The role of immune tolerance in asthma pathogenesis

Galectin-9 in synergy with NF-κB inhibition restores immune regulatory capability in dendritic cells of subjects with food allergy

The pathogenesis of immune tolerance disruption is not fully understood. Galectin-9 (Gal9) has immune regulatory functions. The objective of the present study is to assess the role of Gal9 in maintaining immune tolerance. Blood and intestinal biopsies were taken from patients with food allergy (FA). The status of tolerogenic dendritic cells (tDC) and type 1 regulatory T cells (Tr1 cells) in the samples was evaluated and used as representative parameters of immune tolerance. An FA mouse model was established to assess the role of Gal9 in maintaining immune tolerance. We found that peripheral CD11c+ CD5+ CD1d+ tDC frequency was significantly lower in FA patients as compared to health control (HC) subjects. There was no significant change in CD11c+ DC frequency between the FA group and the HC group. The expression of IL-10 in peripheral tDCs was lower in the FA group than that in the HC group. A positive correlation was detected between the serum levels of IL-10 and Gal9. The expression of Gal9 was observed in intestinal biopsies, which was positively correlated with the serum levels of Gal9 as well as serum IL-10 levels. Peripheral Tr1 cells had lower frequencies in the FA group than in the non-FA (Con) group. tDCs demonstrated the ability to generate Tr1 cells, which was weaker in the FA group as compared with the Con group. Exposure of FA tDCs to Gal9 in culture restored the ability to generate Tr1 cells. In summary, the lower frequency of tDC and Tr1 cell of FA patients was associated with the levels of Gal9. The presence of Gal9 restored the capacity of tDC to generate Tr1 cells.

Dysfunction of S100A4+ effector memory CD8+ T cells aggravates asthma

Progressive loss of effector functions, especially IFN-γ secreting capability, in effector memory CD8⁺ T (CD8⁺ T_EM ) cells plays a crucial role in asthma worsening. However, the mechanisms of CD8⁺ T_EM cell dysfunction remain elusive. Here, we report that S100A4 drives CD8⁺ T_EM cell dysfunction, impairing their protective memory response and promoting asthma worsening in an ovalbumin (OVA)-induced asthmatic murine model. We find that CD8⁺ T_EM cells contain two subsets based on S100A4 expression. S100A4⁺ subsets exhibit dysfunctional effector phenotypes with increased proliferative capability, whereas S100A4^- subsets retain effector function but are more inclined to apoptosis, giving rise a dysfunctional CD8⁺ T_EM cell pool. Mechanistically, S100A4 upregulation of mitochondrial metabolism results in a decrease of acetyl-CoA levels, which impair the transcription of effector genes, especially ifn-γ, facilitating cell survival, tolerance and memory potential. Our findings thus reveal general insights into how S100A4 CD8⁺ T_EM cells reprogram into dysfunctional and less protective phenotypes to aggravate asthma. This article is protected by copyright. All rights reserved.

Vagal-α7nAChR signaling attenuates allergic asthma responses and facilitates asthma tolerance by regulating inflammatory group 2 innate lymphoid cells

Disorders of immune tolerance may lead to allergic asthma. Group 2 innate lymphoid cells (ILC2s) and inflammatory ILC2s (iILC2s) are key players in asthma. The vagus nerve innervating the airways releases acetylcholine or neuropeptides (i.e. calcitonin gene-related peptide) via pulmonary C-fibers (PCFs), which could regulate ILC2 activity upon binding the α7 nicotinic acetylcholine receptor (α7nAChR, coded by Chrna7) or neuropeptide receptors. Whether and how α7nAChR and PCFs regulate asthma and the formation of asthma tolerance via ILC2s or iILC2s are poorly understood. We used vagotomized, PCF degeneration and Chrna7 knockout mice to investigate ovalbumin (OVA)-induced asthma and oral OVA feeding-induced asthma tolerance. Our results revealed that vagotomy could generally suppress lung ILC2s and iILC2s, which mitigated allergic asthma responses but disrupted asthmatic tolerance. Removal of neuropeptides by PCF degeneration also reduced lung ILC2s and iILC2s, attenuating asthma responses, but did not affect asthma tolerance. In comparison, deletion of Chrna7 increased resident ILC2s and trafficking iILC2s in the lung, worsened allergic inflammation and disrupted oral tolerance. Mechanistically, deletion of Chrna7 in asthma-tolerant conditions upregulated T helper 2 cytokine- (Il4, Il13 and Il25) and sphingosine-1-phosphate (S1P)-related genes (S1pr1 and Sphk1). Blockade of S1P reduced iILC2 recruitment into asthmatic lungs. Our work is the first to demonstrate that vagal-α7nAChR signaling engaging with iILC2s and S1P not only alleviates asthma but also facilitates asthma tolerance. These findings may provide a novel therapeutic target for attenuating asthma by enhancing asthmatic tolerance.

iNKT cells with high PLZF expression are recruited into the lung via CCL21-CCR7 signaling to facilitate the development of asthma tolerance in mice

Establishment of immune tolerance is crucial to protect humans against asthma. Promyelocytic leukemia zinc finger (PLZF) is an emerging suppressor of inflammatory responses. CCL21-CCR7 signaling mediates tolerance development. However, whether PLZF and CCL21-CCR7 are required for the development of asthma tolerance is unknown. Here, we found that Zbtb16 (coding PLZF) and Ccl21 were upregulated in OVA-induced asthma tolerance (OT) lungs by RNA-seq. PLZF physically interacted with GATA3 and its expression was higher in GATA3⁺ Th2 cells and ILC2s in OT lungs. Zbtb16-knockdown in lymphocytes promoted the differentiation of CD3e⁺ CD4⁺ T cells, particularly those producing IL-4 and IL-5. Moreover, iNKT cells with high expression of PLZF were recruited into the lungs via draining lymph nodes during tolerance. Blockade of CCL21-CCR7 signaling in OT mice decreased the PLZF⁺  cell population, abolished CCR7-induced PLZF⁺ iNKT recruitment to the lungs, enhanced Th2responses and exacerbated lung pathology. In OT mice, respiratory syncytial virus (RSV) infection impeded PLZF⁺  cell and CCR7⁺ PLZF⁺ iNKT cellrecruitment to the lungs and increased airway resistance. Collectively, these results indicate that PLZF could interact with GATA3 and restrain differentiation of IL-4- and IL-5-producing T cells, iNKT cells with high PLZF expression are recruited to the lungs via CCL21-CCR7 signaling to facilitate the development of asthma tolerance.

Developments in the field of allergy mechanisms in 2015 through the eyes of Clinical & Experimental Allergy

In the first of two papers we described the development in the field of allergy mechanisms as described by Clinical and Experimental Allergy in 2015. Experimental models of allergic disease, basic mechanisms, clinical mechanisms and allergens are all covered. A second paper will cover clinical aspects.

Lung-Infiltrating Foxp3+ Regulatory T Cells Are Quantitatively and Qualitatively Different during Eosinophilic and Neutrophilic Allergic Airway Inflammation but Essential To Control the Inflammation

Understanding functions of Foxp3⁺ regulatory T cells (Tregs) during allergic airway inflammation remains incomplete. In this study, we report that, during cockroach Ag-induced allergic airway inflammation, Foxp3⁺ Tregs are rapidly mobilized into the inflamed lung tissues. However, the level of Treg accumulation in the lung was different depending on the type of inflammation. During eosinophilic airway inflammation, ∼30% of lung-infiltrating CD4 T cells express Foxp3, indicative of Tregs. On the contrary, only ∼10% of infiltrating CD4 T cells express Foxp3 during neutrophilic airway inflammation. Despite the different accumulation, the lung inflammation and inflammatory T cell responses were aggravated following Treg depletion, regardless of the type of inflammation, suggesting regulatory roles for Tregs. Interestingly, however, the extent to which inflammatory responses are aggravated by Treg depletion was significantly greater during eosinophilic airway inflammation. Indeed, lung-infiltrating Tregs exhibit phenotypic and functional features associated with potent suppression. Our results demonstrate that Tregs are essential regulators of inflammation, regardless of the type of inflammation, although the mechanisms used by Tregs to control inflammation may be shaped by environmental cues available to them.

Multiple Inhibitory Pathways Contribute to Lung CD8+ T Cell Impairment and Protect against Immunopathology during Acute Viral Respiratory Infection

Viruses are frequent causes of lower respiratory infection (LRI). Programmed cell death-1 (PD-1) signaling contributes to pulmonary CD8(+) T cell (TCD8) functional impairment during acute viral LRI, but the role of TCD8 impairment in viral clearance and immunopathology is unclear. We now find that human metapneumovirus infection induces virus-specific lung TCD8 that fail to produce effector cytokines or degranulate late postinfection, with minimally increased function even in the absence of PD-1 signaling. Impaired lung TCD8 upregulated multiple inhibitory receptors, including PD-1, lymphocyte activation gene 3 (LAG-3), T cell Ig mucin 3, and 2B4. Moreover, coexpression of these receptors continued to increase even after viral clearance, with most virus-specific lung TCD8 expressing three or more inhibitory receptors on day 14 postinfection. Viral infection also increased expression of inhibitory ligands by both airway epithelial cells and APCs, further establishing an inhibitory environment. In vitro Ab blockade revealed that multiple inhibitory receptors contribute to TCD8 impairment induced by either human metapneumovirus or influenza virus infection. In vivo blockade of T cell Ig mucin 3 signaling failed to enhance TCD8 function or reduce viral titers. However, blockade of LAG-3 in PD-1-deficient mice restored TCD8 effector functions but increased lung pathology, indicating that LAG-3 mediates lung TCD8 impairment in vivo and contributes to protection from immunopathology during viral clearance. These results demonstrate that an orchestrated network of pathways modifies lung TCD8 functionality during viral LRI, with PD-1 and LAG-3 serving prominent roles. Lung TCD8 impairment may prevent immunopathology but also contributes to recurrent lung infections.

Re-challenge with ovalbumin failed to induce bronchial asthma in mice with eosinophilic bronchitis

OBJECTIVE

To investigate whether eosinophilic bronchitis without airway hyperresponsiveness will develop bronchial asthma in allergic mice.

METHODS

Mice were sensitized with OVA on days 0, 7, and 14, challenged on days 21 to 23 (1(st) OVA challenge), and re-challenged on days 46 to 48 (2(nd) OVA challenge), intranasally with 10 (the EB group) and 200 (the AS group) μg OVA. Lung resistance (RL) was assessed 24 h after each challenge and on day 45 followed by analysis of leukocyte distribution in the bronchoalveolar lavage (BAL) fluid and histological examination.

RESULTS

Twenty-four hours after the 1(st) OVA challenge, aerosolized methacholine caused a dose-dependent increase in RL in all groups. At doses ≥1.56 mg/mL, RL in the AS group was significantly higher than that of the NS-1 group (P<0.01 or 0.05) and at doses ≥12.5 mg/mL, RL was markedly higher in the AS group than that of the EB group (P<0.01). The percentage of eosinophils in both the EB group and the AS group was markedly higher than that of the control group. Twenty-four hours after the 2(nd) OVA challenge, at doses ≤12.5 mg/mL, there was no significant difference in RL among all groups (P>0.05). At doses ≥12.5 mg/mL, RL in the AS group was significantly higher than that of the control group and EB group (P<0.01 or 0.05). The percentage of eosinophils in the AS group was noticeably higher than that of the EB group(P<0.05). Furthermore, there was apparent infiltration by inflammatory cells, predominantly eosinophils, into the sub-epithelial region of the bronchus and the bronchioles and around the vessels in the EB and AS group.

CONCLUSION

Re-challenge with low doses of ovalbumin did not increase airway reactivity and failed to induce bronchial asthma in mice with ovalbumin-induced EB.

Effects of n-3 PUFA on the CD4⁺ type 2 helper T-cell-mediated immune responses in Fat-1 mice

SCOPE

It has been suggested that n-3 PUFA can be used as a preventive or therapeutic strategy to control allergic asthma. But little is known about the exact mechanisms by which n-3 PUFA modulates it. Here, the effects of elevated n-3 PUFA on ovalbumin (OVA) induced airway inflammation were investigated using Fat-1 transgenic mice that can convert n-6 PUFA to n-3 PUFA endogenously.

METHODS AND RESULTS

First, we tested whether Fat-1 expression modulates CD4⁺ T-cell activation, proliferation, and differentiation in vitro and found that the Fat-1 expression attenuated all of these CD4⁺ T-cell responses by suppression of T-cell receptor mediated signaling and cytokine-mediated phosphorylation of STATs. When the Fat-1 mice were sensitized and challenged with the OVA, they showed a significant decrease in the recruitment of inflammatory cells into airway, the production of Th2 cytokines, eotaxin, and mucin in the lung, and the concentration of OVA-specific IgE in the serum. Furthermore, the differentiation of CD4⁺ T cells into Th2 was also decreased in the spleen of Fat-1 mice.

CONCLUSION

Our results showed that an elevated level of n-3 PUFA was effective in preventing allergic airway inflammation by modulating the activation and differentiation of CD4⁺ T cells in Fat-1 mice.

TIM4 modulates antigen-specific Th2 cell differentiation in mice with food allergy

AIM: To evaluate the modulatory effect of microbial products on the expression of T cell immunoglobulin and mucin domain 4 (TIM4) in dendritic cells (DCs) and to determine the role of TIM4 in modulating CD4+ T cell activation in allergic response induced by exposure to microbial products.

METHODS: Bone marrow-derived DCs were isolated from Balb/c mice and cultured in vitro. Cultured DCs were divided into control group and Staphylococcal enterotoxin B (SEB)-stimulated group. The expression of TIM4 mRNA in different groups of DCs was measured by reverse transcription-polymerase chain reaction (RT-PCR). The expression of CD11c, MHC-II and CD86 on DCs were measured by flow cytometry. DCs co-cultured with CD4+ T cells in vitro were divided into five groups: control group, SEB group, OVA group, SEB plus ovalbumin (OVA) group, and anti-TIM4 antibody plus SEB and OVA group. Different sets of DCs were co-cultured for 48 h with CD4+ T cells that were obtained from the spleen of allergic mice. Levels of interleukin-4 (IL-4) and interferon-γ (IFN-γ) in culture medium were evaluated by enzyme-linked immunosorbent assay (ELISA).

RESULTS: Compared with the control group, the expression of TIM4 mRNA in DCs was increased significantly in the SEB-stimulated group (0.941 ± 0.018 vs 0.422 ± 0.083, P < 0.05), and SEB up-regulated the expression of TIM-4 in a dose-dependent manner. SEB stimulation also significantly increased the expression of MHC-II and the costimulatory molecule CD86 on DCs compared with control cells (MHC-II: 76.684% ± 3.1803% vs 52.984% ± 3.6026%, P = 0.000; CD86: 89.746% ± 2.113% vs 67.558% ± 0.4341%, P = 0.000). Compared with control DCs co-cultured with CD4+ T cells, the level of IL-4 in culture medium increased significantly (295.834 ± 20.408 vs 78.335 ± 13.109, P < 0.05) and that of IFN-γ decreased significantly (362.109 ± 92.271 vs 761.897 ± 102.967, P < 0.05) in the SEB plus OVA group. The levels of IL-4 and IFN-γ in the SEB group and OVA group showed no significant differences with those in the control group. In contrast, the expression level of IL-4 was significantly lower and that of IFN-γ was significantly higher in the anti-TIM4 antibody group than in the SEB plus OVA group (P < 0.05). The levels of IL-4 and IFN-γ in the anti-TIM4 antibody group showed no significant differences with those in the control group, SEB group and OVA group (90.511 ± 15.500 vs 295.834 ± 20.408; 807.734 ± 95.436 vs 362.109 ± 92.271, both P < 0.05).

CONCLUSION: TIM4 is involved in the pathogenesis of food allergy induced by concurrent exposure to microbial products and food antigen. Inhibition of TIM4 expression can significantly inhibit Th2 cell polarization, effectively correct Th1/Th2 imbalance and thereby prevent the development of allergic reaction.

Gender differences in transcriptional regulation of IL-5 expression by bronchial lymph node cells in a mouse model of asthma

BACKGROUND AND OBJECTIVE

The severity of asthma after puberty is higher in women than in men. Increased numbers of eosinophils in the airways of female mice after antigen challenge was associated with increased levels of T helper (Th)2 cytokines at the site of inflammation, and in human and mouse studies, the profile of cytokines produced by immune cells from women showed greater Th2 predominance. The aim of this study was to investigate gender differences in the development of Th2 immune responses.

METHODS

Male and female C57BL/6 mice were sensitized with ovalbumin. Cells prepared from bronchial lymph nodes were cultured in the absence or presence of ovalbumin. Cytokine concentrations in the culture supernatants were measured, and IL-5 and GATA-binding protein 3 (GATA-3) gene expression were evaluated. T-cell subsets were analysed using specific surface markers.

RESULTS

The concentrations of IL-4, IL-5, IL-13 and IL-10, but not interferon-gamma or transforming growth factor-beta(1), were higher in cell supernatants from female mice than in those from male mice. IL-5 and GATA-3 gene expressions were higher in cells from women than in cells from men. The numbers of CD3(+)CD4(+)T1/ST2(+) cells, but not CD3(+)CD4(+) or CD4(+)CD25(+) cells, were significantly higher in cells from women than in cells from men.

CONCLUSIONS

Greater antigen-induced Th2 cytokine production by bronchial lymph node cells from female mice was associated with enhanced Th2 cell differentiation and increased expression of the Th2-specific transcription factor, GATA-3.

Decreased FOXP3 protein expression in patients with asthma

BACKGROUND

T-regulatory cells (T(reg)) are important in balancing immune responses and maintaining peripheral tolerance. Current evidence suggests that asthma is characterized by a relative deficiency in T(reg), allowing T helper 2 cells to expand. In this study, we aimed to evaluate circulating T(reg), defined by the protein FOXP3, in both control subjects and patients with stable asthma.

METHODS

Peripheral blood mononuclear cells (PBMC) of control (n = 14) and asthmatic patients (n = 29) were labeled for CD4, CD25, and intracellular FOXP3 and analyzed using flow cytometry. In CD3/CD28 stimulated PBMC, the effects of dexamethasone on the transcription factors T-bet, GATA-3, FOXP3, and RORc2 and representative cytokines were studied.

RESULTS

In control subjects and asthmatic patients, numbers of peripheral blood CD4(+)CD25(high) and CD4(+)CD25(high)FOXP3(+) T-cells were similar. However, FOXP3 protein expression within CD4(+)CD25(high) T-cells was significantly decreased in asthmatic patients. There was a tendency for increased FOXP3 expression within CD4(+)CD25(high) T-cells in glucocorticosteroid-treated patients when compared to steroid-naive asthmatic patients. In stimulated PBMC, dexamethasone treatment increased the anti-/proinflammatory transcription ratios of FOXP3/GATA-3, FOXP3/T-bet, and FOXP3/RORc2.

CONCLUSION

Asthmatic patients have decreased FOXP3 protein expression within their CD4(+)CD25(high) T(reg). Our findings also suggest that treatment with inhaled glucocorticosteroids in asthmatics might increase this FOXP3 protein expression within the CD4(+)CD25(high) T-cell population.

Multiple challenges in a mouse model of chemical-induced asthma lead to tolerance: ventilatory and inflammatory responses are blunted, immunologic humoral responses are not

To improve our mouse model of chemical-induced asthma we compared a single with a multiple intranasal challenge protocol. BALB/c mice received toluene diisocyanate (TDI) or vehicle on each ear (days 1 and 8) with the first challenge by intranasal instillation given on day 15. In a "long" protocol, the mice received 1 to 6 intranasal instillations, with 1-week interval. In a "short" protocol, the mice received 6 intranasal challenges over a period of 10 days. The "early" ventilatory response and methacholine reactivity were measured. Broncho-alveolar-lavage (BAL), total serum immunoglobulins and draining lymph nodes were analyzed. After 1, 2 or 3 TDI challenges, a significant increase in airway reactivity, total cell count and neutrophils (15-20%) was found in TDI-treated mice. This response diminished with increasing numbers of challenges in both models. The percentage CD4(+) and CD8(+) cells decreased and the percentage CD19(+) cells increased in the lymph nodes, but these returned to control values with multiple challenges. IL-4 secretion increased in cervical lymph node cells in vitro. Total serum IgE levels were persistently increased in TDI-treated mice. Although humoral signs of allergy remain increased after multiple challenges, diminishing ventilatory and inflammatory responses are indicative of the induction of tolerance.

Chronic inflammation in asthma: a contest of persistence vs resolution

Recent investigations have highlighted that endogenous anti-inflammatory mediators and immune regulating mechanisms are important for the resolution of inflammatory processes. A disruption of these mechanisms can be causally related not only to the initiation of unnecessary inflammation, but also to the persistence of several chronic inflammatory diseases. In asthma, chronic Th-2 driven eosinophilic inflammation of the airways is one of the central abnormalities. To date, elucidating the role of the different pro-inflammatory mediators involved in orchestrating the inflammatory processes in asthma has been the subject of intense research in both humans and animal models. However, the counter-regulatory mechanisms that co-determine the outcome in the contest of resolution vs persistence of the eosinophilic airway inflammation remain poorly understood. These are currently being investigated in animal models of chronic asthma. Elucidating these mechanisms is of relevance, since it can give rise to a new therapeutic approach in the treatment of chronic airway inflammation in asthmatics. This novel concept of treatment involves the stimulation of endogenous anti-inflammatory pathways, rather than solely antagonising the various pro-inflammatory mediators. Here, we review and discuss the current knowledge about these endogenous anti-inflammatory mediators in clinical and experimental asthma.

Epigenetic regulation of airway inflammation

Diverse cellular functions including the regulation of inflammatory gene expression, DNA repair and cell proliferation are regulated by epigenetic changes. Transcriptional co-activators possess intrinsic histone acetyltransferase (HAT) activity, and histone acetylation plays a major role in inflammatory gene expression. Other marks such as histone methylation are also associated with gene induction and gene repression. Recent evidence implicates histone acetylation and methylation as being crucial for the development of tolerance in macrophages and CpG methylation for T regulatory cell development and function. The expression of the enzymes that lay down or remove these epigenetic marks have not been well studied in human airways disease, but reduced HDAC2 expression and activity is reported in lung macrophages, biopsies and blood cells from patients with COPD, severe asthma and smoking asthma. In vitro, inhibitors of histone deacetylases (HDAC) often lead to a further induction of inflammatory gene expression. This is not always the case, however, as HATs and HDACs also target non-histone proteins particularly transcription factors to alter their activity. Furthermore, trichostatin A, an HDAC inhibitor, can reduce inflammation in a murine model of allergic asthma. This effect of HDAC inhibitors may be due to their effects on cell death acting through acetylation of non-histone proteins. The role of epigenetic modifications in inflammatory gene expression and in the control of cell function in the airways is becoming clearer. Targeting specific enzymes involved in this process may lead to new therapeutic agents, in particular, in situations where current anti-inflammatory therapies are currently suboptimal.

Staphylococcal enterotoxin B increases TIM4 expression in human dendritic cells that drives naïve CD4 T cells to differentiate into Th2 cells

Aberrant T helper (Th)2 polarization plays a critical role in the pathogenesis of allergic disorders; the etiology remains unclear. Dendritic cells (DCs) express T cell immunoglobulin mucin domain (TIM)4 that ligates TIM1 on CD4 T cells to drive them to become Th2 cells, but the pathogenic source of TIM4 is unknown. Here we report that a significant increase in TIM4 expression in human DCs was observed in response to Staphylococcal enterotoxin B (SEB) stimulation via Toll-like receptor (TLR)2 and nucleotide-binding oligomerization domain (NOD)1 pathway. Coculture SEB-conditioned DCs with naïve CD4 T cells induced Th2 responses that could be abolished using TLR2 or NOD1 or TIM4 or TIM1 with counterpart antibodies or RNA interference. The results demonstrate that Staphylococcus aureus derived SEB promotes the TIM4 production in human DCs. The interaction between TIM4 and TIM1 drives naïve CD4 T cells to develop to Th2 cells.

Prolonged inhaled allergen exposure can induce persistent tolerance

Murine asthma models suggest that failure of immune tolerance rather than a defective T helper cell type 1 (Th1) immunity underlies the immune biology of Th2-driven allergen-induced airway disease. Intriguingly, prolonged exposures can result in a full waning of inflammation. The mechanisms underlying this observation are not understood. We hypothesized that the fading of inflammation is the result of regulatory processes, characterized by altered dendritic cell (DC)-T cell interactions. First, we implemented a model in which mice developed Th2-driven airway disease. When we subjected these mice to prolonged antigen ovalbumin (OVA) exposures (8 wk), all inflammation disappeared. Re-immunization and re-challenge showed an inability to mount Th2-skewed immune responses, with absence of airway eosinophils, IgE, and Th2 cytokines. Besides specific immune tolerance, bystander protection was observed. A decrease in CD4+CD25+Foxp3+ T-regulatory cells, PD-1, and IL-10 expression was discerned as compared with acute inflammation. In addition, suppression of ICOS and CD28 was found, along with inhibited DC maturation. This process of disease inhibition surprisingly had a long-lasting memory and was not caused by endotoxin signaling through TLR-4. In summary, our results indicate that the disappearance of Th2-driven airway disease upon persistent antigen exposure is associated with the induction of immune tolerance. The tolerant state is antigen-dependent, and extends to bystander antigens. Moreover, this tolerance is characterized by an altered DC-T cell communication and is long-lasting. Our data further suggest that the mechanism of the disease inhibition after allergic airway inflammation differs from the anti-inflammatory mechanisms observed during acute eosinophilic airway inflammation.