Interleukin-2 deficient mice: a new model to study autoimmunity and self-tolerance

The interplay between cytokines, inflammation, and antioxidants: mechanistic insights and therapeutic potentials of various antioxidants and anti-cytokine compounds

Cytokines regulate immune responses essential for maintaining immune homeostasis, as deregulated cytokine signaling can lead to detrimental outcomes, including inflammatory disorders. The antioxidants emerge as promising therapeutic agents because they mitigate oxidative stress and modulate inflammatory pathways. Antioxidants can potentially ameliorate inflammation-related disorders by counteracting excessive cytokine-mediated inflammatory responses. A comprehensive understanding of cytokine-mediated inflammatory pathways and the interplay with antioxidants is paramount for developing natural therapeutic agents targeting inflammation-related disorders and helping to improve clinical outcomes and enhance the quality of life for patients. Among these antioxidants, curcumin, vitamin C, vitamin D, propolis, allicin, and cinnamaldehyde have garnered attention for their anti-inflammatory properties and potential therapeutic benefits. This review highlights the interrelationship between cytokines-mediated disorders in various diseases and therapeutic approaches involving antioxidants.

Novel therapeutic strategies targeting abnormal T-cell signaling in systemic lupus erythematosus

Therapeutic strategies for autoimmune diseases have been based on the use of glucocorticoids and immunosuppressive agents that broadly suppress immune responses. Therefore, organ damage from long-term use and infections due to immunocompromised status have been significant issues. Safer immunosuppressants and biological agents are now available, but there is still an urgent need to develop specific drugs to replace glucocorticoids. T-lymphocytes, central players in immune responses, could be crucial targets in the treatment of autoimmune diseases. Extensive research has been conducted on the phenotypic changes of T-cells in systemic lupus erythematosus, which has led to the discovery of various therapeutic strategies. In this comprehensive review, we discuss novel treatment approaches and target molecules with expected effectiveness in humans and mice, based on research for lymphocytes involved in autoimmune diseases, especially T-cells in SLE.

Low-dose IL-2 therapy in autoimmune diseases: An update review

Regulatory T (Treg) cells are essential for maintaining self-immune tolerance. Reduced numbers or functions of Treg cells have been involved in the pathogenesis of various autoimmune diseases and allograft rejection. Therefore, the approaches that increase the pool or suppressive function of Treg cells in vivo could be a general strategy to treat different autoimmune diseases and allograft rejection. Interleukin-2 (IL-2) is essential for the development, survival, maintenance, and function of Treg cells, constitutively expressing the high-affinity receptor of IL-2 and sensitive response to IL-2 in vivo. And low-dose IL-2 therapy in vivo could restore the imbalance between autoimmune response and self-tolerance toward self-tolerance via promoting Treg cell expansion and inhibiting follicular helper T (Tfh) and IL-17-producing helper T (Th17) cell differentiation. Currently, low-dose IL-2 treatment is receiving extensive attention in autoimmune disease and transplantation treatment. In this review, we summarize the biology of IL-2/IL-2 receptor, the mechanisms of low-dose IL-2 therapy in autoimmune diseases, the application in the progress of different autoimmune diseases, including Systemic Lupus Erythematosus (SLE), Type 1 Diabetes (T1D), Rheumatoid Arthritis (RA), Autoimmune Hepatitis (AIH), Alopecia Areata (AA), Immune Thrombocytopenia (ITP) and Chronic graft-versus-host-disease (GVHD). We also discuss the future directions to optimize low-dose IL-2 treatments.

STAT signaling as a target for intervention: from cancer inflammation and angiogenesis to non-coding RNAs modulation

As a landmark, scientific investigation in cytokine signaling and interferon-related anti-viral activity, signal transducer and activator of transcription (STAT) family of proteins was first discovered in the 1990s. Today, we know that the STAT family consists of several transcription factors which regulate various molecular and cellular processes, including proliferation, angiogenesis, and differentiation in human carcinoma. STAT family members play an active role in transducing signals from cell membrane to nucleus through intracellular signaling and thus activating gene transcription. Additionally, they are also associated with the development and progression of human cancer by facilitating inflammation, cell survival, and resistance to therapeutic responses. Accumulating evidence suggests that not all STAT proteins are associated with the progression of human malignancy; however, STAT3/5 are constitutively activated in various cancers, including multiple myeloma, lymphoma, breast cancer, prostate hepatocellular carcinoma, and non-small cell lung cancer. The present review highlights how STAT-associated events are implicated in cancer inflammation, angiogenesis and non-coding RNA (ncRNA) modulation to highlight potential intervention into carcinogenesis-related cellular processes.

Dysfunctions, Molecular Mechanisms, and Therapeutic Strategies of Regulatory T Cells in Rheumatoid Arthritis

Regulatory T cells (Tregs) represent a distinct subpopulation of CD4⁺ T lymphocytes that promote immune tolerance and maintain immune system homeostasis. The dysfunction of Tregs is tightly associated with rheumatoid arthritis (RA). Although the complex pathogenic processes of RA remain unclear, studies on Tregs in RA have achieved substantial progress not only in fundamental research but also in clinical application. This review discusses the current knowledge of the characterizations, functions, and molecular mechanisms of Tregs in the pathogenesis of RA, and potential therapies for these disorders are also involved.

Dynamic Roles for IL-2-STAT5 Signaling in Effector and Regulatory CD4+ T Cell Populations

CD4⁺ Th cells are responsible for orchestrating diverse, pathogen-specific immune responses through their differentiation into a number of subsets, including T_H1, T_H2, T_H9, T follicular helper, T follicular regulatory, and regulatory T cells. The differentiation of each subset is guided by distinct regulatory requirements, including those derived from extracellular cytokine signals. IL-2 has emerged as a critical immunomodulatory cytokine that both positively and negatively affects the differentiation of individual Th cell subsets. IL-2 signals are propagated, in part, via activation of STAT5, which functions as a key regulator of CD4⁺ T cell gene programs. In this review, we discuss current understanding of the mechanisms that allow IL-2-STAT5 signaling to exert divergent effects across CD4⁺ T cell subsets and highlight specific roles for this pathway in the regulation of individual Th cell differentiation programs.

GM-CSF therapy inhibits chronic graft-versus-host disease via expansion of regulatory T cells

Regulatory T cells (Tregs) attenuate excessive immune responses, making their expansion beneficial in immune-mediated diseases, including allogeneic bone marrow transplantation associated with graft-versus-host disease (GVHD). In addition to interleukin-2, Tregs require T-cell receptor and costimulatory signals from antigen-presenting cells, such as DCs, for their optimal proliferation. Granulocyte-macrophage colony-stimulating factor (GM-CSF) increases DC number and may promote DC-dependent Treg proliferation. Here, we demonstrate that GM-CSF treatment increases CD4⁺ CD8^- DCs, which are associated with Treg expansion. In a mouse model of chronic GVHD (cGVHD), GM-CSF therapy expanded Tregs, protected against the development of skin GVHD, and regulated both Th1 and Th17 responses in the peripheral lymph nodes, resulting in an attenuation of skin cGVHD. Notably, the expanded Tregs were instrumental to GM-CSF-mediated cGVHD inhibition, which was dependent upon an increased ratio of Tregs to conventional T cells rather than augmentation of suppressive function. These data suggest that GM-CSF induces Treg proliferation by expanding CD4⁺ CD8^- DCs, which in turn regulate alloimmune responses in a cGVHD mouse model. Thus, GM-CSF could be used as a therapeutic DC modulator to induce Treg expansion and to inhibit excessive alloimmune responses in immune-related diseases.

Interleukin-2-regulatory T cell axis critically regulates maintenance of hematopoietic stem cells

The role of IL-2 in HSC maintenance is unknown. Here we show that Il2^−/− mice develop severe anomalies in HSC maintenance leading to defective hematopoiesis. Whereas, lack of IL-2 signaling was detrimental for lympho- and erythropoiesis, myelopoiesis was enhanced in Il2^−/− mice. Investigation of the underlying mechanisms of dysregulated hematopoiesis in Il2^−/− mice shows that the IL-2-T_reg cell axis is indispensable for HSC maintenance and normal hematopoiesis. Lack of T_reg activity resulted in increased IFN-? production by activated T cells and an expansion of the HSCs in the bone marrow (BM). Though, restoring T_reg population successfully rescued HSC maintenance in Il2^−/− mice, preventing IFN-? activity could do the same even in the absence of T_reg cells. Our study suggests that equilibrium in IL-2 and IFN-? activity is critical for steady state hematopoiesis, and in clinical conditions of BM failure, IL-2 or anti-IFN-? treatment might help to restore hematopoiesis.

Association of Interleukin-2, but not Interferon-Gamma, single nucleotide polymorphisms with juvenile idiopathic arthritis

BACKGROUND

Cytokines, including interleukin-2 (IL-2) and interferon-gamma (IFN-γ), seem to play a role in the pathogenesis of juvenile idiopathic arthritis (JIA). The aim of this study was to investigate the associations of IL-2 and IFN-γ single nucleotide polymorphisms (SNPs) with susceptibility to JIA in an Iranian population.

METHODS

Genomic DNA of 54 Iranian patients with JIA and 139 healthy unrelated controls were typed for IL-2 (G/T at -330 and +166) as well as IFN-γ gene (A/T at +874), using polymerase chain reaction with sequence-specific primers method, and compared between patients and controls.

RESULTS

A significantly higher frequency of the IL-2 -330 GG genotype (p<0.01) was found in the JIA patients compared to the controls. However, the GT genotype at the same position was notably lower than in controls (p<0.01). Moreover, IL-2 (-330, +166) GT haplotype was more frequent in patients with JIA in comparison with controls. No significant differences was observed between the two groups of case and control for IL-2 (G/T at +166) and IFN-γ (A/T at +874) SNPs.

CONCLUSION

The results of the current study suggest that certain SNPs of IL-2 gene have association with individuals' susceptibility to JIA. However, further investigations are required to confirm the results of this study.

Modulation and the Underlying Mechanism of T Cells in Thymus of Mice by Oral Administration of Sodium Fluoride

The underlying mechanism of thymic T cell regulation has been a hot topic of research in recent years. Fluoride is toxic at high concentrations and fluoride toxicity to thymic T cells was assessed in our study. To explore T cell responses to excess fluoride, different concentrations of fluoride were uptake by mice for 6 weeks. The expression of genes, including Foxn1, Cbx4, DLL4, and IL-7 gene, associated with the development and differentiation of T cells in thymic epithelial cells(TECs) was lower in the experimental groups than that in the control group. The percentages of CD4(+) and CD8(+) T cells that decreased with the fluoride administration were confirmed by flow cytometry. The mRNA levels of immunoregulatory cytokines IL-2 and IL-10, which participate in T cell proliferation, also declined in the experimental groups as compared with the control group. Expression of the T cell function-related genes CD2, PTPRC, CD69, and CD101, which are involved in thymic function in mice, decreased with the fluoride administration. Our findings suggest that the administration of high concentrations of fluoride to mice induces a decrease in CD4(+) and CD8(+) thymus T cells by harming TECs leading to the dysfunction of the thymus by altering the expression of T cell function-related genes and immunoregulatory cytokine production.

Coupled IL-2-dependent extracellular feedbacks govern two distinct consecutive phases of CD4 T cell activation

T cells integrate cell-specific Ag receptor signaling with shared signals mediated by secreted cytokines, which often involve regulatory feedback loops. IL-2 signaling, for example, reduces the synthesis of IL-2 and increases the synthesis of IL-2Rα-chain, whereas both genes require TCR signaling for their activation. The ways by which T cells dynamically integrate these private and public signals during activation are not well understood. We combined robotics, multiparameter flow cytometry, and real-time quantitative PCR to analyze T cell activation at high temporal resolution over several days. Two distinct temporal phases of T cell activation were evident. First, Ag-dependent signals activated low IL-2Rα and high IL-2 production, independent of IL-2 signaling. Subsequently, secreted IL-2 acted as a shared resource driving high IL-2Rα expression, reduced IL-2 synthesis, and cell proliferation. This transition was independent of continued TCR signaling. Our data allowed the determination of the parameters of the IL-2-mediated extracellular positive and negative feedback circuits and demonstrated that the two loops are coupled and become activated at a similar level of IL-2 signaling. We propose that temporal separation of private and shared signals allows T cells to first integrate Ag-specific responses and subsequently share information leading to collective decision making.

Regulatory cells and transplantation tolerance

Transplantation tolerance is a continuing therapeutic goal, and it is now clear that a subpopulation of T cells with regulatory activity (Treg) that express the transcription factor foxp3 are crucial to this aspiration. Although reprogramming of the immune system to donor-specific transplantation tolerance can be readily achieved in adult mouse models, it has yet to be successfully translated in human clinical practice. This requires that we understand the fundamental mechanisms by which donor antigen-specific Treg are induced and function to maintain tolerance, so that we can target therapies to enhance rather than impede these regulatory processes. Our current understanding is that Treg act via numerous molecular mechanisms, and critical underlying components such as mTOR inhibition, are only now emerging.

Mechanisms of Signal Transduction from Receptors of Type I and Type II Cytokines

Cytokines play pivotal roles in regulation of immune responses. Signaling proteins involved in cytokine signal transduction pathways can be potential targets of toxins causing aberrant immune responses. Binding of cytokines to their specific receptors induces activation of signal transduction pathways. In this review, an overview of the cytokine/cytokine receptor system, signaling pathways activated by cytokine receptors, their regulation mechanisms, pathological conditions caused by aberrant cytokine signaling, and issues to be elucidated in the near future is provided.

Competition for IL-2 between Regulatory and Effector T Cells to Chisel Immune Responses

In this review we discuss how the competition for cytokines between different cells of the immune system can shape the system wide immune response. We focus on interleukin-2 (IL-2) secretion by activated effector T cells (T(eff)) and on the competition for IL-2 consumption between T(eff) and regulatory T cells (T(reg)). We discuss the evidence for the mechanism in which the depletion of IL-2 by T(reg) cells would be sufficient to suppress an autoimmune response, yet not strong enough to prevent an immune response. We present quantitative estimations and summarize our modeling effort to show that the tug-of-war between T(reg) and T(eff) cells for IL-2 molecules can be won by T(reg) cells in the case of weak activation of T(eff) leading to the suppression of the immune response. Or, for strongly activated T(eff) cells, it can be won by T(eff) cells bringing about the activation of the whole adaptive immune system. Finally, we discuss some recent applications attempting to achieve clinical effects through the modulation of IL-2 consumption by T(reg) compartment.

Dissecting the effects of endogenous brain IL-2 and normal versus autoreactive T lymphocytes on microglial responsiveness and T cell trafficking in response to axonal injury

IL-2 is essential for T-helper regulatory (Treg) cell function and self-tolerance, and dysregulation of both endogenous brain and peripheral IL-2 gene expression may have important implications for neuronal injury and repair. We used an experimental approach combining mouse congenic breeding and immune reconstitution to test the hypothesis that the response of motoneurons to injury is modulated by the combined effects of IL2-mediated processes in the brain that modulate its endogenous neuroimmunological milieu, and IL2-mediated processes in the peripheral immune system that regulate T cell function (i.e., normal versus autoreactive Treg-deficient T cells). This experimental strategy enabled us to test our hypothesis by disentangling the effect of normal versus autoreactive T lymphocytes from the effect of endogenous brain IL-2 on microglial responsiveness (microglial phagocytic clusters normally associated with dead motoneurons and MHC2(+) activated microglia) and T cell trafficking, using the facial nerve axotomy model of injury. The results demonstrate that the loss of both brain and peripheral IL-2 had an additive effect on numbers of microglial phagocytic clusters at day 14 following injury, whereas the autoreactive status of peripheral T cells was the primary factor that determined the degree to which T cells entered the injured brain and contributed to increased microglial phagocytic clusters. Changes in activated MHC2(+) microglial in the injured FMN were associated with loss of endogenous brain IL-2 and/or peripheral IL-2. This model may provide greater understanding of the mechanisms involved in determining if T cells entering the injured central nervous system (CNS) have damaging or proregenerative effects.

Cutting edge: a novel mechanism bridging innate and adaptive immunity: IL-12 induction of CD25 to form high-affinity IL-2 receptors on NK cells

NK cell expression and use of the IL-2Rα-chain (CD25), required for the high-affinity IL-2R, remain poorly understood. The studies reported in this article demonstrate that infections with murine CMV (MCMV), but not with lymphocytic choriomeningitis virus, induce CD25 on NK cells, along with high levels of IL-12 and IL-18. The cytokines act ex vivo to increase CD25 levels, and IL-12, IL-12R, and STAT4, but not the NK activating receptor Ly49H, are required for peak induction in vivo. All examined NK cell populations are driven into proliferation and incorporate BrdU in response to high ex vivo concentrations of IL-2, but only those from MCMV infection respond to low ex vivo concentrations of IL-2. The numbers of NK cells elicited during MCMV infection are reduced by IL-2 neutralization. Thus, a link between innate and adaptive immunity is established by which composition of innate cytokine responses sets up to promote NK cell use of a factor supporting adaptive responses.

Regulatory T-cells in chronic lymphocytic leukemia and autoimmune diseases

Regulatory T-cells (Tregs) constitute a small subset of cells that are actively involved in maintaining self-tolerance, in immune homeostasis and in antitumor immunity. They are thought to play a significant role in the progression of cancer and are generally increased in patient with chronic lymphocytic leukemia (CLL). Their number correlates with more aggressive disease status and is predictive of the time to treatment, as well. Moreover, it is now clear that dysregulation in Tregs cell frequency and/or function may result in a plethora of autoimmune diseases, including multiple sclerosis, type 1 diabetes mellitus, myasthenia gravis, systemic lupus erythematosus, autoimmune lymphoproliferative disorders, rheumatoid arthritis, and psoriasis. Efforts are made aiming to develop approaches to deplete Tregs or inhibit their function in cancer and autoimmune disorders, as well.

Conditional IL-2 Gene Deletion: Consequences for T Cell Proliferation

To explore the role of interleukin-2 (IL-2) in T cell proliferation, and to circumvent the IL-2 deficiency autoimmune syndrome of conventional il2 gene deletion, mice were created to allow conditional il2 gene deletion when treated with the estrogen analog, tamoxifen (TAM) as adults. Splenocytes from four different mouse strains, C57Bl/6 wild type (WT), conventional IL-2(−/−), TAM-treated Cre recombinase-negative (Cre−)/IL2fl/fl, and Cre recombinase-positive (Cre+)/IL2fl/fl, were activated with anti-CD3 and anti-CD28, and monitored for CD4+ and CD8+ T cell lymphocyte blastogenesis, aerobic glycolysis, BrdU incorporation into newly synthesized DNA, and CFSE dye dilution to monitor cell division. IL-2 production was monitored by quantitative ELISA and multiple additional cytokines were monitored by quantitative protein-bead arrays. Splenocytes from conventional IL-2(−/−) and TAM-treated Cre+ mice resulted in undetectable IL-2 production by ELISA, so that both strains were IL-2-deficient. As monitored by flow cytometry, activated CD4+ and CD8+ T cells from WT, Cre+, and Cre− mice all underwent blastogenesis, whereas far fewer cells from conventional IL-2(−/−) mice did so. By comparison, only cells from IL-2 sufficient WT and Cre− mice switched to aerobic glycolysis as evidenced by a drop in media pH. Blastogenesis was mirrored by BrdU incorporation and CFSE dye dilution by CD4+ and CD8+ T cells from WT, Cre+, and Cre− mice, which were all equivalent, while proliferation of cells from conventional IL-2(−/−) mice was compromised. Splenocytes from IL-2 deficient conventional IL-2(−/−) mice produced low or undetectable other γ_c-chain cytokines (IL-4, IL-7, IL-9, IL-13, IL-15, and IL-21), whereas production of these γ_c-chain cytokines from IL-2-deficient conditional IL-2(−/−) Cre+ mice were comparable with WT and Cre− mice. These results indicate that CD4+ and CD8+ T cell blastogenesis cannot be attributable to IL-2 alone, but a switch to aerobic glycolysis was attributable to IL-2, and proliferation after CD3/CD28 activation is dependent on γ_c-chain cytokines, and not CD3/28 triggering per se.

Interleukin-2 and the septohippocampal system: intrinsic actions and autoimmune processes relevant to neuropsychiatric disorders

The effects of IL-2 on brain development, function, and disease are the result of IL-2's actions in the peripheral immune system and its intrinsic actions in the central nervous system (CNS). Determining whether, and under what circumstances (e.g., development, acute injury), these different actions of IL-2 are operative in the brain is essential to make significant advances in understanding the multifaceted affects of IL-2 on CNS function and disease, including psychiatric disorders. For several decades, there has been a great deal of speculation about the role of autoimmunity in brain disease. More recently, we have learned a great deal about the role of cytokines on neurobiological processes, and there have been many studies that have found peripheral immune alterations in patients with neurological and neuropsychiatric diseases. Despite a plethora of published literature, almost all of this data in humans is correlative and much of the basic research has understandably relied on simpler models (e.g., in vitro models). Good animal models such as our IL-2 knockout mouse model could provide valuable new insight into understanding how the complex biology of a cytokine such as IL-2 can have simultaneous, dynamic effects on multiple systems (e.g., regulating homeostasis in the brain and immune system, autoimmunity that can affect both systems). Animal models can also provide much needed new data elucidating neuroimmunological and autoimmune processes involved in brain development and disease. Such information may ultimately provide critical new insight into the role of brain cytokines and autoimmunity in prominent neurological and neuropsychiatric diseases (e.g., Alzheimer's disease, autism, multiple sclerosis, schizophrenia).

Interleukin-2 and the brain: dissecting central versus peripheral contributions using unique mouse models

Although many studies have documented peripheral immune alterations in patients with psychiatric and neurological disorders, almost all these data in humans are correlative. The actions of IL-2 on neurodevelopment, function, and disease are the result of both IL-2's actions in the peripheral immune system and intrinsic actions in the CNS. Determining if, and under what conditions (e.g., development, acute injury) these different actions of IL-2 are operative in the brain is essential to make advances in understanding the multifaceted affects of IL-2 on CNS function and disease. Mouse models have provided ways to obtain new insights into how the complex biology of a cytokine such as IL-2 can have simultaneous, dynamic effects on multiple systems (e.g., regulating homeostasis in the brain and immune system, autoimmunity that can affect both systems). Here we describe some of the relevant literature and our research using different mouse models. This includes models such as congenic IL-2 knockout mice bred on immunodeficient backgrounds coupled with immune reconstitution strategies used to dissect neuroimmunological processes involved in the development of septohippocampal pathology, and test the hypothesis that dysregulation of the brain's endogenous neuroimmunological milieu may occur with the loss of brain IL-2 gene expression and be involved in initiating CNS autoimmunity. Use of animal models like these in the field of psychoneuroimmunology may lead to critical advances into our understanding of the role of brain cytokines and autoimmunity in neurodegenerative diseases (e.g., Alzheimer's disease), neurodevelopmental disorder (e.g., autism, schizophrenia), and autoimmune diseases including multiple sclerosis.

Immunological variation between inbred laboratory mouse strains: points to consider in phenotyping genetically immunomodified mice

Inbred laboratory mouse strains are highly divergent in their immune response patterns as a result of genetic mutations and polymorphisms. The generation of genetically engineered mice (GEM) has, in the past, used embryonic stem (ES) cells for gene targeting from various 129 substrains followed by backcrossing into more fecund mouse strains. Although common inbred mice are considered "immune competent," many have variations in their immune system-some of which have been described-that may affect the phenotype. Recognition of these immune variations among commonly used inbred mouse strains is essential for the accurate interpretation of expected phenotypes or those that may arise unexpectedly. In GEM developed to study specific components of the immune system, accurate evaluation of immune responses must take into consideration not only the gene of interest but also how the background strain and microbial milieu contribute to the manifestation of findings in these mice. This article discusses points to consider regarding immunological differences between the common inbred laboratory mouse strains, particularly in their use as background strains in GEM.

Autocrine IL-2 is required for secondary population expansion of CD8(+) memory T cells

Two competing theories have been put forward to explain the role of CD4(+) T cells in priming CD8(+) memory T cells: one proposes paracrine secretion of interleukin 2 (IL-2); the other proposes the activation of antigen-presenting cells (APCs) via the costimulatory molecule CD40 and its ligand CD40L. We investigated the requirement for IL-2 by the relevant three cell types in vivo and found that CD8(+) T cells, rather than CD4(+) T cells or dendritic cells (DCs), produced the IL-2 necessary for CD8(+) T cell memory. Il2(-/-) CD4(+) T cells were able to provide help only if their ability to transmit signals via CD40L was intact. Our findings reconcile contradictory elements implicit in each model noted above by showing that CD4(+) T cells activate APCs through a CD40L-dependent mechanism to enable autocrine production of IL-2 in CD8(+) memory T cells.

Loss of CNS IL-2 gene expression modifies brain T lymphocyte trafficking: response of normal versus autoreactive Treg-deficient T cells

Emerging data from our lab and others suggested that dysregulation of the brain's endogenous neuroimmunological milieu may occur with the loss of brain IL-2 gene expression and be involved in initiating processes that lead to CNS autoimmunity. We sought to test our working hypothesis that IL-2 deficiency induces endogenous changes in the CNS that play a key role in eliciting T cell homing into the brain. To accomplish this goal, we used an experimental approach that combined mouse congenic breeding and immune reconstitution. In congenic mice without brain IL-2 (two IL-2 KO alleles) that were reconstituted with a normal wild-type immune system, the loss of brain IL-2 doubled the number of T cells that trafficked into the brain in all regions quantified (hippocampus, septum, and cerebellum) compared to mice with two wild-type brain IL-2 alleles and a wild-type peripheral immune system. Congenic mice with normal brain IL-2 (two wild-type IL-2 alleles) that were immune reconstituted with autoreactive Treg-deficient T cells from IL-2 KO mice developed the expected peripheral autoimmunity (splenomegaly) and had a comparable doubling of T cell trafficking into the hippocampus and septum, whereas they exhibited an additional twofold proclivity for the cerebellum over the septohippocampal regions. Unlike brain trafficking of wild-type T cells, the increased homing of IL-2 KO T cells to the cerebellum was independent of brain IL-2 gene expression. These findings demonstrate that brain IL-2 deficiency induces endogenous CNS changes that may lead to the development of brain autoimmunity, and that autoreactive Treg-deficient IL-2 KO T cells trafficking to the brain could have a proclivity to induce cerebellar neuropathology.

Interleukins, from 1 to 37, and interferon-γ: receptors, functions, and roles in diseases

Advancing our understanding of mechanisms of immune regulation in allergy, asthma, autoimmune diseases, tumor development, organ transplantation, and chronic infections could lead to effective and targeted therapies. Subsets of immune and inflammatory cells interact via ILs and IFNs; reciprocal regulation and counter balance among T(h) and regulatory T cells, as well as subsets of B cells, offer opportunities for immune interventions. Here, we review current knowledge about ILs 1 to 37 and IFN-γ. Our understanding of the effects of ILs has greatly increased since the discoveries of monocyte IL (called IL-1) and lymphocyte IL (called IL-2); more than 40 cytokines are now designated as ILs. Studies of transgenic or knockout mice with altered expression of these cytokines or their receptors and analyses of mutations and polymorphisms in human genes that encode these products have provided important information about IL and IFN functions. We discuss their signaling pathways, cellular sources, targets, roles in immune regulation and cellular networks, roles in allergy and asthma, and roles in defense against infections.

Single-cell quantification of IL-2 response by effector and regulatory T cells reveals critical plasticity in immune response

The sensitivity of T cells to interleukin-2 (IL-2) can vary by three orders of magnitude and is determined by the surface densities of the IL-2 receptor α subunits.

Regulatory T cells inflict a double hit on effector T cells by lowering the bulk IL-2 concentration as well as the sensitivity of effector T cells to this crucial cytokine.

This double hit deprives weakly activated effector T cells of pSTAT5 survival signals while having only minimal effects on strongly activated effector cells that express increased levels of the IL-2 receptor.

Short-term signaling differences lead to a differential functional in terms of proliferation and cell division: regulatory T cell specifically suppress weakly activated effector T cells even at large numbers; small numbers of strongly activated effector T cells overcome the suppression.

Self-/non-self-discrimination in the adaptive immune system relies, to a large extent, on distinctions between self-antigens and foreign antigens as made by individual T cells. As such, single-cell decisions are prone to errors a reliable immune response can be expected to incorporate further proofreading schemes. One such scheme involves long time scale, population-level interactions between effector (T_eff) and regulatory (T_reg) T cells. T_reg cells are often described as immune suppressors; their role as immune regulators can be understood by mapping out the scenarios in which T_reg suppression is either significant or insignificant.

In this study, we have focused on one mechanism that allows T_reg cells to suppress T_eff survival, namely, interleukin-2 (IL-2) deprivation. Following antigen activation, T_eff cells secrete IL-2 and express the α subunit of the IL-2 receptor (IL-2r). The binding of extracellular IL-2 to the IL-2r is crucial for T_eff survival and proliferation and consequently for a full-blown immune response. T_reg cells deplete this IL-2 from the environment and deprive the T_eff cells of this important survival signal. In this tug-of-war for IL-2, we sought to quantitatively describe those scenarios in which IL-2 uptake by T_reg cells suffices to suppress T_eff cell activation and those where it does not.

The core of this competition for IL-2 lies in the fact that IL-2rα is expressed on both T_eff and T_reg cells. To understand how IL-2 binds to its receptor, we measured IL-2r subunit levels on single cells, together with STAT5 phosphorylation as evoked by varied IL-2. Contrary to previous descriptions that set the EC₅₀ of IL-2/IL-2r interaction at 10 pM, we found that the sensitivity of T cells to IL-2 varies over three orders of magnitude concentrations (Figure 1E, experiment). T_eff cells with higher levels of IL-2rα receptor subunit are more sensitive to IL-2, T_reg cells with higher levels of IL-2rα are more efficient in the scavenging of IL-2. IL-2rβ levels, on the other hand, determine response amplitudes. We describe a short time scale, two-step model to quantitatively describe IL-2 binding onto individual cells (Figure 1E, theory).

IL-2r expression levels are therefore a crucial parameter for determining the outcome of the competition for IL-2. We measured the regulation of IL-2r subunits on longer time scales in cultures of either T_eff or T_reg cells. For both cell types, IL-2r levels depend on the exposure to IL-2. For T_eff cells, there is a further dependence on the concentration of antigen by which they were activated.

We then measured IL-2r expression in cocultures of T_reg and T_eff cells. We show how IL-2 secreted by activated T_eff cells suffices in inducing IL-2rα upregulation in the T_reg population. We further show that the presence of T_reg cells decreased IL-2r upregulation in cocultured weakly activated T_eff cells. T_reg cells thus inflict a double hit on T_eff cells by reducing not only extracellular IL-2 concentrations but also the T_eff cells' ability to sense IL-2. T_eff cells activated by high-antigen concentrations exhibit sustained IL-2rα expression that is less prone to this effect. We compared IL-2r levels on T_reg cells and T_eff activated by varied antigen concentrations and found a critical crossover: at low-antigen concentrations T_reg cells have higher IL-2rα than T_eff cells, but this is reversed at high-antigen concentrations.

We constructed a long time scale computational model to quantify the significance of this crossover. The model describes IL-2/IL-2r binding and the regulation of IL-2 and IL-2r expression in populations of T_reg and T_eff cells. For a pure T_eff population, our model predicted a ‘quorum-sensing' threshold implying that sustained pSTAT5 signaling requires a minimal concentration of cells that increases with decreasing activation strength. The model further predicts that the addition of T_reg cells will greatly increase the quorum concentration for weakly activated T_eff cells but have no effect on strongly activated T_eff cells.

We validated the model's predictions in vitro. We show a quorum-sensing threshold for activated T_eff cells. We also show that the presence of a T_reg population suppressed pSTAT5 signaling in a large number of weakly but has little effect on even a few strongly activated T_eff cells (Figure 6C and D). On longer time scales, this translates to the suppression of cell division (Figure 6G and H) and proliferation (Figure 6I) in a manner that discriminates between strongly and weakly activated cells.

We then went to demonstrate that IL-2 deprivation by T_reg cells takes place in vivo. We used IL-2 injections to upregulate IL-2rα levels in T_reg cells. As predicted by our in vitro results, such treatment leads to a suppressive environment in which T_eff cells activated by subsequent antigen/LPS immunization proliferate to a lesser extent. We were able to reverse this suppressive effect by continuing IL-2 treatment post-immunization. This highlights IL-2 as a limiting factor for T_eff proliferation and renders its scavenging by T_reg cells an important mechanism of suppression in vivo.

In conclusion, we formulated a quantitative description of IL-2/IL-2r regulation in mixed population of T_reg and T_eff cells. Population feedback loops that depend on cell numbers, molecular cell surface densities, free molecular densities and timing critically affect the outcome of the competition for IL-2. Such a description allows us to precisely identify the scenarios in which IL-2 deprivation by T_reg cells has a major suppressive role in vitro and better understand the role of this mechanism in vivo.

Understanding how the immune system decides between tolerance and activation by antigens requires addressing cytokine regulation as a highly dynamic process. We quantified the dynamics of interleukin-2 (IL-2) signaling in a population of T cells during an immune response by combining in silico modeling and single-cell measurements in vitro. We demonstrate that IL-2 receptor expression levels vary widely among T cells creating a large variability in the ability of the individual cells to consume, produce and participate in IL-2 signaling within the population. Our model reveals that at the population level, these heterogeneous cells are engaged in a tug-of-war for IL-2 between regulatory (T_reg) and effector (T_eff) T cells, whereby access to IL-2 can either increase the survival of T_eff cells or the suppressive capacity of T_reg cells. This tug-of-war is the mechanism enforcing, at the systems level, a core function of T_reg cells, namely the specific suppression of survival signals for weakly activated T_eff cells but not for strongly activated cells. Our integrated model yields quantitative, experimentally validated predictions for the manipulation of T_reg suppression.

The roles of c-rel and interleukin-2 in tolerance: a molecular explanation of self-nonself discrimination

The molecular mechanisms responsible for the exquisite discrimination between self and nonself molecules have remained enigmatic despite intense investigation. However, with the availability of adequate amounts of anergic lymphocytes produced by double transgenic mice, large numbers of immature B cells from sublethaly irradiated, hematopoietically-synchronized mice, as well as critical gene-deleted mice, it has been possible for the first time to uncover plausible molecular mechanisms that lead to tolerance versus immunity. The Rel family of transcription factors is expressed at different stages of lymphocyte maturation and differentiation. C-Rel is not activated by immature lymphocytes, which undergo either anergy or apoptosis when triggered by antigen receptors, but c-Rel is activated in mature lymphocytes. Antigen receptor triggering induces c-Rel-dependent survival and proliferative genetic programs. In T cells, a critical c-Rel-dependent gene encodes the T-cell growth factor interleukin-2 (IL-2). Thus, T cells from c-Rel gene-deleted mice produce inadequate quantities of IL-2, which renders them immunocompromised and unable to mount normal T-cell proliferative and differentiative responses. In the face of absolute IL-2 deficiency from birth, severe, multiorgan autoimmunity gradually ensues. Also, with more subtle IL-2 deficiency, organ/tissue-specific autoimmune disease becomes evident. Accordingly, both c-Rel and IL-2 appear to be key molecules for tolerance versus immunity, and doubtless will become foci for continued investigation, as well as future therapeutic targets in autoimmune diseases.

Th cells act via two synergistic pathways to promote antiviral CD8+ T cell responses

The mechanisms of how Th cells promote CD8(+) T cell responses during viral infections are largely unknown. In this study, we unraveled the mechanisms of T cell help for CD8(+) T cell responses during vaccinia virus infection. Our results demonstrate that Th cells promote vaccinia virus-specific CD8(+) T cell responses via two interconnected synergistic pathways: First, CD40L expressed by activated CD4(+) T cells instructs dendritic cells to produce bioactive IL-12p70, which is directly sensed by Ag-specific CD8(+) T cells, resulting in increased IL-2Rα expression. Second, Th cells provide CD8(+) T cells with IL-2, thereby enhancing their survival. Thus, Th cells are at the center of an important communication loop with a central role for IL-2/IL-2R and bioactive IL-12.

Influence of FOXP3 on CD4+CD25+ regulatory T cells

FOXP3, a member of the forkhead family of transcriptional regulatory proteins, is expressed predominantly in CD4(+)CD25(+) regulatory T cells. These cells are vital for maintaining peripheral tolerance. A lack of FOXP3 results in severe lymphoproliferative disease and autoimmunity in both mouse and humans, which is the result of an absence of CD4(+)CD25(+)FOXP3(+) regulatory cells. This review discusses the role that this protein plays in the commitment and function of regulatory T cells and its characteristics of FOXP3. We then discuss how, in humans, the induction of FOXP3 in nonregulatory CD4(+) T cells can result in the generation of regulatory T cells in the periphery. A finding that has implications on both how autoimmunity is regulated in vivo as well an impact on the development of therapeutic interventions for the treatment of autoimmunity.

Analysis of multiple candidate genes in association with phenotypes of multiple sclerosis

Multiple sclerosis is a heterogeneous neurological disease with varying degrees of severity. The common hypothesis is that susceptibility to multiple sclerosis and its phenotype are caused by a combination of environmental and genetic factors. The genetic part exerts its effect through several genes, each having modest effects.

We evaluated whether disease severity could be predicted by a model based on clinical data and data from a DNA chip. The DNA chip was designed containing several single nucleotide polymorphisms in 44 genes, previously described to be associated with multiple sclerosis.

A total of 605 patients with multiple sclerosis were included in this analysis, using gender, onset type and age at onset as clinical covariates. We correlated 80 single nucleotide polymorphisms to the degree of disease severity using the following three outcome measures: linear Multiple Sclerosis Severity Score, dichotomous Multiple Sclerosis Severity Score (using a cut-off point of 2.5) and time to reach Expanded Disability Status Scale score 6.

Sixty-nine single nucleotide polymorphisms were included in the analysis. No individual single nucleotide polymorphism showed a significant association; however, a combination of single nucleotide polymorphisms significantly improved the prediction of disease severity in addition to the clinical variables. In all three models the Interleukin 2 gene was included, confirming a previously reported modest effect on disease severity. The highest power was obtained using the dichotomized Multiple Sclerosis Severity Score as outcome.

Several single nucleotide polymorphisms showed their added predictive value over the clinical data in the predictive models. These results support our hypothesis that disease severity is determined by clinical variables and genetic influences (through several genes with small effects) in concert.

Interleukin-2 deficiency-induced T cell autoimmunity in the mouse brain

Interleukin-2 (IL-2) has been implicated in the pathogenesis of neurodevelopmental and neurodegenerative disorders. Studies from our lab have shown that adult IL-2 knockout (KO) mice exhibit septohippocampal pathology and related behavioral deficits. Compared to IL-2 wild-type (WT) mice, IL-2 KO mice have a marked and selective loss of septal cholinergic neurons that occurs between the third postnatal week and adulthood. Given that the development of septal neurons is completed by embryonic day 17 and that IL-2 KO mice exhibit peripheral autoimmunity that develops progressively post-weaning, our data and others led us to postulate that the loss of septal neurons in adult IL-2 KO mice is due to selective autoimmune neurodegeneration that coincides with increasing levels of peripheral autoimmunity. Thus, the present study tested the hypotheses: (1) that T cells selectively target the septum, and; (2) that T lymphocyte infiltration to the septum would correlate with peripheral autoimmune disease. We quantified CD3(+) T cells in the septum, hippocampus, and cerebellum of IL-2 KO and IL-2 WT mice at ages ranging from 2 to 14 weeks. T cells infiltrated the brains of IL-2 deficient mice, but were not selective for the septum. Brain T lymphocyte levels in IL-2 KO mice correlated positively with the degree of peripheral autoimmunity. We did not detect CD19(+) B lymphocytes, IgG-positive lymphocytes or IgG deposition indicative of autoantibodies in the brains of IL-2 KO mice. Further study is needed to understand how IL-2 deficiency-induced autoimmune T lymphocytes interact with endogenous brain cells to alter function and promote disease.

Regulation of Fas-mediated immune homeostasis by an activation-induced protein, Cyclon

Activation-induced cell death (AICD) plays an essential role in the contraction of activated T cells after eradication of pathogen. Fas (APO-1/CD95) is one of the key cell surface proteins that mediate AICD in CD4(+) and CD8(+) T cells. Despite its prime importance in cell death, regulation of Fas expression in T cells is poorly understood. Here we show that Cyclon, a newly identified cytokine-inducible protein, is induced in T cells on T-cell receptor ligation and important for immune homeostasis. Transgenic expression of Cyclon ameliorated autoimmune phenotype in mice lacking subunits of IL-2R. Transgenic expression of Cyclon markedly enhanced AICD through increased expression of Fas whose expression is essential for Cyclon action. Finally, we demonstrated that activated but not resting CD4(+) T cells with targeted deletion of a Cyclon allele show reduced AICD and expression of Fas, indicating a critical role of Cyclon in Fas expression in activated T cells. We think that our data provide insight into expression regulation of Fas in T cells.

Immunologic and therapeutic synergy of IL-27 and IL-2: enhancement of T cell sensitization, tumor-specific CTL reactivity and complete regression of disseminated neuroblastoma metastases in the liver and bone marrow

IL-27 exerts antitumor activity in murine orthotopic neuroblastoma, but only partial antitumor effect in disseminated disease. This study demonstrates that combined treatment with IL-2 and IL-27 induces potent antitumor activity in disseminated neuroblastoma metastasis. Complete durable tumor regression was achieved in 90% of mice bearing metastatic TBJ-IL-27 tumors treated with IL-2 compared with only 40% of mice bearing TBJ-IL-27 tumors alone and 0% of mice bearing TBJ-FLAG tumors with or without IL-2 treatment. Comparable antitumor effects were achieved by IL-27 protein produced upon hydrodynamic IL-27 plasmid DNA delivery when combined with IL-2. Although delivery of IL-27 alone, or in combination with IL-2, mediated pronounced regression of neuroblastoma metastases in the liver, combined delivery of IL-27 and IL-2 was far more effective than IL-27 alone against bone marrow metastases. Combined exposure to IL-27 produced by tumor and IL-2 synergistically enhances the generation of tumor-specific CTL reactivity. Potentiation of CTL reactivity by IL-27 occurs via mechanisms that appear to be engaged during both the initial sensitization and effector phase. Potent immunologic memory responses are generated in mice cured of their disseminated disease by combined delivery of IL-27 and IL-2, and depletion of CD8(+) ablates the antitumor efficacy of this combination. Moreover, IL-27 delivery can inhibit the expansion of CD4(+)CD25(+)Foxp3(+) regulatory and IL-17-expressing CD4(+) cells that are otherwise observed among tumor-infiltrating lymphocytes from mice treated with IL-2. These studies demonstrate that IL-27 and IL-2 synergistically induce complete tumor regression and long-term survival in mice bearing widely metastatic neuroblastoma tumors.

Yin and yang of cytokine regulation in solid organ graft rejection and tolerance

Solid organ transplantation is the therapy of choice for end stage diseases. The alloimmune response generated after transplantation induces the production of a "cytokine storm" that can lead to either the rejection of the organ or graft acceptance. These key decisions, which determine the transplant fate, depend on the type of cytokine response (Th1/Th2). An inflammatory response will lead to graft loss; a tolerogenic response assists in graft acceptance. A balance between different factors often determines outcome. The same cytokine may assist in either allograft rejection or graft survival depending on: (1) the cell types in the vicinity, (2) the amount of each cytokine produced, (3) different sites, and (4) if it acts in a synergistic or antagonistic manner with other cytokines. This review focuses on cytokines that manipulate the alloimmune response after organ transplantation and that play a role either in graft rejection (yin) or tolerance (yang).

A new genetic variant involved in genetic susceptibility to alcoholic liver cirrhosis: -330T>G polymorphism of the interleukin-2 gene

OBJECTIVE

Genetic factors may determine susceptibility to develop alcoholic liver cirrhosis, although it remains uncertain why only a minority of alcoholics suffers from this disease. A decrease in serum levels of interleukin-2 (IL-2) is usually found in alcoholic cirrhotics. In this study we examined the relationship between the -330T>G IL-2 gene (IL2) polymorphism and alcoholic liver cirrhosis.

METHODS

Genotyping of the aforementioned polymorphism was done by polymerase chain reaction and digestion with restriction enzymes in 257 male alcoholics (161 without liver disease and 96 with alcoholic liver cirrhosis) and 101 healthy controls. A logistic regression analysis was performed to adjust for potential confounders and to analyze the model of inheritance.

RESULTS

We found an association between the -330T>G IL2 polymorphism and alcoholic liver cirrhosis: the frequency of the allele T carriers (genotype TT and GT) was significantly higher in alcoholics with cirrhosis (96.9%) than in those without liver disease (89.4%, P=0.043).

CONCLUSION

We report for the first time that the possession of the -330T allele of the IL2 is associated with a higher risk of developing alcoholic liver cirrhosis and this fact may favor the progression of alcoholic liver disease.

Central role of defective interleukin-2 production in the triggering of islet autoimmune destruction

The dynamics of CD4(+) effector T cells (Teff cells) and CD4(+)Foxp3(+) regulatory T cells (Treg cells) during diabetes progression in nonobese diabetic mice was investigated to determine whether an imbalance of Treg cells and Teff cells contributes to the development of type 1 diabetes. Our results demonstrated a progressive decrease in the Treg cell:Teff cell ratio in inflamed islets but not in pancreatic lymph nodes. Intra-islet Treg cells expressed reduced amounts of CD25 and Bcl-2, suggesting that their decline was due to increased apoptosis. Additionally, administration of low-dose interleukin-2 (IL-2) promoted Treg cell survival and protected mice from developing diabetes. Together, these results suggest intra-islet Treg cell dysfunction secondary to defective IL-2 production is a root cause of the progressive breakdown of self-tolerance and the development of diabetes in nonobese diabetic mice.

Nuclear export of NF90 to stabilize IL-2 mRNA is mediated by AKT-dependent phosphorylation at Ser647 in response to CD28 costimulation

IL-2 is one of the most important cytokines required for T cell-mediated immune responses. Costimulation of CD28 in T cells up-regulates IL-2 mRNA levels via transcription activation and mRNA stabilization. Upon T cell activation, NF90, an AU-rich element (ARE)-binding protein, translocates from the nucleus into the cytoplasm, where it binds to the ARE-containing 3' untranslated regions of IL-2 mRNA and slows down degradation of IL-2 mRNA. The translocation of NF90 is mediated through a nuclear export signal at its N terminus, but how it is triggered is still unclear. Phosphorylation of ARE-binding proteins has been reported as a signal transduction pathway to stabilize ARE-containing transcripts. In this study, we demonstrate that AKT phosphorylates NF90 on Ser647 upon CD28 costimulation. This phosphorylation is necessary for nuclear export of NF90 and IL-2 mRNA stabilization by this protein, because a mutation at Ser647 abolished both functions. We observed that treatment of cells with CD28 costimulation induced distinct increase in phosphorylation of AKT and NF90 at Ser647 concomitantly. Phosphorylation at Ser647 of NF90 up-regulated IL-2 production in response to CD28 costimulation. In vivo and in vitro data support a model in which CD28 costimulation activates AKT to phosphorylate NF90 at Ser647 and phosphorylation triggers NF90 to relocate to the cytoplasm and stabilize IL-2 mRNA.

Negative feedback regulation of T cells via interleukin-2 and FOXP3 reciprocity

As interleukin-2 (IL2) is central to the clonal expansion of antigen-selected T cells, we investigated the relationship between IL2 and the negative regulatory transcription factor FOXP3. We found IL2 to be responsible for T cell antigen receptor (TCR)-activated FOXP3 expression by both CD4+ and CD8+ human T cells, and as anticipated, FOXP3 expression restricted TCR-stimulated IL2 expression. However, no evidence could be found that FOXP3+ cells actively suppress IL2 expression by FOXP3- cells. These data are consistent with an IL2/FOXP3-dependent negative feedback loop that normally regulates the T cell immune response. It follows that a defect in this negative feedback loop as a result of a deficiency of either IL2 or FOXP3 will lead to a hyperproliferative autoimmune syndrome, without the necessity of invoking an active suppressive function for FOXP3+ T cells.

Protein kinase C theta plays a fundamental role in different types of chronic colitis

BACKGROUND & AIMS

Dysregulated host/microbial interactions induce the development of colitis by activating deleterious acquired immune responses. Activation of CD4(+) T cells is mainly induced through signaling machinery associated with immunologic synapse (IS). A key molecule associated with the IS is protein kinase C (PKC) theta. However, the role of PKCtheta in the pathogenesis of colitis has not fully been defined.

METHODS

The role of PKCtheta for the acquired-immune responses involved in the development of different types of colitis (CD45RB model, T-cell receptor [TCR] alpha knockout [KO] mice and interleukin [IL]-2KO mice) was examined by generating double KO mice and by utilizing cell transfer approaches.

RESULTS

Adoptive transfer of PKCtheta-deficient naïve CD4(+) T cells failed to induce T helper cell (Th) 1-mediated colitis in the immune-deficient host (CD45RB model). Development of Th2-mediated colitis in TCRalphaKO mice was also inhibited by the absence of PKCtheta. In IL-2KO mice, which develop colitis because of dysregulated T-cell homeostasis, deficiency of PKCtheta in CD4(+) T cells failed to induce the development of severe colitis. Interestingly, absence of PKCtheta led to a remarkable decrease in the proliferation, but not apoptosis, of colonic memory CD4(+) T cells. This impaired proliferation resulted in a marked decrease in the colonic CD4(+) T cells that are capable of producing IL-17. In addition, deficiency of PKCtheta inhibited the production of Th2 cytokines by colonic CD4(+) T cells.

CONCLUSIONS

PKCtheta serves as a common and fundamental signaling molecule in the development of different types of colitis and may represent an attractive target for treating inflammatory bowel disease.

Interleukin-18 gene polymorphism, but not interleukin-2 gene polymorphism, is associated with rheumatoid arthritis

To investigate whether polymorphisms of IL-2 and IL-18 genes are associated with rheumatoid arthritis (RA), polymorphisms of IL-2 and IL-18 genes were detected by polymerase-chain-reaction-based restriction analysis in the patients with RA and normal controls. The results for the IL-18 gene revealed a significant difference between the patients and the normal controls (p = 0.000003), but there was no significant difference for the IL-2 gene (p = 0.876). The IL-18 gene 105A allele was associated with RA in Chinese patients. Individuals possessing the 105A allele had a higher incidence of RA. A lack of association of IL-2 gene polymorphism between RA patients and healthy individuals was noted. The results of this study provide genetic evidence that IL-18-105A/C polymorphism may play an effective role in RA.

Cytokine-neuroantigen fusion proteins: new tools for modulation of myelin basic protein (MBP)-specific T cell responses in experimental autoimmune encephalomyelitis

Fusion proteins incorporating anti-inflammatory cytokines and immunodominant self antigen as separate domains of a single protein may hold promise for development of antigen-specific tolerogenic vaccines. Proteins incorporating rat sequences of IL-1RA, IL-2, IL-4, IL-10, or IL-13 were expressed as fusion proteins containing the major encephalitogenic region of myelin basic protein (MBP). These fusion proteins were expressed via baculovirus (bv) expression systems and were shown to have cytokine-dependent and antigen-specific biological activity. In the case of the IL-2 and IL-4 fusion proteins, covalent linkage of the cytokine and neuroantigen domains resulted in synergistic antigen presentation. These data indicate that the cytokine domain may be able to modulate APC activity and simultaneously target the covalently tethered NAg for enhanced presentation by certain APC subsets. Cytokine/antigen fusion proteins may represent a novel tool for antigen-specific immune modulation in autoimmune disease.

Characterization of immunodeficiency in a patient with growth hormone insensitivity secondary to a novel STAT5b gene mutation

STAT5 proteins are components of the common growth hormone and interleukin 2 family of cytokines' signaling pathway. Mutations in the STAT5b gene, described in 2 patients, lead to growth hormone insensitivity that resembles Laron syndrome. Clinical immunodeficiency was also present, although immunologic defects have not been well characterized thus far. Here we describe a 16-year-old girl who suffered generalized eczema and recurrent infections of the skin and respiratory tract since birth. She also suffered severe chronic lung disease and multiple episodes of herpetic keratitis. Clinical features of congenital growth hormone deficiency were observed, such as persistently low growth rate, severely delayed bone age, and postnatal growth failure resulting from growth hormone resistance. This combined phenotype of growth hormone insensitivity and immunodeficiency was attributable to a homozygous C-->T transition that resulted in a nonsense mutation at codon 152 in exon 5 of the STAT5b gene. This novel mutation determined a complete absence of protein expression. The main immunologic findings were moderate T-cell lymphopenia (1274/mm3), normal CD4/CD8 ratio, and very low numbers of natural killer (18/mm3) and gammadelta T (5/mm3) cells. T cells presented a chronically hyperactivated phenotype. In vitro T-cell proliferation and interleukin 2 signaling were impaired. CD4+ and CD25+ regulatory T cells were significantly diminished, and they probably contributed to the signs of homeostatic mechanism deregulation found in this patient. This new case, in accordance with 2 previously reported cases, definitely demonstrates the significant role of the STAT5b protein in mediating growth hormone actions. Furthermore, the main immunologic findings bring about an explanation for the clinical immunodeficiency features and reveal for the first time the relevant role of STAT5b as a key protein for T-cell functions in humans.