T-Cell repertoire in the blood and lungs of atopic asthmatics before and after ragweed challenge

Biased Generation and In Situ Activation of Lung Tissue-Resident Memory CD4 T Cells in the Pathogenesis of Allergic Asthma

Asthma is a chronic inflammatory disease mediated by allergen-specific CD4 T cells that promote lung inflammation through recruitment of cellular effectors into the lung. A subset of lung T cells can persist as tissue-resident memory T cells (TRMs) following infection and allergen induction, although the generation and role of TRM in asthma persistence and pathogenesis remain unclear. In this study, we used a mouse model of chronic exposure to intranasal house dust mite (HDM) extract to dissect how lung TRMs are generated and function in the persistence and pathogenesis of allergic airway disease. We demonstrate that both CD4⁺ and CD8⁺ T cells infiltrate into the lung tissue during acute HDM exposure; however, only CD4⁺ TRMs, and not CD8⁺ TRMs, persist long term following cessation of HDM administration. Lung CD4⁺ TRMs are localized around airways and are rapidly reactivated upon allergen re-exposure accompanied by the rapid induction of airway hyperresponsiveness independent of circulating T cells. Lung CD4⁺ TRM activation to HDM challenge is also accompanied by increased recruitment and activation of dendritic cells in the lungs. Our results indicate that lung CD4⁺ TRMs can perpetuate allergen-specific sensitization and direct early inflammatory signals that promote rapid lung pathology, suggesting that targeting lung CD4⁺ TRMs could have therapeutic benefit in alleviating recurrent asthma episodes.

Thymic stromal lymphopoietin signaling in CD4(+) T cells is required for TH2 memory

BACKGROUND

Thymic stromal lymphopoietin (TSLP) is a key factor in the development of allergic asthma. Numbers of TH2 memory cells gradually increase in allergic patients with the progression of disease and persist in the lungs during remission, although the mechanism is not clear.

OBJECTIVE

We sought to define the role of TSLP in TH2 memory cell generation and maintenance in vivo.

METHODS

Adoptive transfer of wild-type and thymic stromal lymphopoietin receptor (TSLPR)-deficient ovalbumin-specific CD4(+) T cells before TH2 sensitization was used to define T cell-specific TSLP effects. Atopic dermatitis and increased serum TSLP concentrations were induced by topical application of the vitamin D3 analog MC903. Memory cells in peripheral blood were monitored weekly with flow cytometry. Memory recall was tested after intranasal ovalbumin challenge.

RESULTS

TSLP signaling in CD4(+) T cells is required for the generation/maintenance of memory cells after in vivo priming. TSLPR-deficient CD4(+) T cells have no defects in proliferation but do not survive 1 week after sensitization, and increased TSLP expression during sensitization significantly increased the frequency of memory cells. Although in vitro-differentiated TSLPR-deficient TH2 cells develop into memory cells with equal efficiency to wild-type cells, the recall response to airway antigen challenge is impaired. Moreover, after antigen challenge of mice with established TH2 memory, TSLP signaling in CD4(+) T cells significantly affects memory cell generation/maintenance from secondary effector cells.

CONCLUSION

TSLP signaling in CD4(+) T cells is required for not only TH2 memory cell formation in vivo but also the recall response of the memory cells to local antigen challenge.

Attenuation of airway inflammation by simvastatin and the implications for asthma treatment: is the jury still out?

Although some studies have explained the immunomodulatory effects of statins, the exact mechanisms and the therapeutic significance of these molecules remain to be elucidated. This study not only evaluated the therapeutic potential and inhibitory mechanism of simvastatin in an ovalbumin (OVA)-specific asthma model in mice but also sought to clarify the future directions indicated by previous studies through a thorough review of the literature. BALB/c mice were sensitized to OVA and then administered three OVA challenges. On each challenge day, 40 mg kg⁻¹ simvastatin was injected before the challenge. The airway responsiveness, inflammatory cell composition, and cytokine levels in bronchoalveolar lavage (BAL) fluid were assessed after the final challenge, and the T cell composition and adhesion molecule expression in lung homogenates were determined. The administration of simvastatin decreased the airway responsiveness, the number of airway inflammatory cells, and the interleukin (IL)-4, IL-5 and IL-13 concentrations in BAL fluid compared with vehicle-treated mice (P<0.05). Histologically, the number of inflammatory cells and mucus-containing goblet cells in lung tissues also decreased in the simvastatin-treated mice. Flow cytometry showed that simvastatin treatment significantly reduced the percentage of pulmonary CD4⁺ cells and the CD4⁺/CD8⁺ T-cell ratio (P<0.05). Simvastatin treatment also decreased the expression of the vascular cell adhesion molecule 1 and intercellular adhesion molecule 1 proteins, as measured in homogenized lung tissues (P<0.05) and human epithelial cells. The reduction in the T cell influx as a result of the decreased expression of cell adhesion molecules is one of the mechanisms by which simvastatin attenuates airway responsiveness and allergic inflammation. Rigorous review of the literature together with our findings suggested that simvastatin should be further developed as a potential therapeutic strategy for allergic asthma.

Airway inflammation and IgE production induced by dust mite allergen-specific memory/effector Th2 cell line can be effectively attenuated by IL-35

CD4(+) memory/effector T cells play a central role in orchestrating the rapid and robust immune responses upon re-encounter with specific Ags. However, the immunologic mechanism(s) underlying these responses are still not fully understood. To investigate this, we generated an allergen (major house dust mite allergen, Blo t 5)-specific murine Th2 cell line that secreted IL-4, IL-5, IL-10, and IL-13, but not IL-9 or TNF-α, upon activation by the cognate Ag. These cells also exhibited CD44(high)CD62L(-) and CD127(+) (IL-7Rα(+)) phenotypes, which are characteristics of memory/effector T cells. Experiments involving adoptive transfer of this Th2 cell line in mice, followed by three intranasal challenges with Blo t 5, induced a dexamethasone-sensitive eosinophilic airway inflammation. This was accompanied by elevation of Th2 cytokines and CC- and CXC-motif chemokines, as well as recruitment of lymphocytes and polymorphic mononuclear cells into the lungs. Moreover, Blo t 5-specific IgE was detected 4 d after the last intranasal challenge, whereas elevation of Blo t 5-specific IgG1 was found at week two. Finally, pulmonary delivery of the pVAX-IL-35 DNA construct effectively downregulated Blo t 5-specific allergic airway inflammation, and i.m. injection of pVAX-IL-35 led to long-lasting suppression of circulating Blo t 5-specific and total IgE. This model provides a robust research tool to elucidate the immunopathogenic role of memory/effector Th2 cells in allergic airway inflammation. Our results suggested that IL-35 could be a potential therapeutic target for allergic asthma through its attenuating effects on allergen-specific CD4(+) memory/effector Th2 cell-mediated airway inflammation.

A novel subset of CD4(+) T(H)2 memory/effector cells that produce inflammatory IL-17 cytokine and promote the exacerbation of chronic allergic asthma

The inflammatory cytokine interleukin (IL)-17 is involved in the pathogenesis of allergic diseases. However, the identity and functions of IL-17-producing T cells during the pathogenesis of allergic diseases remain unclear. Here, we report a novel subset of T(H)2 memory/effector cells that coexpress the transcription factors GATA3 and RORγt and coproduce T(H)17 and T(H)2 cytokines. Classical T(H)2 memory/effector cells had the potential to produce IL-17 after stimulation with proinflammatory cytokines IL-1β, IL-6, and IL-21. The number of IL-17-T(H)2 cells was significantly increased in blood of patients with atopic asthma. In a mouse model of allergic lung diseases, IL-17-producing CD4(+) T(H)2 cells were induced in the inflamed lung and persisted as the dominant IL-17-producing T cell population during the chronic stage of asthma. Treating cultured bronchial epithelial cells with IL-17 plus T(H)2 cytokines induced strong up-regulation of chemokine eotaxin-3, Il8, Mip1b, and Groa gene expression. Compared with classical T(H)17 and T(H)2 cells, antigen-specific IL-17-producing T(H)2 cells induced a profound influx of heterogeneous inflammatory leukocytes and exacerbated asthma. Our findings highlight the plasticity of T(H)2 memory cells and suggest that IL-17-producing T(H)2 cells may represent the key pathogenic T(H)2 cells promoting the exacerbation of allergic asthma.

T-cell responses to allergens

The allergic response in human beings is engineered by CD4(+) T lymphocytes, which secrete T(H)2 cytokines in response to activation by allergen-derived peptides. Although T(H)2 cells have been well characterized, defining the properties of allergen-specific T cells has proved challenging in human beings because of their low frequency within the T-cell repertoire. However, recent studies have provided insight into the molecular signature of long-lived human memory T(H)2 cells, which are allergen-specific. T-cell responses directed against allergens develop in early life and are heavily influenced by the type and dose of allergen, and possibly coexposure to microbial products. These responses are susceptible to suppression by regulatory T cells. This article highlights recent advances in the characterization of allergen-specific memory T(H)2 cells and discusses the heterogeneous nature of regulatory T cells and possible mechanisms of action. The relevance of T-cell epitope mapping studies to understanding the unique nature of T-cell responses to different allergens, as well as to peptide vaccine development, is reviewed. Experimental techniques and approaches for analyzing allergen-specific T cells and identifying novel T-cell epitopes are described that may lead to new T-cell-based therapies.

Targeting memory Th2 cells for the treatment of allergic asthma

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

The strength of the OVA-induced airway inflammation in rats is strain dependent

To examine the influence of genetics on the OVA-induced allergic inflammatory response in lungs we compared rats that are genetically Th2-predisposed (Brown Norway, inbred) or not genetically predisposed (Sprague Dawley, outbred). Rats were sensitized with ovalbumin (OVA) and challenged four weeks later with OVA aerosol. Eighteen hours after challenge, lung tissue was studied for evaluation of numbers of eosinophils, neutrophils, macrophages and mast cells, as well as for expression of P-selectin, E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on endothelial cells. From a separate portion of the pulmonary tissue, leucocytes were isolated to analyse numbers of IFNgamma and IL-4 producing cells (ELISPOT assay) and frequencies of T-cell subsets and B cells. We found increased numbers of eosinophils and neutrophils in the lung, an increased number of IL-4 producing cells in lung cell isolates and increased levels of serum (OVA- specific)-IgE in both rat strains. In addition, expression of E-selectin and ICAM-1 was up regulated in both rat strains whereas expression of VCAM-1 was only up regulated in the BN rat. Although the 'allergic' Th2 response to OVA was detectable in both rat strains, it was more pronounced in the BN rat than in the SD rat. However, the SD rat, which is not predisposed to respond in either a Th2 or Th1-like way, appeared capable of mounting an allergic response to OVA. This suggests that other factors than genetic contribute to allergic disease.

Vbeta18.1(+) and V(alpha)2.3(+) T-cell subsets are associated with house dust mite allergy in human subjects

BACKGROUND

The recognition of allergenic peptides by T cells through their T-cell receptor (TCR) represents a crucial step in the initiation of an allergen-specific immune response. In parallel to the superantigen-driven restricted expansion of Vbeta subsets in autoimmune and infectious diseases, reports in animals and human subjects have shown a similar capacity of classical antigens.

OBJECTIVE

The study was performed to analyze the V(alpha)/Vbeta expression in house dust mite (HDM) allergy.

METHODS

The TCR repertoire of 15 subjects with HDM allergy, 22 atopic subjects without HDM allergy, and 19 nonatopic individuals, members of 2 extended and 4 nuclear families, was determined. By using flow cytometry, the expression of 22 Vbeta and 3 V(alpha) elements was analyzed in vivo and after in vitro allergen stimulation.

RESULTS

In comparison with nonatopic and atopic individuals without HDM allergy, freshly isolated PBMCs of individuals with HDM allergy showed a significantly higher frequency of Vbeta18(+) and V(alpha)2.3(+) T cells. Although members of all 3 groups had a similar lymphocyte proliferation response after in vitro stimulation with Der p 1 or Der p 1 peptide(101-131), a significant expansion of Vbeta18(+) and V(alpha)2.3(+) T cells in vitro occurred only in individuals with HDM allergy. Moreover, the degree of expansion correlated with the levels of allergen-specific IgE antibodies. No expansion of Vbeta18(+) and V(alpha)2.3(+) was observed after mitogen stimulation with PHA, indicating allergen specificity of the response.

CONCLUSION

Our results strongly suggest restricted TCR V(alpha)/Vbeta gene use in HDM allergy and might be a step toward TCR-based immunotherapy.

T cell receptor Vbeta expression in patients with allergic asthma before and after repeated low-dose allergen inhalation

The objective of this study was to identify disease-associated T cell subsets by characterizing the lung and blood T cell receptor (TCR) repertoires in allergic asthmatics before and after repeated low-dose allergen challenge. Peripheral blood lymphocyte (PBL) and bronchoalveolar lavage (BAL) samples were obtained from eight patients with allergic asthma before and after a period of repeated low-dose allergen inhalations. RT-PCR followed by Southern blot allowed the quantification of relative Vbeta gene segment usage. Thirteen healthy individuals served as controls at PBL level. PBL as well as BAL T cells of asthmatics displayed a higher usage of Vbeta3, Vbeta5.2, and Vbeta6.1-3 and a lower usage of Vbeta16, Vbeta18, and Vbeta19 compared to PBL of healthy controls. Interestingly, TCR Vbeta7 and Vbeta9 usage was significantly higher in BAL than in PBL in asthmatics before as well as after challenge. TCR repertoire alterations after allergen challenge differed between individuals, with relatively mild changes.

Pulmonary T cells and eosinophils: coconspirators or independent triggers of allergic respiratory pathology?

Etiologic discussions of allergic respiratory pathology frequently engender rabid constituencies of pro-T cell or proeosinophil disciples, each claiming, often with religious fervor, the importance of their leukocyte. However, increasing evidence suggests that the exclusionary rhetoric from either camp is inadequate to explain many of the pathologic changes occurring in the lung. Data from both asthmatic patient and mouse models of allergic respiratory inflammation suggest that, in addition to cell-autonomous activities, T-cell and eosinophil interactions may be critical to the onset and progression of pulmonary pathology. These studies also suggest that T-lymphocyte subpopulations and eosinophils communicate by means of both direct cell-cell interactions and through the secretion of inflammatory signals. Collectively, the data support an expanded view of T-cell and eosinophil activities in the lung, including both immunoregulative activities and downstream effector functions impinging directly on lung function.

Pulmonary T cell repertoire in patients with graft-versus-host disease following blood and marrow transplantation

Pulmonary inflammation is one of the risk factors associated with blood and marrow transplantation (BMT). To determine the potential role of T cells in pulmonary complications after transplantation, we analyzed the T-cell repertoire expressed in bronchoalveolar lavage fluids from eleven patients with graft-versus-host disease following BMT. A reverse transcriptase-polymerase chain reaction was used to amplify rearranged TCR transcripts in unfractionated, CD4+, and CD8+ T cells from bronchoalveolar lavage fluids. The relative expression of TCR variable (V) gene families and the diversity of junctional region lengths associated with different AV and BV gene families were analyzed. Nearly all TCR AV and BV gene families were detected in bronchoalveolar lavage cells from BMT recipients. Oligoclonal patterns of TCR junctional region lengths were observed in unfractionated, CD4+, and CD8+ bronchoalveolar T cells. The oligoclonal expansion of bronchoalveolar T cells in patients was confirmed by DNA sequencing. TCRV gene expression is almost completely restored in the lungs of BMT recipients as early as two weeks after transplantation. Increased oligoclonality among TCR gene families suggests either an incomplete restoration of TCR diversity or an antigen-driven expansion of T cells in the lungs of BMT recipients with graft-versus-host disease, not necessarily related to pulmonary infection.

Polarized Type 1 Cytokine Profile in Bronchoalveolar Lavage T Cells of Patients with Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP) is characterized by an inflammatory lymphocytic alveolitis comprised of both CD8+ and CD4+ T cells. Animal models suggest that HP is facilitated by overproduction of IFN-γ, and that IL-10 ameliorates severity of the disease, indicating a Th1-type response. To determine whether a Th1 phenotype in HP also exists clinically, bronchoalveolar lavage (BAL) and peripheral blood (PB) T cells were obtained from HP individuals and analyzed for Th1 vs Th2 cytokine profiles. It was determined that soluble OKT3-stimulated BAL T cells cocultured with alveolar macrophages produced more IFN-γ and less IL-10 than PB T cells cocultured with monocytes, but no difference was observed in IL-4 production. The monocytic cells did not account for this difference, as CD80 and CD86 expressions were similar, and coculturing PB T cells with alveolar macrophages resulted in no difference in IFN-γ production. Similarly, there was no difference in IL-12 production between stimulated BAL or PB T cells; however, addition of rIL-12 significantly increased production of IFN-γ by BAL T cells, but not by PB T cells. This effect was due to a difference in IL-12R expression. High affinity IL-12R were only present in association with BAL T cells. These studies indicate that clinical HP is characterized by a predominance of IFN-γ-producing T cells, perhaps resulting from a reduction in IL-10 production and an increase in high affinity IL-12R compared with blood T cells.

Short ragweed allergen induces eosinophilic lung disease in HLA-DQ transgenic mice

The human leukocyte antigen (HLA) restriction of the IgE response to different allergens in humans has been a subject of numerous published studies. However, the role and contribution of specific HLA class II molecules in the pathogenesis of allergic airway inflammation are unknown and difficult to assess. HLA-DQ6 and HLA-DQ8 transgenic mice lacking endogenous mouse class II gene expression were actively immunized and later challenged intranasally with short ragweed (SRW) allergenic extract. The HLA-DQ transgenic mice developed pulmonary eosinophilia and lung tissue damage. We also found an increase in total protein (TP) level and IL-5 production in bronchoalveolar lavage (BAL) fluid and an increase in SRW-specific Th2-type immunoglobulins (IgG1, IgG2b) and total serum IgE levels. Under similar treatment, DQ-negative full-sib control mice were normal. The allergic response could be significantly inhibited or abrogated in HLA-DQ mice by systemic treatment with anti-DQ mAb. The in vivo responses of HLA-DQ6 and HLA-DQ8 mice showed differences in terms of levels of eosinophilia, BAL protein, IL-5 concentration, and lung hyperreactivity to inhaled methacholine. These findings demonstrate the crucial role for specific HLA-DQ molecules in SRW-specific CD4(+) T-cell activation and resulting recruitment of eosinophils into the airways.

Molecular mechanisms of CD8+ T cell-mediated delayed hypersensitivity: implications for allergies, asthma, and autoimmunity

Delayed-type hypersensitivity (DTH) is defined as the recruitment of T cells into tissues to be activated by antigen-presenting cells to produce cytokines that mediate local inflammation. CD8+ T cells are now known to mediate DTH responses in allergic contact dermatitis, drug eruptions, asthma, and autoimmune diseases. This inflammatory effector capability of CD8+ cytotoxic T cells was previously poorly recognized, but there is now considerable evidence that these diseases may be mediated by CD8+ DTH. The difference between CD8+ T cells and CD4+ T cells mediating DTH relates to the molecular mechanisms by which antigens are processed and presented to the T cells. Antigens external to the cell are phagocytosed and processed for presentation on MHC class II molecules (eg, HLA-DR) to CD4+ T cells. In contrast, internal cytoplasmic antigens are processed by the endogenous pathway for presentation on MHC class I molecules (eg, HLA-A, -B, and -C) to CD8+ T cells. External allergens can also enter the endogenous pathway to be presented to CD8+ T cells. These include many contact sensitizers, chemical and protein respiratory allergens, viral antigens, metabolic products of drugs, and autoantigens. The resulting CD8+ T-cell response explains the role of CD8+ T-cell DTH mechanisms in allergic contact dermatitis, asthma, drug eruptions, and autoimmune diseases.

Immune dysregulation as a cause for allergic asthma

Allergic asthma is being increasingly understood as a disease caused by Th2-mediated immune responses to inhaled allergens. Most individuals fail to respond to allergens with a Th2 response, and thus, allergic asthma can be considered the result of an abnormally regulated or dysregulated immune response. The prevalence of asthma has risen precipitously in urbanized cultures, as contrasted with third world countries. This observation underlies the heightened efforts in the past few years of basic and applied research efforts to gain a better understanding of both normal and dysregulated immunity to antigens introduced via the airways. This review focuses on recent human studies into the immune dysregulation that results in the asthma phenotype, but also cites selected relevant papers from research with experimental animals.

CD8+ T cells in atopic disease

In recent years there has been a tremendous expansion in our understanding about CD8(+) T cells. We now know that, as for CD4(+) T cells, they can be divided into subsets (Tc1 and Tc2) according to the cytokines they secrete. These subsets may differ in their capacity to kill and may even, in some cases, provide help for B cell antibody production or be involved in the induction of inflammatory responses. In addition, there is a host of cross-regulatory networks between different CD4(+) and CD8(+) subsets that control the magnitude and duration of immune responses. The observation that some antigens that are normally presented by MHC class II and seen by CD4(+) T cells can be presented by MHC class I and stimulate CD8(+) T cells increases the possibility for such interactions. During the next few years we can expect that our understanding of the biology of CD8(+) T cells and their role in immunity will increase.