IL-7R is expressed on the surface of these cells. Following viral infection, the IL-7R is expressed on only a subset of effector CD8 T cells, and has been demonstrated to be important for the survival of these memory precursors. IL-7 message levels remain relatively constant during the T cell response to lymphocytic choriomeningitis virus, but a short-lived burst of GM-CSF is observed soon after infection. Retroviral expression of a chimeric GM-CSF/IL-7R, in which binding of GM-CSF by T cells leads to IL-7 signaling, allows for the delivery of an IL-7 signal in all effector T cells expressing the receptor. In mice infected with lymphocytic choriomeningitis virus, CD8 and CD4 T cells transduced with this chimeric receptor underwent an enhanced proliferative response compared with untransduced populations in the same host. Similarly, TCR transgenic CD8 cells expressing the chimeric receptor produced higher effector numbers during the peak of the T cell response to infection. Surprisingly, the enhanced proliferation did not lead to higher memory numbers, as the subsequent contraction phase was more pronounced in the transduced cell populations. These findings demonstrate that artificial IL-7 signaling during an infection leads to significantly increased Ag-specific effector T cell numbers, but does not result in increased numbers of memory progeny. The extent of contraction may be dictated by intrinsic factors related to the number of prior cell divisions.     

IL-7Rα deficiency in p53null mice exacerbates thymocyte telomere erosion and lymphomagenesis

Interleukin-7 (IL-7) is an essential T-cell survival cytokine. IL-7 receptor (IL-7Rα) deficiency severely impairs T-cell development due to substantial apoptosis. We hypothesized that IL-7Rα(null)-induced apoptosis is partially contributed by an elevated p53 activity. To investigate the genetic association of IL-7/IL-7Rα signaling with the p53 pathway, we generated IL-7Rα(null)p53(null) (DKO) mice. DKO mice exhibited a marked reduction of apoptosis in developing T cells and an augmented thymic lymphomagenesis with telomere erosions and exacerbated chromosomal anomalies, including chromosome duplications, breaks, and translocations. In particular, Robertsonian translocations, in which telocentric chromosomes fuse at the centromeric region, and a complete loss of telomeres at the fusion site occurred frequently in DKO thymic lymphomas. Cellular and molecular investigations revealed that IL-7/IL-7Rα signaling withdrawal diminished the protein synthesis of protection of telomere 1 (POT1), a subunit of telomere protective complex shelterin, leading to telomere erosion and the activation of the p53 pathway. Blockade of IL-7/IL-7Rα signaling in IL-7-dependent p53(null) cells reduced POT1 expression and caused telomere and chromosome abnormalities similar to those observed in DKO lymphomas. This study underscores a novel function of IL-7/IL-7Rα during T-cell development in regulating telomere integrity via POT1 expression and provides new insights into cytokine-mediated survival signals and T-cell lymphomagenesis.     

Signaling of interleukin-17 family cytokines in immunity and inflammation

IL-17 cytokine family, though still young since discovery, has recently emerged as critical players in immunity and inflammatory diseases. The prototype cytokine, IL-17A, plays essential roles in promoting inflammation and host defense. IL-17RA, a member of the IL-17 receptor family, forms a complex with another member, IL-17RC, to mediate effective signaling for IL-17A as well as IL-17F, which is most similar to IL-17A, via Act1 and TRAF6 factors. On the other hand, IL-17RA appears to interact with IL-17RB to regulate signaling by another cytokine IL-25. IL-25, the most distant from IL-17A in the IL-17 family, is involved in allergic disease and defense against helminthic parasites. In this review, we discuss recent advancements on signaling mechanisms and biological functions of IL-17A, IL-17F and IL-25, which will shed light on the remaining IL-17 family cytokines and help understand and treat inflammatory diseases.     

Notch1 and IL-7 receptor interplay maintains proliferation of human thymic progenitors while suppressing non-T cell fates

Notch signaling is critical for T cell development of multipotent hemopoietic progenitors. Yet, how Notch regulates T cell fate specification during early thymopoiesis remains unclear. In this study, we have identified an early subset of CD34high c-kit+ flt3+ IL-7Ralpha+ cells in the human postnatal thymus, which includes primitive progenitors with combined lymphomyeloid potential. To assess the impact of Notch signaling in early T cell development, we expressed constitutively active Notch1 in such thymic lymphomyeloid precursors (TLMPs), or triggered their endogenous Notch pathway in the OP9-Delta-like1 stroma coculture. Our results show that proliferation vs differentiation is a critical decision influenced by Notch at the TLMP stage. We found that Notch signaling plays a prominent role in inhibiting non-T cell differentiation (i.e., macrophages, dendritic cells, and NK cells) of TLMPs, while sustaining the proliferation of undifferentiated thymocytes with T cell potential in response to unique IL-7 signals. However, Notch activation is not sufficient for inducing T-lineage progression of proliferating progenitors. Rather, stroma-derived signals are concurrently required. Moreover, while ectopic IL-7R expression cannot replace Notch for the maintenance and expansion of undifferentiated thymocytes, Notch signals sustain IL-7R expression in proliferating thymocytes and induce IL-7R up-regulation in a T cell line. Thus, IL-7R and Notch pathways cooperate to synchronize cell proliferation and suppression of non-T lineage choices in primitive intrathymic progenitors, which will be allowed to progress along the T cell pathway only upon interaction with an inductive stromal microenvironment. These data provide insight into a mechanism of Notch-regulated amplification of the intrathymic pool of early human T cell progenitors.     

IL-35, a double-edged sword in cancer

Interleukin 35 (IL-35), a cytokine mainly produced by regulatory T cells (Treg cells), is composed of an Epstein-Barr virus–induced gene 3 β-chain and an IL-12 p35 α-chain. IL-35 causes tumorigenicity in cancer, protects cancer cells against apoptosis, and facilitates cancer progression. However, a few reports have referred to its contradictory roles in cancer prevention. Therefore, the exact purpose of this cytokine in cancer development has become a fundamental question that needs to be answered. In this review, we explain the structure of IL-35 and its receptors and their different signaling pathways. Finally, the function of IL-35 in some cancers and the possible application of this cytokine in approaches for cancer therapy have been discussed.     

TGFbeta1 and Treg cells: alliance for tolerance

Transforming growth factor beta1 (TGFbeta1), an important pleiotropic, immunoregulatory cytokine, uses distinct signaling mechanisms in lymphocytes to affect T-cell homeostasis, regulatory T (Treg)-cell and effector-cell function and tumorigenesis. Defects in TGFbeta1 expression or its signaling in T cells correlate with the onset of several autoimmune diseases. TGFbeta1 prevents abnormal T-cell activation through the modulation of Ca2+-calcineurin signaling in a Caenorhabditis elegans Sma and Drosophila Mad proteins (SMAD)3 and SMAD4-independent manner; however, in Treg cells, its effects are mediated, at least in part, through SMAD signaling. TGFbeta1 also acts as a pro-inflammatory cytokine and induces interleukin (IL)-17-producing pathogenic T-helper cells (Th IL-17 cells) synergistically during an inflammatory response in which IL-6 is produced. Here, we will review TGFbeta1 and its signaling in T cells with an emphasis on the regulatory arm of immune tolerance.     

Interleukin-6 up-regulates the expression of interleukin-15 is associated with MAPKs and PI3-K signaling pathways in the human keratinocyte cell line,HaCaT

Interleukin (IL)-15 is an important inflammatory cytokine and plays a key role in autoimmune disease. At present, IL-15 gene expression and regulation related to many innate immunity trigger signals have been clarified in some specific cell types, but the relationship of IL-6 and IL-15 in the human keratinocyte cell line (HaCaT) is unknown. In this study, we investigated the effect of IL-6 on the expression of IL-15 and selected signaling pathways in HaCaT cells. Results demonstrated that IL-6 up-regulated the expression of IL-15 both at the mRNA and protein levels. Meanwhile, IL-6 was able to activate MAPKs-ERK1/2 and PI3K-AKT signaling pathways. Furthermore, the high expression of IL-15 induced by IL-6 was down-regulated while MAPKs-ERK1/2 and PI3K-AKT signaling pathways were, respectively, blocked by PD98059 and LY294002. These findings indicate that the expression of IL-15 up-regulated by IL-6 is associated with MAPKs-ERK1/2 and PI3K-AKT signaling pathways in HaCaT cells.