Characterization of interleukin-15 (IL-15) and the IL-15 receptor complex

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.

Co-expression IL-15 receptor alpha with IL-15 reduces toxicity via limiting IL-15 systemic exposure during CAR-T immunotherapy

Background

Chimeric antigen receptor (CAR)-T cell therapy is a powerful adoptive immunotherapy against both B-cell malignancies and some types of solid tumors. Interleukin (IL) -15 is an important immune stimulator that may provide ideal long-term persistent CAR-T cells. However, higher base line or peak serum IL-15 levels are also related to severe toxicity, such as cytokine release syndrome (CRS), graft-versus-host disease (GVHD), and neurotoxicity.

Methods

We successfully constructed CD19 specific armored CAR-T cells overexpressing IL-I5 and IL-15 receptor alpha (IL-15Ra). In vitro cell differentiation and viability were monitored by flow cytometry, and an in vivo xenograft mouse models was used to evaluate the anti-tumor efficiency and liver damage of CAR-T cells.

Results

CAR-T cells overexpressing IL-15 alone demonstrated enhanced viability, retarded exhaustion in vitro and superior tumor-inhibitory effects in vivo. However, these tumor-free mice had lower survival rates, with serious liver injuries, as a possible result of toxicity. As expected, CAR-T cells overexpressing IL-15 combined with IL-15Ra had reduced CD132 expression and released fewer cytokines (IFNγ, IL-2 and IL-15) in vitro, as well as had the tendency to improve mouse survival via repressing the growth of tumor cells and keeping livers healthier compared to CAR-IL-15 T cells.

Conclusions

These results indicated the importance of IL-15 in enhancing T cells persistence and IL-15Ra in reducing the adverse effects of IL-15, with superior tumor retardation during CAR-T therapy. This study paves the way for the rapid exploitation of IL-15 in adoptive cell therapy in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03626-x.

Type 2 Inflammation in Eosinophilic Esophagitis: From Pathophysiology to Therapeutic Targets

Eosinophilic esophagitis (EoE) is a chronic immune-mediated disease of the esophagus characterized clinically by symptoms related to esophageal dysfunction and histologically by eosinophil-predominant inflammation, whose incidence is rising. It significantly affects patients’ quality of life and, if left untreated, results in fibrotic complications. Although broad consensus has been achieved on first-line therapy, a subset of patients remains non-responder to standard therapy. The pathogenesis of EoE is multifactorial and results from the complex, still mostly undefined, interaction between genetics and intrinsic factors, environment, and antigenic stimuli. A deep understanding of the pathophysiology of this disease is pivotal for the development of new therapies. This review provides a comprehensive description of the pathophysiology of EoE, starting from major pathogenic mechanisms (genetics, type 2 inflammation, epithelial barrier dysfunction, gastroesophageal reflux, allergens, infections and microbiota) and subsequently focusing on the single protagonists of type 2 inflammation (involved cells, cytokines, soluble effectors, surface proteins and transcription factors) that could represent present and future therapeutic targets, while summarizing previous therapeutic approaches in literature.

Metabolic responses in the cortex and hippocampus induced by Il-15rα mutation

Metabolomics showed distinct metabolic phenotypes of the different brain regions related to the IL-15 system, enhancing our understanding of the IL-15 system and its interactions with neuropsychiatric disorders.

Effect of the Electromagnetic Field (EMF) Radiation on Transcriptomic Profile of Pig Myometrium during the Peri-Implantation Period-An In Vitro Study

The electromagnetic field (EMF) affects the physiological processes in mammals, but the molecular background of the observed alterations remains not well established. In this study was tested the effect of short duration (2 h) of the EMF treatment (50 Hz, 8 mT) on global transcriptomic alterations in the myometrium of pigs during the peri-implantation period using next-generation sequencing. As a result, the EMF treatment affected the expression of 215 transcript active regions (TARs), and among them, the assigned gene protein-coding biotype possessed 90 ones (differentially expressed genes, DEGs), categorized mostly to gene ontology terms connected with defense and immune responses, and secretion and export. Evaluated DEGs enrich the KEGG TNF signaling pathway, and regulation of IFNA signaling and interferon-alpha/beta signaling REACTOME pathways. There were evaluated 12 differentially expressed long non-coding RNAs (DE-lnc-RNAs) and 182 predicted single nucleotide variants (SNVs) substitutions within RNA editing sites. In conclusion, the EMF treatment in the myometrium collected during the peri-implantation period affects the expression of genes involved in defense and immune responses. The study also gives new insight into the mechanisms of the EMF action in the regulation of the transcriptomic profile through lnc-RNAs and SNVs.

Attenuation of Allergen-, IL-13-, and TGF-α-induced Lung Fibrosis after the Treatment of rIL-15 in Mice

Endogenous IL-15 deficiency promotes lung fibrosis; therefore, we examined the effect of induced IL-15 in restricting the progression of lung fibrosis. Our objective in this work was to establish a novel therapeutic molecule for pulmonary fibrosis. Western blot, qPCR, and ELISA were performed on the lung tissues of IL-15-deficient mice, and recombinant IL-15 (rIL-15)-treated CC10-IL-13 and CC10-TGF-α mice, and allergen-challenged CC10-IL-15 mice were examined to establish the antifibrotic effect of IL-15 in lung fibrosis. We show that endogenous IL-15 deficiency induces baseline profibrotic cytokine and collagen accumulation in the lung, and pharmacological delivery of rIL-15 downregulates Aspergillus antigen-induced lung collagen, the profibrotic cytokines IL-13 and TGF-β1, and α-SMA⁺ and FSP1⁺ cells in mice. To confirm that overexpression of IL-15 diminishes pulmonary fibrosis, we generated CC10-rtTA-tetO7-IL-15 transgenic mice and challenged them with Aspergillus antigen. Aspergillus antigen-challenged, doxycycline (DOX)-treated CC10-IL-15 transgenic mice exhibited decreased collagen accumulation, profibrotic cytokine (IL-13 and TGF-β1) expression, and α-SMA⁺ and FSP1⁺ cells compared with IL-15-overexpressing mice not treated with DOX. Additionally, to establish that the antifibrotic effect of IL-15 is not limited to allergen-induced fibrosis, we showed that rIL-15 or IL-15 agonist treatment restricted pulmonary fibrosis even in CC10-IL-13 and CC10-TGF-α mice. Mechanistically, we show that T-helper cell type 17 suppressor IL-15-responsive RORγ⁺ T regulatory cells are induced in DOX-treated, allergen-challenged IL-15-overexpressing mice, which may be a novel pathway for restricting progression of pulmonary fibrosis. Taken together, our data establishes antifibrotic activity of IL-15 that might be a novel therapeutic molecule to combat the development of pulmonary fibrosis.

Regulatory effects of IL-15 on allergen-induced airway obstruction

BACKGROUND

Airway obstruction is a physiologic feature of asthma, and IL-15 might have an important role in asthma pathogenesis.

OBJECTIVE

We tested the hypothesis that regulation of IL-15 is critical for preservation of allergen-induced airway hyperresponsiveness (AHR), airway resistance, and compliance in response to methacholine.

METHODS

Airway inflammation, AHR, resistance, and compliance were assessed in Il15 gene-deficient mice and IL-15-overexpressing mice in an allergen-induced murine model of asthma. We assessed eosinophil numbers by using anti-major basic protein immunostaining, goblet cell hyperplasia by using periodic acid-Schiff staining, and cytokine and chemokine levels by performing quantitative PCR and ELISA.

RESULTS

We made a novel observation that IL-15 deficiency promotes baseline airway resistance in naive mice. Moreover, rIL-15 delivery to the lung downregulates expression of proinflammatory cytokines and improves allergen-induced AHR, airway resistance, and compliance. These observations were further validated in doxycycline-inducible CC10-IL-15 bitransgenic mice. Doxycycline-exposed, Aspergillus species extract-challenged CC10-IL-15 bitransgenic mice exhibited significantly reduced levels of proinflammatory cytokines (IL-4, IL-5, and IL-13) and decreased goblet cell hyperplasia. Airway obstruction, including AHR and airway resistance, was diminished in allergen-challenged doxycycline-exposed compared with non-doxycycline-exposed CC10-IL-15 bitransgenic mice. Mechanistically, we observed that IL-15-mediated protection of airway obstruction is associated with induced IFN-γ- and IL-10-producing regulatory CD4+CD25+ forkhead box p3 (Foxp3)+ T cells. Additionally, we found that a human IL-15 agonist (ALT-803) improved airway resistance and compliance in an experimental asthma model.

CONCLUSION

We report our novel finding that IL-15 has a potent inhibitory effect on the airway obstruction that occurs in response to environmental allergens.

Role of IL-15 in the modulation of TGF-β1-mediated inflammation in asthma

Transforming growth factor (TGF)-β1 has an essential role in bronchitis and the induction of bronchial remodelling, which are critical processes in the pathogenesis of asthma. However, the role of interleukin (IL)-15 in asthma inflammation remains unclear. The aim of the present study was to evaluate the effect of TGF-β1 mRNA expression on IL-15 mRNA expression in asthmatic patients and to assess the role of IL-15 in the clinical course of asthma. The study included 221 participants, comprising 130 patients with asthma and 91 healthy volunteers. The participants were subjected to testing using spirometry, as well as the Asthma Control Test™ and Borg Scale. The expression of TGF-β1 and IL-15 mRNA was analyzed in blood samples using reverse transcription-quantitative polymerase chain reaction. Statistical analysis indicated that IL-15 and TGF-β1 mRNA expression each differed significantly between the patient and control groups (P=0.0016 and P=0.033, respectively). A significant correlation was identified between IL-15 expression and TGF-β1 expression (R=0.41, P=0.0005). No correlation was observed between IL-15 expression and the degree of asthma severity, the results of spirometric examination or the frequency of asthma exacerbations. Further analysis revealed that IL-15 expression was elevated following the administration of inhaled glucocorticosteroids (iGCs; P=0.024), and reduced following methylxanthine treatment (P<0.001). The occurrence of dyspnoea differed between the study and control groups, and this was not found to be associated with IL-15 expression. Since IL-15 expression was correlated with TGF-β1 expression among asthmatic patients, and IL-15 expression was elevated following iGC administration, the results of the study suggest that IL-15 activity might be associated with the pathogenesis of asthma.

Effect of Anti-IL-15 Administration on T Cell and NK Cell Homeostasis in Rhesus Macaques

IL-15 has been implicated as a key regulator of T and NK cell homeostasis in multiple systems; however, its specific role in maintaining peripheral T and NK cell populations relative to other γ-chain (γc) cytokines has not been fully defined in primates. In this article, we address this question by determining the effect of IL-15 inhibition with a rhesusized anti-IL-15 mAb on T and NK cell dynamics in rhesus macaques. Strikingly, anti-IL-15 treatment resulted in rapid depletion of NK cells and both CD4(+) and CD8(+) effector memory T cells (TEM) in blood and tissues, with little to no effect on naive or central memory T cells. Importantly, whereas depletion of NK cells was nearly complete and maintained as long as anti-IL-15 treatment was given, TEM depletion was countered by the onset of massive TEM proliferation, which almost completely restored circulating TEM numbers. Tissue TEM, however, remained significantly reduced, and most TEM maintained very high turnover throughout anti-IL-15 treatment. In the presence of IL-15 inhibition, TEM became increasingly more sensitive to IL-7 stimulation in vivo, and transcriptional analysis of TEM in IL-15-inhibited monkeys revealed engagement of the JAK/STAT signaling pathway, suggesting alternative γc cytokine signaling may support TEM homeostasis in the absence of IL-15. Thus, IL-15 plays a major role in peripheral maintenance of NK cells and TEM However, whereas most NK cell populations collapse in the absence of IL-15, TEM can be maintained in the face of IL-15 inhibition by the activity of other homeostatic regulators, most likely IL-7.

Interleukin-15: new kid on the block for antitumor combination therapy

Interleukin (IL)-15 is one of the most promising molecules to be used in antitumor immune therapy, as it is able to stimulate the main killer cells of both the innate and adaptive immune system. Although this cytokine can be used as a stand-alone immunotherapeutic agent, IL-15 will probably be most efficient in combination with other strategies to overcome high tumor burden, immune suppression of the tumor microenvironment and/or the short half-life of IL-15. In this review, we will discuss the combination strategies with IL-15 that have been tested to date in different animal tumor models, which include chemotherapy, other immunostimulatory cytokines, targeted therapy, adoptive cell transfer and gene therapy. In addition, we give an overview of IL-15 combination therapies that are currently tested in clinical studies to treat patients with hematological or advanced solid tumors.

Immune responses evoked by infection with Vibrio anguillarum in zebrafish bath-vaccinated with a live attenuated strain

Live attenuated vaccines are a promising application to control bacterial fish diseases. A live attenuated Vibrio anguillarum vaccine candidate was established in our laboratory to protect fish against vibriosis. To elucidate the mechanism of immunoprotection, it is necessary to compare the different immune responses to infection between vaccinated and non-vaccinated fish. In this study, the expression levels of pathogen-specific antibodies and immune-related genes upon challenge at 28 days post-vaccination were compared between vaccinated and non-vaccinated zebrafish. In the results, the specific antibody levels against virulent V. anguillarum in the vaccinated group did not rise significantly following infection, which suggested that high-affinity antibodies were induced by the vaccine. In the non-vaccinated group, the specific IgM response was triggered at 3 days post-infection and showed a delayed antibody response. Meanwhile, the transcription levels of the genes encoding the pro-inflammatory cytokine IL-1β and the chemokine IL-8 were more highly up-regulated in non-vaccinated fish than in vaccinated fish. This suggests that the overwhelming inflammatory response trigged by infection in non-vaccinated zebrafish was controlled in vaccinated zebrafish. Interestingly, the expression levels of adaptive immune-related genes were increased in vaccinated fish after challenge, compared to the non-vaccinated fish. These results suggest that inoculation with the live attenuated vaccine triggered protection by curbing inflammation and strengthening the adaptive immune response.

Ulinastatin reduces pathogenesis of phosgene-induced acute lung injury in rats

Phosgene (CG) is an industrial chemical used to make plastics, rubbers, dyestuff, and pesticides. Although the inhalation of CG is relatively uncommon, its accidental exposure can lead to acute lung injury (ALI). Ulinastatin, a urinary trypsin inhibitor, has been emerged to use for the treatment of acute inflammatory state of a number of organs including the lung. In this study, we examined the pathogenic changes in the lungs after the inhalation of CG gas and also examined the effect of ulinastatin treatment in reversing these changes in rats. We found that the rats exposed to CG gas at a dose of 5.0 g/m(3) for 5 min led to ALI after 6 h. The signs of lung injury include pulmonary edema, hemorrhage, and cellular infiltration in pulmonary alveoli. In addition, interleukin-15 (IL-15) and intercellular adhesion molecule-1 (ICAM-1) were significantly increased in CG-inhaled animals. Ulinastatin administration at 1 h postexposure significantly reduced the intensity of all the pathological changes in the lungs of these CG-exposed animals. Ulinastatin at a dose of 400 U/g was shown to decrease the total number of cells in bronchoalveolar lavage fluid and the levels of IL-15 and ICAM-1 in the serum. We also found that the structure of the lung was protected by ulinastatin treatment. Thus, our data suggest that ulinastatin can be used as an effective drug for the treatment of CG-induced ALI. The serum levels of IL-15 and ICAM-1 can be used as the markers of lung injury after exposure to CG and may also serve as useful therapeutic targets at an early stage. The effects of long-term treatment of ulinastatin and the mechanisms by which ulinastatin decreases the infiltration of blood cells and reduces cytokines need further investigation.

Immune responses of zebrafish (Danio rerio) induced by bath-vaccination with a live attenuated Vibrio anguillarum vaccine candidate

A fish vaccine candidate, live attenuated Vibrio anguillarum, which can protect fish from vibriosis, was established in our laboratory. In this study, the protective immunological mechanism of live attenuated V. anguillarum was investigated in zebrafish as a model animal. After bath-vaccinated with the live attenuated strain, zebrafish were challenged with wild pathogenic strain to test the immunoprotection of the live attenuated strain. As the results, specific antibody response of fish against V. anguillarum was found to gradually increase during 28 days post-vaccination, and remarkable protection was showed with a high relative protection survival (RPS) of about 90%. Moreover, the vaccination changed the expressions of several immune-related genes in the spleens and livers of zebrafish. Among them, the expressions of pro-inflammatory factors such as IL-1 and IL-8 were tenderly up-regulated with about 3-4 fold in 1-7 days post-vaccination, while MHC II rose to a peak level of 4-fold in 7th day post-vaccination. These results gave some important messages about the mechanism of specific protection induced by live attenuated V. anguillarum and showed the availability of zebrafish model in the evaluation of the vaccine candidate.

Functions of IL-15 in anti-viral immunity: multiplicity and variety

An effective immune response to an invading viral pathogen requires the combined actions of both innate and adaptive immune cells. For example, NK cells and cytotoxic CD8 T cells are capable of the direct engagement of infected cells and the mediation of antiviral responses. Both NK and CD8 T cells depend on common gamma chain (γc) cytokine signals for their development and homeostasis. The γc cytokine IL-15 is very well characterized for its role in promoting the development and homeostasis of NK cells and CD8 T cells, but emerging literature suggests that IL-15 mediates the anti-viral responses of these cell populations during an active immune response. Both NK cells and CD8 T cells must become activated, migrate to sites of infection, survive at those sites, and expand in order to maximally exert effector functions, and IL-15 can modulate each of these processes. This review focuses on the functions of IL-15 in the regulation of multiple aspects of NK and CD8 T cell biology, investigates the mechanisms by which IL-15 may exert such diverse functions, and discusses how these different facets of IL-15 biology may be therapeutically exploited to combat viral diseases.

Association of interleukin-15 single nucleotide polymorphisms with resistance to brucellosis among Iranian patients

Interleukin (IL)-15, a Th1-related cytokine, triggers inflammatory cells' recruitment and increases the expression of interferon gamma (IFN-γ), which is an important cytokine in the immunity against brucellosis. Different single-nucleotide polymorphisms (SNPs) have been observed in the IL-15 gene, so this study aimed to investigate the probable association between these SNPs and susceptibility to brucellosis among Iranian patients. A total of 190 patients with brucellosis and 83 healthy milk farmers who consumed contaminated raw milk and dairy products from animals involved with brucellosis were included in this study. All the patients and the controls were genotyped for four IL-15 polymorphisms at positions 267, 367, 13687 and 14035 using polymerase chain reaction-restriction fragment length polymorphisms. The 267C and 13687A alleles, haplotypes CGCT and CAAA and the 267CC and 13687AA genotypes were significantly more frequent in the controls than in the patients (P = 0.014, 0.03, 0.006, 0.024, 0.026 and 0.01, respectively), so the variation in the IL-15 gene may be one of the factors affecting the resistance to brucellosis. In contrast, the frequency of haplotypes CGCA and TACT was significantly higher in patients compared with controls (P = 0.015 and 0.007, respectively), and interestingly the last one was observed only in the patients; therefore, it may serve as a predictive factor for brucellosis. In conclusion, it could be suggested that IL-15 genetic variants can affect resistance or susceptibility to human brucellosis among Iranian patients.

Edwardsiella tarda flagellar protein FlgD: a protective immunogen against edwardsiellosis

Edwardsiella tarda is a gram-negative bacterium and a causative agent of edwardsiellosis, resulting to severe loss of the aquaculture industry. In this study, based on the reverse vaccinology, sixteen flagellar proteins were selected from highly pathogenic E. tarda EIB202 genome information and in silico analyzed as potential vaccine candidates. Among them, ten recombinant proteins were highly expressed in Escherichia coli and successfully purified. The immunoprotective potentials of these purified recombinant proteins were evaluated in zebrafish model. And recombinant FlgD and FliD were found to lead to a high relative percent survival (RPS, about 70%) against E. tarda EIB202. Furthermore, FlgD required in flagellum hook assembly brought about the similar immune protection in turbot. The immune responses of zebrafish and turbot to recombinant FlgD were also investigated, and the results indicated that its high protection was mainly involved in cellular mediated immune response, corresponding to the intracellular pathogenicity of E. tarda.

Identification of the earliest natural killer cell-committed progenitor in murine bone marrow

Natural killer (NK) cells develop in the bone marrow and are known to gradually acquire the ability to eliminate infected and malignant cells, yet the cellular stages of NK lineage commitment and maturation are incompletely understood. Using 12-color flow cytometry, we identified a novel NK-committed progenitor (pre-NKP) that is a developmental intermediate between the upstream common lymphoid progenitor and the downstream NKP, previously assumed to represent the first stage of NK lineage commitment. Our analysis also refined the purity of NKPs (rNKP) by 6-fold such that 50% of both pre-NKP and rNKP cells gave rise to NKp46+ NK cells at the single-cell level. On transplantation into unconditioned Rag2-/-Il2rγc-/- recipients, both pre-NKPs and rNKPs generated mature NK cells expressing a repertoire of Ly49 family members that degranulated on stimulation ex vivo. Intrathymic injection of these progenitors, however, yielded no NK cells, suggesting a separate origin of thymic NK cells. Unlike the rNKP, the pre-NKP does not express IL-2Rβ (CD122), yet it is lineage committed toward the NK cell fate, adding support to the theory that IL-15 signaling is not required for NK commitment. Taken together, our data provide a high-resolution in vivo analysis of the earliest steps of NK cell commitment and maturation.

The liver plays a major role in clearance and destruction of blood trypomastigotes in Trypanosoma cruzi chronically infected mice

Intravenous challenge with Trypanosoma cruzi can be used to investigate the process and consequences of blood parasite clearance in experimental Chagas disease. One hour after intravenous challenge of chronically infected mice with 5×10⁶ trypomastigotes, the liver constituted a major site of parasite accumulation, as revealed by PCR. Intact parasites and/or parasite remnants were visualized at this time point scattered in the liver parenchyma. Moreover, at this time, many of liver-cleared parasites were viable, as estimated by the frequency of positive cultures, which considerably diminished after 48 h. Following clearance, the number of infiltrating cells in the hepatic tissue notably increased: initially (at 24 h) as diffuse infiltrates affecting the whole parenchyma, and at 48 h, in the form of large focal infiltrates in both the parenchyma and perivascular spaces. Phenotypic characterization of liver-infiltrating cells 24 h after challenge revealed an increase in Mac1⁺, CD8⁺ and CD4⁺ cells, followed by natural killer (NK) cells. As evidence that liver-infiltrating CD4⁺ and CD8⁺ cells were activated, increased frequencies of CD69⁺CD8⁺, CD69⁺CD4⁺ and CD25⁺CD122⁺CD4⁺ cells were observed at 24 and 48 h after challenge, and of CD25⁻CD122⁺CD4⁺ cells at 48 h. The major role of CD4⁺ cells in liver protection was suggested by data showing a very high frequency of interferon (IFN)-γ-producing CD4⁺ cells 24 h after challenge. In contrast, liver CD8⁺ cells produced little IFN-γ, even though they showed an enhanced potential for secreting this cytokine, as revealed by in vitro T cell receptor (TCR) stimulation. Confirming the effectiveness of the liver immune response in blood parasite control during the chronic phase of infection, no live parasites were detected in this organ 7 days after challenge.

Chagas disease, a Latin American illness caused by the protozoan parasite Trypanosoma cruzi, has only rare spontaneous cure, and in most patients a small number of parasites persists for life in the blood and tissues, leading to chronic disorders such as cardiomyopathy. In a murine model of chronic T. cruzi infection we observed that the liver plays an important role in the clearance of blood-circulating parasites. Moreover, parasite accumulation in this organ is followed by their elimination, an effect that is not immediate but seems to depend on the recruitment of leukocytes and on the local production of IFN-γ, a cytokine known to increase the T. cruzi-killing capacity of phagocytes. Our findings contribute to the knowledge of T. cruzi-host interaction, showing the participation of a non-lymphoid organ in parasite control. In addition, they contribute to understanding the multifaceted role the liver plays in the immune response.

Expression of interleukin-15 and its receptor on the surface of stimulated human umbilical vein endothelial cells

Human interleukin-15 (hIL-15) is an important cytokine to activate endothelial cells and can be regulated by many other cytokines. The aim of this study is to examine the ability of interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) to induce the production of human interleukin-15 (hIL-15) and IL-15 receptor (IL-15Ralpha) by human umbilical vein endothelial cells (HUVECs). The data are summarized as follows: 1. Northern blot revealed that IL-15 mRNA was up-regulated by IFN-gamma and TNF-alpha. 2. Intracellular IL-15 protein was visualized by fluorescence microscopy, whereas the expression of IL-15 on the surface of HUVECs was detected by fluorescence activated cell sorting (FACS), and no detectable IL-15 in the medium was verified by ELISA. 3. IL-15Ralpha was detected on the surface of HUVECs by FACS after IFN-gamma and TNF-alpha stimulation, whereas Western blotting revealed that the elevated expression on surface IL-15Ralpha was not due to the increased protein expression. The conclusion demonstrated from our results is that IFN-gamma and TNF-alpha play an important role in regulating the expression of IL-15 and IL-15Ralpha on the surface of HUVECs.

Interleukin-15 expression affects homeostasis and function of B cells through NK cell-derived interferon-gamma

Interleukin-15 (IL-15) is a cytokine important for the development, maturation, and function of many cells of the immune system including NK, NKT, gammadeltaT, and CD8(+) T cells. The relationship between IL-15 and B lymphocytes however, is not well characterized and is the focus of our study. Previous in vitro reports have shown that IL-15 increases proliferation of B lymphocytes and increases antibody secretion however, this relationship remains inadequately defined in vivo. The focus of this study was to examine the role of IL-15 in B cell homeostasis and function in vivo using mice that either over express IL-15 (IL-15tg mice) or are deficient in IL-15 (IL-15(-/-) mice) production. Here we report significant differences between the B cell populations of IL-15(-/-), C57BL/6, and IL-15tg mice. In fact, increased expression of IL-15 resulted in a significant decrease in the percentage and absolute number of CD19(+) cells. In vitro B cell co-cultures implicate interferon-gamma (IFN-gamma) as the factor responsible for inhibiting B cell proliferation. We also show that IL-15 expression affects B cell function, as B cells from IL-15 transgenic mice produce greater amounts of IgG and IgA than IL-15 knockout mice in vitro. Interestingly, despite significant differences in B cell numbers in these strains, there were no significant differences in total antibody titers in serum and vaginal washes of these mice. Results from our in vivo and in vitro experiments suggest that altered expression of IL-15 affects B cell homeostasis through the induction of NK cell-derived IFN-gamma.

Extrinsic and intrinsic regulation of early natural killer cell development

Natural killer (NK) cells are lymphocytes that play a critical role in both adaptive and innate immune responses. These cells develop from multipotent progenitors in the embryonic thymus and neonatal or adult bone marrow and recent evidence suggests that a subset of these cells may develop in the thymus. Thymus- and bone marrow-derived NK cells have unique phenotypes and functional abilities supporting the hypothesis that the microenvironment dictates the outcome of NK cell development. A detailed understanding of the mechanisms controlling this developmental program will be required to determine how alterations in NK cell development lead to disease and to determine how to harness this developmental program for therapeutic purposes. In this review, we discuss some of the known extrinsic stromal-cell derived factors and cell intrinsic transcription factors that function in guiding NK cell development.

IL-15 treatment during acute simian immunodeficiency virus (SIV) infection increases viral set point and accelerates disease progression despite the induction of stronger SIV-specific CD8+ T cell responses

In this study, we examined the effect of in vivo treatment of acutely SIV-infected Mamu-A*01+ rhesus macaques with IL-15. IL-15 treatment during acute infection increased viral set point by 3 logs and accelerated the development of simian AIDS in two of six animals with one developing early minimal lesion SIV meningoencephalitis. Although IL-15 induced a 2- to 3-fold increase in SIV-specific CD8+ T cell and NK cell numbers at peak viremia and reduced lymph node (LN) SIV-infected cells, this had no impact on peak viremia and did not lower viral set point. At viral set point, however, activated SIV-specific CD8+ T cells and NK cells were reduced in the blood of IL-15-treated animals and LN SIV-infected cells were increased. Week 30 LN from IL-15-treated animals had significantly increased Gag-specific CD8+ T cell numbers, whereas total cell, lymphocyte, and CD4+ T cell numbers were reduced. IL-15 treatment significantly reduced anti-SIV Ab concentrations at week 3 and viral set point. IL-15 increased Ki-67+CD4+ T cells at week 1 of treatment and reduced blood CCR5+ and CD45RA-CD62L- CD4+ T cells. The frequency of day 7 Ki-67+CD4+ T cells strongly correlated with viral set point. These findings suggest that CD4+ T cell activation during acute infection determines subsequent viral set point and IL-15 treatment by increasing such activation elevates viral set point. Finally, IL-15-treated acutely SIV-infected primates may serve as a useful model to investigate the poorly understood mechanisms that control viral set point and disease progression in HIV infection.

Adaptive immune responses fail to provide protection against genital HSV-2 infection in the absence of IL-15

IL-15 plays a crucial role in innate defense against viral infections. The role of IL-15 in the generation and function of adaptive immunity, following mucosal immunization, against genital HSV-2 has not been studied. Here, we report that immunized IL-15(-/-) mice were able to generate antibody and T cell-mediated immune responses against HSV-2, comparable to those seen in immunized B6 mice. However, immunized IL-15(-/-) mice were not protected against subsequent HSV-2 challenge, compared to B6 immunized mice, even with a ten times lower challenge dose. We then examined if the adaptive immune responses generated in the absence of IL-15 could provide protection against HSV-2 in an IL-15-positive environment. Adoptive transfer of lymphocytes from immunized IL-15(-/-) to naive mice were able to provide protection against HSV-2 challenge similar to protection with immunized cells from control mice. This suggests that the adaptive immune responses raised in the absence of IL-15 are functional in vivo. Reconstitution of the innate components, particularly IL-15, NK cells and NK cell-derived IFN-gamma, in immunized IL-15(-/-) mice restored their protective adaptive immunity against subsequent genital HSV-2 challenge. Our results clearly suggest that innate antiviral activity of IL-15 is necessary for protective adaptive immunity against genital HSV-2 infection.

Differential cytokine gene expression in CD4+ and CD8+ T cell subsets of calves

The distinct patterns of cytokine expression in CD4+ and CD8+ T cells are well understood in mice and humans. However, little information is available about cytokine expression in bovine CD4+ and CD8+ T cells. In this study, mRNA expression of 19 different cytokines was analyzed in CD4+ and CD8+ T cells of calves with or without Concanavalin A (Con A) stimulation. CD4+ and CD8+ T cell populations were enriched to 98% purity by positive selection using magnetic cell sorting (MACS). CD4+ T cells spontaneously expressed the mRNAs of interleukin-1alpha (IL-1alpha), IL-1beta, IL-2, IL-6, IL-7, IL-8, IL-10, IL-18, IFN-gamma, TNF-alpha, TNF-beta and TGF-beta, and augmented the mRNA expression of IL-10, IFN-gamma and TNF-beta after Con A stimulation. The mRNAs of IL-3, IL-4, IL-5, IL-13 and GM-CSF were newly expressed in Con A-stimulated CD4+ T cells. CD8+ T cells displayed spontaneous mRNA expression of IL-6, IL-18, TNF-alpha, TNF-beta and TGF-beta, and newly expressed the mRNA of IL-2, IL-7, interferon-gamma (IFN-gamma) and GM-CSF after Con A stimulation. It was found that CD4+ T cells expressed the mRNA of 17 cytokines except for IL-12 and IL-15, while CD8+ T cells expressed only the mRNA of 9 cytokines after Con A stimulation. The profile of cytokine mRNA expression was substantially different in the CD4+ and CD8+ T cells of calves, indicating that CD4+ T cells can be distinguished from CD8+ T cells by the cytokine gene expression of IL-1alpha, IL-1beta, IL-3, IL-4, IL-5, IL-8, IL-10 and IL-13. Differential cytokine expression between CD4+ and CD8+ T cells serve to interpret an individual function of T cell subsets in the immune system of calves.

Possible drug targets for celiac disease

Celiac disease (CD) is an intestinal disorder caused by an altered immune response against wheat gluten, a common dietary antigen, and related cereal proteins. Both CD4+ and CD8+ T cells have a role in inducing the intestinal damage, although recent studies have also pinpointed the involvement of the innate immune response in CD pathogenesis. So far, the only available treatment for CD is the strict avoidance of gluten in the diet, but the poor compliance and the associated complications demand alternative therapies. During the last decade, the knowledge of genetic, molecular and cellular mechanisms leading to CD pathogenesis made great progress. The improved understanding of gluten peptides activating either adaptive or innate immune response, of HLA restriction molecules, as well as of cytokines that mediate most of the inflammatory reactions, opens several new promising perspectives for therapeutic intervention. This review discusses both molecular and cellular strategies to treat CD, including the use of proteolytic enzymes active on gluten peptides, antibodies neutralising IL-15 and IFN-gamma, drugs targeting HLA, regulatory cytokines and T cells.

Anti-interleukin-15 prevents arthritis in Borrelia-vaccinated and -infected mice

We showed previously that interleukin-17 (IL-17) plays a significant role in the induction of arthritis associated with Borrelia vaccination and challenge. Little information, however, is available about the chain of immunologic events that leads to the release of IL-17. The production of IL-17 has been linked to stimulation of memory cells by IL-15. Therefore, we hypothesized that IL-15 is involved in the induction of arthritis associated with Borrelia vaccination and infection of mice. Here we present evidence that treatment of Borrelia-vaccinated and -infected mice with anti-IL-15 antibody prevents swelling of the hind paws. More importantly, both anti-IL-15 antibody- and recombinant IL-15 receptor alpha-treated Borrelia-vaccinated and -infected mice were free of major histopathologic indications of arthritis, including hyperplasia, hypertrophy, and vilus formation of the synovium. Similarly, the synovial space and perisynovium were free of inflammatory cells. By contrast, the synovium of nontreated Borrelia-vaccinated and -infected mice had overt hyperplasia, hypertrophy, and vilus formation. Moreover, the synovial space and perisynovium were infiltrated with neutrophils, macrophages, and lymphocytes. Finally, we show that recombinant IL-15 stimulates the release of IL-17 from lymph node cells obtained near the arthritic site. These results suggest that IL-15 plays a major role in orchestrating IL-17 induction of arthritis associated with Borrelia-vaccinated and -infected mice.

Interleukin-12 is not essential for silicosis in mice

BACKGROUND

Silicosis features foci of inflammation where macrophages and lymphocytes precede and accompany fibroblast proliferation, alveolar epithelial hyperplasia, and increased deposition of connective tissue matrix material. In the mouse following silica inhalation there is recruitment of natural killer-, B-, and CD4+ and CD8+ lymphocytes to the alveolar spaces, enlargement of bronchial-associated lymphoid tissues (BALT), and aggregation of lymphocytes surrounding small airways and blood vessels. A substantial fraction of the recruited lung lymphocytes produce interferon-gamma (IFN-gamma), and IFN-gamma gene-deleted mice develop less silicosis than wild-type mice. Interleukin-12 (IL-12) is an important pathway for driving the adaptive immune response towards a TH1-like phenotype. We hypothesized that IL-12 might stimulate lymphocyte activation and the up-regulation of IFN-gamma, and consequently be an essential mediator for silicosis.

RESULTS

C57Bl/6 wild-type (WT) and IL-12 deficient (IL-12 KO) mice were exposed to sham-air or crystobalite silica (61 mg/m3) by inhalation for 5 hours/day for 12 days and then studied from 1 to 112 days after exposure. Mice exposed to sham-air had normal lung histology at all time points. WT mice exposed to titanium dioxide (72 mg/m3) showed pulmonary macrophage recruitment but no increase in lung collagen. Both WT and IL-12 KO mice exposed to silica showed similar progressive lung pathology, increased wet lung weight and increased total lung collagen (hydroxyproline). IL-12 p35 mRNA was not increased in either strain after silica exposure; IL-12 p40 mRNA was up-regulated after silica in WT mice and constitutively absent in the IL-12 KO mice. IL-18 mRNA was not increased after silica exposure. The expression of IL-15 (an important driver for innate immunity, Natural Killer cell activation, and IFN-gamma production) was abundant in air-exposed mice and was increased slightly in the lungs of mice with silicosis.

CONCLUSION

The axis of IL-12 driving IFN-gamma production is not essential for the full manifestations of silicosis in mice exposed to a crystobalite silica aerosol.

A high-efficiency system of natural killer cell cloning

The culture of human natural killer (NK) cell clones has traditionally been a long, laborious process with an efficiency of only 1-2%. Recently, a stem cell growth medium (SCGM) has been described to expand preferentially polyclonal NK cells from peripheral blood. We have tested SCGM in a single cell sorting system and shown a 4-5 fold increase in the number of proliferating NK clones compared to standard RPMI media. The cloning efficiency was further enhanced by the provision of irradiated feeder cells derived from multiple donors combined with the addition of the anti-CD3 antibody, OKT3. The combination of SCGM, single cell sorting and these multiple optimisations enhanced NK cloning efficiency by more than tenfold to greater than 20% for short-term cultures when deriving 10(5) cells and as high as 10% for longer term cultures when deriving more than 2 x 10(6) cells. This novel system thus facilitates the generation of NK clones and allows larger scale studies of NK function that were beyond the scope of previous methodology.

CD8 cell division maintaining cytotoxic memory occurs predominantly in the bone marrow

Long-term persistence of Ag-experienced CD8 cells, a class of T lymphocytes with cytotoxic function, contributes to immunological memory against intracellular pathogens. After Ag clearance, memory CD8 cells are maintained over time by a slow proliferation, primarily cytokine driven. In this article, we show that the bone marrow (BM) is the crucial organ where such basal division of memory CD8 cells occurs. BM memory CD8 cells contain a higher percentage of proliferating cells than their corresponding cells in either spleen or lymph nodes from C57BL/6 mice. This occurs both in the case of memory-phenotype CD44(high) CD8 cells and in the case of Ag-specific memory CD8 cells. Importantly, the absolute number of Ag-specific memory CD8 cells dividing in the BM largely exceeds that in spleen, lymph nodes, liver, and lung taken together. In the BM, Ag-specific memory CD8 cells express lower levels of CD127, i.e., the alpha-chain of IL-7R, than in either spleen or lymph nodes. We interpret these results as indirect evidence that Ag-specific memory CD8 cells receive proliferative signals by IL-7 and/or IL-15 in the BM and propose that the BM acts as a saturable "niche" for the Ag-independent proliferation of memory CD8 cells. Taken together, our novel findings indicate that the BM plays a relevant role in the maintenance of cytotoxic T cell memory, in addition to its previously described involvement in long-term Ab responses.

Cloning and expression of rabbit interleukin-15

In order to understand the inflammatory mechanisms related to rabbit interleukin-15 (RIL-15), we cloned and expressed RIL-15 cDNA gene. A cDNA encoding RIL-15 was cloned from heart mRNA by reverse transcriptase polymerase chain reaction (RT-PCR) amplification using hIL-15 primers. The RIL-15 cDNA contains an open reading frame (ORF) of 162 amino acids (aa) with a 48 aa leader sequence. The predicted molecular weight of the encoded protein (12.5 kDa) matched the size of recombinant IL-15 on Western blotting in an Escherichia coli (pET32a) expression system. Amino acid and nucleotide sequence analyses of RIL-15 revealed 82.7% and 87% homology with human IL-15 (hIL-15), respectively. RIL-15 is similar to the hIL-15 (hIL-15) in that it contains seven cysteine residues. RT-PCR showed that IL-15 is expressed in many tissues in the rabbit, including heart, spleen, lung, liver, muscle and kidney. Expressed and purified recombinant RIL-15, in the absence of the 48 aa leader sequence, stimulated the proliferation of cells of the mouse T cell line, CTLL-2, and its activity is comparable to hIL-15. Western blotting demonstrated that recombinant RIL-15 can be recognized by anti-IL-15 neutralization antibody. Western blotting also confirmed that IL-15 is present in many tissues including heart, spleen, lung, liver, muscle and kidney.

Adaptive and innate immune responses in celiac disease

Celiac disease (CD) is a complex small intestinal disorder due to a dysregulated immune response to wheat gliadin and related proteins which leads to a small intestinal enteropathy. It is generally accepted that CD is a T-cell mediated disease, in which, gliadin derived peptides, either in native form or deamidated by tissue transglutaminase, activate lamina propria infiltrating T lymphocytes which release proinflammatory cytokines. Recent studies indicate that gliadin contains also peptides able to activate an innate immune response. In particular, they induce a selective expansion of IEL, particularly TCRgamma/delta+ and CD8+TCR alpha/beta+ lymphocytes bearing the CD94 NK receptor, as well as a strong epithelial expression of MICA molecules which interact with NKG2D receptor expressed on TCRgamma/delta+ and NK cells. Most of the events of innate immune activation events are inhibited by antibodies neutralizing IL-15, thus confirming the key role of this cytokine as a mediator of intestinal mucosa damage induced by ingestion of gliadin. It remains to be established to what extent the ability of gliadin peptides to activate innate immunity relates to other biological properties exerted not only on celiac cells and tissues; the specificity of celiac patients is probably related to their genetic make up.

Elevated serum interleukin-15 level in acute graft-versus-host disease after hematopoietic cell transplantation

OBJECTIVE

To correlate serum cytokine levels and the development of acute graft-versus-host disease (GVHD), the authors conducted a prospective study on serial measurements of interferon (IFN)-gamma and interleukin (IL)-10, IL-12 and IL-15.

METHODS

The cytokines were measured in 27 subjects by enzyme-linked immunosorbent assay serially for the first 2 months after hematopoietic cell transplantation.

RESULTS

Nineteen subjects with acute GVHD had significantly higher mean peak serum levels of IFN-gamma and IL-15 than the baseline levels at the start of conditioning. The peak level occurred soon after stem cell infusion and returned to the pretransplantation state in the second month. In contrast, there was lesser difference between the mean peak serum levels of IFN-gamma, IL-10, and IL-15 and the baseline level in the eight subjects without GVHD. The peak serum level for IL-15 was, in addition, significantly higher among GVHD subjects than those without GVHD in the first month posttransplantation. However, the level of IL-15 showed no correlation with the severity of GVHD.

CONCLUSIONS

These changes point to a possible role of systemic cytokine secretion in the development of acute GVHD. Elevated levels of IL-15 early in the posttransplant period could be a helpful laboratory predictor of acute GVHD.

Interleukin-21 inhibits dendritic cell activation and maturation

Interleukin 21 (IL-21) is a newly described cytokine with homology to IL-4 and IL-15. They belong to a cytokine family that uses the common gamma chain for signaling but also have their private high-affinity receptors. Since it is well known that IL-4 modulates differentiation and activation of dendritic cells (DCs), we analyzed effects of IL-21 compared with IL-15 on DC differentiation, maturation, and function. Here we show that DCs generated with granulocyte-macrophage colony-stimulating factor (GMCSF) in the presence of IL-21 (IL-21DCs) differentiated into phenotypically and functionally altered DCs characterized by reduced major histocompatibility complex class II (MHCII) expression, high antigen uptake, and low stimulatory capacity for T-cell activation in vitro. Additionally, IL-21DCs completely failed to induce antigen (Ag)-specific T-cell mediated contact hypersensitivity. Furthermore, IL-21 blocked lipopolysaccharide (LPS)-induced activation and maturation of DCs, which was not mediated by release of the anti-inflammatory cytokine IL-10. In contrast, when supplementing GMCSF with IL-15, DCs differentiated into mature antigen-presenting cells (APCs) with low antigen uptake and highly significant increased capacities to stimulate T cells in vitro and in vivo. Taken together, these results identify a dichotomous action of these structurally related cytokines on DCs, establishing IL-21 as inhibitory cytokine on DC activation and IL-15 as potent stimulator of DC function, making both cytokines interesting targets for therapeutic manipulation of DC-induced immune reactions.

Latent tuberculosis: mechanisms of host and bacillus that contribute to persistent infection

Most people infected with Mycobacterium tuberculosis contain the initial infection and develop latent tuberculosis. This state is characterised by evidence of an immune response against the bacterium (a positive tuberculin skin test) but no signs of active infection. It can be maintained for the lifetime of the infected person. However, reactivation of latent infection occurs in about 10% of infected individuals, leading to active and contagious tuberculosis. An estimated 2 billion people worldwide are infected with M tuberculosis--an enormous reservoir of potential tuberculosis cases. The establishment and reactivation of latent infection depend on several factors, related to both host and bacterium. Elucidation of the host immune mechanisms that control the initial infection and prevent reactivation has begun. The bacillus is well adapted to the human host and has a range of evasion mechanisms that contribute to its ability to avoid elimination by the immune system and establish a persistent infection. We discuss here current understanding of both host and bacterial factors that contribute to latent and reactivation tuberculosis.

On-column refolding and characterization of soluble human interleukin-15 receptor alpha-chain produced in Escherichia coli

Interleukin-15 receptor alpha-chain (IL-15Ralpha) is a member of the new cytokine receptor family, which possesses the sushi domain. To investigate the biochemical and biophysical characteristics of soluble human IL-15Ralpha (shIL-15Ralpha), shIL-15Ralpha was recombinantly expressed in Escherichia coli. The shIL-15Ralpha containing a six histidine-tag was expressed as inclusion bodies, which were solubilized with urea, immobilized on a Ni-nitrilotriacetic acid column, and refolded by a decreasing gradient of urea concentration. The refolded shIL-15Ralpha exhibited a highly flexible structure, neutralized human interleukin-15-induced cell proliferation effectively, and bound to its ligand with the same affinity as human IL-15Ralpha on the cell surface, as demonstrated by circular dichroism, a cell proliferation assay, and surface plasmon resonance, respectively. Thus, we succeeded in refolding shIL-15Ralpha to an active form on an affinity column.

Development and functions of natural killer cells

Over the last decade, progress in molecular and cellular biology and gene targeting techniques has removed veils from the mysteries of natural killer (NK) cell development and function. NK cells are derived from hematopoietic stem cells, for which stem cell factor or Flt3 ligand is required in the early stage of differentiation to NK cell progenitors. Interleukin 15 then plays a crucial role for differentiation and/or maturation of NK progenitors into functional NK cells. Several members of the zinc finger, ETS, and interferon regulatory factor transcription factor families are also involved in the lineage commitment of hematopoietic stem or progenitors into NK cells. Animal models as well as patients deficient in NK cells have provided formal evidence that NK cells play an important role in vivo for innate immunity against tumors and viral infections and for linkage to adaptive immunity. Moreover, recent studies have revealed novel human NK cell subsets in peripheral blood that have the phenotypical characteristics CD3- CD16+ CD56+ and CD3- CD16- CD56bright, which are mainly involved in cytotoxicity and cytokine-mediated immunoregulation, respectively.

Upregulation of IL-2 but not IL-15 by allorecognition in human mixed lymphocyte culture

The redundant and pleiotropic effects of cytokines in transplant models have been shown both in vitro and in vivo. IL-2 is clearly not necessary for allograft rejection, possibly due to upregulated IL-15. We examined IL-15 expression using mixed lymphocyte culture (MLC) as an allorecognition model. IL-2 and IL-15 levels were measured by enzyme-linked immunoassay after 120 hours of culture. Cell proliferation in MLC was examined using [(3)H]thymidine uptake in the presence of either anti-IL-2Ralpha chain antibody or anti-IL-2Rgamma chain antibody. While IL-2 was detectable in cell supernates of MLC, IL-15 was not. Stimulation with an Anti-IL-2 gamma chain antibody which blocks the IL-2 gamma chain, a common unit in IL-2/IL-15 receptors, failed to produce additive antiproliferative effects after maximum inhibition by anti-IL-2alpha chain antibody, which is specific for IL-2. In conclusion, experiments in the MLC model suggest that allorecognition upregulates IL-2 but not IL-15 expression.

Interleukin (IL)-15R[alpha]-deficient natural killer cells survive in normal but not IL-15R[alpha]-deficient mice

Natural killer (NK) cells protect hosts against viral pathogens and transformed cells. IL-15 is thought to play a critical role in NK cell development, but its role in the regulation of peripheral NK cells is less well defined. We now find that adoptive transfer of normal NK cells into mice lacking the high affinity interleukin (IL)-15 receptor, IL-15Ralpha, surprisingly results in the abrupt loss of these cells. Moreover, IL-15Ralpha-deficient NK cells can differentiate successfully in radiation bone marrow chimera bearing normal cells. Finally, adoptively transferred IL-15Ralpha-deficient NK cells survive in normal but not IL-15Ralpha-deficient mice. These findings demonstrate that NK cell-independent IL-15Ralpha expression is critical for maintaining peripheral NK cells, while IL-15Ralpha expression on NK cells is not required for this function.

Interleukin-15 interactions with interleukin-15 receptor complexes: characterization and species specificity

Interleukin (IL-) 2 and IL-15 share the IL-2 receptor betagamma c subunits (IL-2Rbetagamma c) but have specific, unique alpha receptor subunits. We studied species specificity of human (hu), simian (si), and mouse (mu) IL-15 and found that hu and si IL-15 behaved similarly in all systems investigated. Hu and mu IL-15 bound hu or mu IL-15Ralpha with equal high affinity in the presence or absence of IL-2Rbetagamma c and exhibited similar proliferative activities on cells containing all three subunits. However, quantitative differences were noted in the specific activity of hu and mu IL-15 in both in vitro and in vivo systems utilizing IL-2Rbetagamma c in the absence of IL-15Ralpha. These data show that hu IL-15 may be used in mouse model systems, however care must be taken when comparing the efficacy and toxicity of cytokines across species.

Systemic administration of IL-15 augments the antigen-specific primary CD8+ T cell response following vaccination with peptide-pulsed dendritic cells

The systemic administration of IL-2 can act as a potent adjuvant for T cell-directed vaccine strategies. However, not only is the administration of IL-2 potentially toxic, but recent evidence suggests that it may also paradoxically limit the duration and magnitude of the cytotoxic T cell response. A recently identified cytokine, IL-15, shares many properties with IL-2 and may provide a preferential means of augmenting T cell-directed vaccine responses. Although well characterized in vitro, there are few data on the ability of IL-15 to augment T cell-mediated responses in vivo. We therefore evaluated the ability of systemic IL-15 to function as a T cell adjuvant in a murine vaccine model. To establish a population of easily identifiable Ag-responsive T cells, naive CD8(+) (OT-1) T cells were first adoptively transferred into mice. Vaccination with peptide-pulsed dendritic cells induced a modest expansion of OT-1 T cells. The addition of systemic IL-15 for 7 days following vaccination resulted in a significant increase in the expansion of responding T cells in the PBL, spleen, and lymph nodes. Importantly, the responding T cells were cytotoxic and maintained a Tc1-biased phenotype. We did not observe either enhanced resistance to activation-induced cell death or preferential generation of memory T cells as a result of treatment with IL-15 compared with IL-2. These studies show for the first time that IL-15 is capable of augmenting the primary CD8(+) T cell response to vaccination and contribute to the basis for future experiments exploring the clinical role of IL-15.

Development and characterization of monoclonal antibodies to chicken interleukin-15

The chicken IL-15 gene was recently cloned and shown to encode a polypeptide with T cell growth factor activity similar to IL-2. To further characterize the chemical and biological properties of chicken IL-15, we generated a panel of monoclonal antibodies against bacterially expressed protein and characterized their binding specificities. All antibodies were reactive by ELISA with recombinant IL-15, but not IL-2, and identified a 15kDa recombinant chicken IL-15 by Western blot analysis. Two antibodies inhibited IL-15-induced proliferation of splenic lymphoblast cells. These monoclonal antibodies will be useful for further structural and immunological studies of chicken IL-15.

The contrasting roles of IL-2 and IL-15 in the life and death of lymphocytes: implications for the immunotherapy of rheumatological diseases

Interleukin-15 (IL-15) is a 14-15-kDa member of the 4alpha helix bundle family of cytokines that stimulate T and NK (natural killer) cells. IL-15 and IL-2 utilize heterotrimeric receptors that include the cytokine-specific private receptors IL-2Ralpha and IL-15Ralpha, as well as two receptor elements that they share, IL-2Rbeta and gammac. Although IL-2 and IL-15 share two receptor subunits and many functions, at times they provide contrasting contributions to T-cell-mediated immune responses. IL-2, through its pivotal role in activation-induced cell death (AICD), is involved in peripheral tolerance through the elimination of self-reactive T cells. In contrast, IL-15 in general manifests anti-apoptotic actions and inhibits IL-2-mediated AICD. IL-15 stimulates the persistence of memory phenotype CD8+ T cells, whereas IL-2 inhibits their expression. Abnormalities of IL-15 expression have been described in patients with rheumatoid arthritis or inflammatory bowel disease and in diseases associated with the retrovirus HTLV-I (human T-cell lymphotropic virus I). Humanized monoclonal antibodies that recognize IL-2Ralpha, the private receptor for IL-2, are being employed to inhibit allograft rejection and to treat T-cell leukemia/lymphoma. New approaches directed toward inhibiting the actions of the inflammatory cytokine, IL-15, are proposed for an array of autoimmune disorders including rheumatoid arthritis as well as diseases associated with the retrovirus HTLV-I.

Interleukin-2 and interleukin-15: immunotherapy for cancer

Interleukin (IL)-2 and IL-15 are two cytokine growth factors that regulate lymphocyte function and homeostasis. Early clinical interest in the use of IL-2 in the immunotherapy of renal cell carcinoma and malignant melanoma demonstrated the first efficacy for cytokine monotherapy in the treatment of neoplastic disease. Advances in our understanding of the cellular and molecular biology of IL-2 and its receptor complex have provided rationale to better utilize IL-2 to expand and activate immune effectors in patients with cancer. Exciting new developments in monoclonal antibodies recognizing tumor targets and tumor vaccines have provided new avenues to combine with IL-2 therapy in cancer patients. IL-15, initially thought to mediate similar biological effects as IL-2, has been shown to have unique properties in basic and pre-clinical studies that may be of benefit in the immunotherapy of cancer. This review first summarizes the differences between IL-2 and IL-15 and highlights that better understanding of normal physiology creates new ideas for the immunotherapy of cancer. The application of high, intermediate, and low/ultra low dose IL-2 therapy in clinical trials of cancer patients is discussed, along with new avenues for its use in neoplastic diseases. The growing basic and pre-clinical evidence demonstrating that IL-15 may be useful in immunotherapy approaches to cancer is also presented.

Innate immunity to Mycobacterium tuberculosis

The different manifestations of infection with Mycobacterium tuberculosis reflect the balance between the bacillus and host defense mechanisms. Traditionally, protective immunity to tuberculosis has been ascribed to T-cell-mediated immunity, with CD4(+) T cells playing a crucial role. Recent immunological and genetic studies support the long-standing notion that innate immunity is also relevant in tuberculosis. In this review, emphasis is on these natural, innate host defense mechanisms, referring to experimental data (e.g., studies in gene knockout mice) and epidemiological, immunological, and genetic studies in human tuberculosis. The first step in the innate host defense is cellular uptake of M. tuberculosis, which involves different cellular receptors and humoral factors. Toll-like receptors seem to play a crucial role in immune recognition of M. tuberculosis, which is the next step. The subsequent inflammatory response is regulated by production of pro- and anti-inflammatory cytokines and chemokines. Different natural effector mechanisms for killing of M. tuberculosis have now been identified. Finally, the innate host response is necessary for induction of adaptive immunity to M. tuberculosis. These basic mechanisms augment our understanding of disease pathogenesis and clinical course and will be of help in designing adjunctive treatment strategies.

Interleukin-15 inhibits spontaneous apoptosis in human eosinophils via autocrine production of granulocyte macrophage-colony stimulating factor and nuclear factor-kappaB activation

Prolonged eosinophil survival, i.e., reduced apoptosis, is implicated in the pathogenesis of chronic allergic inflammation. Here we demonstrate that interleukin (IL)-15, in the presence or absence of tumor necrosis factor (TNF)-alpha, reduces spontaneous apoptosis in freshly isolated human eosinophils. The prosurvival effect of IL-15 was abrogated by neutralizing antibody to granulocyte macrophage-colony stimulating factor (GM-CSF), although GM-CSF was not detected in conditioned media by ELISA. Additionally, the effect of IL-15 on spontaneous eosinophil apoptosis appeared to require nuclear factor-kappaB (NF-kappaB) activation based on evidence for NF-kappaB nuclear translocation and abrogation of the effect by the NF-kappaB inhibitor, Bay 11- 7082. Finally, the data demonstrate that IL-15 expression is higher in the submucosa of endobronchial tissues from subjects with moderate to severe asthma when compared with control subjects. Thus, our results suggest that IL-15, either alone or in combination with TNF-alpha, may perpetuate allergic inflammation by reduction of spontaneous eosinophil apoptosis through autocrine production of GM-CSF and NF-kappaB activation.

CD4(+) T cells are required for the development of cytotoxic CD8(+) T cells during Mycobacterium tuberculosis infection

The control of acute and chronic Mycobacterium tuberculosis infection is dependent on CD4(+) T cells. In a variety of systems CD8(+) T cell effector responses are dependent on CD4(+) T cell help. The development of CD8(+) T cell-mediated immune responses in the absence of CD4(+) T cells was investigated in a murine model of acute tuberculosis. In vitro and in vivo, priming of mycobacteria-specific CD8(+) T cells was unaffected by the absence of CD4(+) T cells. Infiltration of CD8(+) T cells into infected lungs of CD4(-/-) or wild-type mice was similar. IFN-gamma production by lung CD8(+) T cells in CD4(-/-) and wild-type mice was also comparable, suggesting that emergence of IFN-gamma-producing mycobacteria-specific CD8(+) T cells in the lungs was independent of CD4(+) T cell help. In contrast, cytotoxic activity of CD8(+) T cells from lungs of M. tuberculosis-infected mice was impaired in CD4(-/-) mice. Expression of mRNA for IL-2 and IL-15, cytokines critical for the development of cytotoxic effector cells, was diminished in the lungs of M. tuberculosis-infected CD4(-/-) mice. As tuberculosis is frequently associated with HIV infection and a subsequent loss of CD4(+) T cells, understanding the interaction between CD4(+) and CD8(+) T cell subsets during the immune response to M. tuberculosis is imperative for the design of successful vaccination strategies.

Production and characterization of monoclonal antibodies reactive with the chicken interleukin-15 receptor alpha chain

We recently cloned the genes encoding chicken IL-15 and IL-15 receptor (R) alpha proteins. In this study, 12 monoclonal antibodies (mAbs) against recombinant chicken IL-15Ralpha were produced and characterized. By enzyme-linked immunosorbent assay (ELISA), all mAbs showed binding specificity for IL-15Ralpha, but not IL-2 or interferon-gamma, and identified a 25.0kDa protein by immunoblot analysis. Flow cytometric analysis revealed negligible expression of IL-15Ralpha on non-activated lymphocytes from the spleen, thymus or bursa, low but detectable expression on macrophages and high expression on concanavalin A-activated spleen lymphoblasts. Established chicken T cell (RP13) and macrophage (HD11) cell lines expressed substantially higher levels of IL-15Ralpha compared with a B cell line (RP9). Two mAbs inhibited IL-15 dependent proliferation of T cells suggesting that the tertiary structure of the protein domain of native IL-15Ralpha that binds to IL-15 is preserved in the recombinant receptor molecule. These mAbs will be useful reagents for further in vitro and in vivo studies of the biological functions of chicken IL-15 and its receptor.

Interleukin-15 and interleukin-2 enhance non-REM sleep in rabbits

Interleukin (IL)-15 and -2 share receptor- and signal-transduction pathway (Jak-STAT pathway) components. IL-2 is somnogenic in rats but has not been tested in other species. Furthermore, the effects of IL-15 on sleep have not heretofore been described. We investigated the somnogenic actions of IL-15 in rabbits and compared them with those of IL-2. Three doses of IL-15 or -2 (10, 100, and 500 ng) were injected intracerebroventriculary at the onset of the dark period. In addition, 500 ng of IL-15 and -2 were injected 3 h after the beginning of the light period. IL-15 dose dependently increased non-rapid eye movement sleep (NREMS) and induced fever. IL-15 inhibited rapid eye movement sleep (REMS) after its administration during the light period; however, all doses of IL-15 failed to affect REMS if given at dark onset. IL-2 also dose dependently increased NREMS and fever. IL-2 inhibited REMS, and this effect was observed only in the light period. IL-15 and -2 enhanced electroencephalographic (EEG) slow waves during the initial 9-h postinjection period, then, during hours 10-23 postinjection, reduced EEG slow-wave activity. Current data support the notion that the brain cytokine network is involved in the regulation of sleep.