Endogenous Interleukin-15 Research Articles

IL-15 Prevents Renal Fibrosis by Inhibiting Collagen Synthesis: A New Pathway in Chronic Kidney Disease?

Chronic kidney disease (CKD), secondary to renal fibrogenesis, is a public health burden. The activation of interstitial myofibroblasts and excessive production of extracellular matrix (ECM) proteins are major events leading to end-stage kidney disease. Recently, interleukin-15 (IL-15) has been implicated in fibrosis protection in several organs, with little evidence in the kidney. Since endogenous IL-15 expression decreased in nephrectomized human allografts evolving toward fibrosis and kidneys in the unilateral ureteral obstruction (UUO) model, we explored IL-15’s renoprotective role by pharmologically delivering IL-15 coupled or not with its soluble receptor IL-15Rα. Despite the lack of effects on myofibroblast accumulation, both IL-15 treatments prevented tubulointerstitial fibrosis (TIF) in UUO as characterized by reduced collagen and fibronectin deposition. Moreover, IL-15 treatments inhibited collagen and fibronectin secretion by transforming growth factor-β (TGF-β)-treated primary myofibroblast cultures, demonstrating that the antifibrotic effect of IL-15 in UUO acts, in part, through a direct inhibition of ECM synthesis by myofibroblasts. In addition, IL-15 treatments resulted in decreased expression of monocyte chemoattractant protein 1 (MCP-1) and subsequent macrophage infiltration in UUO. Taken together, our study highlights a major role of IL-15 on myofibroblasts and macrophages, two main effector cells in renal fibrosis, demonstrating that IL-15 may represent a new therapeutic option for CKD.

Skeletal muscle interleukin 15 promotes CD8(+) T-cell function and autoimmune myositis.

BackgroundInterleukin 15 (IL-15) is thought to be abundant in the skeletal muscle under steady state conditions based on RNA expression; however, the IL-15 RNA level may not reflect the protein level due to post-transcriptional regulation. Although exogenous protein treatment and overexpression studies indicated IL-15 functions in the skeletal muscle, how the skeletal muscle cell uses IL-15 remains unclear. In myositis patients, IL-15 protein is up-regulated in the skeletal muscle. Given the supporting role of IL-15 in CD8+ T-cell survival and activation and the pathogenic role of cytotoxic CD8+ T cells in polymyositis and inclusion-body myositis, we hypothesize that IL-15 produced by the inflamed skeletal muscle promotes myositis via CD8+ T cells.MethodsExpression of IL-15 and IL-15 receptors at the protein level by skeletal muscle cells were examined under steady state and cytokine stimulation conditions. The functions of IL-15 in the skeletal muscle were investigated using Il15 knockout (Il15−/−) mice. The immune regulatory role of skeletal muscle IL-15 was determined by co-culturing cytokine-stimulated muscle cells and memory-like CD8+ T cells in vitro and by inducing autoimmune myositis in skeletal-muscle-specific Il15−/− mice.ResultsWe found that the IL-15 protein was not expressed by skeletal muscle cells under steady state condition but induced by tumor necrosis factor alpha (TNF-α) and interferon gamma (IFN-γ) stimulation and expressed as IL-15/IL-15 receptor alpha (IL-15Rα) complex. Skeletal muscle cells expressed a scanty amount of IL-15 receptor beta (IL-15Rβ) under either conditions and only responded to a high concentration of IL-15 hyperagonist, but not IL-15. Consistently, deficiency of endogenous IL-15 affected neither skeletal muscle growth nor its responses to TNF-α and IFN-γ. On the other hand, the cytokine-stimulated skeletal muscle cells presented antigen and provided IL-15 to promote the effector function of memory-like CD8+ T cells. Genetic ablation of Il15 in skeletal muscle cells greatly ameliorated autoimmune myositis in mice.ConclusionsThese findings together indicate that skeletal muscle IL-15 directly regulates immune effector cells but not muscle cells and thus presents a potential therapeutic target for myositis.Electronic supplementary materialThe online version of this article (doi:10.1186/s13395-015-0058-2) contains supplementary material, which is available to authorized users.

The Regulation Of Central Nervous System Acute Lymphoblastic Leukemia By Natural Killer Cells

Acute lymphoblastic leukemia (ALL) is the most common childhood malignancy accounting for 80% of leukemias. The involvement of the central nervous system (CNS) by ALL is a major clinical problem and occurs in about 50% of the children without adequate treatment. The introduction of CNS-directed therapy consisting of intrathecal and high dose systemic chemotherapy and, occasionally, cranial irradiation, reduced relapse rate to less than 5% and has become a prerequisite for treating children with ALL. However, substantial neurotoxicity associated with this therapy is a major concern. Moreover the CNS is involved in up to a third from all relapses. To date very little is known about the pathogenesis of CNS leukemia.Our research was promoted by the previous observation that high mRNA expression of interleukin 15 (IL15) in leukemic blasts is associated with increased risk for CNS involvement (Cario et al JCO 2007;25:4813-20). As IL15 is a strong stimulant of Natural Killer (NK) cells, we hypothesized that the increased expression of IL15 may activate NK cells which, in turn, will control residual ALL cells in the peripheral blood but not in the relatively protected central nervous system. To investigate this hypothesis, we utilized two mouse models, a S49-derived T lymphoblastic leukemia syngeneic model and a novel human xenograft ALL model in immune-deficient mice.We found that constitutive expression of IL15 in mouse T lymphoblastic leukemia cells transplanted in neonatal Balb/c mice markedly slowed the development of systemic disease and caused CNS leukemia characterized by pronounced clinical CNS symptoms and subarachnoid infiltration of leukemia cells. This phenotype was accompanied by increase in activated natural killer (NK) cells (from 0.16% to 18.6% P<0.01). Similarly, we demonstrated that transplantation of the human B-cell precursor ALL line 018Z cause isolated CNS leukemia in NOD/SCID mice but induced aggressive systemic and CNS leukemia in NK-deficient NOD scid Il2rg null (NSG) mice. We further found that 018Z cells express and secrete endogenous IL15 and activated NK cells in-vivo in NOD/SCID mice. Remarkably, transplantation of 018Z cells in NOD/SCID mice after antibody mediated depletion of NK cells, resulted in a combined peripheral and CNS leukemia as observed in NSG mice. Mechanistic studies showed that 018Z leukemic blasts are efficiently killed by primary human NK cells and highly express ligands for the NKG2D and the NKp44 activating receptors. Blocking of the NKG2D receptor significantly reduced killing by NK cells.Taken together we show here, for the first time, a crucial role for NK cells in the control of CNS leukemia. We suggest that the association between IL15 expression in ALL blasts and isolated CNS relapse might be explained by activation of NK cells leading to increased surveillance of residual leukemia in the bone marrow but not in the CNS which serve as a sanctuary site for tumor growth. Disclosures:No relevant conflicts of interest to declare.

IL-15 expression in skeletal muscle by resistance exercise training in type 2 diabetic rats

Introduction: Interleukin-15 (IL-15) is reported as a myokine that potentially regulates body composition and glucose metabolism. We investigated the effect of 8 weeks of resistance exercise training on endogenous IL-15 expression in skeletal muscle and glucose tolerance with concomitant changes of body composition in type 2 diabetic rats.Methods: 6 week-old Male ZDF (Zucker diabetic fatty) and ZLC (ZDF Lean Control) rats were randomly divided into 4 groups: sedentary ZDF (Con-ZDF), exercised ZDF (Ex-ZDF), sedentary ZLC (Con-ZLC), and exercised ZLC (Ex-ZLC). Ex-ZDF and Ex-ZLC rats were trained (once every 3 days for 8 weeks) to climb a 1.1-m vertical (80° incline) ladder with weights secured to their tail for progressive workload resistance exercise (the training was started at 50% or 70% of maximal weight of the last trial). Body weight, grip strength and intraperitoneal glucose tolerance test (IPGTT) were evaluated at every week. Body composition was analyzed by PET-CT (Positron Emission Tomography – Computed Tomography) and expression of IL-15 was measured using ELISA in extracted soleus muscle and tibialis anterior muscle.Results: After 8 weeks of resistance training, substantial reduction of the body weight was observed in Ex-ZDF compared to Con-ZDF. Grip strength was also significantly increased in Ex-ZDF compared to Con-ZDF after 8 weeks of regular strength exercise indicating the efficacy of resistance training. Glucose tolerance (IPGTT) was significantly improved in Ex-ZDF (p<0.05) compared to Con-ZDF showing more delayed drop in blood glucose level between 90 min and 120 min. Concurrently, the expression of IL-15 was significantly increased (p<0.01) after training especially in soleus muscle of Ex-ZDF compared to Con-ZDF and also there was a tendency of increase in IL-15 expression in tibialis anterior muscle in Ex-ZDF as well. Accordingly, PET-CT scan showed that muscle quality tended to be higher in Ex-ZDF than Con-ZDF while no significant difference between Con-ZLC and Ex-ZLC.Discussion: 8 weeks of progressive resistance exercise significantly improved glucose tolerance with the concomitant increase of IL-15 expression in hind-limb muscles suggesting that increased level of IL-15 in skeletal muscle by resistance exercise might be a potential mediator in glucose regulation of type 2 diabetes. Further study is needed to elucidate the mechanisms by which how increased IL-15 expression in skeletal muscle by resistance exercise exerts a favorable influence on impaired glucose metabolism in type 2 diabetes mellitus. Introduction: Interleukin-15 (IL-15) is reported as a myokine that potentially regulates body composition and glucose metabolism. We investigated the effect of 8 weeks of resistance exercise training on endogenous IL-15 expression in skeletal muscle and glucose tolerance with concomitant changes of body composition in type 2 diabetic rats. Methods: 6 week-old Male ZDF (Zucker diabetic fatty) and ZLC (ZDF Lean Control) rats were randomly divided into 4 groups: sedentary ZDF (Con-ZDF), exercised ZDF (Ex-ZDF), sedentary ZLC (Con-ZLC), and exercised ZLC (Ex-ZLC). Ex-ZDF and Ex-ZLC rats were trained (once every 3 days for 8 weeks) to climb a 1.1-m vertical (80° incline) ladder with weights secured to their tail for progressive workload resistance exercise (the training was started at 50% or 70% of maximal weight of the last trial). Body weight, grip strength and intraperitoneal glucose tolerance test (IPGTT) were evaluated at every week. Body composition was analyzed by PET-CT (Positron Emission Tomography – Computed Tomography) and expression of IL-15 was measured using ELISA in extracted soleus muscle and tibialis anterior muscle. Results: After 8 weeks of resistance training, substantial reduction of the body weight was observed in Ex-ZDF compared to Con-ZDF. Grip strength was also significantly increased in Ex-ZDF compared to Con-ZDF after 8 weeks of regular strength exercise indicating the efficacy of resistance training. Glucose tolerance (IPGTT) was significantly improved in Ex-ZDF (p<0.05) compared to Con-ZDF showing more delayed drop in blood glucose level between 90 min and 120 min. Concurrently, the expression of IL-15 was significantly increased (p<0.01) after training especially in soleus muscle of Ex-ZDF compared to Con-ZDF and also there was a tendency of increase in IL-15 expression in tibialis anterior muscle in Ex-ZDF as well. Accordingly, PET-CT scan showed that muscle quality tended to be higher in Ex-ZDF than Con-ZDF while no significant difference between Con-ZLC and Ex-ZLC. Discussion: 8 weeks of progressive resistance exercise significantly improved glucose tolerance with the concomitant increase of IL-15 expression in hind-limb muscles suggesting that increased level of IL-15 in skeletal muscle by resistance exercise might be a potential mediator in glucose regulation of type 2 diabetes. Further study is needed to elucidate the mechanisms by which how increased IL-15 expression in skeletal muscle by resistance exercise exerts a favorable influence on impaired glucose metabolism in type 2 diabetes mellitus.

Soluble Interleukin (IL)-15Rα Is Generated by Alternative Splicing or Proteolytic Cleavage and Forms Functional Complexes with IL-15

Interleukin 15 (IL-15) is a pleiotropic cytokine that is hardly detectable in biological fluids. Here, we show that IL-15 forms functional heterocomplexes with soluble high affinity IL-15 receptor alpha (IL-15Ralpha) chain in mouse serum and cell-conditioned medium, which prevents IL-15 detection by ELISA. We also demonstrate that two soluble IL-15Ralpha (sIL-15Ralpha) sushi domain isoforms are generated through a novel alternative splicing mechanism within the IL-15Ralpha gene. These isoforms potentiate IL-15 action by promoting the IL-15-mediated proliferation of the CTLL cell line and interferon gamma production by murine NK cells, which suggests a role in IL-15 transpresentation. Conversely, a full-length sIL-15Ralpha ectodomain released by tumor necrosis factor-alpha-converting enzyme (TACE)-dependent proteolysis inhibits IL-15 activity. Thus, a dual mechanism of sIL-15Ralpha generation exists in mice, giving rise to polypeptides with distinct properties, which regulate IL-15 function.

Trans-presentation of donor-derived interleukin 15 is necessary for the rapid onset of acute graft-versus-host disease but not for graft-versus-tumor activity

AbstractThe “holy grail” of allogeneic stem cell transplantation is to preserve the graft-versus-tumor (GVT) effect while eliminating graft-versus-host disease (GVHD). Endogenous donor-derived interleukin 15 (IL-15) has been implicated in the pathogenesis of acute GVHD, yet the mechanism by which it impacts this lethal process remains unclear. Using the well-described and clinically relevant C57BL/6 → B6D2F1 murine model of acute GVHD, we demonstrate that in trans presentation of IL-15 by donor bone marrow–derived cells is required for the rapid onset of acute GVHD. Recipients of IL-15–/– C57BL/6 bone marrow cells show diminished type 1 polarization of T cells, yet there is no decrease in donor T-cell reconstitution. A molecular basis for these findings is provided with the observation that expression of T-bet, the master control gene for type 1 T-cell functions, is necessary for IL-15–mediated acute GVHD lethality. Finally, we demonstrate that in the absence of donor-derived IL-15, the GVT effect is maintained. These findings thus establish a mechanism by which endogenous donor-derived IL-15 impacts the pathobiology of acute GVHD and GVT activity.

Autocrine role of vascular IL-15 in intimal thickening

Interleukin 15 (IL-15) is a pro-inflammatory cytokine that modulates T cell recruitment and activation, independent of antigen. It has been detected in human atherosclerotic plaques and atherosclerotic plaques of apoE−/− mice. IL-15 regulates fractalkine (FKN)–CX3CR1 chemokine signaling which is involved in atherogenesis and promotes SMC proliferation. We investigated the role of IL-15 in intimal thickening after arterial injury. Treatment of serum-stimulated SMC with IL-15 in vitro attenuated proliferation and suppressed CX3CR1 and FKN mRNA expression. The role of endogenous IL-15 in vivo was investigated in injured carotid arteries of mice. Periadventitial arterial injury resulted in increased IL-15 expression in the media and neointima, paralleled by increased IL-15 receptor α expression. Blockade of endogenous IL-15 increased intimal thickening. FKN and CX3CR1 expression increased after injury and were further augmented after IL-15 blockade. These data suggest that endogenous IL-15 attenuated intimal thickening after arterial injury. The potential mechanism of action is suppression of CX3CR1 signaling.

Membrane-bound and soluble IL-15/IL-15Rα complexes display differential signaling and functions on human hematopoietic progenitors

AbstractMembrane-bound and soluble interleukin-15 (IL-15)/IL-15 receptor α (Rα) complexes trigger differential transcription factor activation and functions on human hematopoietic progenitors. Indeed, human spleen myofibroblasts (SMFs) are characterized by a novel mechanism of IL-15 trans-presentation (SMFmb [membrane-bound]-IL-15), based on the association of an endogenous IL-15/IL-15Rα complex with the IL-15Rβγc chains. SMFmb-IL-15 (1) induces lineage-specific signaling pathways that differ from those controlled by soluble IL-15 in unprimed and committed normal progenitors; (2) triggers survival and proliferation of leukemic progenitors expressing low-affinity IL-15R (M07Sb cells); (3) causes only an antiapoptotic effect on leukemic cells expressing high-affinity receptors (TF1β cells). This behavior is likely due to the IL-15Rα chain present on these cells that interact with the SMFmb-IL-15, inhibiting signal transducer and transcriptional activator 5 (STAT5) activation. On the other hand, the soluble IL-15/IL-15Rα complex (hyper IL-15) displays a dominant pattern of action, activating only those cells expressing low-affinity IL-15R (IL-15Rβγc). Thus, hyper IL-15 induces antiapoptotic effects on M075b cells and the up-regulation of STAT6 activation on adult peripheral blood (PB) pre-natural killer (NK) committed progenitors. The latter effect using 100-fold concentrations of recombinant (r)-IL-15. In conclusion, SMFmb-IL-15 and soluble IL-15Rα/IL-15 complexes seem to play a pivotal role in the control of the survival, proliferation and differentiation of both normal and leukemic circulating progenitors, highlighting new functions of IL-15 and of IL-15Rα.

Targeting interleukin‐15 in patients with rheumatoid arthritis: A proof‐of‐concept study

Interleukin-15 (IL-15) is a proinflammatory, innate response cytokine that mediates pleiotropic effector function in rheumatoid arthritis (RA) inflammatory synovitis. Our objective was to study the ability of HuMax-IL15, a human IgG1 anti-IL-15 monoclonal antibody, to neutralize exogenous and endogenous IL-15 activity in vitro and to perform a phase I-II dose-escalation trial with HuMax-IL15 in patients with active RA. Mononuclear cells from blood and synovial fluid (SF) of RA patients were isolated and cultured in vitro under experimental conditions involving the addition of HuMax-IL15. HuMax-IL15 was administered to 30 RA patients who received no other disease-modifying antirheumatic drugs in a 12-week, dose-ascending, placebo-controlled, double-blind, phase I-II proof-of-concept study. In vitro studies showed that HuMax-IL15 suppressed proliferation and induced apoptosis in an IL-15-dependent cell line, BDB2, and was capable of suppressing the release of interferon-gamma by synovial fluid mononuclear cell (SFMC) cultures induced by exogenous IL-15. Furthermore, HuMax-IL15 F(ab')2 fragments suppressed exogenous IL-15-induced CD69 expression in RA peripheral blood mononuclear cells and SFMCs, which indicates that HuMax-IL15 can specifically neutralize several biologic effects of IL-15 in synovial tissue in vitro. In a phase I-II clinical trial, HuMax-IL15 was well tolerated clinically, with no significant effects on T lymphocyte subset and natural killer cell numbers. Substantial improvements in disease activity were observed according to the American College of Rheumatology criteria for 20% improvement (63% of patients), 50% improvement (38%), and 70% improvement (25%). These clinical data suggest for the first time that IL-15 could represent a novel therapeutic target in RA.

Differential STAT3, STAT5, and NF-κB activation in human hematopoietic progenitors by endogenous interleukin-15: implications in the expression of functional molecules

AbstractDifferent forms of interleukin-15 (IL-15) have been identified and shown to elicit different transduction pathways whose impact on hematopoiesis is poorly understood. We demonstrated herein that hematopoietic CD34+ cells constitutively produced endogenous secreted IL-15 (ES-IL-15) that activated different transcription factors and controlled the expression of several functional proteins, depending on the progenitor source. Thus, nuclear factor-κ B (NF-κ B) was activated in bone marrow (BM) and cord blood (CB) progenitors, whereas signal transducer and activator of transcription 3 (STAT3) and STAT5 activation was restricted to peripheral granulocyte—colony-stimulating factor (G-CSF)—mobilized and BM progenitors, respectively. ES-IL-15 acts through autocrine/paracrine loops controlled by high-affinity receptors involving IL-15 receptor α (IL-15R α). Furthermore, ES-IL-15 was found to differentially control the expression of several functional molecules important for hematopoietic differentiation. Indeed, in BM precursors, neutralizing anti—IL-15 monoclonal antibody (mAb) inhibits the expression of the γ c chain and of the chemokine stromal derived factor-1 (SDF-1) but had no effect on vascular cell adhesion molecule 1 (VCAM-1) and β 1 integrin adhesion molecule expression. Conversely, in CB progenitors, anti—IL-15 mAb inhibited VCAM-1 and β 1 integrin expression without affecting γ c chain expression and, most important, up-regulated SDF-1 expression. In conclusion, unprimed human hematopoietic CD34+ cells secrete cell-unbound IL-15, which activates through autocrine/paracrine loop distinct signaling pathways, depending on the progenitor source, thereby influencing the expression of several molecules important in the control of hematopoiesis. (Blood. 2003;102:109-117)

Intensified regression of colon cancer liver metastases in mice treated with irinotecan and the immunomodulator JBT 3002.

The authors recently reported that tumoricidal activation of macrophages by a new synthetic bacterial lipopeptide, JBT 3002, can augment chemotherapy-mediated tumor-cell killing. The aim of this study was to identify the mechanism responsible for the destruction of metastatic cells. Three daily oral doses of JBT 3002 before once-weekly intraperitoneal injections of 100 mg/kg irinotecan for 3 weeks significantly increased the eradication of established CT-26 murine colon cancer liver metastases compared with treatment with irinotecan alone. Immunohistochemical analyses revealed that the hepatic metastases in mice given combination therapy contained infiltrating CD8+ lymphocytes and a dense infiltrate of macrophages expressing both inducible nitric oxide synthase (iNOS) and interleukin-15. In vitro treatment of peritoneal macrophages with JBT 3002 plus interferon-gamma induced the expression of iNOS and the production of nitric oxide. In the presence of a low (subtoxic) dose of irinotecan, these activated macrophages produced significant lysis of CT-26 cells. The high level of cytotoxicity was inhibited by the specific inducible nitric oxide synthase inhibitor, NG-methyl-L-arginine. In contrast, irinotecan-mediated lysis of normal intestinal epithelial IEC-6 cells was not increased by activated macrophages. Scanning electron microscopy revealed that activated macrophages bound to CT-26 tumor cells but not to normal IEC-6 cells, confirming that nitric oxide-mediated cytotoxicity is specific for tumor cells. Collectively, the results suggest that augmentation of the therapeutic efficacy of irinotecan against colon cancer liver metastases by immunomodulation with JBT 3002 may be associated with elevated inducible nitric oxide synthase and endogenous interleukin-15 in tumor-infiltrating macrophages.

Interleukin-15 production at the early stage after oral infection with Listeria monocytogenes in mice.

We previously reported that exogenous interleukin-15 (IL-15) induces proliferation and activation of intestinal intraepithelial lymphocytes (i-IEL) in naive mice. To investigate the ability of endogenous IL-15 to stimulate i-IEL in vivo, we monitored i-IEL and intestinal epithelial cells (i-EC) in mice after an oral infection with Listeria monocytogenes. Although the populations of alphabeta and gammadelta i-IEL were not significantly changed after the oral infection, the expression level of interferon-gamma (IFN-gamma) was increased both at transcriptional and protein levels, and a conversely marked decrease in interleukin-4 (IL-4) was detected in the i-IEL on day 1 after infection as compared with before infection. The T helper 1 (Th1)-biased response of i-IEL coincided with a peak response of IL-15 production in the i-EC after oral infection. These results suggested that IL-15 produced from i-EC may be at least partly involved in the stimulation of i-IEL to produce IFN-gamma after oral infection with L. monocytogenes.

Interleukin-15 may be responsible for early activation of intestinal intraepithelial lymphocytes after oral infection with Listeria monocytogenes in rats.

Exogenous interleukin-15 (IL-15) stimulates intestinal intraepithelial lymphocytes (i-IEL) from mice to proliferate and produce gamma interferon (IFN-gamma) in vitro. To determine whether endogenous IL-15 is involved in activation of i-IEL during intestinal infection, we examined IL-15 synthesis by intestinal epithelial cells (i-EC) after infection with Listeria monocytogenes in rats. In in vitro experiments, invasion of L. monocytogenes into IEC-6 cells, a rat small intestine epithelial cell line, evidently induced IL-15 mRNA expression coincident with nuclear factor kappaB (NF-kappaB) activation, which is essential for IL-15 gene expression. IL-15 synthesis was detected in rat i-EC on day 1 after an oral inoculation of L. monocytogenes in vivo. The numbers of T-cell receptor (TCR) gamma delta+ T cells, NKR.P1(+) cells, and CD3(+) CD8(+) alpha alpha cells in i-IEL were significantly increased on day 1 after oral infection. The i-IEL from infected rats produced larger amounts of IFN-gamma upon stimulation with immobilized anti-TCR gamma delta or anti-NKR.P1 monoclonal antibodies. These results suggest that IL-15 produced by i-EC may stimulate significant fractions of i-IEL to produce IFN-gamma at an early phase of oral infection with L. monocytogenes.