Interleukin-15 gene expression in human astrocytes and microglia in culture

Immunometabolic Adaptation of CD19-Targeted CAR T Cells in the Central Nervous System Microenvironment of Patients Promotes Memory Development

Metabolic reprogramming is a hallmark of T-cell activation, and metabolic fitness is fundamental for T-cell-mediated antitumor immunity. Insights into the metabolic plasticity of chimeric antigen receptor (CAR) T cells in patients could help identify approaches to improve their efficacy in treating cancer. Here, we investigated the spatiotemporal immunometabolic adaptation of CD19-targeted CAR T cells using clinical samples from CAR T-cell-treated patients. Context-dependent immunometabolic adaptation of CAR T cells demonstrated the link between their metabolism, activation, differentiation, function, and local microenvironment. Specifically, compared with the peripheral blood, low lipid availability, high IL15, and low TGFβ in the central nervous system microenvironment promoted immunometabolic adaptation of CAR T cells, including upregulation of a lipolytic signature and memory properties. Pharmacologic inhibition of lipolysis in cerebrospinal fluid led to decreased CAR T-cell survival. Furthermore, manufacturing CAR T cells in cerebrospinal fluid enhanced their metabolic fitness and antileukemic activity. Overall, this study elucidates spatiotemporal immunometabolic rewiring of CAR T cells in patients and demonstrates that these adaptations can be exploited to maximize the therapeutic efficacy of CAR T cells.

SIGNIFICANCE

The spatiotemporal immunometabolic landscape of CD19-targeted CAR T cells from patients reveals metabolic adaptations in specific microenvironments that can be exploited to maximize the therapeutic efficacy of CAR T cells.

Interleukin-15 alters hippocampal synaptic transmission and impairs episodic memory formation in mice

Cytokines are potent immunomodulators exerting pleiotropic effects in the central nervous system (CNS). They influence neuronal functions and circuit activities with effects on memory processes and behaviors. Here, we unravel a neuromodulatory activity of interleukin-15 (IL-15) in mouse brain. Acute exposure of hippocampal slices to IL-15 enhances gamma-aminobutyricacid (GABA) release and reduces glutamatergic currents, while chronic treatment with IL-15 increases the frequency of hippocampal miniature inhibitory synaptic transmission and impairs memory formation in the novel object recognition (NOR) test. Moreover, we describe that serotonin is involved in mediating the hippocampal effects of IL-15, because a selective 5-HT3A receptor antagonist prevents the effects on inhibitory neurotransmission and ameliorates mice performance in the NOR test. These findings provide new insights into the modulatory activities of cytokines in the CNS, with implications on behavior.

Immunology of amyotrophic lateral sclerosis - role of the innate and adaptive immunity

This review aims to summarize the latest evidence about the role of innate and adaptive immunity in Amyotrophic Lateral Sclerosis (ALS). ALS is a devastating neurodegenerative disease affecting upper and lower motor neurons, which involves essential cells of the immune system that play a basic role in innate or adaptive immunity, that can be neurotoxic or neuroprotective for neurons. However, distinguishing between the sole neurotoxic or neuroprotective function of certain cells such as astrocytes can be challenging due to intricate nature of these cells, the complexity of the microenvironment and the contextual factors. In this review, in regard to innate immunity we focus on the involvement of monocytes/macrophages, microglia, the complement, NK cells, neutrophils, mast cells, and astrocytes, while regarding adaptive immunity, in addition to humoral immunity the most important features and roles of T and B cells are highlighted, specifically different subsets of CD4+ as well as CD8+ T cells. The role of autoantibodies and cytokines is also discussed in distinct sections of this review.

Molecular characterization and expression analysis of interleukin-15 (IL-15) genes in orange-spotted grouper (Epinephelus coioides) in response to Vibrio harveyi challenge

As a member of the γc family, interleukin 15 plays an important function in the immune response. In this study, we cloned an IL15 from Epinephelus coioides (named Ec-IL15). The open reading frame of Ec-IL15 is 528 bp, encoding 175 amino acids. Sequence alignment analysis showed that EcIL-15 has a conserved Pfam: IL15 domain and four cysteine residues. Subcellular localization studies have shown that Ec-IL15 is distributed in whole cells. In healthy groupers, Ec-IL15 was expressed in all 11 tissues tested and the highest in liver. After ConA, PHA, LPS and poly I:C stimulation, Ec-IL15 expression of HKLs was significantly upregulated. After V. harveyi infection, the expression of Ec-IL15 in 9 tissues was significantly upregulated and peaked within 48 h. In addition, recombinant Ec-IL15 protein can not only stimulate HKLs proliferation and cytokine expression, but also has the potential as an immune enhancer.

Interleukin 15 modulates the effects of poly I:C maternal immune activation on offspring behaviour

Maternal infections during pregnancy are linked with an increased risk for disorders like Autism Spectrum Disorder and schizophrenia in the offspring. Although precise mechanisms are still unclear, clinical and preclinical evidence suggest a strong role for maternal immune activation (MIA) in the neurodevelopmental disruptions caused by maternal infection. Previously, studies using the Polyinosinic:Polycytidylic (Poly I:C) MIA preclinical model showed that cytokines like Interleukin 6 (Il6) are important mediators of MIA's effects. In this study, we hypothesized that Il15 may similarly act as a mediator of Poly I:C MIA, given its role in the antiviral immune response. To test this hypothesis, we induced Poly I:C MIA at gestational day 9.5 in wildtype (WT) and Il15^−/− rat dams and tested their offspring in adolescence and adulthood. Poly I:C MIA and Il15 knockout produced both independent and synergistic effects on offspring behaviour. Poly I:C MIA decreased startle reactivity in adult WT offspring but resulted in increased adolescent anxiety and decreased adult locomotor activity in Il15^−/− offspring. In addition, Poly I:C MIA led to genotype-independent effects on locomotor activity and prepulse inhibition. Finally, we showed that Il15^−/− offspring exhibit distinct phenotypes that were unrelated to Poly I:C MIA including altered startle reactivity, locomotion and signal transduction in the auditory brainstem. Overall, our findings indicate that the lack of Il15 can leave offspring either more or less susceptible to Poly I:C MIA, depending on the phenotype in question. Future studies should examine the contribution of fetal versus maternal Il15 in MIA to determine the precise developmental mechanisms underlying these changes.

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Poly I:C MIA decreases startle reactivity in adult WT but not Il15^−/− offspring.

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Il15^−/− offspring exposed to Poly I:C MIA show altered PPI and open field exploration.

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Il15^−/− rats exhibit distinct behavioural phenotypes independent from MIA.

Phenotypic Resemblance to Neuropsychiatric Disorder and Altered mRNA Profiles in Cortex and Hippocampus Underlying IL15Rα Knockout

Background

Previous studies of the functions of IL15Rα have been limited to immune activities and skeletal muscle development. Immunological factors have been identified as one of the multiple causes of psychosis, and neurological symptoms have been described in IL15Rα knockout (KO) mice. Seeking to explore possible mechanisms for this in the IL15Rα^-/- mouse brain, we analyzed gene expression patterns in the cortex and hippocampus using the RNA-seq technique.

Methods

IL15Rα KO mice were generated and littermate wildtype (WT) mice were used as a control group. A Y-maze was used to assess behavior differences between the two groups. The cortex and hippocampus of 3-month-old male mice were prepared and RNA-seq and transcriptome analysis were performed by gene set enrichment analysis (GSEA).

Results

Compared with the WT group, IL15Rα KO animals showed higher speed in the novel arm and more entrance frequency in the old arm in the Y-maze experiment. GSEA indicated that 18 pathways were downregulated and 13 pathways upregulated in both cortex and hippocampus from the GO, KEGG, and Hallmark gene sets. The downregulated pathways formed three clusters: respiratory chain and electron transport, regulation of steroid process, and skeletal muscle development.

Conclusion

IL15Rα KO mice exhibit altered expression of multiple pathways, which could affect many functions of the brain. Lipid biosynthesis and metabolism in the central nervous system (CNS) should be investigated to provide insights into the effect of IL15Rα on psychosis in this murine model.

Altered astrocytic function in experimental neuroinflammation and multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) that affects about 2.5 million people worldwide. In MS, the patients' immune system starts to attack the myelin sheath, leading to demyelination, neurodegeneration, and, ultimately, loss of vital neurological functions such as walking. There is currently no cure for MS and the available treatments only slow the initial phases of the disease. The later-disease mechanisms are poorly understood and do not directly correlate with the activity of immune system cells, the main target of the available treatments. Instead, evidence suggests that disease progression and disability are better correlated with the maintenance of a persistent low-grade inflammation inside the CNS, driven by local glial cells, like astrocytes and microglia. Depending on the context, astrocytes can (a) exacerbate inflammation or (b) promote immunosuppression and tissue repair. In this review, we will address the present knowledge that exists regarding the role of astrocytes in MS and experimental animal models of the disease.

Glia-immune interactions post-ischemic stroke and potential therapies

IMPACT STATEMENT

This article reviews glial cell interactions with the immune system post-ischemic stroke. Research has shown that glial cells in the brain play a role in altering phenotypes of other glial cells and have downstream immune cell targets ultimately regulating a neuroinflammatory response. These interactions may play a deleterious as well as beneficial role in stroke recovery. Furthermore, they may provide a novel way to approach potential therapies, since current stroke drug therapy is limited to only one Food and Drug Administration-approved drug complicated by a narrow therapeutic window. Until this point, most research has emphasized neuroimmune interactions, but little focus has been on bidirectional communication of glial-immune interactions in the ischemic brain. By expanding our understanding of these interactions through a compilation of glial cell effects, we may be able to pinpoint major modulating factors in brain homeostasis to maintain or discover ways to suppress irreversible ischemic damage and improve brain repair.

Transcriptional analysis of immune-relevant genes in the mucus of Labeo rohita, experimentally infected with Argulus siamensis

The knowledge of mucosa-associated molecular events that occur during infections is scarce despite the well-established importance of mucus in fish immunity. Using qRT-PCR, we analyzed the immune gene expression patterns in mucus of Labeo rohita experimentally infected with an ectoparasite Argulus siamensis. Mucus samples were collected at 0 h, 12 h, 24 h, 3 d, 7 d, 15 d, and 30 d post challenge of L. rohita with metanauplii of A. siamensis. All interleukins studied herein (IL 6, IL 15, and IL 1β) showed significant upregulation of expression levels in mucus of A. siamensis-infected fish compared to control samples. Further, the expression levels of molecules involved in pathogen recognition, toll like receptor 22, and pathogen presentation, β2 microglobulin, were found to be significantly upregulated in experimental samples until 7 d post challenge compared to control samples. The upregulated expression of lysozyme G at all time points post infection indicated the early activation of acute phase responses in mucus of infected L. rohita. Moreover, the expression levels of natural killer cell enhancing factor B were found to be higher in infected fish than they were in the control fish. The early upregulation of the immune genes observed herein reinforces the role of mucus as the first line of defense against pathogenic assault; furthermore, it expands our understanding of mucosal-immune responses to A. siamensis infection, which can aid development of immunological interventions.

Chronic ethanol intake induces partial microglial activation that is not reversed by long-term ethanol withdrawal in the rat hippocampal formation

Neuroinflammation has been implicated in the pathogenesis of several disorders. Activation of microglia leads to the release of pro-inflammatory mediators and microglial-mediated neuroinflammation has been proposed as one of the alcohol-induced neuropathological mechanisms. The present study aimed to examine the effect of chronic ethanol exposure and long-term withdrawal on microglial activation and neuroinflammation in the hippocampal formation. Male rats were submitted to 6 months of ethanol treatment followed by a 2-month withdrawal period. Stereological methods were applied to estimate the total number of microglia and activated microglia detected by CD11b immunohistochemistry in the hippocampal formation. The expression levels of the pro-inflammatory cytokines TNF-α, COX-2 and IL-15 were measured by qRT-PCR. Alcohol consumption was associated with an increase in the total number of activated microglia but morphological assessment indicated that microglia did not exhibit a full activation phenotype. These data were supported by functional evidence since chronic alcohol consumption produced no changes in the expression of TNF-α or COX-2. The levels of IL-15 a cytokine whose expression is increased upon activation of both astrocytes and microglia, was induced by chronic alcohol treatment. Importantly, the partial activation of microglia induced by ethanol was not reversed by long-term withdrawal. This study suggests that chronic alcohol exposure induces a microglial phenotype consistent with partial activation without significant increase in classical cytokine markers of neuroinflammation in the hippocampal formation. Furthermore, long-term cessation of alcohol intake is not sufficient to alter the microglial partial activation phenotype induced by ethanol.

Astrocyte-derived interleukin-15 exacerbates ischemic brain injury via propagation of cellular immunity

Astrocytes are believed to bridge interactions between infiltrating lymphocytes and neurons during brain ischemia, but the mechanisms for this action are poorly understood. Here we found that interleukin-15 (IL-15) is dramatically up-regulated in astrocytes of postmortem brain tissues from patients with ischemic stroke and in a mouse model of transient focal brain ischemia. We generated a glial fibrillary acidic protein (GFAP) promoter-controlled IL-15-expressing transgenic mouse (GFAP-IL-15^tg) line and found enlarged brain infarcts, exacerbated neurodeficits after the induction of brain ischemia. In addition, knockdown of IL-15 in astrocytes attenuated ischemic brain injury. Interestingly, the accumulation of CD8⁺ T and natural killer (NK) cells was augmented in these GFAP-IL-15^tg mice after brain ischemia. Of note, depletion of CD8⁺ T or NK cells attenuated ischemic brain injury in GFAP-IL-15^tg mice. Furthermore, knockdown of the IL-15 receptor α or blockade of cell-to-cell contact diminished the activation and effector function of CD8⁺ T and NK cells in GFAP-IL-15^tg mice, suggesting that astrocytic IL-15 is delivered in trans to target cells. Collectively, these findings indicate that astrocytic IL-15 could aggravate postischemic brain damage via propagation of CD8⁺ T and NK cell-mediated immunity.

Homeostatic cytokines in immune reconstitution and graft-versus-host disease

For numerous patients, allogeneic stem cell transplantation (SCT) is the only therapeutic option that could potentially cure their disease. Despite significant progress made in clinical management of allogeneic SCT, acute graft-versus-host disease (aGVHD) remains the second cause of death after disease recurrence. aGVHD is highly immunosuppressive and the adverse effect of allogeneic SCT on T cell regeneration is typically more important than the levels of immunosuppression normally seen after autologous SCT. In these patients, immune reconstitution often takes several years to occur and restoring immunocompetence after allogeneic SCT represents an important challenge, principally because clinical options are limited and current methods used to accelerate immune reconstitution are associated with increased GVHD. Interleukin-7 and IL-15 are both under clinical investigation and demonstrate the greatest potential on peripheral T cells regeneration in mice and humans. However, awareness has been raised about the use of IL-7 and IL-15 after allogeneic SCT with regards to potential adverse effects on aGVHD. In this review, we will discuss about recent progress made in lymphocyte regeneration, the critical role played by IL-7 and IL-15 in T cell homeostasis and how these cytokines could be used to improve immune reconstitution after allogeneic SCT.

Molecular characterization of interleukin 15 mRNA from rohu, Labeo rohita (Hamilton): Its prominent role during parasitic infection as indicated from infection studies

Interleukin 15 (IL-15) is an important cytokine of fish immune system. Sequence characterization of IL-15 from rohu, Labeo rohita revealed a mRNA sequence of 1064 bp with coding sequence of 567 bp and signal peptide of 16 amino acids. There are four characteristic sequence features viz., presence of four out-of-frame AUG initiation codons, four highly conserved cysteine residues, constitutive expression in all tissues and evolutionary similarity. The ontogeny study revealed maternal transfer of this molecule and higher expression up to 3 h post-fertilization in fertilized embryos. Its expression was down-regulated in anterior and posterior kidneys, intestine and liver tissues of rohu infected with Aeromonas hydrophila. Mild up-regulation in liver and higher expression in spleen was noticed in rohu stimulated with poly I:C (poly ionosinic:cytidylic), whereas down-regulation was observed in intestine and kidney tissues. However, a consistent higher expression was noticed in kidney and skin tissues during Argulus siamensis infection. Therefore, rohu IL-15 might possess more defensive role during early development and parasitic infection.

Serum interleukin (IL)-15 as a biomarker of Alzheimer's disease

Interleukin (IL-15), a pro-inflammatory cytokine has been studied as a possible marker of Alzheimer’s disease (AD); however its exact role in neuro-inflammation or the pathogenesis AD is not well understood yet. A Multiple Indicators Multiple Causes (MIMIC) approach was used to examine the relationship between serum IL-15 levels and AD in a well characterized AD cohort, the Texas Alzheimer's Research and Care Consortium (TARCC). Instead of categorical diagnoses, we used two latent construct d (for dementia) and g’ (for cognitive impairments not contributing to functional impairments) in our analysis. The results showed that the serum IL-15 level has significant effects on cognition, exclusively mediated by latent construct d and g’. Contrasting directions of association lead us to speculate that IL-15’s effects in AD are mediated through functional networks as d scores have been previously found to be specifically related to default mode network (DMN). Our finding warrants the need for further research to determine the changes in structural and functional networks corresponding to serum based biomarkers levels.

Molecular pathways: interleukin-15 signaling in health and in cancer

Interleukin-15 (IL-15) is a proinflammatory cytokine involved in the development, survival, proliferation, and activation of multiple lymphocyte lineages utilizing a variety of signaling pathways. IL-15 utilizes three distinct receptor chains in at least two different combinations to signal and exert its effects on the immune system. The binding of IL-15 to its receptor complex activates an "immune-enhancing" signaling cascade in natural killer cells and subsets of T cells, as well as the induction of a number of proto-oncogenes. Additional studies have explored the role of IL-15 in the development and progression of cancer, notably leukemia of large granular lymphocytes, cutaneous T-cell lymphoma, and multiple myeloma. This review provides an overview of the molecular events in the IL-15 signaling pathway and the aberrancies in its regulation that are associated with chronic inflammation and cancer. We briefly explore the potential therapeutic opportunities that have arisen as a result of these studies to further the treatment of cancer. These involve both targeting the disruption of IL-15 signaling as well as IL-15-mediated enhancement of innate and antigen-specific immunity.

Interleukin-15 enhances cellular proliferation and upregulates CNS homing molecules in pre-B acute lymphoblastic leukemia

Genome-wide association studies have consistently implicated the interleukin-15 (IL-15) gene in acute lymphoblastic leukemia (ALL) biology, including associations with disease susceptibility, and increased risk of central nervous system (CNS) involvement. However, whether pre-B ALL blasts directly respond to IL-15 is unknown. Here, we show that most pre-B ALL primary samples and cell lines express IL-15 and components of its receptor and that primary pre-B ALL cells show increased growth in culture in response to IL-15. Investigation of mechanisms of action using IL-15-responsive SD-1 cells shows this growth advantage is maximal under low-serum conditions, mimicking those found in cerebrospinal fluid. IL-15 also upregulates PSGL-1 and CXCR3, molecules associated with CNS trafficking. Investigation of downstream signaling pathways indicates that IL-15 induces signal transducer and activator of transcription 5 (STAT5), extracellular signal-regulated kinase (ERK) 1/2, and to a lesser extent phosphatidylinositol 3-kinase (PI3K) and nuclear factor κB (NF-κB) phosphorylation. The IL-15-mediated growth advantage is abolished by mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MEK/ERK), PI3K, and NF-κB inhibitors but preserved in the presence of STAT5 inhibition. Together, these observations provide a mechanistic link between increased levels of IL-15 expression and leukemogenesis, high-risk disease, and CNS relapse and suggest potential therapeutic targets.

Preoperative cerebrospinal fluid cytokine levels and the risk of postoperative delirium in elderly hip fracture patients

Background

Aging and neurodegenerative disease predispose to delirium and are both associated with increased activity of the innate immune system resulting in an imbalance between pro- and anti-inflammatory mediators in the brain. We examined whether hip fracture patients who develop postoperative delirium have altered levels of inflammatory mediators in cerebrospinal fluid (CSF) prior to surgery.

Methods

Patients were 75 years and older and admitted for surgical repair of an acute hip fracture. CSF samples were collected preoperatively. In an exploratory study, we measured 42 cytokines and chemokines by multiplex analysis. We compared CSF levels between patients with and without postoperative delirium and examined the association between CSF cytokine levels and delirium severity. Delirium was diagnosed with the Confusion Assessment Method; severity of delirium was measured with the Delirium Rating Scale Revised-98. Mann–Whitney U tests or Student t-tests were used for between-group comparisons and the Spearman correlation coefficient was used for correlation analyses.

Results

Sixty-one patients were included, of whom 23 patients (37.7%) developed postsurgical delirium. Concentrations of Fms-like tyrosine kinase-3 (P=0.021), Interleukin-1 receptor antagonist (P=0.032) and Interleukin-6 (P=0.005) were significantly lower in patients who developed delirium postoperatively.

Conclusions

Our findings fit the hypothesis that delirium after surgery results from a dysfunctional neuroinflammatory response: stressing the role of reduced levels of anti-inflammatory mediators in this process.

Trial registration

The Effect of Taurine on Morbidity and Mortality in the Elderly Hip Fracture Patient.

Registration number: NCT00497978. Local ethical protocol number: NL16222.094.07.

Brain interleukin-15 in neuroinflammation and behavior

Interleukin (IL)-15 is a ubiquitously expressed cytokine existing in both intracellular and secretory forms. Here we review the expression, regulation, and functions of IL15 and its receptors in the brain. IL15 receptors show robust upregulation after neuroinflammation, suggesting a major role of IL15 signaling in cerebral function. Involvement of the IL15 system in neuropsychiatric behavior is reflected by the effects of IL15, IL15Rα, and IL2Rγ deletions on neurobehavior and neurotransmitters, the effects of IL15 treatment on neuronal activity, and the potential role of IL15 in neuroplasticity/neurogenesis. The results show that IL15 modulates GABA and serotonin transmission. This may underlie deficits in mood (depressive-like behavior and decreased normal anxiety) and memory, as well as activity level, sleep, and thermoregulation. Although IL15 has only a low level of permeation across the blood-brain barrier, peripheral IL15 is able to activate multiple signaling pathways in neurons widely distributed in CNS regions. The effects of IL15 in "preventing" neuropsychiatric symptoms in normal mice implicate a potential therapeutic role of this polypeptide cytokine.

The role of IL-15 in activating STAT5 and fine-tuning IL-17A production in CD4 T lymphocytes

IL-15 is an important IL-2-related cytokine whose role in Th17 cell biology has not been fully elucidated. In this study, we show that exogenous IL-15 decreased IL-17A production in Th17 cultures. Neutralization of IL-15 using an Ab led to increases in IL-17A production in Th17 cultures. Both Il15(-/-) and Il15r(-/-) T cell cultures displayed higher frequency of IL-17A producers and higher amounts of IL-17A in the supernatants compared with those of wild-type (WT) cells in vitro. IL-15 down-modulated IL-17A production independently of retinoic acid-related orphan receptor-γt, Foxp3, and IFN-γ expression. Both Th17 cells and APCs produced IL-15, which induced binding of STAT5, an apparent repressor to the Il17 locus in CD4 T cells. Also, in a model of myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (EAE), Il15(-/-) mice displayed exacerbated inflammation-correlating with increased IL-17A production by their CD4(+) T cells-compared with WT controls. Exogenous IL-15 administration and IL-17A neutralization reduced the severity of EAE in Il15(-/-) mice. Taken together, these data indicate that IL-15 has a negative regulatory role in fine-tuning of IL-17A production and Th17-mediated inflammation.

Proinflammatory cytokines in serum and cerebrospinal fluid of CIDP patients

INTRODUCTION

Little is known about the role of cytokines in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Interleukin (IL)-12 and IL-15 are the major growth and differentiation factors for Th-1 cells and IL-17 is a marker of Th-17 cell expansion and activation, a high proinflammatory new subset of T cells that induce severe autoimmunity.

PATIENTS AND METHODS

We measured by enzyme-like immunosorbent assay serum and cerebrospinal fluid (CSF) levels of IL-15, IL-12, and IL-17 in 24 patients with CIDP and 12 patients with other non-inflammatory neurological disorders and serum levels in 16 healthy subjects.

RESULTS

We found a positive association of CSF IL-12 (P = 0·012) with CIDP presence (P<0·001).

CONCLUSIONS

Our findings suggest that IL-12 may be involved as potential marker of immune activation in CIDP. The increase in its levels in CSF may be a marker of initiation of Th-1 cell-mediated immunity.

The role of IL-15 in central nervous system disorders

IL-15 is a proinflammatory cytokine. It is produced by activated blood monocytes, macrophages, dendritic cells, and activated glial cells. It promotes T-cell proliferation, induction of cytolytic effector cells including natural killer and cytotoxic cells and stimulates B-cell to proliferate and secrete immunoglobulins. Little information is available on the exact role of IL-15 in the neurological diseases. Microglial cells are the main regulators of both innate and adaptive immune responses in the central nervous system (CNS). IL-15 may be involved in the inflammatory reactions and microglial activation of some common CNS disorders such as multiple sclerosis, Alzheimer's and Parkinson's disease, but its exact role in their pathogenesis is not clear.

Interleukin-15 affects serotonin system and exerts antidepressive effects through IL15Rα receptor

Contrary to the reduction of depressive-like behavior observed in several strains of cytokine receptor knockout mice, mice lacking the specific receptor for interleukin (IL)-15 showed increased immobility in tail suspension and modified forced swimming tests. There was also a reduction in social interactions. The hippocampus of the IL15Rα knockout mice had decreased mRNA for 5-HT(1A), increased mRNA for 5-HT(2C), and region-specific changes of serotonin reuptake transporter (SERT) immunoreactivity. Fluoxetine (the classic antidepressant Prozac, which inhibits 5-HT(2C) and SERT) reduced the immobility of the IL15Rα knockout mice in comparison with their pretreatment baseline. Together with the unchanged performance of the IL15Rα knockout mice on the rotarod, this response to fluoxetine indicates that the immobility reflects depression. Wildtype mice responded to IL15 treatment with improvement of immobility induced by forced swimming, whereas the knockout mice failed to respond. Thus, the cognate IL15 receptor is necessary for the antidepressive activity of IL15. In ex vivo studies, IL15 decreased synaptosomal uptake of 5-HT, and modulated the expression of 5-HT(2C) and SERT in cultured neurons in a dose- and time-dependent manner. Thus, the effect of IL15 on serotonin transmission may underlie the depressive-like behavior of IL15Rα knockout mice. We speculate that IL15 is essential to maintain neurochemical homeostasis and thereby plays a role in preventing neuropsychiatric symptoms.

Contribution of astrocyte-derived IL-15 to CD8 T cell effector functions in multiple sclerosis

The contribution of local factors to the activation of immune cells infiltrating the CNS of patients with multiple sclerosis (MS) remains to be defined. The cytokine IL-15 is pivotal in the maintenance and activation of CD8 T lymphocytes, a prominent lymphocyte population found in MS lesions. We investigated whether astrocytes are a functional source of IL-15 sufficient to enhance CD8 T lymphocyte responses and whether they provide IL-15 in the inflamed CNS of patients with MS. We observed that human astrocytes in primary cultures increased surface IL-15 levels upon activation with combinations of proinflammatory cytokines. Expanded human myelin autoreactive CD8 T lymphocytes cultured with such activated astrocytes displayed elevated lytic enzyme content, NKG2D expression, and Ag-specific cytotoxicity. These functional enhancements were abrogated by anti-IL-15-blocking Abs. Immunohistochemical analysis of brain tissue sections obtained from patients with MS demonstrated colocalization for IL-15 and the astrocyte marker glial fibrillary acidic protein within white matter lesions. The majority of astrocytes (80-90%) present in demyelinating MS lesions expressed IL-15, whereas few astrocytes in normal control brain sections had detectable IL-15. IL-15 could be detected in the majority of Iba-1-expressing microglia in the control sections, albeit in lower numbers when compared with microglia/macrophages in MS lesions. Furthermore, infiltrating CD8 T lymphocytes in MS lesions were in close proximity to IL-15-expressing cells. Astrocyte production of IL-15 resulting in the activation of CD8 T lymphocytes ascribes a role for these cells as contributors to the exacerbation of tissue damage during MS pathogenesis.

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.

Interleukin-15 receptor is essential to facilitate GABA transmission and hippocampal-dependent memory

Interleukin-15 (IL15) is a cytokine produced by normal brain, but the functions of the IL15 system in normal adults are not yet clear. The hypothesis that the hippocampal IL15 system is essential for memory consolidation was tested by use of IL15Ralpha knock-out mice in behavioral, biochemical, immunohistological, and electron microscopic analyses. The knock-out mice showed deficits in memory, determined by the Stone T-maze and fear conditioning. In their hippocampi, the concentration of GABA was significantly lower. There were region-specific changes of the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD), with increased GAD-67-immunopositive interneurons in the stratum oriens of the CA1 region of the hippocampus, accompanied by nonsignificant reduction of GAD-67 synapses in the CA3 region. Western blotting showed an increase of GAD-65, but not GAD-67, in the hippocampal homogenate. The ultrastructure of the hippocampus remained intact in the knock-out mice. To further test the hypothesis that IL15 directly modulates GABA turnover by reuptake mechanisms, the dose-response relationship of IL15 on (3)H-GABA uptake was determined in two neuronal cell lines. The effective and nontoxic dose was further used in the synaptosomal uptake studies. IL15 decreased the uptake of (3)H-GABA in synaptosomes from the forebrain of wild-type mice. Consistent with this, IL15Ralpha knock-out mice had increased synaptosomal uptake of (3)H-GABA. Overall, the results show novel functions of a unique cytokine in normal hippocampal activity by regulating GABA transmission.

Blockade of IL-15 activity inhibits microglial activation through the NFkappaB, p38, and ERK1/2 pathways, reducing cytokine and chemokine release

Reactive glia formation is one of the hallmarks of damage to the CNS, but little information exists on the signals that direct its activation. Microglial cells are the main regulators of both innate and adaptative immune responses in the CNS. The proinflammatory cytokine IL-15 is involved in regulating the response of T and B cells, playing a key role in regulating nervous system inflammatory events. We have used a microglial culture model of inflammation induced by LPS and IFNgamma to evaluate the role of IL-15 in the proinflammatory response. Our results indicate that IL-15 is necessary for the reactive response, its deficiency (IL-15-/-) leading to the development of a defective proinflammatory response. Blockade of IL-15, both with blocking antibodies or with the ganglioside Neurostatin, inhibited the activation of the NFkappaB pathway, decreasing iNOS expression and NO production. Inhibiting IL-15 signaling also blocked the activation of the mitogen-activated protein kinase (MAPK) pathways ERK1/2 and p38. The major consequence of these inhibitory effects, analyzed using cytokine antibody arrays, was a severe decrease in the production of chemokines, cytokines and growth factors, like CCL17, CCL19, IL-12, or TIMP-1, that are essential for the development of the phenotypic changes of glial activation. In conclusion, activation of the IL-15 system seems a necessary step for the development of glial reactivity and the regulation of the physiology of glial cells. Modulating IL-15 activity opens the possibility of developing new strategies to control gliotic events upon inflammatory stimulation.

Aggravated experimental autoimmune encephalomyelitis in IL-15 knockout mice

IL-15 initially identified as a T proliferating cytokine has several structural and biological similarities with IL-2 and has been associated with a number of autoimmune diseases. Because of the scarcity of information available on the role of IL-15 in MS pathogenesis, we have investigated how the absence of IL-15 affected the development of experimental autoimmune encephalomyelitis, a mouse model of MS. Following immunization of IL-15(-/-) and C57BL/6 mice with MOG(35-55), we observed a more severe neurological impairment in the IL-15 knockout mice than in the wild-type group. The enhanced disease severity in IL-15(-/-) mice was associated with greater demyelination in the spinal cord, increased immune cell infiltration and inflammation. These events may be related to the higher CD4/CD8 ratio and the almost absent NK cell activity, congenital immune features of IL-15KO mice. Moreover, we found that the fractalkine receptor CX3CR1 was overexpressed in the spinal cord of IL-15(-/-) mice, mainly localized on infiltrating CD8(+) T cells. How these findings are contributing to the aggravated EAE development in IL-15 KO mice remain unclear and need to be further investigated.

IL-15 receptor deletion results in circadian changes of locomotor and metabolic activity

Interleukin-15 (IL-15) is a cytokine produced in the normal brain that acts on its specific receptor IL-15Ralpha and co-receptors IL-2Rbeta and IL-2Rgamma in neuronal cells. The functions of the cerebral IL-15 system, however, are not yet clear. To test the hypothesis that IL-15Ralpha regulates metabolic activity and body temperature, we quantified the specific metabolic phenotype of IL-15Ralpha knockout mice. These normal-appearing mice were leaner with lower fat composition. During the entire circadian cycle, the knockout mice had a significantly higher acrophase in locomotor activity and heat dissipation. During the light phase, there was significantly greater food intake, oxygen consumption, and carbon dioxide production. The difference in the dark and light phases suggests that IL-15Ralpha participates in circadian rhythm regulation. The higher oxygen consumption in the light phase indicates adaptive thermogenesis in the knockout mice. The body temperature of the receptor knockout mice was significantly higher than the control in the light phase, and this was mainly caused by a large difference occurring between 0600 and 0900 h. In addition to the metabolic chamber studies and circadian rhythm analyses, qPCR of hypothalamic homogenates indicated higher mRNA expression of orexin and transient receptor potential vanilloid 4 cation channels. Consistent with a direct role of IL-15Ralpha in the hypothalamus, IL-15 treatment of the wild-type mice induced c-Fos expression in the preoptic area. We conclude that activation of hypothalamic neurons by IL-15 in mice contributes to thermoregulation and modifies the metabolic phenotype.

Effects of interleukin-15 on neuronal differentiation of neural stem cells

Interleukin-15 (IL-15) signaling has pleiotropic actions in many cell types during development and has been best studied in cells of immune system lineage, where IL-15 stimulates proliferation of cytotoxic T cells and induces maturation of natural killer cells. A few reports have indicated that IL-15 and the IL-15 receptor are expressed in central nervous system tissues and neuronal cell lines. Because this aspect of IL-15 action is poorly studied, we used cultured rat neural stem cells (NSCs) to study IL-15 signal transduction and activity. Primary cultures of rat NSCs in culture will form neurospheres and will differentiate into neuron, astrocyte, and oligodendrocyte progenitors under permissive conditions. We found by immunofluorescence that the IL-15Ralpha subunit of the IL-15 receptor was expressed in NSCs and differentiating neurons, but not astrocyte or oligodendrocyte progenitors. We also showed that IL-15 treatment reduced MAP-2 protein levels in neurons and could reduce neurite outgrowth in differentiating neurons but did not affect NSC proliferation, and cell proportions and viability of the corresponding lineage cells. In the presence of a STAT3 inhibitor, Stattic, IL-15 no longer reduced MAP-2 protein levels. IL-15 treatment caused STAT3 phosphorylation. Furthermore, using anti-IL-15Ralpha antibody to block IL-15 signaling completely inhibited IL-15-induced phosphorylation of STAT3 and prevented IL-15 from decreasing neurite outgrowth. In conclusion, IL-15 may influence neural cell differentiation through a signal transduction pathway involving IL-15Ralpha and STAT3. This signal transduction modifies MAP-2 protein levels and, consequently, the differentiation of neurons from NSCs, as evidenced by reduced neurite outgrowth.

Cerebral microvascular IL15 is a novel mediator of TNF action

The blood-brain barrier is a gatekeeper and modulatory interface for the CNS. Cerebral endothelial cells are the major component of the blood-brain barrier, and they modify inflammatory signals from the circulation to the CNS by production and secretion of secondary substances. The inflammatory mediators induced by tumor necrosis factor alpha (TNF) were determined by microarray analysis of RBE4 cerebral endothelial cells, at 0, 6, 12, or 24 h after TNF treatment. Interleukin (IL)-15 and its receptors were among the most robustly up-regulated genes. This was confirmed by real-time RT-PCR and western blotting. The three subunits of the IL15 receptor complex (IL15Ralpha, IL2Rbeta, and IL2Rgamma) showed differential regulation by TNF in their time course and amplitude of increased expression. Consistent with increased expression of the specific high affinity receptor IL15Ralpha, TNF increased cellular uptake of (125)I-IL15 and enhanced the fluorescent intensity of Alexa568-IL15 in RBE4 cells. TNF treatment in mice also increased the level of expression of IL15 receptors in enriched cerebral microvessels. We conclude that the cerebral microvascular IL15 system is a novel inflammatory mediator that transduces the actions of TNF.

Circulating interleukin-15 and RANTES chemokine in MS patients: effect of treatment with methylprednisolone in patients with relapse

INTRODUCTION

Interleukin-15 (IL-15) is a proinflammatory cytokine. RANTES is a member of the beta chemokines subfamily with strong chemoattractant activity for T lymphocytes and monocytes.

MATERIALS AND METHODS

We measured by enzyme-like immunosorbent assay (ELISA) serum levels of IL-15 and RANTES in 24 patients with MS in relapse, 27 patients with stable MS and 21 healthy subjects. Serum levels of IL-15 and RANTES were also measured before, 5 days and 1 month after onset of treatment with methylprednisolone i.v.

RESULTS

IL-15 serum levels were higher in patients with relapse compared with patients in stable stage of the disease and healthy subjects (p=0.001 and p=0.008 respectively). RANTES serum levels were increased in patients with relapse and stable disease as compared to healthy subjects (p=0.01). IL-15 and RANTES levels were not decreased after treatment with corticosteroids.

CONCLUSIONS

Our findings suggest a possible role of IL-15 and RANTES in MS. Treatment with methylprednisolone in relapse had no effect on serum IL-15 and RANTES levels.

Permeation of blood-borne IL15 across the blood-brain barrier and the effect of LPS

Interleukin15 (IL 15) is a proinflammatory cytokine with elevated concentrations in autoimmune diseases involving the periphery (e.g. rheumatoid arthritis) and CNS (e.g. multiple sclerosis). Its interactions with the blood-brain barrier (BBB) were studied in normal and lipopolysaccharide (LPS)-treated mice. (125)I-IL15 remained intact for at least 10 min after i.v. injection and reached CNS parenchyma with regional differences between brain and spinal cord. Both in vivo and in situ brain perfusion of (125)I-IL15 showed that its permeation of the BBB was non-saturable. LPS induced a significant increase of IL15 uptake by the brain and spinal cord, partly related to a higher general permeability of the BBB. The results suggest that the BBB is an interface for blood-borne IL15 to interact with the CNS in the basal state and during inflammation.

Circulating interleukin-15 and RANTES chemokine in Parkinson's disease

Interleukin-15 promotes T-cell proliferation, induction of cytolytic effector cells including natural killer (NK) and cytotoxic cells and stimulates B-cell to proliferate and secrete immunoglobulins. RANTES is a C-C beta chemokine with strong chemoattractant activity for T lymphocytes and monocytes.

OBJECTIVES

The objective of our study was to find out whether IL-15 and RANTES are involved in the possible inflammatory reactions of PD.

PATIENTS AND METHODS

We measured by immunoassay serum IL-15 and RANTES levels in 41 patients with PD in comparison with serum levels in 19 healthy subjects age and sex-matched. IL-15 and RANTES levels were correlated with sex, age, disease duration. H-Y stage and the UPDRS III score in all the studied groups and were also correlated with treatment status in PD patients.

RESULTS

The PD group presented with significantly increased RANTES levels as compared to the control group (P = 0.0009). No difference was observed as regards IL-15 levels. A strong and significant correlation between RANTES levels and UPDRS III score was observed in PD patients (R(s) = 0.42, P = 0.007). Untreated patients had significantly higher RANTES levels as compared to the controls.

CONCLUSIONS

Our findings may suggest a recruitment of activated monocytes, macrophages and T lymphocytes to sites of inflammation in the central nervous system of PD patients.

Molecular and Functional Characterization of IL-15 in Rainbow TroutOncorhynchus mykiss:A Potent Inducer of IFN-γ Expression in Spleen Leukocytes

IL-15 is a member of the common gamma-chain family of cytokines that possess a heterogeneous repertoire of activities on various cells of the immune system. We report here the first functional characterization of a fish IL-15 in rainbow trout. The trout IL-15 gene is 6-kb long and contains six exons and five introns that transcribe into a 1.2-kb mRNA containing seven out-of-frame AUG initiation codons and translate into a 193-aa peptide. Potential sites for transcriptional activators and repressors have been identified in the trout IL-15 gene. Like IL-15 from other species, trout IL-15 is closely linked to an INPP4B gene, but there is also a BCL10 gene located between the IL-15 and INPP4B genes. Three alternative splicing variants of the trout IL-15 gene have also been identified and their expression in vivo was studied. Trout IL-15 expression is present in all the tissues and cell lines studied. Recombinant trout IFN-gamma selectively increased IL-15 expression but had little effect on other cytokines such as IL-1 beta and IL-11. Recombinant trout IL-15 preferentially stimulated splenic leukocytes from healthy fish, where it induced a large increase in IFN-gamma expression, with little, if any, effect on IL-1 beta expression. This effect was quite long-lived, and was still apparent 24 h poststimulation. Although the exact cell types being affected have still to be determined, it is clear that once produced IL-15 will have a profound affect on the ability of the fish immune system to activate antimicrobial defenses and genes induced themselves by IFN-gamma.

Enrichment and persistence of virus-specific CTL in the brain of simian immunodeficiency virus-infected monkeys is associated with a unique cytokine environment

The host reaction to infection of the brain contributes to a number of CNS pathologies including neuro-AIDS. In this study, we have identified the accumulation of SIV-specific CTL in the brains of SIV-infected animals who have neurophysiological abnormalities but are otherwise asymptomatic. SIV-specific CTL enter the brain early after viral infection and are maintained in the brain even when those reactive with an immunodominant epitope in Tat are lost from the rest of the body. The specialized CNS environment contributes to this unique outcome. Following SIV infection, brain levels of IL-15 were significantly elevated whereas IL-2 was absent, creating an environment that favors CTL persistence. Furthermore, in response to IL-15, brain-derived CD8(+) T cells could expand in greater numbers than those from spleen. The accumulation, persistence, and maintenance of CTL in the brain are closely linked to the increased levels of IL-15 in the absence of IL-2 in the CNS following SIV infection.

IL-15 and IL-15R alpha gene deletion: effects on T lymphocyte trafficking and the microglial and neuronal responses to facial nerve axotomy

IL-15 is a potent T cell chemoattractant, and this cytokine and its unique alpha subunits, IL-15R alpha, can modify immune cell expression of several T cell chemokines and their receptors. Facial nerve axotomy in mice leads to T cell migration across an intact blood-brain-barrier (BBB), and under certain conditions T cells can provide neuroprotection to injured neurons in the facial motor nucleus (FMN). Although chemokines and chemoattractant cytokines are thought to be responsible for T cell migration to the injured cell bodies, data addressing this question are lacking. This study tested the hypothesis that T cell homing to the axotomized FMN would be impaired in knockout (KO) mice with the IL-15 and IL-15R alpha genes deleted, and sought to determine if microglial responsiveness and motoneuron death are affected. Both IL-15KO and IL-15R alpha KO mice exhibited a marked reduction in CD3(+) T cells and had fewer MHC2(+) activated microglia in the injured FMN than their respective WT controls at day 14 post-axotomy. Although there was a relative absence of T cell recruitment into the axotomized FMN in both knockout strains, IL-15R alpha KO mice had five times more motoneuron death (characterized by perineuronal microglial clusters engulfing dead motoneurons) than their WT controls, whereas dead neurons in IL-15KO did not differ from their WT controls. Further studies are needed to dissect the mechanisms that underlie these observations (e.g., central vs. peripheral immune contributions).

Microglia and inflammation: impact on developmental brain injuries

Inflammation during the perinatal period has become a recognized risk factor for developmental brain injuries over the past decade or more. To fully understand the relationship between inflammation and brain development, a comprehensive knowledge about the immune system within the brain is essential. Microglia are resident immune cells within the central nervous system and play a critical role in the development of an inflammatory response within the brain. Microglia are critically involved with both the innate and adaptive immune system, regulating inflammation and cell damage within the brain via activation of Toll-like receptors, production of cytokines, and a myriad of other intracellular and intercellular processes. In this article, microglial physiology is reviewed along with the role of microglia in developmental brain injuries in humans and animal models. Last, microglial functions within the innate and adaptive immune system will be summarized. Understanding the processes of inflammation and microglial activation is critical for formulating effective preventative and therapeutic strategies for developmental brain injuries.

Levels of IL-15 in Serum and Cerebrospinal Fluid of Patients with Behçet's Disease

Interleukin-15 (IL-15) is a novel proinflammatory cytokine, involved in the pathogenesis of inflammatory/autoimmune disease. The objective of our study was to measure serum and cerebrospinal fluid (CSF) IL-15 levels in patients with Behçet's disease (BD). CSF/serum IL-15 ratio was introduced to assess the origin of elevated IL-15 levels. We measured serum and CSF-IL-15 levels in 40 patients with BD (20 patients in active stage). Inflammatory and non-inflammatory neurological disease patients acted as controls. Active BD patients have significantly higher serum IL-15 levels (median 10.4 pg/ml; range 5.3-17.4) compared with BD in remission (6.05 pg/ml; 4-10.4) and healthy controls (4.65 pg/ml; 3.9-6.2). Similar serum IL-15 levels were found in active neuro-BD and inflammatory neurological disease (9.5 pg/ml; 5-13). Elevated levels of IL-15 were observed in CSF samples from neuro-BD patients (11 pg/ml; 8.5-15) and inflammatory neurological disease patients (10 pg/ml; 6.5-14) compared with patients with non-inflammatory neurological disease (4 pg/ml; 4-5.5; P < 0.001). Vascular cerebral BD lesions were associated with high CSF/serum IL-15 ratio. Our findings suggest that IL-15 is involved in BD inflammatory process, particularly in vasculitis foci, as an elevated CSF/serum IL-15 ratio characterizes vascular cerebral lesions.

IL-15 is elevated in cerebrospinal fluid of patients with Alzheimer's disease and frontotemporal dementia

Interleukin-15 is a novel proinflammatory cytokine. It is produced by activated blood monocytes, macrophages, and glial cells. The objective of our study was to assess the role of interleukin-15 as a marker of increased proinflammatory activity in patients with Alzheimer's disease and frontotemporal dementia. We measured cerebrospinal fluid interleukin-15 levels in 17 patients with Alzheimer's disease and 7 patients with frontotemporal dementia in comparison with 17 patients with amyotrophic lateral sclerosis and 15 patients with Parkinson's disease. Patients with Alzheimer's disease and frontotemporal dementia had significantly higher cerebrospinal fluid interleukin-15 levels compared with patients with noninflammatory neurological diseases (P < .05 and P < .01, respectively). In Alzheimer's disease, a significant positive correlation was noted between interleukin-15 levels and age of onset (R = .48, P = .05). Our findings suggest that interleukin-15 may be implicated in the pathophysiology of Alzheimer's disease and frontotemporal dementia.

Mouse hepatitis virus pathogenesis in the central nervous system is independent of IL-15 and natural killer cells

Infection by the neurotropic JHM strain of mouse hepatitis virus (JHMV) results in an acute encephalomyelitis associated with demyelination. T cells are critical in controlling viral replication, but also contribute to central nervous system (CNS) pathogenesis. To reveal a role for innate effectors in anti-viral immunity and neurological disease, JHMV pathogenesis was studied in mice deficient in interleukin-15 (IL-15^−/−) and natural killer (NK) cells. Clinical disease, CNS inflammation and demyelination in infected IL-15^−/− mice were similar to wild-type mice. Despite the absence of NK cells and suboptimal CD8⁺ T cell responses, IL-15^−/− mice controlled JHMV replication as efficiently as wild-type mice. Similar kinetics of class I and class II upregulation on microglia further suggested no role of NK cells in regulating major histocompatibility complex (MHC) molecule expression on resident CNS cells. IL-15 and NK cells thus appear dispensable for anti-viral immunity and CNS pathogenesis during acute JHMV infection.

Regulation by GD3 of the proinflammatory response of microglia mediated by interleukin-15

The interleukin (IL)-15-dependent immune responses of murine microglia were strongly affected by low concentrations of the ganglioside GD3. The ganglioside binding to IL-15 inhibited the proinflammatory effects of the cytokine, reducing IL-15-dependent T-cell proliferation as well as mRNA expression for IL-15Ralpha, p65, and NFATc2 in the N13 murine microglial cell line. Treatment of primary murine microglial cultures with GD3 abolished IL-15 production, without affecting cellular viability, but decreased the production of nitric oxide, a direct sensor of inflammation and nuclear factor-kappaB activity. We conclude that low doses of GD3 could inhibit specific proinflammatory mechanisms and modulate the inflammatory environment, leading to a less reactive scene. Microglial cells are one of the main actors in the inflammatory events that follow CNS trauma or an autoimmune disease episode, modulating the internal production of cytokines, growth factors, and other homeostatic molecules that may determine the evolution and outcome of tissue damage. Proinflammatory cytokines have a relevant role in the initial events, and modulation of their activity by gangliosides could cut down their harmful effects and interfere with invasion of the CNS by peripheral immune cells. The antiinflammatory properties of GD3 could be significant in the treatment of pain subsequent to CNS damage.

Microglia and inflammation-mediated neurodegeneration: multiple triggers with a common mechanism

Inflammation, a common denominator among the diverse list of neurodegenerative diseases, has recently been implicated as a critical mechanism responsible for the progressive nature of neurodegeneration. Microglia are the resident innate immune cells in the central nervous system and produce a barrage of factors (IL-1, TNFalpha, NO, PGE2, superoxide) that are toxic to neurons. Evidence supports that the unregulated activation of microglia in response to environmental toxins, endogenous proteins, and neuronal death results in the production of toxic factors that propagate neuronal injury. In the following review, we discuss the common thread of microglial activation across numerous neurodegenerative diseases, define current perceptions of how microglia are damaging neurons, and explain how the microglial response to neuronal damage results in a self-propelling cycle of neuron death.

IL-15 is elevated in serum and cerebrospinal fluid of patients with multiple sclerosis

Interleukin-15 (IL-15) is a novel proinflammatory cytokine having similar biological activities to IL-2 which is implicated in the pathogenesis of multiple sclerosis. It is produced by activated blood monocytes, macrophages and glial cells. There is little information about the involvement of IL-15 in the development of multiple sclerosis (MS). The objective of our study was to measure IL-15 serum and cerebrospinal fluid (CSF) levels in MS patients and to correlate serum and CSF IL-15 concentrations with clinical parameters of the disease. CSF IL-15/Serum IL-15 ratio (c/s IL-15 ratio) was introduced to assess the origin of elevated IL-15 levels.

MATERIALS AND METHODS

We measured serum and CSF IL-15 levels in 52 patients with MS and 36 age and gender matched patients with inflammatory (IND) and non-inflammatory neurological diseases (NIND) studied as control groups. IL-15 levels were correlated with clinical parameters as duration, disability, MRI activity and clinical subtypes of the disease.

RESULTS

MS patients were found to have significantly higher serum IL-15 levels compared with IND (p=0.00016) and NIND patients (p=0.00045). Elevated levels of IL-15 were also found in CSF samples from MS patients compared with patients with IND (p=0.00034) and NIND (p=0.0003). Among MS subgroups there were no statistically different IL-15 serum and CSF concentrations. No significant correlation of serum and CSF IL-15 concentrations with MRI activity, disability assessed by EDSS score and duration of the disease were also found. C/S IL-15 ratio was found lower in MS patients compared with IND (p=0.01) and not significantly different compared with NIND patients (p=0.14) suggesting that systemic activation might be the source of high CSF IL-15 levels in MS patients.

CONCLUSIONS

Our findings suggest a possible role of IL-15 in the immunopathogenetic mechanisms of MS.

Microglia in health and disease

Microglia, one of three glial cell types in the central nervous system (CNS), play an important role as resident immunocompetent and phagocytic cells in the CNS in the event of injury and disease. It was del Rio Hortega in 1927 who determined that microglia belong a distinct glial cell type apart from astrocytes and oligodendrocytes, and since 1970s there has been wide recognition that microglia are immune effectors in the CNS that respond to pathological conditions and participate in initiation and progression of neurological disorders including Alzheimer's disease, Parkinson's disease, multiple sclerosis, and acquired immune deficiency syndrome dementia complex by releasing potentially cytotoxic molecules such as proinflammatory cytokines, reactive oxygen intermediates, proteinases and complement proteins. There is also evidence to suggest that microglia are capable of secreting neurotrophic or neuron survival factors upon activation via inflammation or injury. It is thus timely to review current status of knowledge on biology and immunology of microglia, and consider new directions of investigation on microglia in health and disease.