Defective suppression of Th2 cytokines by CD4+CD25+ regulatory T cells in birch allergics during birch pollen season

Specific immunotherapy to birch allergen does not enhance suppression of Th2 cells by CD4(+)CD25(+) regulatory T cells during pollen season

INTRODUCTION

The aim of this study was to investigate the suppressive capacity of CD25(+) regulatory T cells on birch allergen-induced T-cell responses during the first birch pollen season after initiation of specific immunotherapy (SIT).

METHODS

CD25(pos) and CD25(neg) T cells were purified from blood of birch-allergic SIT patients and birch-allergic controls, stimulated with birch pollen extract, and analyzed for T-cell proliferation and production of interferon gamma (IFN-gamma), interleukin (IL)-5 and IL-10.

RESULTS

We show that allergen-induced proliferation and IFN-gamma production were suppressed equally well by CD25(pos) T cells from SIT patients and controls, while the IL-5 production was not suppressed by either of the groups. IL-10 levels were higher in SIT patients relative to controls only when CD25(neg) and CD25(pos) were cultured together. Furthermore, neither FOXP3 levels nor proportions of CD25(high) T cells were enhanced in SIT patients compared to allergic controls.

DISCUSSION

These results suggest that the Th2-suppressive capacity of allergen-stimulated CD25(pos) Treg in vitro is not improved by SIT in spite of increased IL-10 production from T cells.

Regulatory T cells and asthma

Airway inflammation in asthma is characterized by activation of T helper type-2 (Th2) T cells, IgE production and eosinophilia. In many cases, this process is related to an inappropriate T cell response to environmental allergens, and other T cell-dependent pathways may also be involved (such as Th17). Regulatory T cells (Tregs) are T cells that suppress potentially harmful immune responses. Two major subsets of Treg are CD25(hi), Foxp3(+)Tregs and IL-10-producing Tregs. There is evidence that the numbers or function of both subsets may be deficient in patients with atopic allergic disease. Recent work has extended these findings into the airway in asthma where Foxp3 expression was reduced and CD25(hi) Treg-suppressive function was deficient. In animal models of allergic airways disease, Tregs can suppress established airway inflammation and airway hyperresponsiveness, and protocols to enhance the development, recruitment and function of Tregs have been described. Together with studies of patients and in vitro studies of human T cells, these investigations are defining potential interventions to enhance Treg function in the airway in asthma. Existing therapies including corticosteroids and allergen immunotherapy act on Tregs, in part to increase IL-10 production, while vitamin D3 and long-acting beta-agonists enhance IL-10 Treg function. Other possibilities may be enhancement of Treg function via histamine or prostanoid receptors, or by blocking pro-inflammatory pathways that prevent suppression by Tregs (activation of Toll-like receptors, or production of cytokines such as IL-6 and TNF-alpha). As Tregs can also suppress the potentially beneficial immune response important for controlling infections and cancer, a therapeutic intervention should target allergen- or site-specific regulation.

Th2 cells as targets for therapeutic intervention in allergic bronchial asthma

Th2 cells play a central role in the pathogenesis of allergic bronchial asthma, since each of their characteristic cytokines such as IL-4, IL-5, IL-9 and IL-13 contributes to hallmarks of this disease, including airway eosinophilia, increased mucus production, production of allergen-specific IgE and development of airway hyper-responsiveness. Therefore, these cells are predisposed as target cells for therapeutic intervention. Experimental approaches targeted Th2-type effector cytokines, Th2-cell recruitment and Th2-cell development. Another strategy uses the immunomodulatory potential of tolerance-inducing cytokines such as IL-10 or of cytokines such as IL-12, IL-18 and IFN-gamma that are able to induce a counterbalancing Th1 immune response.

Regulatory cells, cytokine pattern and clinical risk factors for asthma in infants and young children with recurrent wheeze

BACKGROUND

Several risk factors for asthma have been identified in infants and young children with recurrent wheeze. However, published literature has reported contradictory findings regarding the underlying immunological mechanisms.

OBJECTIVES

This study was designed to assess and compare the immunological status during the first 2 years in steroid-naive young children with >or= three episodes of physician-confirmed wheeze (n=50), with and without clinical risk factors for developing subsequent asthma (i.e. parental asthma or a personal history of eczema and/or two of the following: wheezing without colds, a personal history of allergic rhinitis and peripheral blood eosinophilia >4%), with age-matched healthy controls (n=30).

METHODS

Peripheral blood CD4(+)CD25(+) and CD4(+)CD25(high) T cells and their cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), GITR and Foxp3 expression were analysed by flow cytometry. Cytokine (IFN-gamma, TGF-beta and IL-10), CTLA-4 and Foxp3 mRNA expression were evaluated (real-time PCR) after peripheral blood mononuclear cell stimulation with phorbol 12-myristate 13-acetate (PMA) (24 h) and house dust mite (HDM) extracts (7th day).

RESULTS

Flow cytometry results showed a significant reduction in the absolute number of CD4(+)CD25(high) and the absolute and percentage numbers of CD4(+)CD25(+)CTLA-4(+) in wheezy children compared with healthy controls. Wheezy children at a high risk of developing asthma had a significantly lower absolute number of CD4(+)CD25(+) (P=0.01) and CD4(+)CD25(high) (P=0.04), compared with those at a low risk. After PMA stimulation, CTLA-4 (P=0.03) and Foxp3 (P=0.02) expression was diminished in wheezy children compared with the healthy children. After HDM stimulation, CTLA-4 (P=0.03) and IFN-gamma (P=0.04) expression was diminished in wheezy children compared with healthy children. High-risk children had lower expression of IFN-gamma (P=0.03) compared with low-risk and healthy children and lower expression of CTLA-4 (P=0.01) compared with healthy children.

CONCLUSIONS

Although our findings suggest that some immunological parameters are impaired in children with recurrent wheeze, particularly with a high risk for asthma, further studies are needed in order to assess their potential as surrogate predictor factors for asthma in early life.

Augmentation of regulatory T cells in allergic individuals by recombinant Der f 2 peptide with fungal immunomodulatory peptide fve

BACKGROUND

The suppressive function of regulatory T (Treg) cells is compromised in allergic individuals, and the augmentation of Treg cells has been demonstrated after successful allergen immunotherapy.

OBJECTIVE

To evaluate the effect of Dermatophagoides farinae fragments (Der f 2 N-peptides) that do not bind specific IgE in conjunction with the fungal immunomodulatory peptide fve (FIP-fve) on Treg cells derived from individuals with allergic rhinitis.

METHODS

CD4+CD25+ T cells were isolated from peripheral blood mononuclear cells of 11 patients with allergic rhinitis and 7 nonallergic individuals using immunomagnetic beads. Cells were cultured with medium, Der f 2, FIP-fve, FIP-fve plus Der f 2, and FIP-fve plus Der f 2 N-peptides for 6 days in the presence of antigen-presenting cells. The percentages and function of Foxp3+CD4+CD25+ Treg cells, interleukin (IL) 10+, and transforming growth factor beta (TGF-beta)+ Treg cells were measured.

RESULTS

The percentage of Foxp3+ Treg cells in CD4+CD25+ T cells was significantly increased in D farinae allergic patients by Der f 2 N-peptides in conjunction with FIP-fve. Both IL-10+ and TGF-beta+ Treg cells were significantly increased in the presence of Der f 2 N-peptides and FIP-fve compared with other groups. The function of Treg cells induced by Der f 2 N-peptides and FIP-fve could be demonstrated by the inhibition of bromodeoxyuridine uptake by peripheral blood mononuclear cells.

CONCLUSION

The percentage of IL-10+ and TGF-beta+ cells in Foxp3+CD4+CD25+ T cells can be up-regulated by Der f 2 N-peptides in conjunction with FIP-fve only in D farinae allergic individuals. These results indicate that non-IgE-mediated fragments of allergen in conjunction with FIP-fve might have therapeutic effects on Treg cells derived from allergic individuals.

The "Microflora Hypothesis" of allergic disease

Predisposition to allergic disease is a complex function of an individual's genetic background and, as is the case with multi-gene traits, environmental factors have important phenotypic consequences. Over a span of decades, a dramatic increase in the prevalence of allergic disease in westernized populations suggests the occurrence of critical changes in environmental pressures. Recently, it has been shown that the microbiota (i.e. microflora) of allergic individuals differs from that of non-allergic ones and that differences are detectable prior to the onset of atopy, consistent with a possible causative role. Features of the westernized lifestyle that are known to alter the microbiota, such as antibiotics and diet, are also associated with allergy in humans. In this chapter, we discuss the "Microflora Hypothesis" for allergy which predicts that an "unhealthy" microbiota composition, now commonly found within westernized communities, contributes to the development of allergy and conversely, that restoring a "healthy" microbiota, perhaps through probiotic supplementation, may prevent the development of allergy or even treat existing disease. In testing this hypothesis, our laboratory has recently reported that mice can develop allergic airway responses if their microbiota is altered at the time of first allergen exposure.

Regulatory T cells in bronchial asthma

The main focus of this review was the role of a specific subset of T cells with immunomodulatory or immunosuppressive activities, termed regulatory T cells (Tregs), in the pathogenesis and treatment of bronchial asthma. Evidence that these cells are important in maintaining immune homeostasis in health and exhibit impaired activity in active disease will be discussed. Their therapeutic potential is perhaps best highlighted by evidence that therapies with demonstrated efficacy in allergic and asthmatic disease are associated with the induction or restoration of regulatory T-cell function, e.g. glucocorticoids, allergen immunotherapy. Strategies to improve the safety and efficacy of these treatments and that induce or boost Tregs in bronchial asthma are discussed.

Soluble interleukin-10 and transforming growth factor-beta in children with acute exacerbation of allergic asthma

Cytokine-mediated interactions among inflammatory cells may contribute to pathogenesis of allergic asthma. To understand the role of soluble interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta) on the disease activity and regulation in asthma, changes in serum concentrations of IL-10 and TGF-beta elaborated by activated T-lymphocyte before and after prednisolone therapy with clinical improvement were determined. Circulating levels of IL-10 and TGF-beta in sera from 16 normal control subjects and in sera from 22 allergic asthmatic children with acute exacerbation and in stable condition were respectively detected by commercially available enzyme-linked immunosorbent assay kits. The mean concentrations of serum IL-10 in asthmatics with acute exacerbation (6.77 +/- 4.08 pg/mL) and during stable condition (5.14 +/- 1.17 pg/mL) were lower than that in control subjects (7.15 +/- 4.72 pg/mL). However, the difference was not statistically significant among these three study groups. The mean concentration of serum TGF-beta in stable asthmatics (40.73 +/- 15.95 pg/mL) was significantly higher than that in asthmatics with acute exacerbation (27.64 +/- 3.66 pg/mL; p < 0.05) and that in healthy control group (28.77 +/- 8.35 pg/mL; p < 0.05), while there was no statistical difference between the latter two groups. This study provides further evidence that serum TGF-beta, rather than IL-10, may play a role in regulation of disease activity and serve as an indicator for clinical control of allergic asthmatics.

Primary immune deficiencies with aberrant IgE production

IgE antibodies play a central role in the pathogenesis of atopic diseases and in host immunity against parasitic infections. IgE has potent activities on mast cells and basophils. IgE class switching is a very tightly controlled process, and serum IgE levels are very low compared with other immunoglobulin isotypes. Transcription factors that activate or inhibit the IgE gene promoter, as well as T(H)1 and T(H)2 cytokines are important in the regulation of IgE levels. Hyper-IgE syndrome; Wiskott-Aldrich syndrome; immunodysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX); Omenn syndrome; and atypical complete DiGeorge syndrome are primary immune deficiencies that are associated with elevated serum IgE levels. Increased IgE levels in IPEX, Wiskott-Aldrich syndrome and Omenn syndrome are likely related to increased T(H)2 cytokine production caused by decreased a number or function of CD4(+)CD25(+)forkhead box protein P3(+) regulatory T cells. The link between signal transducer and activator of transcription 3 mutations and elevated serum IgE levels in hyper-IgE syndrome is unclear. Insight into IgE regulation provided by the study of primary immune deficiencies with elevated IgE has important implications for allergic diseases.

Selective deregulation in chemokine signaling pathways of CD4+CD25(hi)CD127(lo)/(-) regulatory T cells in human allergic asthma

BACKGROUND

CD4+CD25(hi)CD127(lo)/(-) regulatory T cells have been suggested to be critical regulators of inflammatory processes in allergic asthma. Recent studies reported a selective decrease in the frequency of regulatory T cells in the bronchoalveolar lavage fluid of allergic asthmatic (AA) subjects, prompting the possibility of defective recruitment of these cells to the airway in response to chemokines produced during asthmatic inflammation.

OBJECTIVES

This study aimed to characterize the chemotactic profile of circulating regulatory T cells in AA subjects in response to chemokines abundantly produced in airway inflammation, such as CCL1, CCL17, and CCL22.

METHODS

The study was performed in a cohort of 26 AA, 16 healthy control, and 16 non-AA subjects. We used chemotaxis assays to evaluate cell migration, flow cytometry to examine chemokine receptor expression, and phospho-ELISA to study consequent signaling pathways in regulatory T cells.

RESULTS

Regulatory T cells, but not CD4+CD25(-)T cells, from AA subjects showed decreased chemotactic responses, specifically to CCL1, in comparison with their healthy control and non-AA counterparts. Decreased CCL1-mediated chemotaxis in AA regulatory T cells was associated with decreased phosphorylation of protein kinase B (AKT), a protein involved in chemokine intracellular signaling. Furthermore, the decreased chemotactic response to CCL1 in AA regulatory T cells significantly correlated with asthma severity and decreased pulmonary function in AA subjects.

CONCLUSIONS

These results provide the first evidence of dysfunction in the chemokine signaling pathway in AA regulatory T cells.

Interleukin-4 suppresses the cytotoxic potential of in vitro generated, adaptive regulatory CD4 T cells by down-regulation of granzyme B

Regulatory CD4+ T cells (Tregs) control immune responses using secretion of anti-inflammatory cytokines and/or cytotoxic mechanisms and play a central role in the outcomes of several immune pathologies. Previous studies suggest an impaired function of Tregs in allergy, especially during allergen seasons, but the underlying mechanism is not known. Therefore, we analysed the impact of the T helper type 2 cytokine interleukin (IL)-4 on in vitro generated adaptive Tregs (aTregs), which have been reported to use the granzyme B (GrB)/perforin pathway to kill autologous immune cells. aTregs were generated by co-ligation of CD3 and CD46 on CD4+ T lymphocytes and granzyme expression was analysed using flow cytometry. To quantify GrB and perforin expression as well as IL-10 secretion in response to IL-4, specific enzyme-linked immunosorbent assays were performed in cell lysates and/or culture supernatants. Using a flow cytometry-based cytotoxicity assay the impact of IL-4 on the cytotoxic potential of aTregs was investigated. While IL-4 did not affect IL-10 secretion and perforin expression in aTregs, a significant suppression of GrB synthesis was detected in the presence of IL-4. In addition, IL-4-mediated suppression of GrB led to impaired cytotoxicity of aTregs against K562 target cells. In conclusion, our data suggest that IL-4 might play a role in impaired aTreg function in allergy.

Suppression of murine allergic airway disease by IL-2:anti-IL-2 monoclonal antibody-induced regulatory T cells

Regulatory T cells (Treg) play a decisive role in many diseases including asthma and allergen-induced lung inflammation. However, little progress has been made developing new therapeutic strategies for pulmonary disorders. In the current study we demonstrate that cytokine:antibody complexes of IL-2 and anti-IL-2 mAb reduce the severity of allergen-induced inflammation in the lung by expanding Tregs in vivo. Unlike rIL-2 or anti-IL-2 mAb treatment alone, IL-2:anti-IL-2 complexes dampened airway inflammation and eosinophilia while suppressing IL-5 and eotaxin-1 production. Mucus production, airway hyperresponsiveness to methacholine, and parenchymal tissue inflammation were also dramatically reduced following IL-2:anti-IL-2 treatment. The suppression in allergic airway disease was associated with a marked expansion of Tregs (IL-10(+)CD4(+)CD25(+) and Foxp3(+)CD4(+)CD25(+)) in the tissues, with a corresponding decrease in effector T cell responses. The ability of IL-2:anti-IL-2 complexes to suppress airway inflammation was dependent on Treg-derived IL-10, as IL-10(+/+), but not IL-10(-/-) Tregs, were capable of mediating the suppression. Furthermore, a therapeutic protocol using a model of established airway allergy highlighted the ability of IL-2:anti-IL-2 complexes to expand Tregs and prevent successive airway inflammation and airway hyperresponsiveness. This study suggests that endogenous Treg therapy may be a useful tool to combat the rising incidence of allergic airway disease.

XCL1 enhances regulatory activities of CD4+ CD25(high) CD127(low/-) T cells in human allergic asthma

Chemokine-mediated recruitment of regulatory cell subsets to the airway during inflammation and enhancement of their activities are potential strategies for therapeutic development in allergic asthma (AA). In this study, we aim to explore the role of XCL1, a chemokine associated with immune suppression and allergy, on CD4(+)CD25(high)CD127(low/-) regulatory T cell (Treg) function in AA. Flow cytometry and PCR analysis showed a reduction in XCL1 and XCR1 expression in AA Treg compared with healthy control and nonallergic asthmatic counterparts. This reduction in XCL1 expression was associated with the suboptimal regulatory function of Treg in AA. Interestingly, incubation with recombinant human XCL1 significantly increased Treg-mediated suppression and cytotoxicity by up-regulating expression of XCL1 and chief effector molecules of Treg function. Altogether, these results suggest an association between dysregulated XCL1 expression and reduced Treg activities in AA, as well as a potential role of XCL1 in reversing defective Treg function in the disease.

Foxp3+ T regulatory cells (Tregs) are increased in nasal polyps (NP) after treatment with intranasal steroid

The pathogenesis of chronic rhinosinusitis (CRS) with nasal polyps(NP) is still poorly understood. To evaluate the role of Foxp3+ T regulatory cells (Tregs) in the pathogenesis and management of NP, we investigated the location and expression of Foxp3 in NP before and after treatment with intranasal steroid. NP specimens were obtained from 14 patients with NP before and after intranasal administration of mometasone (50 microg/day for 4 weeks). Foxp3 was detected by double immunofluorescence stain, quantitative reverse transcriptase polymerase chain reaction (RT-PCR), flow cytometry and western blot. The concentration of interleukin(IL)-10 in supernatants of homogenized tissue was measured by enzyme-linked immunosorbent assay (ELISA). We found that Foxp3 and IL-10 were downregulated in NP compared to the control mucosa (P<0.05). Foxp3 and IL-10 expression were increased significantly after intranasal steroid treatment (P<0.05). And Foxp3 was tightly correlated with IL-10 in NP (P<0.05) after treatment. These data suggest that Foxp3 is downregulated in NP and intranasal steroid attenuates the chronic inflammatory response by enhancing the expression and function of Foxp3 in NP.

Increased cytotoxicity of CD4+ invariant NKT cells against CD4+CD25hiCD127lo/- regulatory T cells in allergic asthma

CD4+CD25(hi)CD127(lo/-) regulatory T cells (Treg) have been implicated in the resolution of asthma-associated inflammation while the opposite role of CD4+ invariant NKT (iNKT) cells has been the subject of recent investigations. Studies here focused on mechanisms of interaction between CD4+ iNKT cells and Treg to further explore their roles in allergic asthma (AA). Flow cytometry analysis revealed a significant increase in the expression of the natural cytotoxicity receptors NKp30 and NKp46 by CD4+ iNKT cells in AA subjects compared to healthy controls (HC) and non-allergic asthmatics (NA). Subsequent intracellular staining showed that CD4+ iNKT cells also expressed higher levels of granzyme B and perforin in AA than HC. In in vitro killing assays, AA CD4+ iNKT cells selectively killed autologous Treg, but not CD4+CD25- T cells, more potently than HC and NA counterparts. This increased cytotoxicity positively correlated with asthma severity and granzyme B/perforin expression of CD4+ iNKT cells. Furthermore, it could be abrogated by either inhibition of the granzyme B-/perforin-dependent cell death pathway or oral corticosteroid administration. Altogether, these findings suggest that increased cytotoxicity of CD4+ iNKT cells against Treg might contribute to dysfunctional cellular interactions in AA.

Update: the role of FoxP3 in allergic disease

PURPOSE OF REVIEW

T-regulatory cells play a key role in allergic and asthmatic inflammatory airway diseases. This review discusses the importance of a critical gene associated with T-regulatory cells. Forkhead box P3 is a forkhead-winged helix transcription factor gene involved in immune function in allergy and asthma.

RECENT FINDINGS

Recently, many functions of forkhead box P3 and its influence on the immune system have been elucidated. T-regulatory cells that are CD4+CD25+ and express forkhead box P3, influence the development and expression of atopy and allergic response. The exact mechanisms are not yet delineated, but multiple recent studies provide greater understanding of the mechanism of forkhead box P3 and its influence on these T-regulatory cells.

SUMMARY

Greater understanding of the molecular and immunological mechanisms underlying the T-regulatory cells and forkhead box P3 will permit the development of targeted treatment modalities to influence disease processes such as allergic rhinitis and bronchial asthma.

Immunologic and inflammatory mechanisms that drive asthma progression to remodeling

Although histologic features of airway remodeling have been well characterized in asthma, the immunologic and inflammatory mechanisms that drive progression of asthma to remodeling are still incompletely understood. Conceptually, airway remodeling may be a result of persistent inflammation and/or aberrant tissue repair mechanisms. It is likely that several immune and inflammatory cell types and mediators are involved in mediating airway remodeling. In addition, different features of airway remodeling are likely mediated by different inflammatory pathways. Several important candidate mediators of remodeling have been identified, including TGF-beta and T(H)2 cytokines (including IL-5 and IL-13), as well as vascular endothelial growth factor, a disintegrin and metalloproteinase 33, and matrix metalloproteinase 9. Mouse models of airway remodeling have provided important insight into potential mechanisms by which TGF-beta activation of the Smad-2/3 signaling pathway may contribute to airway remodeling. Human studies have demonstrated that anti-IL-5 reduces levels of airway eosinophils expressing TGF-beta, as well as levels of airway remodeling as assessed by bronchial biopsies. Further such studies confirming these observations, as well as alternate studies targeting additional individual cell types, cytokines, and mediators, are needed in human subjects with asthma to determine the role of candidate mediators of inflammation on the development and progression of airway remodeling.

Regulatory T cells and human disease

The main function of our immune system is to protect us from invading pathogens and microorganisms by destroying infected cells, while minimizing collateral damage to tissues. In order to maintain this balance between immunity and tolerance, current understanding of the immune system attributes a major role to regulatory T cells (Tregs) in controlling both immunity and tolerance. Various subsets of Tregs have been identified based on their expression of cell surface markers, production of cytokines, and mechanisms of action. In brief, naturally occurring thymic-derived CD4+CD25+ Tregs are characterized by constitutive expression of the transcription factor FOXP3, while antigen-induced or adaptive Tregs are mainly identified by expression of immunosuppressive cytokines (interleukin-10 (IL-10) and/or transforming growth factor-beta (TGF-beta)). While Tregs in normal conditions regulate ongoing immune responses and prevent autoimmunity, imbalanced function or number of these Tregs, either enhanced or decreased, might lead, respectively, to decreased immunity (e.g., with tumor development or infections) or autoimmunity (e.g., multiple sclerosis). This review will discuss recent research towards a better understanding of the biology of Tregs, their interaction with other immune effector cells, such as dendritic cells, and possible interventions in human disease.

Regulatory T cell therapy as individualized medicine for asthma and allergy

PURPOSE OF REVIEW

Regulatory T cells have been identified as key players in the maintenance of peripheral tolerance, which prevents inappropriate immune responses to both self-antigens and innocuous allergens. This review aims to provide an update on our current understanding of the therapeutic potential of naturally occurring and adaptive regulatory T cell subsets in allergic and asthmatic disease.

RECENT FINDINGS

Evidence is emerging that regulatory T cells control aberrant immune responses to allergens in health and exhibit impaired function in active disease. These data provide a rationale for developing therapeutic strategies that promote regulatory T cell numbers or function in patients.

SUMMARY

Preclinical studies of adoptive transfer of antigen-specific regulatory T cells into mouse models of allergic airway disease ameliorate the inflammatory response and in some studies airway hyperresponsiveness. Although these studies are encouraging this remains an invasive and expensive therapeutic protocol for the treatment of allergic disease in humans and a number of concerns relating to safety and efficacy exist. Existing therapies, both allergen specific immunotherapy and nonspecific treatments such as glucocorticoids, induce IL-10 secreting T regulatory populations in patients. Strategies to combine allergen immunotherapy with add-on treatments or adjuvants with the potential to boost regulatory T cells, safety and efficacy remain a major research focus.

The functional insufficiency of human CD4+CD25 high T-regulatory cells in allergic asthma is subjected to TNF-alpha modulation

BACKGROUND

Natural CD4(+)CD25(high)Foxp3(+) regulatory T (nTreg) cells are important in maintaining immunologic tolerance, but their role in the pathogenesis of allergic asthma is unclear. We studied the function of nTreg cells in allergic asthmatic children and assessed the factors which may relate to the functional insufficiency of nTreg cells.

METHODS

The percentage of CD4(+)CD25(high) Treg cells, the expression of Foxp3, and the cell-induced suppressive activity of nTreg cells isolated from nonatopic controls, allergic asthmatics, and allergen-specific immunotherapy (AIT)-treated asthmatic patients were studied.

RESULTS

Although the percentage of nTreg in peripheral blood mononuclear cells was increased, the expression of Foxp3 and its cell-induced suppressive activity were significantly lower in Dermatophagoides pteronyssinus (Der p)-sensitive asthmatic children when compared to nonatopic controls. In contrast, the expression of Foxp3 and the functional activity of nTreg cells were reversed in allergic asthmatics who received AIT. The addition of recombinant tumor necrosis factor (TNF)-alpha directly downregulated Foxp3 expression and abrogated the cell-induced suppressive function of Treg cells. The anti-TNF-alpha reagent, etanercept, restored the functional activity and Foxp3 expression of CD4(+)CD25(high) Treg derived from allergic asthmatics.

CONCLUSIONS

The functional insufficiency of nTreg cells in patients with allergic asthma may be related to the enhanced production of TNF-alpha and its effect on the Foxp3 expression. These results may explain, in part, the effectiveness of anti-TNF-alpha therapy in the treatment of allergic asthma.

The major horse allergen Equ c 1 contains one immunodominant region of T cell epitopes

BACKGROUND

Despite the fact that most significant mammalian respiratory allergens are lipocalin proteins, information on the human T cell reactivity to these allergenic proteins is largely missing.

OBJECTIVE

Knowing the T cell epitopes in allergens is a prerequisite for developing novel preparations for allergen immunotherapy.

METHODS

Specific T cell lines were generated with recombinant Equ c 1 from the peripheral blood mononuclear cells (PBMCs) of 10 horse-allergic subjects. For determining T cell epitopes, the lines were stimulated with 16mer synthetic Equ c 1 peptides overlapping by 14 amino acids. The binding capacity of Equ c 1 peptides to human leucocyte antigen class II molecules was determined by the competitive ELISA.

RESULTS

The major horse allergen Equ c 1 resembles two other lipocalin allergens, the major cow allergen Bos d 2 and the major dog allergen Can f 1, in that it is weakly stimulatory for the PBMCs of sensitized subjects. Moreover, the T cell epitopes of Equ c 1 are clustered in a few regions along the molecule, as is the case with Bos d 2 and Can f 1. Similar to Bos d 2, Equ c 1 contains one immunodominant epitope region at the carboxy-terminal end of the molecule. The T cell lines of eight horse-allergic subjects out of 10 showed strong reactivity to one or both of the two overlapping peptides, p143-158 and p145-160, in this region. The region probably contains two overlapping epitopes.

CONCLUSION

The 18mer peptide p143-160 from the immunodominant region of Equ c 1 is a potential candidate for the peptide-based immunotherapy of horse-sensitized subjects.

Immune regulation by CD4+CD25+ T cells and interleukin-10 in birch pollen-allergic patients and non-allergic controls

BACKGROUND

CD4+CD25+ regulatory T (Treg) cells and the cytokines IL-10 or TGF-beta play key roles in the maintenance of T cell homeostasis and tolerance to infectious and non-infectious antigens such as allergens.

OBJECTIVE

To investigate the regulation of immune responses to birch pollen allergen compared with influenza antigen by Treg cells obtained from birch pollen-allergic patients and non-allergic controls.

METHODS

Peripheral blood was collected from 10 birch pollen-allergic patients and 10 non-allergic healthy controls. CD4+CD25+ and CD4+CD25- cells isolated by magnetic-activated cell sorting were co-cultured and stimulated with birch pollen extract or influenza vaccine in the absence or presence of anti-IL-10 or soluble TGF-betaRII.

RESULTS

CD4+CD25+ cells from non-allergic controls were able to suppress influenza antigen and birch pollen stimulated effector cell proliferation, whereas CD4+CD25+ cells from allergic patients suppressed influenza antigen-, but not birch pollen-stimulated proliferation. The production of Th1 cytokines, but not Th2 cytokines, was suppressed by CD4+CD25+ cells from both allergic patients and controls, upon stimulation with birch pollen extract. Neutralization of IL-10 led to significantly increased production of IFN-gamma in cultures with CD4+CD25- T effector cells. In addition, six-fold higher concentrations of TNF-alpha were detected after neutralization of IL-10 in both CD4+CD25- and CD4+CD25+ cell cultures from allergic patients and controls.

CONCLUSION

We demonstrate that the allergen-specific suppressive function of CD4+CD25+ cells from allergic patients is impaired compared with non-allergic controls. Moreover, neutralization of IL-10 enhances the production of TNF-alpha, suggesting counter-acting properties of IL-10 and TNF-alpha, where IL-10 promotes tolerance and suppression by Treg cells and TNF-alpha promotes inflammatory responses.

Regulatory T cells in allergy and asthma

Allergic diseases including asthma have risen considerably in prevalence in the last 50 years. A concomitant rise in autoimmune disease suggests a defect in immunoregulation, rather than a reduction in T-helper type 1 immunity. Immune responses to innocuous environmental antigens in health are characterized by dominant regulation through the production of interleukin-10 and transforming growth factor-beta. Recent studies suggest that diverse populations of regulatory T cells (Treg) play an important role in regulating T-helper type 2 (Th2) responses to allergens, maintaining functional tolerance. Regulatory responses appear to be compromised in allergic individuals but may be reconstituted to some extent with specific allergen immunotherapy. In experimental models, Treg can suppress Th2 responses to allergen, airway eosinophilia, mucous hypersecretion, and airway hyperresponsiveness. Further studies are required to precisely define the mechanisms of development and action of these cells, and to identify and evaluate novel targets for the treatment of allergic diseases.

Role of regulatory T cells and FOXP3 in human diseases

Immune regulation and tolerance are specific functions of the immune system, meaning at prevention or limitation of effector immune responses against inner and external insults. Regulatory T (Treg) cells are crucial players in this immune balance network. Research over the last 10 years has significantly contributed to characterizing Treg cell features, their mechanisms of function, and their role in human pathologies. The discovery of FOXP3 as an essential transcription factor not only for differentiation and function of naturally occurring Treg cells but also for regulation of intracellular molecules related to effector T-cell responses has provided new insights into the pathogenesis of immune-mediated diseases. Interestingly, there is increasing evidence that the individual signature of genes relevant for immune regulation definitely influences the final outcome of an immune response.

Microbial manipulation of immune function for asthma prevention: inferences from clinical trials

The "hygiene hypothesis" proposes that the increase in allergic diseases in developing countries reflects a decrease in infections during childhood. Cohort studies suggest, however, that the risks of asthma are increased in children who suffer severe illness from a viral respiratory infection in infancy. This apparent inconsistency can be reconciled through consideration of epidemiologic, clinical, and animal studies. The elements of this line of reasoning are that viral infections can predispose to organ-specific expression of allergic sensitization, and that the severity of illness is shaped by the maturity of immune function, which in turn is influenced by previous contact with bacteria and viruses, whether pathogenic or not. Clinical studies of children and interventional studies of animals indeed suggest that the exposure to microbes through the gastrointestinal tract powerfully shapes immune function. Intestinal microbiota differ in infants who later develop allergic diseases, and feeding Lactobacillus casei to infants at risk has been shown to reduce their rate of developing eczema. This has prompted studies of feeding probiotics as a primary prevention strategy for asthma. We propose that the efficacy of this approach depends on its success in inducing maturation of immune function important in defense against viral infection, rather than on its effectiveness in preventing allergic sensitization. It follows that the endpoints of studies of feeding probiotics to infants at risk for asthma should include not simply tests of responsiveness to allergens, but also assessment of intestinal flora, immune function, and the clinical response to respiratory viral infection.

Activation of naturally occurring lung CD4(+)CD25(+) regulatory T cells requires CD8 and MHC I interaction

Naturally occurring Foxp3(+)CD4(+)CD25(+) T cells (nTregs) isolated from lungs of naive mice regulate allergic airway hyperresponsiveness (AHR) and inflammation. Here, we demonstrate the critical requirement for engagement of MHC class I on CD4(+)CD25(+) T cells by CD8 for the functional activation of these nTregs. Suppression of allergen-induced AHR and inflammation by nTregs was abolished in mice treated with anti-CD8. Correspondingly, decreased levels of IL-10 and TGF-beta and increased levels of Th2 cytokines in bronchoalveolar lavage were detected in these treated mice. Similarly, nTregs isolated from beta2m(-/-) mice or from mice treated with anti-MHC I antibody in vitro before intratracheal transfer failed to modulate AHR or inflammation. Coculture of nTregs with CD8(+) T cells increased IL-10 and TGF-beta. Addition of anti-MHC I or anti-CD8 reduced IL-10 and TGF-beta. These results demonstrate that functional activation of nTregs requires the interaction between MHC I on CD4(+)CD25(+) T cells and CD8.

Effects of pollen and nasal glucocorticoid on FOXP3+, GATA-3+ and T-bet+ cells in allergic rhinitis

BACKGROUND

T-regulatory cells (Treg) affect the balance of T(H)2 and T(H)1 cells. Treg, T(H)2 and T(H)1 cells are regulated by the FOXP3, GATA-3 and T-bet transcription factors respectively. Our aim was to determine the number of FOXP3(+), GATA-3(+) and T-bet(+) cells in nasal mucosa in symptom-free allergic rhinitis (AR) patients vs healthy controls, as well as the effects of natural pollen exposure and concomitant nasal glucocorticoid treatment on these cells.

METHODS

Nasal biopsies were taken from healthy controls and patients with grass-pollen AR preseason. The AR patients were randomized to receive treatment with either fluticasone propionate (FP) or a placebo, and additional biopsies were taken during the pollen season. FOXP3(+), GATA-3(+) and T-bet(+) cells in nasal mucosa were quantified by immunohistochemistry.

RESULTS

The number of FOXP3(+) and GATA-3(+) cells, but not T-bet(+) cells, was significantly higher in AR patients vs controls preseason. The number of FOXP3(+) cells remained unchanged in the former group after the pollen season but decreased significantly in the nasal mucosa as a result of FP treatment. The pollen season substantially increased the number of GATA-3(+) cells, which was inhibited by FP. The number of T-bet(+) cells was not affected by pollen or FP.

CONCLUSION

These data suggest that nasal glucocorticoids attenuate the allergic inflammation partly by reducing the number of T(H)2 cells, but not by means of local upregulation of Treg cells. The local relationship between T(H)1 and T(H)2 cells as well as between Treg and T(H)2 is maintained by nasal glucocorticoid treatment.

[Regulatory cells]

The role of regulatory T cells in the induction and maintenance of peripheral tolerance has received growing attention during the last years. Several subsets of regulatory T cells were described based on their surface markers and cytokine production, but nevertheless, there are no specific markers for any subsets and their classification relies on their suppression mechanism. It is unknown which of the subgroups of regulatory T cells is more important in the prevention and control of allergic diseases, being commonly accepted its importance in homeostasis.

The levels of CD4+CD25+ regulatory T cells in paediatric patients with allergic rhinitis and bronchial asthma

Our purpose was to determine whether numbers of CD4(+)CD25(+) T [T regulatory (T(reg))] cells and mRNA expression of functional molecules of T(reg) are related to airway allergy and disease severity in 51 paediatric patients with allergic rhinitis or bronchial asthma and 47 healthy controls. Surface markers were evaluated with flow cytometry, and mRNA was determined with real-time polymerase chain reaction. Children with allergic disease had fewer CD4(+)CD25(+) T cells (8 x 49% +/- 2 x 41% versus 9 x 58% +/- 2 x 43%, P<0 x 05) and CD4(+)CD25(hi) T cells (1 x 32% +/- 0 x 68% versus 1 x 70% +/- 0 x 68%, P<0 x 01) than control subjects. Numbers of CD4(+)CD25(+) and CD4(+)CD25(hi) T lymphocytes were higher in children with persistent allergic rhinitis and/or moderate-severe bronchial asthma than in those with respective milder disease. The number of T(reg) cells was correlated positively with total immunoglobulin E level. The mRNA expression of forkhead box P3 (FoxP3) was increased in moderate-severe versus mild asthma (2 x 93 +/- 0 x 38 versus 1 x 60 +/- 0 x 31, P< 0 x 01). Patients with moderate-severe bronchial asthma also had increased mRNA expression of interleukin (IL)-10 compared with patients with mild asthma (15 x 24 +/- 4 x 07 versus 3 x 77 +/- 2 x 18, P<0 x 01). The suppressive function of T(reg) cells from patients with more severe asthma was competent in vitro. On average, decreased numbers of T(reg) cells in children with allergic airway disease might represent a defect of the T(reg) population. With increased expression of FoxP3 and IL-10 in T(reg) from patients with relatively severe allergic disease, adaptive and functional T(reg) might be generated in response to aggravated atopy and disease severity.

Quantitative and functional impairment of pulmonary CD4+CD25hi regulatory T cells in pediatric asthma

BACKGROUND

Asthma is characterized by a T(H)2 immune response. CD4(+)CD25(hi) regulatory T cells (Tregs) have been proposed to prevent allergic diseases through suppression of T(H)2 responses.

OBJECTIVE

We sought to investigate the role of CD4(+)CD25(hi) T cells in children with asthma.

METHODS

CD4(+)CD25(hi) Tregs and forkhead/winged-helix transcription factor FOXP3 mRNA levels were quantified in peripheral blood and bronchoalveolar lavage fluid (BALF) of 18 children with asthma, 10 children with chronic cough, and 13 control subjects without lung diseases. CD4(+)CD25(hi) T cells were isolated from peripheral blood and BALF of asthmatic patients and control subjects, and their capacity to suppress proliferation and cytokine/chemokine production of autologous responder T cells was analyzed.

RESULTS

CD4(+)CD25(hi) T cells were decreased in BALF of asthmatic children compared with values in children with cough or control subjects. In children with asthma, inhaled corticosteroid treatment was associated with increased percentages of CD4(+)CD25(hi) T cells in peripheral blood and BALF. Isolated BALF and peripheral blood CD4(+)CD25(hi) T cells from nonasthmatic subjects suppressed proliferation and cytokine/chemokine production by CD4(+)CD25(-) responder T cells. BALF CD4(+)CD25(hi) T cells from asthmatic subjects failed to suppress proliferation and production of T(H)2-associated cytokines and chemokines by CD4(+)CD25(-) responder T cells, which was restored after use of inhaled corticosteroids.

CONCLUSION

These findings provide the first evidence that pulmonary CD4(+)CD25(hi) Tregs are impaired in pediatric asthma.

CLINICAL IMPLICATIONS

Pulmonary Tregs might represent a therapeutic target in pediatric asthma.

A Possible Role of CD4+CD25+ T Cells as Well as Transcription Factor Foxp3 in the Dysregulation of Allergic Rhinitis

BACKGROUND

Allergic rhinitis (AR) is a Th2 predominant disease, and its pathogenic mechanism is still poorly understood. CD4(+)CD25(+) T cells account for approximately 5% to 10% peripheral CD4(+) T cells and has been shown to regulate the activation of effector T cells in the periphery. The activity of CD4(+)CD25(+) T cells is associated with the transcription factor Foxp3. The present study aimed to evaluate the possible role of CD4(+)CD25(+) T cells as well as Foxp3 in the pathogenesis of AR.

METHODS

Nasal tissues and peripheral blood mononuclear cells (PBMCs) were obtained from 17 patients with AR and 11 control subjects. Foxp3 was detected in nasal tissues by immunohistochemistry and real-time reverse transcription-polymerase chain reaction (RT-PCR). CD4(+)CD25(+) T cells and Foxp3 were evaluated in PBMCs by using flow cytometry. Concentrations of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) were measured by enzyme-linked immunosorbent assay (ELISA) in cultured PBMCs in the presence or absence of stimulation with phorbol ester (PMA) and Ionomycin.

RESULTS

The numbers of Foxp3(+) cells was 129.5 +/- 35.6 and 44.2 +/- 20.5 cells/mm(2) in nasal mucosa of two groups (P < .05). There were less Foxp3(+) lymphocytes and decreased Foxp3 mRNA in AR compared with the control (P < .05). The frequencies of the CD4(+)CD25(+) population in PBMCs of two groups were 1.99 +/- 0.95% and 3.55 +/- 1.27% (P < .05). There was significant difference in the frequencies of the Foxp3(+)CD4(+) CD25(+) population (1.81 +/- 0.77 vs 3.37 +/- 1.04, P < .05) and mean fluorescence intensity (MFI) of Foxp3 (5.93 +/- 2.64 vs 11.72 +/- 4.29, P < .05) in PBMCs of two groups. After stimulation, the concentrations of IL-2 and IFN-gamma were 182.72 +/- 85.11 pg/mL and 348.94 +/- 151.88 pg/mL in PBMCs with AR, while those were 90.6 +/- 61.5 pg/mL and 155.64 +/- 68.33 pg/mL in controls (P < .05).

CONCLUSION

Our results indicate that CD4(+) CD25(+) regulatory T cells as well as Foxp3 may play a crucial role in immunological imbalance of AR. These findings suggest that increasing Foxp3 and CD4(+)CD25(+) T cells have the potential to be new therapeutic targets for the treatment of AR.

Changes in immune regulation in response to examination stress in atopic and healthy individuals

BACKGROUND

Stress can aggravate the allergic inflammation, but determinants of disturbed immune regulation are largely unknown.

OBJECTIVE

To determine systemic immunological, local inflammatory and functional airway responses to stress in healthy and atopic individuals.

METHODS

Forty-one undergraduate students, 22 with allergy of whom 16 had asthma, and 19 healthy controls, were studied in a low-stress period and in association with a large exam. Subjects completed questionnaires on stress and health behaviours, underwent lung function tests, bronchial methacholine challenge, measurements of exhaled nitric oxide and urine cortisol. Blood cells were phenotyped, and cytokines from mononuclear blood cells were analysed.

RESULTS

Perceived stress and anxiety increased in both groups during the exam period while cortisol increased only in the atopy group. Cytokine production decreased broadly in response to stress in both groups, which was paralleled by an increase in the proportion of regulatory T cells (CD4(+)CD45RO(+)CD25(bright)). Interestingly, atopic individuals, but not controls, reacted with a decreased T-helper type 1/T-helper type 2 (Th1/Th2) ratio and a decrease in natural killer (NK) cell numbers in response to stress. In control subjects only, exhaled nitric oxide decreased and forced expiratory volume in one second increased during stress.

CONCLUSION

Atopic and non-atopic subjects shared some immune changes in response to stress, such as a dramatic decline in cytokines and an increase in the number of regulatory T cells in peripheral blood. However, other stress-induced immune changes were unique to atopic individuals, such as a skewed Th1/Th2 ratio and reduced NK cell numbers, indicating that some pathogenic mechanisms in atopics may be more strongly affected by stress than others.

Association between CD4(+)CD25(high) T cells and atopy in children

BACKGROUND

There is evidence that CD4(+)CD25(high) T-regulatory cells are important for establishing tolerance to allergens, but information in children is limited.

OBJECTIVE

To test the hypothesis that greater numbers and function of CD4(+)CD25(high) T cells are associated with a reduced risk of childhood allergies and wheezing.

METHODS

A cohort of 151 six-year-old children from atopic families was analyzed for peripheral blood CD4(+)CD25(high) and CD4(+)CD25(int) T cells by flow cytometry and for clinical and immunologic correlates of atopy. The associations between these variables were assessed by regression analysis.

RESULTS

Factors positively associated with % CD4(+)CD25(high)/CD4 T cells were male sex, number of positive allergen-specific IgE tests, total IgE, season, and 1-month average total pollen count preceding blood draw. The percentage of CD4(+)CD25(high)/total CD4 T cells did not correlate with induced cytokine production, and correlated negatively with suppressive capacity of CD4(+)CD25(+) T cells (r = -0.45; P = .034). The percentage of CD4(+)CD25(int)/CD4 T cells was 54% higher in pollen-sensitized children compared with nonsensitized children in spring (P = .023 for interaction), and correlated positively with IL-5, IL-10, and IL-13 (P < or = .001 for all).

CONCLUSION

Our findings suggest that blood CD4(+)CD25(high) cells are a mixture of activated and regulatory T cells, and that these cells could be seasonally regulated by environmental factors such as pollen exposure.

CLINICAL IMPLICATIONS

Seasonal increases in CD4CD25(high) expression in children with allergy may represent systemic immune activation caused by pollen exposures.

Use of multiple peptides containing T cell epitopes is a feasible approach for peptide-based immunotherapy in Can f 1 allergy

We have previously shown that the major dog allergen Can f 1 contains seven T cell epitope regions, none of which was preferentially recognized. To identify the immune characteristics of Can f 1 epitopes and to verify their suitability for peptide-based allergen immunotherapy, short-term T cell lines were generated with epitope-containing peptides from peripheral blood mononuclear cells of Can f 1 skinprick test-positive allergic and healthy control subjects. The lines were examined for their proliferative capacity and cytokine production upon stimulation with the allergen peptide, a homologous peptide from human tear lipocalin (TL) and Can f 1 and TL proteins. Can f 1 peptides induced proliferation of T cells and gave rise to T cell lines with comparable efficiencies. In particular, the T cell lines of allergic subjects induced with p33-48 and p107-122 favoured the production of interferon-gamma and interleukin-10, respectively. A greater number of Can f 1-specific T cell lines were generated from allergic than from healthy individuals. Two p107-122-induced Can f 1-specific T cell lines also reacted to a homologous peptide of human TL. Our results suggest that several T cell epitope-containing peptides should be used in combination for specific immunotherapy in Can f 1 allergy.

Naturally occurring lung CD4(+)CD25(+) T cell regulation of airway allergic responses depends on IL-10 induction of TGF-beta

Peripheral tolerance to allergens is mediated in large part by the naturally occurring lung CD4(+)CD25(+) T cells, but their effects on allergen-induced airway responsiveness have not been well defined. Intratracheal, but not i.v., administration of naive lung CD4(+)CD25(+) T cells before allergen challenge of sensitized mice, similar to the administration of the combination of rIL-10 and rTGF-beta, resulted in reduced airway hyperresponsiveness (AHR) and inflammation, lower levels of Th2 cytokines, higher levels of IL-10 and TGF-beta, and less severe lung histopathology. Significantly, CD4(+)CD25(+) T cells isolated from IL-10(-/-) mice had no effect on AHR and inflammation, but when incubated with rIL-10 before transfer, suppressed AHR, and inflammation, and was associated with elevated levels of bronchoalveolar lavage TGF-beta levels. By analogy, anti-TGF-beta treatment reduced regulatory T cell activity. These data identify naturally occurring lung CD4(+)CD25(+) T cells as capable of regulating lung allergic responses in an IL-10- and TGF-beta-dependent manner.

CD4+ CD25+ regulatory T cells in human pregnancy: development of a Treg-MLC-ELISPOT suppression assay and indications of paternal specific Tregs

The current study was aimed at developing a one-way mixed leucocyte culture-enzyme-linked immunospot (MLC-ELISPOT) assay for the study of CD4(+) CD25(+) regulatory T (T(reg)) cells and applying this method in the study of antifetal immune reactions during human pregnancy. Twenty-one pregnant women and the corresponding fathers-to-be, and 10 non-pregnant control women and men, participated in the study. CD4(+) CD25(+) cells were isolated from peripheral blood mononuclear cells (PBMC) by immunomagnetic selection. Maternal/control PBMC were stimulated with paternal or unrelated PBMC in MLC. Secretion of interleukin-4 (IL-4) and interferon-gamma (IFN-gamma) from responder cells, with or without the presence of autologous T(reg) cells, was analysed by ELISPOT. PBMC from pregnant women showed increased secretion of IL-4 compared to controls. In pregnant and non-pregnant controls, T(reg) cells suppressed IFN-gamma reactivity against paternal and unrelated alloantigens. Interestingly, T(reg) cells suppressed IL-4 secretion against paternal but not unrelated alloantigens during pregnancy. We have successfully developed a model for studying T(reg) cells in antifetal cytokine reactions during pregnancy. Results indicate that T(reg) cells contribute to strict regulation of both T helper type 1-like and type 2-like antifetal immune reactions. Interestingly, T helper type 2-like cells specific to unrelated alloantigens are able to escape the suppression of T(reg) cells, which would allow for IL-4, alongside CD4(+) CD25(+) T(reg) cells, to control potentially detrimental IFN-gamma reactions during pregnancy.

Interleukin-10-secreting regulatory T cells in allergy and asthma

Allergic diseases, including asthma, are chronic inflammatory disorders originating from an aberrant immune response to innocuous antigens in our environment (allergens). In susceptible individuals, sensitization to allergen leads to the induction of allergen-specific T-helper type 2 (Th2) responses and immunoglobulin E (IgE) production. Subsequent challenge with allergen results in IgE-mediated mast cell activation and the recruitment and activation of effector cells, leading to clinical symptoms of disease. In this review, we discuss evidence that the anti-inflammatory cytokine interleukin-10 (IL-10) offers therapeutic promise for the control of asthma and allergy. We highlight the potential role of IL-10 secretion by a specialized T-cell subset, T regulatory cells, to prevent allergic inflammation in healthy individuals and to provide long-term relief from disease symptoms in allergic patients.

The role of immune tolerance in asthma pathogenesis

Immune-mediated tolerance encompasses a wide spectrum of mechanisms that can prevent unnecessary and potentially harmful inflammatory responses. An increasing number of scientific publications provide proof for the concept that an impairment of immune-tolerance mechanisms might be causally related to the development of unwanted Th2-driven, allergen-induced airway diseases. In this review, we discuss immune tolerance and the evidence supporting its role in asthma pathogenesis.

Regulatory T cells as potential immunotherapy in allergy

PURPOSE OF REVIEW

CD4 regulatory T cells are fundamental for the induction and maintenance of immunological tolerance to self and foreign-antigens, including allergens. Here we discuss recent advances in the field of regulatory T cells and how this knowledge can be exploited to treat and prevent allergy.

RECENT FINDINGS

Current research suggest that naturally occurring CD4CD25 regulatory T cells together with inducible IL-10-producing CD4 regulatory T cells actively control allergic responses and that their function or numbers may contribute to the development or progression of allergy. Indeed, successful treatment of allergy by allergen-specific immunotherapy may depend on the induction of IL-10 secreting CD4 T cells. Work has begun to reveal the impact of various pharmaceutical treatments on naturally occurring CD25 regulatory T cells. In addition, recent findings point to an important role for toll-like receptors in the tuning of regulatory T cell function and homeostasis. This may link the hygiene hypothesis to regulatory T cells and open up new possibilities for early intervention in allergic disease.

SUMMARY

The identification of a role for regulatory T cells in allergic disease has provided a host of new therapeutic possibilities, with the potential prospect of safe and long-term alleviation of allergic diseases.

Worms and allergy

Worms and asthma are associated with a type 2 immune response, but evidence has accumulated that helminth infection is negatively associated with atopy, prevalence of allergic diseases and severity of asthma. One important difference between these polarized type 2 responses is that in allergy modulation of the immunological response is not appropriate, whereas in infection with helminths, several host mechanisms down-regulate the host immune response. As a result, patients infected with worms have a decrease in both type 1 and type 2 responses. The main mechanism involved in this down-modulation is increased production of IL-10, but expansion of regulatory T cells and NKT cells may also participate. Regarding the interaction between worms and allergy, a few variables need to be taken in account: phase (acute or chronic) of helminth infection, parasite load and species of helminth. In animals and humans, acute helminth infection may increase manifestations of allergy, whereas chronic infection with parasites decreases atopy. The modulation of the immune response by helminths is dependent on having an adequate parasite load. Moreover, although several helminth species have been shown to modulate immune responses, most in vitro and in vivo studies have focused on the importance of Schistosoma mansoni in down-modulating allergic reactions.

The regulation of allergy and asthma

Allergic diseases and asthma are caused by exaggerated T-helper 2 (Th2)-biased immune responses in genetically susceptible individuals. Tolerance to allergens is a mechanism that normally prevents such responses, but the specific immunological events that mediate tolerance in this setting are poorly understood. A number of recent studies indicate that regulatory T cells (Tregs) play an important role in controlling such Th2-biased responses. Tregs involved in regulating allergy and asthma consist of a family of related types of T cells, including natural CD25+ Tregs as well as inducible forms of antigen-specific adaptive Tregs. Impaired expansion of natural and/or adaptive Tregs is hypothesized to lead to the development of allergy and asthma, and treatment to induce allergen-specific Tregs could provide curative therapies for these problems.

Inhibition of the allergic response by regulatory T cells

PURPOSE OF REVIEW

Allergic diseases are caused by the overdevelopment of T-helper type 2 biased immune responses in susceptible individuals. A number of recent studies indicate that regulatory T cells play an important role in controlling such T-helper type 2 biased responses not only in animal models, but in humans as well, and these will be reviewed in this article.

RECENT FINDINGS

A family of regulatory cells appears to be involved in regulating allergies. Both naturally occurring CD4CD25 regulatory T cells and inducible forms of antigen-specific regulatory T cells, both expressing the transcription factor foxp3, have been shown to inhibit the inappropriate immune responses involved in allergic diseases. Impaired expansion of natural or adaptive regulatory T cells is hypothesized to lead to the development of allergy, and treatment to induce allergen-specific regulatory T cells could provide curative therapies for allergy and asthma.

SUMMARY

Allergen-specific regulatory T cells play an important role in controlling the development of allergy and asthma.

Selective roles and dysregulation of interleukin-10 in allergic disease

There is mounting evidence to support a role for interleukin (IL)-10 in the regulation of both allergic and nonallergic immune responses. The current view is that IL-10 influences Th2-driven allergic processes by altering the interplay between Th1 and Th2 effector cells. However, lack of a clear delineation of the different types of IL-10-secreting regulatory T cells poses a major challenge in defining IL-10-mediated immune pathways, which govern the development, persistence, and modulation of allergic status. This is compounded by observations that undermine the credibility of the Th1/Th2 paradigm as a model for allergic disease. Nevertheless, enhanced IL-10 secretion by T cells during conventional immunotherapy, coupled with evidence of a link between genetics and high IL-10 production to a specific allergen, suggests that IL-10 induction is an appropriate goal of therapy. Knowledge of the targeted patient population and design of an immunogen (ie, peptide or modified allergen) within this context are likely to provide improved results over conventional immunotherapy.

Regulatory T cells in human disease and their potential for therapeutic manipulation

Regulatory T cells are proposed to play a central role in the maintenance of immunological tolerance in the periphery, and studies in many animal models demonstrate their capacity to inhibit inflammatory pathologies in vivo. At a recent meeting [Clinical Application of Regulatory T Cells, 7-8 April 2005, Horsham, UK, organized by the authors of this review, in collaboration with the British Society for Immunology and Novartis] evidence was discussed that certain human autoimmune, infectious and allergic diseases are associated with impaired regulatory T-cell function. In contrast, evidence from several human cancer studies and some infections indicates that regulatory T cells may impair the development of protective immunity. Importantly, certain therapies, both those that act non-specifically to reduce inflammation and antigen-specific immunotherapies, may induce or enhance regulatory T-cell function. The purpose of this review was to summarize current knowledge on regulatory T-cell function in human disease, and to assess critically how this can be tailored to suit the therapeutic manipulation of immunity.

Factors responsible for differences between asymptomatic subjects and patients presenting an IgE sensitization to allergens. A GA2LEN project

The synthesis of allergen-specific IgE is required for the development of allergic diseases including allergic rhinitis and allergic asthma (patients), but many individuals with allergen-specific IgE do not develop symptoms (asymptomatic subjects). Differences may exist between asymptomatic subjects and patients. Whether the presence of allergen-specific IgE translates into clinical allergy most likely depends on a complex interplay of multiple factors. These include a family history of atopy, the levels of total serum IgE and, allergen-specific IgE or IgG, epitope-specificity of IgE and their degree of polyclonality (mono- vs polysensitized), as yet unidentified serum factors, the balance of T regulatory cells (Treg) and Th1/Th2 cells, the polymorphisms of the high affinity receptor for IgE (FcepsilonRI) and other factors regulating the activation of FcepsilonRI-bearing cells. Asymptomatic subjects may be more often monosensitized than patients who may be more often polysensitized. There are many unanswered important questions that need to be addressed in order to better understand how IgE sensitization translates into clinical allergy. The assessment of differences between the asymptomatic and symptomatic groups of subjects represent one of the scientific programs of Global Allergy and Asthma European Network funded by the European Union and the hypotheses underlying these differences are presented in this paper.