The CXCL10/CXCR3 Axis Mediates Human Lung Mast Cell Migration to Asthmatic Airway Smooth Muscle

The K+ channels K(Ca)3.1 and K(v)1.3 as novel targets for asthma therapy

Asthma affects 10% of the UK population and is an important cause of morbidity and mortality at all ages. Current treatments are either ineffective or carry unacceptable side effects for a number of patients; in consequence, development of new approaches to therapy are important. Ion channels are emerging as attractive therapeutic targets in a variety of non-excitable cells. Ion channels conducting K(+) modulate the activity of several structural and inflammatory cells which play important roles in the pathophysiology of asthma. Two channels of particular interest are the voltage-gated K(+) channel K(v)1.3 and the intermediate conductance Ca(2+)-activated K(+) channel K(Ca)3.1 (also known as IK(Ca)1 or SK4). K(v)1.3 is expressed in IFNgamma-producing T cells while K(Ca)3.1 is expressed in T cells, mast cells, macrophages, airway smooth muscle cells, fibroblasts and epithelial cells. Both channels play important roles in cell activation, migration, and proliferation through the regulation of membrane potential and calcium signalling. We hypothesize that K(Ca)3.1- and/or K(v)1.3-dependent cell processes are one of the common denominators in asthma pathophysiology. If true, these channels might serve as novel targets for the treatment of asthma. Emerging evidence lends support to this hypothesis. Further validation through the study of the role that these channels play in normal and asthmatic airway cell (patho)physiology and in vivo models will provide further justification for the assessment of small molecule blockers of K(v)1.3 and K(Ca)3.1 in the treatment of asthma.

Molecular regulation of mast cell development and maturation

Mast cells play a crucial role in the pathogenesis of allergic diseases. In recent years, tremendous progresses have been made in studies of mast cell origination, migration, proliferation, maturation and survival, and the cytokines regulating these activities. These advances have significantly improved our understandings to mast cell biology and to the molecular mechanisms of mast cells in the pathogenesis of allergic diseases.

Essential involvement of cross-talk between IFN-gamma and TNF-alpha in CXCL10 production in human THP-1 monocytes

Interferon (IFN)-gamma-induced protein 10 (IP-10/CXCL10), a CXC chemokine, has been documented in several inflammatory and autoimmune disorders including atopic dermatitis and bronchial asthma. Although CXCL10 could be induced by IFN-gamma depending on cell type, the mechanisms regulating CXCL10 production following treatment with combination of IFN-gamma and TNF-alpha have not been adequately elucidated in human monocytes. In this study, we showed that TNF-alpha had more potential than IFN-gamma to induce CXCL10 production in THP-1 monocytes. Furthermore, IFN-gamma synergistically enhanced the production of CXCL10 in parallel with the activation of NF-kappaB in TNF-alpha-stimulated THP-1 cells. Blockage of STAT1 or NF-kappaB suppressed CXCL10 production. JAKs inhibitors suppressed IFN-gamma plus TNF-alpha-induced production of CXCL10 in parallel with activation of STAT1 and NF-kappaB, while ERK inhibitor suppressed production of CXCL10 as well as activation of NF-kappaB, but not that of STAT1. IFN-gamma-induced phosphorylation of JAK1 and JAK2, whereas TNF-alpha induced phosphorylation of ERK1/2. Interestingly, IFN-gamma alone had no effect on phosphorylation and degradation of IkappaB-alpha, whereas it significantly promoted TNF-alpha-induced phosphorylation and degradation of IkappaB-alpha. These results suggest that TNF-alpha induces CXCL10 production by activating NF-kappaB through ERK and that IFN-gamma induces CXCL10 production by increasing the activation of STAT1 through JAKs pathways. Of note, TNF-alpha-induced NF-kappaB may be the primary pathway contributing to CXCL10 production in THP-1 cells. IFN-gamma potentiates TNF-alpha-induced CXCL10 production in THP-1 cells by increasing the activation of STAT1 and NF-kappaB through JAK1 and JAK2.

Mast cell-dependent contraction of human airway smooth muscle cell-containing collagen gels: influence of cytokines, matrix metalloproteases, and serine proteases

In asthma, mast cells infiltrate the airway smooth muscle cell layer and secrete proinflammatory and profibrotic agents that contribute to airway remodeling. To study the effects of mast cell activation on smooth muscle cell-dependent matrix contraction, we developed coculture systems of human airway smooth muscle cells (HASM) with primary human mast cells derived from circulating progenitors or with the HMC-1 human mast cell line. Activation of primary human mast cells by IgE receptor cross-linking or activation of HMC-1 cells with C5a stimulated contraction of HASM-embedded collagen gels. Contractile activity could be transferred with conditioned medium from activated mast cells, implicating involvement of soluble factors. Cytokines and proteases are among the agents released by activated mast cells that may promote a contractile response. Both IL-13 and IL-6 enhanced contraction in this model and the activity of IL-13 was ablated under conditions leading to expression of the inhibitory receptor IL-13Ralpha2 on HASM. In addition to cytokines, matrix metalloproteinases (MMPs), and serine proteases induced matrix contraction. Inhibitor studies suggested that, although IL-13 could contribute to contraction driven by mast cell activation, MMPs were critical mediators of the response. Both MMP-1 and MMP-2 were strongly expressed in this system. Serine proteases also contributed to contraction induced by mast cell-activating agents and IL-13, most likely by mediating the proteolytic activation of MMPs. Hypercontractility is a hallmark of smooth muscle cells in the asthmatic lung. Our findings define novel mechanisms whereby mast cells may modulate HASM-driven contractile responses.

CD40 and OX40 ligand are differentially regulated on asthmatic airway smooth muscle

BACKGROUND

CD40 and OX40 Ligand (OX40L) are cell-surface molecules expressed on airway smooth muscle (ASM) that can enhance inflammatory cell activation and survival. The aim of this study was to examine the effect of tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) on ASM CD40 and OX40L expression.

METHODS

CD40 and OX40L expression on human ASM cells from asthmatic and nonasthmatic donors following stimulation with TNF-alpha and/or IFN-gamma was measured using cell-surface enzyme-linked immunosorbent assay (ELISA) and flow cytometry. Involvement of signalling pathway was investigated with pharmacological inhibitors. Soluble TNF receptor levels were quantified by ELISA.

RESULTS

Interferon-gamma and TNF-alpha synergistically increased CD40 expression to a greater extent on asthmatic than on nonasthmatic ASM. In contrast, IFN-gamma reduced TNF-alpha-induced OX40L expression to a similar extent in both cell types. TNF-alpha and IFN-gamma induced CD40 via nuclear factor-kappaB (NF-kappaB) and signal transducer and activator of transcription-3 in both cell types and modulated OX40L via NF-kappaB and c-Jun N terminal kinase in nonasthmatic cells. Similar effects on the induction of OX40L in asthmatic cells were seen with NF-kappaB, but these were not statistically significant. The reduced OX40L expression with TNF-alpha and IFN-gamma involved extracellular regulated kinase 1/2 activation.

CONCLUSION

Asthmatic ASM may modulate airway inflammation locally by increasing CD40 and OX40L expression in response to cytokines. IFN-gamma may regulate ASM pro-inflammatory actions by differentially modulating ASM CD40 and OX40L expression.

Dimethylfumarate inhibits NF-{kappa}B function at multiple levels to limit airway smooth muscle cell cytokine secretion

The antipsoriatic dimethylfumarate (DMF) has been anecdotically reported to reduce asthma symptoms and to improve quality of life of asthma patients. DMF decreases the expression of proinflammatory mediators by inhibiting the transcription factor NF-kappaB and might therefore be of interest for the therapy of inflammatory lung diseases. In this study, we determined the effect of DMF on platelet-derived growth factor (PDGF)-BB- and TNFalpha-induced asthma-relevant cytokines and NF-kappaB activation by primary human asthmatic and nonasthmatic airway smooth muscle cells (ASMC). Confluent nonasthmatic and asthmatic ASMC were incubated with DMF (0.1-100 microM) and/or dexamethasone (0.0001-0.1 microM), NF-kappaB p65 siRNA (100 nM), the NF-kappaB inhibitor helenalin (1 microM) before stimulation with PDGF-BB or TNFalpha (10 ng/ml). Cytokine release was measured by ELISA. NF-kappaB, mitogen and stress-activated kinase (MSK-1), and CREB activation was determined by immunoblotting and EMSA. TNFalpha-induced eotaxin, RANTES, and IL-6 as well as PDGF-BB-induced IL-6 expression was inhibited by DMF and by dexamethasone from asthmatic and nonasthmatic ASMC, but the combination of both drugs showed no glucocorticoid sparing effect in either of the two groups. NF-kappaB p65 siRNA and/or the NF-kappaB inhibitor helenalin reduced PDGF-BB- and TNFalpha-induced cytokine expression, suggesting the involvement of NF-kappaB signaling. DMF inhibited TNFalpha-induced NF-kappaB p65 phosphorylation, NF-kappaB nuclear entry, and NF-kappaB-DNA complex formation, whereas PDGF-BB appeared not to activate NF-kappaB within 60 min. Both stimuli induced the phosphorylation of MSK-1, NF-kappaB p65 at Ser276, and CREB, and all were inhibited by DMF. These data suggest that DMF downregulates cytokine secretion not only by inhibiting NF-kappaB but a wider range of NF-kappaB-linked signaling proteins, which may explain its potential beneficial effect in asthma.

Intrinsic asthma: is it intrinsic to the smooth muscle?

The traditional view of the pathophysiology of asthma is that its characteristic features are secondary to a major allergic or immunological dysfunction. However, this does not explain intrinsic asthma, which can occur in the absence of atopy. An alternative view is that an abnormality in the airway smooth muscle cell, which is capable of producing inflammatory, immunological and growth factors as well as molecules, which facilitate interaction with inflammatory cells, is the primary or instigating event. Evidence is rapidly accumulating that the smooth muscle is abnormal, in that it proliferates faster, produces more chemokines and cytokines as well as a different profile of extracellular matrix proteins than its non-asthmatic counterpart. These abnormalities may arise from altered calcium homoeostasis leading to increased mitochondrial biogenesis and/or decreases in the levels of key transcription factors such as CCAAT enhancer binding protein-alpha. Conditions under which smooth muscle is ablated, such as bronchial thermoplasty, may help us to understand more about the contribution of an airway smooth muscle dysfunction to asthma aetiology.

An imbalance in C/EBPs and increased mitochondrial activity in asthmatic airway smooth muscle cells: novel targets in asthma therapy?

The asthma prevalence was increasing over the past two decades worldwide. Allergic asthma, caused by inhaled allergens of different origin or by food, is mediated by inflammatory mechanisms. The action of non-allergic asthma, induced by cold air, humidity, temperature or exercise, is not well understood. Asthma affects up to 15% of the population and is treated with anti-inflammatory and muscle relaxing drugs which allow symptom control. Asthma was first defined as a malfunction of the airway smooth muscle, later as an imbalanced immune response of the lung. Recent studies placed the airway smooth muscle again into the focus. Here we summarize the molecular biological basis of the deregulated function of the human airway smooth muscle cell as a cause or important contributor to the pathology of asthma. In the asthmatic human airway smooth muscle cells, there is: (i) a deregulation of cell differentiation due to low levels of maturation-regulating transcription factors such as CCAAT/enhancer binding proteins and peroxisome proliferator-activated receptors, thereby reducing the cells threshold to proliferate and to secrete pro-inflammatory cytokines under certain conditions; (ii) a higher basal energy turnover that is due to increased number and activity of mitochondria; and (iii) a modified feedback mechanism between cells and the extracellular matrix they are embedded in. All these cellular pathologies are linked to each other and to the innate immune response of the lung, but the sequence of events is unclear and needs further investigation. However, these findings may present the basis for the development of novel curative asthma drugs.

Interleukin (IL)-10 inhibits RANTES-, tumour necrosis factor (TNF)- and nerve growth factor (NGF)-induced mast cell migratory response but is not a mast cell chemoattractant

Interleukin (IL)-10 is an important immunoregulatory cytokine with multiple biologic effects on different cell types. This cytokine also affects mast cell development, survival and activity. Mast cells are well known for their role in diverse pathophysiological processes including inflammatory events. Mast cell number in tissues is high and relatively constant. However, it is well established that these cells accumulate at the sites of inflammation in response to chemoattractants, e.g. RANTES, tumour necrosis factor (TNF) and nerve growth factor (NGF). In the present study, we examined whether IL-10 influenced RANTES-, TNF- and NGF-induced rat peritoneal mast cell migration. We also studied whether IL-10 could act as mast cell chemoattractant. We provided evidence, for the first time ever, that IL-10 influenced mature mast cell migration, i.e. it strongly decreased RANTES-induced mast cell migration and completely inhibited mast cell migratory response to TNF and NGF. The effective concentration of IL-10 that inhibited RANTES-, TNF- and NGF-induced mast cell migratory response was in the nanomolar range. The inhibitory effect of IL-10 on cytokine-stimulated mast cell migration was specific, as it was completely blocked by anti-IL-10R antibodies, and STAT3-dependent. In addition, our results have shown that IL-10 was not a mast cell chemoattractant. Thus, our findings clearly demonstrated that IL-10 may affect mast cell number within tissue by inhibiting local mast cell accumulation stimulated by chemotactic factors.

Fibrocyte localization to the airway smooth muscle is a feature of asthma

BACKGROUND

Airway smooth muscle (ASM) hyperplasia is a hallmark of asthma that is associated with disease severity and persistent airflow obstruction.

OBJECTIVES

We sought to investigate whether fibrocytes, a population of peripheral blood mesenchymal progenitors, are recruited to the ASM compartment in asthma.

METHODS

We assessed the number of fibrocytes in bronchial biopsy specimens and peripheral blood from subjects with mild-to-severe refractory asthma versus healthy control subjects. In vitro we investigated potential mechanisms controlling fibrocyte migration toward the ASM bundle.

RESULTS

Fifty-one subjects with asthma and 33 control subjects were studied. In bronchial biopsy specimens, the number of fibrocytes was increased in the lamina propria of subjects with severe refractory asthma (median [interquartile range] number, 1.9/mm(2) [1.7/mm(2)]) versus healthy control subjects (median [interquartile range] number, 0/mm(2) [0.3/mm(2)], P < .0001) and in the ASM bundle of subjects with asthma of all severities (subjects with severe asthma, median [interquartile range] number, 3.8/mm(2) [9.4/mm(2)]; subjects with mild-to-moderate asthma, median [interquartile range] number, 1.1/mm(2) [2.4/mm(2)]); healthy control subjects, (median [interquartile range] number, 0/mm(2) [0/mm(2)]); P = .0004). In the peripheral blood the fibrocyte number was also increased in subjects with severe refractory asthma (median [interquartile range] number, 1.4 x 10(4)/mL [2.6 x 10(4)/mL]) versus healthy control subjects (median [interquartile range] number, 0.4 x 10(4)/mL [1.0 x 10(4)/mL], P = .002). We identified that in vitro ASM promotes fibrocyte chemotaxis and chemokinesis (distance of migration after 4.5 hours, 31 microm [2.9 microm] vs 17 microm [2.4 microm], P = .0001), which was in part mediated by platelet-derived growth factor (mean inhibition by neutralizing antibody, 16% [95% CI, 2% to 32%], P = .03) but not by activation of chemokine receptors.

CONCLUSION

This study provides the first evidence that fibrocytes are present in the ASM compartment in asthma and that ASM can augment fibrocyte migration. The importance of fibrocytes in the development of ASM hyperplasia and airway dysfunction in asthma remains to be determined.

Dermatophagoides farinae extract induces severe atopic dermatitis in NC/Nga mice, which is effectively suppressed by the administration of tacrolimus ointment

Atopic dermatitis (AD) is a chronic inflammatory skin disease, which is accompanied by marked increases in the levels of inflammatory cells, including mast cells and eosinophils as well as T cells and macrophages. To investigate the expression pattern of chemokines in AD, a house dust mite, Dermatophagoides farinae extracts (DfE)-induced NC/Nga AD model was developed in mice, and this model was used to determine the expression levels of chemokines in atopic lesions using DNA microarrays and RT-PCR. When NC/Nga mice were repeatedly treated with DfE for 4 to 7 weeks on the back skin, the mRNA expression levels of CCL20/LARC, CCL24/eotaxin-2, CCL17/TARC, and CCL11/eotaxin-1 were markedly induced and lesser of CCL2/MCP-1, within the inflammatory lesion of the back skin. Immunohistochemical staining revealed the expression of these chemokines in the epidermis and dermis of DfE-treated NC/Nga mice. Interestingly, repeated application of tacrolimus ointment potently inhibited DfE-induced atopic dermatitis in NC/Nga mice concomitant with the inhibition of these changes in chemokine gene and protein expression levels particularly of CCL20/LARC, CCL17/TARC, and CCL11/eotaxin-1. These data indicate that severe atopic dermatitis induced by DfE accompanies elevated chemokine levels, and it was proposed that tacrolimus ointment is beneficial for the treatment of severe AD.

The cytokine network in asthma and chronic obstructive pulmonary disease

Asthma and chronic obstructive pulmonary disease (COPD) are very common inflammatory diseases of the airways. They both cause airway narrowing and are increasing in incidence throughout the world, imposing enormous burdens on health care. Cytokines play a key role in orchestrating the chronic inflammation and structural changes of the respiratory tract in both asthma and COPD and have become important targets for the development of new therapeutic strategies in these diseases.

Noncontractile functions of airway smooth muscle cells in asthma

Although pivotal in regulating bronchomotor tone in asthma, airway smooth muscle (ASM) also modulates airway inflammation and undergoes hypertrophy and hyperplasia, contributing to airway remodeling in asthma. ASM myocytes secrete or express a wide array of immunomodulatory mediators in response to extracellular stimuli, and in chronic severe asthma, increases in ASM mass may render the airway irreversibly obstructed. Although the mechanisms by which ASM secretes cytokines and chemokines are the same as those regulating immune cells, there exist unique ASM signaling pathways that may provide novel therapeutic targets. This review provides an overview of our current understanding of the proliferative as well as the synthetic properties of ASM.

Structural aspects of airway remodeling in asthma

Airway remodeling in asthma is a complex process that involves structural changes in virtually all tissues of the airway wall. The histologic changes to the airways consist of epithelial proliferation and goblet cell differentiation, subepithelial fibrosis, airway smooth muscle (ASM) growth, angiogenesis, matrix protein deposition, gland hyperplasia and hypertrophy, and nerve proliferation. Cytokines, chemokines, and growth factors from inflammatory cells and structural cells contribute to remodeling. There are complex interactions among the various signaling pathways involving matrix metalloproteinases that are required for growth factor release. The physiologic consequences of remodeling are airway hyperresponsiveness from ASM growth and mucus hypersecretion from gland and goblet cell hyperplasia. Airway stiffening is a probable contributor to airway hyperresponsiveness through attenuation of the transmission of potently bronchodilating cyclical stress to the ASM during breathing. The epidermal growth factor receptor's role in remodeling and its interaction with other potential causes of remodeling are discussed.

Actin reorganization is involved in vasoactive intestinal peptide induced human mast cells priming to fraktalkine-induced chemotaxis

We recently reported a novel neuro-immuno co-operation between vasoactive intestinal peptide (VIP) and fraktalkine (FKN) in recruiting human mast cells to the asthmatic airway that provided a classical example of priming effect on mast cells migratory function, but the role of the F-actin in human mast cell chemotaxis’ priming is poorly defined. Therefore the aim of this study was to further investigate the biophysical role of the cytoskeletal element; the F-actin, intracellular reorganization and its polymerization in mast cell priming of chemotaxis function. In the present communication it is shown by immunofluoresence confocal microscopy analysis that physical F-actin intracellular reorganization in a membrane bound manner on human mast cell is involved in VIP-induced priming of human mast cell chemotaxis against FKN. The F-actin reorganization was calcium independent and without modification of its contents as assessed by fluorescence-activated cell scanning analysis. These results identify a novel role for the biophysical association of F-actin in the crosstalk between neuro-inflammatory mediators and mast cells and may be an important target for therapeutic modalities in allergic inflammation.

Engagement of the EP2 prostanoid receptor closes the K+ channel KCa3.1 in human lung mast cells and attenuates their migration

Human lung mast cells (HLMC) express the Ca(2+)-activated K(+) channel K(Ca)3.1, which plays a crucial role in their migration to a variety of diverse chemotactic stimuli. K(Ca)3.1 activation is attenuated by the beta(2)-adrenoceptor and the adenosine A(2A) receptor through a G(s)-coupled mechanism independent of cyclic AMP. Prostaglandin E(2) promotes degranulation and migration of mouse bone marrow-derived mast cells through the G(i)-coupled EP(3) prostanoid receptor, and induces LTC(4) and cytokine secretion from human cord blood-derived mast cells. However, PGE(2) binding to the G(s)-coupled EP(2) receptor on HLMC inhibits their degranulation. We show that EP(2) receptor engagement closes K(Ca)3.1 in HLMC. The EP(2) receptor-specific agonist butaprost was more potent than PGE(2) in this respect, and the effects of both agonists were reversed by the EP(2) receptor antagonist AH6809. Butaprost markedly inhibited HLMC migration induced by chemokine-rich airway smooth muscle-conditioned media. Interestingly, PGE(2) alone was chemotactic for HLMC at high concentrations (1 microM), but was a more potent chemoattractant for HLMC following EP(2) receptor blockade. Therefore, the G(s)-coupled EP(2) receptor closes K(Ca)3.1 in HLMC and attenuates both chemokine- and PGE(2)-dependent HLMC migration. EP(2) receptor agonists with K(Ca)3.1 modulating function may be useful for the treatment of mast cell-mediated disease.

Activation of Toll-like receptors 2, 3, and 4 on human melanoma cells induces inflammatory factors

Toll-like receptors (TLR) have been shown to be expressed on various types of cancers; however, their functional activity is not known. We examined TLR profiles of human melanoma cells and showed that TLR2, TLR3, and TLR4 were found to be highly expressed. By PCR array analysis, specific stimulation of TLR2, TLR3, and TLR4 on melanoma cells showed significant activation of the adaptor protein MyD88, as well as downstream signal transduction factors nuclear factor-kappaB and inflammatory response-related factors. Specific ligand activation of TLR2, TLR3, and TLR4 was shown to induce cell migration. Peripheral blood lymphocytes and melanoma purified RNA was shown to activate TLR3 on melanoma cells. These studies show expression and functional activity of specific TLRs on melanoma cells and as potential therapeutic targets to control tumor progression.

Mast cells promote airway smooth muscle cell differentiation via autocrine up-regulation of TGF-beta 1

Asthma is a major cause of morbidity and mortality worldwide. It is characterized by airway dysfunction and inflammation. A key determinant of the asthma phenotype is infiltration of airway smooth muscle bundles by activated mast cells. We hypothesized that interactions between these cells promotes airway smooth muscle differentiation into a more contractile phenotype. In vitro coculture of human airway smooth muscle cells with beta-tryptase, or mast cells with or without IgE/anti-IgE activation, increased airway smooth muscle-derived TGF-beta1 secretion, alpha-smooth muscle actin expression and agonist-provoked contraction. This promotion to a more contractile phenotype was inhibited by both the serine protease inhibitor leupeptin and TGF-beta1 neutralization, suggesting that the observed airway smooth muscle differentiation was driven by the autocrine release of TGF-beta1 in response to activation by mast cell beta-tryptase. Importantly, in vivo we found that in bronchial mucosal biopsies from asthmatics the intensity of alpha-smooth muscle actin expression was strongly related to the number of mast cells within or adjacent to an airway smooth muscle bundle. These findings suggest that mast cell localization in the airway smooth muscle bundle promotes airway smooth muscle cell differentiation into a more contractile phenotype, thus contributing to the disordered airway physiology that characterizes asthma.

Signalling mechanisms regulating the activation of human eosinophils by mast-cell-derived chymase: implications for mast cell-eosinophil interaction in allergic inflammation

Allergic diseases such as asthma and allergic dermatitis are associated with the degranulation of mast cells. Chymase, a mast-cell-specific protease, is the major component in mast cell granules that can induce eosinophil infiltration into inflammatory sites. We examined the immunopathological mechanisms for the activation of eosinophils by chymase in allergic inflammation. Cytokines were measured by cytometric bead array Flex Sets multiplex assay using flow cytometry and enzyme-linked immunosorbent assay. Adhesion molecules, migration and intracellular signalling pathways were assessed by flow cytometry, Boyden chamber assay and Western blot, respectively. Chymase suppressed the apoptosis of eosinophils and induce the release of the cytokine interleukin-6 (IL-6) and chemokines CXCL8, CCL2 and CXCL1 by eosinophils dose-dependently. It also up-regulated the surface expression of adhesion molecule CD18 and stimulated the chemokinetic migration of eosinophils. The expressions of adhesion molecules, cytokines and chemokines, and chemokinetic migration were differentially regulated by the activation of extracellular signal-regulated kinase, p38 mitogen-activated protein kinase, Akt, Janus-activated kinase and nuclear factor-kappaB pathways. Chymase therefore plays a pivotal immunological role in the interaction between mast cells and eosinophils in allergic diseases such as allergic dermatitis by inducing adhesion molecule-mediated chemokinetic migration and inflammatory cytokines and chemokines of eosinophils, through multiple intracellular signalling molecules and transcription factor. Our results therefore provide a further biochemical basis for the pathogenesis of allergic inflammation consequent on the interaction between mast cells and eosinophils, and give insight for the development of new therapies.

Vitamin D and glucocorticoids differentially modulate chemokine expression in human airway smooth muscle cells

BACKGROUND AND PURPOSE

Chemokines play a critical role in the pathogenesis of asthma and facilitate the recruitment of inflammatory cells in the airways. Evidence now suggests that airway smooth muscle (ASM) may serve as a source of chemokines in inflamed airways. Although vitamin D has potent anti-inflammatory properties in vitro in some cell types, its effects on ASM cells remain unclear. Here, we investigated whether 1alpha, 25-dihydroxy vitamin D3 (calcitriol) modulated chemokine production in ASM.

EXPERIMENTAL APPROACH

Human ASM cell cultures were derived from tracheal samples taken during surgery. ASM cells were treated with tumour necrosis factor alpha (TNFalpha) and/or interferon gamma (IFNgamma) for 24 h in the presence of calcitriol and/or the glucocorticoid fluticasone added 2 h before. RANTES (regulated upon activation, normal T-cell expressed and secreted), interferon-inducible protein 10 (IP-10) and fractalkine (FKN) levels in cell supernatants were measured by ELISA.

KEY RESULTS

In TNFalpha-treated cells, calcitriol inhibited RANTES and IP-10 secretion in a concentration-dependent manner. FKN levels were negligible. In TNFalpha/IFNgamma-treated cells, whereas fluticasone or calcitriol alone partially inhibited RANTES secretion (by 38 and 20%, respectively), the combination of both drugs additively inhibited RANTES secretion (by 60%). No effect was observed on IP-10 secretion. Whereas fluticasone enhanced FKN secretion (by 50%), calcitriol significantly decreased FKN levels (by 50%). Interestingly, calcitriol blocked the stimulatory effect of fluticasone on FKN secretion, which was inhibited by 60% with the combination of calcitriol and fluticasone.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that vitamin D uniquely modulates human ASM expression of chemokines and may exert some beneficial effects in the treatment of steroid-resistant patients with asthma.

Targeting human mast cells expressing g-protein-coupled receptors in allergic diseases

The G-protein-coupled receptors (GPCRs) are the largest known group of integral membrane receptor proteins and are the most common targets of pharmacotherapy. Mast cells (MCs) have been reported to play an important role in allergic diseases, such as urticaria and bronchial asthma. There is an increasing body of clinical evidence that MCs are recruited into allergic reactions by non-IgE-dependent mechanisms. Human MCs are activated and secrete histamine in response to neuropeptides, such as substance P and somatostatin, mediated by a GPCR, MRGX2. The microenvironment surrounding MCs in their resident tissues is likely to contain multiple factors that modify antigen-dependent MC activation. MCs express various GPCRs, and since the function of human MCs is modulated by various GPCR ligands, such as adenosine and sphingosine-1-phosphate, which are present in high levels in the bronchial alveolar lavage fluid of asthmatic patients, the GPCRs expressed on MCs may play an important role in human allergic diseases. The GPCRs expressed on MCs may serve as drug targets for the treatment of allergic diseases.

The airway smooth muscle CCR3/CCL11 axis is inhibited by mast cells

BACKGROUND

Airway smooth muscle hyperplasia is a feature of asthma, and increases with disease severity. CCR3-mediated recruitment of airway smooth muscle progenitors towards the airway smooth muscle bundle has been proposed as one possible mechanism involved in airway smooth muscle hyperplasia. Mast cells are microlocalized to the airway smooth muscle bundle and whether mast cells influence CCR3-mediated migration is uncertain.

METHODS

We examined the expression of CCR3 by primary cultures of airway smooth muscle cells from asthmatics and nonasthmatics. CCR3 function was examined using intracellular calcium measurements, chemotaxis, wound healing, cell proliferation and survival assays. We investigated the recovery and function of both recombinant and airway smooth muscle-derived CCL11 (eotaxin) after co-culture with beta-tryptase and human lung mast cells.

RESULTS

Airway smooth muscle expressed CCR3. Airway smooth muscle CCR3 activation by CCL11 mediated intracellular calcium elevation, concentration-dependent migration and wound healing, but had no effect on proliferation or survival. Co-culture with beta-tryptase or mast cells degraded recombinant and airway smooth muscle-derived CCL11, and beta-tryptase inhibited CCL11-mediated airway smooth muscle migration.

CONCLUSIONS

CCL11 mediates airway smooth muscle migration. However co-culture with beta-tryptase or mast cells degraded recombinant and airway smooth muscle-derived CCL11 and inhibited CCL11-mediated airway smooth muscle migration. Therefore these findings cast doubt on the importance of the CCL11/CCR3 axis in the development of airway smooth muscle hyperplasia in asthma.

Human airway smooth muscle promotes human lung mast cell survival, proliferation, and constitutive activation: cooperative roles for CADM1, stem cell factor, and IL-6

The microlocalization of mast cells within specific tissue compartments is thought to be critical for the pathophysiology of many diverse diseases. This is particularly evident in asthma where they localize to the airway smooth muscle (ASM) bundles. Mast cells are recruited to the ASM by numerous chemoattractants and adhere through CADM1, but the functional consequences of this are unknown. In this study, we show that human ASM maintains human lung mast cell (HLMC) survival in vitro and induces rapid HLMC proliferation. This required cell-cell contact and occurred through a cooperative interaction between membrane-bound stem cell factor (SCF) expressed on ASM, soluble IL-6, and CADM1 expressed on HLMC. There was a physical interaction in HLMC between CADM1 and the SCF receptor (CD117), suggesting that CADM1-dependent adhesion facilitates the interaction of membrane-bound SCF with its receptor. HLMC-ASM coculture also enhanced constitutive HLMC degranulation, revealing a novel smooth muscle-driven allergen-independent mechanism of chronic mast cell activation. Targeting these interactions in asthma might offer a new strategy for the treatment of this common disease.

Asthma: eosinophil disease, mast cell disease, or both?

Although there is much circumstantial evidence implicating eosinophils as major orchestrators in the pathophysiology of asthma, recent studies have cast doubt on their importance. Not only does anti-interleukin-5 treatment not alter the course of the disease, but some patients with asthma do not have eosinophils in their airways, whereas patients with eosinophilic bronchitis exhibit a florid tissue eosinophilia but do not have asthma. In contrast, mast cells are found in all airways and localize specifically to key tissue structures such as the submucosal glands and airway smooth muscle within asthmatic bronchi, irrespective of disease severity or phenotype. Here they are activated and interact exclusively with these structural cells via adhesive pathways and through the release of soluble mediators acting across the distance of only a few microns. The location of mast cells within the airway smooth muscle bundles seems particularly important for the development and propagation of asthma, perhaps occurring in response to, and then serving to aggravate, an underlying abnormality in asthmatic airway smooth muscle function. Targeting this mast cell-airway smooth muscle interaction in asthma offers exciting prospects for the treatment of this common disease.

Regulation of inflammation by airway smooth muscle

Inflammatory mediators play a critical role in the pathogenesis of chronic airway diseases and facilitate the recruitment, activation, and trafficking of inflammatory cells in the airways. Compelling evidence now shows that airway smooth muscle expresses adhesion molecules and secretes inflammatory mediators. Airway myocytes also express a repertoire of immunomodulatory proteins such as Toll-like receptors, chemokines, and cytokines. The underlying mechanisms by which these molecules modulate airway inflammation and the physiological consequences of these molecules are now being elucidated, suggesting that airway smooth muscle plays an important role in orchestrating and perpetuating airway inflammation, remodeling, and fibrosis in chronic airway diseases.

Mast cell and monocyte recruitment by S100A12 and its hinge domain

S100A12 is expressed at sites of acute, chronic, and allergic inflammation. S100 proteins have regions of high sequence homology, but the "hinge" region between the conserved calcium binding domains is structurally and functionally divergent. Because the murine S100A8 hinge domain (mS100A8(42-55)) is a monocyte chemoattractant whereas the human sequence (hS100A8(43-56)) is inactive, we postulated that common hydrophobic amino acids within the S100A12 hinge sequence may be functional. The hinge domain, S100A12(38-53), was chemotactic for human monocytes and murine mast cells in vitro. S100A12(38-53) provoked an acute inflammatory response similar to that elicited by S100A12 in vivo and caused edema and leukocyte and mast cell recruitment. Circular dichroism studies showed that S100A12(38-53) had increased helical structure in hydrophobic environments. Mutations in S100A12(38-53) produced using an alanine scan confirmed that specific hydrophobic residues (I44A, I47A, and I53A) on the same face of the helix were critical for monocyte chemotaxis in vitro and generation of edema in vivo. In a hydrophobic environment such as the cell membrane, these critical residues would likely align on one face of an alpha-helix to facilitate receptor interaction. Interaction is unlikely to occur via the receptor for advanced glycation end products but, rather, via a G-protein-coupled mechanism.

Tumor necrosis factor (TNF) is a potent rat mast cell chemoattractant

It is well known that mast cell number increases in local tissues under different pathophysiologic conditions, although the humoral factors that stimulate local mast cell accumulation within tissues are not yet well known. Taking into account that tumor necrosis factor (TNF) influences tissue mast cell activity in various ways, the aim of the present study was to investigate the chemotactic activity of TNF for rat peritoneal mast cells. We have found that TNF induces mast cell migratory response in a dose-dependent manner, even in the absence of extracellular matrix (ECM) proteins. Significant migration was observed at concentrations of TNF as low as approximately 3 fM; higher TNF concentrations caused significant inhibition of spontaneous mast cell migration. In the presence of ECM proteins, TNF induced migration of mast cells in a biphasic manner, with peaks of migration occurring at approximately 0.3 fM and approximately 60 pM (in the presence of fibronectin) and at approximately 0.6 fM and approximately 600 pM (in the presence of laminin). Under the same experimental conditions, RANTES induced dose-dependent mast cell migration, and the optimal concentration of this chemokine for maximal migration was approximately 13 nM. The mast cell migratory response to lower concentrations of TNF was chemotactic and to higher TNF concentrations was due to chemokinesis. TNF-induced mast cell migration was completely blocked by neutralizing anti-TNF and anti-TNFR1 antibodies. The tyrosine kinase inhibitor, genistein, significantly abrogated mast cell migration toward TNF. Additionally, we have documented that TNF does not induce degranulation of rat mast cells. Taken together, our results indicate that TNF serves as an extremely potent chemotactic factor for rat mast cells that would cause accumulation of these cells at the site of diverse pathophysiologic conditions accompanied by inflammation.

T-helper 1-related chemokines in the exacerbation of childhood asthma

BACKGROUND

T-helper (Th) 2 cytokines are thought to mediate most of the allergic inflammatory responses associated with atopic asthma. But the Th1-related chemokine, interferon-inducible protein 10 (IP-10)/CXCL10, was the predominant chemokine measured during human allergic pulmonary late-phase reaction. The aim of the present study was to evaluate the role of Th1- and Th2- related chemokines in the pathogenesis of asthma exacerbation.

METHODS

Plasma levels of the Th2-related C-C chemokine I-309 (CCL1), the Th1-related CXC chemokines IP-10, and the monokine induced by interferon-gamma (Mig)/CXCL9 were measured in patients with stable asthma.

RESULTS

These results were compared to the results measured prior to, and after corticosteroid treatment, in patients who experienced asthma exacerbations. A significant increase in the plasma levels of IP-10 and Mig, but not I-309, were found in patients with an acute exacerbation in contrast to patients with stable asthma. Plasma levels of IP-10 and Mig were significantly higher in patients during an acute asthma exacerbation than during a subsequent convalescent period.

CONCLUSIONS

The Th1-related CXC chemokines IP-10 and Mig may be useful inflammatory markers of asthma exacerbation in children.

Tyrosine sulfation is prevalent in human chemokine receptors important in lung disease

Post-translational sulfation of tyrosines affects the affinity and binding of at least some chemokine receptors to their ligand(s) and has been hypothesized to be a feature in all chemokine receptors. This binding initiates downstream signaling cascades. By this mechanism, tyrosine sulfation can influence the cells involved in acute and chronic events of cellular immunity. These events include leukocyte trafficking and airway inflammation important in asthma and chronic obstructive pulmonary disease (COPD). We are using computational methods to convert the poorly defined hypothesis of more widespread sulfation of chemokine receptors to more specific assessments of how closely the sequence environment of each tyrosine residue resembles the sequence environment of tyrosine residues proven to be sulfated. Thus, we provide specific and readily tested hypotheses about the tyrosine residues in all of the chemokine receptors. Tyrosine sulfation was predicted with high scores in the N-terminus domain of 13 out of 18 human chemokine receptor proteins using a position-specific scoring matrix, which was determined to be 94.2% accurate based on Receiver Operating Characteristic analysis. The remaining chemokine receptors have sites exhibiting features of tyrosine sulfation. These putative sites demonstrate clustering in a manner consistent with known tyrosine sulfation sites and conservation both within the chemokine receptor family and across mammalian species. Human chemokine receptors important in asthma and COPD, such as CXCR1, CXCR2, CXCR3, CXCR4, CCR1, CCR2, CCR3, CCR4, CCR5, and CCR8, contain at least one known or predicted tyrosine sulfation site. Recognition that tyrosine sulfation is found in most clinically relevant chemokine receptors could help the development of specific receptor-ligand antagonists to modulate events important in airway diseases.

IgE alone promotes human lung mast cell survival through the autocrine production of IL-6

Background

Mast cells play a key role in asthma and recent evidence indicates that their ongoing activation in this disease is mediated, in part, via IgE in the absence of antigen. In this study we have examined whether IgE alone enhances human lung mast cell (HLMC) survival.

Methods

Purified HLMC were cultured for 4 weeks and survival assays then performed over 10 days following cytokine withdrawal in the presence or absence of human myeloma IgE. Quantitative real time RT-PCR was carried out to examine IL-6 mRNA expression and IL-6 protein was measured in HLMC supernatants by ELISA.

Results

IgE alone promoted the survival of HLMC in a dose-dependent manner following cytokine withdrawal. IgE-induced survival was eliminated with the addition of neutralising anti-IL-6 antibody but not by the addition of neutralising anti-stem cell factor. IgE sensitisation initiated profound upregulation of IL-6 mRNA in HLMC, and IL-6 concentrations were also raised in the culture supernatants of IgE-exposed cells.

Conclusion

These data taken together suggest that IgE in the absence of antigen promotes HLMC survival through the autocrine production of IL-6. This provides a further mechanism through which IL-6 and IgE contribute to the pathogenesis of asthma, and through which anti-IgE therapy might achieve its therapeutic effect.

Is airway smooth muscle the "missing link" modulating airway inflammation in asthma?

Airway smooth muscle (ASM) plays a central role in regulating bronchomotor tone in patients with asthma. New evidence, however, suggests that ASM may also orchestrate and perpetuate airway inflammation by promoting the recruitment, activation, and trafficking of inflammatory cells in the airways. This review addresses the immunomodulatory function of ASM and highlights how such function may have therapeutic implications in the management of asthma.

The mast cell and allergic diseases: role in pathogenesis and implications for therapy

Mast cells have long been recognized for their role in the genesis of allergic inflammation; and more recently for their participation in innate and acquired immune responses. Mast cells reside within tissues including the skin and mucosal membranes, which interface with the external environment; as well as being found within vascularized tissues next to nerves, blood vessels and glandular structures. Mast cells have the capability of reacting both within minutes and over hours to specific stimuli, with local and systemic effects. Mast cells express the high affinity IgE receptor (FcepsilonRI) and upon aggregation of FcepsilonRI by allergen-specific IgE, mast cells release and generate biologically active preformed and newly synthesized mediators which are involved in many aspects of allergic inflammation. While mast cells have been well documented to be essential for acute allergic reactions, more recently the importance of mast cells in reacting through pattern recognition receptors in innate immune responses has become recognized. Moreover, as our molecular understanding of the mast cell has evolved, novel targets for modulation have been identified with promising therapeutic potential.

IFN-gamma-induced protein 10 is a novel biomarker of rhinovirus-induced asthma exacerbations

BACKGROUND

Rhinovirus-induced acute asthma is the most frequent trigger for asthma exacerbations.

OBJECTIVE

We assessed which inflammatory mediators were released from bronchial epithelial cells (BECs) after infection with rhinovirus and then determined whether they were also present in subjects with acute virus-induced asthma, with the aim to identify a biomarker or biomarkers for acute virus-induced asthma.

METHODS

BECs were obtained from bronchial brushings of steroid-naive asthmatic subjects and healthy nonatopic control subjects. Cells were infected with rhinovirus 16. Inflammatory mediators were measured by means of flow cytometry with a cytometric bead array. Subjects with acute asthma and virus infection were recruited; they were characterized clinically by using lung function tests and had blood taken to measure the inflammatory mediators identified as important by the BEC experiments.

RESULTS

IFN-gamma-induced protein 10 (IP-10) and RANTES were released in the greatest quantities, followed by IL-6, IL-8, and TNF-alpha. Dexamethasone treatment of BECs only partially suppressed IP-10 and TNF-alpha but was more effective at suppressing RANTES, IL-6, and IL-8. In acute clinical asthma serum IP-10 levels were increased to a greater extent in those with acute virus-induced asthma (median of 604 pg/mL compared with 167 pg/mL in those with non-virus-induced acute asthma, P < .01). Increased serum IP-10 levels were predictive of virus-induced asthma (odds ratio, 44.3 [95% CI, 3.9-100.3]). Increased serum IP-10 levels were strongly associated with more severe airflow obstruction (r = -0.8; P < .01).

CONCLUSIONS

IP-10 release is specific to acute virus-induced asthma.

CLINICAL IMPLICATIONS

Measurement of serum IP-10 could be used to predict a viral trigger to acute asthma.

Role of mast cells in airway remodeling

The extent of airway remodeling correlates with severity of asthma. Persistent airway hyperresponsiveness (AHR) is associated with airway remodeling, but not with inflammation. The increase in ASM mass is recognized as one of the most important factors related to AHR and to the severity of asthma. The infiltration of ASM by mast cells (MCs) is associated with the disordered airway function. The mediators such as tryptase and cytokines from MCs can modulate ASM cell function and induce goblet cell hyperplasia. MCs were found to contribute to the development of multiple features of chronic asthma in MC-deficient mice. Therefore, MCs play an important role not only in immediate hypersensitivity and late phase inflammation but also in tissue remodeling in the airway.

Vascular remodeling is a feature of asthma and nonasthmatic eosinophilic bronchitis

RATIONALE

Increased vascularity and expression of vascular endothelial growth factor (VEGF) are recognized features of the asthmatic airway. The association of vascular remodeling with airway hyperresponsiveness (AHR) is unclear.

OBJECTIVE

To assess vascular remodeling and sputum VEGF concentration in subjects with asthma, subjects with nonasthmatic eosinophilic bronchitis (EB), and healthy controls.

METHODS

In cohort 1, 19 patients with asthma (Global Initiative for Asthma [GINA] 1-2, n = 9; GINA 3-5, n = 10), 10 patients with EB, and 11 healthy matched controls were recruited. Expression of the endothelial marker EN4 was assessed in bronchial biopsy samples. Vessels were counted using the validated mean Chalkley count by a blind observer. For cohort 2, a second independent cohort of 31 patients with asthma (GINA 1-2, n = 11; GINA 3-5, n = 20), 14 patients with EB, and 15 matched controls was recruited. Induced sputum supernatant VEGF was measured by ELISA.

RESULTS

The mean chalkley count was significantly greater in GINA 3-5 asthma (5.2 [0.4]) and EB (4.8 [0.3]) compared with controls (3.5 [0.5]) and demonstrated a significant inverse correlation with the postbronchodilator FEV(1)% predicted in patients with asthma (R(2) = 0.28; P = .02). Sputum VEGF concentration was also increased in GINA 3-5 asthma (2365 [1361-4110] pg/g) and EB (4699 [2818-7834] pg/g) compared with controls (1094 [676-1774] pg/g) and was inversely related to postbronchodilator FEV(1)% predicted in asthma (R(2) = 0.2; P = .01).

CONCLUSION

Vascular remodeling is a feature of asthma, and EB and is inversely associated with the postbronchodilator FEV(1) in asthma, suggesting that vascular remodeling is associated with airflow obstruction but not AHR.

CLINICAL IMPLICATIONS

Vascular remodeling is dissociated from AHR in asthma and associated with airflow limitation.

Adenosine closes the K+ channel KCa3.1 in human lung mast cells and inhibits their migration via the adenosine A2A receptor

Human lung mast cells (HLMC) express the Ca2+-activated K+ channel KCa3.1, which opens following IgE-dependent activation. This hyperpolarises the cell membrane and potentiates both Ca2+ influx and degranulation. In addition, blockade of KCa3.1 profoundly inhibits HLMC migration to a variety of diverse chemotactic stimuli. KCa3.1 activation is attenuated by the beta2adrenoceptor through a Galphas-coupled mechanism independent of cyclic AMP. Adenosine is an important mediator that both attenuates and enhances HLMC mediator release through the Galphas-coupled A2A and A2B adenosine receptors, respectively. We show that at concentrations that inhibit HLMC degranulation (10(-5)-10(-3) M), adenosine closes KCa3.1 both dose-dependently and reversibly. KCa3.1 suppression by adenosine was reversed partially by the selective adenosine A2A receptor antagonist ZM241385 but not by the A2B receptor antagonist MRS1754, and the effects of adenosine were mimicked by the selective A2A receptor agonist CGS21680. Adenosine also opened a depolarising current carried by non-selective cations. As predicted from the role of KCa3.1 in HLMC migration, adenosine abolished HLMC chemotaxis to asthmatic airway smooth muscle-conditioned medium. In summary, the Galphas-coupled adenosine A2A receptor closes KCa3.1, providing a clearly defined mechanism by which adenosine inhibits HLMC migration and degranulation. A2A receptor agonists with channel-modulating function may be useful for the treatment of mast cell-mediated disease.

Differential regulation of chemokine expression by Th1 and Th2 cytokines and mechanisms of eotaxin/CCL-11 expression in human airway smooth muscle cells

BACKGROUND

Airway smooth muscle (ASM) cells may contribute to the pathogenesis of asthma including airway inflammation and remodeling. We focused our study on the regulation of chemokine expression by cytokines and analyzed the mechanisms of eotaxin/CCL-11 expression in ASM cells.

METHODS

Human ASM cells were cultured in vitro and treated with IL-4, interferon-gamma (IFNgamma), and tumor necrosis factor-alpha (TNFalpha). Secretion of chemokines into the culture medium was analyzed by ELISA. Expression of eotaxin mRNA was analyzed by reverse transcription-polymerase chain reaction (RT-PCR). Binding of transcription factor signal transducer activator of transcription (STAT) 6 to the eotaxin promoter-derived DNA was analyzed by pull-down Western blot. To assess transcriptional regulation of eotaxin, cells were transfected with eotaxin promoter-luciferase reporter plasmids, and activity was determined by dual luciferase assay.

RESULTS

The Th2 cytokine IL-4 preferentially stimulated the expression of the CC chemokine receptor (CCR) 3-ligand chemokines eotaxin, eotaxin-3, and MCP-4. The Th1 cytokine IFNgamma stimulated the expression of chemokines IP-10 and RANTES. IL-4 stimulated nuclear translocation of signal transducer activator of transcription 6 (STAT6) and its binding to the eotaxin promoter region. IL-4 activated the eotaxin promoter and its activity was inhibited by mutation of the binding site for STAT6 in the promoter.

CONCLUSIONS

The Th2 cytokine IL-4 preferentially stimulated the expression of CCR3 ligand chemokines including eotaxin in ASM cells. The transcription factor STAT6 may play a pivotal role in the activation of eotaxin transcription in response to IL-4.

Chemokines and their receptors as potential targets for the treatment of asthma

Asthma is a chronic and sometimes fatal disease, which affects people of all ages throughout the world. Important hallmarks of asthma are airway inflammation and remodelling, with associated bronchial hyperresponsiveness and variable airflow obstruction. These features are orchestrated by cells of both the innate (eosinophils, neutrophils and mast cells) and the adaptive (T(H)2 T cells) immune system, in concert with structural airway cells. Chemokines are important for the recruitment of both immune and structural cells to the lung, and also for their microlocalisation within the lung tissue. Specific blockade of the responses elicited by chemokines and chemokine receptors responsible for the pathological migration of airway cells could therefore be of great therapeutic interest for the treatment of asthma.

Inflammation of bronchial smooth muscle in allergic asthma

BACKGROUND

Recent observations in asthma suggest that bronchial smooth muscle is infiltrated by inflammatory cells including mast cells. Such an infiltration may contribute to airway remodelling that is partly due to an increase in smooth muscle mass. Whether muscle increase is the result of smooth muscle cell hypertrophy remains controversial and has not been studied by ultrastructural analysis. A morphometric analysis of airway smooth muscle (ASM) was undertaken in asthmatic patients using electron microscopy to examine the interactions between ASM cells and inflammatory cells.

METHODS

ASM specimens were obtained from 14 asthmatic subjects and nine non-asthmatic controls undergoing fibreoptic endoscopy. Inflammatory cell counts were assessed by immunohistochemistry, and ultrastructural parameters were measured using electron microscopy in a blinded fashion on smooth muscle cells and inflammatory cells.

RESULTS

ASM from asthmatic patients was infiltrated by an increased number of mast cells and lymphocytes. Smooth muscle cells and their basal lamina were thicker in asthmatic patients (9.5 (0.8) and 1.4 (0.2) microm) than in controls (6.7 (0.4) and 0.7 (0.1) microm). In asthmatics the extracellular matrix was frequently organised in large amounts between ASM cells. Myofibroblasts within smooth muscle bundles were only observed in asthmatics, some of them displaying a close contact with ASM cells.

CONCLUSION

In asthma, airway myositis is characterised by a direct interaction between ASM cells and mast cells and lymphocytes. Smooth muscle remodelling was present, including cell hypertrophy and abnormal extracellular matrix deposition moulding ASM cells.

Translational mini-review series on Toll-like receptors: networks regulated by Toll-like receptors mediate innate and adaptive immunity

The Toll-like receptor (TLR) family provide key components of mammalian immunity and are part of the earliest surveillance mechanisms responding to infection. Their activation triggers the innate immune response, and is crucial to the successful induction of Th1/Th2-phenotyped adaptive immunity. Innate immunity was long considered to be non-specific and somewhat simple compared to adaptive immunity, mediated via the engulfment and lysis of microbial pathogens by phagocytic cells such as macrophages and neutrophils, and involving no complex protein-protein interactions. The emergence of the TLR field has contributed to a revision of our understanding, and innate immunity is now viewed as a highly complex process, in line with adaptive immunity. This review will give a brief overview of our current knowledge of TLR biology, and will focus on TLRs as key components in complex networks that activate, integrate and select the appropriate innate and adaptive immune responses in the face of immunological danger.

New and emerging roles for mast cells in host defence

Mast cells are highly effective sentinel cells, found close to blood vessels and especially common sites of potential infection, such as the skin, airways and gastrointestinal tract. Mast cells participate actively in the innate immune responses to many pathogens through a broad spectrum of mediators that can be selectively generated. They also have a role as innate effector cells in enhancing the earliest processes in the development of acquired immune responses. Studies of bacterial and parasitic models have revealed mast cell dependent regulation of effector cell recruitment, mucosal barrier function and lymph node hypertrophy. An important role for mast cells in viral infection is also implied by several in vivo and in vitro studies. There are multiple direct and indirect pathways by which mast cells can be selectively activated by pathogens including Toll-like receptors, co-receptors and complement component receptors. Understanding the mechanisms and scope of the contribution of mast cells to host defence will be crucial to regulating their activity therapeutically.

Lymphocyte-independent connective tissue mast cells populate murine synovium

OBJECTIVE

Mast cells (MCs) are a heterogeneous population of tissue-resident bone marrow-derived cells; distinct MC subpopulations are situated at specific microanatomic locations. The phenotype of the murine synovial MC remains undefined. Since MCs have been implicated in the pathogenesis of inflammatory arthritis, we sought to define the phenotype of the murine synovial MC population in normal and arthritic joints. We also examined the contribution of lymphocytes to synovial MC physiology.

METHODS

The MC phenotype in healthy and K/BxN serum transfer-induced arthritic synovial tissue was defined using immunohistochemical staining of prototypic MC-specific proteases (murine MC proteases [mMCP] 1, 2, 4, 5, 6, and 7) (chymases and tryptases). MC numbers and density were determined by histomorphometry in healthy and arthritic synovia. The lymphocyte contribution to MC populations was assessed using RAG-null mice.

RESULTS

We found that synovial MCs display a connective tissue mast cell (CTMC) phenotype in both normal and arthritic synovial tissue, which expresses mMCP-4, -5, -6, and -7, but not mMCP-1 or mMCP-2. In addition, MC hyperplasia was seen in the arthritic synovium. In RAG-null mice, the phenotype and degree of MC hyperplasia were identical to those observed in normal mice with and without arthritis. Furthermore, in contrast to skin CTMCs, all synovial MCs expressed mMCP-6, demonstrating discrete differences between synovial CTMCs and other anatomic CTMC populations.

CONCLUSION

Our findings demonstrate that the murine synovial MC population is composed of lymphocyte-independent CTMCs and identify arthritic synovium as a model system by which to gain insight into the poorly understood physiology of CTMCs in chronic inflammation.

New targets for modifying mast cell activation in asthma

Mast cells play a central role in innate immunity and in orchestrating the asthmatic response. Current medication relies on beta-agonists to relieve bronchoconstriction and steroids to reduce inflammation. However, recently drugs such as leukotriene-receptor antagonists and anti-immunoglobulin E have come on to the market. In this paper, a number of potential targets for modifying mast cell activation in asthma are reviewed. Some are already under study, including clinical trials (eg, tryptase inhibitors); others are more speculative (eg, inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity). In each case, where data are available, the action of the agents on human lung mast cells is described.

Cooperative molecular and cellular networks regulate Toll-like receptor-dependent inflammatory responses

Viral and bacterial pathogens cause inflammation via Toll-like receptor (TLR) signaling. We have shown that effective responses to LPS may depend on cooperative interactions between TLR-expressing leukocytes and TLR-negative tissue cells. The aim of this work was to determine the roles of such networks in response to agonists of TLRs associated with antiviral and autoimmune responses. The TLR3 agonist poly(I:C) activated epithelial cells, primary endothelial cells, and two types of primary human smooth muscle cells (airway [ASMC] and vascular) directly, while the TLR7/8 agonist R848 required the presence of leukocytes to activate ASMC. In keeping with these data, ASMC expressed TLR3 but not TLR7 or TLR8. Activation of ASMC by poly(I:C) induced a specific cytokine repertoire characterized by induction of CXCL10 generation and the potential to recruit mast cells. We subsequently explored the ability of TLR agonists to cooperate in the induction of inflammation. Dual stimulation with LPS and poly(I:C) caused enhanced cytokine generation from epithelial and smooth muscle cells when in the presence of leukocytes. Thus, inflammatory responses to pathogens are regulated by networks in which patterns of TLR expression and colocalization of tissue cells and leukocytes are critical.

Leukocyte navigation mechanisms as targets in airway diseases

Respiratory diseases, including asthma and chronic obstructive pulmonary disease, are among the most significant diseases in terms of their disabling effects and healthcare burden. A characteristic feature of almost all respiratory diseases is the accumulation and activation of inflammatory leukocytes in the lung or airway. Recent advances in the understanding of the molecules and intracellular signalling events controlling these processes are now translating to new therapeutic entities. In this article, the process of leukocyte accumulation is summarized, together with the preclinical and clinical evidence supporting the utility of the individual components of this process as targets for disease therapy.

Chemokine concentrations and mast cell chemotactic activity in BAL fluid in patients with eosinophilic bronchitis and asthma, and in normal control subjects

BACKGROUND

Asthma and eosinophilic bronchitis share many immunopathologic features including increased numbers of eosinophils and mast cells in the superficial airway. The mast cell chemotactic activity of airway secretions has not been assessed in patients with eosinophilic bronchitis.

OBJECTIVES

To investigate the concentration of chemokines in bronchial wash samples and BAL fluid, and the mast cell chemotactic activity in BAL fluid from subjects with asthma and eosinophilic bronchitis, and from healthy control subjects.

METHODS

We measured the concentrations of CCL11, CXCL8, and CXCL10 in bronchial wash samples and BAL fluid from 14 subjects with eosinophilic bronchitis, 14 subjects with asthma, and 15 healthy control subjects. Mast cell chemotaxis to BAL fluid from these subjects was examined using the human mast cell line HMC-1.

RESULTS

The bronchial wash sample and BAL fluid concentrations of CXCL10 and CXCL8 was increased in subjects with eosinophilic bronchitis compared to those in subjects with asthma and healthy control subjects (p < 0.05). The CCL11 concentration was below the limit of detection in most subjects. BAL fluid from subjects with eosinophilic bronchitis was chemotactic for mast cells (1.4-fold migration compared to a control, 95% confidence interval, 1.1 to 1.9; p = 0.04) and was inhibited by blocking CXCR1 (45% inhibition; p = 0.002), CXCR3 (38% inhibition; p = 0.034), or both (65% inhibition; p = 0.01). BAL fluid from the subjects with asthma and healthy control subjects was not chemotactic for mast cells. Mast cell migration to BAL fluid was correlated with the concentration of CXCL8 (r = 0.42; p = 0.031) and CXCL10 (r = 0.52; p = 0.007).

CONCLUSION

In subjects with eosinophilic bronchitis, CXCL8 and CXCL10 concentrations were elevated in airway secretions. These chemokines may play a key role in mast cell recruitment to the superficial airway in this condition.