Interleukin-2 gene deletion produces a robust reduction in susceptibility to experimental autoimmune encephalomyelitis in C57BL/6 mice

Induction of IL-2 by interleukin-12 p40 homodimer and IL-12, but not IL-23, in microglia and macrophages: Implications for multiple sclerosis

The level of IL-2 increases markedly in serum and central nervous system (CNS) of patients with multiple sclerosis (MS) and animals with experimental allergic encephalomyelitis (EAE). However, mechanisms by which IL-2 is induced under autoimmune demyelinating conditions are poorly understood. The present study underlines the importance of IL-12p40 homodimer (p402), the so-called biologically inactive molecule, in inducing the expression of IL-2 in mouse BV-2 microglial cells, primary mouse and human microglia, mouse peritoneal macrophages, RAW264.7 macrophages, and T cells. Interestingly, we found that p402 and IL-12p70 (IL-12), but not IL-23, dose-dependently induced the production of IL-2 and the expression of IL-2 mRNA in microglial cells. Similarly, p402 also induced the activation of IL-2 promoter in microglial cells and RAW264.7 cells. Among various stimuli tested, p402 was the most potent stimulus followed by IFN-γ, bacterial lipopolysaccharide, HIV-1 gp120, and IL-12 in inducing the activation of IL-2 promoter in microglial cells. Moreover, p402, but not IL-23, increased NFATc2 mRNA expression and the transcriptional activity of NFAT. Furthermore, induction of IL-2 mRNA expression by over-expression of p40, but not by p19, cDNA indicated that p40, but not p19, is responsible for the induction of IL-2 mRNA in microglia. Finally, by using primary microglia from IL to 12 receptor β1 deficient (IL-12Rβ1-/-) and IL-12 receptor β2 deficient (IL-12Rβ2-/-) mice, we demonstrate that p402 induces the expression of IL-2 via IL-12Rβ1, but not IL-12Rβ2. In experimental autoimmune encephalomyelitis, an animal model of MS, neutralization of p402 by mAb a3-1d led to decrease in clinical symptoms and reduction in IL-2 in T cells and microglia. These results delineate a new biological function of p402, which is missing in the so-called autoimmune cytokine IL-23, and raise the possibility of controlling increased IL-2 and the disease process of MS via neutralization of p402.

Impact of a Demyelination-Inducing Central Nervous System Virus on Expression of Demyelination Genes in Type 2 Lymphoid Cells

We recently reported the role of type 2 innate lymphoid cells (ILC2s) in central nervous system (CNS) demyelination using a model of CNS demyelination involving recombinant herpes simplex virus 1 (HSV-1) that constitutively expresses mouse interleukin 2 (HSV-IL-2). In this investigation, we studied how ILC2s respond to HSV-IL-2 at the cellular level using cytokine and gene expression profiling. ILC2s infected with HSV-IL-2 expressed higher levels of granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-5, IL-6, IL-13, IP-10, MIP-2, and RANTES, which include proinflammatory cytokines, than did those infected with parental control virus. In contrast, T_H2 cytokines IL-4 and IL-9, which are typically expressed by ILC2s, were not induced upon HSV-IL-2 infection. Transcriptome sequencing (RNA-seq) analysis of HSV-IL-2 infected ILC2s showed significant upregulation of over 350 genes and downregulation of 157 genes compared with parental virus-infected ILC2s. Gene Ontology (GO) term analysis indicated that genes related to "mitosis" and "inflammatory response" were among the upregulated genes, suggesting that HSV-IL-2 infection drives the excessive proliferation and atypical inflammatory response of ILC2s. This change in ILC2 activation state could underlie the pathology of demyelinating diseases.IMPORTANCE Innate lymphocytes have plasticity and can change functionality; type 2 innate lymphoid cells (ILC2s) can convert to ILC1 or ILC3 cells or change their activation state to produce IL-17 or IL-10 depending on environmental cues. In this study, we investigated the gene and cytokine profiles of ILC2s, which play a major role in HSV-IL-2-induced CNS demyelination. ILC2s infected with HSV-IL-2 displayed a massive remodeling of cellular state. Additionally, ILC2s infected with HSV-IL-2 differed from those infected with parental HSV in cellular and viral gene expression profiles and in cytokine/chemokine induction, and they displayed enhanced activation and proinflammatory responses. These changes in ILC2 activation state could underlie the pathology of demyelinating diseases. These results also highlight the possible importance of pathogens as environmental cues to modify innate lymphocyte functionalities.

Type 2 Innate Lymphoid Cells Induce CNS Demyelination in an HSV-IL-2 Mouse Model of Multiple Sclerosis

We previously reported that infection of different mouse strains with a recombinant HSV-1 expressing IL-2 (HSV-IL-2) caused CNS demyelination. Histologic examination of infected IL-2rα^-/-, IL-2rβ^-/-, and IL-2rγ^-/- mice showed demyelination in the CNS of IL-2rα^-/- and IL-2rβ^-/- mice but not in the CNS of IL-2rγ^-/--infected mice. No demyelination was detected in mice infected with control virus. IL-2rγ^-/- mice that lack type 2 innate lymphoid cells (ILC2s) and ILCs, play important roles in host defense and inflammation. We next infected ILC1^-/-, ILC2^-/-, and ILC3^-/- mice with HSV-IL-2 or wild-type (WT) HSV-1. In contrast to ILC1^-/- and ILC3^-/- mice, no demyelination was detected in the CNS of ILC2^-/--sinfected mice. However, transfer of ILC2s from WT mice to ILC2^-/- mice restored demyelination in infected recipient mice. CNS demyelination correlated with downregulation of CCL5 and CXCL10. This study demonstrates that ILC2s contribute to HSV-IL-2-induced CNS demyelination in a mouse model of multiple sclerosis.

Co-delivery of autoantigen and b7 pathway modulators suppresses experimental autoimmune encephalomyelitis

Autoimmune diseases such as multiple sclerosis (MS) are characterized by the breakdown of immune tolerance to autoantigens. Targeting surface receptors on immune cells offers a unique strategy for reprogramming immune responses in autoimmune diseases. The B7 signaling pathway was targeted using adaptations of soluble antigen array (SAgA) technology achieved by covalently linking B7-binding peptides and disease causing autoantigen (proteolipid peptide (PLP)) to hyaluronic acid (HA). We hypothesized that co-delivery of a B7-binding peptide and autoantigen would suppress experimental autoimmune encephalomyelitis (EAE), a murine model of MS. Three independent B7-targeted SAgAs were created containing peptides to either inhibit or potentially stimulate the B7 signaling pathway. Surprisingly, all SAgAs were found to suppress EAE disease symptoms. Altered cytokine expression was observed in primary splenocytes isolated from SAgA-treated mice, indicating that SAgAs with different B7-binding peptides may suppress EAE through different immunological mechanisms. This antigen-specific immunotherapy using SAgAs can successfully suppress EAE through co-delivery of autoantigen and peptides targeting with the B7 signaling pathway.

Unexpected phenotype of mice lacking Shcbp1, a protein induced during T cell proliferation

T cell development and activation are highly regulated processes, and their proper execution is important for a competent immune system. Shc SH2-domain binding protein-1 (Shcbp1) is an evolutionarily conserved protein that binds to the adaptor protein ShcA. Studies in Drosophila and in cell lines have strongly linked Shcbp1 to cell proliferation, embryonic development, growth factor signaling, and tumorigenesis. Here we show that Shcbp1 expression is strikingly upregulated during the β-selection checkpoint in thymocytes, and that its expression tightly correlates with proliferative stages of T cell development. To evaluate the role for Shcbp1 during thymic selection and T cell function in vivo, we generated mice with global and conditional deletion of Shcbp1. Surprisingly, the loss of Shcbp1 expression did not have an obvious effect during T cell development. However, in a mouse model of experimental autoimmune encephalomyelitis (EAE), which depends on CD4⁺ T cell function and mimics multiple features of the human disease multiple sclerosis, Shcbp1 deficient mice had reduced disease severity and improved survival, and this effect was T cell intrinsic. These data suggest that despite the striking upregulation of Shcbp1 during T cell proliferation, loss of Shcbp1 does not directly affect T cell development, but regulates CD4⁺ T cell effector function in vivo.

The association of -330 interleukin-2 gene polymorphism with its plasma concentration in Iranian multiple sclerosis patients

Multiple sclerosis (MS) is a chronic neuroinflammatory demyelinating disease of the central nervous system. The cytokine genes are involved in autoimmune diseases such as MS. In this study, we report the influence of -330 interleukin-2 (IL2) gene polymorphism on its plasma levels in a group of Iranian MS patients. In this study 100 MS patients and 100 ethnically, age, and sex matched healthy controls were selected from Medical Genetics Department of Sarem Women Hospital. Blood samples of all individuals were collected in EDTA tubes. The restriction fragment length polymorphism PCR (RFLP) method was applied to determine various alleles and genotypes in these individuals. Plasma concentration of IL2 was measured in all the samples using human IL2 kit. The frequency of -330 T/T IL2 genotype was higher in MS patients compared to normal individuals. Accordingly, the plasma levels of IL2 were significantly higher (P < 0.0001) in patients when compared to the control group. In conclusion, in case of MS patients the -330 T/T IL2 genotype is associated with higher plasma levels of IL2.

Role of interleukin-2 and herpes simplex virus 1 in central nervous system demyelination in mice

We have reported previously that ocular infection of different strains of mice with recombinant herpes simplex virus 1 (HSV-1) constitutively expressing interleukin-2 (IL-2) provokes central nervous system (CNS) demyelination and optic neuropathy, as determined by changes in visual evoked cortical potentials and pathological changes in the optic nerve and CNS, whereas recombinant viruses expressing IL-4, gamma interferon, IL-12p35, IL-12p40, or IL-12p70 do not induce this neuropathy. The goal of this study was to dissect the mechanism underlying the interplay between the immune system (elevation of IL-2) and an environmental factor (infection with HSV-1) that elicits this pathology. Similar results were obtained upon delivery of IL-2 into the mouse brain using osmotic minipumps or injection of mice with recombinant IL-2 protein, IL-2 DNA, or IL-2 synthetic peptides prior to infection with wild-type (wt) HSV-1 strains McKrae and KOS. The critical role of IL-2 is further supported by our data, indicating that a single mutation at position T27A in IL-2 completely blocks the HSV-1-induced pathology. This study shows a novel model of autoimmunity in which viral infection and enhanced IL-2 cause CNS demyelination.

Control of TH17 cells occurs in the small intestine

Interleukin (IL)-17-producing T helper cells (T_H17) are a recently identified CD4⁺ T cell subset distinct from T helper type 1 (T_H1) and T helper type 2 (T_H2) cells¹. T_H17 cells can drive antigen specific autoimmune diseases and are considered the main population of pathogenic T cells driving experimental autoimmune encephalomyelitis (EAE)², the mouse model for multiple sclerosis. The factors that are needed for the generation of T_H17 cells have been well-characterized^3–6. However, where and how the immune system controls T_H17 cells in vivo remains unclear.

Here, by using a model of tolerance induced by CD3-specific antibody, a model of sepsis and influenza A viral infection (H1N1), we show that pro-inflammatory T_H17 cells can be redirected to and controlled in the small intestine. T_H17-specific IL-17A secretion induced expression of the chemokine CCL20 in the small intestine, facilitating the migration of these cells specifically to the small intestine via the CCR6/CCL20 axis. Moreover, we found that T_H17 cells are controlled by two different mechanisms in the small intestine: first, they are eliminated via the intestinal lumen and simultaneously pro-inflammatory T_H17 cells acquire a regulatory phenotype with in vitro and in vivo immune-suppressive properties (rT_H17). These results identify mechanisms limiting T_H17 cell pathogenicity and implicate the gastrointestinal tract as a site for control of T_H17 cells.

Use of cytokine immunotherapy to block CNS demyelination induced by a recombinant HSV-1 expressing IL-2

We previously have described a model of multiple sclerosis (MS) in which constitutive expression of murine interleukin (IL)-2 by herpes simplex virus type 1 (HSV-1) (HSV-IL-2) causes central nervous system (CNS) demyelination in different strains of mice. In the current study, we investigated whether this HSV-IL-2-induced demyelination can be blocked using recombinant viruses expressing different cytokines or by injection of plasmid DNA. We have found that coinfection of HSV-IL-2-infected mice with recombinant viruses expressing IL-12p35, IL-12p40 or IL-12p35+IL-12p40 did not block the CNS demyelination, and that coinfection with a recombinant virus expressing interferon (IFN)-γ exacerbated it. In contrast, coinfection with a recombinant virus expressing IL-4 reduced demyelination, whereas coinfection of HSV-IL-2-infected mice with a recombinant HSV-1 expressing the IL-12 heterodimer (HSV-IL-12p70) blocked the CNS demyelination in a dose-dependent manner. Similarly, injection of IL-12p70 DNA blocked HSV-IL-2-induced CNS demyelination in a dose-dependent manner and injection of IL-35 DNA significantly reduced CNS demyelination. Injection of mice with IL-12p35 DNA, IL-12p40 DNA, IL-12p35+IL-12p40 DNA or IL-23 DNA did not have any effect on HSV-IL-2-induced demyelination, whereas injection of IL-27 DNA increased the severity of the CNS demyelination in the HSV-IL-2-infected mice. This study demonstrates for the first time that IL-12p70 can block HSV-IL-2-induced CNS demyelination and that IL-35 can also reduce this demyelination, whereas IFN-γ and IL-27 exacerbated the demyelination in the CNS of the HSV-IL-2-infected mice. Our results suggest a potential role for IL-12p70 and IL-35 signaling in the inhibition of HSV-IL-2-induced immunopathology by preventing development of autoaggressive T cells.

IL-2 suppression of IL-12p70 by a recombinant HSV-1 expressing IL-2 induces T-cell auto-reactivity and CNS demyelination

To evaluate the role of cellular infiltrates in CNS demyelination in immunocompetent mice, we have used a model of multiple sclerosis (MS) in which different strains of mice are infected with a recombinant HSV-1 expressing IL-2. Histologic examination of the mice infected with HSV-IL-2 demonstrates that natural killer cells, dendritic cells, B cells, and CD25 (IL-2rα) do not play any role in the HSV-IL-2-induced demyelination. T cell depletion, T cell knockout and T cell adoptive transfer experiments suggest that both CD8⁺ and CD4⁺ T cells contribute to HSV-IL-2-induced CNS demyelination with CD8⁺ T cells being the primary inducers. In the adoptive transfer studies, all of the transferred T cells irrespective of their CD25 status at the time of transfer were positive for expression of FoxP3 and depletion of FoxP3 blocked CNS demyelination by HSV-IL-2. The expression levels of IL-12p35 relative to IL-12p40 differed in BM-derived macrophages infected with HSV-IL-2 from those infected with wild-type HSV-1. HSV-IL-2-induced demyelination was blocked by injecting HSV-IL-2-infected mice with IL-12p70 DNA. This study demonstrates that suppression of the IL-12p70 function of macrophages by IL-2 causes T cells to become auto-aggressive. Interruption of this immunoregulatory axis results in demyelination of the optic nerve, the spinal cord and the brain by autoreactive T cells in the HSV-IL-2 mouse model of MS.

Cerebral interleukin-15 shows upregulation and beneficial effects in experimental autoimmune encephalomyelitis

Interleukin (IL)-15 can cross the blood-brain barrier to act on its specific brain receptor (IL15Ralpha) and co-receptors. The important roles of neuronal IL15 and IL15Ralpha in experimental autoimmune encephalomeylitis (EAE) are suggested by the upregulation of IL15Ralpha mRNA in different regions of the brain and spinal cord, and by double-labeling immunohistochemistry showing neuronal localization of IL15 and IL15Ralpha in different neurons. Contrary to expectations, IL15 treatment lessened EAE severity. IL15 knockout mice showed heightened susceptibility to EAE with significantly higher scores that were decreased by treatment with IL15. Thus, IL15 improves this CNS autoimmune disorder as a potential therapeutic agent.

Systems-based medicine approaches to understand and treat complex diseases. The example of multiple sclerosis

Systems medicine is an emerging concept that acknowledges the complexity of a multitude of non-linear interactions among molecular and physiological variables. Under this new paradigm, rather than a collection of symptoms, diseases are seen as the product of deviations from a robust steady state compatible with life. This concept requires the incorporation of mathematics and physics to the more classical arsenal of physiology and molecular biology with which physicians are trained today. This review explores the diverse types of information that can be accumulated towards the understanding of multiple sclerosis (MS), a complex autoimmune disease that targets the central nervous system (CNS). The challenge of data integration and modeling of dynamical systems is discussed in the context of disease susceptibility and response to treatment. A theoretical framework that supports the use of combination therapy is also presented.

Optic neuritis in different strains of mice by a recombinant HSV-1 expressing murine interleukin-2

PURPOSE

The authors have shown previously that a recombinant HSV-1 that constitutively expresses two copies of murine IL-2 (HSV-IL-2) induces demyelination by activated CD8(+) T cells in the brain and spinal cord of ocularly infected female BALB/c mice. The present study was conducted to determine whether the ocular infection with this recombinant virus induces optic neuritis independent of virus dose, major histocompatibility complex (MHC) background, or sex.

METHODS

Female BALB/c, C57BL/6, SJL/6, and 129SVE mice and male BALB/c mice were ocularly infected with different doses of recombinant HSV-IL-2 virus. Demyelination of optic nerves in infected mice was monitored histologically using Luxol fast blue staining and by measurement of visual-evoked cortical potentials (VECPs).

RESULTS

Both focal and diffuse regions of demyelination of the optic nerves were observed in the HSV-IL-2-infected mice as early as day 10 after infection and as late as day 60 after infection (the final experimental time point) in all strains of mice tested. Optic nerve demyelination was not observed in control mice ocularly infected with HSV-IL-4 or wild-type HSV-1. VECP responses were delayed significantly in the HSV-IL-2-infected mice compared with mice infected with control viruses.

CONCLUSIONS

The results demonstrate for the first time that a combination of viral infection and constitutive expression of IL-2, but not IFN-gamma or IL-4, can result in demyelination and visual impairment in the optic nerves of ocularly infected mice.

Exercise and brain health--implications for multiple sclerosis: Part II--immune factors and stress hormones

Part I of this review addressed the possible modulatory role of exercise on neuronal growth factors to promote brain health in neurodegenerative diseases such as multiple sclerosis (MS), which is characterized by varied patterns of inflammation, demyelination and axonal loss. Part II presents evidence that supports the potential neuroprotective effect of exercise on the modulation of immune factors and stress hormones in MS. Many current therapies used to attenuate MS progression are mediated, at least in part, through alterations in the relative concentrations of pro- and anti-inflammatory cytokines. Exercise-induced alterations in local and systemic cytokine production may also benefit immune function in health and disease. Exercise immunomodulation appears to be mediated by a complex interaction of hormones, cytokines and neural factors that may favorably influence immune variables in MS. The promising interplay between exercise and brain health in MS deserves further investigation.

Exogenous IL-12 suppresses experimental autoimmune encephalomyelitis (EAE) by tuning IL-10 and IL-5 levels in an IFN-γ-dependent way

Endogenous IL-12 is considered to be required for the generation and function of pathogenic Th1 effector cells in experimental autoimmune encephalomyelitis (EAE). We show here that IL-12 administration together with the immunization suppressed actively induced CREAE in SJL/J and in Biozzi/ABH mice and even subsequent spontaneous relapse incidence and severity in Biozzi ABH mice. IL-12 given during remission of primary disease inhibited re-induced relapses in SJL/J, but not spontaneous relapses in Biozzi mice. The protective effect of IL-12 is time- and dose-dependent. Protection is accompanied by subsequent increased production of IL-10 and IL-5 by lymph node and spleen cells and an inhibition of cell proliferation. Mice depleted of IFN-gamma by administration of neutralizing antibodies were poorly protected by exogenous IL-12, indicating that the inhibitory effect of IL-12 is partially IFN-gamma dependent.

Control of interleukin-2 gene transcription: a paradigm for inducible, tissue-specific gene expression

Interleukin-2 (IL-2) is a key cytokine that controls immune cell function, in particular the adaptive arm of the immune system, through its ability to control the clonal expansion and homeostasis of peripheral T cells. IL-2 is produced almost exclusively by T cells in response to antigenic stimulation and thus provides an excellent example of a cell-specific inducible gene. The mechanisms that control IL-2 gene transcription have been studied in detail for the past 20 years and our current understanding of the nature of the inducible and tissue-specific controls will be discussed.

Treatment of Mice with the Suppressor of Cytokine Signaling-1 Mimetic Peptide, Tyrosine Kinase Inhibitor Peptide, Prevents Development of the Acute Form of Experimental Allergic Encephalomyelitis and Induces Stable Remission in the Chronic Relapsing/Remitting Form

We have previously characterized a novel tyrosine kinase inhibitor peptide (Tkip) that is a mimetic of suppressor of cytokine signaling 1 (SOCS-1) and inhibits JAK2 phosphorylation of the transcription factor STAT1alpha. We show in this study that Tkip protects mice against experimental allergic encephalomyelitis (EAE), an animal model for multiple sclerosis. Mice are immunized with myelin basic protein (MBP) for induction of disease. Tkip (63 mug) administered every other day suppressed the development of acute EAE in 75% of New Zealand White (NZW) mice. Furthermore, Tkip completely protected SJL/J mice, which where induced to get the relapsing/remitting form of EAE, against relapses compared with control groups in which >70% of the mice relapsed after primary incidence of disease. Protection of mice by Tkip was similar to that seen with the type I IFN, IFN-tau. Protection of mice correlated with lower MBP Ab titers in Tkip-treated groups as well as suppression of MBP-induced proliferation of splenocytes taken from EAE-afflicted mice. Cessation of Tkip and IFN-tau administration resulted in SJL/J mice relapsing back into disease. Prolonged treatment of mice with Tkip produced no evidence of cellular toxicity or weight loss. Consistent with its JAK2 inhibitory function, Tkip also inhibited the activity of the inflammatory cytokine TNF-alpha, which uses the STAT1alpha transcription factor. The data presented in this study show that Tkip, like the type I IFN, IFN-tau, inhibits both the autoreactive cellular and humoral responses in EAE and ameliorates both the acute and chronic relapsing/remitting forms of EAE.

CD8+-dependent CNS demyelination following ocular infection of mice with a recombinant HSV-1 expressing murine IL-2

Demyelinating diseases comprise a spectrum of immunopathologic syndromes in which myelin, the fatty covering of nerve cell fibers in the brain and spinal cord, is destroyed. In this study, we have shown for the first time that ocular infection of BALB/c mice with a recombinant herpes simplex virus type 1 (HSV-1) expressing IL-2 (HSV-IL-2) results in CNS demyelination as determined by light microscopy and EM. The demyelinated lesions involve periventricular white matter, brain stem, and spinal cord white matter. Demyelination was detected in the CNS of infected mice up to 75 days (the longest time point tested) post HSV-IL-2 infection. In contrast, mice infected with HSV-IFN-gamma or HSV-IL-4, which are identical to HSV-IL-2 but express IFN-gamma or IL-4 instead of IL-2, did not exhibit demyelination. Control mice infected with wild-type HSV-1 or parental virus also remained free of these symptoms. During early times (days 3-7), post-infection with HSV-IL-2 virus, a T(H)1 + T(H)2 pattern of cytokines was produced by lymphocytes of infected mice while mice infected with HSV-IFN-gamma or control viruses produced a T(H)1 pattern of cytokine. By day 21 post-infection, all infected groups exhibited a T(H)1 pattern of response. Immunohistochemistry and FACS analyses of infiltrates in the brains and spinal cords of HSV-IL-2-infected mice showed elevations in CD4+ and CD8+ T cells and macrophages. However, T cell depletion studies suggest that only central memory CD8+ T cells are directly involved in the demyelination process, with macrophages being involved through a bystander effect.

Changes in hippocampal IL-15, related cytokines, and neurogenesis in IL-2 deficient mice

Previous studies have demonstrated that interleukin-2 knockout (KO) mice exhibit alterations in hippocampal cytoarchitecture. Several lines of evidence suggest that these variations may result from immune dysregulation and/or autoimmunity. Thus, this study sought to compare adult IL-2 KO mice and wild-type littermates (8-12 weeks of age), the age where differences in hippocampal cytoarchitecture have previously been observed, for differences in measures of neuroimmunological status in the hippocampus. Furthermore, because IL-15 shares the same receptor subunits for signal transduction as IL-2 (IL-2/15Rbeta and gammac) that are enriched in the hippocampus and may induce inflammatory processes in IL-2 KO mice, we sought to test the hypothesis that IL-15 is elevated in the hippocampus of IL-2 KO mice. Compared to wild-type mice, IL-2 KO mice exhibited increased hippocampal protein concentrations of IL-15 as well as IL-12, IP-10, and MCP-1. These cytokine changes, however, did not correlate with levels in the peripheral circulation, and there were no T cells or an increase in MHCII-positive microglia in the hippocampus of IL-2 KO mice. Since elevated levels of certain inflammatory cytokines may impair hippocampal neurogenesis, we also tested the hypothesis that changes in neuroimmunological status would be associated with reductions in neurogenesis of neurons in the dentate gyrus of IL-2 KO mice. Contrary to this hypothesis, compared to wild-type mice, male IL-2 KO mice exhibited increased neurogenesis in both the infrapyramidal and suprapyramidal limbs of the granule cell layer of the dentate gyrus, differences that were not observed between females. These findings indicate that IL-2 gene deletion alters the neuroimmunological status of the mouse hippocampus through a dysregulation of cytokines produced by CNS cells, and in males, these changes are associated with increased hippocampal neurogenesis.

Effects of the multiple sclerosis associated −330 promoter polymorphism in IL2 allelic expression

The -330 IL2 gene promoter polymorphism has been associated with multiple sclerosis (MS) [J. Neuroimmunol. 119 (2001) 101], but the basis underlying this association remains unknown to date. In the present work, we have found that IL2 promoter-luciferase constructs, transfected in Jurkat cell line, showed twofold higher levels of gene expression in the -330 G allele. However, the transcriptional effect of this polymorphism in lymphocytes showed that the G allele was related to lower expression of IL2. This difference increased in the patient group. Divergence between in vivo and in vitro influence of the -330 IL2 promoter polymorphic site suggests the existence of additional unknown polymorphisms affecting gene regulation. Our data show an increased IL2 expression among GT and TT genotypes previously associated with susceptibility to MS.

IL-2 gene knockout affects T lymphocyte trafficking and the microglial response to regenerating facial motor neurons

Following facial nerve axotomy in mice, T cells cross the intact blood-brain barrier (BBB), home to nerve cell bodies in the facial motor nucleus (FMN), and augment neuroregenerative processes. The pivotal T cell immunoregulatory cytokine, IL-2, appears to have bidirectional effects on neuronal and microglial cell function, suggesting rival hypotheses that IL-2 could either enhance or disrupt processes associated with regeneration of axotomized facial motor neurons. We tested these competing hypotheses by comparing the effect of facial nerve axotomy on C57BL/6-IL-2(-/-) knockout and C57BL/6-IL-2(+/+) wild-type littermates. Since IL-2 may also be produced endogenously in the brain, we also sought to determine whether differences between the knockout and wild-type mice were attributable to loss of IL-2 gene expression in the CNS, loss of peripheral sources of IL-2 and the associated effects on T cell function, or a combination of these factors. To address this question, we bred novel congenic mice with the SCID mutation (mice lacking T cell derived IL-2) that were homozygous for either the IL-2 knockout or wild-type gene alleles (C57BL/6scid-IL-2(-/-) and C57BL/6scid-IL-2(+/+) littermates, respectively). Groups were assessed for differences in (1) T lymphocytes entering the axotomized FMN; (2) perineuronal CD11b(+) microglial phagocytic clusters, a measure of motor neuron death; and (3) activated microglial cells as measured by MHC-II positivity. C57BL/6-IL-2(-/-) knockout mice had significantly higher numbers of T cells and lower numbers of activated MHC-II-positive microglial cells in the regenerating FMN than wild-type littermates, although the number of CD11b(+) phagocytic microglia clusters did not differ. Thus, despite the significant impairment of T cell function known to be associated with loss of peripheral IL-2, the increased number of T cells entering the axotomized FMN appears to have sufficient activity to support neuroregenerative processes. Congenic C57BL/6scid-IL-2(-/-) knockout mice had lower numbers of CD11b(+) microglial phagocytic clusters than congenic C57BL/6scid-IL-2(+/+) wild-type littermates, suggesting that loss of the IL-2 gene in the CNS (and possibly the loss of other unknown sources of the gene) enhanced neuronal regeneration. Further study of IL-2's complex actions in neuronal injury may provide greater understanding of key variables that determine whether or not immunological processes in the brain are proregenerative.

An assessment of the association between IL-2 gene polymorphisms and Japanese patients with multiple sclerosis

Interleukin-2 (IL-2) is a cytokine intimately involved with both the function and regulation of the immune system. Genetic analysis of experimental autoimmune encephalomyelitis (EAE) provides strong evidence supporting the candidacy of IL-2 as a susceptibility gene. We investigated the association of two single nucleotide polymorphisms (SNPs) at position -384 in the promoter region and +114 in the first exon of the IL-2 gene through a case-control study involving 113 Japanese patients with multiple sclerosis (MS) and 118 healthy controls. Our results showed no significant differences in the distribution of the two polymorphisms between MS patients and controls. Furthermore, no association was observed between IL-2 gene polymorphisms and clinical characteristics, such as clinical course and age at disease onset. Together, our findings suggest that IL-2 gene polymorphisms do not influence the susceptibility to MS or the clinical characteristics of MS in Japanese patients.

Alterations in septohippocampal cholinergic neurons resulting from interleukin-2 gene knockout

Interleukin-2 (IL-2) has potent effects on acetylcholine (ACh) release from septohippocampal cholinergic neurons and trophic effects on fetal septal and hippocampal neuronal cultures. Previous work from our lab showed that the absence of endogenous IL-2 leads to impaired hippocampal neurodevelopment and related behaviors. We sought to extend this work by testing the hypotheses that the loss of IL-2 would result in reductions in cholinergic septohippocampal neuron cell number and the density of cholinergic axons found in the hippocampus of IL-2 knockout mice. Stereological cell counting and imaging techniques were used to compare C57BL/6-IL-2(-/-) knockout and C57BL/6-IL-2(+/+) wild-type mice for differences in choline acetyltransferase (ChAT)-positive somata in the medial septum and vertical limb of the diagonal band of Broca (MS/vDB) and acetylcholine esterase (AChE)-labeled cholinergic axons in hippocampal projection fields. IL-2 knockout mice had significantly lower numbers (26%) of MS/vDB ChAT-positive cell bodies than wild-type mice; however, there were no differences in striatal ChAT-positive neurons. Although AChE-positive axon density in CA1, CA3b, the internal, and external blades of the dentate gyrus did not differ between the knockout and wild-type mice, the distance across the granular cell layer of the external blade of the dentate gyrus was reduced significantly in IL-2 knockout mice. Further research is needed to determine whether these outcomes in IL-2 knockout mice may be due to the absence of central and/or peripheral IL-2 during brain development or neurodegeneration secondary to autoimmunity.

Analysis of -631 and -475 interleukin-2 promoter single nucleotide polymorphisms in multiple sclerosis

We have analysed the interleukin-2 (IL-2) promoter single nucleotide polymorphisms -475 A/T and -631 G/A, relative to the initiation codon, in patients with multiple sclerosis (MS) and in healthy controls. Both groups showed a very low frequency of T at -475 and A at -631. Our results suggest that these polymorphisms do not contribute to MS susceptibility.

IL-2 and autoimmune disease

A decade after the first description of IL-2-deficient mice, the redundancy of IL-2 as a T cell growth factor is well accepted and the focus of research has shifted to the unexpected multiorgan autoimmunity and inflammation observed in mice lacking components of the IL-2/IL-2R system. So far, a set of defects at the levels of repertoire selection, the generation of suppressive regulatory T cells, T cell homing and clonal contraction via activation induced cell death (AICD) have been documented. We propose that these individual defects jointly contribute to the severe disturbance of T cell homeostasis and self-tolerance underlying the immunopathology of the IL-2 deficiency syndrome.

Effects of interleukin-2 on the expression of corticotropin-releasing hormone in nerves and lymphoid cells in secondary lymphoid organs from the Fischer 344 rat

This study examined the influence of interleukin (IL)-2 on corticotropin releasing hormone (CRH) immunoreactivity in the Fischer 344 (F344) rat spleen. Rats were given either vehicle or 1, 10, 25, 50, 100, or 200 ng of human recombinant (hr)IL-2 by intraperitoneal (i.p.) injection, and were sacrificed 0.5, 1, 4, 12, or 24 h after treatment. Spleens and mesenteric lymph nodes were prepared for immunocytochemistry to localize CRH. In spleens from vehicle-treated animals, CRH immunoreactivity was present in several types of cells of the immune system, but CRH(+) nerves were not observed in either spleens or lymph nodes from vehicle-treated animals. Treatment with IL-2 induced CRH expression in nerves in the spleen in a dose- and time-dependent manner. CRH(+) nerves were not found in the mesenteric lymph nodes after IL-2 treatment, instead a dramatic time- and dose-dependent accumulation of CRH(+) cells (resembling small lymphocytes and large granular mononuclear cells) in the cortex and medulla. These findings indicate that IL-2 stimulates the synthesis of CRH in nerves that innervate the F344 rat spleen, and promote the appearance of CRH(+) immunocytes into draining mesenteric lymph nodes.

Allelic expression and interleukin-2 polymorphisms in multiple sclerosis

We have investigated the association of two single nucleotide polymorphisms (SNPs) at positions -384 and 114 in the human interleukin-2 (hIL-2) with multiple sclerosis (MS). For two of the -384 genotypes (G/T, T/T), we observed an association with the susceptibility to secondary progressive (SP) course of MS (P=0.005 and P=0.013, respectively). Expression level differences of the IL-2 alleles (between one- and three-fold) were not attributable to the -384 promoter polymorphism. These data indicate for the first time the relevance of the il-2 gene locus in human MS and its possible involvement in other autoimmune diseases.

Superantigen overcomes resistance of IL-6-deficient mice towards MOG-induced EAE by a TNFR1 controlled pathway

Experimental autoimmune encephalomyelitis (EAE) induced by myelin oligodendrocyte glycoprotein peptide 35-55 (MOG) leads to a chronic form of disease characterized by demyelination, inflammation and gliosis in the central nervous system (CNS). Recently IL-6 and LT alpha were found to be required for induction of the disease. The main features associated with EAE resistance of IL-6(-/-) and LT alpha(-/-) mice were reduced T cell proliferation and endothelial activation. As shown here treatment of MOG-immunized IL-6(-/-) mice with staphylococcal enterotoxin B (SEB)reversed their resistance to MOG-induced EAE. SEB failed to restore susceptibility to EAE in LT alpha(-/-) mice. The effect of SEB to induce EAE in IL-6(-/-) mice depends on TNF receptor type 1 (TNFR1) signaling because IL-6/TNF/LT alpha(-/-) and IL-6/TNFR1(-/-) are refractory to SEB. TNFR1 is involved in SEB induced trafficking of T cells into the CNS as evidenced by the failure to up-regulate VCAM-1 on CNS endothelium and lack of accumulation of V beta 8(+) T cells in the CNS of IL-6/TNFR1(-/-) mice upon immunization with MOG and treatment with SEB. The course of SEB triggered EAE in MOG immunized IL-6(-/-) mice was characterized by reduced severity and duration of clinical manifestations, which were associated with a significant drop of CNS infiltrating neutrophils and MIP-2 expression after peak disease. Taken collectively the effect of SEB to overcome EAE resistance points to a transient IL-6 independent but TNFR1 dependent proinflamatory pathway in EAE pathogenesis and suggests a crucial function for IL-6 in disease perpetuation.

Brain-immune interactions in neuropsychiatry: highlights of the basic science and relevance to pathogenic factors and epiphenomena

Unraveling the significant complexity of brain-immune interactions could provide essential new insights and potential treatment considerations for the clinical neurosciences. Despite considerable research relating immunological changes to major neuropsychiatric disorders, it has been difficult to establish that immunological processes are involved in the development of central nervous system pathology associated with these disorders. This brief article highlights some of the landmark basic studies and seeks to convey essential principles guiding research in brain-immune interactions. Research in this area often incorporates several disciplines, ranging from psychology and neuroscience to immunology and molecular genetics. The clinical implications of this area of research are discussed, with emphasis on the challenge of disentangling pathogenic factors and valid markers of disease from epiphenomena.