Interleukin-2 as a neurotrophic factor for supporting the survival of neurons cultured from various regions of fetal rat brain

Characterizing the neuroimmune environment of offspring in a novel model of maternal allergic asthma and particulate matter exposure

Inflammation during pregnancy is associated with an increased risk for neurodevelopmental disorders (NDD). Increased gestational inflammation can be a result of an immune condition/disease, exposure to infection, and/or environmental factors. Epidemiology studies suggest that cases of NDD are on the rise. Similarly, rates of asthma are increasing, and the presence of maternal asthma during pregnancy increases the likelihood of a child being later diagnosed with NDD such as autism spectrum disorders (ASD). Particulate matter (PM), via air pollution, is an environmental factor known to worsen the symptoms of asthma, but also, PM has been associated with increased risk of neuropsychiatric disorders. Despite the links between asthma and PM with neuropsychiatric disorders, there is a lack of laboratory models investigating combined prenatal exposure to asthma and PM on offspring neurodevelopment. Thus, we developed a novel mouse model that combines exposure to maternal allergic asthma (MAA) and ultrafine iron-soot (UIS), a common component of PM. In the current study, female BALB/c mice were sensitized for allergic asthma with ovalbumin (OVA) prior to pregnancy. Following mating and beginning on gestational day 2 (GD2), dams were exposed to either aerosolized OVA to induce allergic asthma or phosphate buffered saline (PBS) for 1 h. Following the 1-h exposure, pregnant females were then exposed to UIS with a size distribution of 55 to 169 nm at an average concentration of 176 ± 45 μg/m3) (SD), or clean air for 4 h, over 8 exposure sessions. Offspring brains were collected at postnatal days (P)15 and (P)35. Cortices and hippocampal regions were then isolated and assessed for changes in cytokines using a Luminex bead-based multiplex assay. Analyses identified changes in many cytokines across treatment groups at both timepoints in the cortex, including interleukin-1 beta (IL-1β), and IL-17, which remained elevated from P15 to P35 in all treatment conditions compared to controls. There was a suppressive effect of the combined MAA plus UIS on the anti-inflammatory cytokine IL-10. Potentially shifting the cytokine balance towards more neuroinflammation. In the hippocampus at P15, elevations in cytokines were also identified across the treatment groups, namely IL-7. The combination of MAA and UIS exposure (MAA-UIS) during pregnancy resulted in an increase in microglia density in the hippocampus of offspring, as identified by IBA-1 staining. Together, these data indicate that exposure to MAA, UIS, and MAA-UIS result in changes in the neuroimmune environment of offspring that persist into adulthood.

Characterizing the Neuroimmune Environment of Offspring in a Novel Model of Maternal Allergic Asthma and Particulate Matter Exposure

Autism spectrum disorders (ASD) are neurodevelopmental disorders characterized by the presence of decreased social interactions and an increase in stereotyped and repetitive behaviors. Epidemiology studies suggest that cases of ASD are on the rise. Similarly, rates of asthma are increasing, and the presence of maternal asthma during pregnancy increases the likelihood of a child being later diagnosed with ASD. Particulate matter (PM), via air pollution, is an environmental factor known to worsen the symptoms of asthma, but also, PM has been associated with increased risk of neuropsychiatric disorders including ASD. Despite the links between asthma and PM with neuropsychiatric disorders, there is a lack of laboratory models investigating combined prenatal exposure to asthma and PM on offspring neurodevelopment. Thus, we developed a novel mouse model that combines exposure to maternal allergic asthma (MAA) and ultrafine iron-soot (UIS), a common component of PM. In the current study, female BALB/c mice were primed for allergic asthma with ovalbumin (OVA) prior to pregnancy. Following mating and beginning on gestational day 2 (GD2), dams were exposed to either aerosolized OVA or phosphate buffered saline (PBS) for 1 hour. Following the 1-hour exposure, pregnant females were then exposed to UIS or clean air for 4 hours. Offspring brains were collected at postnatal days (P)15 and (P)35. Cortices and hippocampal regions were then isolated and assessed for changes in cytokines using a Luminex bead-based multiplex assay. Analyses identified changes in many cytokines across treatment groups at both timepoints in the cortex, including interleukin-1 beta (IL-1β), IL-2, IL-13, and IL-17, which remained elevated from P15 to P35 in all treatment conditions compared to controls. In the hippocampus at P15, elevations in cytokines were also identified across the treatment groups, namely interferon gamma (IFNγ) and IL-7. The combination of MAA and UIS exposure (MAA-UIS) during pregnancy resulted in an increase in microglia density in the hippocampus of offspring, as identified by IBA-1 staining. Together, these data indicate that exposure to MAA, UIS, and MAA-UIS result in changes in the neuroimmune environment of offspring that persist into adulthood.

Microglia in the Neuroinflammatory Pathogenesis of Alzheimer's Disease and Related Therapeutic Targets

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease worldwide, characterized by progressive neuron degeneration or loss due to excessive accumulation of β-amyloid (Aβ) peptides, formation of neurofibrillary tangles (NFTs), and hyperphosphorylated tau. The treatment of AD has been only partially successful as the majority of the pharmacotherapies on the market may alleviate some of the symptoms. In the occurrence of AD, increasing attention has been paid to neurodegeneration, while the resident glial cells, like microglia are also observed. Microglia, a kind of crucial glial cells associated with the innate immune response, functions as double-edge sword role in CNS. They exert a beneficial or detrimental influence on the adjacent neurons through secretion of both pro-inflammatory cytokines as well as neurotrophic factors. In addition, their endocytosis of debris and toxic protein like Aβ and tau ensures homeostasis of the neuronal microenvironment. In this review, we will systematically summarize recent research regarding the roles of microglia in AD pathology and latest microglia-associated therapeutic targets mainly including pro-inflammatory genes, anti-inflammatory genes and phagocytosis at length, some of which are contradictory and controversial and warrant to further be investigated.

Increased Retinal Ganglion Cell Survival by Exogenous IL-2 Depends on IL-10, Dopamine D1 Receptors, and Classical IL-2/IL-2R Signaling Pathways

Interleukin-2 (IL-2) is a classical pro-inflammatory cytokine known to display neuroprotective roles in the central nervous system including the retina. In the present study, we investigate the molecular targets involved in the neurotrophic effect of IL-2 on retinal ganglion cells (RGC) after optic nerve axotomy. Analysis of retrograde labeling of RGC showed that common cell survival mediators, as Trk receptors, Src, PI3K, PKC, and intracellular calcium do not mediate the neurotrophic effect of IL-2 on RGC. No involvement of MAPK p38 was also observed. However, other MAPKs as MEK and JNK appear to be mediating this IL-2 effect. Our data also indicate that JAK2/3 are important intracellular proteins for the IL-2 effect. Interestingly, we demonstrate that the IL-2 effect depends on dopamine D1 receptors (D1R), the cAMP/PKA pathway, interleukin-10 (IL-10), and NF-κB, suggesting that RGC survival induced by IL-2 encompasses a molecular network of major complexity. In addition, treatment of retinal cells with recombinant IL-10 or 6-Cl-pb (D1R full agonist) was able to increase RGC survival similar to IL-2. Taken together, our results suggest that after optic nerve axotomy, the increase in RGC survival triggered by IL-2 is mediated by IL-10 and D1R along with the intracellular pathways of MAPKs, JAK/STAT, and cAMP/PKA.

Interleukin-2 improves amyloid pathology, synaptic failure and memory in Alzheimer's disease mice

Interleukin-2 (IL-2)-deficient mice have cytoarchitectural hippocampal modifications and impaired learning and memory ability reminiscent of Alzheimer's disease. IL-2 stimulates regulatory T cells whose role is to control inflammation. As neuroinflammation contributes to neurodegeneration, we investigated IL-2 in Alzheimer's disease. Therefore, we investigated IL-2 levels in hippocampal biopsies of patients with Alzheimer's disease relative to age-matched control individuals. We then treated APP/PS1ΔE9 mice having established Alzheimer's disease with IL-2 for 5 months using single administration of an AAV-IL-2 vector. We first found decreased IL-2 levels in hippocampal biopsies of patients with Alzheimer's disease. In mice, IL-2-induced systemic and brain regulatory T cells expansion and activation. In the hippocampus, IL-2 induced astrocytic activation and recruitment of astrocytes around amyloid plaques, decreased amyloid-β42/40 ratio and amyloid plaque load, improved synaptic plasticity and significantly rescued spine density. Of note, this tissue remodelling was associated with recovery of memory deficits, as assessed in the Morris water maze task. Altogether, our data strongly suggest that IL-2 can alleviate Alzheimer's disease hallmarks in APP/PS1ΔE9 mice with established pathology. Therefore, this should prompt the investigation of low-dose IL-2 in Alzheimer's disease and other neuroinflammatory/neurodegenerative disorders.

Enrichment pathway analysis. The inflammatory genetic background in Bipolar Disorder

INTRODUCTION

The pathophysiology of Bipolar Disorder (BD) is yet to be fully characterized. In the last years attention was focused on neurodevelopment or neurodegenerative events. In this context, hyper- and hypo- activation of inflammatory cascades may play a role in modulating the architecture and function of neuronal tissues. In the present paper we tested the enrichment of molecular pathways related to inflammatory cascades (IL-1, IL-2, IL-6, IL-8, TNF and INF) testing whether genes related to these systems hold more variations associated with the risk for BD than expected.

METHODS

~7000 bipolar patients and controls with genome-wide data available from NIMH dataset were analyzed. SNPs were imputed, checked for quality control, pruned and tested for association (0.01<p). Fisher test was conducted to test the enrichment within the pathways and the association was permutated (10(5) times) to limit false positive findings.

RESULTS

As a result, IL-6, IL-8 and IFN related pathways held twice to thrice the number of expected variants associated with BD. These tests resisted the permutation analysis.

LIMITATIONS

The restricted number of inflammatory components included in the analysis and the lack of functional consequences for some of the SNPs analyzed may be biased; however, these choices helped the authors to lighten the statistical computational load for the analyses and at the same time included possibly hidden SNPs in linkage disequilibrium with the analyzed variations.

CONCLUSIONS

We bring evidence that the inflammatory cascades may be genetically varied in Bipolar patients. This genetic background may explain part of the pathophysiology of the disorder.

Effects of Brain-Derived IL-2 Deficiency and the Development of Autoimmunity on Spatial Learning and Fear Conditioning

Interleukin-2 (IL-2) has been implicated in neurological disorders including multiple sclerosis and Alzheimer’s disease. Peripheral IL-2 deficiency in gene-deleted mice results in T cell mediated autoimmunity that begins to develop slowly after weaning and progressively increases through adulthood. Loss of brain-derived IL-2 results in neurobiological and behavioral abnormalities, and may contribute to the development of CNS autoimmunity by modifying the neuroimmunological milieu of the brain. We have shown previously that IL-2 knockout (KO) mice have altered learning acquisition in the Morris water-maze. Hypothesizing that the learning acquisition deficits in IL-2KO would be associated largely with the loss of brain-derived IL-2, the present study sought to determine if these cognitive alterations are due to the loss the IL-2 gene in the brain and/or autoimmunity resulting from loss of the gene in the peripheral immune system. We found that SCID congenic mice (mice free of IL-2 deficiency induced peripheral autoimmunity) without brain IL-2 (two IL-2KO alleles) did not differ from SCID congenic mice with normal brain IL-2 (two WT IL-2 alleles); thus, contrary to our hypothesis, loss of brain-derived IL-2 did not affect learning acquisition in the water-maze. Compared to adult WT littermates (9 weeks), adult IL-2KO mice with autoimmunity exhibited alterations in learning acquisition in the Morris water-maze whereas younger pre-autoimmune IL-2KO mice (5 weeks) had performance comparable to younger WT littermates, suggesting that the water-maze learning deficits in IL-2KO mice were associated with the development of peripheral autoimmunity. As IL-2KO mice have cytoarchitectural alterations in the dentate gyrus, circuitry involved in the differentiation of contexts (versus places), we also compared IL-2KO mice and littermates in a contextual fear discrimination paradigm. IL-2KO mice were found to have reduced conditioned fear discrimination that was not related to age-associated autoimmunity. Together, these findings suggest that complex interactions between IL-2 deficiency in the brain and immune system may modify brain processes involved in different modalities of learning and memory.

Regionally-specified second trimester fetal neural stem cells reveals differential neurogenic programming

Neural stem/progenitor cells (NSC) have the potential for treatment of a wide range of neurological diseases such as Parkinson Disease and multiple sclerosis. Currently, NSC have been isolated only from hippocampus and subventricular zone (SVZ) of the adult brain. It is not known whether NSC can be found in all parts of the developing mid-trimester central nervous system (CNS) when the brain undergoes massive transformation and growth. Multipotent NSC from the mid-trimester cerebra, thalamus, SVZ, hippocampus, thalamus, cerebellum, brain stem and spinal cord can be derived and propagated as clonal neurospheres with increasing frequencies with increasing gestations. These NSC can undergo multi-lineage differentiation both in vitro and in vivo, and engraft in a developmental murine model. Regionally-derived NSC are phenotypically distinct, with hippocampal NSC having a significantly higher neurogenic potential (53.6%) over other sources (range of 0%–27.5%, p<0.004). Whole genome expression analysis showed differential gene expression between these regionally-derived NSC, which involved the Notch, epidermal growth factor as well as interleukin pathways. We have shown the presence of phenotypically-distinct regionally-derived NSC from the mid-trimester CNS, which may reflect the ontological differences occurring within the CNS. Aside from informing on the role of such cells during fetal growth, they may be useful for different cellular therapy applications.

Peripheral interleukin-2 level is associated with negative symptoms and cognitive performance in schizophrenia

Although several studies have pointed to a possible role of interleukin 2 (IL-2) in schizophrenia (SZ), association between IL-2 and the different groups of symptoms has not been explored. The objective of this study was to investigate a possible correlation of peripheral IL-2 levels with symptoms and cognitive performance in patients with SZ. In addition, we compared the plasma levels of IL-2 between patients with SZ and healthy controls. Twenty-nine chronically medicated outpatients with SZ according to DSM-IV were compared with twenty-six healthy controls. The patients were evaluated with the Positive and Negative Syndrome Scale (PANSS), the Calgary Depression Scale for Schizophrenia (CDSS), the Clinical Global Impression (CGI) and the Global Assessment of Functioning (GAF). All the participants had blood collected into EDTA tubes by venipuncture between 9:00 and 10:00AM. Plasma concentrations of IL-2 were determined by cytometric bead array. A computerized neuropsychological battery assessed verbal learning, verbal fluency, working memory, set shifting, executive function, inhibition and intelligence. Patients with SZ had lower levels of IL-2 than healthy controls (p<0.001). In the SZ group, IL-2 levels were positively correlated with scores in the digit span test (rho=0.416, P=0.025) and intelligence (rho=0.464, P=0.011). We also found a negative correlation between IL-2 and total score in the negative subscale of PANSS (rho=-0.447, p=0.015). Our findings suggest that IL-2 may be involved in the mechanisms related to cognitive deterioration and negative symptomatology in schizophrenia.

Loss of cholinergic phenotype in septohippocampal projection neurons: relation to brain versus peripheral IL-2 deficiency

In the peripheral immune system, IL-2 is essential for immune homeostasis, normal T regulatory cell function, and self-tolerance. IL-2 knockout (IL-2KO) mice develop spontaneous autoimmunity characterized by increased T cell trafficking to multiple organs. The IL-2 gene is also expressed in the brain, and in vitro studies have shown that IL-2 is a potent modulator of acetylcholine release from septohippocampal neurons and exerts trophic effects on septal neurons in culture. We previously described the apparent loss of cholinergic cell bodies in the medial septum of IL-2KO mice. Here we investigated if loss of brain-derived IL-2, or autoimmunity stemming from loss of peripheral IL-2, is responsible for the alteration in choline acetyltransferase (ChAT) expression in the medial septum of IL-2KO mice. To accomplish this objective, we compared ChAT-positive neurons between wild-type (WT) mice, IL-2KO mice, and congenic mice with a double gene deletion for the IL-2 gene and the recombinase activating gene-2 (RAG-2) which are referred to as IL-2KO/RAG-2KO mice (congenic mice which lack mature T and B cells as well as peripheral and brain-derived IL-2). We found that the loss of ChAT staining did not coincide with an overall loss of cells in the medial septum, suggesting that loss of brain IL-2 results in a change in cholinergic phenotype unrelated to cell death. No differences were noted in the endogenous expression of cytokines and chemokines tested in the medial septum. Evaluation of BDNF and NGF levels between WT and IL-2KO mice in medial septal homogenates revealed that IL-2KO mice have markedly higher levels of NGF in the medial septum compared to WT mice. Our findings suggest that brain-derived IL-2 plays an essential role in the maintainance of septohippocampal projection neurons in vivo.

Loss of Neuronal Phenotype and Neurodegeneration: Effects of T Lymphocytes and Brain Interleukin-2

Loss of neuronal phenotype and reversal of neuronal atrophy have been demonstrated in different models of central nervous system (CNS) injury. These processes may be generalizable to different types of brain neurons and circuitry. The idea that some injured neurons may lose their phenotype and/or atrophy with the potential to rejuvenate is a remarkable and potentially promising form of neuronal plasticity that is not well understood. In this paper, we present some of our laboratory's basic neuroimmunology research showing that peripheral T cells entering the CNS, and brain-derived interleukin-2 (IL-2), play significant roles in these intriguing processes. Our findings suggest, for example, that T cell immunosenesence could be involved in related processes of brain aging and contribute to neurodegenerative disease. Neuroimmunological approaches may provide new insights into yet undiscovered factors and brain mechanisms that regulate changes in neuronal integrity associated with aging and disease. Such findings could have important implications for discovering more effective strategies for treating patients with neurotrauma and neurodegenerative diseases (e.g., Alzheimer's disease).

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.

Protein kinases JAK and ERK mediate protective effect of interleukin-2 upon ganglion cells of the developing rat retina

Interleukin-2 (IL-2), a prototypical pro-inflammatory cytokine firstly related to T cells differentiation, exerts pleiotrophic functions in several areas of the central nervous system. Previously we had described the neurotrophic roles of this interleukin upon retinal neurons. Therefore, the aim of this work was to investigate the signaling pathways involved in the neuroprotective effect of IL-2 on axotomized RGC. Herein we demonstrated that at postnatal day 2 IL-2 receptor α subunit (IL-2Rα) is expressed in inner plexiform layer, retinal ganglion cells layer and retinal nerve fibers layer. Moreover, using a model of organotypic retinal explants and rhodamine dextran retrograde labeling for specifically quantify RGC, we showed that IL-2 increased the survival of axotomized RGC after 2 (85.43±5.43%) and 5 (50.23%±5.32) days in vitro. Western blot analysis demonstrated that IL-2 treatment increased the phosphorilation of both extracellular signal-regulated kinases (ERK)1/2 and AKT (~two fold). However, its neuroprotective effect upon RGC was dependent of Janus kinase (JAK) and ERK1/2 activity but not of AKT activity. Taken together our results showed that the IL-2 neuroprotective action upon RGC in vitro is mediated by JAK and ERK1/2 activation.

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.

Differences in the injury/sprouting response of splenic noradrenergic nerves in Lewis rats with adjuvant-induced arthritis compared with rats treated with 6-hydroxydopamine

Sympathetic nerves in the spleen undergo an injury and sprouting response with development of adjuvant-induced arthritis (AA), a model of rheumatoid arthritis (RA). The objective of the present study was to determine whether this injury and sprouting response is disease-specific or occurs in a non-specific manner similar to injury and sprouting responses following sympathectomy with specific neurotoxins. Changes in noradrenergic (NA) innervation in spleens from Lewis rats 28 days following adjuvant treatment to induce arthritis and/or local 6-hydroxydopamine (6-OHDA) treatment to destroy NA nerves were examined using immunocytochemistry for tyrosine hydroxylase (TH). We observed significant increases in sympathetic innervation of hilar regions, sites of nerve entry into the spleen, and a striking decline in innervation of splenic regions distant to the hilus in arthritic compared to non-arthritic rats. While increased hilar and decreased distal NA innervation in arthritic rats was strikingly similar to that of non-arthritic 6-OHDA-treated rats, there were differences in splenic compartments innervated by sympathetic nerves between these groups. In 6-OHDA-treated rats, NA nerves re-innervated splenic compartments normally innervated by sympathetic nerves. In arthritic rats, sympathetic nerves returned to normally innervated splenic compartments, but also abundantly innervated red pulp. These findings suggest that splenic sympathetic nerves undergo a disease-associated injury/sprouting response with disease development that alters the normal pattern and distribution of NA innervation. The altered sympathetic innervation pattern is likely to change NA signaling to immune cell targets, which could exert long-term regulatory influences on initiation, maintenance, and resolution of immune responses that impact disease pathology.

Role of IL-15 in spinal cord and sciatic nerve after chronic constriction injury: regulation of macrophage and T-cell infiltration

The release of inflammatory mediators from immune and glial cells either in the peripheral or CNS may have an important role in the development of physiopathological processes such as neuropathic pain. Microglial, then astrocytic activation in the spinal cord, lead to chronic inflammation, alteration of neuronal physiology and neuropathic pain. Standard experimental models of neuropathic pain include an important peripheral inflammatory component, which involves prominent immune cell activation and infiltration. Among potential immunomodulators, the T-cell cytokine interleukin-15 (IL-15) has a key role in regulating immune cell activation and glial reactivity after CNS injury. Here we show, using the model of chronic constriction of the sciatic nerve (CCI), that IL-15 is essential for the development of the early inflammatory events in the spinal cord after a peripheral lesion that generates neuropathic pain. IL-15 expression in the spinal cord was identified in both astroglial and microglial cells and was present during the initial gliotic and inflammatory (NFkappaB) response to injury. The expression of IL-15 was also identified as a cue for macrophage and T-cell activation and infiltration in the sciatic nerve, as shown by intraneural injection of the cytokine and activity blockage approaches. We conclude that the regulation of IL-15 and hence the initial events following its expression after peripheral nerve injury could have a future therapeutic potential in the reduction of neuroinflammation.

Transient ischemia-induced changes of interleukin-2 and its receptor β immunoreactivity and levels in the gerbil hippocampal CA1 region

Interlukin-2 (IL-2) is an important cytokine in the brain: IL-2 and its receptors are involved with inflammatory processes. Chronological changes in IL-2 level in serum, and IL-2 and its receptor (IL-2 receptor beta, IL-2Rbeta) immunoreactivities and levels were examined in the hippocampal CA1 region after transient forebrain ischemia in gerbils. IL-2 level in serum significantly decreased 12 h after ischemia/reperfusion. IL-2 immunoreactivity was detected in the somata of pyramidal cells in sham-operated group. At 15 min after ischemia, IL-2 immunoreactivity was shown in non-pyramidal cells as well as pyramidal cells. One day after ischemia, IL-2 immunoreactivity was lowest, and IL-2 immunoreactivity is shown in non-pyramidal cells from 2 days after ischemia. Four days after ischemia, IL-2 immunoreactivity was shown in dying pyramidal cells. IL-2Rbeta immunoreactivity in the sham-operated and 15 min-3 min post-ischemic groups is detected in the cell membrane of pyramidal cells. From 3 h after ischemia, IL-2Rbeta immunoreactivity is found in cytoplasm and nuclei, but not in cell membrane. IL-2Rbeta immunoreactivity decreases from 6 h after ischemia and is shown mainly in non-pyramidal cells from 3 days after ischemia. The data of Western blot analyses for IL-2 and IL-2Rbeta was similar to the immunohistochemical data. IL-2 infusion into cerebrospinal fluid did not protect hippocampal neurons from ischemic damage. These results suggest that IL-2 and IL-2Rbeta show malfunction from 3 h after ischemia, and exogenous IL-2 does not protect ischemic neuronal damage.

Distribution of a novel protein AgK114 expression in the normal tissues of adult mice: dual expression of AgK114 and growth hormone in anterior pituitary cells

The novel antigen K114 (AgK114) has been previously identified in normal hamster skin, and its expression has been up-regulated accompanying tissue damages of the skin, although there is no information on its biological functions. To determine the physiological role of AgK114, we prepared anti-mouse AgK114 monoclonal antibody and studied its tissue distribution in healthy adult mice by immunocytochemistry. A widespread and unique expression of AgK114 peptide was found in the selected organs of various systems (hair follicle cells and sebaceous gland of skin, ciliated epithelial cells of trachea and bronchial tube, striated portion of submandibular gland, distal convoluted tubule cells of kidney, ciliated epithelial cells of oviduct, medulla of adrenal gland and anterior lobe of pituitary gland). Interestingly, dual expression of AgK114 peptide and growth hormone in somatotrophs was found in anterior lobe of pituitary gland by double immunocytochemistry. AgK114 peptide was expressed widely in many regionally well-defined cellular systems in various peripheral tissues, suggesting that AgK114 peptide may have some roles of physiological functions in these organs. The data from our current study have provided a rationale for further studies of functional roles of AgK114 peptide in a variety of organs or tissues under physiological conditions.

Changes in the density and distribution of sympathetic nerves in spleens from Lewis rats with adjuvant-induced arthritis suggest that an injury and sprouting response occurs

Previously we demonstrated reduced norepinephrine concentrations in spleens from Lewis rats with adjuvant-induced arthritis (AA), an animal model of rheumatoid arthritis. This study extends these findings, examining the anatomical localization and density of sympathetic nerves in the spleen with disease development. Noradrenergic (NA) innervation in spleens of Lewis rats was examined 28 days following adjuvant treatment to induce arthritis or vehicle for the adjuvant by using fluorescence histochemistry for catecholamines, with morphometric analysis and immunocytochemistry for tyrosine hydroxylase. In AA rats, sympathetic nerve density in the hilar regions, where NA nerves enter the spleen, was increased twofold over that observed in vehicle-treated rats. In contrast, there was a striking twofold decline in the density of NA nerves in splenic regions distal to the hilus in arthritic rats compared with nonarthritic rats. In both treatment groups, NA nerves distributed to central arterioles, white pulp regions, trabeculae, and capsule. However, NA nerve density was reduced in the white pulp but was increased in the red pulp in AA rats compared with non-AA rats. These findings indicate an injury/sprouting response with disease development whereby NA nerves die back in distal regions and undergo a compensatory sprouting response in the hilus. The redistribution of NA nerves from white pulp to red pulp suggests that these nerves signal activated immune cells localized in the red pulp in AA. Although the mechanisms of this redistribution of NA nerves into the red pulp are not known, it may be due to migration from white pulp to red pulp of target immune cells that provide trophic support for these nerves. The redistribution of NA nerves into the red pulp may be critical in modulating immune functions that contribute to the chronic inflammatory stages of arthritis.

Kainate-activated currents in the ventral tegmental area of neonatal rats are modulated by interleukin-2

Interleukin (IL)-2 is a potent modulator of neurotransmission and neuronal development in the mesolimbic and mesostriatal systems. It is also implicated in pathologies (including schizophrenia, Parkinson's disease, autism, cognitive disorders) that are linked with abnormalities in these systems. Since the kainate receptor plays an essential role in mesolimbic neuronal development and excitability, we examined the effects of physiologically relevant concentrations of IL-2 on kainate-activated current (I(KA)) in voltage-clamped neurons freshly isolated from the ventral tegmental area (VTA) of 3- to 14-day-old rats. IL-2 (0.01-10 ng/ml) alone had no effect on membrane conductance. When co-applied with kainate, IL-2 significantly decreased I(KA). IL-2 (2 ng/ml) shifted the kainate concentration-response curve to the right in a parallel manner, significantly increasing the EC(50) without changing the maximal I(KA). IL-2 inhibition of I(KA) was voltage-dependent, being greater at negative potentials. IL-2 did not alter the reversal potential. These findings suggest that IL-2 potently modulates kainate receptors of developing mesolimbic neurons. We suggest that IL-2 plays a role in the excitability of developing neurons in the mesolimbic system. Inasmuch as increased I(KA) is associated with excitotoxicity, coupled with the present observation that IL-2 inhibits I(KA), we suggest an adaptive role for IL-2 in limiting excitotoxicity in the developing brain. IL-2 might thus be required for normal cell development in the mesolimbic and mesostriatal systems.

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.

IL-2 deficiency results in altered septal and hippocampal cytoarchitecture: relation to development and neurotrophins

We have found previously that brain IL-2 receptors are enriched in the hippocampal formation, and that loss of this cytokine results in cytoarchitectural alterations in the hippocampus and septum and related behavioral changes in IL-2 knockout (IL-2 KO) mice. These alterations included decreased cholinergic somata in the medial septum/vertical limb of the diagonal band of Broca (MS/vDB) and decreased distance across the infrapyramidal (IP) granule cell layer (GCL) of the dentate gyrus (DG). To extend our previous findings, several experiments were conducted comparing IL-2 KO mice and wild-type littermates to determine (1) whether the GABAergic projection neurons of IL-2 KO mice in this region were also affected; (2) if the reduction in septal cholinergic projection neurons found in adult IL-2 KO mice is present at weaning (and prior to the development of peripheral autoimmune disease); and (3) if loss of IL-2 may result in changes in the neurotrophins, brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF), involved in maintenance of hippocampal neurons. No differences in GABAergic neurons in the MS/vDB were found in adult mice, and the reduction in cholinergic neurons seen in adult IL-2 KO mice was not found in animals at postnatal day 21. The number of neurons in the IP-GCL was also significantly reduced. Compared to wild-type mice, IL-2 KO mice had significantly reduced concentration of BDNF protein and increased concentrations of NGF. These data suggest that the septohippocampal neuronal loss in IL-2 KO mice is selective for the cholinergic neurons and appears to be due to a failure in neuronal maintenance/survival that may be, in part, associated with changes in neurotrophins.

Hydrophobic dipeptide Leu-Ile protects against neuronal death by inducing brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor synthesis

We investigated whether certain hydrophobic dipeptides, Leu-Ile, Leu-Pro, and Pro-Ile, which partially resemble the site on FK506 that binds to immunophilin, could stimulate glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) synthesis in cultured neurons and found only Leu-Ile to be an active dipeptide. Leu-Ile protected against the death of mesencephalic neurons from wild-type mice but not from mice lacking the BDNF or GDNF gene. Next, we examined the effects of i.p. or i.c.v. administration of Leu-Ile on BDNF and GDNF contents. Both types of administration increased the contents of BDNF and GDNF in the striatum of mice. Also, peripheral administration of Leu-Ile inhibited dopaminergic (DA) denervation caused by unilateral injection of 6-hydroxydopamine (6-OHDA) into the striatum of mice. The number of rotations following a methamphetamine challenge was lower in the Leu-Ile-treated group than in the nontreated group. Next, we compared the calcineurin activity and immunosuppressant activity of Leu-Ile with those of FK506. Leu-Ile was not inhibitory toward calcineurin cellular activity in cultured neuronal cells. Furthermore, Leu-Ile did not suppress concanavalin A (ConA)-induced synthesis/secretion of interleukin-2 by cultured spleen cells, suggesting that the immunosuppressant activity of Leu-Ile may be negligible when used as a therapeutic tool for neurodegenerative diseases.

Permeability of the mouse blood-brain barrier to murine interleukin-2: predominance of a saturable efflux system

Interleukin (IL)-2, a T helper (TH)1 cell-derived glycoprotein with potent neuromodulatory effects, is implicated in the etiology and pathogenesis of various psychiatric and neurological disorders. Paralleling these findings, chronic IL-2 intravenous immunotherapy may induce similar psychopathological outcomes. The findings that acute or repeated injections of IL-2 induce motor and cognitive abnormalities in rodents are consistent with these clinical findings, and raise the possibility that IL-2 crosses the blood-brain barrier (BBB) to alter brain function. However, little is known about the ability of IL-2 to enter the brain or whether its effects vary with the chronicity of IL-2 treatment. Here, we found that radioactively labeled mouse IL-2 (I-IL-2) given intravenously entered the brain at a low rate (Ki=0.142+/-0.044microl/g-min) by a non-saturable process. Repeated injections of either IL-2 or vehicle altered the kinetics of entry without producing a net effect on IL-2 entry. When I-IL-2 was given by brain perfusion, the entry rate greatly increased over 10-fold to 2.2+/-0.805microl/g-min. This suggests a circulating factor is retarding the entry of IL-2 into the brain. A paradoxic increase in the rate of I-IL-2 entry into brain occurred when an excess of unlabeled IL-2 was included in the brain perfusate, suggesting a saturable CNS-to-blood efflux system. Intracerebroventricular injection of I-IL-2 with and without unlabeled IL-2 confirmed the presence of a saturable efflux system. We conclude that IL-2 entry into the brain is low because of the absence of a blood-to-brain transporter and further retarded by circulating factors and a CNS-to-blood efflux system. This is the first description of a saturable CNS-to-blood efflux system for a cytokine. We postulate that this efflux system may protect the brain from circulating IL-2.

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.

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.

Interleukin-2-induced increases in climbing behavior: inhibition by dopamine D-1 and D-2 receptor antagonists

Interleukin (IL)-2 is a potent modulator of dopamine activity in the mesocorticolimbic and mesostriatal systems. It is also associated with behavioral changes (increased motor activity) and psychopathological outcomes (schizophrenia, Parkinson's Disease, cognitive deficits) that at least partly reflect aberrations in central dopaminergic transmission. Nonetheless, there is no evidence that a functional link exists between IL-2, dopaminergic processes, and related behavioral changes. We thus determined if IL-2 treatment increases the expression of climbing behavior, a behavior that is linked with dopamine D-1 and/or D-2 receptors and one used to test the efficacy of neuroleptics. IL-2 treatment (5-daily i.p. injections; 0.4 microg/BALB/c mouse) induced a marked 2-fold increase in climbing scores; a single injection had no effect. IL-2-induced increases in climbing behavior were completely blocked by a selective dopamine D-1 receptor antagonist (SCH 23390; 0.05 or 0.2 mg/kg; i.p.), or by a relatively high dose of a D-2 antagonist (sulpiride; 80 mg/kg; i.p.). In contrast, MK-801, a noncompetitive NMDA receptor antagonist, had no effect. This is the first demonstration of a functional link between IL-2, dopaminergic receptors, and behavior. These findings could shed light on the mechanisms by which IL-2 increases vulnerability to psychiatric abnormalities associated with aberrations in central dopaminergic processes.

IL-2/15 receptor-beta gene deletion alters neurobehavioral performance

The common IL-2/15 receptor-beta (IL-2/15Rbeta) is an essential signaling subunit that is shared exclusively by IL-2 and IL-15, and is enriched in the hippocampal formation and related limbic regions. We have previously shown that mice lacking IL-2 exhibit alterations in hippocampal-dependent learning, sensorimotor gating and accompanying reductions in hippocampal infrapyramidal mossy neuronal fiber length. Although the effects of exogenous IL-2 on various aspects of forebrain neuronal function are well documented, it is unclear whether IL-15 has neuromodulatory actions. Here we sought to test the hypothesis that the combined loss of the ability of IL-2 and IL-15 to signal through IL-2/15Rbeta in the brain would influence neurobehavioral performance, in particular spatial learning and memory performance. To test this hypothesis, we compared several different domains of behavior in mice that had one or both IL-2/15Rbeta gene alleles deleted. Compared with C57BL/6-IL-2/15Rbeta+/+ wild-type and C57BL/6-IL-2/15Rbeta+/- heterozygote littermates, C57BL/6-IL-2/15Rbeta-/- knockout mice exhibited a deficit in prepulse inhibition of the acoustic startle reflex (PPI). The IL-2/15Rbeta knockout mice also showed significant reductions in acoustic startle reactivity, and modest differences in behavior in the elevated plus-maze test indicative of reduced levels of fearfulness in response to novelty. The IL-2/15Rbeta knockout mice did not differ in locomotor activity in either the plus-maze or the Morris water-maze, and contrary to our working hypothesis, they did not differ in spatial learning or memory performance in the water-maze. Further studies are required to determine if these behavioral alterations may be attributable to factors such as the loss of the ability of IL-15 and/or IL-2 to modulate limbic neurons, autoimmunity or genetic factors associated with IL-2/15Rbeta gene deletion.

Interleukin-2 potentiates novelty- and GBR 12909-induced exploratory activity

Interleukin (IL)-2 is a cytokine that influences exploratory behavior and central dopamine activity in rodents, and induces schizophrenic-like behavior and cognitive deficits in humans. We presently report that a single i.p. injection of murine IL-2 (0.05-0.80 microg/mouse) induced significant increases in novelty-induced locomotion and exploration in BALB/c mice. These measures were not significantly altered in mice that were pre-exposed to the test cage prior to cytokine injection. The IL-2-induced behavioral changes were not further augmented by repeated intermittent injections (five daily i.p. injections; 0.4 microg/mouse), however. Nonetheless, during the treatment period, activity scores of IL-2-treated mice significantly exceeded those of mice receiving saline; hence, repeated injections of IL-2 induced a persistent behavioral activation. IL-2 treatment also increased sensitivity to the behavior-stimulating effects of GBR 12909, a highly selective dopamine uptake inhibitor. This effect was a very long-lasting one since the dopamine agonist was administered 6 weeks after cessation of IL-2 treatment. The latter finding indicates that IL-2 interacts with the mesolimbic dopamine system, changing its sensitivity to seemingly different substances. Based on these data, and those of Zalcman and colleagues (S. Zalcman, I. Savina, R.A. Wise, Interleukin-6 increases sensitivity to the locomotor-stimulating effects of amphetamine in rats, Brain Res. 847 (1999) 276-283), it is suggested that cytokines can influence the development of behavioral abnormalities that are characteristic of aberrant mesolimbic dopamine activity via sensitization-like processes.

C-fos and IL-2 gene expression in rat brain cells and splenic lymphocytes after nonantigenic and antigenic stimuli

Immunostimulatory or immunosuppressive stress models were used: (1) rotation stress (RS) and (2) immobilization (restraint) stress (IS). Intravenous injection of tetanus toxoid (anatoxin) (TT) was chosen as the antigenic stimulus (500 micrograms/kg weight), and intravenous injection of saline solution was used as the control. Splenic lymphocytes (CBA mice) or different brain structures (Wistar and Sprague-Dawley rats) were analyzed. The c-fos and interleukin-2 (IL-2) mRNA expression was measured using a digoxigenin (Dig)-labeled cDNA probe by spot or in situ hybridization. Rotation stress stimulated IL-2 mRNA synthesis in lymphocytes in the presence of ConA and rIL-2 by 40%. IL-2 mRNA synthesis in lymphoid cells obtained from animals after IS and after IS in combination with the administration in vitro of the cytotoxic drug CsA to the splenic lymphocytes was inhibited (30% and 99%), accordingly, as compared with control rats. Induction of c-fos mRNA synthesis in rat brain cells was noted 30 minutes after RS in the hypothalamus (lateralis hypothalamic area, LHA), thalamus, corpus collosum, and sensorimotor zone of the brain cortex. IL-2 mRNA synthesis was shown two hours after RS in the same structures. The increased number of c-fos mRNA-positive cells two hours after TT injection was shown in the posterior hypothalamus area (PHA), LHA, dorsomedial nucleus (DMH), ventromedial nucleus (VMH), and anterior hypothalamus area (AHA) as compared to the effect of i.v. saline injection. Moreover, IL-2 mRNA-positive cell induction was noted in the PHA, DMH, and VMH. Six hours after TT injection, c-fos mRNA expression was decreased in the PHA, LHA, and AHA. Activation of c-fos and IL-2 mRNA was detected in the paraventricularis nucleus 6 hours after TT i.v. injection. Thus, inhibition or stimulation of IL-2 gene expression in lymphoid cells depends on the nature of the stressors. RS or antigenic stimuli induce c-fos and IL-2 gene expression in definite structures of the brain. The dynamics of this process are time dependent. The partial correlation between c-fos and IL-2 mRNA expression in localization in brain structures and time dependence was shown.

Cloning the full-length IL-2/15 receptor-beta cDNA sequence from mouse brain: evidence of enrichment in hippocampal formation neurons

Numerous studies have implicated interleukin-2 (IL-2) in various brain processes, and more recently, several studies have also attributed neurobiological actions to interleukin-15 (IL-15). On lymphocytes, receptors for IL-2 and IL-15 share a common subunit, the IL-2/15 receptor-beta (IL-2/15Rbeta) that is essential for intracellular signaling. Although a short segment of IL-2/15Rbeta has been cloned (0.35 kb) from normal brain cells, attempts to isolate the full-length cDNA have been unsuccessful, suggesting the possibility that the genes expressed by brain cells and lymphocytes may differ. Using conventional and anchored PCR cloning strategies, we isolated the full-length cDNA of IL-2/15Rbeta (2038 bp) from well-perfused, normal mouse forebrain. The coding sequence and the adjacent 5' and 3' UTR sequences from brain and lymphocyte were found to be fully homologous. Although evidence of expression of IL-2/15Rbeta can be found in many brain regions using PCR, clear evidence of gene expression by in situ hybridization was detectable only in the hippocampal formation, habenula and piriform cortex. This same pattern of mRNA expression in situ was also observed for the common gamma subunit shared by IL-2 and IL-15. In the hippocampus, IL-2/15Rbeta expression was localized to neurons by high resolution in situ hybridization and evidence of IL-2 receptor protein expression was also detected by radioligand receptor binding using hippocampal homogenates. Comparison of undifferentiated and differentiated, immortalized H19-7 hippocampal neurons showed that IL-2/15Rbeta was constitutively expressed across disparate stages of hippocampal neuronal differentiation. These data indicate that IL-2/15Rbeta may serve to modulate neuronal processes in the hippocampus and associated limbic brain regions.

Interleukin-2 modulates N-methyl-D-aspartate receptors of native mesolimbic neurons

Interleukin (IL)-2 is a brain-derived cytokine that influences mesocorticolimbic dopamine release, and is associated with pathological outcomes that are mediated, at least in part, by aberrations in mesolimbic neurotransmission. The mechanisms by which IL-2 modulates mesolimbic transmission, however, are not known. The NMDA receptor/channel (NMDAR) plays an essential role in neuronal excitability of mesolimbic neurons; we thus examined in neonatal rats the effects of IL-2 on NMDA-activated current (I(NMDA)) in voltage-clamped neurons freshly isolated from the ventral tegmental area (VTA), the site of origin of the mesolimbic system. IL-2 (0.01-500 ng/ml) alone had no effect on membrane conductance. When co-applied with NMDA, IL-2 (50-500 ng/ml) significantly potentiated I(NMDA). In contrast, doses as low as 0.01 ng/ml markedly decreased the NMDA response. Dose-response analysis showed that IL-2 ( > 50 ng/ml) increased the maximal I(NMDA), without changing the EC(50), indicating that IL-2 potentiates I(NMDA) by increasing the efficacy of the NMDAR. Moreover, current-voltage analysis revealed that IL-2 potentiation of I(NMDA) was voltage-dependent, being greater at negative potentials. In contrast, IL-2 inhibition of I(NMDA) was voltage-independent, and IL-2 did not alter the reversal potential. Additionally, IL-2 (1 ng/ml) shifted the NMDA concentration-response curve to the right, significantly increasing the EC(50) for NMDA without changing the maximal I(NMDA), suggesting that IL-2 inhibits the NMDAR by a competitive mechanism. IL-2 thus acts as a potent modulator of the NMDAR. IL-2-induced alterations of responses to NMDAR activation may contribute to synaptic plasticity in the mesolimbic system and to pathological outcomes associated with this system.

Immunohistochemical localization of interleukin-2 and its receptor subunits alpha, beta and gamma in the main olfactory bulb of the rat

Endogenous interleukin-2 (IL-2) was found in the adult rat brain, however, it has not been reported whether this cytokine is present in the olfactory bulb. Immunohistochemical techniques were used to examine the cellular localization of IL-2 and its receptor subunits in the main olfactory bulb of the rat. Strong IL-2 immunoreactivity was localized in glial cells, specifically in the olfactory nerve layer, glomerular layer and external plexiform layer. IL-2 mRNA was detected in the olfactory bulb by RT-PCR. All three IL-2 receptor subunits also showed distinct laminar distributions. The IL-2Ralpha and IL-2Rbeta immunoreactivity was found both in neurons and glial cells, whereas IL-2Rgamma imunoreactivity was found in glial cells, and thus resembled IL-2 immunostaining. The present results demonstrated a wide distribution of IL-2 and its receptor subunits in the main olfactory bulb of the rat, suggesting that IL-2 might play a role in the olfactory function through autocrine or paracrine pathways. The exclusive high expression of IL-2 in glial cells in distinct laminar structures, where neuron-glia interactions are closely associated with olfactory nerve regeneration, imply that IL-2 might be involved in the process of nerve regeneration in the olfactory bulb.

Interleukin-2 and interleukin-4 increase the survival of retinal ganglion cells in culture

Natural cell death is a degenerative phenomenon observed during the normal development of the nervous system. The neuroprotective effects of cytokines produced by neuronal, glial or infiltrating cells on neurons have been extensively studied. In this work we studied the role of interleukin (IL)-2 and IL-4 on the survival of retinal ganglion cells (RGC) after 48 h in culture. Our results demonstrate that the effect of both ILs was dose-dependent and the treatment with either IL-2 (50 U/ml) or IL-4 (5 U/ml) induced a 2-fold increase in RGC survival. The effect of IL-4, but not of IL-2, was totally abolished by either 20 microM 5-fluoro-2'-deoxyuridine, an inhibitor of cell proliferation, or by 1 microM telenzepine, an inhibitor of M1 muscarinic receptor. Our results suggest that both cytokines could play an important role during the development of retinal tissue as well as during retina trauma.

Impaired learning and memory and altered hippocampal neurodevelopment resulting from interleukin-2 gene deletion

Interleukin-2 (IL-2), the protypical T cell growth factor and immunoregulatory cytokine produced by lymphocytes, has been implicated as a brain neurotrophic factor and neuromodulator. The consequences of the absence of endogenous IL-2 on brain development and function were unknown. Brain IL-2 receptors are enriched in the hippocampal formation, an area critical for the acquisition and consolidation of spatial learning and memory. Thus, we tested the hypothesis that mice lacking IL-2 would exhibit alterations in hippocampal-dependent learning and neurodevelopment. Compared with C57BL/6-IL-2+/+ wild-type mice, we observed that C57BL/6-IL-2-/- gene knockout mice had markedly impaired spatial learning and memory in the Morris water maze. No significant deficits in parameters of learning and memory performance were found in severe combined immunodeficient (SCID) mice (C57BL/6scid), however, suggesting that the impaired spatial learning and memory exhibited by IL-2 knockout mice is not attributable to generalized immunodeficiency resulting from the absence of endogenous IL-2. Examination of other domains of behavioral performance showed that the IL-2 knockout and wildtype mice did not differ in measures of fearfulness or locomotor activity in an elevated plus maze, or in reflexive startle responses to auditory stimuli--although prepulse inhibition of acoustic startle (PPI) was increased significantly in IL-2 knockout mice. The spatial learning and memory impairment in IL-2 knockout mice was accompanied by reductions in hippocampal infrapyramidal mossy neuronal fiber length, a factor shown previously to correlate positively with spatial learning ability. These findings indicate that, in addition to being a pivotal cytokine in immune regulation, IL-2 may play a role in the development and regulation of brain neurons involved in spatial learning and memory.

L-deprenyl-induced increase in IL-2 and NK cell activity accompanies restoration of noradrenergic nerve fibers in the spleens of old F344 rats

Previously, we have hypothesized a causal relationship between some measures of immunosenescence and the age-related decline in sympathetic noradrenergic (NA) nerve fibers in spleen and lymph nodes of F344 rats. In the present study, we investigated this interrelationship further by measuring NK cell activity, Con A-induced IL-2 production, norepinephrine (NE) concentration, and morphological localization of NA and neuropeptide-Y (NPY) nerve fibers in the spleens of old (21 months old) male F344 rats after 10 weeks of daily treatment with low doses of L-deprenyl, an irreversible monoamine oxidase-B inhibitor, followed by a 9-day wash-out period. NK cell activity and Con A-induced IL-2 production were increased in deprenyl-treated old rats in comparison to untreated and saline-treated old rats. Deprenyl treatment did not alter the percentage of CD5+ T-cells, but moderately increased the percentage of sIgM+ B-cells in the spleens of old rats. In addition to changes in immune responses, NE content and the volume density of NA and NPY nerve fibers were partially augmented in the spleens of deprenyl-treated old rats. In a separate study, various concentrations of deprenyl were added in vitro to spleen cells from young and old F344 rats to examine the direct effects of the drug on Con A-induced IL-2 production. In contrast to in vivo treatment, in vitro addition of deprenyl did not alter the Con A-induced IL-2 production by splenocytes from old rats. Together, these results suggest that the ability of deprenyl to enhance certain immune responses are interlinked to the restoration of sympathetic NA and NPY nerve fibers in the spleens of old rats.

Psychoneuroimmunology and the cytokine action in the CNS: implications for psychiatric disorders

1. Parallel to the current rapid development of new immunological methods, immune mechanisms are gaining more importance for our understanding of psychiatric disorders. The purpose of this article is to review basic and clinical investigations that elucidate the relationship between the CNS and the immune system. 2. The topical literature dealing with the interactions of immune system, neurotransmitters, psychological processes, and psychiatric disorders, especially in relation to cytokines, is reviewed. 3. An activation of the immune system in schizophrenia and depressive disorders has repeatedly been described. Cytokines, actively transported into the CNS, play a key role in this immune activation. It was recently observed that cytokines activate astrocytes and microglia cells, which in turn produce cytokines by a feedback mechanism. Moreover, they strongly influence the dopaminergic, noradrenergic, and serotonergic neurotransmission. 4. There are indications that the cascade of cytokines can be activated by neuronal processes. These findings close a theoretical gap between stress and its influence on immunity. Psychomotor, sickness behavior and sleep are related to IL-1; disturbances of memory and cognitive impairment are to IL-2, in part also to TNF-alpha. The hypersecretion of IL-2 is assumed to have a prominent influence on schizophrenia, and IL-6, on depressive disorders. 5. Although single cytokines most likely do not have a specificity for certain psychiatric disorders, a characteristic pattern of cytokine actions in the CNS, including influences of the cytokines on the blood-brain barrier, seems to play a role in psychiatric disorders. This may have therapeutic implications for the future.

Molecular cloning of the cDNA coding sequence of IL-2 receptor-gamma (gammac) from human and murine forebrain: expression in the hippocampus in situ and by brain cells in vitro

IL-2 has been implicated in various neurobiological processes of the mammalian CNS. To understand how IL-2 acts in the brain, our lab has sought to determine the molecular pharmacological characteristics of brain IL-2 receptors (IL-2R). The lymphocyte IL-2Rgamma, an essential subunit for IL-2 signaling, is also a common subunit (gammac) for multiple immune cytokine receptors (e.g., IL-4R, IL-7R, IL-9R, IL-15R). Having previously cloned the alpha and beta subunits of the IL-2R heterotrimer complex from normal murine forebrain, we examined the hypothesis that the brain IL-2Rgamma is derived from the same or a closely related gene coding sequence as that expressed by lymphocytes. In this study, we cloned and sequenced the full-length IL-2Rgamma coding region from saline-perfused mouse forebrain and from a human hippocampal library. The cDNA sequences of IL-2Rgamma from human and murine brain were 100% homologous to their lymphocyte sequences. Northern blot analysis showed that the mRNA transcripts in murine brain were the expected size, but the predominant transcript expressed in the brain was different than in the spleen. Compared to the spleen, very low levels of IL-2Rgamma were expressed in the forebrain. In the murine hippocampus, a region where a number of neurobiological actions of IL-2 have been reported, IL-2Rgamma mRNA was detected over the dentate gyrus and CA1-CA4 by in situ hybridization histochemistry. IL-2Rgamma was found to be constitutively expressed by murine HN33.dw hippocampal neuronal cells, murine NB41A3 neuroblastoma cells, astrocyte-enriched mixed glial cell cultures, and in SCID mouse forebrain. The human cortical neuronal cell lines, HCN-1A and HCN-2, did not express the IL-2Rgamma gene. These data suggest the possibility that, in addition to being essential in IL-2 signaling in brain, IL-2Rgamma could be a common subunit (gammac) for multiple cytokine receptors which may be operative in the mammalian CNS.

Neurotoxic consequences of central long-term administration of interleukin-2 in rats

Interleukin-2 is an immunoregulatory cytokine with several recently established CNS activities. Central effects of interleukin-2 include growth promotion for neuronal and glial cells as well as modulatory influences on neurotransmission and hormone release. However, little is known about the consequences in the CNS of chronically elevated levels of interleukin-2. Alterations in the interleukin-2/interleukin-2 receptor system are not only associated with CNS trauma, inflammation and certain neuropathologies; elevated interleukin-2 concentrations are especially induced during the therapeutic use of interleukin-2 in cancer treatments. In the present study, intracerebroventricular (i.c.v.) interleukin-2 infusions (5 15 U/h) were performed in Sprague Dawley rats for up to 14 days. Interleukin-2-treated animals showed significantly increased plasma levels of corticosterone indicating an hyperfunctioning of the hypothalamic-pituitary-adrenocortical axis that lasted over the 14 day infusion period. Moreover, the performance of interleukin-2-treated animals in the Morris swim maze task was transiently impaired. Quantitative receptor autoradiographic analyses revealed changes in the binding levels of cholinergic M1 and M2 as well as dopaminergic D1 and D2 receptors in selected brain areas in which interleukin-2 was shown to modulate neurotransmission and which are enriched with interleukin-2 receptor expression. Decreased receptor binding levels were observed in the frontoparietal cortex (M2, D1, D2), hippocampal CA1 region (M1, M2) and the nucleus accumbens (D2). Histological and immunohistochemical examination of the brains of interleukin-2-treated animals revealed multiple alterations. Interleukin-2 treatment resulted in an intracranial accumulation of non-neural, MHC class II-positive cells as well as T and B lymphocytes within the infused brain hemisphere. Cellular infiltrates were associated with angiogenesis and the deposition of extracellular matrix material, such as fibronectin. Adjacent brain regions that were partly invaded and dislodged by the cellular masses were characterized by reactive astrogliosis, microglial activation, endothelial upregulation of adhesion molecules, myelin damage and neuronal loss. Together the data suggest that persistently elevated central levels of interleukin-2 can interfere with several CNS functions and may lead to nervous tissue injury. These findings could be relevant to CNS pathologies characterized by abnormal interleukin-2 production and to central responses to interleukin-2 treatments.

Interleukin-2 increases choline acetyltransferase activity in septal-cell cultures

Interleukin-2 (IL-2) is a potent modulator of in vitro acetylcholine release in hippocampal slices [Hanisch et al. (1993) J. Neurosci., 13:3368]. In order to further investigate the cellular nature of this effect, we used embryonic septal-cell cultures (E17), known to be enriched with the cholinergic phenotype. Septal cells were grown at different plating densities under serum-free conditions. The effect of IL-2 on the expression of the cholinergic phenotype was determined using choline acetyltransferase (ChAT) activity and acetylcholinesterase (AChE) cytochemistry. IL-2 significantly enhanced ChAT activity in 5-day-old cultures (5 days in vitro). The amplitude of increases correlated with plating density. At 5 x 10(5) cells/well, the increase in ChAT activity was 35-55% greater than control values in the presence of 10(-14)-10(-10) M IL-2, whereas at 7.5 x 10(5) cells/well, this increase was substantially lower (20%) and only observed at concentrations between 10(-13)-10(-11) M. At 10(6) cells/well, IL-2 had no effect on ChAT activity. The IL-2-induced increase in ChAT activity was significantly inhibited in the presence of an IL-2 receptor antibody. Moreover, this increase was not dependent upon trophic actions, as the number of AChE-positive cells or their morphological characteristics were not altered by IL-2. Taken together, these results suggest that IL-2 can stimulate, at pM concentrations, ChAT activity by acting via its own receptors expressed by septal neurons.

CSF IL-1 and IL-2 in medicated schizophrenic patients and normal volunteers

It is clear that cytokines exert a variety of modulatory actions on the central nervous system. As part of our work exploring the relationship between immune activation and psychosis, we measured cerebrospinal fluid (CSF) IL-1 alpha and IL-2 levels in 60 medicated schizophrenic patients and in 21 normal volunteers using a competitive enzyme immunoassay. The two groups did not differ significantly in their mean cytokine levels: 1.01 (0.149) ng/ml (patients) vs. 1.28 (0.150) ng/ml (controls) for IL-1 alpha and 0.970 (0.038) ng/ml (patients) vs. 1.25 (0.086) ng/ml (controls) for IL-2. There was a significant positive correlation between CSF IL-1 alpha and IL-2 levels for all subjects (r = 0.50, n = 44, p = 0.0001).

Evidence for direct and indirect mechanisms in the potent modulatory action of interleukin-2 on the release of acetylcholine in rat hippocampal slices

1. The biphasic nature of the potent modulatory action of interleukin-2 (IL-2) on hippocampal acetylcholine (ACh) release was investigated by use of brain slice superfusion. 2. Both the potentiating (10(-13) M) and inhibitory (10(-9) M) effects of IL-2 on hippocampal ACh release were stimulation-dependent and were blocked by a neutralizing IL-2 receptor antibody, suggesting the activation of typical IL-2 receptors in both cases. 3. Tetrodotoxin (TTX: 10 microM) failed to block the potentiation of ACh release induced by a very low concentration of IL-2 (10(-13) M) suggesting a direct effect on cholinergic nerve terminals. 4. In contrast, the inhibitory effect seen at a higher concentration (10(-9) M) was TTX-sensitive, and hence indicative of an indirect action. 5. To establish the nature of this intermediate mediator, blockers of nitric oxide synthesis, and of opioid and gamma-aminobutyric acid (GABA) receptors were used. Only GABAA and GABAB receptor antagonists altered the inhibitory action of IL-2, suggesting the participation of GABA as mediator. 6. Taken together, these results provide further evidence for the potent role of IL-2 in the modulation of cholinergic function in the rat hippocampus.

Neurotoxicity induced by interleukin-2: involvement of infiltrating immune cells

Interleukin-2 (IL-2), a key regulator of immune functions, also has potent effects on neurons and glia. IL-2 modulates neural cell growth and survival and transmitter and hormone releases and is thought to mediate neuroimmune interactions. Investigating the neuroendocrine consequences of chronically elevated central nervous system (CNS) levels of IL-2, we recently observed marked neurotoxicity [Hanisch et al. (1994) Endocrinology 135:2465-2472]. In the present study, we characterize in detail the modifications in brain tissue architecture as they result in Sprague-Dawley rats from intracerebroventricular (i.c.v.) administration of low amounts of IL-2 (5 and 15 U/h, respectively, delivered by means of osmotic minipumps for up to 14 days). Histological inspection of the brains revealed massive cellular infiltrates in the ipsilateral hemisphere. The infiltrates were associated with pronounced angiogenesis and changes in the composition of the extracellular matrix. These anatomical changes apparently developed between day 7 and 14. They were specific for IL-2 and were not seen in animals treated, for example, with heat-inactivated IL-2 (controls). We further show that chronic central administration of IL-2 let to T and B lymphocyte invasion of the brain and an intracranial agglomeration of large numbers of MHC class II-positive cells. Immunocytochemistry revealed a widespread inundation of CNS tissue and a decoration of glial cells and neurons by endogenous antibodies. Tissue regions around the IL-2-induced infiltrates showed myelin destruction and neuronal cell loss. Chronically elevated CNS levels of IL-2 may, thus, not only interfere with neurotransmission and endocrine functions but also severely disturb tissue homeostasis. Therefore, the present findings could be relevant to brain injuries, CNS disorders, and clinical treatments associated with increased IL-2 levels or involving an immune component.