Reversal of allergic airway hyperreactivity after long-term allergen challenge depends on gammadelta T cells

Decoding innate lymphoid cells and innate-like lymphocytes in asthma: pathways to mechanisms and therapies

Asthma is a chronic inflammatory lung disease driven by a complex interplay between innate and adaptive immune components. Among these, innate lymphoid cells (ILCs) and innate-like lymphocytes have emerged as crucial players in shaping the disease phenotype. Within the ILC family, group 2 ILCs (ILC2s), in particular, contribute significantly to type 2 inflammation through their rapid production of cytokines such as IL-5 and IL-13, promoting airway eosinophilia and airway hyperreactivity. On the other hand, innate-like lymphocytes such as invariant natural killer T (iNKT) cells can play either pathogenic or protective roles in asthma, depending on the stimuli and lung microenvironment. Regulatory mechanisms, including cytokine signaling, metabolic and dietary cues, and interactions with other immune cells, play critical roles in modulating their functions. In this review, we highlight current findings on the role of ILCs and innate-like lymphocytes in asthma development and pathogenesis. We also examine the underlying mechanisms regulating their function and their interplay with other immune cells. Finally, we explore current therapies targeting these cells and their effector cytokines for asthma management.

Effect of immunostimulation with bacterial lysate on the clinical course of allergic rhinitis and the level of γδT, iNKT and cytotoxic T cells in children sensitized to grass pollen allergens: A randomized controlled trial

BACKGROUND

There are many drugs for allergic rhinitis (AR), however, these drugs show variable clinical effectiveness and some side effects. Therefore, new methods of AR pharmacotherapy are being sought.

OBJECTIVES

The objectives of this study were to evaluate the efficacy of polyvalent mechanical bacterial lysate (PMBL) therapy in improving the clinical course of grass pollen-induced AR (seasonal AR, SAR) in children and its effect on changes in the blood level of the γδT, iNKT and cytotoxic T cell subsets.

METHODS

Fifty children with SAR were enrolled in this study and were randomly assigned to either the PMBL group or the placebo group. The severity of SAR symptoms was assessed using the total nasal symptom score (TNSS) and visual analogue scale (VAS). During two visits (V1, V2), peak nasal inspiratory flow (PNIF) was measured and peripheral blood was collected for immunological analyses. The study also included 2 telephone contacts (TC1, TC2).

RESULTS

The severity of the nasal symptoms of SAR on the TNSS scale was revealed to have a significantly lower impact in the PMBL group vs the placebo group at measuring points TC1 and V2 (p = 0.01, p = 0.009, respectively). A statistically significantly lower mean severity of nasal symptoms of SAR on the VAS scale was recorded for children in the PMBL group compared to the placebo group at measuring points TC1, V2 and TC2 (p = 0.04, p = 0.04, p = 0.03, respectively). The compared groups do not show significant differences in terms of PNIF values at individual measuring points. There were no statistically significant changes in immune variables. For both groups, there was a statistically significant association between the level of Th1-like γδT cells and the severity of SAR symptoms expressed on the TNSS scale (p = 0.03) - the lower the level of Th1-like γδT cells, the higher the TNSS value.

CONCLUSION

Administration of sublingual PMBL tablets during the grass pollen season proves to have a high efficacy in alleviating SAR symptoms in children sensitized to grass pollen allergens. Th1-like γδT cells may be used as potential markers for SAR severity in children.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, identifier (NCT04802616).

Ex vivo assays show human gamma-delta T cells specific for common allergens are Th1-polarized in allergic donors

Gamma-delta (γδ) T cells contribute to the pathology of many immune-related diseases; however, no ex vivo assays to study their activities are currently available. Here, we established a methodology to characterize human allergen-reactive γδ T cells in peripheral blood using an activation-induced marker assay targeting upregulated 4-1BB and CD69 expression. Broad and reproducible ex vivo allergen-reactive γδ T cell responses were detected in donors sensitized to mouse, cockroach, house dust mite, and timothy grass, but the response did not differ from that in non-allergic participants. The reactivity to 4 different allergen extracts was readily detected in 54.2%-100% of allergic subjects in a donor- and allergen-specific pattern and was abrogated by T cell receptor (TCR) blocking. Analysis of CD40L upregulation and intracellular cytokine staining revealed a T helper type 1 (Th1)-polarized response against mouse and cockroach extract stimulation. These results support the existence of allergen-reactive γδ T cells and their potential use in rebalancing dysregulated Th2 responses in allergic diseases.

T-cell responses in asthma exacerbations

OBJECTIVE

Asthma is a chronic lung disease comprising multiple endotypes and characterized by periodic exacerbations. A diverse array of T cells has been found to contribute to all endotypes of asthma in pathogenic and regulatory roles. Here, we review the contributions of CD4+, CD8+, and unconventional T cells in allergic and nonallergic asthma.

DATA SOURCES

Review of published literature pertaining to conventional and unconventional T-cell types in asthma.

STUDY SELECTIONS

Recent peer-reviewed articles pertaining to T cells in asthma, with additional peer-reviewed studies for context.

RESULTS

Much research in asthma has focused on the roles of CD4+ TH cells. Roles for TH2 cells in promoting allergic asthma pathogenesis have been well-described, and the recent description of pathogenic TH2A cells provides additional insight into these responses. Other TH types, notably TH1 and TH17, have been linked to neutrophilic and steroid-resistant asthma phenotypes. Beyond CD4+ T cells, CD8+ Tc2 cells are also strongly associated with allergic asthma. An emerging area for study is unconventional T-cell types, including γδT, invariant natural killer T, and mucosal-associated invariant T cells. Although data in asthma remain limited for these cells, their ability to bridge innate and adaptive responses likely makes them key players in asthma. A number of asthma therapies target T-cell responses, and, although data are limited, they seem to modulate T-cell populations.

CONCLUSION

Given the diversity and heterogeneity of asthma and T-cell responses, there remain many rich avenues for research to better understand the pathogenesis of asthma. Despite the breadth of T cells in asthma, approved therapeutics remain limited to TH2 networks.

Innate-like Lymphocytes and Innate Lymphoid Cells in Asthma

Asthma is a chronic pulmonary disease, highly associated with immune disorders. The typical symptoms of asthma include airway hyperresponsiveness (AHR), airway remodeling, mucus overproduction, and airflow limitation. The etiology of asthma is multifactorial and affected by genetic and environmental factors. Increasing trends toward dysbiosis, smoking, stress, air pollution, and a western lifestyle may account for the increasing incidence of asthma. Based on the presence or absence of eosinophilic inflammation, asthma is mainly divided into T helper 2 (Th2) and non-Th2 asthma. Th2 asthma is mediated by allergen-specific Th2 cells, and eosinophils activated by Th2 cells via the secretion of interleukin (IL)-4, IL-5, and IL-13. Different from Th2 asthma, non-Th2 asthma shows little eosinophilic inflammation, resists to corticosteroid treatment, and occurs mainly in severe asthmatic patients. Previous studies of asthma primarily focused on the function of Th2 cells, but, with the discovery of non-Th2 asthma and the involvement of innate lymphoid cells (ILCs) in the pathogenesis of asthma, tissue-resident innate immune cells in the lung have become the focus of attention in asthma research. Currently, innate-like lymphocytes (ILLs) and ILCs as important components of the innate immune system in mucosal tissues are reportedly involved in the pathogenesis of or protection against both Th2 and non-Th2 asthma. These findings of the functions of different subsets of ILLs and ILCs may provide clues for the treatment of asthma.

γδ T Lymphocytes in Asthma: a Complicated Picture

A minor subset (approximately 5%) of peripheral T cells has their TCR build up from γ and δ chains instead of α and β-those are the γδ T lymphocytes. They can be functionally divided into subsets, e.g., Th1-, Th2-, Th9-, Th17-, Tfh-, and Treg-like γδ T cells. They share some specifics of both innate and adaptive immunity, and are capable of rapid response to a range of stimuli, including some viral and bacterial infections. Atopic diseases, including asthma, are one of major health-related problems of modern western societies. Asthma is one of the most common airway diseases, affecting people of all ages and having potential life-threatening consequences. In this paper, we review the current knowledge about the involvement of γδ T cells in the pathogenesis of asthma and its exacerbations. We summarize both the studies performed on human subjects as well as on the murine model of asthma. γδ T cells seem to be involved in the pathogenesis of asthma, different subsets probably perform opposite functions, e.g., symptom-exacerbating Vγ1 and symptom-suppressing Vγ4 in mice model of asthma.

Human γδ T-Cell Control of Mucosal Immunity and Inflammation

Human γδ T-cells include some of the most common "antigen-specific" cell types in peripheral blood and are enriched yet further at mucosal barrier sites where microbial infection and tumors often originate. While the γδ T-cell compartment includes multiple subsets with highly flexible effector functions, human mucosal tissues are dominated by host stress-responsive Vδ1+ T-cells and microbe-responsive Vδ2+ T-cells. Widely recognized for their potent cytotoxicity, emerging data suggest that γδ T-cells also exert strong influences on downstream adaptive immunity to pathogens and tumors, in particular via activation of antigen-presenting cells and/or direct stimulation of other mucosal leukocytes. These unique functional attributes and lack of MHC restriction have prompted considerable interest in therapeutic targeting of γδ T-cells. Indeed, several drugs already in clinical use, including vedolizumab, infliximab, and azathioprine, likely owe their efficacy in part to modulation of γδ T-cell function. Recent clinical trials of Vδ2+ T-cell-selective treatments indicate a good safety profile in human patients, and efficacy is set to increase as more potent/targeted drugs continue to be developed. Key advances will include identifying methods of directing γδ T-cell recruitment to specific tissues to enhance host protection against invading pathogens, or alternatively, retaining these cells in the circulation to limit peripheral inflammation and/or improve responses to blood malignancies. Human γδ T-cell control of mucosal immunity is likely exerted via multiple mechanisms that induce diverse responses in other types of tissue-resident leukocytes. Understanding the microenvironmental signals that regulate these functions will be critical to the development of new γδ T-cell-based therapies.

Spectrum of T-lymphocyte activities regulating allergic lung inflammation

Despite advances in the treatment of asthma, optimization of symptom control remains an unmet need in many patients. These patients, labeled severe asthma, are responsible for a substantial fraction of the disease burden. In these patients, research is needed to define the cellular and molecular pathways contributing to disease which in large part are refractory to corticosteroid treatment. The causes of steroid-resistant asthma are multifactorial and result from complex interactions of genetics, environmental factors, and innate and adaptive immunity. Adaptive immunity, addressed here, integrates the activities of distinct T-cell subsets and by definition is dynamic and responsive to an ever-changing environment and the influences of epigenetic modifications. These T-cell subsets exhibit different susceptibilities to the actions of corticosteroids and, in some, corticosteroids enhance their functional activation. Moreover, these subsets are not fixed in lineage differentiation but can undergo transcriptional reprogramming in a bidirectional manner between protective and pathogenic effector states. Together, these factors contribute to asthma heterogeneity between patients but also in the same patient at different stages of their disease. Only by carefully defining mechanistic pathways, delineating their sensitivity to corticosteroids, and determining the balance between regulatory and effector pathways will precision medicine become a reality with selective and effective application of targeted therapies.

Monitoring inflammation and airway remodeling by fluorescence molecular tomography in a chronic asthma model

BACKGROUND

Asthma is a multifactorial disease for which a variety of mouse models have been developed. A major drawback of these models is represented by the transient nature of the airway pathology peaking 24-72 h after challenge and resolving in 1-2 weeks. We characterized the temporal evolution of pulmonary inflammation and tissue remodeling in a recently described mouse model of chronic asthma (8 week treatment with 3 allergens: Dust mite, Ragweed, and Aspergillus; DRA).

METHODS

We studied the DRA model taking advantage of fluorescence molecular tomography (FMT) imaging using near-infrared probes to non-invasively evaluate lung inflammation and airway remodeling. At 4, 6, 8 or 11 weeks, cathepsin- and metalloproteinase-dependent fluorescence was evaluated in vivo. A subgroup of animals, after 4 weeks of DRA, was treated with Budesonide (100 µg/kg intranasally) daily for 4 weeks.

RESULTS

Cathepsin-dependent fluorescence in DRA-sensitized mice resulted significantly increased at 6 and 8 weeks, and was markedly inhibited by budesonide. This fluorescent signal well correlated with ex vivo analysis such as bronchoalveolar lavage eosinophils and pulmonary inflammatory cell infiltration. Metalloproteinase-dependent fluorescence was significantly increased at 8 and 11 weeks, nicely correlated with collagen deposition, as evaluated histologically by Masson's Trichrome staining, and airway epithelium hypertrophy, and was only partly inhibited by budesonide.

CONCLUSIONS

FMT proved suitable for longitudinal studies to evaluate asthma progression, showing that cathepsin activity could be used to monitor inflammatory cell infiltration while metalloproteinase activity parallels airway remodeling, allowing the determination of steroid treatment efficacy in a chronic asthma model in mice.

Allergen-induced IL-6 trans-signaling activates γδ T cells to promote type 2 and type 17 airway inflammation

BACKGROUND

A variant in the IL-6 receptor (IL-6R) gene increases asthma risk and is predicted to decrease IL-6 classic signaling and increase IL-6 trans-signaling. This suggests that inhibition of IL-6 trans-signaling, but not classic signaling, might suppress allergic airway inflammation.

OBJECTIVES

We sought to determine whether IL-6 signaling contributes to (1) acute experimental asthma induced by clinically relevant allergens and (2) variation in asthma clinical phenotypes in asthmatic patients.

METHODS

Mice were sensitized to house dust mite (HDM) or cockroach at day 0, treated with IL-6R inhibitors at day 13, and challenged with the same allergen at days 14 to 17. End points were measured 3 hours after the final challenge. IL-6 and soluble IL-6 receptor (sIL-6R) expression in induced sputum of asthmatic patients was correlated with asthma clinical phenotypes.

RESULTS

Both HDM and cockroach induced a type 2/type 17 cytokine profile and mixed granulocytic inflammation in the airways. Both allergens increased IL-6 expression in the airways, but only cockroach induced sIL-6R expression. Therefore HDM challenge promoted IL-6 classic signaling but not trans-signaling; in this model treatment with anti-IL-6R did not suppress airway inflammation. In contrast, cockroach-induced inflammation involved activation of IL-6 trans-signaling and production of IL-17A by γδ T cells. Anti-IL-6R, selective blockade of sIL-6R, or γδ T-cell deficiency significantly attenuated cockroach-induced inflammation. Asthmatic patients with high airway IL-6 and sIL-6R levels were enriched for the neutrophilic and mixed granulocytic subtypes.

CONCLUSION

Experimental asthma associated with both high IL-6 and high sIL-6R levels in the airways is attenuated by treatment with IL-6R inhibitors.

Eosinophils contribute to the resolution of lung-allergic responses following repeated allergen challenge

BACKGROUND

Eosinophils accumulate at the site of allergic inflammation and are critical effector cells in allergic diseases. Recent studies have also suggested a role for eosinophils in the resolution of inflammation.

OBJECTIVE

To determine the role of eosinophils in the resolution phase of the response to repeated allergen challenge.

METHODS

Eosinophil-deficient (PHIL) and wild-type (WT) littermates were sensitized and challenged to ovalbumin (OVA) 7 or 11 times. Airway inflammation, airway hyperresponsiveness (AHR) to inhaled methacholine, bronchoalveolar lavage (BAL) cytokine levels, and lung histology were monitored. Intracellular cytokine levels in BAL leukocytes were analyzed by flow cytometry. Groups of OVA-sensitized PHIL mice received bone marrow from WT or IL-10(-/-) donors 30 days before the OVA challenge.

RESULTS

PHIL and WT mice developed similar levels of AHR and numbers of leukocytes and cytokine levels in BAL fluid after OVA sensitization and 7 airway challenges; no eosinophils were detected in the PHIL mice. Unlike WT mice, sensitized PHIL mice maintained AHR, lung inflammation, and increased levels of IL-4, IL-5, and IL-13 in BAL fluid after 11 challenges whereas IL-10 and TGF-β levels were decreased. Restoration of eosinophil numbers after injection of bone marrow from WT but not IL-10-deficient mice restored levels of IL-10 and TGF-β in BAL fluid as well as suppressed AHR and inflammation. Intracellular staining of BAL leukocytes revealed the capacity of eosinophils to produce IL-10.

CONCLUSIONS

After repeated allergen challenge, eosinophils appeared not essential for the development of AHR and lung inflammation but contributed to the resolution of AHR and inflammation by producing IL-10.

The role of the γ δ T cell in allergic diseases

The predominant distribution of γδ T cells in the mucosal and epithelial tissues makes these unconventional lymphocytes the “guards” to contact external environment (like allergens) and to contribute to immune surveillance, as well as “vanguards” to participate in initiating mucosal inflammation. Therefore, γδ T cells have been considered to bridge the innate and adaptive immunity. The role these cells play in allergy seems to be complicated and meaningful, so it makes sense to review the characteristics and role of γδ T cells in allergic diseases.

γδT cells suppress inflammation and disease during rhinovirus-induced asthma exacerbations

Most asthma exacerbations are triggered by virus infections, the majority being caused by human rhinoviruses (RV). In mouse models, γδT cells have been previously demonstrated to influence allergen-driven airways hyper-reactivity (AHR) and can have antiviral activity, implicating them as prime candidates in the pathogenesis of asthma exacerbations. To explore this, we have used human and mouse models of experimental RV-induced asthma exacerbations to examine γδT-cell responses and determine their role in the immune response and associated airways disease. In humans, airway γδT-cell numbers were increased in asthmatic vs. healthy control subjects during experimental infection. Airway and blood γδT-cell numbers were associated with increased airways obstruction and AHR. Airway γδT-cell number was also positively correlated with bronchoalveolar lavage (BAL) virus load and BAL eosinophils and lymphocytes during RV infection. Consistent with our observations of RV-induced asthma exacerbations in humans, infection of mice with allergic airways inflammation increased lung γδT-cell number and activation. Inhibiting γδT-cell responses using anti-γδTCR (anti-γδT-cell receptor) antibody treatment in the mouse asthma exacerbation model increased AHR and airway T helper type 2 cell recruitment and eosinophilia, providing evidence that γδT cells are negative regulators of airways inflammation and disease in RV-induced asthma exacerbations.

γδ T Lymphocytes Coordinate Eosinophil Influx during Allergic Responses

Tissue eosinophil infiltration, which is a hallmark of allergic and helminthic diseases, is mainly coordinated by T lymphocytes, via the production of eosinophilotactic chemokines. Among T lymphocyte subsets, lymphocytes expressing γδ T cell receptor have been determined as a key factor for eosinophil accumulation via direct and indirect mechanisms. This knowledge is strongly supported by the fact that, in different experimental models of eosinophilic airway inflammation and helminth-induced Th2 lung inflammation, an evident tissue accumulation of γδ T lymphocytes is observed. In addition, the depletion of γδ T lymphocytes is correlated with the impairment of eosinophil accumulation in inflamed tissue. γδ T lymphocytes are non-conventional T lymphocytes, which comprise a minor T lymphocyte subset, mainly distributed in the tissue, and present crucial roles in innate and acquired immune responses. γδ T lymphocytes recognize several danger- and pathogen-associated molecular pattern molecules and stress antigens in a MHC-independent fashion and can provide rapid tissue-specific responses, via the production of a wide range of chemical mediators capable to modulate other cell populations. These mediators include chemoattractant cytokines and chemokines that attract eosinophils into the tissue by either direct recognition (such as IL-5, CCL11/eotaxin), or indirect mechanisms via the modulation of αβ T lymphocytes and macrophages (through the production of interferon-γ, IL-4, and CCL2/Monocyte chemoattractant protein-1, MCP-1, for example). The present review presents an overview of how γδ T lymphocytes coordinate eosinophil accumulation in allergy, by focusing on their role in airway inflammation and by discussing the involvement of cytokines and chemokines in this phenomenon.

Persistent activation of dendritic cells after resolution of allergic airway inflammation breaks tolerance to inhaled allergens in mice

RATIONALE

Polysensitization of patients who are allergic is a common feature. The underlying immunologic mechanism is not clear. The maturation status of dendritic cells (DCs) is considered to be important for priming naive T cells in the draining lymph nodes. We hypothesized that chronic airway inflammation can induce an enhanced maturation of airway DCs and facilitate subsequent priming to neoallergens.

OBJECTIVES

To investigate whether chronic airway inflammation could induce an altered activation of airway DCs in mice and whether this influences the development of allergic sensitization.

METHODS

Balb/c mice were repeatedly challenged with DCs to induce a chronic airway inflammation. We evaluated (1) the induction of the main characteristic features of human asthma including persistent remodeling, (2) the maturation status of airway DCs 1 month after inflammation resolved, (3) whether this influences tolerance to inhaled neoallergen, and (4) what type of T helper response would be induced by DCs.

MEASUREMENTS AND MAIN RESULTS

Airway DCs displayed a mature phenotype after complete resolution of airway eosinophilia. Inhalation of a neoallergen without any adjuvant was able to induce airway inflammation in postinflammation lungs but not in control lungs. One month after inflammation, airway DCs were able to induce Th2 polarization in naive T cells consistent with the up-regulation of the Th2 skewing molecules Ym1/2 and OX-40L compared with DCs of control airways.

CONCLUSIONS

This study provides evidence that sustained maturation of DCs after resolution of Th2-mediated inflammation can contribute to polysensitization.

Combined sensitization of mice to extracts of dust mite, ragweed, and Aspergillus species breaks through tolerance and establishes chronic features of asthma

BACKGROUND

Existing asthma models develop tolerance when chronically exposed to the same allergen.

OBJECTIVE

We sought to establish a chronic model that sustains features of asthma long after discontinuation of allergen exposure.

METHODS

We immunized and exposed mice to a combination of single, double, or triple allergens (dust mite, ragweed, and Aspergillus species) intranasally for 8 weeks. Airway hyperreactivity (AHR) and morphologic features of asthma were studied 3 weeks after allergen exposure. Signaling effects of the allergens were studied on dendritic cells.

RESULTS

Sensitization and repeated exposure to a single allergen induced tolerance. Sensitization to double and especially triple allergens broke through tolerance and established AHR, eosinophilic inflammation, mast cell and smooth muscle hyperplasia, mucus production, and airway remodeling that persisted at least 3 weeks after allergen exposure. Mucosal exposure to triple allergens in the absence of an adjuvant was sufficient to induce chronic airway inflammation. Anti-IL-5 and anti-IL-13 antibodies inhibited inflammation and AHR in the acute asthma model but not in the chronic triple-allergen model. Multiple allergens produce a synergy in p38 mitogen-activated protein kinase signaling and maturation of dendritic cells, which provides heightened T-cell costimulation at a level that cannot be achieved with a single allergen.

CONCLUSIONS

Sensitivity to multiple allergens leads to chronic asthma in mice. Multiple allergens synergize in dendritic cell signaling and T-cell stimulation that allows escape from the single allergen-associated tolerance development.

Requirement of L-selectin for gammadelta T lymphocyte activation and migration during allergic pleurisy: co-relation with eosinophil accumulation

Intra-thoracic antigenic challenge (ovalbumin, 12.5 microg/cavity) led to increased numbers of gammadelta T lymphocytes in pleural cavities, blood and thoracic lymph nodes in sensitized mice within 48 h. Part of these cells expressed CD62L, which increased on gammadelta T cell surfaces obtained from lymph nodes after ovalbumin (OVA) challenge. Selectin blockade by fucoidan pre-treatment (10 mg/kg, i.v.) impaired in vivo increase in CD25(+) and c-fos(+) gammadelta T cell numbers in lymph nodes, indicating a role for selectins on gammadelta T lymphocyte activation and proliferation. In vivo selectin blockade by fucoidan or alpha-CD62L mAb (200 microg/mice, i.p.) also inhibited OVA-induced gammadelta T cell accumulation in pleural cavities. Confirming the direct effect of CD62L on gammadelta T cell transmigration, the migration of i.v. adoptively-transferred CFSE-labeled gammadelta T lymphocytes into pleural cavities of challenged recipient mice was impaired by fucoidan ex vivo treatment. It is noteworthy that eosinophil influx was also impaired in those mice, indicating that reduced eosinophil migration by CD62L in vivo blockade depended on gammadelta T cell migration via CD62L molecules. Accordingly, pleural gammadelta T lymphocytes from fucoidan-treated mice presented reduced OVA-induced IL-5 and CCL11 production. Supporting these data, the depletion of Vgamma4 T lymphocytes, which are pulmonary gammadelta T cells, decreased OVA-induced eosinophil influx into allergic site. Such results demonstrate that CD62L is crucial for the activation of gammadelta T cells in lymph nodes, for their migration into inflamed tissue and for the modulation of eosinophil influx during allergic response.

Role of γδ T Cells in Lung Inflammation

The resident population of γδ T cells in the normal lung is small but during lung inflammation, γδ T cells can increase dramatically. Histological analysis reveals diverse interactions between γδ T cells and other pulmonary leukocytes. Studies in animal models show that γδ T cells play a role in allergic lung inflammation where they can protect normal lung function, that they also are capable of resolving infection-induced pulmonary inflammation, and that they can help preventing pulmonary fibrosis. Lung inflammation threatens vital lung functions. Protection of the lung tissues and their functions during inflammation is the net-effect of opposing influences of specialized subsets of γδ T cells as well as interactions of these cells with other pulmonary leukocytes.

Vγ1+ γδ T cells reduce IL-10-producing CD4+CD25+ T cells in the lung of ovalbumin-sensitized and challenged mice

In OVA-sensitized and challenged mice, gammadelta T cells expressing Vgamma1 enhance airway hyperresponsiveness (AHR) but the underlying mechanism is unclear. These cells also reduce IL-10 levels in the airways, suggesting that they might function by inhibiting CD4(+)CD25(+) regulatory T cells (T(reg)) or other CD4(+) T cells capable of producing IL-10 and suppressing AHR. Indeed, sensitization and challenge with OVA combined with inactivation of Vgamma1(+) cells increased CD4(+)CD25(+) cells in the lung, and markedly those capable of producing IL-10. The cellular change was associated with increased IL-10 and TGF-beta levels in the airways, and a decrease of IL-13. T(reg) include naturally occurring Foxp3(+) T(reg), inducible Foxp3(-) T(reg), and antigen-specific T(reg) many of which express folate receptor 4 (FR4). Although Foxp3 gene expression in the lung was also increased pulmonary CD4(+) T cells, expressing Foxp3-protein or FR4 remained stable. Therefore, the inhibition by Vgamma1(+) gammadelta T cells might not be targeting Foxp3(+) T(reg) but rather CD4(+) T cells destined to produce IL-10.

Evidence that CD8+ dendritic cells enable the development of gammadelta T cells that modulate airway hyperresponsiveness

Airway hyperresponsiveness (AHR), a hallmark of asthma and several other diseases, can be modulated by gammadelta T cells. In mice sensitized and challenged with OVA, AHR depends on allergen-specific alphabeta T cells; but Vgamma1+ gammadelta T cells spontaneously enhance AHR, whereas Vgamma4+ gammadelta T cells, after being induced by airway challenge, suppress AHR. The activity of these gammadelta T cell modulators is allergen nonspecific, and how they develop is unclear. We now show that CD8 is essential for the development of both the AHR suppressor and enhancer gammadelta T cells, although neither type needs to express CD8 itself. Both cell types encounter CD8-expressing non-T cells in the spleen, and their functional development in an otherwise CD8-negative environment can be restored with transferred spleen cell preparations containing CD8+ dendritic cells (DCs), but not CD8+ T cells or CD8- DCs. Our findings suggest that CD8+ DCs in the lymphoid tissues enable an early step in the development of gammadelta T cells through direct cell contact. DC-expressed CD8 might take part in this interaction.

Involvement of CC chemokines in gammadelta T lymphocyte trafficking during allergic inflammation: the role of CCL2/CCR2 pathway

In the present study, we show that the intra-thoracic injection of ovalbumin (OVA, 12.5 microg per cavity) into C57BL/10 mice induced a significant increase in gammadelta T lymphocyte numbers in the pleural cavity, blood and thoracic lymph node of challenged mice. Such increase was significant within 12 h, peaked within 48 h and returned to basal counts within 120 h. Levels of CC chemokine ligand (CCL)-2/monocyte chemotactic protein-1, CCL5/regulated upon activation, normal T cell expressed and secreted, CCL3/macrophage inflammatory protein-1 alpha and CCL25/thymus-expressed chemokine were above control values in pleural washes recovered 24 h after OVA challenge (OPW) and were likely produced by pleural macrophages and mesothelial cells. Antigenic challenge also induced an up-regulation in CC chemokine receptor (CCR)-2, CCR5 and CCR9 on gammadelta T cells from pleural cavities, blood and lymph nodes, suggesting that cells found in mice pleural cavity migrate from secondary lymphoid organs into the inflammatory site via blood stream. The in vitro neutralization of CCL2 (but not of CCL3, CCL5 or CCL25) abrogated OPW-induced gammadelta T lymphocyte transmigration. Confirming such results, the in vivo administration of alpha-CCL2 mAb inhibited gammadelta T lymphocyte accumulation in the pleural cavity of challenged mice, whereas the blockade of CCL3, CCL5 or CCL25 showed no effect on gammadelta T cell mobilization. In addition, OVA challenge failed to induce gammadelta T lymphocyte accumulation in the pleural cavity of C57BL/6 CCR2 knockout mice, which also showed decreased numbers of these cells in blood and lymph nodes when compared with wild-type mice. Overall, such results demonstrate that CCR2/CCL2 pathway is crucial for gammadelta T lymphocyte mobilization during the allergic response.

Mice depleted of alphabeta but not gammadelta T cells are resistant to mortality caused by cecal ligation and puncture

The present study was undertaken to determine whether the mice depleted of alphabeta or gammadelta T cells show resistance to acute polymicrobial sepsis caused by cecal ligation and puncture (CLP). T-cell receptor beta knockout (betaTCRKO) and T-cell receptor delta knockout (deltaTCRKO) mice were used. An additional group of mice was treated with an antibody against the alphabeta T-cell receptor to induce alphabeta T-cell depletion; a subset of alphabeta T cell-deficient mice was also treated with anti-asialoGM1 to deplete natural killer (NK) cells. The mice underwent CLP and were monitored for survival, temperature, acid-base balance, bacterial counts, and cytokine production. The betaTCRKO mice and the wild-type mice treated with anti-beta T-cell receptor (anti-TCRbeta) antibody showed improved survival after CLP compared with wild-type mice. The treatment of alphabeta T cell-deficient mice with anti-asialoGM1further improved survival after CLP, especially when the mice were treated with imipenem. The improved survival observed in alphabeta T cell-deficient mice was associated with less hypothermia, improved acid-base balance, and decreased production of the proinflammatory cytokines interleukin (IL) 6 and macrophage inflammatory protein (MIP) 2. Compared with wild-type controls, the overall survival was not improved in deltaTCRKO mice. The concentrations of IL-6 and MIP-2 in plasma and cytokine mRNA expression in tissues were not significantly different between wild-type and deltaTCRKO mice. These studies indicate that mice depleted of alphabeta but not of gammadelta T cells are resistant to mortality in an acutely lethal model of CLP. The depletion of NK cells caused further survival benefit in alphabeta T cell-deficient mice. These findings suggest that alphabeta T and NK cells mediate or facilitate CLP-induced inflammatory injury.

Human gammadelta T cells modulate the mite allergen-specific T-helper type 2-skewed immunity

BACKGROUND

Gammadelta T cells have been described as one of immune regulators in patients with infection, malignancy, and allergy.

OBJECTIVE

To elucidate the ability of gammadelta T cells as an allergen immunotherapy candidate, the effectiveness of human gammadelta T cells in allergen-specific T-helper type 2 (Th2)-type T cells was evaluated in vitro.

METHODS

House dust mite-specific Th2-type T cell clones, Bacillus Calmette-Guerin (BCG)-specific Th1-type T cell clones, and gammadelta T cell lines were established from the peripheral blood mononuclear cells of two patients with allergic rhinitis. The effectiveness of gammadelta T cells and BCG-specific Th1-type T cell clones in the modulation of allergen-specific Th2 cells in terms of their cytokine productions was evaluated.

RESULTS

In response to cognate antigens, the gammadelta T cell lines demonstrated a proliferation and production of IFN-gamma that exceeded that of BCG-specific Th1-type T cell clones (mean stimulation index: 14.5 vs. 2.8, mean IFN-gamma: 130.5 vs. 10.0 pg/mL). When the gammadelta T cell lines and mite-allergen-specific Th2 clones were co-cultured with each other, only the levels of IL-4 (mean, -87%) decreased, but not the levels of IL-5 and IL-13, with an increasing concentration of gammadelta T cell antigen and IFN-gamma production (mean, +730%).

CONCLUSION

These results demonstrated that gammadelta T cells derived from allergic patients might thus have a partial ability to modulate allergen-specific Th2-skewed immunity.

gammadelta T lymphocytes-selectable cells within the innate system?

Lymphocytes expressing gammadelta T cell receptors (TCR) constitute an entire system of functionally specialized subsets that have been implicated in the regulation of immune responses, including responses to pathogens and allergens, and in tissue repair. The gammadelta TCRs share structural features with adaptive receptors and peripheral selection of gammadelta T cells occurs. Nevertheless, their specificities may be primarily directed at self-determinants, and the responses of gammadelta T cells exhibit innate characteristics. Continuous cross talk between gammadelta T cells and myeloid cells is evident in histological studies and in in vitro co-culture experiments, suggesting that gammadelta T cells play a functional role as an integral component of the innate immune system.

Loss of pro-apoptotic Bim promotes accumulation of pulmonary T lymphocytes and enhances allergen-induced goblet cell metaplasia

Immunological tolerance during prolonged exposure to allergen is accompanied by a shift in the lymphocyte content and a reduction of goblet cell metaplasia (GCM). Bim initiates negative selection of autoreactive T and B cells and shut down of T cell immune responses in vivo. The present study investigated whether Bim plays a role in the resolution of GCM during prolonged exposure to allergen. Loss of Bim increased T lymphocyte numbers in the bronchoalveolar lavage at 4 and 15 days of allergen exposure. The numbers of pulmonary CD4(+)8(-), CD4(-)8(+), and gammadelta T cells were significantly higher in naive and allergen-challenged bim(-/-) mice compared with wild-type (WT) littermates. When activated, pulmonary bim(-/-) T cells produced increased levels of IFNgamma compared with bim(+/+) T cells. No differences were noted in the total numbers of epithelial cells per millimeter of basal lamina between bim(+/+) and bim(-/-) mice, and the rate of resolution over 15 days of exposure was similar in both groups of mice. However, GCM was significantly enhanced and expression of IL-13Ralpha2 was reduced in bim(-/-) mice compared with WT mice at 4 days. Furthermore, treatment of bronchiolar explant cultures with increasing IFNgamma levels reduced immunostaining for IL-13Ralpha2. Collectively, these studies suggest that, during prolonged exposure to allergen, Bim plays no role in the resolution of GCM, but increased IFNgamma levels in bim(-/-) mice may be responsible for reduced expression of IL-13Ralpha2 and enhanced GCM despite similar levels of IL-13 in bim(+/+) and bim(-/-) mice.

Roles of apoptosis in airway epithelia

The airway epithelium functions primarily as a barrier to foreign particles and as a modulator of inflammation. Apoptosis is induced in airway epithelial cells (AECs) by viral and bacterial infections, destruction of the cytoskeleton, or by exposure to toxins such as high oxygen and polycyclic hydrocarbons. Various growth factors and cytokines including TGF-beta, IFN-gamma, or the activators of the death receptors, TNF-alpha and FasL, also induce apoptosis in AECs. However, cell death is observed in maximally 15% of AECs after 24 h of treatment. Preincubation with IFN-gamma or a zinc deficiency increases the percentage of apoptotic AECs in response to TNF-alpha or FasL, suggesting that AECs have mechanisms to protect them from cell death. Apoptosis of AECs is a major mechanism in reducing cell numbers after hyperplastic changes in airway epithelia that may arise due to major injuries in response to LPS or allergen exposures. Resolution of hyperplastic changes or changes during prolonged exposure to an allergen is primarily regulated by the Bcl-2 family of proteins. Fas and FasL are both expressed in AECs, and their main function may be to control inflammation by inducing Fas-induced death in inflammatory cells without inducing apoptosis in neighboring cells. Furthermore, AECs engulf dying eosinophils to clear them by phagocytosis. Therefore, in the airway epithelium apoptosis serves three main roles: (1) to eliminate damaged cells; (2) to restore homeostasis following hyperplastic changes; and (3) to control inflammation, and thereby support the barrier and anti-inflammatory functions.

Bronchus- and nasal-associated lymphoid tissues

The bronchus-associated lymphoid tissue (BALT) and the nasal-associated lymphoid tissue (NALT) constitute organized lymphoid aggregates that are capable of T- and B-cell responses to inhaled antigens. BALT, located mostly at bifurcations of the bronchus in animals and humans, is present in the fetus and develops rapidly following birth, especially in the presence of antigens. Humoral immune responses elicited by BALT are primarily immunoglobulin A secretion both locally and by BALT-derived B cells that have trafficked to distant mucosal sites. Similarly located T-cell responses have been noted. On the basis of these findings, the BALT can be thought of as functionally analogous to mucosal lymphoid aggregates in the intestine and is deemed a member of the common mucosal immunologic system. NALT has been described principally in the rodent nasal passage as two separate lymphoid aggregates. It develops after birth, likely in response to antigen, and B- and T-cell responses parallel those that occur in BALT. It is not known whether NALT cells traffic to distant mucosal sites, although mucosal responses have been detected after nasal immunization. NALT appears from many studies to be a functionally distinct lymphoid aggregate when compared with BALT and Peyer's patches. It may exist, however, in humans as a diffuse collection of isolated lymphoid follicles.

Distribution and leukocyte contacts of γδ T cells in the lung

Pulmonary gammadelta T cells protect the lung and its functions, but little is known about their distribution in this organ and their relationship to other pulmonary cells. We now show that gammadelta and alphabeta T cells are distributed differently in the normal mouse lung. The gammadelta T cells have a bias for nonalveolar locations, with the exception of the airway mucosa. Subsets of gammadelta T cells exhibit further variation in their tissue localization. gammadelta and alphabeta T cells frequently contact other leukocytes, but they favor different cell-types. The gammadelta T cells show an intrinsic preference for F4/80+ and major histocompatibility complex class II+ leukocytes. Leukocytes expressing these markers include macrophages and dendritic cells, known to function as sentinels of airways and lung tissues. The continuous interaction of gammadelta T cells with these sentinels likely is related to their protective role.

Mismatched antigen prepares gamma delta T cells for suppression of airway hyperresponsiveness

Gammadelta T cells suppress airway hyperresponsiveness (AHR) induced in allergen-challenged mice but it is not clear whether the suppression is allergen specific. The AHR-suppressive cells express TCR-Vgamma4. To test whether the suppressive function must be induced, we adoptively transferred purified Vgamma4(+) cells into gammadelta T cell-deficient and OVA-sensitized and -challenged recipients (B6.TCR-Vgamma4(-/-)/6(-/-)) and measured the effect on AHR. Vgamma4(+) gammadelta T cells isolated from naive donors were not AHR-suppressive, but Vgamma4(+) cells from OVA-stimulated donors suppressed AHR. Suppressive Vgamma4(+) cells could be isolated from lung and spleen. Their induction in the spleen required sensitization and challenge. In the lung, their function was induced by airway challenge alone. Induction of the suppressors was associated with their activation but it did not alter their ability to accumulate in the lung. Vgamma4(+) gammadelta T cells preferentially express Vdelta4 and -5 but their AHR-suppressive function was not dependent on these Vdeltas. Donor sensitization and challenge not only with OVA but also with two unrelated allergens (ragweed and BSA) induced Vgamma4(+) cells capable of suppressing AHR in the OVA-hyperresponsive recipients, but the process of sensitization and challenge alone (adjuvant and saline only) was not sufficient to induce suppressor function, and LPS as a component of the allergen was not essential. We conclude that AHR-suppressive Vgamma4(+) gammadelta T cells require induction. They are induced by allergen stimulation, but AHR suppression by these cells does not require their restimulation with the same allergen.

Insights into the pathogenesis of asthma utilizing murine models

Asthma is a common syndrome in children and adults. Despite the increasing prevalence and socioeconomic burden, the underlying pathophysiology remains poorly defined in a large percentage of asthmatics. Animal models and, in particular, murine models of allergic airway disease have helped to reveal some of the potential underlying mechanisms and have played an important role in identifying the importance of T cells and TH2 cytokines in development of allergen-induced inflammation and airway hyperresponsiveness. In addition, other cell types including mast cells and eosinophils have been implicated in the development of some aspects of the disease. To further understand this complex syndrome, the development of animal models which mimic elements of this chronic airway disease is essential.

Effects of anticytokine therapy in a mouse model of chronic asthma

The relative contribution of Th2 and Th1 cytokines to the pathogenesis of lesions of chronic asthma remains poorly understood. To date, therapeutic inhibition of Th2 cytokines has proved disappointing. We used a clinically relevant model of chronic allergic asthma in mice to compare the effects of administering neutralizing antibodies to interleukin (IL)-13, IL-5, and interferon-gamma (IFN-gamma) to animals with established disease. As has been observed in clinical studies, anti-IL-5 inhibited both inflammation and remodeling but had no effect on airway responsiveness to methacholine. Anti-IL-13 effectively suppressed eosinophil recruitment and accumulation of chronic inflammatory cells in the airways. This treatment also partially suppressed changes of airway wall remodeling, including goblet cell hyperplasia/metaplasia and subepithelial fibrosis, but had limited ability to inhibit airway hyperreactivity (AHR). In contrast, treatment with anti-IFN-gamma markedly suppressed AHR. This antibody inhibited accumulation of chronic inflammatory cells but did not affect eosinophil recruitment or changes of remodeling. We conclude that inhibition of IL-5 is beneficial and that inhibition of IL-13 has considerable potential as a therapeutic strategy in chronic asthma, that IFN-gamma may play an important role in the pathogenesis of AHR, and that co-operative interaction between Th2 and Th1 cytokines contributes to the pathogenesis of the lesions of chronic asthma.