Levels of interleukin-15-expressing blood mononuclear cells are elevated in multiple sclerosis

IL-15 Is Overexpressed in γδ T Cells and Correlates with Disease Severity in Relapsing-Remitting Multiple Sclerosis

Interleukin 15 (IL-15) is known to be involved in the pathogenesis of multiple sclerosis (MS). An animal study revealed a distinct subset of IL-15-producing γδ T cells that correlate with disease severity. The aim of the current study was to test whether such a subset is also present in humans and its importance for the pathogenesis of MS. The peripheral blood from 29 patients with relapsing-remitting MS (including 6 relapses) and 22 controls was stained with monoclonal antibodies and analyzed with flow cytometry. The existence of IL-15+ γδ T cells was confirmed. Moreover, the percentage of IL-15+ γδ T is significantly increased in MS patients and correlates with disease severity. Nevertheless, additional functional studies are needed to fully understand the importance of those cells in multiple sclerosis pathogenesis.

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.

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.

B cell-derived IL-15 enhances CD8 T cell cytotoxicity and is increased in multiple sclerosis patients

Multiple lines of evidence suggest that CD8 T cells contribute to the pathogenesis of multiple sclerosis (MS). However, the sources and involvement of cytokines such as IL-15 in activating these cells is still unresolved. To investigate the role of IL-15 in enhancing the activation of CD8 T cells in the context of MS, we determined cell types expressing the bioactive surface IL-15 in the peripheral blood of patients and evaluated the impact of this cytokine on CD8 T cell cytotoxicity and migration. Flow cytometric analysis showed a significantly greater proportion of B cells and monocytes from MS patients expressing IL-15 relative to controls. We established that CD40L activation of B cells from healthy donors increased their IL-15 levels, reaching those of MS patients. We also demonstrated an enhanced cytotoxic profile in CD8 T cells from MS patients upon stimulation with IL-15. Furthermore, we showed that IL-15 expressed by B cells and monocytes is sufficient and functional, enhancing granzyme B production by CD8 T cells upon coculture. Exposure of CD8 T cells to this cytokine enhanced their ability to kill glial cells as well as to migrate across an in vitro inflamed human blood-brain barrier. The elevated levels of IL-15 in patients relative to controls, the greater susceptibility of CD8 T cells from patients to IL-15, in addition to the enhanced cytotoxic responses by IL-15-exposed CD8 T cells, stresses the potential of therapeutic strategies to reduce peripheral sources of IL-15 in MS.

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.

Role of interleukin-15 in the development of mouse olfactory nerve

Interleukin (IL)-15 interacts with components of the IL-2 receptor (R) and exhibits T cell-stimulating activity similar to that of IL-2. In addition, IL-15 is widely expressed in many cell types and tissues, including the central nervous system. We provide evidence of a novel role of IL-15 in olfactory neurogenesis. Both IL-15 and IL-15R alpha were expressed in neuronal precursor cells of the developing olfactory epithelium in mice. Adult IL-15R alpha knockout mice had fewer mature olfactory neurons and proliferating cells than wild-type. Our results suggest that IL-15 plays an important role in regulating cell proliferation in olfactory neurogenesis.

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.

Oligoclonal myelin-reactive T-cell infiltrates derived from multiple sclerosis lesions are enriched in Th17 cells

In this study, acute and chronic brain and spinal cord lesions, and normal appearing white matter (NAWM), were resected post-mortem from a patient with aggressive relapsing-remitting multiple sclerosis (MS). T-cell infiltrates from the central nervous system (CNS) lesions and NAWM were separated and characterized in-vitro. All infiltrates showed a proliferative response against multiple myelin peptides. Studies of the T-cell receptor (TCR)Vbeta and Jbeta usage revealed a very skewed repertoire with shared complementarity-determining region (CDR)3 lengths detected in all CNS lesions and NAWM. In the acute lesion, genomic profiling of the infiltrating T-cells revealed up-regulated expression of TCRalpha and beta chain, retinoic acid-related orphan nuclear hormone receptor C (RORC) transcription factor, and multiple cytokine genes that mediate Th17 cell expansion. The differentially expressed genes involved in regulation of Th17 cells represent promising targets for new therapies of relapsing-remitting MS.

Membrane bound IL-15 is increased on CD14 monocytes in early stages of MS

IL-15 is a pro-inflammatory cytokine whose three-dimensional structure is similar to that of IL-2. IL-2 and IL-15 have similar as well as distinct biological functions. An active form of IL-15 that is membrane bound has also been described. Furthermore, IL-15 is known to play a role in autoimmune diseases. We thus investigated the expression of membrane bound IL-15 on monocytes (CD14+ cells) and studied its effect on T cell activation in MS patients. We found that unstimulated CD14+ cells from relapsing remitting MS patients had increased membrane bound IL-15. Those with high surface levels of IL-15 on monocytes were in the early stages of the disease. In addition, we found that T cells of MS patients had enhanced responsiveness to IL-15 and there was increased expression of IL-15 receptor on CD4+ T cells. Thus, IL-15 may be an important cytokine that drives Th1 responses early in the course of the disease and could serve as a target for immunotherapy and as an early marker in the immunologic staging of MS.

Increased CD8+ central memory T cells in patients with multiple sclerosis

A T-cell-mediated autoimmune process against central nervous system myelin is believed to underlie the pathogenesis of multiple sclerosis (MS). Formation of immunological memory is based on the differentiation of naïve T cells to memory T cells after exposure to antigens and specific cytokines. The aim of this study was to analyse peripheral blood mononuclear cells in patients with MS for different T-cell subsets including naïve and memory T cells. Flow cytometry and enzyme-linked immunosorbent assay were used to analyse memory T-cell subsets and plasma concentration of interleukin-15 (IL-15) in peripheral blood of MS patients, patients with other neurological disorders and healthy controls. MS patients had a skewed distribution of T cells with an increased level of CD8+/CCR7+/CD45RA - central memory T cells (TCM) compared to healthy controls. In addition, MS patients showed significantly higher levels of plasma IL-15 than healthy controls did. Upregulated CD8+ TCM in MS patients may reflect a persistent chronic inflammatory response that may have been induced during early stages of the disease. This derangement may be important for maintaining chronic inflammation in MS.

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.

Differential Expression of CD11c by Peripheral Blood NK Cells Reflects Temporal Activity of Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disease, showing a great degree of variance in temporal disease activity. We have recently demonstrated that peripheral blood NK cells biased for secreting IL-5 (NK2 bias) are associated with the remission state of MS. In this study, we report that MS patients in remission differentially express CD11c on NK cell surface (operationally defined as CD11chigh or CD11clow). When we compared CD11chigh or CD11clow patients, the expression of IL-5 and GATA-3 in NK cells supposed to endow a disease-protective NK2 phenotype was observed in CD11clow but not in CD11chigh patients. In contrast, the CD11chigh group showed a higher expression of HLA-DR on NK cells. In vitro studies demonstrated that NK cell stimulatory cytokines such as IL-15 would up-regulate CD11c expression on NK cells. Given previous evidence showing an association between an increased level of proinflammatory cytokines and temporal disease activity in MS, we postulate that inflammatory signals may play a role in inducing the CD11chigh NK cell phenotype. Follow-up of a new cohort of patients showed that 6 of 10 CD11chigh MS patients developed a clinical relapse within 120 days after evaluation, whereas only 2 of 13 CD11clow developed exacerbated disease (p = 0.003). As such, a higher expression of CD11c on NK cells may reflect the temporal activity of MS as well as a loss of regulatory NK2 phenotype, which may allow us to use it as a potential biomarker to monitor the immunological status of MS patients.

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.

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.

Reduced 2,4-dinitro-1-fluorobenzene-induced contact hypersensitivity response in IL-15 receptor??-deficient mice correlates with diminished CCL5/RANTES and CXCL10/IP-10 expression

Using a model of 2,4-dinitro-1-fluorobenzene-induced contact hypersensitivity (CHS) we found that, as compared with wild-type mice, IL-15 receptor alpha chain (IL-15Ralpha)-deficient mice showed significantly less ear swelling. This decreased response was associated with diminished expression of CCL5/RANTES and CXCL10/IP-10, chemokines critical for effector cell recruitment, in the inflamed tissue. We determined that both the number of CD8(+) T cells infiltrating the affected skin and the production of CCL5/RANTES by antigen-stimulated CD8(+) T cells were decreased in IL-15Ralpha(-/-) mice. The lower levels of CXCL10/IP-10 suggested that the IL-15Ralpha(-/-) mice had reduced production of IFN-gamma, the primary inducer of CXCL10/IP-10, which was in fact the case. However, by contrast with CCL5/RANTES, the diminished levels of IFN-gamma were likely due to the decreased number of skin-infiltrating CD8(+) T cells, since IFN-gamma production by antigen-stimulated CD8(+) T cells was comparable between wild-type and IL-15Ralpha(-/-) mice. Our data suggest a positive, pro-inflammatory feedback loop involving CCL5/RANTES, IFN-gamma and CXCL10/IP-10 that underlies the CHS reaction and that is disrupted, likely primarily by a defect in CCL5/RANTES production, in mice lacking IL-15Ralpha, resulting in impaired leukocyte recruitment and inflammation. Moreover, it is particularly noteworthy that the defect in CCL5/RANTES expression in CD8(+) T cells is intrinsic to the absence of IL-15Ralpha, indicating that IL-15Ralpha is critical for CCL5/RANTES expression in CD8(+) T cells.

Reduced cumulative incidence of diabetes but not insulitis following administration of chimeric human IL-15-murine IgG2b in NOD mice

BACKGROUND

It has been recently demonstrated that apoptosis is involved in beta-cell destruction in the NOD mouse model of diabetes. The aim of the present study was to investigate whether IL-15, a cytokine involved in the modulation of the apoptotic process, is capable of modifying the natural history of diabetes and/or insulitis in pre-diabetic NOD mice. The rationale for the use of IL-15-IgG2b recombinant cytokine is related to its long half-life (28 +/- 4 h).

METHODS

At 10 weeks of age, 2 groups of 24 female mice were treated with single or multiple i.p. doses of IL-15-IgG2b respectively. As control, 2 groups of 24 age- and litter-matched female mice were injected intra-peritoneally with single or multiple doses of IgG2b immunoglobulin.

RESULTS

Diabetes incidence at 33 weeks of age was lower in the group of mice treated with multiple doses than in the control group (p = 0.03). The cumulative incidence of diabetes at 33 weeks of age between single-dose treated mice and the control group was similar. No significant differences in the calculated index of insulitis were observed in all treated and control mice.

CONCLUSIONS

We conclude that IL-15-IgG2b reduces the cumulative incidence of diabetes, without affecting the extent and severity of the insulitis process. Considering this and the well-defined anti-apoptotic effects of IL-15, we suggest that the reduction of diabetes incidence could be due to a down-regulation of beta-cell apoptosis.

Increased levels of IL-15 mRNA in relapsing--remitting multiple sclerosis attacks

IL-15 is a proinflammatory cytokine which has recently been implicated in multiple sclerosis (MS) pathogenesis, where it may play a role in the initiation and/or progression of the disease. We have used reverse transcriptase-polymerase chain reaction (RT-PCR) to study IL-15 mRNA levels in peripheral blood mononuclear cells (PBMC) from healthy controls and relapsing-remitting MS (RRMS) patients in a stable phase of the disease and during a bout, both before and after corticosteroid treatment (CST). IL-15 mRNA expression was found to be similar in controls and stable patients. We have detected an increased level of IL-15 mRNA in PBMC of patients with a relapse, which was maintained after CST. We have also found an inverse correlation between PBMC IL-15 mRNA levels at the onset of the relapse and the time elapsed since the previous attack, as well as an absence of correlation between IL-15 mRNA levels and the patient demographic and clinical characteristics. Results in the present work further suggest a role for IL-15 in MS pathophysiology.