Neutrophil-dominated Airway Inflammation Research Articles

Chemoattractants and cytokines in primary ciliary dyskinesia and cystic fibrosis: key players in chronic respiratory diseases.

Patients with primary ciliary dyskinesia (PCD) and cystic fibrosis (CF), two inherited disorders, suffer from recurrent airway infections characterized by persistent bacterial colonization and uncontrollable inflammation. Although present in high counts, neutrophils fail to clear infection in the airways. High levels of C-X-C motif chemokine ligand 8/interleukin-8 (CXCL8/IL-8), the most potent chemokine to attract neutrophils to sites of infection, are detected in the sputum of both patient groups and might cause the high neutrophil influx in the airways. Furthermore, in CF, airway neutrophils are highly activated because of the genetic defect and the high levels of proinflammatory chemoattractants and cytokines (e.g., CXCL8/IL-8, tumor necrosis factor-α and IL-17). The overactive state of neutrophils leads to lung damage and fuels the vicious circle of infection, excessive inflammation and tissue damage. The inflammatory process in CF airways is well characterized, whereas the lung pathology in PCD is far less studied. The knowledge of CF lung pathology could be useful to guide molecular investigations of the inflammatory processes in PCD lungs. Current available therapies can not completely remedy the chronic airway infections in these diseases. This review gives an overview of the role that chemoattractants and cytokines play in these neutrophil-dominated lung pathologies. Finally, the most frequently applied treatments in CF and PCD and new experimental therapies to reduce neutrophil-dominated airway inflammation are described.

Bcl-2 inhibitors reduce steroid-insensitive airway inflammation

Asthmatic inflammation is dominated by accumulation of either eosinophils, neutrophils, or both in the airways. Disposal of these inflammatory cells is the key to disease control. Eosinophilic airway inflammation is responsive to corticosteroid treatment, whereas neutrophilic inflammation is resistant and increases the burden of global health care. Corticosteroid-resistant neutrophilic asthma remains mechanistically poorly understood and requires novel effective therapeutic strategies. We sought to explore the underlying mechanisms of airway inflammation persistence, as well as corticosteroid resistance, and to investigate a new strategy of effective treatment against corticosteroid-insensitive neutrophilic asthma. Mouse models of either eosinophil-dominated or neutrophil-dominated airway inflammation were used in this study to test corticosteroid sensitivity invivo and invitro. We also used vav-Bcl-2 transgenic mice to confirm the importance of granulocytes apoptosis in the clearance of airway inflammation. Finally, the Bcl-2 inhibitors ABT-737 or ABT-199 were tested for their therapeutic effects against eosinophilic or neutrophilic airway inflammation and airway hyperresponsiveness. Overexpression of Bcl-2 protein was found to be responsible for persistence of granulocytes in bronchoalveolar lavage fluid after allergic challenge. This was important because allergen-induced airway inflammation aggravated and persisted in vav-Bcl-2 transgenic mice, in which nucleated hematopoietic cells were overexpressed with Bcl-2 and resistant to apoptosis. The Bcl-2 inhibitors ABT-737 or ABT-199 play efficient roles in alleviation of either eosinophilic or corticosteroid-resistant neutrophilic airway inflammation by inducing apoptosis of immune cells, such as eosinophils, neutrophils, TH2 cells, TH17cells, and dendritic cells. Moreover, these inhibitors were found to be more efficient than steroids to induce granulocyte apoptosis exvivo from patients with severe asthma. Apoptosis of inflammatory cells is essential for clearance of allergen-induced airway inflammation. The Bcl-2 inhibitors ABT-737 or ABT-199 might be promising drugs for the treatment of airway inflammation, especially for corticosteroid-insensitive neutrophilic airway inflammation.

Astragalus polysaccharide modulates ER stress response in an OVA-LPS induced murine model of severe asthma

Endoplasmic reticulum (ER) stress has been recently revealed to play a pivotal role in the pathogenesis of severe asthma. Astragalus polysaccharide (APS), a major bioactive component from Astragalus membranaceus, exerts immunomodulatory and anti-inflammatory effects and has been shown to suppress ER stress in chronic diseases such as type-2 diabetes. However, the pharmaceutical application of APS in the treatment of severe asthma is unknown. The results obtained here indicate that APS significantly attenuates eosinophils and neutrophil-dominant airway inflammation by reducing the mRNA levels of Cxcl5, Il8, and chemokine (C-C motif) ligand 20 (Ccl20) and the protein levels of IL13RA and IL17RA. APS also inhibits the activation of unfolded protein response by decreasing the levels of ER stress markers such as C/EBP homologous protein (CHOP), which was associated with a reduction of PERK phosphorylation. Moreover, APS substantially blocks the nuclear translocation of ATF6 and NF-κB p65. Interestingly, we observed that APS markedly suppresses mucus hypersecretion by decreasing the levels of mucin (MUC) 5AC and MUC5B, which might be due to inhibition of goblet cells differentiation by suppressing the expression of IRE1β-correlated genes. In summary, APS can have potential pharmaceutical application in treatment of severe asthma.

Genetic Deletion and Pharmacological Inhibition of PI3K γ Reduces Neutrophilic Airway Inflammation and Lung Damage in Mice with Cystic Fibrosis-Like Lung Disease.

Purpose. Neutrophil-dominated airway inflammation is a key feature of progressive lung damage in cystic fibrosis (CF). Thus, reducing airway inflammation is a major goal to prevent lung damage in CF. However, current anti-inflammatory drugs have shown several limits. PI3Kγ plays a pivotal role in leukocyte recruitment and activation; in the present study we determined the effects of genetic deletion and pharmacologic inhibition of PI3Kγ on airway inflammation and structural lung damage in a mouse model of CF lung disease. Methods. βENaC overexpressing mice (βENaC-Tg) were backcrossed with PI3Kγ-deficient (PI3Kγ KO) mice. Tissue damage was assessed by histology and morphometry and inflammatory cell number was evaluated in bronchoalveolar lavage fluid (BALF). Furthermore, we assessed the effect of a specific PI3Kγ inhibitor (AS-605240) on inflammatory cell number in BALF. Results. Genetic deletion of PI3Kγ decreased neutrophil numbers in BALF of PI3Kγ KO/βENaC-Tg mice, and this was associated with reduced emphysematous changes. Treatment with the PI3Kγ inhibitor AS-605240 decreased the number of neutrophils in BALF of βENaC-Tg mice, reproducing the effect observed with genetic deletion of the enzyme. Conclusions. These results demonstrate the biological efficacy of both genetic deletion and pharmacological inhibition of PI3Kγ in reducing chronic neutrophilic inflammation in CF-like lung disease in vivo.

S100A8, S100A9 and S100A12 activate airway epithelial cells to produce MUC5AC via extracellular signal-regulated kinase and nuclear factor-κB pathways.

Airway mucus hyperproduction is a common feature of chronic airway diseases such as severe asthma, chronic obstructive pulmonary disease and cystic fibrosis, which are closely associated with neutrophilic airway inflammation. S100A8, S100A9 and S100A12 are highly abundant proteins released by neutrophils and have been identified as important biomarkers in many inflammatory diseases. Herein, we report a new role for S100A8, S100A9 and S100A12 for producing MUC5AC, a major mucin protein in the respiratory tract. All three S100 proteins induced MUC5AC mRNA and the protein in normal human bronchial epithelial cells as well as NCI-H292 lung carcinoma cells in a dose-dependent manner. A Toll-like receptor 4 (TLR4) inhibitor almost completely abolished MUC5AC expression by all three S100 proteins, while neutralization of the receptor for advanced glycation end-products (RAGE) inhibited only S100A12-mediated production of MUC5AC. The S100 protein-mediated production of MUC5AC was inhibited by the pharmacological agents that block prominent signalling molecules for MUC5AC expression, such as mitogen-activated protein kinases, nuclear factor-κB (NF-κB) and epidermal growth factor receptor. S100A8, S100A9 and S100A12 equally elicited both phosphorylation of extracellular signal-regulated kinase (ERK) and nuclear translocation of NF-κB/degradation of cytosolic IκB with similar kinetics through TLR4. In contrast, S100A12 preferentially activated the ERK pathway rather than the NF-κB pathway through RAGE. Collectively, these data reveal the capacity of these three S100 proteins to induce MUC5AC production in airway epithelial cells, suggesting that they all serve as key mediators linking neutrophil-dominant airway inflammation to mucin hyperproduction.

Characteristics of eosinophilic and non-eosinophilic asthma during treatment with inhaled corticosteroids

Objective: Eosinophilic inflammation in the respiratory tract is a hallmark of bronchial asthma. In naïve cases, the inflammatory profile is associated with disease severity and reactivity to inhaled corticosteroids (ICS). Sustained airway eosinophilia has been reported during ICS treatment. However, the immunological characteristics of these cases are not known and it is unclear if this situation contributes to asthma control. This study was performed to determine the answer of these questions. Methods: To compare phenotypes of eosinophilic and non-eosinophilic asthma (EA and NEA, respectively) under ICS treatment, clinical data were obtained from asthmatic subjects (n = 22) and healthy controls (n = 10), and the leukocyte compositions of induced sputum and peripheral blood were determined. T lymphocyte profiles in systemic blood were assessed by flow cytometry. Results: A higher frequency of emergency room visits was observed in the NEA group, which had a higher neutrophil count relative to the total inflammatory cell population in induced sputum than the EA group (59.5 versus 36.6%; p < 0.01). The fraction of helper T (Th)17 lymphocytes as well as the ratio of Th17 to regulatory T cells (Treg) in the peripheral blood was higher in the NEA than in the EA group (0.24 versus 0.13; p < 0.05). Conclusions: Th17 were more prevalent than Treg cells in the peripheral blood of NEA patients under ICS treatment, corresponding to neutrophil-dominant airway inflammation and a severe asthmatic phenotype. Thus, an imbalance in Th17/Treg may be associated with the pathogenesis of NEA in patients undergoing ICS treatment.

Low-intensity aerobic exercise training attenuates airway inflammation and remodeling in a rat model of steroid-resistant asthma

Background Aerobic exercise can improve symptoms, reduce airway inflammation, and even ameliorate airway remodeling in asthmatic animals and patients. However, previous studies have focused mainly on the effect of aerobic exercise on steroid-sensitive asthma (SSA). The goals of this study were to determine the effect of low-intensity aerobic exercise training on airway hyperresponsiveness, inflammation, and remodeling in a rat model of steroid-resistant asthma (SRA) and to identify the potential mechanisms underlying these effects. Methods Endotoxin-free ovalbumin with or without lipopolysaccharide were applied to establish rat models of SRA and SSA, respectively. Airway hyperresponsiveness, inflammation, remodeling, expression of interleukin (IL)-25, IL-33, thymic stromal lymphopoietin (TSLP), high mobility group box-1 (HMGB1), and IL-17 in bronchoalveolar lavage fluid (BALF), and the role of dexamethasone (DXM) were compared between these two asthmatic rat models. The effect of low-intensity aerobic exercise training and anti-HMGB1 treatment on airway hyperresponsiveness, inflammation, and remodeling in SRA rats also was evaluated. Results SRA rats developed neutrophil-dominated airway inflammation ((29.5±4.1)% of the total cell numbers in BALF), whereas SSA rats developed eosinophil-dominated airway inflammation ((24.0±6.1)% of the total cell numbers in BALF). Compared with SSA rats, SRA rats had more severe airway hyperresponsiveness, lower levels of IL-25 ((33.6±10.3) vs. (104.8±24.9) pg/ml), IL-33 ((87.5±25.0) vs. (226.6±40.7) pg/ml), and TSLP ((1 933.2±899.5) vs. (7 224.0±992.1) pg/ml), and higher levels of HMGB1 ((21.2±4.5) vs. (5.4±1.6) ng/ml) and IL-17 ((780.5±261.7) vs. (291.4±76.4) pg/ml) in BALF (all P &lt;0.05). However, there was no significant difference in goblet cell hyperplasia, subepithelial collagen thickness, and airway smooth muscle remodeling between the two groups. Compared with control SSA rats, airway hyperresponsiveness, inflammation, and remodeling in SRA rats were less sensitive to DXM treatment. Anti-HMGB1 treatment attenuated airway hyperresponsiveness, inflammation, and remodeling in SRA rats to a certain extent and was accompanied by lower levels of IL-17 ((369.2±126.7) vs. (780.5±261.7) pg/ml in control SRA rats) in BALF (P &lt;0.05). Low-intensity aerobic exercise training decreased the expression of both HMGB1 ((14.1±2.9) vs. (21.2±4.5) ng/ml in control SRA rats) and IL-17 ((545.3±148.6) vs. (780.5±261.7) pg/ml in control SRA rats) in BALF (all P &lt;0.05) and was accompanied by improved airway hyperresponsiveness, inflammation, and remodeling in SRA rats (all P &lt;0.05). Conclusions Low-intensity aerobic exercise training attenuated airway hyperresponsiveness, inflammation, and remodeling in a rat model of SRA. Decreased HMGB1 and IL-17 levels in BALF by aerobic exercise training at least partly contributed to the improvements of SRA.

Peroxisome proliferator-activated receptor-gamma expression in dendritic cells determines immune tolerance versus immune activation (HYP6P.256)

Abstract Dendritic cells (DCs) play a central role in regulating immune tolerance and activation but the molecular axis within DCs that dictates immune outcome is unknown. We investigated the role of Peroxisome proliferator-activated receptor-gamma (PPARγ) in DCs in establishment of immune tolerance in the airways using an experimental model. Using mice with selective deletion of PPARγ in CD11c+ cells (PPARγΔ) to ablate PPARγ expression in DCs, we show that DC-specific PPARγ expression exerts a dual role whose collective goal in response to inhaled antigen is to not only promote de novo Foxp3 expression in T cells but to actively dampen T effector cell development. We demonstrate that PPARγ plays a crucial role in enhancing aldh1a2 expression in lung CD103+ DCs under tolerogenic conditions and when tolerized PPARγΔ mice were antigen-challenged, a complete loss of immune tolerance with increased neutrophil-dominated airway inflammation was observed. Absence of PPARγ promoted the expression of multiple pro-inflammatory cytokines such as IL-6 and IL-23 in DCs, limited Foxp3 induction but augmented IL-17 production in T cells with significant increase in the frequency of dual Foxp3+RORγt+ CD4+ T cells in PPARγΔ mice. In summary, our study identifies PPARγ as a central regulator in DC-mediated programming of the Foxp3/RORγt balance in CD4+ T cells dictating tolerance versus inflammation upon antigen provocation.

Peroxisome proliferator-activated receptor-gamma in CD11c+ lung dendritic cells programs peripheral CD4+ T cells for Foxp3 induction during airway tolerance. (P6001)

Abstract Peroxisome proliferator-activated receptor-gamma (PPARγ) is a widely expressed molecular regulator with anti-inflammatory functions. However, whether it has an anti-inflammatory role in dendritic cells (DCs) that influence the Treg/Teffector balance has not been experimentally addressed. In this study, we investigated the role of PPARγ in DCs regulating the delicate balance between tolerance versus inflammation in the periphery using a model of airway induced tolerance by inhaled allergen. Using mice with selective deletion of PPARγ in CD11c+ cells, we observed that PPARγ expression in CD11chi lung DCs is essential for de novo Foxp3 expression in CD4+ T cells. We demonstrate that PPARγ plays a crucial role in enhancing aldh1a2 expression in lung CD103+ DCs under tolerogenic conditions with significantly less expression of the enzyme in these cells when mice are immunized for airway inflammation. When tolerized CD11ccre/+ PPARγfl/fl mice were antigen-challenged, a complete loss of immune tolerance with increased neutrophil-dominated airway inflammation was observed. Taken together, our study identifies PPARγ as a central regulator in DC-mediated programming of Foxp3 expression in naive CD4+ T cells dictating tolerance versus inflammation upon antigen provocation.

Mechanism of E-cadherin redistribution in bronchial airway epithelial cells in a TDI-induced asthma model

E-cadherin (epithelial cadherin), a transmembrane protein, provides essential architecture and immunological function to the airway epithelium, a barrier structure that plays an essential role in asthma pathogenesis. Toluene diisocyanate (TDI) is currently one of the leading causes of occupational asthma. However, relatively few studies have been undertaken to determine the biological effects of TDI on the barrier properties of airway epithelium, but it is known that TDI can damage airway epithelial tight junctions in vitro. Here, we hypothesize that TDI can injure E-cadherin both in normal and allergic-induced airway epithelium. To test this, we developed a murine model of TDI-induced asthma characterized by neutrophil-dominated airway inflammation, epithelial shedding, and obvious aberrant distribution of E-cadherin. Pretreatment with dexamethasone (DEX) significantly rescued the immunoreactivity of E-cadherin, accompanied by increased neutrophils in bronchoalveolar lavage fluid (BALF). In vitro, TDI-human serum albumin (HSA)-induced redistribution of E-cadherin was associated with extracellular signal-regulated kinase (ERK)1/2 activation. The inhibition of phospho-ERK (p-ERK)1/2 by DEX can partly reverse this reaction. These results indicate that E-cadherin redistribution may be an important contributor in the generation of TDI-induced asthma.

The Inhibitory Role of Hydrogen Sulfide in Airway Hyperresponsiveness and Inflammation in a Mouse Model of Asthma

Cystathionine γ-lyase (CSE) is one of the major enzymes producing hydrogen sulfide (H2S) in lungs, participating in the regulation of respiratory functions. The role of CSE-derived H2S in eosinophil-dominant inflammation in allergic diseases has been unclear. The objective of this study was to explore the protective role of H2S against allergen-induced airway hyperresponsiveness (AHR) and inflammation. CSE expression and H2S production rate were assessed in mouse lung tissues with ovalbumin (OVA)-induced acute asthma. AHR, airway inflammation, and Th2 response in wild-type (WT) mice were compared with those in CSE gene knockout (KO) mice. The effect of NaHS, an exogenous H2S donor, was also evaluated on these parameters. CSE expression was absent and H2S production rate was significantly lower in the lungs of CSE KO mice when compared with WT littermates. OVA challenge decreased lung CSE expression and H2S production in WT mice. CSE deficiency resulted in aggravated AHR, increased airway inflammation, and elevated levels of Th2 cytokines such as IL-5, IL-13, and eotaxin-1 in bronchoalveolar lavage fluid after OVA challenge. The aforementioned alterations were reversed by exogenous H2S treatment. More importantly, NaHS supplement rescued CSE KO mice from the aggravated pathological process of asthma. The CSE/H2S system plays a critical protective role in the development of asthma. A new therapeutic potential for asthma via targeting CSE/H2S metabolism is indicated.

DC‐derived TSLP promotes Th2 polarization in LPS‐primed allergic airway inflammation

Thymic stromal lymphopoietin (TSLP) plays important roles in the pathogenesis of allergic diseases. Whether and how TSLP is involved in the initial priming of T helper type-2 (Th2) differentiation against harmless antigen remains unclear. Using an intranasal sensitization protocol with OVA and LPS, we showed that TSLP signaling is required for low-dose LPS-induced Th2 inflammation, but not for high-dose LPS-induced Th1 immunity. We further demonstrated that low-dose LPS-activated bone marrow-derived dendritic cells expressed relatively high Tslp but low Il12a, and were able to prime naïve DO11.10 T cells to differentiate into Th2 cells in a TSLP-dependent manner. After transfer into wild-type recipient mice, the low-dose LPS-activated OVA-loaded dendritic cells (DCs) induced airway eosinophilia, but primed neutrophil-dominated airway inflammation when TSLP-deficient DCs were used. These studies demonstrate that TSLP released by DCs in response to a low concentration of LPS plays a role in priming Th2 differentiation and thus may serve as a polarizing third signal, in addition to antigen/MHC class II and co-stimulatory factors, from antigen-presenting DCs to direct effector T-cell differentiation.

Role of neutrophils in persistent airway obstruction due to refractory asthma

One of the clinical manifestations of refractory asthma (RA) in a certain group of patients is persistent airway obstruction (PAO), despite treatment with high doses of inhaled and/or systemic corticosteroids. Airway neutrophilic inflammation is frequently observed in RA; however, the relationship between neutrophilic inflammation and PAO has not been evaluated in this group of patients. The aim of this study was to compare the clinical parameters and patterns of inflammatory cells between patients with or without PAO due to RA, and to identify the factors associated with PAO. Seventy-seven patients with RA were recruited from a cohort of 2298 asthmatic patients. Sputum differential cell counts were performed at initial presentation. Clinical and physiological parameters were compared between patients with (n = 19) or without PAO (n = 58). The group with PAO had a longer duration of asthma and a higher frequency of near-fatal asthma than the non-PAO group, although higher doses of inhaled corticosteroids were used in the PAO group (P = 0.037). Neutrophilic inflammation was predominant in the group with PAO, whereas eosinophilic inflammation was predominant in the non-PAO group (P = 0.003). When both groups were stratified according to smoking status, the non-smoking PAO group had the longest duration of asthma, with early onset of asthma (P < 0.05). The non-smoking PAO group tended to have the highest percentage of sputum neutrophils. Irrespective of smoking status, the percentage of sputum eosinophils was significantly higher in the non-PAO group than in the PAO group. Patients with PAO due to RA show different clinical manifestations when compared with those without PAO and have neutrophil-dominant airway inflammation.

Inhibition of Toll-Like Receptor 2-Mediated Interleukin-8 Production in Cystic Fibrosis Airway Epithelial Cells via theα7-Nicotinic Acetylcholine Receptor

Cystic Fibrosis (CF) is an inherited disorder characterised by chronic inflammation of the airways. The lung manifestations of CF include colonization with Pseudomonas aeruginosa and Staphylococcus aureus leading to neutrophil-dominated airway inflammation and tissue damage. Inflammation in the CF lung is initiated by microbial components which activate the innate immune response via Toll-like receptors (TLRs), increasing airway epithelial cell production of proinflammatory mediators such as the neutrophil chemokine interleukin-8 (IL-8). Thus modulation of TLR function represents a therapeutic approach for CF. Nicotine is a naturally occurring plant alkaloid. Although it is negatively associated with cigarette smoking and cardiovascular damage, nicotine also has anti-inflammatory properties. Here we investigate the inhibitory capacity of nicotine against TLR2- and TLR4-induced IL-8 production by CFTE29o- airway epithelial cells, determine the role of α7-nAChR (nicotinic acetylcholine receptor) in these events, and provide data to support the potential use of safe nicotine analogues as anti-inflammatories for CF.

TLR-Induced Inflammation in Cystic Fibrosis and Non-Cystic Fibrosis Airway Epithelial Cells

Cystic fibrosis (CF) is a genetic disease characterized by severe neutrophil-dominated airway inflammation. An important cause of inflammation in CF is Pseudomonas aeruginosa infection. We have evaluated the importance of a number of P. aeruginosa components, namely lipopeptides, LPS, and unmethylated CpG DNA, as proinflammatory stimuli in CF by characterizing the expression and functional activity of their cognate receptors, TLR2/6 or TLR2/1, TLR4, and TLR9, respectively, in a human tracheal epithelial line, CFTE29o(-), which is homozygous for the DeltaF508 CF transmembrane conductance regulator mutation. We also characterized TLR expression and function in a non-CF airway epithelial cell line 16HBE14o(-). Using RT-PCR, we demonstrated TLR mRNA expression. TLR cell surface expression was assessed by fluorescence microscopy. Lipopeptides, LPS, and unmethylated CpG DNA induced IL-8 and IL-6 protein production in a time- and dose-dependent manner. The CF and non-CF cell lines were largely similar in their TLR expression and relative TLR responses. ICAM-1 expression was also up-regulated in CFTE29o(-) cells following stimulation with each agonist. CF bronchoalveolar lavage fluid, which contains LPS, bacterial DNA, and neutrophil elastase (a neutrophil-derived protease that can activate TLR4), up-regulated an NF-kappaB-linked reporter gene and increased IL-8 protein production in CFTE29o(-) cells. This effect was abrogated by expression of dominant-negative versions of MyD88 or Mal, key signal transducers for TLRs, thereby implicating them as potential anti-inflammatory agents for CF.

Interleukin-1, Neutrophil Elastase, and Lipopolysaccharide: Key Pro- Inflammatory Stimuli Regulating Inflammation in Cystic Fibrosis

Cystic fibrosis (CF) is a common fatal genetic disease among Caucasians of European descent that is characterized by neutrophil-dominated airway inflammation due to intrinsic cellular abnormalities in the affected epithelial cells. A number of proinflammatory stimuli are responsible for aggravating inflammatory responses in CF bronchial epithelium. Two important host-derived factors with potent proinflammatory effects in CF are interleukin-1 (IL-1) and neutrophil elastase (NE). Microbial-derived factors also have importance in the CF lung, as a significant factor by which pulmonary inflammation is mediated in CF is by Pseudomonas aeruginosa infection. Pseudomonas antigens, including lipopolysaccharide (LPS), can exacerbate pulmonary inflammation in CF by exaggerating proinflammatory gene expression via Toll-like receptor (TLR) activation. TLRs belong to a family of proteins that can recognize and discriminate a diverse array of microbial antigens. Following their activation TLRs transduce intracellular signals that regulate proinflammatory gene expression. Intriguingly IL-1, NE and LPS all utilize the same intracellular signaling pathways to induce their effects. This review will summarise what is known regarding the roles of these important proinflammatory stimuli and their effects on CF epithelium and describe current and novel therapeutic strategies for the treatment of CF lung disease. Keywords: interleukin-1, neutrophil elastase, lipopolysaccharide, cystic fibrosis, inflammation

Use of modulators of airways inflammation in patients with CF.

One of the hallmarks of cystic fibrosis (CF) lung disease is the presence of intense, neutrophil-dominated airway inflammation, and many researchers have focused on developing therapies to reduce inflammation in CF lung disease. Systemic corticosteroids can delay progression of lung disease, but at the cost of unacceptable side effects. Inhaled corticosteroids are widely used, but their efficacy has yet to be demonstrated in a controlled fashion. Ibuprofen has also been shown to delay disease progression, but its use has been limited by the need to obtain individual pharmacokinetics and concern about side effects. Other treatments with potential anti-inflammatory effects include pentoxifylline, leukotriene antagonists, docosahexaenoic acid, and azithromycin. Few, if any, large clinical studies of these therapies have been published, but several are presently underway. Because neutrophil elastase appears to be a key mediator of tissue damage in CF lung disease, anti-elastase compounds have also been studied, including alpha-1-protease inhibitor, secretory leukocyte protease inhibitor, and small molecule inhibitors. There have been no large-scale controlled trials of these therapies in CF. More recently, investigators have focused on cytokine modulation, using either interleukin-10 or interferon gamma. Some complementary and alternative medicine therapies may also have anti-inflammatory effects, although their clinical value has yet to be demonstrated in a rigorously-controlled fashion. In summary, numerous anti-inflammatory therapies have been applied to CF lung disease, but more large, well-controlled studies will need to be performed to determine their true clinical usefulness.

Persistent infections and immunity in cystic fibrosis

Cystic fibrosis (CF) is the most common autosomal recessive lethal disease in the Caucasian population. Chronic respiratory infections with Pseudomonas aeruginosa, neutrophil-dominated airway inflammation and progressive lung damage are the major causes of morbidity and mortality in CF. Two persistent infection phenotypes expressed by this bacterium are biofilm and mucoidy. Biofilm, also called the microcolony mode of growth is the surface-associated adherent bacterial community, while mucoidy refers to a phenotype conducive to copious amounts of mucoid exopolysaccharide (MEP)/alginate that provides a matrix for mature biofilms conferring resistance to host defenses and antibiotics. Recent completion of the whole genomic sequence of the standard reference strain P. aeruginosa PAO1 has led to discoveries that many clinical isolates of this species possess unique genomic sequences (genomic islands) due to horizontal gene transfer. We propose this type of genetic exchange may play an important role in causing intrinsic genomic diversity of this organism. Therefore, the diversity, as revealed through profiles of restriction fragment length polymorphism (RFLP), may be linked to an array of novel and unexplored pathogenic mechanisms in P. aeruginosa. CF mouse models, while displaying many clinical similarities to human CF, have yet to demonstrate a chronic pulmonary disease phenotype. This review is intended to provide an overview of P. aeruginosa persistent infection phenotypes (biofilm and mucoidy) and an aerosol infection mouse model for CF. Genomic diversity of P. aeruginosa and its implications in the pathogenesis in CF will also be discussed.

Monitoring inflammation in CF. Cytokines.

In cystic fibrosis (CF), chronic airway infection and neutrophil-dominated airway inflammation lead to progressive lung disease. Cytokines play an important role in the inflammatory response. Evidence suggests that cytokine production is altered or dysregulated in CF. Moreover, polymorphisms in cytokines may be linked to disease severity by acting as modifier genes. This article reviews the current state of knowledge regarding individual cytokines and CF lung disease, with an eye towards the possibility that cytokines may be used as outcome measures in clinical trials in CF. In addition, cytokines may eventually serve as targets for novel anti-inflammatory therapies in CF.

Innate lung defenses and compromised Pseudomonas aeruginosa clearance in the malnourished mouse model of respiratory infections in cystic fibrosis.

Cystic fibrosis (CF) is characterized by dysfunction of the digestive and respiratory tracts resulting in generalized malnutrition and chronic respiratory infections. Chronic lung infections with Pseudomonas aeruginosa, intense neutrophil-dominated airway inflammation, and progressive lung disease are the major cause of high morbidity and mortality in CF. Here we investigated the effects of malnutrition in CF on innate lung defenses, susceptibility to P. aeruginosa colonization, and associated inflammation, using aerosol models of acute and chronic infections in normal, malnourished, and transgenic mice. CFTR(m1Unc-/-) knockout mice displayed body weight variations and showed variable pulmonary clearance of P. aeruginosa. This variability was not detected in bitransgenic CFTR(m1Unc-/-)(FABP-hCFTR) mice in which the intestinal defect had been corrected. Diet-induced protein calorie malnutrition in C57BL/6J mice resulted in impaired pulmonary clearance of P. aeruginosa. Tumor necrosis factor alpha (TNF-alpha) and nitrite levels detected upon exposure to P. aeruginosa aerosols were lower in the lungs of the malnourished C57BL/6J mice relative than in lungs of mice fed a normal diet. The role of TNF-alpha and reactive nitrogen intermediates in P. aeruginosa clearance was tested in TNF-alpha and inducible nitric oxide synthase (iNOS) knockout mice. P. aeruginosa clearance was diminished in transgenic TNF-alpha- and iNOS-deficient mice. In contrast to the effects of TNF-alpha and iNOS, gamma interferon knockout mice retained a full capacity to eliminate P. aeruginosa from the lung. Malnutrition also contributed to excessive inflammation in C57BL/6J mice upon chronic challenge with P. aeruginosa. The repeatedly infected malnourished host did not produce interleukin-10, a major anti-inflammatory cytokine absent or diminished in the bronchoalveolar fluids of CF patients. These results are consistent with a model in which defective CFTR in the intestinal tract leads to nutritional deficiency which in turn contributes to compromised innate lung defenses, bacterial colonization, and excessive inflammation in the CF respiratory tract.