The C-C chemokine receptors CCR4 and CCR8 identify airway T cells of allergen-challenged atopic asthmatics

Asthma: future directions

Asthma continues to be a significant health care problem, as reflected by the increasing rise in disease morbidity and mortality. Because steroids are relatively safe, clinically effective, and easy to administer, they remain the gold standard of treatment. After many decades of use, however, it is apparent that inhaled corticosteroids have failed to halt the progression of the asthma epidemic. Newer, more effective drugs are being developed to combat this disease, and the interest in developing new medications to treat allergic disease and asthma has increased exponentially. The financial burden of asthma has also been a significant motivating factor in the development of new medications. It is estimated that in 1998 the total cost of asthma on society was $11 billion [175]. This consideration has further intensified the quest to develop more effective asthma medications. Table 1 reviews the wide array of drugs currently being investigated. With the development and approval of novel asthma treatments, millions of asthma sufferers will undoubtedly have increased therapeutic options for control of their disease in the near future.

Induction of macrophage-derived chemokine/CCL22 expression in experimental autoimmune encephalomyelitis and cultured microglia: implications for disease regulation

Macrophage-derived chemokine (MDC/CCL22) and its receptor CCR4 have been implicated in chronic inflammatory processes and in the homing of monocytes, Th2 cells and regulatory T-cell subsets. Here, we demonstrate that MDC and CCR4 mRNAs are expressed in the central nervous system (CNS) of mice developing relapsing-remitting and chronic-relapsing forms of experimental autoimmune encephalomyelitis (EAE). By immunohistochemistry, we show that MDC is produced by CNS-infiltrating leukocytes and intraparenchymal microglia, whereas CCR4 is expressed on some invading leukocytes. Upon in vitro activation, mouse microglia express MDC transcripts and secrete bioactive MDC that induces chemotaxis of Th2, but not Th1 cells. We suggest that MDC produced by microglia could regulate Th1-mediated CNS inflammation by facilitating the homing of Th2 and, possibly, regulatory T cells into the lesion site.

Plasma concentration of thymus and activation-regulated chemokine is elevated in childhood asthma

BACKGROUND

Thymus and activation-regulated chemokine (TARC) is responsible for the trafficking of T(H)2 lymphocytes into sites of allergic inflammation. Serum TARC levels correlate with the severity of atopic dermatitis. The relationship between this marker and the occurrence and severity of asthma has not been evaluated.

OBJECTIVE

We tested whether plasma TARC level is a useful marker for asthma and atopy in children.

METHODS

Plasma total IgE levels were measured by means of microparticle immunoassay, and specific IgE levels to common aeroallergens were measured by using a fluorescent enzyme immunoassay. We used a sandwich enzyme immunoassay to measure plasma TARC concentrations.

RESULTS

Sixty asthmatic children and 28 age- and sex-matched control subjects were recruited, with mean logarithmic plasma total IgE levels of 2.66 +/- 0.60 kIU/L and 1.74 +/- 0.58 kIU/L, respectively (P <.0001). The median plasma TARC concentration was higher in asthmatic patients without inhaled corticosteroid treatment (131.0 pg/mL) compared with those seen in steroid-treated patients (97.5 pg/mL) and control subjects (76.0 pg/mL; P =.01 and P <.0001, respectively). Plasma TARC concentration was found to correlate with total IgE level in plasma (r = 0.219, P =.04). This marker was also increased in subjects who were sensitized to cat allergen (P =.001) but not in subjects sensitized to other aeroallergens. Disease severity score, FEV(1) value, and atopy were not associated with increased plasma TARC levels.

CONCLUSION

Our results suggest that plasma TARC concentrations are elevated in childhood asthma. This marker is also linked to plasma total IgE levels and cat allergen sensitization.

Chemokine receptor antagonism as an approach to anti-inflammatory therapy: 'just right' or plain wrong?

Inflammation plays a pivotal role in exacerbating a wide array of human diseases. The chemokines are a group of proteins that control the movement and activation of the immune cells involved in all aspects of the inflammatory response. Recently, their cognate receptors have attracted considerable interest as therapeutic targets, in part because they are G-protein-coupled receptors, which have been antagonized successfully before by the pharmaceutical industry. Indeed, several companies have now reported the development of selective small-molecule chemokine receptor antagonists, and some of these compounds have even entered human Phase I clinical trials. Preclinical studies of the responsiveness of murine models of inflammation to either pharmacologic or genetic intervention have suggested that antagonism of some chemokine receptors may well prove to be a safe and efficacious approach to anti-inflammatory therapy.

New asthma targets: recent clinical and preclinical advances

Current asthma therapy is directed at the relief of chronic inflammation or improving lung function through bronchodilation. These approaches treat the overt symptoms of asthma but do not approach underlying causes of the disease. Such therapies have limited efficacy and for a number of patients the disease remains poorly controlled. The short-term future of asthma therapy will probably focus on the treatment of multiple symptoms to provide improved lung function. Long-term approaches to asthma will have to focus on modulation of the mechanisms that are the underlying causes of the various asthmatic pathophysiologies. These targets include a number of TH2-type T-cell-generated cytokines and chemokines, G-protein-coupled receptors, TH2-related transcription factors, neurotrophins and adhesion molecules. Additional new targets and understanding of asthma may also arise from genetic analysis.

Cutting edge: Th2 cell trafficking into the allergic lung is dependent on chemoattractant receptor signaling

Th2 cells are recruited to the lung where they mediate the asthma phenotype. Since the molecular mechanisms regulating Th2 cell trafficking remain unknown, we sought to determine whether trafficking of Th2 cells into the lung is mediated by G alpha i-coupled chemoattractant receptors. We show here that in contrast to untreated Th2 cells, pertussis toxin-treated Th2 cells were unable to traffic into the lung, airways, or lymph nodes following Ag challenge and therefore were unable to induce allergic inflammation in vivo. Pertussis toxin-treated Th2 cells were functional cells, however, and when directly instilled into the airways of mice, bypassing their need to traffic to the lung, were able to induce airway eosinophilic inflammation. These studies conclusively demonstrate that trafficking of Th2 cells into the lung is an active process dependent on chemoattractant receptors.

Eosinophil recruitment in type-2 hypersensitivity pulmonary granulomas: source and contribution of monocyte chemotactic protein-3 (CCL7)

Monocyte chemotactic protein-3 (MCP-3/CCL7) has potent eosinophil chemoattractant properties. The present study determined its relative contribution to the formation of Th2 cytokine-mediated (type-2) eosinophil-rich interstitial lung granulomas induced by antigens of Schistosoma mansoni eggs. Both MCP-3 transcripts and protein levels were more strongly expressed in lungs with type-2 than with type-1 (mycobacterial antigen-elicited Th1-mediated) granulomas. In vivo treatment with neutralizing antibodies demonstrated that MCP-3 abrogated eosinophil accumulation in type-2 lesions by 40 to 50%. Immunohistochemical staining revealed that MCP-3 localized to vessels in or near granulomas suggesting that endothelial cells were an important in situ source of MCP-3. Maximal MCP-3 transcript expression was abrogated by anti-interleukin-4 treatment. Furthermore, cultured mouse lung endothelial cells displayed augmented MCP-3 production in response to interleukin-4. Together, these results suggest that MCP-3 contributes to a significant component of eosinophil recruitment in the type-2 interstitial granuloma formation and Th2 cytokines promote its production.

Chemokine responses in schistosomal antigen-elicited granuloma formation

Host immune systems have evolved specialized responses to multicellular parasites. This is well represented by the type 2 granulomatous response to Schistosoma mansoni egg antigens, which is an eosinophil-rich inflammatory response mediated by Th2-associated cytokines. Using Ag-bead models of pulmonary granuloma formation in mice, we defined characteristic chemokine (CK) profiles in the granulomatous lungs. Our findings point to a role for C-C chemokine receptor-2 (CCR2) and CCR3 agonists such as monocyte chemotactic proteins (MCPs) 1/CCL2, 3/CCL7 and 5/CCL12 as important participants that are subject to regulation by Th2 cytokines interleukin (IL)-4 and IL-13. CCR4 and CCR8 agonists are also likely contributors. Analysis of CK receptor knockout mice revealed that CCR2 ligands (e.g. MCP-1 and 5) promoted early phase granuloma macrophage accumulation, whereas anti-MCP-3 (CCL7) antibody treatment abrogated eosinophil recruitment. CCR8 knockout mice also demonstrated impaired eosinophil recruitment but this appeared to be related to impaired Th2 cell function. Transcript analysis of CD4+ T cells generated during schistosome granuloma formation failed to show biased CCR8 expression but, having a more limited receptor repertoire, these cells were likely more dependent on CCR8 ligands. Together, these studies indicate an intricate involvement of chemokines in various stages and aspects of schistosomal egg Ag-elicited granuloma formation.

Increased expression of the chemokine receptor CXCR3 and its ligand CXCL10 in peripheral airways of smokers with chronic obstructive pulmonary disease

CXCR3 is a chemokine receptor preferentially expressed on lymphocytes, particularly on type-1 T-lymphocytes. Smokers who develop chronic obstructive pulmonary disease (COPD) have a chronic bronchopulmonary inflammation that is characterized by an increased infiltration of T-lymphocytes, particularly CD8(+), in the airways and lung parenchyma. To investigate the expression of CXCR3 and its ligand interferon-induced protein 10/CXCL10 in COPD, we counted the number of CXCR3(+) cells and analyzed the expression of CXCL10 in the peripheral airways of 19 patients undergoing lung resection for localized pulmonary lesions. We examined lung specimens from seven smokers with fixed airflow limitation (COPD), five smokers with normal lung function, and seven nonsmoking subjects with normal lung function. The number of CXCR3(+) cells was immunohistochemically quantified in the epithelium, in the submucosa, and in the adventitia of peripheral airways. The number of CXCR3(+) cells in the epithelium and submucosa was increased in smokers with COPD as compared with nonsmoking subjects, but not as compared with smokers with normal lung function. Immunoreactivity for the CXCR3-ligand CXCL10 was present in the bronchiolar epithelium of smokers with COPD but not in the bronchiolar epithelium of smoking and nonsmoking control subjects. Most CXCR3(+) cells coexpressed CD8 and produced interferon gamma. These findings suggest that the CXCR3/CXCL10 axis may be involved in the T cell recruitment that occurs in peripheral airways of smokers with COPD and that these T cells may have a type-1 profile.

Cytokines and chemoattractants in allergic inflammation

It is now generally accepted type 2 T helper (Th2) cytokines and some chemoattractants play an essential role in the pathogenesis of the allergic inflammation. The effects of Th2 cytokines, such as interleukin (IL)-4, IL-5, IL-9, and IL-13, account for virtually all the pathophysiological manifestations of allergy and asthma. Moreover, both Th2 cells and the effector cells usually present in the areas of allergic inflammation (basophils, mast cells, and eosinophils) express chemoattractant receptors, such as CCR3, CCR4, CCR8 and CRTH2. Therefore, interactions of eotaxin(s), eotaxin/CCL11, RANTES/CCL5, and MCP-1/CCL2, MCP-2/CCL8, MCP-3/CCL7, MCP-4/CCL13 with CCR3 are responsible for the recruitment of basophils, eosinophils and mast cells, whereas interactions of CCR4 with MDC/CCL22 or TARC/CCL17, CCR8 with I-309/CCL1, and CRTH2 with prostaglandin D(2) play a critical role in the allergen-induced recruitment of Th2 cells in the target tissues of allergic inflammation. The demonstration that Th2-polarized responses against allergens represent the triggering event for the development of allergic diseases, together with the recognition that some chemoattractants are responsible for the recruitment of both Th2 cells and other effector cells of allergic inflammation, can provide the conceptual basis for the development of new therapeutic strategies in allergic conditions.

Elevated levels of thymus- and activation-regulated chemokine in bronchoalveolar lavage fluid from patients with eosinophilic pneumonia

Thymus- and activation-regulated chemokine (TARC/CCL17) is a lymphocyte-directed CC chemokine, which plays a role in the recruitment of CC chemokine receptor-4 positive T helper 2 (Th2) cells. In this study, we measured concentrations of TARC and Th2 cell-derived cytokines in bronchoalveolar lavage (BAL) fluid, as well as TARC concentrations in serum from patients with eosinophilic pneumonia and other interstitial lung diseases. TARC was significantly elevated in BAL fluids from patients with eosinophilic pneumonia (median, 240 pg/ml), whereas TARC was undetectable (< 7 pg/ml) in most cases of hypersensitivity pneumonitis, sarcoidosis, and idiopathic pulmonary fibrosis, as well as in healthy control subjects. Also, when present, quantities were less than 20 pg/ml. Elevated concentrations of interleukin (IL)-4, IL-5, and IL-13 were also detected in BAL fluid from patients with eosinophilic pneumonia. Interestingly, TARC concentrations in BAL fluids were closely correlated with the concentrations of IL-5 and IL-13. A serial examination showed that elevated TARC in BAL fluid rapidly fell to below detectable limits preceding decreases in IL-5 concentration and eosinophil percentage. Our results, in concordance with previous studies, demonstrate the potential activity of TARC for recruiting Th2 cells to the lungs and suggest a significant role for TARC in the pathogenesis of eosinophilic pneumonia.

The identification, characterization, and distribution of guinea pig CCR4 and epitope mapping of a blocking antibody

Th2 lymphocytes play a central role in the control and maintenance of allergic inflammation. The chemokine receptor CCR4 is preferentially expressed on the surface of Th2 lymphocytes polarised in vitro. However, CCR4 is found on the surface of a significant proportion of circulating memory T lymphocytes, some of which are capable of producing the Th1-associated cytokine interferon gamma. To investigate the function of CCR4 on guinea pig (gp) T lymphocytes, we identified the open-reading frame of gpCCR4, which encodes a 361-amino acid protein with 88 and 81% amino acid identity to human and murine CCR4 sequences, respectively. Cells transfected with gpCCR4 migrated toward the human and murine orthologues of the CCR4 ligands, macrophage-derived chemokine and thymus and activation-regulated chemokine. Surface expression of CCR4, using an anti-human CCR4 monoclonal antibody, 10E4, was detected on approximately 12% of guinea pig peripheral blood T helper cells, and CCR4(+) guinea pig thymocytes were detected in low numbers. However, CCR4(+) T helper cells constituted approximately 9% of the T lymphocyte population within the normal guinea pig lung and 52% of the guinea pig bronchoalveolar lavage fluid, which is consistent with a role for CCR4 in T lymphocyte development and trafficking through normal tissues. Subsequent analysis of chimeric chemokine receptors indicated that 10E4, a functional inhibitor of gpCCR4 responses, recognized the amino terminus of CCR4.

Inflammatory mediators in uveitis: differential induction of cytokines and chemokines in Th1- versus Th2-mediated ocular inflammation

Ocular inflammation leads to vision loss through the destruction and scarring of delicate tissues along the visual axis. To identify inflammatory mediators involved in this process, we used real time RT-PCR to quantify the expression of mRNA transcripts of 34 cytokines, 26 chemokines, and 14 chemokine receptors at certain time points during T cell-mediated ocular inflammation. We induced disease by adoptive transfer of Ag-specific Th1 or Th2 cells into recipients expressing the target Ag in their eyes. We also compared the mediator expression patterns seen in adoptive transfer-induced inflammation with that seen in mouse eyes developing experimental autoimmune uveoretinitis. In addition, we used laser capture microdissection to examine chemokine mRNA production by both retinal pigment epithelium cells and infiltrating leukocytes in inflamed eyes. Major findings included the following: 1) Three patterns of expression of the inflammation-related molecules were seen in recipients of adoptively transferred Th cells: preferential expression in Th1 recipients, or in Th2 recipients, or similar expression in both recipient groups. 2) In experimental autoimmune uveoretinitis, the inflammatory mediator expression pattern largely paralleled that seen in Th1-induced disease. 3) Both retinal pigment epithelium and infiltrating leukocytes expressed chemokine transcripts in distinct, but overlapping patterns in inflamed eyes. 4) Interestingly, transcripts of multiple cytokines, chemokines, and chemokine receptors were constitutively expressed in high levels in mouse eyes. Seven of these molecules have not been previously associated with the eye. These data underscore the multiplicity of mediators that participate in the pathogenesis of eye inflammation and point to upstream cytokines as potential therapeutic targets.

Chemokines, innate and adaptive immunity, and respiratory disease

Selective leukocyte trafficking and recruitment is primarily regulated by a specific family of small proteins called "chemokines". This extended family shepherds and guides leukocytes through their lives, facilitating their development, regulating their interactions with other leukocyte types, and guiding their recruitment to sites of inflammation. Through the actions of chemokines, allergen sensitization is regulated in atopic asthma, through the controlled migration of dendritic cells, T- and B-lymphocytes, mast cells and basophils. Subsequently, atopic inflammation is driven by chemokine-directed recruitment of eosinophils, basophils and lymphocytes. Diseases from cancer to chronic obstructive pulmonary disease to interstitial fibrosis are all potential targets for chemokine receptor antagonism. Innate immunity (the early pattern-recognition responses to stimuli such as lipopolysaccharide, viral proteins and bacterial DNA) needs to bridge the gap to specific immunity and antibody production and immunological memory. Again, chemokines are likely to be fundamental mediators of these responses. Chemokines are fundamental regulators of leukocyte homeostasis and inflammation, and their antagonism by small molecule chemokine receptor antagonists may be of enormous importance in the future treatment of human respiratory disease.

Infections

Infection, in particular by respiratory viruses, plays an important role in triggering exacerbations and has also been implicated in the etiology of asthma and chronic obstructive pulmonary disease (COPD). This chapter reviews the epidemiological evidence that implicates infectious pathogens as triggers. The chapter also discusses the mechanisms of interaction between the host-pathogen response and preexisting airway pathology resulting in an exacerbation. Much of the treatment of infective exacerbations for both asthma and COPD is symptomatic, consisting of bronchodilators or supportive in the form of oxygen, and in severe cases it includes noninvasive or invasive ventilatory measures. The current therapy for virus-induced exacerbations of asthma and COPD relies on increased treatment of preexisting disease. Antibiotics are indicated for bacterial infections. The effective use of antiviral agents, particularly for influenza viruses, requires viral diagnosis, commencement of treatment early in the course of an exacerbation, or the targeting of high-risk groups for prophylaxis. Alternative strategies for drug development involve the identification of key factors common to exacerbations induced by a range of different viruses. Increased knowledge of the host–virus interaction can help in designing treatments that can increase virus clearance and minimize immunopathology.

Emerging immune targets for the therapy of allergic asthma

Recent discoveries on the molecular and cellular basis of asthma have markedly altered our understanding of this common respiratory disorder. These insights have come during an unexplained period of rising disease incidence and severity and are now being applied to develop improved therapies. This review explores the latest advances in our understanding of the pathogenesis of allergic asthma, and provides insight into the expanding collaborations between research scientists, clinicians and the pharmaceutical industry in the race to control the asthma epidemic.

Antichemokine immunotherapy for allergic diseases

Chemokines have emerged as critical regulators of leukocyte function and as such represent attractive new targets for the therapy of allergic diseases. Recent studies have revealed important roles for the chemokine family in both the afferent and efferent limbs of the immune system, orchestrating and integrating innate and acquired immune responses. A subset of chemokines including eotaxin-1 (also called CCL11), eotaxin-2 (CCL24), eotaxin-3 (CCL26), MCP (monocyte chemoattractant protein)-3 (CCL7), MCP (monocyte chemoattractant protein)-4 (CCL13), TARC (thymus- and activation-regulated chemokine) (CCL17), and MDC (macrophage-derived chemokine) (CCL22) are highly expressed in allergic inflammation and are regulated by T helper type 2 cytokines. Receptors for these chemokines, including CCR3 (CC chemokine receptor 3), CCR4 (CC chemokine receptor 4) and CCR8 (CC chemokine receptor 8) are expressed on key leukocytes associated with allergic inflammation, such as T helper type 2 cells, eosinophils, mast cells and basophils, establishing a subset of chemokine/chemokine receptors potentially important in allergic inflammation. Recent data using inhibitory antibodies and chemokine antagonists support the concept that interfering with this subset of chemokines and their receptors represents a new approach to allergy immunotherapy.

Role of chemokines in the pathogenesis of asthma

The prevalence of asthma has risen drastically in the last two decades, with a worldwide impact on health care systems. Although several factors contribute to the development of asthma, inflammation seems to be a common factor that leads to the most severe asthmatic responses. In the past decade, researchers have characterized a large group of chemotactic cytokines, also known as chemokines, which are implicated in asthmatic inflammation. These chemokines control and direct the migration and activation of various leukocyte populations. Targeting chemokines should lead to new ways of controlling the inflammatory asthmatic response.