Overexpression of IL-15 in vivo enhances Tc1 response, which inhibits allergic inflammation in a murine model of asthma

The IL-15 / sIL-15Rα complex modulates immunity without effect on asthma features in mouse

BACKGROUND

Interleukin 15 (IL-15) is a growth and modulating factor for B, T lymphocytes and natural killer cells (NK). Its action on innate and adaptive immunity is modulated by its alpha chain receptor (IL-15Rα). The IL-15/sIL-15Rα complex (IL-15Cx) increases the bioavailability and activity of the cytokine in vivo. IL-15Cx has been used in diseases to dampen IL-15 inflammation by the use of soluble IL-15Ralpha specificity. Here, we aim to evaluate the interest of IL-15Cx in a mouse model of asthma.

METHODS

Using a mouse model of asthma consisting in percutaneous sensitization and intranasal challenge with total house dust mite extract, we evaluated the effect of IL-15Cx injected intraperitoneally four times after a first nasal challenge. Respiratory function was assessed by the technique of forced oscillations (Flexivent®). The effect on bronchial remodeling was evaluated by lung histology. The inflammatory status was analyzed by flow cytometry.

RESULTS

We observed that the IL-15Cx modulates lung and systemic inflammation by increasing NK cells, CD8⁺ memory T cells and regulatory cells. However, IL-15Cx displays no effect on bronchial hyperreactivity, bronchial remodeling nor cellular bronchial infiltrate, but limits the secretion of bronchial mucus and modulates only inflammatory response in a HDM-allergic asthma murine model.

CONCLUSIONS

IL-15Cx has a limited effect on immune response in asthma and has no effect on lung function in mice. Thus, it limits its therapeutic potential but might suggest a combinatory potential with other therapeutics.

Distinct transcriptomic profiles of early-onset atopic dermatitis in blood and skin of pediatric patients

BACKGROUND

Atopic dermatitis (AD) predominantly affects young children, but our understanding of AD pathogenesis is based on skin and blood samples from long-standing adult AD. Genomic biopsy profiling from early pediatric AD showed significant Th2 and Th17/Th22-skewing, without the characteristic adult Th1 up-regulation. Because obtaining pediatric biopsies is difficult, blood gene expression profiling may provide a surrogate for the pediatric skin signature.

OBJECTIVE

To define the blood profile and associated biomarkers of early moderate-to-severe pediatric AD.

METHODS

We compared microarrays and reverse transcription polymerase chain reaction (RT-PCR) of blood cells from 28 AD children (<5 years and within 6 months of disease onset) to healthy control blood cells. Differentially expressed genes (DEGs) in blood (fold change [FCH] > 1.2 and false discovery rate [FDR] < 0.05) were then compared with skin DEGs.

RESULTS

Eosinophil and Th2 markers (IL5RA, IL1RL1/ST2, HRH4, CCR3, SIGLEC8, PRSS33, CLC from gene arrays; IL13/IL4/CCL22 from RT-PCR) were up-regulated in early pediatric AD blood, whereas IFNG/Th1 was decreased. Th1 markers were negatively correlated with clinical severity (EASI, pruritus, transepidermal water loss [TEWL]), whereas Th2/Th17-induced interleukin (IL)-19 was positively correlated with SCORAD. Although a few RT-PCR-defined immune markers (IL-13/CCL22) were increased in blood, as previously also reported for skin, minimal overlap based on gene array DEGs was seen.

CONCLUSION

The whole blood signature of early moderate-to-severe pediatric AD blood cells show predominantly a Th2/eosinophil profile; however, markers largely differ from the skin profile. Given their complementarity, pooling of biomarkers from blood and skin may improve profiling and predictions, providing insight regarding disease course, allergic comorbidity development, and response to systemic medications.

OK-432 Administration Inhibits Murine Allergic Rhinitis at the Induction Phase, through the Macrophage Activation with TLR2 Signaling Pathway

OK-432, a preparation of a low-virulence strain (Su) of Streptococcus pyogenes (Group A) killed by a penicillin and lyophilized, is a stiff inducer of Th1 cytokines, and exerts anti-cancer effects in tumor-bearing mice. OK-432 has been reported to consist of many bacterial components, such as peptidoglycan, M-protein, etc. However, it is yet to be ascertained which bacterial component induces T helper 1 (Th1) responses. For the last decade, Toll-like receptor (TLR) family proteins are well elucidated to play a role in recognizing bacterial components and inducing interleukin (IL)-12 from macrophages. Above all, peptidoglycan seems to be the agonist of TLR2 rather than the obverse. In our present study, the role of TLR2 for the recognition of OK-432 by macrophages and the effects of OK-432 are examined on murine allergic rhinitis model. Interestingly, results show IL-12 production by macrophages derived from TLR2 knock-out (ko) mice was significantly decreased, in comparison with that of macrophages derived from wild-type mice. Moreover, in TLR2 ko mice, no regulatory effect of OK-432 was observed on an allergic rhinitis model. These data indicate that TLR2 signaling is involved in regulating OK-432-induced anti-T helper 2 (Th2) immunity, and may offer a new prophylactic and therapeutic approach using OK-432 to downregulate allergic disorders, such as allergic rhinitis.

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.

IL-15-deficient mice develop enhanced allergic responses to airway allergen exposure

BACKGROUND

Interleukin-15 is a pleiotropic cytokine that is critical for the development and survival of multiple haematopoietic lineages. Mice lacking IL-15 have selective defects in populations of several pro-allergic immune cells including natural killer (NK) cells, NKT cells, and memory CD8⁺ T cells. We therefore hypothesized that IL-15^-/- mice will have reduced inflammatory responses during the development of allergic airway disease (AAD).

OBJECTIVE

To determine whether IL-15^-/- mice have attenuated allergic responses in a mouse model of AAD.

METHODS

C57BL/6 wild-type (WT) and IL-15^-/- mice were sensitized and challenged with ovalbumin (OVA), and the development of AAD was ascertained by examining changes in airway inflammatory responses, Th2 responses, and lung histopathology.

RESULTS

Here, we report that IL-15^-/- mice developed enhanced allergic responses in an OVA-induced model of AAD. In the absence of IL-15, OVA-challenged mice exhibited enhanced bronchial eosinophilic inflammation, elevated IL-13 production, and severe lung histopathology in comparison with WT mice. In addition, increased numbers of CD4⁺ T and B cells in the spleens and bronchoalveolar lavage (BAL) were also observed. Examination of OVA-challenged IL-15Rα^-/- animals revealed a similar phenotype resulting in enhanced airway eosinophilia compared to WT mice. Adoptive transfer of splenic CD8⁺ T cells from OVA-sensitized WT mice suppressed the enhancement of eosinophilia in IL-15^-/- animals to levels observed in WT mice, but had no further effects.

CONCLUSION AND CLINICAL RELEVANCE

These data demonstrate that mice with an endogenous IL-15 deficiency are susceptible to the development of severe, enhanced Th2-mediated AAD, which can be regulated by CD8⁺ T cells. Furthermore, the development of disease as well as allergen-specific Th2 responses occurs despite deficiencies in several IL-15-dependent cell types including NK, NKT, and γδ T cells, suggesting that these cells or their subsets are dispensable for the induction of AAD in IL-15-deficient mice.

CD4⁺ and CD8⁺ T cells play a central role in a HDM driven model of allergic asthma

Background

The incidence of asthma is increasing at an alarming rate and while the current available therapies are effective in the majority of patients they fail to adequately control symptoms at the more severe end of the disease spectrum. In the search to understand disease pathogenesis and find effective therapies animal models are often employed. As exposure to house dust mite (HDM) has a causative link, it is thought of as the allergen of choice for modelling asthma.

The objective was to develop a HDM driven model of asthmatic sensitisation and characterise the role of key allergic effector cells/mediators.

Methods

Mice were sensitised with low doses of HDM and then subsequently challenged. Cellular inflammation, IgE and airway responsiveness (AHR) was assessed in wild type mice or CD4⁺/CD8⁺ T cells, B cells or IgE knock out mice.

Results

Only those mice sensitised with HDM responded to subsequent low dose topical challenge. Similar to the classical ovalbumin model, there was no requirement for systemic alum sensitisation. Characterisation of the role of effector cells demonstrated that the allergic cellular inflammation and AHR was dependent on CD4⁺ and CD8⁺ T cells but not B cells or IgE. Finally, we show that this model, unlike the classic OVA model, appears to be resistant to developing tolerance.

Conclusions

This CD4⁺/CD8⁺ T cell dependent, HDM driven model of allergic asthma exhibits key features of asthma. Furthermore, we suggest that the ability to repeat challenge with HDM means this model is amenable to studies exploring the effect of therapeutic dosing in chronic, established disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-016-0359-y) contains supplementary material, which is available to authorized users.

Lymphocyte-based model systems for allergy research: a historic overview

During the last decades, a multitude of studies applying distinct in vitro and in vivo model systems have contributed greatly to our better understanding of the initiation and regulation of inflammatory processes leading to allergic diseases. Over the years, it has become evident that among lymphocytes, not only IgE-producing B cells and allergy-orchestrating CD4(+) helper cells but also cytotoxic CD8(+) T cells, γδ-T cells and innate lymphoid cells, as well as regulatory lymphocytes, might critically shape the immune response towards usually innocuous allergens. In this review, we provide a historic overview of pioneering work leading to the establishment of important lymphocyte-based model systems for allergy research. Moreover, we contrast the original findings with our currently more refined knowledge to appreciate the actual validity of the respective models and to reassess the conclusions obtained from them. Conflicting studies and interpretations are identified and discussed. The tables are intended to provide an easy overview of the field not only for scientists newly entering the field but also for the broader readership interested in updating their knowledge. Along those lines, herein we discuss in vitro and in vivo approaches to the investigation of lymphocyte effector cell activation, polarization and regulation, and describe depletion and adoptive transfer models along with gene knockout and transgenic (tg) methodologies. In addition, novel attempts to establish humanized T cell antigen receptor tg mouse models for allergy research are described and discussed.

Novel identified receptors on mast cells

Mast cells (MC) are major participants in the allergic reaction. In addition they possess immunomodulatory roles in the innate and adaptive immune reactions. Their functions are modulated through a number of activating and inhibitory receptors expressed on their surface. This review deals with some of the most recently described receptors, their expression patterns, ligand(s), signal transduction mechanisms, possible cross-talk with other receptors and, last but not least, regulatory functions that the MC can perform based on their receptor expression in health or in disease. Where the receptor role on MC is still not clear, evidences from other hematopoietic cells expressing them is provided as a possible insight for their function on MC. Suggested strategies to modulate these receptors’ activity for the purpose of therapeutic intervention are also discussed.

Effect of IL-15 on IgG versus IgE antibody-secreting cells in vitro

Immunoglobulin E (IgE) antibodies are major contributors to the pathology of atopic and allergic diseases as well as to immune response to helminth infections. Development of an adequate immunoglobulin G (IgG) immune response against infectious agents and vaccine antigens is considered in most cases as crucial for protection from disease. In vivo and in vitro production of IgE and IgG depends on cytokines and other soluble factors. Recently it has been shown that IgG antibody secreting cells (ASCs) can be generated by in vitro maturation of blood cells with Interleukin- (IL-)15 and CpG DNA or other stimulation cocktails, while IgE-ASCs develop upon cultivation with anti-CD40 and IL-4. In the present study we employed an enzyme linked immunospot assay (ELISPOT) to assess the capacity of individuals to develop into either IgE-ASCs or IgG-ASCs upon stimulation with different combinations of stimulation cocktails in order to investigate the influence of cytokines that are dysregulated in IgE-mediated immune reactions on ASC generation. Furthermore, we modified the method to assess IgG- and IgE-ASCs specific for two model antigens causing allergic rhinitis in humans. We demonstrate that IL-15, which is important for development of IgG-ASCs, decreases the number of IgE-ASCs when added to media commonly used for in vitro development of IgE-ASCs. We show that our method is suitable for the detection of specific and non-specific IgE-ASCs and IgG-ASCs and allows the investigation of the interplay between IgG-ASCs and IgE-ASCs in different populations.

Treatment of allergic asthma: modulation of Th2 cells and their responses

Atopic asthma is a chronic inflammatory pulmonary disease characterised by recurrent episodes of wheezy, laboured breathing with an underlying Th2 cell-mediated inflammatory response in the airways. It is currently treated and, more or less, controlled depending on severity, with bronchodilators e.g. long-acting beta agonists and long-acting muscarinic antagonists or anti-inflammatory drugs such as corticosteroids (inhaled or oral), leukotriene modifiers, theophyline and anti-IgE therapy. Unfortunately, none of these treatments are curative and some asthmatic patients do not respond to intense anti-inflammatory therapies. Additionally, the use of long-term oral steroids has many undesired side effects. For this reason, novel and more effective drugs are needed. In this review, we focus on the CD4+ Th2 cells and their products as targets for the development of new drugs to add to the current armamentarium as adjuncts or as potential stand-alone treatments for allergic asthma. We argue that in early disease, the reduction or elimination of allergen-specific Th2 cells will reduce the consequences of repeated allergic inflammatory responses such as lung remodelling without causing generalised immunosuppression.

Modulation of NK cell autocrine-induced eosinophil chemotaxis by interleukin-15 and vitamin D(3): a possible NK-eosinophil crosstalk via IL-8 in the pathophysiology of allergic rhinitis

Natural killer cells (NK) secrete eosinophilotactic cytokines, however, whether they contribute to eosinophil chemotaxis by secreting IL-8 is not known. We investigated the ability of CD56+CD3-ve (NK cells) to induce chemotaxis of peripheral blood eosinophils from allergic rhinitis (AR) patients, through IL-8 secretion, and the effects of IL-15, the NK cell proactivating cytokine, and calcitriol: 1α, 25-dihydroxy Vitamin D₃ (vitamin D₃), the immunomodulator agent, in this scenario. Herein, it is shown that supernatants from unstimulated NK cells exhibited chemotactic activity against eosinophil. This effect was significantly augmented by IL-15 (1 ng/mL) treatment, resulting in an increase in the chemotactic index of approximately 3 folds and was abrogated by neutralizing antibody (Ab) to IL-8 in a dose-dependent fashion. The amount of IL-8 secreted by NK cells was increased by IL-15 treatment from levels of 88.64 ± 21.5 to 178.9 ± 23.6 Pg/mL and was significantly reduced by 10⁻⁶ M vitamin D₃ to levels of 59.2 ± 16.3 Pg/mL. Our results indicate a novel inflammatory crosstalk between NK cells and eosinophils via IL-15/IL-8 axis that can be modulated by vitamin D₃.

T cell subsets related with a sex difference in IL-5 production

BACKGROUND

Before puberty, the prevalence and severity of asthma are higher in boys than in girls, but this pattern is reversed after puberty. The underlying mechanisms of these gender differences in asthma are not fully understood. Using murine models of allergic asthma, a sex difference in Th2 cytokine production has been suggested to contribute to the gender differences in asthma. Therefore, we determined which subsets of T cells are involved in the sex difference in Th2 cytokine production.

METHODS

Splenocytes from wild-type mice and CD4+ T cell-, CD8+ T cell-, and iNKT cell-deficient mice were stimulated with anti-CD3/CD28 antibodies for 3 days, and the concentrations of IL-4, IL-5, IL-13, and IFN-γ in the cultures were measured by ELISA.

RESULTS

IL-5, but not IL-4 and IL-13, concentrations in culture derived from female wild-type mice were significantly higher than those in male wild-type mice. The sex difference in IL-5 concentrations was not observed in the cultures of splenocytes from CD4+ and CD8+ T cell-deficient mice. The disappearance of the sex differences in CD4+ and CD8+ T cell-deficient mice was attributable to a decrease in IL-5 concentration in female mice and an increase in IL-5 concentration in male mice. In iNKT cell-deficient mice, the sex difference was still observed. There was no significant difference between the sexes in any type of mice with respect to IFN-γ production.

CONCLUSIONS

There was a sex difference in IL-5 production by splenocytes stimulated by TCR activation. The difference might be attributable to sex differences in CD4+ and CD8+ T cell functions.

Interleukins, from 1 to 37, and interferon-γ: receptors, functions, and roles in diseases

Advancing our understanding of mechanisms of immune regulation in allergy, asthma, autoimmune diseases, tumor development, organ transplantation, and chronic infections could lead to effective and targeted therapies. Subsets of immune and inflammatory cells interact via ILs and IFNs; reciprocal regulation and counter balance among T(h) and regulatory T cells, as well as subsets of B cells, offer opportunities for immune interventions. Here, we review current knowledge about ILs 1 to 37 and IFN-γ. Our understanding of the effects of ILs has greatly increased since the discoveries of monocyte IL (called IL-1) and lymphocyte IL (called IL-2); more than 40 cytokines are now designated as ILs. Studies of transgenic or knockout mice with altered expression of these cytokines or their receptors and analyses of mutations and polymorphisms in human genes that encode these products have provided important information about IL and IFN functions. We discuss their signaling pathways, cellular sources, targets, roles in immune regulation and cellular networks, roles in allergy and asthma, and roles in defense against infections.

Functional involvement of dual specificity phosphatase 16 (DUSP16), a c-Jun N-terminal kinase-specific phosphatase, in the regulation of T helper cell differentiation

Naïve CD4(+) T helper (Th) cells differentiate into distinct subsets of effector cells (Th1, Th2, Th17, and induced regulatory T cells (iTreg)) expressing different sets of cytokines upon encounter with presented foreign antigens. It has been well established that Th1/Th2 balance is critical for the nature of the following immune responses. Previous reports have demonstrated important roles of c-Jun N-terminal kinase (JNK) in Th1/Th2 balance, whereas the regulatory mechanisms of JNK activity in Th cells have not been elucidated. Here, we show that dual specificity phosphatase 16 (DUSP16, also referred to as MKP-M or MKP-7), which preferentially inactivates JNK, is selectively expressed in Th2 cells. In the in vitro differentiation assay of naïve CD4(+) cells, DUSP16 expression is up-regulated during Th2 differentiation and down-regulated during Th1 differentiation. Chromatin immunoprecipitation revealed the increased acetylation of histone H3/H4 at the dusp16 gene promoter in CD4(+) T cells under the Th2 condition. Adenoviral transduction of naïve CD4(+) T cells with DUSP16 resulted in increased mRNA expression of IL-4 and GATA-3 in Th2 and decreased expression of IFNγ and T-bet in Th1 differentiation. In contrast, transduction of a dominant negative form of DUSP16 had the reverse effects. Furthermore, upon immunization, T cell-specific dusp16 transgenic mice produced antigen-specific IgG2a at lower amounts, whereas DN dusp16 transgenic mice produced higher amounts of antigen-specific IgG2a accompanied by decreased amounts of antigen-specific IgG1 and IgE than those of control mice. Together, these data suggest the functional role of DUSP16 in Th1/Th2 balance.

Increase of Th2 and Tc1 cells in patients with Kimura's disease

OBJECTIVE

A Th1/Th2 cytokine imbalance with a predominance of Th2 cytokines has been suggested to be of pathogenic importance in Kimura's disease.

METHODS

To evaluate the role of Th1/Th2 cytokines in Kimura's disease, the subsets of Th1, Th2, Tc1 and Tc2 cells from patients with Kimura's disease were examined by intracellular cytokine flow cytometry. The expressions of IL-5, eotaxin and RANTES in the lesions were investigated by RT-PCR.

RESULTS

The population of Th2 and Tc1 cells in Kimura's disease was significantly increased compared with these cells in control (p<0.05). Th1 and Tc2 cells in Kimura's disease were not significantly increased compared with control subjects. The titers of IgE and the number of Th2 cells were correlated. The expression of IL-5 and RANES was observed in the lesions of patients with Kimura's disease.

CONCLUSION

These results indicate that the predominance of Th2 and Tc1 cells might contribute to the mechanism in pathogenesis of Kimura's disease.

Toll-like receptor 7-triggered immune response in the lung mediates acute and long-lasting suppression of experimental asthma

RATIONALE

Toll-like receptor (TLR) 7/8 ligands are promising candidate drugs for the treatment of allergic asthma and rhinitis. Although their clinical application depends on the development of strategies for topical administration to the lung, this has not been explored in preclinical disease models.

OBJECTIVES

To examine the therapeutic effectiveness, persistence of effect, and mode of action of intranasal TLR7 ligand administration in allergic airway disease.

METHODS

Wild-type, IFN-alpha receptor (IFN-alphaR)(-/-), IFN-gamma(-/-), CD8(-/-), TLR7(-/-), and radiation-induced chimeric mice deficient in hematopoietic TLR7 expression were subjected to an established model of allergic airway disease. R-848, a specific TLR7 agonist in mice, was administered prophylactically or therapeutically and effects of treatment on helper T-cell type 2 (Th2) responses, eosinophilia, goblet cell metaplasia, and airway hyperresponsiveness were assessed.

MEASUREMENTS AND MAIN RESULTS

Intranasal R-848 administration induced a transient immune response characterized by type I interferon production and infiltration of innate immune cells into the lung. This conferred long-term suppression of allergic airway disease via two complementary molecular processes, one mediated by type I interferons and providing acute protection by directly inhibiting effector Th2 responses, and one mediated by immunoregulatory CD8(+) T cells and inducing long-lasting protection by suppressing Th2 responses in an IFN-gamma-dependent manner.

CONCLUSIONS

Intranasal R-848 administration is an effective treatment for allergic airway disease. It hijacks an otherwise proinflammatory immune process triggered by TLR7 to mediate long-lasting disease suppression. This provides important insight into the efficacy and mode of action of TLR7 ligands in murine models of allergic airway disease and paves the way for their clinical application in humans.

CD8+ T cells in asthma: friend or foe?

While it is well established that CD4(+) T lymphocytes play a crucial role in the initiation, progression and persistence of asthma, the role of CD8(+) T cells is less understood. CD8(+) T cells form functionally similar subsets which exhibit similar cytokine profiles as Th1 and Th2 cells, known as Tc1 and Tc2. Evidence from animal studies suggest that CD8(+) T cells are capable of regulating IgE production through the induction of IL-12 and IL-18 production in dendritic cells, and that CD8(+) T cells may act to moderate Th2 polarisation within the localised lymph nodes during allergic sensitisation. Such findings have led to the suggestion that Th1 polarising, CD8(+) T cell-inducing vaccines would inhibit the development of airway hyperresponsiveness (AHR) and Th2 cell infiltration. Despite these positive findings, the role of CD8(+) T cells within the lung remains poorly understood. While CD8(+) T cells, particularly those expressing the Tc1 phenotype, are capable of moderating inflammation and suppressing AHR, it has been postulated that Tc2 CD8(+) T cells predominate within established asthma and may act to amplify the inappropriate immune response which defines the condition. Within the clinic, the association between CD8(+) T cells and asthma is almost universally defined as injurious, further suggesting a prejudicial role for these cells within the established disease. CD8(+) T cells may be a valuable potential target for therapeutic intervention, either by potentiating their regulatory effects prior to the development of sensitisation, or through suppressing their pro-inflammatory properties within established atopy.

Innate responsiveness of CD8 memory T-cell populations nonspecifically inhibits allergic sensitization

BACKGROUND

Infection or stimulation of the innate immune system by nonspecific microbial antigens is thought to educate the immune system to respond appropriately to allergens, preventing allergy.

OBJECTIVE

To determine the immunologic pathways that might explain how infection/microbial exposure inhibits allergic sensitization.

METHODS

Immunologic studies of non-antigen-specific functions of CD8 memory cells, their maturation in vivo, and their effects in a mouse asthma model, to test the hypothesis that CD8 memory is shaped by innate immunity in a way that can inhibit allergic disease.

RESULTS

We found that CD8 memory T-cell (CD8 Tm) populations bridge innate and adaptive immunity by responding to either antigen or cytokines alone. CD8 Tm populations partially subvert the clonal selection process by activating their neighbors through induction of dendritic cell IL-12. Stimulation of innate or acquired immunity in the lung or gut causes expansion/maturation of CD8 Tm populations, which provide an early source of cytokines, enhance T(H)1 immunity, and inhibit allergic sensitization and airway inflammation/hyperresponsiveness in a non-antigen-specific fashion.

CONCLUSION

CD8 T-cell-mediated immune memory is long-lived and can retain its capacity for rapid cytokine release in a nonantigen-specific fashion. This novel type of memory enhances T(H)1 over T(H)2 immunity and prevents allergic sensitization after exposure to environmental antigens or infection.

New drugs targeting Th2 lymphocytes in asthma

Asthma represents a profound worldwide public health problem. The most effective anti-asthmatic drugs currently available include inhaled beta2-agonists and glucocorticoids and control asthma in about 90-95% of patients. The current asthma therapies are not cures and symptoms return soon after treatment is stopped even after long term therapy. Although glucocorticoids are highly effective in controlling the inflammatory process in asthma, they appear to have little effect on the lower airway remodelling processes that appear to play a role in the pathophysiology of asthma at currently prescribed doses. The development of novel drugs may allow resolution of these changes. In addition, severe glucocorticoid-dependent and resistant asthma presents a great clinical burden and reducing the side-effects of glucocorticoids using novel steroid-sparing agents is needed. Furthermore, the mechanisms involved in the persistence of inflammation are poorly understood and the reasons why some patients have severe life threatening asthma and others have very mild disease are still unknown. Drug development for asthma has been directed at improving currently available drugs and findings new compounds that usually target the Th2-driven airway inflammatory response. Considering the apparently central role of T lymphocytes in the pathogenesis of asthma, drugs targeting disease-inducing Th2 cells are promising therapeutic strategies. However, although animal models of asthma suggest that this is feasible, the translation of these types of studies for the treatment of human asthma remains poor due to the limitations of the models currently used. The myriad of new compounds that are in development directed to modulate Th2 cells recruitment and/or activation will clarify in the near future the relative importance of these cells and their mediators in the complex interactions with the other pro-inflammatory/anti-inflammatory cells and mediators responsible of the different asthmatic phenotypes. Some of these new Th2-oriented strategies may in the future not only control symptoms and modify the natural course of asthma, but also potentially prevent or cure the disease.

Divergent Effects of Biolistic Gene Transfer in a Mouse Model of Allergic Airway Inflammation

Particle-mediated epidermal delivery (PMED) of allergen genes efficiently prevents systemic sensitization and suppresses specific immunoglobulin E synthesis. We investigated in a mouse model of allergic airway disease the effect of PMED on the elicitation of local inflammatory reactions in the lung. BALB/c mice were biolistically transfected with plasmids encoding beta-galactosidase (betaGal) as model allergen under control of the DC-targeting fascin promoter and the ubiquitously active cytomegalovirus promoter, respectively. Mice were challenged intranasally with betaGal-protein with or without intermediate sensitization with betaGal adsorbed to aluminiumhydroxide. Subsequently, local cytokine production and recruitment of IFN-gamma-producing CD8(+) effector T cells into the airways were determined, and inflammatory parameters such as cellular infiltration in the bronchoalveolar lavage (BAL) and airway hyperresponsiveness (AHR) were measured. PMED of betaGal-encoding plasmids before sensitization significantly reduced frequencies of eosinophils in the BAL and shifted the local T helper (Th) cell response from a distinct Th2 response toward a Th1-biased response. However, AHR triggered by allergen challenge via the airways was not alleviated in vaccinated mice. Most important, we show that PMED using betaGal-encoding DNA without subsequent sensitization recruited Tc1 cells into the lung and caused a Th1-prone local immune response after subsequent intranasal provocation, accompanied by neutrophilic infiltration into the airways and elicitation of AHR. We conclude that robust Th1/Tc1 immune responses, although highly effective in the counter-regulation of local Th2-mediated pathology, might as well trigger local inflammatory reactions in the lung and provoke the induction of AHR in the mouse model of allergic airway disease.

Mechanism of Inflammation in Murine Eosinophilic Myocarditis Produced by Adoptive Transfer with Ovalbumin Challenge

BACKGROUND

Interleukin (IL)-5, RANTES and CC chemokine receptor 3 (CCR3) are essential for induction of eosinophil recruitment in organs, but the precise pathogenesis of eosinophilic myocarditis is still unclear. We investigated the relationships between these cytokines and receptors in the development of inflammation in murine myocarditis produced by adoptive transfer, with reference to eosinophil infiltration and signal transduction.

METHODS

The splenocytes from male donor DBA/2 mice were separated after ovalbumin (OVA) sensitization. These cells had a CD4/CD8 ratio of approximately 3.0. Cells (2.0 x 10(7)) were individually transfused to recipient adoptive male DBA/2 mice, and OVA challenge was performed serially. The heart and spleen of the recipient were analyzed to determine the kinetics of IL-5, RANTES, CCR3 and eosinophil production with simultaneous determination of Janus kinase 3 (JAK3) mRNA.

RESULTS

Approximately 85% of recipient mice developed myocarditis; 35% had recognizable cell infiltration in the left ventricular endocardium, an effect which was absent in control mice. Eosinophilic myocarditis was usually associated with animals having several degenerative changes in myocardial cells, and IL-5, RANTES and CCR3 expressions were usually present in these eosinophils (p < 0.05). CCR3 and JAK3 mRNAs were detected in the spleens and hearts of recipient animals providing histological evidence for kinetics related to eosinophil infiltration.

CONCLUSION

The murine model of adoptive transferred myocarditis is suitable for studying the mechanism of eosinophilic myocarditis. A unique pathogenesis of this disorder may be controlled by the synergism of CD4 dominancy in the donor and JAK-STAT signaling in the recipient, which may cause recruitment of eosinophils into heart lesions.

Interleukin-15 prevents concanavalin A-induced liver injury in mice via NKT cell-dependent mechanism

Administration of concanavalin A (Con A) induces a rapid and severe liver injury in mice. Natural killer T (NKT) cells are recognized to be the key effector cells, and a variety of cytokines [e.g., interleukin 4 (IL-4), IL-5, interferon gamma (IFN-gamma), and tumor necrosis factor alpha (TNF-alpha)] have been shown to play vital roles in Con A-induced liver injury, whereas the role of IL-15, a critical cytokine in the development and homeostasis of NKT cells, remains obscure. In this study, pretreatment with IL-15 prevented mice from Con A-induced mortality, elevation of serum transaminase, liver necrosis, and hepatocyte apoptosis. Depletion of NKT cells abolished Con A-induced liver injury, which could be restored by adoptive transfer of purified NKT cells but not by that of in vivo or in vitro IL-15-treated hepatic NKT cells. Furthermore, transfer of wild-type NKT cells to CD1d-/- mice restored liver injury, whereas transfer of IL-15-treated NKT cells did not. IL-15 pretreatment decreased the NKT-derived IL-4, IL-5, and TNF-alpha production, thereby resulting in less infiltration of eosinophils, which play a critical role in Con A-induced liver injury. In conclusion, IL-15 protects against Con A-induced liver injury via an NKT cell-dependent mechanism by reducing their production of IL-4, IL-5, and infiltration of eosinophils. These findings suggest that IL-15 may be of therapeutic relevance in human autoimmune-related hepatitis.

IL-15 prevents allergic rhinitis through reactivation of antigen-specific CD8+ cells

BACKGROUND

Allergic rhinitis is one of the most common allergic inflammatory diseases characterized by a predominant TH2 response with antigen-specific IgE synthesis. IL-15 plays important roles in activation and maintenance of memory CD8+T cells capable of producing IFN-gamma, which regulates TH2 responses.

OBJECTIVE

To investigate the roles of endogenous IL-15 in allergic inflammation, we examined allergic rhinitis in IL-15 knockout (KO) mice sensitized with ovalbumin followed by intranasal rechallenge with ovalbumin.

METHODS

IL-15KO mice were sensitized intraperitoneally with ovalbumin/complete Freund's adjuvant on day 0 and ovalbumin/IFA on day 7, and then were intranasally challenged with ovalbumin on days 21, 22, 23, 24, and 25. Nasal symptoms and histologic changes were examined. IgE production and TH2 responses were measured by ELISA. Purified CD8+T cells or recombinant IL-15 were administered into ovalbumin-sensitized mice.

RESULTS

The levels of IgE production and TH2 responses in IL-15KO mice were comparable to those in control mice after ovalbumin sensitization. However, sneezing, infiltration of eosinophils into the nasal mucosa, and TH2 cytokine production were aggravated in ovalbumin-sensitized IL-15KO mice after intranasal challenge with ovalbumin. Adoptive transfer of CD8+6 T cells from ovalbumin-sensitized mice suppressed the TH2 responses in mice but not in IL-15KO mice. Administration of IL-15 with ovalbumin significantly prevented the development of allergic rhinitis in ovalbumin-sensitized mice.

CONCLUSION

We demonstrate with IL-15KO mice that endogenous IL-15 plays an important role in suppression of allergic rhinitis at effector phase. Intranasal administration of IL-15 is useful as a therapeutic approach to control allergic rhinitis.

CLINICAL IMPLICATIONS

Intranasal administration of recombinant IL-15 might become new immunotherapy for allergic rhinitis.

Increased GILZ expression in transgenic mice up-regulates Th-2 lymphokines

GILZ (glucocorticoid-induced leucine zipper), a gene induced by dexamethasone, is involved in control of T lymphocyte activation and apoptosis. In the present study, using Gilz transgenic mice (TG), which overexpress GILZ in the T-cell lineage, we demonstrate that Gilz is implicated in T helper-2 (Th-2) response development. After in vitro stimulation by CD3/CD28 antibodies, peripheral naive CD4+ T cells from TG mice secrete more Th-2 cytokines such as interleukin-4 (IL-4), IL-5, IL-13, and IL-10, and produce less Th-1 cytokines such as interferon-gamma (IFN-gamma) than wild-type mice (WT). CD4+ TG lymphocytes up-regulated Th-2 cytokine expression in the specific response to ovalbumin chicken egg (OVA) antigen immunization. Up-regulation correlated with increased expression of GATA-3 and signal transducer and activator of transcription 6 (Stat6), Th-2-specific transcription factors and decreased expression of T-bet, a transcription factor involved in Th-1 differentiation. Finally, in TG mice delayed-type hypersensitivity, a Th-1 response, was inhibited and bleomycin-induced pulmonary fibrosis, a Th-2 mediated disease, was more severe. These results indicate that Gilz contributes to CD4+ commitment toward a Th-2 phenotype and suggest this contribution may be another mechanism accounting for glucocorticoid immunomodulation.

Targeting memory Th2 cells for the treatment of allergic asthma

Th2 memory cells play an important role in the pathogenesis of allergic asthma. Evidence from patients and experimental models indicates that memory Th2 cells reside in the lungs during disease remission and, upon allergen exposure, become activated effectors involved in disease exacerbation. The inhibition of memory Th2 cells or their effector functions in allergic asthma influence disease progression, suggesting their importance as therapeutic targets. They are allergen specific and can potentially be suppressed or eliminated using this specificity. They have distinct activation, differentiation, cell surface phenotype, migration capacity, and effector functions that can be targeted singularly or in combination. Furthermore, memory Th2 cells residing in the lungs can be treated locally. Capitalizing on these unique attributes is important for drug development for allergic asthma. The aim of this review is to present an overview of therapeutic strategies targeting Th2 memory cells in allergic asthma, emphasizing Th2 generation, differentiation, activation, migration, effector function, and survival.

Blocking IL-15 prevents the induction of allergen-specific T cells and allergic inflammation in vivo

IL-15 has been shown to accelerate and boost allergic sensitization in mice. Using a murine model of allergic sensitization to OVA, we present evidence that blocking endogenous IL-15 during the sensitization phase using a soluble IL-15Ralpha (sIL-15Ralpha) suppresses the induction of Ag-specific, Th2-differentiated T cells. This significantly reduces the production of OVA-specific IgE and IgG and prevents the induction of a pulmonary inflammation. Release of proinflammatory TNF-alpha, IL-1beta, IL-6, and IL-12 as well as that of Th2 cytokines IL-4, IL-5, and IL-13 into the bronchi are significantly reduced, resulting in suppressed recruitment of eosinophils and lymphocytes after allergen challenge. It is of clinical relevance that the airway hyper-responsiveness, a major symptom of human asthma bronchiale, is significantly reduced by sIL-15Ralpha treatment. Ex vivo analysis of the draining lymph nodes revealed reduced numbers of CD8, but not CD4, memory cells and the inability of T cells of sIL-15Ralpha-treated mice to proliferate and to produce Th2 cytokines after in vitro OVA restimulation. This phenomenon is not mediated by enhanced numbers of CD4(+)/CD25(+) T cells. These results show that IL-15 is important for the induction of allergen-specific, Th2-differentiated T cells and induction of allergic inflammation in vivo.

Anti-inflammatory role of interleukin-15 in Crohn's disease

BACKGROUND

Interleukin (IL)-15 is overexpressed in intestinal tissue with active Crohn's disease (CD). However, its role in the pathogenesis of the disease remains uncertain. We studied the effects of IL-15 on colonic mucosal proinflammatory cytokine response in vitro using organ culture of human colonic explants.

METHODS

Colonic tissue was obtained from (1) resections in pediatric CD patients (inflamed and noninflamed) and (2) rectal biopsies in patients with CD undergoing colonoscopy (n = 31) and controls (n = 9). In preliminary experiments, explants from the resections were cultured in the presence or absence of a simulated T(H)1 stimulation using ionomycin (Io) and phorbol-myristate-acetate (PMA), with or without IL-15, or in medium alone. Rectal biopsies were cultured in the same conditions as above, with or without adding a monoclonal anti-IL-15 neutralizing antibody (mAb). Levels of interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and IL-2R alpha were measured by enzyme-linked immunosorbent assay.

RESULTS

IL-15, in the absence of Io + PMA, did not induce the expression of IFN-gamma, TNF-alpha, or IL-2R alpha. Only inflamed explants from resections stimulated with Io + PMA expressed IFN-gamma, TNF-alpha, and IL-2R alpha. This T(H)1 stimulatory effect was inhibited by IL-15 in a dose-dependent fashion. In rectal biopsy explants, inflamed, noninflamed CD, and control tissue responded to stimulation with Io + PMA (P < 0.05) with increased IFN-gamma and TNF-alpha (P < 0.05). This response was again inhibited by IL-15. The inhibitory effect of IL-15 was specifically reversed by anti-IL-15 mAb (P < 0.05). The data for the CD group were also analyzed according to the severity of colonic inflammation and medication use.

CONCLUSIONS

Our results suggest a possible anti-inflammatory role for IL-15 in CD. We postulate that its overexpression in CD potentially represents a protective mechanism against the exaggerated T(H)1 immune response.

Donor-derived IL-15 is critical for acute allogeneic graft-versus-host disease

Interleukin-15 (IL-15) is a pleiotropic proinflammatory cytokine with inefficient posttranscriptional processing. We hypothesized that endogenous IL-15 could affect disease progression in the well-described C57Bl/6 (B6)-->(C57Bl/6 x DBA/2) F1 hybrid (B6D2F1) murine model of acute allogeneic graft-versus-host disease (GVHD). B6D2F1 allogeneic recipients received transplants of IL-15(-/-) B6 bone marrow cells or B6 bone marrow cells expressing a murine IL-15 transgene (IL-15 tg) modified for efficient translation and secretion. Mice that received transplants of IL-15(-/-) B6 bone marrow cells displayed a significantly longer median survival time (MST) compared with mice that received transplants of wild-type (wt) B6 bone marrow; in contrast, mice that received transplants of IL-15 tg B6 bone marrow cells had a dramatically decreased MST. This decrease in survival was associated with a substantial activation and expansion of effector-memory (CD44highCD62Llow) CD8+ T lymphocytes. Finally, in vivo depletion of either CD4+ or CD8+ T lymphocyte subsets significantly prolonged survival in mice receiving IL-15 tg B6 marrow, while depletion of both CD4+ and CD8+ T cells provided complete protection from acute GVHD. We thus show that acute GVHD is attenuated in the absence of donor bone marrow-derived IL-15 and conclude that donor-derived IL-15 is a critical mediator of T-cell function in acute GVHD.

CD56+Cells Induce Steroid Resistance in B Cells Exposed to IL-15

Interleukin-2 can induce steroid resistance in T cells. IL-15 shares biological activities with IL-2, as both cytokines use IL-2Rgamma for signal transduction. We therefore sought to determine whether IL-15 contributes to induction of PBMC corticosteroid resistance. Surprisingly, we found that incubation of unfractionated PBMC with IL-15 for 48 h resulted in the inhibition of glucocorticoid receptor (GCR) nuclear translocation in response to dexamethasone (DEX) treatment in CD19-positive B cells significantly greater than CD19-negative non-B cells (p < 0.01). However, pure B cells incubated with IL-15 responded normally with nuclear translocation of GCR in response to steroids, but failed to translocate GCR when they were grown in the presence of CD19(-) cells. Coculture of B cells with CD3(+) (T cells), CD14(+) (monocytes), or CD56(+) (NK and NKT cells) in the presence of IL-15 revealed that only CD56(+) cells contributed to the steroid insensitivity of B cells. IL-15 stimulation significantly increased production of IL-4 by CD56(+) cells (p < 0.02). Treatment of purified B cells with combination IL-15/IL-4 resulted in abrogation of glucocorticoid receptor nuclear translocation and the inability of DEX to suppress cytokine production by B cells. In the presence of IL-4-neutralizing Ab, when B cells were cocultured with CD56(+) cells and IL-15, the B cells were found to be steroid sensitive, i.e., DEX induced GCR nuclear translocation. This study demonstrates that B cells develop steroid resistance in the presence of CD56(+) cells after IL-15 stimulation. Furthermore, IL-15 and IL-4 have the capacity to induce B cell insensitivity to steroids.

T-cell immunotherapy of allergic disease: the role of CD8+ T cells

PURPOSE OF REVIEW

The scope of this review is to place recent advances in T-cell immunotherapy into an account of our understanding of the potential role of CD8+ T cells in the pathogenesis of allergic disease.

RECENT FINDINGS

Studies over the last year suggest that changes in CD8+ T-cell function may represent key events in successful T-cell immunotherapy. The first human human leukocyte antigen class I allergen epitopes have now been described and will provide further insights into the role of allergen-specific CD8+ T cells.

SUMMARY

The coupling of recent technical advances in the study of antigen-specific T cells with the knowledge of human allergen class I epitopes will promote rapid progress in the field, with potential consequences for the diagnosis, monitoring and immunotherapeutic treatment of affected individuals.

CD8+ T cells and immunoregulatory networks in asthma

It is well established that infection with respiratory viruses can cause acute local inflammation in humans and is a leading cause in the hospitalization of asthmatics. Less well recognized is the potential for viral infections to actually protect against the development of asthma, as are the cellular mechanisms which might underlie such protection. This review outlines the basic immunological pathways involved in atopic asthma and details the currently recognized cellular mechanisms induced by respiratory viral infections which can protect against the development of asthma. Specifically, it appears that virus infection induced memory T cells that remain in tissues, e.g. the lung and airways, can under certain circumstances create a local cytokine milieu which inhibits the development of ensuing allergic immune responses at that site. One key aspect of this immune modulation is the cytokine-dependent communication which occurs between the innate and the adaptive immune systems. The mechanistic principles underlying this form of immunomodulation should be taken into consideration when developing future forms of therapy and rational vaccine design.

Migration of primary and memory CD8 T cells

Our results indicate that a substantial proportion of the antimicrobial CD8 and CD4 T cell response is focused in non-lymphoid tissues. This finding makes teleological sense since maximum protection against infection is better served by the widespread presence of effector and memory cells. In the case of CD8 T cells, it appears that irrespective of the site at which initial activation of naive cells occurs, the end result is production of effector cells with broad migratory capabilities. Memory T cells perhaps have more restricted migratory abilities as compared to effector cells, although this needs to be tested definitively. Our results suggest that memory CD8 T cells in the intestinal LP may not be part of the recirculating pool of memory cells, though our data does not preclude the possibility that migrants from outside the mucosa contribute to the LP memory pool. Our data also demonstrates that CD8 memory T cells in non-lymphoid tissue exhibit heightened effector function as compared to their splenic counterparts. Whether these findings indicate the existence of distinct lineages of memory cells remains to be seen. The functional abilities of migrating memory cells could be modulated by the migration process and/or by the environmental milieu of a particular tissue. Although the development of CD8 memory T cells is a complex process requiring multiple signalling pathways, we identified IL-7 as an important player in memory generation. Much further work is needed to decipher the cellular and molecular mechanisms of memory induction as well as to learn the in vivo functional significance of memory cell subsets.

Association between increased levels of IL-2 and IL-15 and outcome in patients with early acute respiratory distress syndrome

BACKGROUND

Acute respiratory distress syndrome remains a serious, often fatal, condition, despite progress in modern critical care treatment. Cytokines play an important role in the pathogenesis of the syndrome, although their role in the evolution and outcome has not been clearly elucidated. We explored whether the measurement of serum and bronchoalveolar lavage IL-2 and IL-15 at the time of hospital admission can predict the outcome of this syndrome.

METHODS

Serum and bronchoalveolar lavage levels of IL-2 and IL-15 were measured in eight patients with ARDS (group A) and 26 patients on high risk for ARDS development who never developed ARDS (group B) from samples obtained at the time of admission.

RESULTS

Serum IL-2 (P > 0.05) and IL-15 (P < 0.05) levels were higher in group A than in group B. Serum levels of both cytokines were higher in patients who did not survive in both of the groups A and B compared to those who survived (P < 0.05, and P < 0.0001, respectively). The only significant change in BALF was the higher level of IL-15 in surviving group A patients (P < 0.05) when compared with the non survivors of the same group. For a serum cut-off level of 173 pg mL(-1) for IL-2 and 250 pg mL(-1) for IL-15, they exhibited a very high positive predictive value (PPV), negative predictive value (NPV), sensitivity and specificity for survival (100% in all). A positive correlation was found between serum levels of both cytokines and APACHE II score (IL-2, r = 0.61, and IL-15, r = 0.62, respectively, and P < 0.0001 for both).

CONCLUSION

Determination of serum IL-2 and IL-15 levels may be a valuable and simple aid to improve identification of patients with ARDS or at risk for ARDS who are at high risk of subsequent mortality.

Overexpression of interleukin-15 prevents the development of murine retrovirus-induced acquired immunodeficiency syndrome

LP-BM5 murine leukemia virus (MuLV) infection causes murine acquired immunodeficiency syndrome (MAIDS), a disease characterized by varied functional abnormalities of immunocompetent cells. We found that MAIDS progression was severely retarded in IL-15 transgenic (Tg) mice constructed with cDNA encoding secretable IL-15 under the control of an MHC class I promoter. Several immune defects, including impaired natural killer activity, depressed IFN-gamma production by T cells stimulated with anti-T cell receptor cross-linking, and increased susceptibility to Mycobacterium bovis infection, were prevented in IL-15 Tg mice inoculated with LP-BM5 MuLV. Cytotoxic T lymphocyte response to a highly antigenic 10-mer peptide encoded by LP-BM5-defective virus gag p12 gene was detected in the spleen and peritoneal exudate cells from IL-15 Tg mice infected with LP-BM5 MuLV. Intramuscular injection of cDNA encoding secretable IL-15 also prevented the development of MAIDS. These results indicate that IL-15 prevents the progression of MAIDS and may provide insight into an immunotherapeutic approach using the IL-15 gene for controlling retrovirus-induced immunodeficiency.

Overexpression of interleukin-15 in vivo enhances antitumor activity against MHC class I-negative and -positive malignant melanoma through augmented NK activity and cytotoxic T-cell response

Interleukin (IL)-15, a pleiotropic cytokine, is involved in the development and maintenance of NK cells and memory CD8+ T cells. We examined the effects of in vivo overexpression of IL-15 on protection against 2 types of murine B16 melanoma lines, MHC class I-negative B16.44 and MHC class I-positive B16F10 cells, using IL-15 transgenic (Tg) mice that we have recently constructed. The tumor growth was severely retarded in IL-15 Tg mice after subcutaneous (s.c.) inoculation with B16.44 or B16F10 cells. IL-15 Tg mice showed an augmented NK cell activity against B16.44 cells, and in vivo depletion of NK cells by anti-asialoGM1 Ab treatment abrogated the antitumor activity in IL-15 Tg mice. On the other hand, IL-15 Tg mice inoculated with B16F10 cells developed a significant level of CTL response against B16F10 cells, and in vivo depletion of CD8+ T cells by anti-CD8 MAb treatment abrogated the antitumor activity. Thus, overexpression of IL-15 augmented antitumor activity against different tumors via augmentation of different antitumor mechanisms. These results suggest a possible therapeutic application of IL-15 for human neoplasms expressing a wide range of MHC class molecules.

Lactoferrin immunomodulation of DTH response in mice

Improved nontoxic adjuvants, especially adjuvants capable of inducing cell-mediated immunity (CMI), are needed for research in immunology and for development of human and veterinary vaccines. Bovine Lactoferrin, an effector molecule shown to directly participate in host defense, was assessed at various concentrations as an adjuvant component for induction of DTH responses to sheep red blood cells (SRBC). Subcutaneous immunization with Lactoferrin enhanced delayed type hypersensitivity (DTH) in CBA mice in a dose-dependent fashion; DTH responses were most significantly increased when sensitization was accomplished using Lactoferrin at 50 microg/dose and 250 microg/dose. Furthermore, Lactoferrin admixed with suboptimal dose of SRBC enhanced DTH responses by over 17-fold. Peritoneal cells collected from mice intraperitoneally injected with a 100 microg/dose of Lactoferrin demonstrated modest, but significant, production of TNF-alpha, IL-12 and MIP-1alpha when cultured in vitro, compared to saline-injected controls. J774A.1 murine macrophages stimulated with Lactoferrin resulted in increased TNF-alpha protein production, and upregulated IL-12 and IL-15 mRNA. Levels of message for chemokines MIP-1alpha and MIP-2 were also increased in a dose-dependent way. Taken together, these results indicate that Lactoferrin as an adjuvant may stimulate macrophages to generate a local environment likely to push immune responses towards development and maintenance of CMI.

Overexpression of IL-15 in vivo increases antigen-driven memory CD8+ T cells following a microbe exposure

To elucidate potential roles of IL-15 in the maintenance of memory CD8+ T cells, we followed the fate of Ag-specific CD8+ T cells directly visualized with MHC class I tetramers coupled with listeriolysin O (LLO)(91-99) in IL-15 transgenic (Tg) mice after Listeria monocytogenes infection. The numbers of LLO(91-99)-positive memory CD8+ T cells were significantly higher at 3 and 6 wk after infection than those in non-Tg mice. The LLO(91-99)-positive CD8+ T cells produced IFN-gamma in response to LLO(91-99), and an adoptive transfer of CD8+ T cells from IL-15 Tg mice infected with L. monocytogenes conferred a higher level of resistance against L. monocytogenes in normal mice. The CD44+ CD8+ T cells from infected IL-15 Tg mice expressed the higher level of Bcl-2. Transferred CD44+ CD8+ T cells divided more vigorously in naive IL-15 Tg mice than in non-Tg mice. These results suggest that IL-15 plays an important role in long-term maintenance of Ag-specific memory CD8+ T cells following microbial exposure via promotion of cell survival and homeostatic proliferation.

Decreased IL-15 may contribute to elevated IgE and acute inflammation in atopic dermatitis

PBMC and acute skin lesions of patients with atopic dermatitis (AD) are characterized by increased IL-4 and IL-13, but decreased IFN-gamma production. This bias toward an increased Th2 cytokine profile may contribute to the elevated IgE levels and acute skin inflammation seen in AD. In this study, we examined the levels of IL-15, a Th1-like cytokine, in the PBMC and the skin lesions of AD patients. IL-15 secretion by Staphylococcal enterotoxin B-treated PBMC of AD patients was significantly lower than that of normals and psoriasis patients (p < 0.001). Membrane-bound IL-15 expression as measured by mean fluorescence intensity and percentage of IL-15-positive cells in Staphylococcal enterotoxin B-treated monocytes of AD patients (644 +/- 49% and 12.7 +/- 0.6%, respectively) were significantly lower than that of normals (869 +/- 56% and 15.8 +/- 1.2%, respectively) and psoriasis patients (1488 +/- 217% and 22.7 +/- 0.8%, respectively; p < 0.0007 and p < 0.0001, respectively). The membrane-bound IL-15 expression was also significantly lower in the control monocytes of AD patients compared with that in normals and psoriasis patients. There was no significant difference in the absolute number or percentage of monocytes between the study subjects. However, psoriasis skin lesions were found to have significantly more IL-15 mRNA-expressing cells (22.4 +/- 1.7) compared with that in acute AD (7.5 +/- 1.7) and chronic AD (13.7 +/- 1.7) skin lesions (p < 0.05). IL-15 enhanced IFN-gamma production by the PBMC of AD patients (p < 0.01), but not by that of normal individuals or psoriasis patients. In addition, IL-15 was found to suppress IgE synthesis (p < 0.01) by the PBMC of AD patients. These data support the concept that reduced IL-15 expression may contribute to the pathogenesis of AD.

Overexpression of IL-15 in vivo enhances protection against Mycobacterium bovis bacillus Calmette-Guérin infection via augmentation of NK and T cytotoxic 1 responses

To investigate the immunomodulating effects of IL-15 in vivo on mycobacterial infection, we used IL-15-transgenic (Tg) mice, which were recently constructed with cDNA-encoding secretable isoform of IL-15 precursor protein under the control of a MHC class I promoter. The IL-15-Tg mice exhibited resistance against infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG), as assessed by bacteria growth. IFN-gamma level in serum was significantly higher in IL-15-Tg mice than in non-Tg mice after BCG infection. NK cells were remarkably increased, and Ag-specific T cytotoxic 1 response mediated by CD8+ T cells producing IFN-gamma was significantly augmented in the IL-15-Tg mice following BCG infection. Neutralization of endogenous IFN-gamma by in vivo administration of anti-IFN-gamma mAb deteriorated the clearance of the bacteria. Depletion of of NK cells or CD8+ T cells by in vivo administration of anti-asialo-GM(1) Ab or anti-CD8 mAb hampered the exclusion of bacteria. Thus, overexpression of IL-15 in vivo enhanced protection against BCG infection via augmentation of NK and T cytotoxic 1 responses.