Requirement for CD28 in the effector phase of allergic airway inflammation

Central to the pathogenesis of allergic airway inflammation are the activation and differentiation of T lymphocytes. This process requires the participation of the CD28 costimulatory receptor. Blockade of CD28 has been demonstrated to prevent inflammation and airway hyperreactivity in a murine model of asthma. Whether this is due specifically to defects in initial T cell activation or whether effector responses are also impaired has not been determined. Using adoptive transfer studies of Ag-specific lymphocytes, we demonstrate that CD28 has a critical role in both the induction and effector phase of allergic airway inflammation. Transfer of in vitro activated and Th2-differentiated Ag-specific lymphocytes from wild-type hosts restored inflammation, but not tissue eosinophilia in CD28-deficient recipients. Furthermore, similarly activated and differentiated CD28-deficient lymphocytes were ineffective at mediating inflammation in wild-type recipients. Secondary cytokine and proliferative responses of activated Th2 cells were highly dependent on CD28 in vitro. Moreover, eosinophil recruitment to both the lung and peritoneum is impaired by the lack of CD28, suggesting a generalized defect in the ability of eosinophils to accumulate at sites of inflammation in vivo. These data identify a novel role for CD28 in the effector phase of allergic airway inflammation and suggest that inhibition of this pathway may be a useful therapeutic intervention in previously sensitized individuals.     

E. coli pneumonia induces CD18-independent airway neutrophil migration in the absence of increased lung vascular permeability

We examined the relationship between neutrophil [polymorphonuclear leukocyte (PMN)] influx and lung vascular injury in response to Escherichia coli pneumonia. We assessed lung tissue PMN uptake by measuring myeloperoxidase and transvascular PMN migration by determining PMN counts in lung interstitium and bronchoalveolar lavage fluid (BALF) in mice challenged intratracheally with E. coli. Lung vascular injury was quantified by determining microvessel filtration coefficient (Kf,c), a measure of vascular permeability. We addressed the role of CD18 integrin in the mechanism of PMN migration and lung vascular injury by inducing the expression of neutrophil inhibitory factor, a CD11/CD18 antagonist. In control animals, we observed a time-dependent sixfold increase in PMN uptake, a fivefold increase in airway PMN migration, and a 20-fold increase in interstitial PMN uptake at 6 h after challenge. Interestingly, Kf,c increased minimally during this period of PMN extravasation. CD11/CD18 blockade reduced lung tissue PMN uptake consistent with the role of CD18 in mediating PMN adhesion to the endothelium but failed to alter PMN migration in the tissue. Moreover, CD11/CD18 blockade did not affect Kf,c. Analysis of BALF leukocytes demonstrated diminished oxidative burst compared with leukocytes from bacteremic mice, suggesting a basis for lack of vascular injury. The massive CD11/CD18-independent airway PMN influx occurring in the absence of lung vascular injury is indicative of an efficient host-defense response elicited by E. coli pneumonia.     

Regulation of cockroach antigen-induced allergic airway hyperreactivity by the CXCR3 ligand CXCL9

Allergic airway disease is characterized by a robust lymphocytic infiltrate, elaboration of Th2-type inflammatory mediators, pulmonary eosinophil accumulation, and airway hyperreactivity. The CXCR3 ligands, CXCL9 (monokine induced by IFN-gamma) and CXCL10 (IFN-inducible protein, 10 kDa), are IFN-gamma-inducible, Th1-type chemokines. As CXCL10 has been previously shown to participate in the modulation of allergic inflammation, we were interested in investigating the possible role that CXCL9 may play in this inflammatory response. Expression of CXCL9 was primarily identified in airway epithelial cells by immunohistochemical staining. Airway neutralization of CXCL9 at the time of allergen challenge significantly increased airway hyperreactivity, airway eosinophil accumulation, and IL-4 levels in the bronchoalveolar lavage while significantly decreasing airway levels of IL-12. In contrast, introduction of exogenous CXCL9 into the airway at the time of allergen challenge dramatically reduced airway hyper-reactivity and eosinophil accumulation. Moreover, pulmonary levels of IL-4 were significantly reduced, whereas levels of IL-12 were significantly increased, with exogenous CXCL9 treatment. In lymphocytes restimulated with CXCL9 and allergen in vitro, CXCL9 down-regulated IL-4 expression and up-regulated IFN-gamma expression, suggesting that CXCL9 is able to direct activated lymphocytes toward a Th1-type phenotype. Additionally, CXCL9 was shown to inhibit CC chemokine ligand 11-induced eosinophil chemotaxis in in vitro assays. Taken together, our results demonstrate that the CXCR3 ligand CXCL9 is involved in regulation of the allergic response in the lung by regulation of lymphocyte activation and eosinophil recruitment.     

Novel approach to inhibit asthma-mediated lung inflammation using anti-CD147 intervention

Extracellular cyclophilins have been well described as chemotactic factors for various leukocyte subsets. This chemotactic capacity is dependent upon interaction of cyclophilins with the cell surface signaling receptor CD147. Elevated levels of extracellular cyclophilins have been documented in several inflammatory diseases. We propose that extracellular cyclophilins, via interaction with CD147, may contribute to the recruitment of leukocytes from the periphery into tissues during inflammatory responses. In this study, we examined whether extracellular cyclophilin-CD147 interactions might influence leukocyte recruitment in the inflammatory disease allergic asthma. Using a mouse model of asthmatic inflammation, we show that 1) extracellular cyclophilins are elevated in the airways of asthmatic mice; 2) mouse eosinophils and CD4+ T cells express CD147, which is up-regulated on CD4+ T cells upon activation; 3) cyclophilins induce CD147-dependent chemotaxis of activated CD4+ T cells in vitro; 4) in vivo treatment with anti-CD147 mAb significantly reduces (by up to 50%) the accumulation of eosinophils and effector/memory CD4+ T lymphocytes, as well as Ag-specific Th2 cytokine secretion, in lung tissues; and 5) anti-CD147 treatment significantly reduces airway epithelial mucin production and bronchial hyperreactivity to methacholine challenge. These findings provide a novel mechanism whereby asthmatic lung inflammation may be reduced by targeting cyclophilin-CD147 interactions.     

IFN-gamma-inducible protein 10 (CXCL10) contributes to airway hyperreactivity and airway inflammation in a mouse model of asthma

Allergic asthma is an inflammatory disease of the airways characterized by eosinophilic inflammation and airway hyper-reactivity. Cytokines and chemokines specific for Th2-type inflammation predominate in asthma and in animal models of this disease. The role of Th1-type inflammatory mediators in asthma remains controversial. IFN-gamma-inducible protein 10 (IP-10; CXCL10) is an IFN-gamma-inducible chemokine that preferentially attracts activated Th1 lymphocytes. IP-10 is up-regulated in the airways of asthmatics, but its function in asthma is unclear. To investigate the role of IP-10 in allergic airway disease, we examined the expression of IP-10 in a murine model of asthma and the effects of overexpression and deletion of IP-10 in this model using IP-10-transgenic and IP-10-deficient mice. Our experiments demonstrate that IP-10 is up-regulated in the lung after allergen challenge. Mice that overexpress IP-10 in the lung exhibited significantly increased airway hyperreactivity, eosinophilia, IL-4 levels, and CD8(+) lymphocyte recruitment compared with wild-type controls. In addition, there was an increase in the percentage of IL-4-secreting T lymphocytes in the lungs of IP-10-transgenic mice. In contrast, mice deficient in IP-10 demonstrated the opposite results compared with wild-type controls, with a significant reduction in these measures of Th2-type allergic airway inflammation. Our results demonstrate that IP-10, a Th1-type chemokine, is up-regulated in allergic pulmonary inflammation and that this contributes to the airway hyperreactivity and Th2-type inflammation seen in this model of asthma.     

E- and P-selectins are essential for the development of cockroach allergen-induced airway responses

Peribronchial inflammation contributes to the pathophysiology of allergic asthma. In many vascular beds, adhesive interactions between leukocytes and the endothelial surface initiate the recruitment of circulating cells. Previous studies using OVA-induced airway hyperreactivity indicated that P-selectin, a member of the selectin family expressed by activated platelets and endothelium, contributed to both inflammation and bronchoconstriction. The current study used cockroach allergen (CRA), an allergen that induces asthmatic responses in both humans and mice, to further investigate the role of selectins in the development of peribronchial inflammation and airway hyperreactivity. P- and E-selectin mRNAs were detected in extracts of CRA-sensitized animals beginning shortly after intratracheal challenge with CRA. The P-selectin mRNA was transiently induced at early time points while up-regulation of the E-selectin mRNA was more prolonged. Mice with targeted deletions in E-selectin (E(-)), P-selectin (P(-)), and both genes (E(-)/P(-)) showed 70-85% reductions in airway hyperreactivity, peribronchial inflammation, and eosinophil accumulation. The P(-) and E(-)/P(-) groups showed the most profound reductions. The transfer of splenic lymphocytes from CRA-primed E(-)/P(-) into naive wild-type (WT) mice produced the same level of airway hyperreactivity as transfers from CRA-primed WT into naive WT hosts, indicating that peripheral immunization was similar. The observed changes in the selectin-deficient animals were not related to inadequate sensitization, because CRA priming and challenge increased serum IgE levels. Furthermore, pulmonary Th2-type cytokines and chemokines in the E-selectin(-/-) and WT animals were similar. The findings indicate that both P- and E-selectin contribute to CRA-induced peribronchial inflammation and airway hyperreactivity.     

Human leukocytes express ephrinB2 which activates microvascular endothelial cells

EphrinB2-EphB4 interaction modulates the migration/adhesion of various cell types, including endothelial cells (EC) and peripheral blood leukocytes (PBLs). We hypothesize that the Ephrin/Eph signaling mechanism plays a role in mediating EC/leukocyte interactions during inflammation. PBLs were isolated from human blood, stimulated with inflammatory mediators, and total RNA or protein assayed for EphrinB2 expression. PBLs demonstrated differential expression profiles of EphrinB2 mRNA or protein, depending on cell subtype and stimulus. Human iris tissue and iris EC (HIEC) were examined for the expression of EphB4 mRNA and protein. Some blood vessels were EphB4(+), while stimulation of purified HIEC did not alter their expression of EphB4. HIEC treated with sEphrinB2/Fc from 0 to 60min did exhibit changes in their phospho-Erk1/2 levels. These observations indicate that stimulated lymphocytes express EphrinB2, which has the potential to activate EC. This suggests a novel mechanism by which EC and lymphocytes communicate to regulate cell activation/migration during inflammation.     

Blockade of CD49d inhibits allergic airway pathologies independent of effects on leukocyte recruitment

Lymphocyte and/or eosinophil recruitment is dependent on the sequential interactions between adhesion molecules expressed on activated endothelial cells and both leukocyte subtypes. Endothelial P- and E-selectins mediate tethering and rolling of leukocytes through interactions with P-selectin glycoprotein ligand-1 (PSGL-1), and diapedesis subsequently occurs by engagement of endothelial vascular cell adhesion molecule-1 and CD49d (alpha(4)-integrins). The anti-inflammatory potential of interfering with these adhesive interactions was assessed with an ovalbumin challenge mouse model of asthma. Administration of a soluble form of PSGL-1 reduced eosinophils (80%) and lymphocytes (50%) in bronchoalveolar lavage fluid without affecting epithelial changes or airway hyperreactivity (AHR). In contrast, although administration of anti-CD49d monoclonal antibodies (PS/2) resulted in similar reductions in eosinophils (75%) and lymphocytes (50%), PS/2 reduced and abolished mucous cell metaplasia and AHR, respectively. Administration of both PSGL-1 and PS/2 had the additive effect of eliminating eosinophils from the airways (96% decrease), with few or no additional reductions (relative to PS/2 administration alone) in lymphocyte recruitment, mucous cell metaplasia, or AHR. These data show that eosinophils and lymphocytes differentially utilize adhesive interactions during recruitment and that the inhibition of AHR is independent of this recruitment.     

Role of regulator of G protein signaling 16 in inflammation-induced T lymphocyte migration and activation

Chemokine-induced T lymphocyte recruitment to the lung is critical for allergic inflammation, but chemokine signaling pathways are incompletely understood. Regulator of G protein signaling (RGS)16, a GTPase accelerator (GTPase-activating protein) for Galpha subunits, attenuates signaling by chemokine receptors in T lymphocytes, suggesting a role in the regulation of lymphocyte trafficking. To explore the role of RGS16 in T lymphocyte-dependent immune responses in a whole-organism model, we generated transgenic (Tg) mice expressing RGS16 in CD4(+) and CD8(+) cells. rgs16 Tg T lymphocytes migrated to CC chemokine ligand 21 or CC chemokine ligand 12 injection sites in the peritoneum, but not to CXC chemokine ligand 12. In a Th2-dependent model of allergic pulmonary inflammation, CD4(+) lymphocytes bearing CCR3, CCR5, and CXCR4 trafficked in reduced numbers to the lung after acute inhalation challenge with allergen (OVA). In contrast, spleens of sensitized and challenged Tg mice contained increased numbers of CD4(+)CCR3(+) cells producing more Th2-type cytokines (IL-4, IL-5, and IL-13), which were associated with increased airway hyperreactivity. Migration of Tg lymphocytes to the lung parenchyma after adoptive transfer was significantly reduced compared with wild-type lymphocytes. Naive lymphocytes displayed normal CCR3 and CXCR4 expression and cytokine responses, and compartmentation in secondary lymphoid organs was normal without allergen challenge. These results suggest that RGS16 may regulate T lymphocyte activation in response to inflammatory stimuli and migration induced by CXCR4, CCR3, and CCR5, but not CCR2 or CCR7.     

IL-22 is produced by innate lymphoid cells and limits inflammation in allergic airway disease

Interleukin (IL)-22 is an effector cytokine, which acts primarily on epithelial cells in the skin, gut, liver and lung. Both pro- and anti-inflammatory properties have been reported for IL-22 depending on the tissue and disease model. In a murine model of allergic airway inflammation, we found that IL-22 is predominantly produced by innate lymphoid cells in the inflamed lungs, rather than TH cells. To determine the impact of IL-22 on airway inflammation, we used allergen-sensitized IL-22-deficient mice and found that they suffer from significantly higher airway hyperreactivity upon airway challenge. IL-22-deficiency led to increased eosinophil infiltration lymphocyte invasion and production of CCL17 (TARC), IL-5 and IL-13 in the lung. Mice treated with IL-22 before antigen challenge displayed reduced expression of CCL17 and IL-13 and significant amelioration of airway constriction and inflammation. We conclude that innate IL-22 limits airway inflammation, tissue damage and clinical decline in allergic lung disease.     

Complement-dependent immune complex-induced bronchial inflammation and hyperreactivity

Bronchoconstriction responses in the airway are caused by multiple insults and are the hallmark symptom in asthma. In an acute lung injury model in mice, IgG immune complex deposition elicited severe airway hyperreactivity that peaked by 1 h, was maintained at 4 h, and was resolved by 24 h. The depletion of complement with cobra venom factor (CVF) markedly reduced the hyperreactive airway responses, suggesting that complement played an important role in the response. Blockade of C5a with specific antisera also significantly reduced airway hyperreactivity in this acute lung model. Complement depletion by CVF treatment significantly reduced tumor necrosis factor and histamine levels in bronchoalveolar lavage fluids, correlating with reductions in airway hyperreactivity. To further examine the role of specific complement requirement, we initiated the immune complex response in C5-sufficient and C5-deficient congenic animals. The airway hyperreactivity response was partially reduced in the C5-deficient mice. Complement depletion with CVF attenuated airway hyperreactivity in the C5-sufficient mice but had a lesser effect on the airway hyperreactive response and histamine release in bronchoalveolar lavage fluids in C5-deficient mice. These data indicate that acute lung injury in mice after deposition of IgG immune complexes induced airway hyperreactivity that is C5 and C5a dependent.     

Pharmacological model for airway hypersensitivity produced by propranolol and reserpine in guinea pigs

Combined treatment with propranolol and reserpine enhanced acetylcholine-induced doseresponse curves for bronchoconstriction in guinea pigs in vivo. This airway hyperreactivity model was investigated pharmacologically. (1) Increased capillary permeability and increases in leukocytes in bronchoalveolar lavage fluid (BALF) were not observed after this combined treatment. (2) The increased airway sensitivity to acetylcholine produced by propranolol and reserpine was inhibited by ketotifen and theophylline, reported in clinical studies to inhibit airway hyperreactivity. (3) Two leukotriene (LT) receptor antagonists, MCI-826 and FPL-55712, clearly inhibited this increased airway reactivity. (4) A thromboxane A₂ (TXA₂) receptor antagonist, ONO-3708, and TXA₂ synthetase inhibitor, OKY-046, also inhibited this increased airway reactivity.These results suggest that the airway hyperreactivity model produced by propranolol and reserpine in guinea pigs is a valuable pharmacological tool for investigating a remedy and LT and TXA₂ may be involved in the onset of this airway hyperreactivity.     

Eosinophil tissue recruitment to sites of allergic inflammation in the lung is platelet endothelial cell adhesion molecule independent

Platelet endothelial cell adhesion molecule (PECAM or CD31) is a cell adhesion molecule expressed on circulating leukocytes and endothelial cells that plays an important role in mediating neutrophil and monocyte transendothelial migration in vivo. In this study, we investigated whether eosinophils, like neutrophils and monocytes, utilize PECAM for tissue recruitment to sites of allergic inflammation in vivo. Eosinophils express similar levels of PECAM as neutrophils as assessed by FACS analysis. RT-PCR studies demonstrate that eosinophils like neutrophils express the six extracellular domains of PECAM. Eosinophils exhibit homophilic binding to recombinant PECAM as assessed in a single-cell micropipette adhesion assay able to measure the biophysical strength of adhesion of eosinophils to recombinant PECAM. The strength of eosinophil adhesion to recombinant PECAM is the same as that of neutrophil binding to recombinant PECAM and can be inhibited with an anti-PECAM Ab. Although eosinophils express functional PECAM, anti-PECAM Abs did not inhibit bronchoalveolar lavage eosinophilia, lung eosinophilia, and airway hyperreactivity to methacholine in a mouse model of OVA-induced asthma in vivo. Thus, in contrast to studies that have demonstrated that neutrophil and monocyte tissue recruitment is PECAM dependent, these studies demonstrate that eosinophil tissue recruitment in vivo in this model is PECAM independent.     

Slit2 regulates attractive eosinophil and repulsive neutrophil chemotaxis through differential srGAP1 expression during lung inflammation

Directional migration of leukocytes is an essential step in leukocyte trafficking during inflammatory responses. However, the molecular mechanisms governing directional chemotaxis of leukocytes remain poorly understood. The Slit family of guidance cues has been implicated for inhibition of leuocyte migration. We report that Clara cells in the bronchial epithelium secreted Slit2, whereas eosinophils and neutrophils expressed its cell-surface receptor, Robo1. Compared to neutrophils, eosinophils exhibited a significantly lower level of Slit-Robo GTPase-activating protein 1 (srGAP1), leading to activation of Cdc42, recruitment of PI3K to Robo1, enhancment of eotaxin-induced eosinophil chemotaxis, and exaggeration of allergic airway inflammation. Notably, OVA sensitization elicited a Slit2 gradient at so-called bronchus-alveoli axis, with a higher level of Slit2 in the bronchial epithelium and a lower level in the alveolar tissue. Aerosol administration of rSlit2 accelerated eosinophil infiltration, whereas i.v. administered Slit2 reduced eosinophil deposition. In contrast, Slit2 inactivated Cdc42 and suppressed stromal cell-derived factor-1α-induced chemotaxis of neutrophils for inhibiting endotoxin-induced lung inflammation, which were reversed by blockade of srGAP1 binding to Robo1. These results indicate that the newly identified Slit2 gradient at the bronchus-alveoli axis induces attractive PI3K signaling in eosinophils and repulsive srGAP1 signaling in neutrophils through differential srGAP1 expression during lung inflammation.     

CpG oligodeoxynucleotides can reverse Th2-associated allergic airway responses and alter the B7.1/B7.2 expression in a murine model of asthma

CpG oligodeoxynucleotides (CpG-ODN) administered during Ag sensitization or before Ag challenge can inhibit allergic pulmonary inflammation and airway hyperreactivity in murine models of asthma. In this study, we investigated whether CpG-ODN can reverse an ongoing allergic pulmonary reaction in a mouse model of asthma. AKR mice were sensitized with conalbumin followed by two intratracheal challenges at weekly intervals. CpG-ODN was administered 24 h after the first Ag challenge. CpG-ODN administration reduced Ag-specific IgE levels, bronchoalveolar lavage fluid eosinophils, mucus production, and airway hyperreactivity. We found that postchallenge CpG-ODN treatment significantly increased IFN-gamma concentrations and decreased IL-13, IL-4, and IL-5 concentrations in bronchoalveolar lavage fluids and spleen cell culture supernatants. Postchallenge CpG-ODN treatment also increased B7.1 mRNA expression and decreased B7.2 mRNA expression in lung tissues. These results suggest that CpG-ODN may have potential for treatment of allergic asthma by suppressing Th2 responses during IgE-dependent allergic airway reactions. The down-regulation of Th2 responses by CPG-ODN may be associated with regulation of the costimulatory factors B7.1 and B7.2.     

Soluble guanylyl cyclase expression is reduced in allergic asthma

Soluble guanylyl cyclase (sGC) is an enzyme highly expressed in the lung that generates cGMP contributing to airway smooth muscle relaxation. To determine whether the bronchoconstriction observed in asthma is accompanied by changes in sGC expression, we used a well-established murine model of allergic asthma. Histological and biochemical analyses confirmed the presence of inflammation in the lungs of mice sensitized and challenged with ovalbumin (OVA). Moreover, mice sensitized and challenged with OVA exhibited airway hyperreactivity to methacholine inhalation. Steady-state mRNA levels for all sGC subunits (alpha1, alpha2, and beta1) were reduced in the lungs of mice with allergic asthma by 60-80%, as estimated by real-time PCR. These changes in mRNA were paralleled by changes at the protein level: alpha1, alpha2, and beta1 expression was reduced by 50-80% as determined by Western blotting. Reduced alpha1 and beta1 expression in bronchial smooth muscle cells was demonstrated by immunohistochemistry. To study if sGC inhibition mimics the airway hyperreactivity seen in asthma, we treated na?ve mice with a selective sGC inhibitor. Indeed, in mice receiving ODQ the methacholine dose response was shifted to the left. We conclude that sGC expression is reduced in experimental asthma contributing to the observed airway hyperreactivity.     

New perspectives on the mechanical basis for airway hyperreactivity and airway hypersensitivity in asthma.

We revisit the airway wall model of Lambert et. al. (Lambert RK, Wiggs BR, Kuwano K, Hogg JC, and Pare PD. J Appl Physiol 74: 2771-2781, 1993). We examine in detail the notion of a general airway bistability such that the airway lumen can suddenly decrease from a relatively open to a relatively closed condition without needing additional increase in active airway smooth muscle (ASM) tension during the stimulation. The onset of this bistability is an emergent consequence of the balance of forces associated with airway wall properties, parenchymal tissue properties, maximum lung elastic recoil, and the maximum stress that the ASM can generate. In healthy lungs, we find that all these properties reside in conditions that largely prevent the emergence of the bistability even during maximum ASM stimulation. In asthmatic airways, however, the airway wall and ASM remodeling conditions can tip the balance so as to promote the onset of the bistability at a lower dose of ASM stimulation (enhanced sensitivity) and then work to amplify the maximum constriction reached by each airway (enhanced reactivity). Hence, a larger fraction of asthmatic airways can display overall airway hyperreactivity. Simulations studies examine the role of increasing ASM maximum tension, airway wall stiffening, reduced lung volume, and decreased parenchymal tethering. Results predict that the single most important factor causing this airway hyperreactivity is amplified maximum ASM tension and not a thickening of the airway wall per se.     

Bone morphogenetic protein signalling in airway epithelial cells during regeneration

Mechanisms of lung regeneration after injury remain poorly understood. Bone morphogenetic protein 4 (BMP4) is critical for lung morphogenesis and regulates differentiation of the airway epithelium during development, although its mechanism of action is unknown. The role of BMPs in adult lungs is unclear. We hypothesised that BMP signalling is involved in regeneration of damaged adult airways after injury. Our aims were to characterise the regeneration process in 1-nitronaphthalene (1-NN) injured airways, to determine if and when BMP signalling is activated during this process and investigate the effects of BMP4 on normal adult airway epithelial cells (AECs). Rats were injected with 50 mg/kg 1-NN and protein expression in AECs was examined by Western blotting of lung lysis lavage, and by immunofluorescence, at 6, 24, 48 and 96 h post injection. Expression of signalling molecules p-ERK-1, p-ERK-2 and p-Smad1/5/8 in AECs peaked at 6 h post injection, coincident with maximal inflammation and prior to airway denudation which occurred at 24 h. While airways were re-epithelialised by 48 h, AEC proliferation peaked later at 96 h post 1-NN injection. In vitro, BMP4 induced a mesenchymal-like morphology in normal AECs, downregulated E-cadherin expression and increased migration in a wound closure assay. Thus, following acute injury, increased BMP signalling in AECs coincides with inflammation and precedes airway denudation and re-epithelialisation. Our data indicate that, similar to its role in controlling tissue architecture during development, BMP signalling regulates regeneration of the airways following acute injury, involving downregulation of E-cadherin and induction of migration in AECs.     

Neurotrophins in bronchial asthma

Allergic bronchial asthma (BA) is characterized by chronic airway inflammation, development of airway hyperreactivity and recurrent reversible airway obstruction. T-helper 2 cells and their products have been shown to play an important role in this process. In contrast, the mechanisms by which immune cells interact with the cells residing in lung and airways, such as neurons, epithelial or smooth muscle cells, still remains uncertain. Sensory and motor neurons innervating the lung exhibit a great degree of functional plasticity in BA defined as 'neuronal plasticity'. These neurons control development of airway hyperresponsiveness and acute inflammatory responses, resulting in the concept of 'neurogenic inflammation'. Such quantitative and/or qualitative changes in neuronal functions are mediated to a great extent by a family of cytokines, the neurotrophins, which in turn are produced by activated immune cells, among others in BA. We have therefore developed the concept that neurotrophins such as nerve growth factor and brain-derived neurotrophic factor link pathogenic events in BA to dysfunctions of the immune and nervous system.     

Effect of a novel leukotoriene synthesis inhibitor, BAY x1005, on the antigen- and LPS-induced airway hyperresponsiveness in guinea pigs

Due to the inhibition of 5-lipoxygenase-activating protein (FLAP), BAY x1005 is a new selective inhibitor of leukotriene synthesis. The effects of BAY x1005 on the antigen- and bacterial lipopolysaccharide (LPS)-induced airway hyperresponsiveness in guinea pigs were investigated. Six times provocation of aeroantigen caused biphasic increases in airway resistance which peaked at 1 hr (immediate phase reaction) and 4 hrs (late phase reaction). It also caused airway hyperreactivity to acetylcholine. BAY x1005 at doses of 10mg/kg and 30mg/kg significantly inhibited antigen-induced increase in respiratory resistance (Rrs) at 1 and 4 hrs after the last antigen challenge. Simultaneously, BAY x1005 inhibited the antigen-induced airway hyperresponsiveness at doses of 10 and 30mglkg and airway eosinophilia (bronchoalveolar lavage study) at a dose of 30 mg/kg. In addition, BAY x1005 at a dose of 30mg/kg inhibited bacterial LPS-induced airway hyperreactivity to acetylcholine. In this model, BAY x1005 did not affect the increase of the number of leukocytes in bronchoalveolar lavage fluid.These results suggest that BAY x1005 is a potent anti-asthmatic agent with an inhibitory action to airway hyperreactivity.