Role of CD4(+) CD25(+) regulatory T cells in T helper 2 cell-mediated allergic inflammation in the airways

Regulatory T cell monitoring in severe eosinophilic asthma patients treated with mepolizumab

Severe eosinophilic asthma (SEA) has been associated with T-helper type 2 (Th2) inflammatory response. A good understanding of T cell functions in asthma is important for therapy, especially in the choice of biological treatments for severe cases. Mepolizumab, an IL-5 antagonist, is indicated for the treatment of severe asthma. Regulatory T cells (Tregs) suppress inflammation by secreting cytokines that inhibit Th2 cell proliferation. We investigated peripheral Treg, CD4, CD8, CD19 and NK cell percentages and their relationship to clinical and functional parameters, including peripheral eosinophils, before and after anti-IL5 treatment. Subjects were 14 adult SEA patients (9 male, 54.1 ± 11.6 years), treated with mepolizumab, and 10 controls. T cells (CD4 and CD8), CD19, NK and Tregs were evaluated by flow cytometry. Comparison of lung function parameters before and after treatment with mepolizumab (T0 and T1) showed an increase in FEV1, FEV1/FVC ratio and a reduction in blood eosinophil percentages. CD8 and CD16/56⁺ CD3⁺ were significantly higher in SEA patients than controls (P = .04 and P = .03, respectively). A decrease in CD45+, CD8 + and CD16/56⁺ CD3⁺ cell percentages was observed between T0 and T1 (P = .02, P = .04, P = .03, respectively). A significant increase in Treg percentages (P = .0001) was recorded between T0 and T1. Mepolizumab therapy was found to modulate immune response, restoring immune balance in patients with SEA.

Therapeutic Effect of C-C Chemokine Receptor Type 1 (CCR1) Antagonist BX471 on Allergic Rhinitis

Objective and Design

Allergic rhinitis (AR) is an immunoglobulin E (IgE)-mediated inflammatory respiratory hypersensitivity characterized by elevated Th2 cytokines and infiltration of inflammatory cells to nasal tissues. BX471 is a small-molecule C-C chemokine receptor type 1 (CCR1) antagonist involved in suppression of inflammation via blocking of primary ligands. In this study, we examined the anti-inflammatory effect of BX471 on ovalbumin (OVA)-induced AR mice model.

Materials and Methods

Levels of OVA-specific IgE and Th1 cytokines were determined by enzyme-linked immunosorbent assay (ELISA). Nasal expression of proinflammatory mediators was assessed by real-time polymerase chain reaction (RT-qPCR). Nasal-cavity sections were stained with hematoxylin and eosin (HE) and periodic acid-Schiff (PAS) to study eosinophil infiltration and goblet cell metaplasia. Relative protein levels of Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-kB), Toll-like Receptor 4 (TLR4) and Toll-like-receptor 2 (TLR2) were assessed by Western Blot. Percentage of CD4⁺CD25⁺Foxp3⁺ T regulatory cells (Treg) was measured by flow cytometry.

Results

Mice treated with BX471 showed significantly relieved sneezing and nasal-rubbing behaviors. The expression of nasal proinflammatory factors was significantly downregulated by BX471, and protein levels of tumor necrosis factor alpha (TNF- α) and NF-kB were suppressed. Blockade of CCR1 ligands inhibited eosinophil recruitment in nasal cavity. In addition, Treg cells population were upregulated in BX471-treated mice.

Conclusion

BX471 exerts anti-inflammatory effects in a mouse model of AR by inhibiting CCR1-mediated TNF-α production, which subsequently suppresses NF-kB activation in inflammatory cells, leading to a decrease in Th2 cytokines, IL-1β, VCAM-1, GM-CSF, RANTES, and MIP-1α expression levels, thus inhibiting eosinophil recruitment to nasal mucosa. In addition, BX-471 exhibits anti-allergic effect by increasing Treg cell population. Overall, BX471 represents a promising therapeutic strategy against AR.

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Regulatory T Cells in Respiratory Health and Diseases

Respiratory diseases compromise the health of millions of people all over the world and are strongly linked to the immune dysfunction. CD4+FOXP3+ T regulatory cells, also known as Tregs, have a central role maintaining tissue homeostasis during immune responses. Their activity and clinical impact have been widely studied in different clinical conditions including autoimmune diseases, inflammatory conditions, and cancer, amongst others. Tregs express transcription factor forkhead box P3 (FOXP3), which allows regulation of the immune response through anti-inflammatory cytokines such as IL-10 or transforming growth factor beta (TGF-β) and direct cell-to-cell interaction. Maintenance of immune tolerance is achieved via modulation of effector CD4+ T helper 1, 2 or 17 (Th1, Th2, Th17) cells by Tregs. This review highlights the recent progress in the understanding of Tregs in different disorders of the respiratory system.

Tissue-Restricted Adaptive Type 2 Immunity Is Orchestrated by Expression of the Costimulatory Molecule OX40L on Group 2 Innate Lymphoid Cells

The local regulation of type 2 immunity relies on dialog between the epithelium and the innate and adaptive immune cells. Here we found that alarmin-induced expression of the co-stimulatory molecule OX40L on group 2 innate lymphoid cells (ILC2s) provided tissue-restricted T cell co-stimulation that was indispensable for Th2 and regulatory T (Treg) cell responses in the lung and adipose tissue. Interleukin (IL)-33 administration resulted in organ-specific surface expression of OX40L on ILC2s and the concomitant expansion of Th2 and Treg cells, which was abolished upon deletion of OX40L on ILC2s (Il7raCre/+Tnfsf4fl/fl mice). Moreover, Il7raCre/+Tnfsf4fl/fl mice failed to mount effective Th2 and Treg cell responses and corresponding adaptive type 2 pulmonary inflammation arising from Nippostrongylus brasiliensis infection or allergen exposure. Thus, the increased expression of OX40L in response to IL-33 acts as a licensing signal in the orchestration of tissue-specific adaptive type 2 immunity, without which this response fails to establish.

Antiallergic Effects of Trichostatin A in a Murine Model of Allergic Rhinitis

Objectives

Trichostatin A (TSA), an inhibitor of histone deacetylase, has been shown to play an important role in attenuating asthmatic inflammation. However, the effect of TSA in allergic rhinitis is not known. The aims of this study were to investigate the effect of TSA on allergic nasal inflammation and on the induction of regulatory T cells in a murine model of allergic rhinitis.

Methods

BALB/c mice were sensitized intraperitoneally with ovalbumin (OVA) and then challenged intranasally with OVA. TSA (1 mg/kg) was given to the treatment group, and multiple parameters of allergic responses were evaluated to determine the effects of TSA on allergic rhinitis. Allergic nasal symptom scores, including frequency of rubbing and sneezing, were checked. Eosinophil infiltrations were stained with Chromotrope 2R, and the expression levels of OVA-specific IgE, T-helper 1 (Th1) cytokine (interferon-gamma [IFN-γ]), Th2 cytokines (interleukin [IL] 4 and IL-5) and Treg (Foxp3, IL-10, and transforming growth factor-beta [TGF-β]) were measured by quantitative reverse transcription-polymerase chain reaction or enzyme-linked immunosorbent assay.

Results

TSA reduced the scores of allergic nasal symptoms and the amount of eosinophil infiltration into the nasal mucosa. TSA suppressed OVA-specific IgE levels and reduced expression of the IL-4 and IL-5. However, the expression of IFN-γ was unchanged in the treatment group. The levels of Foxp3, IL-10, and TGF-β were increased in pretreatment with TSA as compared to control group.

Conclusion

This study shows that TSA induced antiallergic effects by decreasing eosinophilic infiltration and Th2 cytokines in a murine model of allergic rhinitis via regulation of Tregs. Thus, TSA may be considered a potentially therapeutic agent in treating allergic rhinitis.

Regulatory T Cell Depletion Abolishes the Protective Effect of Dietary Galacto-Oligosaccharides on Eosinophilic Airway Inflammation in House Dust Mite-Induced Asthma in Mice

BACKGROUND

In a murine model for house dust mite (HDM)-induced asthma, dietary galacto-oligosaccharides have been shown to suppress allergic symptoms. Previously, CD25+ regulatory T cells (Tregs) induced by nondigestible oligosaccharides were found to protect against allergy development.

OBJECTIVE

The aim of the current study was to examine the effect of anti-CD25-induced Treg depletion in a murine HDM-induced asthma model and to study the contribution of Tregs in the protective effect of dietary intervention with galacto-oligosaccharides.

METHODS

Male BALB/c mice (aged 6-8 wk) were intranasally sensitized and challenged with phosphate-buffered saline (PBS) or HDM. Two weeks before sensitization and throughout the whole experiment, mice were fed a control or 1% w/w galacto-oligosaccharide diet. Tregs were depleted by anti-mouse CD25 antibody (intraperitoneally injected). On day 14, T helper cell subtypes in lung and spleen were analyzed and cytokines were measured. Leukocyte subtypes were analyzed in the bronchoalveolar lavage fluid, and interleukin (IL)-33 and chemokines were measured in lung homogenate supernatants.

RESULTS

Anti-CD25 treatment depleted CD25+ Forkhead box P3+ Tregs in the lung and spleen of control and HDM-allergic mice (P < 0.0001) by >70% while increasing the percentage of activated T helper cells (P < 0.05) and type 2 T helper cells (P < 0.05). This was associated with increased IL-10, IL-4, and IL-13 concentrations in supernatants of ex vivo restimulated lung cells (P < 0.01). Bronchoalveolar lavage fluid leukocyte numbers and percentages of eosinophils and lymphocytes were greater in HDM-allergic mice compared with PBS mice (P < 0.01) but remained unaffected by the anti-CD25 treatment. Galacto-oligosaccharides decreased airway eosinophilia compared with HDM-allergic mice fed the control diet (from 47.8% ± 6.7% to 26.6% ± 8.5%, P < 0.01). This protective effect was lost in anti-CD25-treated mice (P < 0.05). In lung homogenates of HDM-allergic mice, IL-33 was increased compared with PBS mice (from 2.8 ± 0.3 to 5.4 ± 0.6 ng protein/mg, P < 0.01). Galacto-oligosaccharides abrogated the increase in IL-33 compared with HDM-allergic mice fed the control diet (3.0 ± 0.6 ng protein/mg, P < 0.05), which was abolished by the anti-CD25 treatment (P < 0.01).

CONCLUSIONS

Treg depletion enhances pulmonary type 2 T helper cell frequency and cytokine release in HDM-induced asthma in mice. Galacto-oligosaccharides decreased airway eosinophilia and IL-33 concentrations in the lung, which was abrogated by Treg depletion. This indicates that galacto-oligosaccharides have a beneficial effect in the prevention of HDM-induced allergic asthma by supporting pulmonary Treg function.

Risk factors for persistence of asthma in children: 10-year follow-up

OBJECTIVE

Risk factors related to the outcome of childhood asthma are not yet well established. We aimed to investigate the long-term outcome for children with asthma to determine the risk factors in predicting persistence of disease.

METHODS

Sixty-two children with asthma were evaluated retrospectively at the end of a 10-year follow-up. Patients were asked to complete a questionnaire requesting clinical information, and underwent physical examination, skin prick testing, a pulmonary function test and bronchial provocation testing. Immunologic parameters evaluated were allergen-specific IgE and IgG4 levels, and allergen-induced generation of CD4(+)CD25(+) cells.

RESULTS

Mean age at final assessment was 15.9 ± 3.6 years, and duration of follow-up was 10.30 ± 1.27 years. Fifty percent of patients outgrew their asthma during the 10-year follow-up period. All the non-atopic patients outgrew their disease during the study period, whereas 67% of atopic patients did not. We identified two risk factors independently related to the persistence of symptoms: presence of bronchial hyper-responsiveness and presence of rhinitis. Atopic children who were in remission demonstrated significantly higher allergen-induced CD4(+)CD25(+) T cells compared to healthy controls.

CONCLUSIONS

Atopy, presence of rhinitis, positive and presence of bronchial hyper-reactivity are important risk factors for the persistence of asthma in children. Allergen-induced CD4(+)CD25(+) T cells were higher in the atopic children who outgrew their disease, implicating an immunological mechanism of asthma remission in children.

Increased bronchial density of CD25+Foxp3+ regulatory T cells in occupational asthma: relationship to current smoking

To identify activated T cell subset in the asthmatic bronchia, we developed a triple-colour immunohistofluorescence labelling technique on cryo-section to discriminate activated CD4+CD25+ T cells, (effector T cells) from Foxp3+ regulatory T cells (Treg). Additional coexpression of activation and proliferation markers was also examined in situ. Bronchial biopsies were taken from 20 aluminium potroom workers (12 smokers) with asthma (>12% reversibility), 15 non-asthmatic potroom workers (7 smokers) and 10 non-smoking, non-exposed controls. Non-smoking asthmatics had significantly higher subepithelial density of both Tregs, effector T cells, activated (HLA-DR+) CD8+ and activated CD4+ T cells. Moreover, both Tregs, effector T cells and CD8+ T cells proliferated in the non-smoking asthmatics, only. Although smoking asthmatics had no asthma-associated increase in bronchial T cell, both had a significantly increase in effector T cell to Treg ratios. The significantly increased bronchial density of Tregs, effector T cells, proliferative T cells and activated CD8+ T cells in non-smoking asthmatics clearly showed that both the effector T cells and the inhibitory Treg system were activated in asthma.

Absence of Foxp3+ regulatory T cells during allergen provocation does not exacerbate murine allergic airway inflammation

Regulatory T cells (Tregs) play a non-redundant role in maintenance of immune homeostasis. This is achieved by suppressing both, priming of naïve cells and effector cell functions. Although Tregs have been implicated in modulating allergic immune responses, their influence on distinct phases of development of allergies remains unclear. In this study, by using bacterial artificial chromosome (BAC)-transgenic Foxp3-DTR (DEREG) mice we demonstrate that the absence of Foxp3⁺ Tregs during the allergen challenge surprisingly does not exacerbate allergic airway inflammation in BALB/c mice. As genetic disposition due to strain specificity may contribute significantly to development of allergies, we performed similar experiment in C57BL/6 mice, which are less susceptible to allergy in the model of sensitization used in this study. We report that the genetic background does not influence the consequence of this depletion regimen. These results signify the temporal regulation exerted by Foxp3⁺ Tregs in limiting allergic airway inflammation and may influence their application as potential therapeutics.

Regulatory T cells and the control of the allergic response

The study of immune regulation and tolerance has been traditionally associated with self/nonself-discrimination. However, the finding that dominant tolerance, a model that puts in evidence the active role of regulatory T cells, can develop to nonself-antigens suggests that the imposition of tolerance can be context dependent. This paper reviews the emerging field of acquired immune tolerance to non-self antigens, with an emphasis on the different subsets of induced regulatory T cells that appear to specialize in specific functional niches. Such regulatory mechanisms are important in preventing the onset of allergic diseases in healthy individuals. In addition, it may be possible to take advantage of these immune regulatory mechanisms for the induction of tolerance in cases where pathological immune responses are generated to allergens occurring in nature, but also to other immunogens such as biological drugs developed for medical therapies.

Tregs promote the differentiation of Th17 cells in silica-induced lung fibrosis in mice

Background

Silicosis is an occupational lung disease caused by inhalation of silica dust and characterized by lung inflammation and fibrosis. Previous study showed that Tregs regulate the process of silicosis by modulating the maintenance of immune homeostasis in the lung. Th17 cells share reciprocal developmental pathway with Tregs and play a pivotal role in the immunopathogenesis of many lung diseases by recruiting and activating neutrophils, but the regulatory function of Tregs on Th17 response in silica induced lung fibrosis remains to be explored.

Methodology/Principal Findings

To evaluate the role of Th17 and IL-17 in the development of silicosis and their interaction with Tregs, Treg-depleted mice model was generated and exposed to silica to establish experimental model of silica-induced lung fibrosis. Here we showed that silica increased Th17 response in lung fibrosis. Tregs depletion enhanced the neutrophils accumulation and attenuated Th17 response in silica induced lung fibrosis. Both mRNA and protein results showed that Tregs exerted its modulatory function on Th17 cells and IL-17 by regulating TGF-β1 and IL-1β.

Conclusion/Significance

Our study suggested that Tregs could promote Th17 cells differentiation by regulating TGF-β1 and IL-1β in silica induced lung fibrosis of mice, which further the understanding of the progress of silicosis and provide a new insight in the regulatory mechanism of Th17 by Tregs in lung inflammation.

Association between functional polymorphisms of Foxp3 gene and the occurrence of unexplained recurrent spontaneous abortion in a Chinese Han population

Unexplained recurrent spontaneous abortion (URSA) is an alloimmune disease associated with the failure of fetal-maternal immunologic tolerance in which the regulatory T lymphocytes (Treg) play a pivotal role. It is well known that Forkhead box P3 (Foxp3) is a crucial regulatory factor for the development and function of Treg cells. It has also been established that deficiency of the Foxp3 gene suppresses the regulatory function of Treg cells. To determine if functional polymorphisms at the Foxp3 loci are associated with URSA in humans, we genotyped four common polymorphisms of Foxp3 gene in 146 unrelated URSA patients and 112 healthy women. The results showed that rs3761548A/C and rs2232365A/G polymorphisms were significantly associated with URSA. Additionally, we found that the allelic distribution of rs5902434 del/ATT in URSA group was slightly different from that in the control group. We conclude that functional polymorphisms of the Foxp3 gene may confer an important susceptibility to URSA in the Chinese Han population, probably by altering Foxp3 function and/or its expression.

Impaired Ca²⁺ regulation of CD4⁺CD25⁺ regulatory T cells from pediatric asthma

BACKGROUND

CD4(+)CD25(+) regulatory T (T(reg)) cells can control the allergic response to allergen, airway eosinophilia and airway hypersensitivity. We speculated that chronic inflammation persisting in asthma airways is dependent on abnormalities of these T(reg) cells. There are differences in the pathology of asthma in adults and children, and the airways of pediatric asthma are considered to be more naive than those of adults. Therefore, we analyzed the functionality of T(reg) cells in pediatric asthma and the relationship between T(reg) function and asthma symptoms.

METHODS

The anergic state, which is one of the defining properties of T(reg), was analyzed by measuring intracellular Ca(2+) influx following T cell receptor (TCR) stimulation. FOXP3-positive cells and FOXP3 mRNA expression were measured by flow analysis and real-time PCR with the SYBR method, respectively.

RESULTS

CD45RO(+) cells make up approximately 99% of CD4(+)CD25(high) T cells and 89% of CD4(+)CD25(low) T cells in human adult blood. The proportion of CD45RO(+) cells in CD4(+)CD25(+) (high + low) T cells from pediatric asthma was much smaller (about 56%). Interestingly, our data indicated that CD45RO(+) T(reg) cells from pediatric asthma aberrantly increased intracellular Ca(2+) concentrations following TCR activation compared with pediatric nonasthma controls.

CONCLUSION

These impaired CD45RO(+) T(reg) cell functions were correlated with asthma symptoms. The correlation was observed in the group with a highly expressed atopic phenotype and longer duration of asthma. We suggest that chronic inflammation in pediatric asthma airways may be the result of impaired regulatory functions of CD45RO(+) T(reg) cells.

Selective depletion of Foxp3+ Treg during sensitization phase aggravates experimental allergic airway inflammation

Recent studies highlight the role of Treg in preventing unnecessary responses to allergens and maintaining functional immune tolerance in the lung. We investigated the role of Treg during the sensitization phase in a murine model of experimental allergic airway inflammation by selectively depleting the Treg population in vivo. DEpletion of REGulatory T cells (DEREG) mice were depleted of Treg by diphtheria toxin injection. Allergic airway inflammation was induced using OVA as a model allergen. Pathology was assessed by scoring for differential cellular infiltration in bronchoalveolar lavage, IgE and IgG1 levels in serum, cytokine secretion analysis of lymphocytes from lung draining lymph nodes and lung histology. Use of DEREG mice allowed us for the first time to track and specifically deplete both CD25(+) and CD25(-) Foxp3(+) Treg, and to analyze their significance in limiting pathology in allergic airway inflammation. We observed that depletion of Treg during the priming phase of an active immune response led to a dramatic exacerbation of allergic airway inflammation in mice, suggesting an essential role played by Treg in regulating immune responses against allergens as early as the sensitization phase via maintenance of functional tolerance.

CD4+CD25+Foxp3+ regulatory T cells depletion may attenuate the development of silica-induced lung fibrosis in mice

BACKGROUND

Silicosis is an occupational lung disease caused by inhalation of silica dust characterized by lung inflammation and fibrosis. Previous study showed that Th1 and Th2 cytokines are involved in silicosis, but Th1/Th2 polarization during the development of silicosis is still a matter of debate. Regulatory T cells (Treg cells) represent a crucial role in modulation of immune homeostasis by regulating Th1/Th2 polarization, but their possible implication in silicosis remains to be explored.

METHODOLOGY/PRINCIPAL FINDINGS

To evaluate the implication of Treg cells in the development of silicosis, we generated the Treg-depleted mice model by administration of anti-CD25 mAbs and mice were exposed to silica by intratracheal instillation to establish experimental model of silica-induced lung fibrosis. The pathologic examinations show that the Treg-depleted mice are susceptive to severer inflammation in the early stage, with enhanced infiltration of inflammatory cells. Also, depletion of Treg cells causes a delay of the progress of silica-induced lung fibrosis in mice model. Further study of mRNA expression of cytokines reveals that depletion of Tregs leads to the increased production of Th1-cytokines and decreased production of Th2-cytokine. The Flow Cytometry and realtime PCR study show that Treg cells exert the modulation function both directly by expressing CTLA-4 at the inflammatory stage, and indirectly by secreting increasing amount of IL-10 and TGF-β during the fibrotic stage in silica-induced lung fibrosis.

CONCLUSION/SIGNIFICANCE

Our study suggests that depletion of Tregs may attenuate the progress of silica-induced lung fibrosis and enhance Th1 response and decelerate Th1/Th2 balance toward a Th2 phenotype in silica-induced lung fibrosis. The regulatory function of Treg cells may depend on direct mechanism and indirect mechanism during the inflammatory stage of silicosis.

IL-2 and IL-4 stimulate MEK1 expression and contribute to T cell resistance against suppression by TGF-beta and IL-10 in asthma

The T cell-driven airway inflammation in chronic asthma is uninhibited and sustained. We examined the resistance of T cells from asthmatic patients against suppression by TGF-β, IL-10 and glucocorticoids and explored its signaling mechanism. CD4(+)CD25(-) T cells from allergic asthmatic subjects demonstrated increased TCR-stimulated proliferation as compared with healthy and chronic obstructive pulmonary disease controls. This proliferation was resistant to inhibition by TGF-β, IL-10, and dexamethasone and to anergy induction. CD4 T cells from asthmatic patients, but not chronic obstructive pulmonary disease, allergic rhinitis, and healthy subjects, showed increased expression of MEK1, heightened phosphorylation of ERK1/2, and increased levels of c-Fos. IL-2 and IL-4 stimulated the expression of MEK1 and c-Fos and induced T cell resistance. The inhibition of MEK1 reversed, whereas induced expression of c-Fos and JunB promoted T cell resistance against TGF-β- and IL-10-mediated suppression. We have uncovered an IL-2- and IL-4-driven MEK1 induction mechanism that results in heightened ERK1/2 activation in asthmatic T cells and make them resistant to certain inhibitory mechanisms.

A standardized aqueous extract of Anoectochilus formosanus modulated airway hyperresponsiveness in an OVA-inhaled murine model

Anoectochilus formosanus HAYATA, a Chinese herb, is a valued folk medicine for fever, pain, and diseases of the lung and liver. Allergic asthma is characterized by increased serum IgE level and inflammation of the airways with high levels of interleukin (IL)-4 and IL-5 in bronchoalveolar lavage fluids (BALF). Constriction of airway smooth muscle and development of airway hyperresponsiveness (AHR) are the most important symptoms of allergic asthma. In our previous study, a standardized aqueous extract of A. formosanus (SAEAF) was used to modulate innate immunity of normal mice. In this study, airway inflammatory infiltrations, including T cell differentiation, cytokine modulation, allergic antibodies estimation, pulmonary pathology, and enhanced pause (Penh) of AHR were used to evaluate SAEAF treatment of an ovalbumin (OVA)-inhaled airway allergic murine model. The resulting cytokine profiles demonstrated that SAEAF can significantly reduce Th2 polarization after administration of SAEAF in OVA inhalation. These results also suggest that SAEAF modulates cytokine secretion in allergic asthma. Modulated natural T regulatory cells (CD25+/CD4+, Treg) were also shown to increase immuno-suppression in the allergic lung inflammation and further down-regulate airway inflammatory infiltration in eosinophils and macrophages. Finally, decreased airway anti-OVA IgE secretion and reduced AHR were observed. Our results indicate that the administration of SAEAF can modulate cytokines and T cell subpopulation by regulating inflammatory cell infiltration and modulating the allergic response.

1,25-dihydroxyvitamin D3 enhances the ability of transferred CD4+ CD25+ cells to modulate T helper type 2-driven asthmatic responses

The severity of allergic diseases may be modified by vitamin D. However, the immune pathways modulated by the active form of vitamin D, 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], are yet to be fully elucidated. In this study, naturally occurring CD4(+) CD25(+) cells from the skin-draining lymph nodes (SDLN) of mice treated with topical 1,25(OH)(2)D(3) had an increased ability to suppress T helper type 2 (Th2) -skewed immune responses. CD4(+) CD25(+) cells transferred from mice treated with topical 1,25(OH)(2)D(3) into ovalbumin (OVA) -sensitized mice challenged intranasally with OVA 18 hr later, significantly suppressed the capacity of airway-draining lymph node (ADLN) cells to proliferate and secrete cytokines in response to further OVA stimulation ex vivo. The CD4(+) CD25(+) cells from 1,25(OH)(2)D(3)-treated mice also reduced airway hyperresponsiveness and the proportions of neutrophils and eosinophils in bronchoalveolar lavage fluid (BALF). To test the effect of 1,25(OH)(2)D(3) on cells able to respond to a specific antigen, CD4(+) CD25(+) cells were purified from the SDLN of OVA-T-cell receptor (TCR) transgenic mice treated 4 days earlier with topical 1,25(OH)(2)D(3). CD4(+) CD25(+) cells from OVA-TCR mice treated with 1,25(OH)(2)D(3) were able to alter BALF cell content and suppress ADLN responses to a similar degree to those cells from non-transgenic mice, suggesting that the effect of 1,25(OH)(2)D(3) was not related to TCR signalling. In summary, topical 1,25(OH)(2)D(3) increased the regulatory capacity of CD4(+) CD25(+) cells from the SDLN to suppress Th2-mediated allergic airway disease. This work highlights how local 1,25(OH)(2)D(3) production by lung epithelial cells may modulate the suppressive activity of local regulatory T cells.

CD4+CD25+ T cell depletion impairs tolerance induction in a murine model of asthma

BACKGROUND

Regulatory T cells (Tregs) are key players in controlling the development of airway inflammation. However, their role in the mechanisms leading to tolerance in established allergic asthma is unclear.

OBJECTIVE

To examine the role of Tregs in tolerance induction in a murine model of asthma.

METHODS

Ovalbumin (OVA) sensitized asthmatic mice were depleted or not of CD25(+) T cells by anti-CD25 PC61 monoclonal antibody (mAb) before intranasal treatment (INT) with OVA, then challenged with OVA aerosol. To further evaluate the respective regulatory activity of CD4(+)CD25(+) and CD4(+)CD25(-) T cells, both T cell subsets were transferred from tolerized or non-tolerized animals to asthmatic recipients. Bronchoalveolar lavage fluid (BALF), T cell proliferation and cytokine secretion were examined.

RESULTS

Intranasal treatment with OVA led to increased levels of IL-10, TGF-beta and IL-17 in lung homogenates, inhibition of eosinophil recruitment into the BALF and antigen specific T cell hyporesponsiveness. CD4(+)CD25(+)Foxp3(+) T cells were markedly upregulated in lungs and suppressed in vitro and in vivo OVA-specific T cell responses. Depletion of CD25(+) cells before OVA INT severely hampered tolerance induction as indicated by a strong recruitment of eosinophils into BALF and a vigorous T cell response to OVA upon challenge. However, the transfer of CD4(+)CD25(-) T cells not only suppressed antigen specific T cell responsiveness but also significantly reduced eosinophil recruitment as opposed to CD4(+)CD25(+) T cells. As compared with control mice, a significantly higher proportion of CD4(+)CD25(-) T cells from OVA treated mice expressed mTGF-beta.

CONCLUSION

Both CD4(+)CD25(+) and CD4(+)CD25(-) T cells appear to be essential to tolerance induction. The relationship between both subsets and the mechanisms of their regulatory activity will have to be further analyzed.

Characterization of regulatory T cells in urban newborns

BACKGROUND

In the United States, asthma prevalence is particularly high among urban children. Although the underlying immune mechanism contributing to asthma has not been identified, having impaired T regulatory (Treg) cells at birth may be a determining factor in urban children. The objective of this study was to compare Treg phenotype and function in cord blood (CB) of newborns to those in peripheral blood (PB) of a subset of participating mothers.

METHODS

Treg numbers, expression, and suppressive function were quantified in subjects recruited prenatally from neighborhoods where >/= 20% of families have incomes below the poverty line. Proportion of Treg cells and expression of naïve (CD45RA) or activated (CD45RO, CD69, and HLA-DR) markers in CD4+T cells was measured by flow cytometry. Treg suppressive capacity was determined by quantifying PHA-stimulated lymphocyte proliferation in mononuclear cell samples with and without CD25 depletion.

RESULTS

In an urban cohort of 119 newborns and 82 mothers, we found that newborns had similar number of cells expressing FOXP3 as compared to the mothers but had reduced numbers of CD4+CD25+bright cells that predominantly expressed the naïve (CD45RA) rather than the activated/memory (CD45RO) phenotype found in the mothers. Additionally, the newborns had reduced mononuclear cell TGF-beta production, and reduced Treg suppression of PHA-stimulated lymphocyte proliferation compared to the mothers.

CONCLUSION

U.S. urban newborns have Treg cells that express FOXP3, albeit with an immature phenotype and function as compared to the mothers. Longitudinal follow-up is needed to delineate Treg cell maturation and subsequent risk for atopic diseases in this urban birth cohort.

Inhibition of cAMP degradation improves regulatory T cell-mediated suppression

Naturally occurring regulatory T cells (nTreg cells) are crucial for the maintenance of peripheral tolerance. We have previously shown that a key mechanism of their suppressive action is based on a contact-dependent transfer of cAMP from nTreg cells to responder T cells. Herein, we further elucidate the important role of cAMP for the suppressive properties of nTreg cells. Prevention of cAMP degradation by application of the phosphodiesterase 4 inhibitor rolipram led to strongly increased suppressive potency of nTreg cells for Th2 cells in vitro and in vivo. Detailed analyses revealed that rolipram caused, in the presence of nTreg cells, a synergistic increase of cAMP in responder Th2 cells. In vivo, the application of nTreg cells in a strictly Th2-dependent preclinical model of asthma had only a marginal effect. However, the additional treatment with rolipram led to a considerable reduction of airway hyperresponsiveness and inflammation in a prophylactic as well as in a therapeutic model. This amelioration was correlated with enhanced cAMP-levels in lung Th2 cells in vivo. Collectively, these data support our observation that cAMP has a key function for nTreg cell-based suppression and they clearly demonstrate that the effect of cAMP on T responder cells can be greatly enhanced upon application of phosphodiesterase 4 inhibitors.

Possible involvement of regulatory T cells in tumor onset and progression in primary breast cancer

BACKGROUND

The FOXP3 mRNA expression and the other regulatory T cell-related molecules were investigated and compared with clinicopathological parameters in human primary breast cancer.

METHOD

This study included 136 breast cancer patients operated in our department from 2003 to 2006. Total RNA was extracted from frozen normal breast and breast cancer tissues, and the expression of FOXP3, IL-10, TGFbeta1 and CCL22 mRNA was evaluated using quantitative real-time RT-PCR.

RESULT

FOXP3, IL-10, TGFbeta1 and CCL22 mRNA expressions were significantly higher in cancer tissue than in normal tissue, not only at pT1, 2, and 3 stages but also at the DCIS stage. There were positive correlations between FOXP3 and IL-10, FOXP3 and TGFbeta1, as well as FOXP3 and CCL22 mRNA expressions, respectively. FOXP3 and IL-10 mRNA expressions were significantly upregulated in PgR-negative or HER2-positive tumors.

CONCLUSION

These results suggest that regulatory T cells are involved in tumor onset and progression in human primary breast cancer, possibly contributing to poor prognosis of patients with breast cancer.

Frequency of Foxp3+CD4CD25+ T cells is associated with the phenotypes of allergic asthma

BACKGROUND AND OBJECTIVE

A forkhead/winged-helix family transcriptional repressor, Foxp3, is highly expressed on CD4(+)CD25(+) T regulatory cells. The role of Foxp3(+)CD4(+)CD25(+) T regulatory cells in asthma remains to be elucidated. Using mouse models and peripheral blood mononuclear cells (PBMC) from subjects with allergic asthma, we aimed to explore whether Foxp3(+)CD4(+)CD25(+) T regulatory cells associate with asthma phenotypes.

METHODS

Foxp3(+)CD4(+)CD25(+) T cells were detected by FACS and the correlation between the frequency of Foxp3(+)CD4(+)CD25(+) T cells and asthma phenotypes was assessed.

RESULTS

The frequency of Foxp3(+)CD4(+)CD25(+) T cells among total CD4(+)CD25(+) T cells in the lungs showed an inverse correlation with eosinophilic inflammation in BALB/c, A/J and C57BL/6 strains. In addition, the frequency of Foxp3(+)CD4(+)CD25(+) T cells was inversely correlated with BHR and allergen-specific IgE levels in the serum of A/J mice. In BALB/c mice, the frequency of Foxp3(+)CD4(+)CD25(+) T cells correlated with the level of IL-10 in BAL fluid. The inverse correlation between the frequency of Foxp3(+)CD4(+)CD25(+) T cells and eosinophilic inflammation disappeared when mice were treated with anti-IL-10 receptor mAb during allergen challenge. Interestingly, intracellular cytokine staining of lung cells revealed that IL-10 was predominantly produced by Foxp3(-)CD4(+)CD25(+) T cells. The frequency of Foxp3(+)CD4(+)CD25(+) T cells among total CD4(+)CD25(+) T cells in PBMC of asthmatics was significantly lower than that of healthy subjects, although there was no significant correlation between the frequency of Foxp3(+)CD4(+)CD25(+) T cells and asthma severity.

CONCLUSIONS

These results suggest a role for lung Foxp3(+)CD4(+)CD25(+) T cells in the regulation of asthma phenotypes, presumably through an IL-10-mediated mechanism.

Regulatory T cells and their role in rheumatic diseases: a potential target for novel therapeutic development

Regulatory T cells have an important role in limiting immune reactions and are essential regulators of self-tolerance. Among them, CD4+CD25high regulatory T cells are the best-described subset. In this article, we summarize current knowledge on the phenotype, function, and development of CD4+CD25high regulatory T cells. We also review the literature on the role of these T cells in rheumatic diseases and discuss the potential for their use in immunotherapy.

Differential regulatory function of resting and preactivated allergen-specific CD4+ CD25+ regulatory T cells in Th2-type airway inflammation

Although CD4(+)CD25(+) regulatory T (Treg) cells are known to suppress Th1 cell-mediated immune responses, their effect on Th2-type immune responses remains unclear. In this study we examined the role of Treg cells in Th2-type airway inflammation in mice. Depletion and reconstitution experiments demonstrated that the Treg cells of naive mice effectively suppressed the initiation and development of Th2-driven airway inflammation. Despite effective suppression of Th2-type airway inflammation in naive mice, adoptively transferred, allergen-specific Treg cells were unable to suppress airway inflammation in allergen-presensitized mice. Preactivated allergen-specific Treg cells, however, could suppress airway inflammation even in allergen-presensitized mice by accumulating in the lung, where they reduced the accumulation and proliferation of Th2 cells. Upon activation, allergen-specific Treg cells up-regulated CCR4, exhibited enhanced chemotactic responses to CCR4 ligands, and suppressed the proliferation of and cytokine production by polarized Th2 cells. Collectively, these results demonstrated that Treg cells are capable of suppressing Th2-driven airway inflammation even in allergen-presensitized mice in a manner dependent on their efficient migration into the inflammatory site and their regulation of Th2 cell activation and proliferation.

Cellular aspects of atopic dermatitis

Atopic dermatitis (AD) is a highly pruritic, chronic, and relapsing inflammatory skin disease. Recent interest in AD has been sparked by reports of its increasing prevalence and its contribution to increasing health care costs. A precise understanding of immunologic mechanisms is crucial for the development of effective treatment strategies for AD. Various studies reveal that AD has a multifactorial cause with the activation of complex immunologic and inflammatory pathways. This review will discuss cellular-mediated immunological pathomechanisms of AD. Emphasis will be given to the role played by T cells, antigen-presenting cells, eosinophils, and keratinocytes. We also examine the immunological effect of superantigens on various inflammatory cells including T regulatory cells.

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.

Single administration of low dose cyclophosphamide augments the antitumor effect of dendritic cell vaccine

Single administration of low dose cyclophosphamide (CTX) was previously reported to enhance the antitumor efficacy of immunotherapies. To investigate the possible mechanisms for this effect, we examined whether a single administration of low dose CTX could augment the immunogenicity of dendritic cell (DC) vaccines. Fifty milligrams per kilogram body weight dose of CTX was administrated intraperitoneally to mice after B16 melanoma or C26 colon carcinoma tumor models were established, DC vaccine generated from mouse bone marrow and pulsed with B16 or C26 tumor cells lysates were vaccinated 4 days later. CTX treatment potentiated the antitumor effects of the DC vaccine, and increased the proportion of IFN-gamma secreting lymphocytes in spleens. Furthermore, a significantly reduced proportion of CD4+CD25+FoxP3+ regulatory T (Treg) cells was detected by flow cytometry in spleen lymphocytes from tumor-bearing mice treated with CTX. Thus, a single administration of low dose CTX could augment antitumor immune responses of DC vaccine by reducing the proportion of CD4+CD25+FoxP3+ Treg cells in tumor-bearing mice. Our results suggested a possible mechanism of CTX-induced immunopotentiation and provided a strategy of immunotherapy combining a low dose CTX with DC vaccine.

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.

[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.

Nonhematopoietic NADPH oxidase regulation of lung eosinophilia and airway hyperresponsiveness in experimentally induced asthma

Pulmonary eosinophilia is one of the most consistent hallmarks of asthma. Infiltration of eosinophils into the lung in experimental asthma is dependent on the adhesion molecule vascular cell adhesion molecule-1 (VCAM-1) on endothelial cells. Ligation of VCAM-1 activates endothelial cell NADPH oxidase, which is required for VCAM-1-dependent leukocyte migration in vitro. To examine whether endothelial-derived NADPH oxidase modulates eosinophil recruitment in vivo, mice deficient in NADPH oxidase (CYBB mice) were irradiated and received wild-type hematopoietic cells to generate chimeric CYBB mice. In response to ovalbumin (OVA) challenge, the chimeric CYBB mice had increased numbers of eosinophils bound to the endothelium as well as reduced eosinophilia in the lung tissue and bronchoalveolar lavage. This occurred independent of changes in VCAM-1 expression, cytokine/chemokine levels (IL-5, IL-10, IL-13, IFNgamma, or eotaxin), or numbers of T cells, neutrophils, or mononuclear cells in the lavage fluids or lung tissue of OVA-challenged mice. Importantly, the OVA-challenged chimeric CYBB mice had reduced airway hyperresponsiveness (AHR). The AHR in OVA-challenged chimeric CYBB mice was restored by bypassing the endothelium with intratracheal administration of eosinophils. These data suggest that VCAM-1 induction of NADPH oxidase in the endothelium is necessary for the eosinophil recruitment during allergic inflammation. Moreover, these studies provide a basis for targeting VCAM-1-dependent signaling pathways in asthma therapies.

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.

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.

Targeting of CD25 and glucocorticoid-induced TNF receptor family-related gene-expressing T cells differentially modulates asthma risk in offspring of asthmatic and normal mother mice

Immunological mechanisms leading to increased asthma susceptibility in early life remain obscure. In this study, we examined the effects of neonatal Ab treatments targeting T cell populations on the development of an asthma syndrome. We used a model of increased asthma susceptibility where offspring of asthmatic BALB/c mother mice are more prone (than normal pups) to develop the disease. Neonatal pretreatment of naive pups with mAb directed against the IL-2Ralpha chain (CD25), the costimulatory molecule glucocorticoid-induced TNFR family related gene, and the inhibitory molecule CTLA-4 elicited contrasting effects in offspring depending on the mother's asthma status. Specifically, neonatal CD25(high) T cell depletion stimulated asthma susceptibility in normal offspring whereas it ameliorated the condition of pups born of asthmatic mothers. Conversely, glucocorticoid-induced TNFR family related gene ligation as a primary signal reduced the spleen cellularity and largely abrogated asthma susceptibility in asthma-prone offspring, without inducing disease in normal pups. Striking changes in Th1/Th2 cytokine levels, especially IL-4, followed mAb pretreatment and were consistent with the impact on asthma susceptibility. These results point to major differences in neonatal T cell population and responsiveness related to maternal asthma history. Interventions that temporarily remove and/or inactivate specific T cell subsets may therefore prove useful to attenuate early life asthma susceptibility and prevent the development of Th2-driven allergic airway disease.

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.

Complement regulates inhalation tolerance at the dendritic cell/T cell interface

Pulmonary exposure to innocuous aeroallergens is a common event leading to inhalation tolerance. Distinct subsets of pulmonary dendritic cells (DC) and regulatory T cells (T(Reg)) play critical roles in mediating and maintaining such tolerance. In asthmatics, the same aeroallergens drive a maladaptive, Th2-biased immune response resulting in airway inflammation and airway hyper-reactivity. The mechanisms underlying the breakdown of inhalation tolerance, leading to the Th2-driven inflammation in rising numbers of asthmatic patients from industrialized countries remain elusive. The recent resurgence of interest in the role of the innate immune mediators in regulating adaptive immune response has sparked studies aimed at identifying the role of complement in allergic asthma. In this context, an unexpected role for the anaphylatoxin C5a receptor in allergic sensitization has been found. In models of experimental allergic asthma, ablation of C5aR signaling during initial allergen exposure either induced or enhanced Th2 sensitization. Mechanistically, C5aR signaling directly affected the function of distinct pulmonary DC subsets that induce or control allergen-induced adaptive immune responses. Signaling pathways downstream of C5 may also impact the function of T(Reg), as T(Reg) from C5 sufficient, but not from C5 deficient mice, suppress DC activation and subsequent development of Th2-driven inflammation. The emerging paradigm is that constitutive local generation of C5a and C5aR signaling in airway DCs controls inhalation tolerance directly as well as indirectly through sensitization of airway DCs for T(Reg)-mediated immunosuppression.

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.

Schistosoma japonicum egg antigens stimulate CD4 CD25 T cells and modulate airway inflammation in a murine model of asthma

A number of epidemiological and clinical studies have suggested an inverse association between allergy and helminth infection, such as Schistosomiasis. Therefore, we hypothesize that Schistosoma japonicum egg antigens, a type of native antigen, can induce production of CD4(+) CD25(+) T cells with regulatory activity, modulating airway inflammation and inhibiting asthma development. The frequency of CD4(+) CD25(+) T cells was determined by flow cytometry for mice treated with ovalbumin (OVA), CD25(+) depletion/OVA, schistosome egg antigens, schistosome egg antigens/OVA and for control mice. The ability of CD25(+) T cells from these mice to suppress T-cell proliferation and cytokine production was investigated both in vivo and in vitro. Results showed that the CD4(+) CD25(+) T cells of OVA-treated mice exhibited impaired control of dysregulated mucosal T helper 2 responses compared to the controls (P < 0.05). Depletion of CD25(+) cells accelerated OVA-induced airway inflammation and increased the expression of interleukin (IL)-5 and IL-4. Treatment with schistosome egg antigens increased the number and suppressive activity of CD4(+) CD25(+) T cells, which made IL-10, but little IL-4. In a murine model of asthma, S. japonicum egg antigens decreased the expression of Th2 cytokines, relieved antigen-induced airway inflammation, and inhibited asthma development. Thus, we provided evidence that S. japonicum egg antigens induced the production of CD4(+) CD25(+) T cells, resulting in constitutive immunosuppressive activity and inhibition of asthma development. These results reveal a novel form of protection against asthma and suggest a mechanistic explanation for the protective effect of helminth infection on the development of allergy.

Roles of CD4+CD25+ T cells in the development of experimental murine allergic conjunctivitis

BACKGROUND

CD25+ regulatory T (T reg) cells play a suppressive role in experimental autoimmune uveoretinitis as well as experimental airway inflammation but their involvement in the development of allergic conjunctivitis (AC) remains unclear. We therefore investigated whether T reg cells play a role in the development of experimental AC (EC).

METHODS

BALB/c and C57BL/6 mice were actively immunized with ragweed (RW). The mice were treated with an anti-CD25 Ab (PC61) or control normal rat IgG (nrIgG) either 2 days prior to active immunization or during the induction phase (days 0, 2, 4, 6 and 8). Ten days after active immunization, the mice were challenged with RW-containing drops. Twenty-four hours after the challenge, the conjunctivas were harvested for histological analysis of eosinophil infiltration, and the spleens were harvested for cell culture for splenocyte transfer. Cultured splenocytes were transferred into syngeneic mice, and 4 days after the transfer, the recipient mice were challenged with RW. Twenty-four hours after the challenge, conjunctivas were collected for histological analysis.

RESULTS

Pretreatment with PC61 did not affect EC in either strain of mice; however, treatment with PC61 during the induction phase significantly suppressed EC in C57BL/6 mice. In contrast, transfer of RW-primed splenocytes from mice treated with PC61 induced EC that was significantly more severe regardless of strain and treatment protocol.

CONCLUSIONS

The finding that T reg cells play a suppressive role in the development of EC in splenocyte transfer experiments suggests that modulation of T reg cells may be a possible therapy for AC.

Functional study of CD4+CD25+ regulatory T cells in health and autoimmune hepatitis

Regulatory CD4(+)CD25(+) T cells (Tregs) are defective numerically and functionally in autoimmune hepatitis (AIH). We have investigated and compared the mechanism of action of Tregs in healthy subjects and in AIH patients using Transwell experiments, where Tregs are cultured either in direct contact with or separated from their targets by a semipermeable membrane. We also studied Treg FOXP3 expression and effect on apoptosis. Direct contact is necessary for Tregs to suppress proliferation and IFN-gamma production by CD4(+)CD25(-) and CD8(+) T cells in patients and controls. Moreover, in both, direct contact of Tregs with their targets leads to increased secretion of regulatory cytokines IL-4, IL-10, and TGF-beta, suggesting a mechanism of linked immunosuppression. Tregs/CD4(+)CD25(-) T cell cocultures lead to similar changes in IFN-gamma and IL-10 secretion in patients and controls, whereas increased TGF-beta secretion is significantly lower in patients. In contrast, in patients, Tregs/CD8(+) T cell cocultures lead to a higher increase of IL-4 secretion. In AIH, Treg FOXP3 expression is lower than in normal subjects. Both in patients and controls, FOXP3 expression is present also in CD4(+)CD25(-) T cells, although at a low level and not associated to suppressive function. Both in patients and controls, addition of Tregs does not influence target cell apoptosis, but in AIH, spontaneous apoptosis of CD4(+)CD25(-) T cells is reduced. In conclusion, Tregs act through a direct contact with their targets by modifying the cytokine profile and not inducing apoptosis. Deficient CD4(+)CD25(-) T cell spontaneous apoptosis may contribute to the development of autoimmunity.

Naturally Occurring CD4+Foxp3+ Regulatory T Cells Are an Essential, IL-10-Independent Part of the Immunoregulatory Network in Schistosoma mansoni Egg-Induced Inflammation

In acute and chronic schistosomiasis, survival of the host requires a carefully balanced immune response against highly immunogenic parasite eggs. We characterized the phenotype, distribution, and functional role of CD4(+)Foxp3(+) naturally occurring regulatory T cells (naTregs) in schistosome egg-induced inflammation. In adoptive transfer experiments and by intracellular staining for Foxp3, we demonstrate significant frequencies of naTregs in hepatic granulomas and draining lymphoid tissues of mice infected with the trematode Schistosoma mansoni. Strikingly, egg-induced inflammation does not change the normal ratio between naTregs and effector CD4(+) T cells at the inflammatory site or in lymphoid organs in acute or chronic disease. However, increasing frequencies of CD103-expressing cells in the naTreg compartment indicate a change in phenotype for naTregs with disease progression. Because CD103 was described recently as an activation marker for naTregs, we speculate that naTregs in chronic schistosomiasis are potentially more suppressive. Furthermore, we found that most naTregs do not contribute to egg-induced IL-4 and IL-10 production. Importantly, depletion of CD25(+) naTregs strongly enhances the frequency of IL-4-producing effector T cells in acute egg-induced inflammation. It does not change clonal expansion of activated CD4(+) T cells. This regulation of egg-induced cytokine production does not require the presence of IL-10. These data demonstrate that naTregs limit egg-induced effector-cytokine production in our model. Our results identify naTregs as an important, IL-10-independent part of the regulatory network in schistosome egg-induced inflammation.

The sphingosine 1-phosphate receptor agonist FTY720 differentially affects the sequestration of CD4+/CD25+ T-regulatory cells and enhances their functional activity

The sphingosine 1-phosphate (S1P) receptor agonist FTY720 is well known for its immunomodulatory activity, sequestering lymphocytes from blood and spleen into secondary lymphoid organs and thereby preventing their migration to sites of inflammation. Because inflammation is critically dependent on a balance between Ag-specific Th/effector cells and T-regulatory cells, we investigated the effect of FTY720 on T-regulatory cell trafficking and functional activity. An increased number of CD4+/CD25+ T cells was found in blood and spleens of FTY720-treated mice, and transfer of these cells resulted in a significantly more pronounced accumulation in spleens but not lymph nodes after treatment, suggesting that this compound differentially affects the homing properties of T-regulatory cells compared with other T cell subsets. Indeed, CD4+/CD25+ T cells express lower levels of S1P1 and S1P4 receptors and demonstrate a reduced chemotactic response to S1P. Moreover, analysis of the functional response of FTY720-treated CD4+/CD25+ T cells revealed an increased suppressive activity in an in vitro Ag-specific proliferation assay. This correlated with enhanced function in vivo, with T-regulatory cells obtained from FTY720-treated mice being able to suppress OVA-induced airway inflammation. Thus, FTY720 differentially affects the sequestration of T-regulatory cells and importantly, increases the functional activity of T-regulatory cells, suggesting that it may have disease-modifying potential in inflammatory disorders.

Association of IL-18 promoter polymorphisms with predisposition to Type 1 diabetes

AIMS

IL-18, a potent IFN-gamma-inducing cytokine, is capable of polarizing the immune response to a Th1 phenotype. Recent studies have demonstrated an association between single-nucleotide polymorphisms located at positions -607 (A/C) and -137 (C/G) in the promoter region of IL-18 gene and Type 1 diabetes. The aim of the present study was to determine whether the same polymorphisms of the gene were associated with Type 1 diabetes in Iranians.

METHODS

In 112 patients with Type 1 diabetes and 194 non-diabetic control subjects, these two single-nucleotide polymorphisms were analysed by sequence-specific PCR.

RESULTS

Allele and genotype frequencies of the IL-18 gene polymorphisms were similar in the whole group of Type 1 diabetic patients and controls. However, categorizing patients according to age at onset of diabetes revealed a significant difference in distribution of the genotypes at position -137 between patients with older age at onset (> 15 years) (GG 49%, GC 34%, CC 17%) and control subjects (GG 57.7%, GC 36.6%, CC 5.7%) (P = 0.027). Frequency of the C allele at position -137 was significantly higher in these patients than in controls (P = 0.038). Moreover, there was an association between -607AA/-137CC genotype combination and susceptibility to Type 1 diabetes in this subgroup of patients (pc = 0.027).

CONCLUSIONS

The results of this study show that polymorphisms of IL-18 promoter confer susceptibility to Type 1 diabetes in Iranian individuals with onset at older ages. Further investigations are necessary to clarify the effect of IL-18 variants on immune regulation.

Regulatory T cells and IL-10 in allergic inflammation

Recent studies suggest that human regulatory T (T reg) cells protect against the development of allergic and asthmatic disease and that their function is impaired during active disease. Two new studies contribute to our understanding of the role that T reg cells play in the control of allergic airway disease in mice. However, these studies also highlight several outstanding questions in the field.

[T regulatory lymphocytes, atopy and asthma: a new concept in three dimensions]

BACKGROUND

Allergic inflammation is considered to be the result of a pattern of Th2 lymphocyte activation. However this inflammation, relevant for atopy and infiltration of affected tissues by eosinophils, is insufficient by itself to explain the clinical features of asthma. Several studies have demonstrated that Th2 type inflammation was also associated in asthma with a Th1 response, with production of gamma interferon. It has recently been shown that the regulatory T lymphocytes (Treg) which produce IL-10 and/or TGF-beta and induce tolerance are defective in allergic patients. In addition, these lymphocytes increase during specific immunotherapy. Their decrease could explain the Th2 activation found in atopic patients.

PERSPECTIVE

We review the potential importance of Treg cells in atopy and also asthma, and propose a concept whereby the allergic inflammatory response would not be due to a Th1/Th2 imbalance, but rather to a Treg deficiency progressively rising from normal to atopic, from atopy to asthma and from asthma to acute exacerbations.

CONCLUSION

Three dimensions of inflammation need therefore to be taken into account: Th1, Th2 and Treg.