Contribution of CCR4 and CCR8 to antigen-specific T(H)2 cell trafficking in allergic pulmonary inflammation

A randomized, controlled, crossover study in patients with mild and moderate asthma undergoing treatment with traditional Chinese acupuncture

OBJECTIVES

This study sought to verify the effects of acupuncture as an adjuvant treatment for the control of asthma.

METHODS

This was a randomized, controlled, crossover trial conducted at the Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo. A total of 74 patients with mild/moderate, persistent asthma were randomized into two therapeutic groups: Group A - 31 patients underwent 10 real weekly acupuncture sessions, followed by a 3-week washout period and 10 sham weekly acupuncture sessions; and Group B - 43 patients underwent 10 sham weekly acupuncture sessions, followed by a 3-week washout period and 10 real weekly acupuncture sessions. Patients used short- and long-acting β-2 agonists and inhaled corticosteroids when necessary. Prior to treatment and after each period of 10 treatment sessions, the patients were evaluated for spirometry, induced sputum cell count, exhaled nitric oxide (NO) and with the Short Form 36 (SF-36) and Questionnaire on Quality of Life-Asthma (QQLA) questionnaires. Daily peak flow and symptom diaries were registered. The level of significance adopted was 5% (α=0.05).

RESULTS

In Group B, after real acupuncture, there was a decrease in eosinophils (p=0.035) and neutrophils (p=0.047), an increase in macrophages (p=0.001) and an improvement in peak flow (p=0.01). After sham acupuncture treatment, patients experienced less coughing (p=0.037), wheezing (p=0.013) and dyspnea (p=0.014); similarly, after real acupuncture, patients reported less coughing (p=0.040), wheezing (p=0.012), dyspnea (p<0.001) and nocturnal awakening episodes (p=0.009). In Group A, there was less use of rescue medication (p=0.043). After the sham procedure, patients in Group A experienced less coughing (p=0.007), wheezing (p=0.037), dyspnea (p<0.001) and use of rescue medication (p<0.001) and after real acupuncture, these patients showed improvements in functional capacity (p=0.004), physical aspects (p=0.002), general health status (p<0.001) and vitality (p=0.019). Sham acupuncture also led to significant differences in symptoms, but these were not different from those seen with real acupuncture. Spirometry and exhaled NO levels did not show a difference between sham and real acupuncture treatment. In addition, no significant difference was demonstrated between treatments regarding the quality of life evaluation.

CONCLUSION

Real and sham acupuncture have different effects and outcomes on asthma control. The crossover approach was not effective in this study because both interventions led to improvement of asthma symptoms, quality of life and inflammatory cell counts. Thus, sham acupuncture cannot serve as a placebo in trials with acupuncture as the main intervention for asthma.

Targeting chemokine receptors in disease--a case study of CCR4

Since their early 1990s, the chemokine receptor family of G protein-coupled receptors (GPCRs) has been the source of much pharmacological endeavour. Best known for their key roles in recruiting leukocytes to sites of infection and inflammation, the receptors present themselves as plausible drug targets for therapeutic intervention. In this article, we will focus our attention upon CC Chemokine Receptor Four (CCR4) which has been implicated in diseases as diverse as allergic asthma and lymphoma. We will review the discovery of the receptors and their ligands, their perceived roles in disease and the successful targeting of CCR4 by both small molecule antagonists and monoclonal antibodies. We will also discuss future directions and strategies for drug discovery in this field.

IL-3 synergises with basophil-derived IL-4 and IL-13 to promote the alternative activation of human monocytes

Basophil-derived IL-4 is involved in the alternative activation of mouse monocytes, as recently shown in vivo. Whether this applies to human basophils and monocytes has not been established yet. Here, we sought to characterise the interaction between basophils and monocytes and identify the molecular determinants. A basophil-monocyte co-culture model revealed that IL-3 and basophil-derived IL-4 and IL-13 induced monocyte production of CCL17, a marker of alternative activation. Critically, IL-3 and IL-4 acted directly on monocytes to induce CCL17 production through histone H3 acetylation, but did not increase the recruitment of STAT5 or STAT6. Although freshly isolated monocytes did not express the IL-3 receptor α chain (CD123), and did not respond to IL-3 (as assessed by STAT5 phosphorylation), the overnight incubation with IL-4 (especially if associated with IL-3) upregulated CD123 expression. IL-3-activated JAK2-STAT5 pathway inhibitors reduced the CCL17 production in response to IL-3 and IL-4, but not to IL-4 alone. Interestingly, monocytes isolated from allergen-sensitised asthmatic patients exhibited a higher expression of CD123. Taken together, our data show that the JAK2-STAT5 pathway modulates both basophil and monocyte effector responses. The coordinated activation of STAT5 and STAT6 may have a major impact on monocyte alternative activation in vitro and in vivo.

IL-4/CCL22/CCR4 axis controls regulatory T-cell migration that suppresses inflammatory bone loss in murine experimental periodontitis

Inflammatory bone resorption is a hallmark of periodontitis, and Tregs and Th2 cells are independently associated with disease progression attenuation. In this study, we employed an infection-triggered inflammatory osteolysis model to investigate the mechanisms underlying Treg and Th2 cell migration and the impact on disease outcome. Aggregatibacter actinomycetemcomitans-infected C57Bl/6 (wild-type [WT]) mice develop an intense inflammatory reaction and alveolar bone resorption, and Treg and Th2 cell migration is temporally associated with disease progression attenuation. Tregs extracted from the lesions preferentially express CCR4 and CCR8, whereas Th2 cells express CCR3, CCR4, and CCR8. The absence of CCR5 and CCR8 did not significantly impact the migration of Tregs and Th2 cells or affect the disease outcome. CCR4KO mice presented a minor reduction in Th2 cells in parallel with major impairment of Treg migration, which was associated with increased inflammatory bone loss and higher proinflammatory and osteoclastogenic cytokine levels. The blockade of the CCR4 ligand CCL22 in WT mice resulted in an increased inflammatory bone loss phenotype similar to that in the CCR4KO strain. Adoptive transfer of CCR4(+) Tregs to the CCR4KO strain revert the increased disease phenotype to WT mice-like levels; also, the in situ production of CCL22 in the lesions is mandatory for Tregs migration and the consequent bone loss arrest. The local release of exogenous CCL22 provided by poly(lactic-co-glycolic acid) (PLGA) microparticles promotes migration of Tregs and disease arrest in the absence of endogenous CCL22 in the IL-4KO strain, characterized by the lack of endogenous CCL22 production, defective migration of Tregs, and exacerbated bone loss. In summary, our results show that the IL-4/CCL22/CCR4 axis is involved in the migration of Tregs to osteolytic lesion sites, and attenuates development of lesions by inhibiting inflammatory migration and the production of proinflammatory and osteoclastogenic mediators.

Abnormal chemokine receptor profile on circulating T lymphocytes from nonallergic asthma patients

BACKGROUND

T lymphocytes are involved in the pathogenesis of nonallergic asthma. The objective of this study was to characterize the subset distribution and pattern of chemokine receptor expression in circulating T lymphocyte subsets from nonallergic asthma patients.

METHODS

Forty stable nonallergic asthma patients and 16 sex- and age-matched healthy donors were studied. Twelve patients did not receive inhaled steroids (untreated patients), 16 received 50-500 μg b.i.d. of inhaled fluticasone propionate (FP) (standard-dose patients), and 12 received over 500 μg b.i.d. of inhaled FP (high-dose patients) for at least 12 months prior to the beginning of this study and were clinically well controlled. Flow cytometry was performed using a panel of monoclonal antibodies (4 colors).

RESULTS

Nonallergic asthma patients treated with high doses of inhaled FP showed a significant reduction in the percentages of CD3+ T lymphocytes compared to healthy controls. Untreated patients showed a significant increase in CCR6 expression in CD8+CD25+ and CD8+CD25+bright T cells compared to healthy controls. The results were similar for CXCR3 and CCR5 expression. In patients treated with standard doses of FP, CCR5 expression was significantly increased in CD3+ T lymphocytes relative to healthy controls.

CONCLUSIONS

The different groups of clinically stable nonallergic asthmatic patients showed distinct patterns of alterations in subset distribution as well as CCR6, CXCR3, and CCR5 expression on circulating T lymphocytes. .

Chemerin suppresses murine allergic asthma by inhibiting CCL2 production and subsequent airway recruitment of inflammatory dendritic cells

BACKGROUND

Chemerin has been implicated to play opposing roles, either pro-inflammatory or anti-inflammatory, in various tissue inflammation processes primarily through the regulation of tissue recruitment of immune cells. However, the effect of chemerin in allergic asthma has not yet been explored. We sought to investigate the role of chemerin in the murine model of allergic asthma and explore the underlying mechanism.

METHODS

We examined the effect of intranasal (i.n.) administration of chemerin during antigen challenge in murine models of asthma. Moreover, we examined whether administration of CCL2 or bone marrow-derived dendritic cells (BMDCs) transfer reversed the effects of chemerin on ovalbumin-induced asthma. We finally examined the effect of chemerin on CCL2 expression in activated lung epithelial cells in vitro.

RESULTS

The administration of chemerin attenuated allergic airway inflammation and airway hyperreactivity during antigen challenge. Chemerin treatment caused significant decreases in BALF CD4(+) T-cell accumulation and mRNA expression of Th2-attracting chemokines, CCL17 and CCL22, which was accompanied by significantly decreased BALF CD11c(+) CD11b(+) inflammatory DC accumulation and CCL2 production. Furthermore, airway administration of exogenous CCL2 or adoptive transfer of CD11c(+) CD11b(+) BMDCs abrogated the suppressive effects of chemerin on allergic asthma. Finally, in vitro study showed that chemerin inhibited CCL2 secretion by low-dose LPS-stimulated lung epithelial cells, which led to decreased chemotaxis of BMDCs.

CONCLUSIONS

Our study demonstrates that chemerin plays a protective role in allergic asthma by suppressing airway recruitment of inflammatory CD11c(+) CD11b(+) DCs through the inhibition of CCL2 secretion by active lung epithelial cells.

Tailored immune responses: novel effector helper T cell subsets in protective immunity

Differentiation of naïve CD4⁺ cells into functionally distinct effector helper T cell subsets, characterised by distinct "cytokine signatures," is a cardinal strategy employed by the mammalian immune system to efficiently deal with the rapidly evolving array of pathogenic microorganisms encountered by the host. Since the T(H)1/T(H)2 paradigm was first described by Mosmann and Coffman, research in the field of helper T cell biology has grown exponentially with seven functionally unique subsets having now been described. In this review, recent insights into the molecular mechanisms that govern differentiation and function of effector helper T cell subsets will be discussed in the context of microbial infections, with a focus on how these different helper T cell subsets orchestrate immune responses tailored to combat the nature of the pathogenic threat encountered.

Dectin-2 regulates the effector phase of house dust mite-elicited pulmonary inflammation independently from its role in sensitization

The myeloid C-type lectin receptor Dectin-2 directs the generation of Th2 and Th17 immune responses to the house dust mite Dermatophagoides farinae through the generation of cysteinyl leukotrienes and proinflammatory cytokines, respectively, but a role for Dectin-2 in effector phase responses has not been described. In this study, we demonstrate that administration of the Dectin-2 mAb solely at the time of D. farinae challenge abrogated eosinophilic and neutrophilic inflammation in the bronchoalveolar lavage fluid and Th1, Th2, and Th17 inflammation in the lung of previously sensitized mice. Furthermore, Dectin-2 null mice (Clec4n(-/-)) sensitized with the adoptive transfer of D. farinae-pulsed wild-type (WT) bone marrow-derived dendritic cells (DCs) also had less D. farinae-elicited pulmonary inflammation, supporting an effector function for Dectin-2. The protection from pulmonary inflammation seen with the Dectin-2 mAb or in Clec4n(-/-) mice was associated with little or no reduction in lung-draining lymph node cells or their cytokine production and with no reduction in serum IgE. WT and Clec4n(-/-) mice recipients, sensitized with D. farinae-pulsed WT bone marrow-derived DCs, had comparable levels of D. farinae-elicited IL-6, IL-23, TNF-α, and cysteinyl leukotrienes in the lung. By contrast, D. farinae-elicited CCL4 and CCL8 production from pulmonary CD11c(+)CD11b(+)Ly6C(+) and CD11c(+)CD11b(+)Ly6C(-)CD64(+) monocyte-derived DCs was reduced in Clec4n(-/-) recipients. Addition of CCL8 at the time of D. farinae challenge abrogated the protection from eosinophilic, neutrophilic, and Th2 pulmonary inflammation seen in Clec4n(-/-) recipients. Taken together, these results reveal that Dectin-2 regulates monocyte-derived DC function in the pulmonary microenvironment at D. farinae challenge to promote the local inflammatory response.

Pathogenic memory type Th2 cells in allergic inflammation

Immunological memory is a hallmark of adaptive immunity. Memory CD4 T helper (Th) cells are central to acquired immunity, and vaccines for infectious diseases are developed based on this concept. However, memory Th cells also play a critical role in the pathogenesis of various chronic inflammatory diseases, including asthma. We refer to these populations as 'pathogenic memory Th cells.' Here, we review recent developments highlighting the functions and characteristics of several pathogenic memory type Th2 cell subsets in allergic inflammation. Also discussed are the similarities and differences between pathogenic memory Th2 cells and recently identified type 2 innate lymphoid cells (ILC2), focusing on cytokine production and phenotypic profiles.

Targeted reduction of CCR4⁺ cells is sufficient to suppress allergic airway inflammation

BACKGROUND

Bronchial asthma is characterized by allergic airway inflammation involving C-C chemokine receptor type 4 (CCR4)-positive Th2 cells. As such, we hypothesize that the disease can be alleviated by targeted-elimination of CCR4⁺ cells. Thymus and activation-regulated chemokine (TARC)-PE38, a TARC fused the exotoxin fragment PE38 from Pseudomonas aeruginosa, has been shown to efficiently kill CCR4⁺ cells by delivering the exotoxin fragment PE38 into CCR4⁺ cells. To test our hypothesis, we examined whether TARC-PE38 could suppress allergic airway inflammation in a mouse model of house dust mite (HDM)-induced allergic airway inflammation.

METHODS

We evaluated the effect of TARC-PE38 on the major characteristics of HDM-induced allergic airway inflammation. Airway hyperresponsiveness, lung histopathology, lung Th1/Th2 cell populations, and concentrations of Th1/Th2 cytokines in the lungs were assessed in HDM-sensitized and challenged mice in the presence and absence of TARC-PE38.

RESULTS

TARC-PE38 efficiently suppressed allergic airway inflammation by significantly reducing airway hyperresponsiveness, the overall area of inflammation, and goblet cell hyperplasia. In HDM-sensitized and challenged mice, TARC-PE38 specifically reduced the numbers of CCR4⁺ cells. This reduction was associated with a significant decrease in the production of Th2 cytokines in the airway,and a decrease in the number of leukocytes, including macrophages, eosinophils and lymphocytes, within the subepithelial area of the lungs and airway lumen. TARC-PE38 had noeffect on Th1 cells.

CONCLUSION

Our data suggest that the elimination of CCR4⁺ cells via TARC-PE38 treatment is sufficient to control allergic airway inflammation and airway hyperresponsiveness.

International Union of Basic and Clinical Pharmacology. [corrected]. LXXXIX. Update on the extended family of chemokine receptors and introducing a new nomenclature for atypical chemokine receptors

Sixteen years ago, the Nomenclature Committee of the International Union of Pharmacology approved a system for naming human seven-transmembrane (7TM) G protein-coupled chemokine receptors, the large family of leukocyte chemoattractant receptors that regulates immune system development and function, in large part by mediating leukocyte trafficking. This was announced in Pharmacological Reviews in a major overview of the first decade of research in this field [Murphy PM, Baggiolini M, Charo IF, Hébert CA, Horuk R, Matsushima K, Miller LH, Oppenheim JJ, and Power CA (2000) Pharmacol Rev 52:145-176]. Since then, several new receptors have been discovered, and major advances have been made for the others in many areas, including structural biology, signal transduction mechanisms, biology, and pharmacology. New and diverse roles have been identified in infection, immunity, inflammation, development, cancer, and other areas. The first two drugs acting at chemokine receptors have been approved by the U.S. Food and Drug Administration (FDA), maraviroc targeting CCR5 in human immunodeficiency virus (HIV)/AIDS, and plerixafor targeting CXCR4 for stem cell mobilization for transplantation in cancer, and other candidates are now undergoing pivotal clinical trials for diverse disease indications. In addition, a subfamily of atypical chemokine receptors has emerged that may signal through arrestins instead of G proteins to act as chemokine scavengers, and many microbial and invertebrate G protein-coupled chemokine receptors and soluble chemokine-binding proteins have been described. Here, we review this extended family of chemokine receptors and chemokine-binding proteins at the basic, translational, and clinical levels, including an update on drug development. We also introduce a new nomenclature for atypical chemokine receptors with the stem ACKR (atypical chemokine receptor) approved by the Nomenclature Committee of the International Union of Pharmacology and the Human Genome Nomenclature Committee.

Suppressive effects of a novel CC chemokine receptor 4 antagonist on Th2 cell trafficking in ligand- and antigen-induced mouse models

CC chemokine receptor 4 (CCR4) has been implicated as a preferential marker for T helper type 2 (Th2) cells, and is believed to be involved in the pathology of allergic diseases by controlling Th2 cell trafficking into inflamed tissues. The objective of the study was to characterize the pharmacological properties of E0001-163, a novel CCR4 antagonist. E0001-163 was tested in both in vitro chemotaxis assays as well as in vivo mouse models of CCR4 ligand-induced air pouch and antigen-induced airway inflammation by utilizing in vitro-polarized Th2 cells. In vitro, E0001-163 inhibited migratory response of human Th2-polarized cells to CCL22, a CCR4 ligand, with an IC50 value of 11.9 nM. E0001-163 significantly suppressed CCL22-induced Th2 cell trafficking into mouse air pouch in a dose-dependent manner at doses of 3 and 10mg/kg, suggesting that E0001-163 has an inhibitory effect on CCR4-mediated T cell trafficking in vivo. In addition, E0001-163 partially decreased Th2 cell trafficking and the level of IL-4 in the lungs in Th2-tansferred and ovalbumin (OVA)-challenged mice. T cell trafficking involves multiple chemokine receptors both in acute and chronic phases, and our findings suggest that CCR4, together with other chemokine receptors, may be involved in Th2 cell trafficking under disease conditions.

Human leukocyte antigen-G and regulatory T cells during specific immunotherapy for pollen allergy

BACKGROUND

TH2-biased immune responses are important in allergy pathogenesis. Mechanisms of allergen-specific immunotherapy (SIT) might include the induction of regulatory T cells (Tregs) and immunoglobulin (Ig) G4 blocking antibodies, a reduction in the number of effector cells, and skewing of the cytokine profile towards a TH1-polarized immune response. We investigated the effects of SIT on T cells, on immunomodulation of human leukocyte antigen (HLA)-G, which has been associated with allergy, on regulatory cytokine expression, and on serum allergen-specific antibody subclasses (IgE and IgG4).

METHODS

Eleven birch and/or grass pollen-allergic patients and 10 healthy nonatopic controls were studied before and during SIT. Tregs, chemokine receptors, soluble HLA-G (sHLA-G), Ig-like transcript (ILT) 2, specific IgE, and IgG4 were studied. Peripheral blood mononuclear cells (PBMCs) were stimulated with pollen extract in vitro and immune factors were evaluated.

RESULTS

During SIT, the main changes in the peripheral blood were an increase in CXCR3(+)CD4(+)CD25(+)CD127(low/-) Tregs and a decrease in CCR4(+)CD4(+)CD25(+)CD127(low/-) Tregs, an increase in allergen-specific IgG4, and a decrease in sHLA-G during the first half of the treatment period. In the PBMC in vitro experiments, the following changes were observed upon allergen-stimulation: an increase in CD4(+)CD25(+)CD127(low/-) Tregs and ILT2(+)CD4(+)CD25(+)CD127(low/-) Tregs, an increase in IL-10 and IL-2 levels, and an increase in sHLA-G that was most pronounced at the start of SIT.

CONCLUSIONS

The changes in CXCR3(+)CD4(+)CD25(+)CD127(low/-) Treg, IgG4, and sHLA-G levels in the peripheral blood and in ILT2(+) Treg, IL-10, IL-2, and sHLA-G levels upon in vitro allergen stimulation suggest an upregulation in immunomodulatory factors and, to some degree, a shift towards TH1 during SIT.

Mucosal immunity and the onset of allergic disease

Mucosal barriers encounter an environment that is rich in pathogens that possess mechanisms for invading mucosal tissues. These barriers also encounter innocuous antigens, such as foods, airborne antigens, and microbiota. The mucosa has developed a sophisticated immune system that can mount robust immune responses against pathogenic antigens, while maintaining mucosal tolerance against non-pathogenic antigens. Accumulating evidence indicates that the mucosal epithelium, dendritic cells, and a subtype of T cells with regulatory properties play important roles in the development and maintenance of mucosal tolerance. Moreover, the micribiota also contribute to regulating the mucosal immune system. A failure to develop or the breakdown of mucosal tolerance can result in allergic diseases, such as food allergy and asthma. By taking advantage of the unique characteristics of the mucosal immune system, strategies that induce regulatory cells in vivo and, thereby, reconstitute mucosal tolerance may be used to develop novel therapies that are suitable for treating or preventing of allergic diseases.

Lung dendritic cells imprint T cell lung homing and promote lung immunity through the chemokine receptor CCR4

T cell trafficking into the lung is critical for lung immunity, but the mechanisms that mediate T cell lung homing are not well understood. Here, we show that lung dendritic cells (DCs) imprint T cell lung homing, as lung DC-activated T cells traffic more efficiently into the lung in response to inhaled antigen and at homeostasis compared with T cells activated by DCs from other tissues. Consequently, lung DC-imprinted T cells protect against influenza more effectively than do gut and skin DC-imprinted T cells. Lung DCs imprint the expression of CCR4 on T cells, and CCR4 contributes to T cell lung imprinting. Lung DC-activated, CCR4-deficient T cells fail to traffic into the lung as efficiently and to protect against influenza as effectively as lung DC-activated, CCR4-sufficient T cells. Thus, lung DCs imprint T cell lung homing and promote lung immunity in part through CCR4.

Compartmentalized chemokine-dependent regulatory T-cell inhibition of allergic pulmonary inflammation

BACKGROUND

Induction of endogenous regulatory T (Treg) cells represents an exciting new potential modality for treating allergic diseases, such as asthma. Treg cells have been implicated in the regulation of asthma, but the anatomic location in which they exert their regulatory function and the mechanisms controlling the migration necessary for their suppressive function in asthma are not known. Understanding these aspects of Treg cell biology will be important for harnessing their power in the clinic.

OBJECTIVE

We sought to determine the anatomic location at which Treg cells exert their regulatory function in the sensitization and effector phases of allergic asthma and to determine the chemokine receptors that control the migration of Treg cells to these sites in vivo in both mice and human subjects.

METHODS

The clinical efficacy and anatomic location of adoptively transferred chemokine receptor-deficient CD4(+)CD25(+) forkhead box protein 3-positive Treg cells was determined in the sensitization and effector phases of allergic airway inflammation in mice. The chemokine receptor expression profile was determined on Treg cells recruited into the human airway after bronchoscopic segmental allergen challenge of asthmatic patients.

RESULTS

We show that CCR7, but not CCR4, is required on Treg cells to suppress allergic airway inflammation during the sensitization phase. In contrast, CCR4, but not CCR7, is required on Treg cells to suppress allergic airway inflammation during the effector phase. Consistent with our murine studies, human subjects with allergic asthma had an increase in CCR4-expressing functional Treg cells in the lungs after segmental allergen challenge.

CONCLUSION

The location of Treg cell function differs during allergic sensitization and allergen-induced recall responses in the lung, and this differential localization is critically dependent on differential chemokine function.

Epigenetically mediated pathogenic effects of phenanthrene on regulatory T cells

Phenanthrene (Phe), a polycyclic aromatic hydrocarbon (PAH), is a major constituent of urban air pollution. There have been conflicting results regarding the role of other AhR ligands 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD) and 6-formylindolo [3,2-b]carbazole (FICZ) in modifying regulatory T cell populations (Treg) or T helper (Th)17 differentiation, and the effects of Phe have been understudied. We hypothesized that different chemical entities of PAH induce Treg to become either Th2 or Th17 effector T cells through epigenetic modification of FOXP3. To determine specific effects on T cell populations by phenanthrene, primary human Treg were treated with Phe, TCDD, or FICZ and assessed for function, gene expression, and phenotype. Methylation of CpG sites within the FOXP3 locus reduced FOXP3 expression, leading to impaired Treg function and conversion of Treg into a CD4⁺CD25^lo Th2 phenotype in Phe-treated cells. Conversely, TCDD treatment led to epigenetic modification of IL-17A and conversion of Treg to Th17 T cells. These findings present a mechanism by which exposure to AhR-ligands mediates human T cell responses and begins to elucidate the relationship between environmental exposures, immune modulation, and initiation of human disease.

Antagonism of chemokine receptor CCR8 is ineffective in a primate model of asthma

BACKGROUND

Expression of the T-cell-associated chemokine receptor CCR8 and its ligand CCL1 have been demonstrated to be elevated in patients with asthma. CCR8 deficiency or inhibition in models of allergic airway disease in mice resulted in conflicting data.

OBJECTIVE

To investigate the effects of a selective small molecule CCR8 inhibitor (ML604086) in a primate model of asthma.

METHODS

ML604086 and vehicle were administered by intravenous infusion to 12 cynomolgus monkeys during airway challenge with Ascaris suum. Samples were collected throughout the study to measure pharmacokinetics (PK) and systemic CCR8 inhibition, as well as inflammation, T helper 2 (Th2) cytokines and mucus in bronchoalveolar lavage (BAL). Airway resistance and compliance were measured before and after allergen challenge, and in response to increasing concentrations of methacholine.

RESULTS

ML604086 inhibited CCL1 binding to CCR8 on circulating T-cells>98% throughout the duration of the study. However, CCR8 inhibition had no significant effect on allergen-induced BAL eosinophilia and the induction of the Th2 cytokines IL-4, IL-5, IL-13 and mucus levels in BAL. Changes in airway resistance and compliance induced by allergen provocation and increasing concentrations of methacholine were also not affected by ML604086.

CONCLUSIONS

These results clearly demonstrate a dispensable role for CCR8 in ameliorating allergic airway disease in atopic primates, and suggest that strategies other than CCR8 antagonism should be considered for the treatment of asthma.

Regulatory T cells migrate to airways via CCR4 and attenuate the severity of airway allergic inflammation

We have previously shown that regulatory T (Treg) cells that accumulate in the airways of allergic mice upregulate CC-chemokine receptor 4 (CCR4) expression. These Treg cells suppressed in vitro Th2 cell proliferation but not type 2 cytokine production. In the current study, using a well-established murine model of allergic lung disease or oral tolerance, we evaluated the in vivo activity of Treg cells in allergic airway inflammation with special focus on CCR4 function. We found that allergic, but not tolerant, mice treated with anti-CD25 Ab showed increased airway eosinophilia and IL-5- or IL-4-producing Th2 cells when compared with untreated mice. Notably, mice with CCR4 deficiency displayed an augmented airway allergic inflammation compared with wild-type or CCR2 knockout (KO) mice. The allergic phenotype of CCR4KO mice was similar to that observed in anti-CD25-treated mice. The exacerbated allergic inflammation of CCR4KO mice was directly associated with an impaired migration of Treg cells to airways and augmented frequency of pulmonary Th2 cells. Adoptive transfer of CD25(+)CD4(+) T cells expressing high levels of CCR4, but not CCR4KO CD25(+)CD4(+) T cells, attenuated the severe airway Th2 response of CCR4KO mice. Our results show that CCR4 is critically involved in the migration of Treg cells to allergic lungs that, in turn, attenuate airway Th2 activation and allergic eosinophilic inflammation.

Experimental advances in understanding allergic airway inflammation

Asthma is largely an inflammatory disease, with the development of T cell mediated inflammation in the lung following exposure to allergen or other precipitating factors. Currently, the major therapies for this disease are directed either at relief of bronchoconstriction (ie beta-agonists) or are non-specific immunomodulators (ie, corticosteroids). While much attention has been paid to factors that regulate the initiation of an inflammatory response, chronic inflammation may also be due to defects in regulatory mechanisms that limit or terminate immune responses. In this review, we explore the elements controlling both the recruitment of T cells to the lung and their function. Possibilities for future therapeutic intervention are highlighted.

Toll-like receptor-2 agonist-allergen coupling efficiently redirects Th2 cell responses and inhibits allergic airway eosinophilia

Toll-like receptor (TLR) agonists beneficially modulate allergic airway inflammation. However, the efficiency of TLR agonists varies considerably, and their exact cellular mechanisms (especially of TLR 2/6 agonists) are incompletely understood. We investigated at a cellular level whether the administration of the pharmacologically improved TLR2/6 agonist S-[2,3-bispalmitoyiloxy-(2R)-propyl]-R-cysteinyl-amido-monomethoxy polyethylene glycol (BPP) conjugated to antigenic peptide (BPP-OVA) could divert an existing Th2 response and influence airway eosinophilia. The effects of BPP-OVA on airway inflammation were assessed in a classic murine sensitization/challenge model and an adoptive transfer model, which involved the adoptive transfer of in vitro differentiated ovalbumin (OVA)-specific Th2 cells. Functional T-cell stimulation by lung dendritic cells (DCs) was determined both in vitro and in vivo, combined with a cytokine secretion analysis. A single mucosal application of BPP-OVA efficiently delivered antigen, led to TLR2-mediated DC activation, and resulted in OVA-specific T-cell proliferation via lung DCs in vivo. In alternative models of allergic airway disease, a single administration of BPP-OVA before OVA challenge (but not BPP alone) significantly reduced airway eosinophilia, most likely through altered antigen-specific T-cell stimulation via DCs. Analyses of adoptively transferred Th2-biased cells after BPP-OVA administration in vivo suggested that BPP-OVA guides antigen-specific Th2 cells to produce significantly higher amounts of IFN-γ upon allergen challenge. In conclusion, our data show for the first time that a single mucosal administration of a TLR 2/6 agonist-allergen conjugate can provoke IFN-γ responses in Th2-biased cells and alleviate allergic airway inflammation.

Enhanced Tim3 activity improves survival after influenza infection

Influenza is a major cause of morbidity and mortality in the United States. Studies have shown that excessive T cell activity can mediate pneumonitis in the setting of influenza infection, and data from the 2009 H1N1 pandemic indicate that critical illness and respiratory failure postinfection were associated with greater infiltration of the lungs with CD8+ T cells. T cell Ig and mucin domain 3 (Tim3) is a negative regulator of Th1/Tc1-type immune responses. Activation of Tim3 on effector T cells has been shown to downregulate proliferation, cell-mediated cytotoxicity, and IFN-γ production, as well as induce apoptosis. In this article, we demonstrate that deletion of the terminal cytoplasmic domain of the Tim3 gene potentiates its ability to downregulate Tc1 inflammation, and that this enhanced Tim3 activity is associated with decreased phosphorylation of the TCR-CD3ζ-chain. We then show that mice with this Tim3 mutation infected with influenza are protected from morbidity and mortality without impairment in viral clearance or functional heterotypic immunity. This protection is associated with decreased CD8+ T cell proliferation and decreased production of inflammatory cytokines, including IFN-γ. Furthermore, the Tim3 mutation was protective against mortality in a CD8+ T cell-specific model of pneumonitis. These data suggest that Tim3 could be targeted to prevent immunopathology during influenza infection and demonstrate a potentially novel signaling mechanism used by Tim3 to downregulate the Tc1 response.

Pulmonary CCL18 recruits human regulatory T cells

CCL18 is both a constitutively expressed and an inducible chemokine, whose role in the inflammatory reaction is poorly known. The aim of this study was to evaluate whether CCL18 has the capacity to attract human T cells with a regulatory function (regulatory T cells [Treg]). Results from chemotaxis assays performed on different types of Treg showed that CD4(+)CD25(+)CD127(low) cells, but neither T regulatory type 1 clones nor Treg differentiated in vitro with anti-CD3/CD46 mAbs, were recruited by CCL18 in a dose-dependent manner. CCL18-recruited memory CD4(+) T cells were enriched in CD25(high), CD25(+)CD127(low), latency-associated peptide/TGF-β1, and CCR4-expressing T cells, whereas there was no enrichment in Foxp3(+) cells as compared with controls. Stimulated CCL18-recruited memory T cells produced significantly increased amounts of the regulatory cytokines IL-10 and TGF-β1, as well as IL-4, but not IFN-γ and IL-17. Cell surface CCL18 binding was found predominantly on IL-10(+) (26.3 ± 5.8%) and on a few latency-associated peptide/TGF-β1(+) (18.1 ± 1.9%) and IL-4(+) (14.5 ± 2.9%) memory T cells. In an in vivo model of SCID mice grafted with human skin and reconstituted with autologous PBMCs, the intradermal injection of CCL18 led to the cutaneous recruitment of CD4(+), CD25(+), and IL-10(+) cells, but not Foxp3(+) cells. Furthermore, CCL18-recruited memory T cells inhibited the proliferation of CD4(+)CD25(-) effector T cells through an IL-10-dependent mechanism. These data suggest that CCL18 may contribute to maintaining tolerance and/or suppressing deleterious inflammation by attracting memory Tregs into tissues, particularly in the lung, where it is highly and constitutively expressed.

T cell homing to epithelial barriers in allergic disease

Allergic inflammation develops in tissues that have large epithelial surface areas that are exposed to the environment, such as the lung, skin and gut. In the steady state, antigen-experienced memory T cells patrol these peripheral tissues to facilitate swift immune responses against invading pathogens. In at least two allergy-prone organs, the skin and the gut, memory T cells are programmed during the initial antigen priming to express trafficking receptors that enable them to preferentially home to these organs. In this review we propose that tissue-specific memory and inflammation-specific T cell trafficking facilitates the development of allergic disease in these organs. We thus review recent advances in our understanding of tissue-specific T cell trafficking and how regulation of T cell trafficking by the chemokine system contributes to allergic inflammation in mouse models and in human allergic diseases of the skin, lung and gut. Inflammation- and tissue-specific T lymphocyte trafficking pathways are currently being targeted as new treatments for non-allergic inflammatory diseases and may yield effective new therapeutics for allergic diseases.

Hepatic macrophage migration and differentiation critical for liver fibrosis is mediated by the chemokine receptor C-C motif chemokine receptor 8 in mice

Chemokines critically control the infiltration of immune cells upon liver injury, thereby promoting hepatic inflammation and fibrosis. The chemokine receptor CCR8 can affect trafficking of monocytes/macrophages, monocyte-derived dendritic cells (DCs) and T-helper cell (Th) subsets, but its role in liver diseases is currently unknown. To investigate the functional role of CCR8 in liver diseases, ccr8(-/-) and wild-type (WT) mice were subjected to chronic experimental injury models of carbon tetrachloride (CCl(4) ) administration and surgical bile duct ligation (BDL). CCR8 was strongly up-regulated in the injured liver. Ccr8(-/-) mice displayed attenuated liver damage (e.g., ALT, histology, and TUNEL) compared to WT mice and were also protected from liver fibrosis in two independent injury models. Flow cytometry revealed reduced infiltrates of liver macrophages, neutrophils and natural killer cells, whereas hepatic CD4(+) T cells increased. The main CCR8-expressing cells in the liver were hepatic macrophages, and CCR8 was functionally necessary for CCL1-directed migration of inflammatory but not for nonclassical monocytes into the liver. Moreover, the phenotype of liver macrophages from injured ccr8(-/-) animals was altered with increased expression of DC markers and enhanced expression of T-cell-attracting chemokine macrophage inflammatory protein 1-alpha (MIP-1α/CCL3). Correspondingly, hepatic CD4(+) T cells showed increased Th1 polarization and reduced Th2 cells in CCR8-deficient animals. Liver fibrosis progression, but also subsequent T-cell alterations, could be restored by adoptively transferring CCR8-expressing monocytes/macrophages into ccr8(-/-) mice during experimental injury.

CONCLUSIONS

CCR8 critically mediates hepatic macrophage recruitment upon injury, which subsequently shapes the inflammatory response in the injured liver, affecting macrophage/DC and Th differentiation. CCR8 deficiency protects the liver against injury, ameliorating initial inflammatory responses and hepatic fibrogenesis. Inhibition of CCR8 or its ligand, CCL1, might represent a successful therapeutic target to limit liver inflammation and fibrosis progression.

Lung dendritic cells in respiratory viral infection and asthma: from protection to immunopathology

Lung dendritic cells (DCs) bridge innate and adaptive immunity, and depending on context, they also induce a Th1, Th2, or Th17 response to optimally clear infectious threats. Conversely, lung DCs can also mount maladaptive Th2 immune responses to harmless allergens and, in this way, contribute to immunopathology. It is now clear that the various aspects of DC biology can be understood only if we take into account the functional specializations of different DC subsets that are present in the lung in homeostasis or are attracted to the lung as part of the inflammatory response to inhaled noxious stimuli. Lung DCs are heavily influenced by the nearby epithelial cells, and a model is emerging whereby direct communication between DCs and epithelial cells determines the outcome of the pulmonary immune response. Here, we have approached DC biology from the perspective of viral infection and allergy to illustrate these emerging concepts.

Immunological basis of reversible and fixed airways disease

Asthma is characterized by airflow obstruction that is usually completely reversible either spontaneously or in response to treatment. However, a small subset of patients with asthma display FAO (fixed airflow obstruction) despite optimal treatment, a feature more commonly associated with smoking-induced COPD (chronic obstructive pulmonary disease). Why some asthma patients develop FAO is not understood, and it is not clear whether (i) they represent a subset of patients with more severe disease, (ii) they share some characteristics of patients who develop COPD, or (iii) they represent a different disease entity altogether. The present review compares the pulmonary inflammatory profile of asthma patients with FAO with those without FAO, as well as COPD sufferers. The inflammation in asthma patients with FAO can vary from neutrophilic with CD8 T-cell involvement, similar to that of COPD, to eosinophilic with CD4 Th2 cell involvement, akin to that of asthma patients without FAO. Although studies of FAO in asthma sufferers would benefit hugely from consistent inclusion criteria, further research work is also required to shed more light on the immunological processes involved.

Lipid-cytokine-chemokine cascades orchestrate leukocyte recruitment in inflammation

Chemoattractants are pivotal mediators of host defense, orchestrating the recruitment of immune cells into sites of infection and inflammation. Chemoattractants display vast chemical diversity and include bioactive lipids, proteolytic fragments of serum proteins, and chemokines (chemotactic cytokines). All chemoattractants induce chemotaxis by activating seven-transmembrane-spanning GPCRs expressed on immune cells, establishing the concept that all chemoattractants are related in function. However, although chemoattractants have overlapping functions in vitro, recent in vivo data have revealed that they function, in many cases, nonredundantly in vivo. The chemically diverse nature of chemoattractants contributes to the fine control of leukocyte trafficking in vivo, with sequential chemoattractant use guiding immune cell recruitment into inflammatory sites. Lipid mediators frequently function as initiators of leukocyte recruitment, attracting the first immune cells into tissues. These initial responding immune cells produce cytokines locally, which in turn, induce the local release of chemokines. Local chemokine production then markedly amplifies subsequent waves of leukocyte recruitment. These new discoveries establish a paradigm for leukocyte recruitment in inflammation--described as lipid-cytokine-chemokine cascades--as a driving force in the effector phase of immune responses.

Attenuation of antigen-induced airway hyperresponsiveness and inflammation in CXCR3 knockout mice

Background

CD8+ T cells participate in airway hyperresponsiveness (AHR) and allergic pulmonary inflammation that are characteristics of asthma. CXCL10 by binding to CXCR3 expressed preferentially on activated CD8+ T cells, attracts T cells homing to the lung. We studied the contribution and limitation of CXCR3 to AHR and airway inflammation induced by ovalbumin (OVA) using CXCR3 knockout (KO) mice.

Methods

Mice were sensitized and challenged with OVA. Lung histopathological changes, AHR, cellular composition and levels of inflammatory mediators in bronchoalveolar lavage (BAL) fluid, and lungs at mRNA and protein levels, were compared between CXCR3 KO mice and wild type (WT) mice.

Results

Compared with the WT controls, CXCR3 KO mice showed less OVA-induced infiltration of inflammatory cells around airways and vessels, and less mucus production. CXCR3 KO mice failed to develop significant AHR. They also demonstrated significantly fewer CD8+ T and CD4+ T cells in BAL fluid, lower levels of TNFα and IL-4 in lung tissue measured by real-time RT-PCR and in BAL fluid by ELISA, with significant elevation of IFNγ mRNA and protein expression levels.

Conclusions

We conclude that CXCR3 is crucial for AHR and airway inflammation by promoting recruitment of more CD8+ T cells, as well as CD4+ T cells, and initiating release of proinflammatory mediators following OVA sensitization and challenge. CXCR3 may represent a novel therapeutic target for asthma.

Selective down-regulation of Th2 cell-mediated airway inflammation in mice by pharmacological intervention of CCR4

BACKGROUND

The chemokine receptor CCR4 has been implicated in Th2 cell-mediated immune responses. However, other T cell subsets are also known to participate in allergic inflammation.

OBJECTIVE

The role of CCR4 in Th1, Th2, and Th17 cell-mediated allergic airway inflammation was investigated.

METHOD

We generated an allergic airway inflammation model by adoptive transfer of in vitro-polarized ovalbumin (OVA)-specific Th1, Th2, and Th17 cells. The effect of a low-molecular weight CCR4 antagonist, Compound 22, on this model was examined.

RESULTS

Upon in vitro polarization of DO11.10 naïve T cells, Th1- and Th2-polarized cells dominantly expressed CXCR3 and CCR4, respectively, while Th17-polarized cells expressed CCR6 and CCR4. Intranasal OVA-challenge of mice transferred with each T cell subset induced accumulation of T cells in the lungs. Eosinophils were also massively accumulated in Th2-transferred mice, whereas neutrophils were preferentially recruited in Th1- and Th17-transferred mice. Compound 22, as well as anti-CCL17 or anti-CCL22 antibody selectively suppressed accumulation of Th2 cells and eosinophils in the lungs of Th2-transferred and OVA-challenged mice. Compound 22 also inhibited bronchial hyperresponsiveness but had little effect on goblet cell hyperplasia in Th2-transferred and OVA-challenged mice.

CONCLUSIONS AND CLINICAL RELEVANCE

There were notable differences in allergic lung inflammation mediated by different T cell subsets. CCR4 blockage was selectively effective for suppression of Th2-mediated allergic inflammation by blocking infiltration of Th2 cells.

Treatment of allergic asthma: modulation of Th2 cells and their responses

Atopic asthma is a chronic inflammatory pulmonary disease characterised by recurrent episodes of wheezy, laboured breathing with an underlying Th2 cell-mediated inflammatory response in the airways. It is currently treated and, more or less, controlled depending on severity, with bronchodilators e.g. long-acting beta agonists and long-acting muscarinic antagonists or anti-inflammatory drugs such as corticosteroids (inhaled or oral), leukotriene modifiers, theophyline and anti-IgE therapy. Unfortunately, none of these treatments are curative and some asthmatic patients do not respond to intense anti-inflammatory therapies. Additionally, the use of long-term oral steroids has many undesired side effects. For this reason, novel and more effective drugs are needed. In this review, we focus on the CD4+ Th2 cells and their products as targets for the development of new drugs to add to the current armamentarium as adjuncts or as potential stand-alone treatments for allergic asthma. We argue that in early disease, the reduction or elimination of allergen-specific Th2 cells will reduce the consequences of repeated allergic inflammatory responses such as lung remodelling without causing generalised immunosuppression.

The human cutaneous chemokine system

Irrespective of the immune status, the vast majority of all lymphocytes reside in peripheral tissues whereas those present in blood only amount to a small fraction of the total. It has been estimated that T cells in healthy human skin outnumber those present in blood by at least a factor of two. How lymphocytes within these two compartments relate to each other is not well understood. However, mounting evidence suggest that the study of T cell subsets present in peripheral blood does not reflect the function of their counterparts at peripheral sites. This is especially true under steady-state conditions whereby long-lived memory T cells in healthy tissues, notably those in epithelial tissues at body surfaces, are thought to fulfill a critical immune surveillance function by contributing to the first line of defense against a series of local threats, including microbes, tumors, and toxins, and by participating in wound healing. The relative scarcity of information regarding peripheral T cells and the factors regulating their localization is primarily due to inherent difficulties in obtaining healthy tissue for the extraction and study of immune cells on a routine basis. This is most certainly true for humans. Here, we review our current understanding of T cell homing to human skin and compare it when possible with gut-selective homing. We also discuss candidate chemokines that may account for the tissue selectivity in this process and present a model whereby CCR8, and its ligand CCL1, selectively regulate the homeostatic migration of memory lymphocytes to skin tissue.

A Th1/Th2-associated chemokine imbalance during infancy in children developing eczema, wheeze and sensitization

BACKGROUND

Analyses of circulating chemokines offer novel tools to investigate the T helper (Th)1/Th2 imbalance in allergic disease in vivo.

OBJECTIVE

To relate circulating Th1- and Th2-associated chemokines in infancy to allergic disease, sensitization and probiotic supplementation.

METHODS

Circulating levels of Th1-associated CXC-chemokine ligand (CXCL)9, CXCL10 and CXCL11 and Th2-associated CC-chemokine ligand (CCL)17 and CCL22 were assessed with Luminex and CCL18 with enzyme-linked immunosorbent assay at birth (n=109), 6 (n=104), 12 (n=116) and 24 months (n=123) in 161 infants completing a double-blind placebo-controlled allergy prevention trial with Lactobacillus reuteri during the last month of gestation and through the first year of life. The infants were followed regarding the development of allergic disease and sensitization until 2 years of age.

RESULTS

The Th2-associated chemokines CCL17 and CCL22 were the highest at birth and then decreased, whereas CCL18 and the Th1-associated chemokines increased with age. High Th2-associated chemokine levels were observed in children developing allergic disease. Sensitization was preceded by elevated levels of the Th2-associated CCL22 and reduced levels of the Th1-associated CXCL11 already at birth. The Th2-associated CCL17 was also elevated at birth in infants developing recurrent wheeze. A high Th2/Th1 ratio (CCL22/CXCL10) at birth associated with both sensitization and eczema development. The presence of L. reuteri in stool in the first week of life was associated with low CCL17 and CCL22 and high CXCL11 levels at 6 months of age. High Th1-associated chemokine levels were associated with day-care.

CONCLUSION AND CLINICAL RELEVANCE

Allergic disease and sensitization in infancy was associated with low circulating Th1- and high Th2-associated chemokine levels already from birth. Circulating chemokines are useful for investigating the Th1/Th2 imbalance in allergic disease in vivo. Elucidation of the role of chemokines in allergic diseases may lead to future treatments (ClinicalTrials.gov NCT01285830).

Targeting CXCR3 reduces ligand-induced T-cell activation but not development of lung allergic responses

BACKGROUND

Asthma is a chronic airway inflammatory disease that is associated with a large influx of inflammatory cells. Several chemokines and chemokine receptors play critical roles in the development of allergic airway inflammation.

OBJECTIVE

Because polarized human T(H)2 cells express a functional CXCR3 chemokine receptor, we evaluated the effects of a selective CXCR3 inhibitor in a mouse model of allergic airway disease.

METHODS

Ovalbumin-specific CD8(+) T effector cells were generated from OT-1 mice in the presence of interleukin 2. The activity of a CXCR3 inhibitor was examined in vitro by monitoring Ca(2+) influx after receptor ligation. In vivo, the activity was assessed in sensitized and challenged mice by monitoring airway function, inflammatory parameters, including cellular infiltrates and cytokines in the bronchoalveolar lavage fluid.

RESULTS

Approximately 40% of CD8(+) T effector cells expressed the CXCR3 receptor. In vitro, CXCR3 antagonism reduced Ca(2+) influx after receptor engagement. In contrast, the CXCR3 antagonist had little to no effect on airway function or inflammatory parameters despite adequate exposure levels.

CONCLUSIONS

CXCR3 antagonism did not prevent allergen-induced airway hyperresponsiveness or airway inflammation in a mouse allergy model despite having activity in in vitro functional assays.

Genome-wide analysis reveals unique regulation of transcription of Th2-specific genes by GATA3

Differentiation of naive CD4 T cells into Th2 cells is accompanied by chromatin remodeling and increased expression of a set of Th2-specific genes, including those encoding Th2 cytokines. IL-4-mediated STAT6 activation induces high levels of transcription of GATA3, a master regulator of Th2 cell differentiation, and enforced expression of GATA3 induces Th2 cytokine expression. However, it remains unclear whether the expression of other Th2-specific genes is induced directly by GATA3. A genome-wide unbiased chromatin immunoprecipitation assay coupled with massive parallel sequencing analysis revealed that GATA3 bound to 1279 genes selectively in Th2 cells, and 101 genes in both Th1 and Th2 cells. Simultaneously, we identified 26 highly Th2-specific STAT6-dependent inducible genes by DNA microarray analysis-based three-step selection processes, and among them 17 genes showed GATA3 binding. We assessed dependency on GATA3 for the transcription of these 26 Th2-specific genes, and 10 genes showed increased transcription in a GATA3-dependent manner, whereas 16 genes showed no significant responses. The transcription of the 16 GATA3-nonresponding genes was clearly increased by the introduction of an active form of STAT6, STAT6VT. Therefore, although GATA3 has been recognized as a master regulator of Th2 cell differentiation, many Th2-specific genes are not regulated by GATA3 itself, but in collaboration with STAT6.

Dendritic cells and airway epithelial cells at the interface between innate and adaptive immune responses

Because they can recognize and sample inhaled allergens, dendritic cells (DC) have been shown to be responsible for the initiation and maintenance of adaptive Th2 responses in asthma. It is increasingly clear that DC functions are strongly influenced by a crosstalk with neighboring cells like epithelial cells. Whereas the epithelium was initially considered only as a barrier, it is now seen as a central player in controlling the function of lung DCs through release of innate cytokines-promoting Th2 responses. Clinically relevant allergens, as well as known environmental and genetic risk factors for allergy and asthma, often interfere directly or indirectly with the innate immune functions of airway epithelial cells and DC. A better understanding of these interactions might lead to a better prevention and ultimately to new treatments for asthma.

Targeting chemokine receptors in allergic disease

The directed migration of cells in response to chemical cues is known as chemoattraction, and plays a key role in the temporal and spatial positioning of cells in lower- and higher-order life forms. Key molecules in this process are the chemotactic cytokines, or chemokines, which, in humans, constitute a family of approx. 40 molecules. Chemokines exert their effects by binding to specific GPCRs (G-protein-coupled receptors) which are present on a wide variety of mature cells and their progenitors, notably leucocytes. The inappropriate or excessive generation of chemokines is a key component of the inflammatory response observed in several clinically important diseases, notably allergic diseases such as asthma. Consequently, much time and effort has been directed towards understanding which chemokine receptors and ligands are important in the allergic response with a view to therapeutic intervention. Such strategies can take several forms, although, as the superfamily of GPCRs has historically proved amenable to blockade by small molecules, the development of specific antagonists has been has been a major focus of several groups. In the present review, I detail the roles of chemokines and their receptors in allergic disease and also highlight current progress in the development of relevant chemokine receptor antagonists.

Mouse CCL8, a CCR8 agonist, promotes atopic dermatitis by recruiting IL-5+ T(H)2 cells

Mouse CCL8 is a CC chemokine of the monocyte chemoattractant protein (MCP) family whose biological activity and receptor usage have remained elusive. Here we show that CCL8 is highly expressed in the skin, where it serves as an agonist for the chemokine receptor CCR8 but not for CCR2. This distinguishes CCL8 from all other MCP chemokines. CCL8 responsiveness defined a population of highly differentiated, CCR8-expressing inflammatory T helper type 2 (T(H)2) cells enriched for interleukin (IL)-5. Ccr8- and Ccl8-deficient mice had markedly less eosinophilic inflammation than wild-type or Ccr4-deficient mice in a model of chronic atopic dermatitis. Adoptive transfer studies established CCR8 as a key regulator of T(H)2 cell recruitment into allergen-inflamed skin. In humans, CCR8 expression also defined an IL-5-enriched T(H)2 cell subset. The CCL8-CCR8 chemokine axis is therefore a crucial regulator of T(H)2 cell homing that drives IL-5-mediated chronic allergic inflammation.

Origin and functional specializations of DC subsets in the lung

Lung DC bridge innate and adaptive immunity, and depending on the context, induce Th1, Th2 or Th17 response, to optimally clear infections. Conversely, lung DC can also prevent overt and harmful immune responses to harmless inhaled antigens via induction of Treg cells or via induction of neutralizing mucosal IgA antibodies. Here, we propose that these functions are not the result of a single population of DC, and instead, subsets of DC perform specialized functions.

IL-2-controlled expression of multiple T cell trafficking genes and Th2 cytokines in the regulatory T cell-deficient scurfy mice: implication to multiorgan inflammation and control of skin and lung inflammation

Scurfy (Sf) mice bear a mutation in the Foxp3 transcription factor, lack regulatory T cells (Treg), develop multiorgan inflammation, and die prematurely. The major target organs affected are skin, lungs, and liver. “Sf mice lacking the Il2 gene (Sf.Il2–/–), despite being devoid of Treg, did not develop skin and lung inflammation, but the inflammation in liver remained [corrected]. Genome-wide microarray analysis revealed hundreds of genes that were differentially regulated among Sf, Sf.Il2(-/-), and B6 CD4(+) T cells, but the most significant changes were those encoding receptors for trafficking/chemotaxis/retention and cytokines. Our study suggests that IL-2 controls the skin and lung inflammation in Sf mice in an apparent "organ-specific" manner through two novel mechanisms: by regulating the expression of genes encoding a variety of receptors for T cell trafficking/chemotaxis/retention and by regulating Th2 cell expansion and cytokine production. Thus, IL-2 is potentially a master regulator for multiorgan inflammation and an underlying etiological factor for various diseases associated with skin and lung inflammation.

CX3CR1 is required for airway inflammation by promoting T helper cell survival and maintenance in inflamed lung

Allergic asthma is a T helper type 2 (T(H)2)-dominated disease of the lung. In people with asthma, a fraction of CD4(+) T cells express the CX3CL1 receptor, CX3CR1, and CX3CL1 expression is increased in airway smooth muscle, lung endothelium and epithelium upon allergen challenge. Here we found that untreated CX3CR1-deficient mice or wild-type (WT) mice treated with CX3CR1-blocking reagents show reduced lung disease upon allergen sensitization and challenge. Transfer of WT CD4(+) T cells into CX3CR1-deficient mice restored the cardinal features of asthma, and CX3CR1-blocking reagents prevented airway inflammation in CX3CR1-deficient recipients injected with WT T(H)2 cells. We found that CX3CR1 signaling promoted T(H)2 survival in the inflamed lungs, and injection of B cell leukemia/lymphoma-2 protein (BCl-2)-transduced CX3CR1-deficient T(H)2 cells into CX3CR1-deficient mice restored asthma. CX3CR1-induced survival was also observed for T(H)1 cells upon airway inflammation but not under homeostatic conditions or upon peripheral inflammation. Therefore, CX3CR1 and CX3CL1 may represent attractive therapeutic targets in asthma.

T(H)2 heterogeneity: Does function follow form?

T(H)2 immune responses are required for the 2 fundamental pathological processes characteristic of allergic disease: IgE-mediated hypersensitivity and eosinophilic inflammation. The 3 established T(H)2 cytokines, IL-4, IL-5, and IL-13, each play a nonredundant role in allergic disease pathology. The recent explosion of T(H) subpopulations combined with the wide availability of polychromatic cytokine staining has facilitated the discovery of T(H)2 lineage heterogeneity. In this article we review T(H)2 heterogeneity and ask the following question: At what point do these subpopulations graduate from in vitro curiosities to immunologically robust therapeutic targets? We propose criteria to establish a T-cell subset as a biologically relevant entity and address the evidence to support these T(H)2 subpopulations having a unique function or specific contribution to allergic pathology or host defense.

The role of dendritic and epithelial cells as master regulators of allergic airway inflammation

Lung dendritic cells bridge innate and adaptive immunity, integrating a variety of stimuli from allergens, microbial colonisation, environmental pollution, and innate immune cells into a signal for T lymphocytes of the adaptive immune system. Dendritic cells have a pivotal role in the activation of T helper (Th) 2 cells and allergic inflammation. Lung dendritic cells can also prevent harmful immune responses to innocuous inhaled antigens via induction of regulatory T cells or Th1 cells. In our Review, we discuss how understanding the biology of dendritic cells is crucial for understanding the interaction between allergens, the environment, and genetics, and focus on how dendritic cells conspire with airway epithelial cells and innate pro-Th2 cells to cause allergic sensitisation and asthma.

The transcription factor PU.1 is required for the development of IL-9-producing T cells and allergic inflammation

CD4⁺ T helper cells acquire effector phenotypes that promote specialized inflammatory responses. We show that the ETS family transcription factor, PU.1 was required for the development of an interleukin 9 (IL-9)-secreting subset of T_H cells. Decreasing PU.1 expression either by conditional deletion in murine T cells or siRNA in human T cells impaired IL-9 production, while ectopic PU.1 expression promoted IL-9 production. Mice with PU.1-deficient T cells developed normal T_H2 responses in vivo, but exhibited attenuated allergic pulmonary inflammation corresponding to decreased Il9 and chemokine expression in peripheral T cells and in lungs as compared to wild-type mice. Together, these data suggest a critical role for PU.1 in generating the T_H9 phenotype and in the development of allergic inflammation.

Expression of CCR8 is increased in asthma

Background

Chemokines and their receptors could play key roles in the recruitment of T cells to the asthmatic lung. CCR8 is preferentially expressed on T-helper type 2 cells, and is thought to play a role in the pathogenesis of human asthma.

Objective

Determine the expression of CCR8 on T cells in blood, bronchoalveolar lavage (BAL) and bronchial mucosa from asthmatics and normal subjects.

Methods

CCR8 expression in blood and BAL from asthma and normal subjects was studied using flow cytometry. CCR8 expression on IFN-γ⁺ and IL-4⁺/IL-13⁺ blood and BAL T cells was studied following stimulation with Phorbol–Myristate–Acetate and Calcium Ionophore. Paraffin-embedded bronchial biopsies were used to study CCR8 in bronchial epithelium.

Results

The percentage of CD3⁺ cells expressing CCR8 in the blood was higher in asthmatics (4.7±0.4%) compared with normal subjects (3.0±0.4%; P<0.01). There was an approximately sixfold enrichment of CCR8 on IL-4⁺/IL-13⁺ cells compared with IFN-γ⁺ T cells (P<0.001) in both asthmatic and normal subjects in both blood and BAL. Significantly more BAL T cells expressed CCR8 in asthmatic (8.6±0.8%) compared with normal subjects (3.9±0.7%) (P<0.01). In paired blood-BAL samples from asthmatics, significantly more CCR8+CD3⁺ T cells were present in BAL (9.0±0.9%) than in blood (5.6±0.9%; P<0.05). There were more CCR8-positive cells in bronchial biopsies from asthmatic (93±11 cells/mm²) compared with normal subjects (30±16 cells/mm²) (P<0.05). The ligand CCL1 was increased in the BAL of asthmatics compared with normal subjects (35±6 vs. 12.9±7 pg/mL; P<0.05).

Conclusion

There may be a role for CCR8 in the recruitment of T cells to the lung in asthmatics.

Cite this as: K. Mutalithas, C. Guillen, C. Raport, R. Kolbeck, D. Soler, C. E. Brightling, I. D. Pavord and A. J. Wardlaw, Clinical & Experimental Allergy, 2010 (40) 1175–1185.

Key advances in mechanisms of asthma, allergy, and immunology in 2009

The year 2009 was marked by rapid progress in understanding cellular and chemical mechanisms in the pathogenesis of asthma and other allergic disorders. Studies published in the Journal of Allergy and Clinical Immunology described advances in our knowledge of signaling molecules and pathways, cytokines, and activation and tolerance in asthma and murine models of this disease; food allergy; anaphylaxis and immediate hypersensitivity; mast cells and their disorders; atopic dermatitis; allergic conjunctivitis; nasal polyposis; and hypereosinophilic syndromes. Additional studies provided novel information about the induction and regulation of allergic inflammation and the genetic determinants of asthma and responsiveness to asthma therapy. Critical features of these studies and their potential effect on human atopic disorders are summarized here.