Showing papers by "Donna E. Davies published in 2001"

The contribution of interleukin (IL)-4 and IL-13 to the epithelial-mesenchymal trophic unit in asthma

Abstract: Interleukin (IL)-4 and IL-13 are key proinflammatory cytokines in asthma. Studies in transgenic mice show that both cytokines cause inflammation, but only IL-13 causes subepithelial fibrosis, a characteristic feature of asthma. We compared the in vitro profibrogenic effects of IL-4 and IL-13 using bronchial fibroblasts from asthmatic subjects. In the presence of transforming growth factor (TGF)-beta the cells transformed into contractile myofibroblasts and expressed alpha-smooth muscle actin and procollagen I. IL-4 and IL-13 also stimulated proliferation, but were relatively ineffective in promoting myofibroblast transformation. TGF-beta was more potent than the cytokines in stimulating release of endothelin-1 and vascular endothelial growth factor, whereas IL-4 and IL-13 were more potent stimuli for eotaxin release. Although neither IL-4 nor IL-13 induced profibrotic responses, both cytokines caused a corticosteroid-insensitive stimulation of TGF-beta2 release from primary bronchial epithelial cells. These data indicate that epithelial activation by IL-13 or IL-4 plays a critical role in initiating remodeling through release of TGF-beta2. TGF-beta2 then activates the underlying myofibroblasts to secrete matrix proteins and smooth muscle and vascular mitogens to propagate remodeling changes into the submucosa. In contrast, direct activation of submucosal fibroblasts by IL-4 and IL-13 has a proinflammatory effect via eotaxin release and recruitment of eosinophils into the airways.

Signal transducer and activator of transcription 6 (STAT-6) expression and function in asthmatic bronchial epithelium.

Abstract: Background: Asthma is associated with increased production of IL-4 and IL-13. Objective: Because many of the effects of these cytokines are mediated by activation of signal transducer and activator of transcription 6 (STAT-6), we investigated expression and function of this transcription factor in the airways. Methods: STAT-6 expression was investigated through use of immunohistochemistry or RT-PCR applied to bronchial biopsy specimens or brushings from normal control or asthmatic subjects. STAT-6 function was investigated by means of Western blotting and ELISA applied to primary epithelial cell cultures. Results: Immunohistochemistry revealed that the bronchial epithelium was the major site of STAT-6 expression, both cytoplasmic and nuclear staining being observed. The level of STAT-6 expression in subjects with mild asthma (median [range] percent epithelial staining, 3.4% [0% to 16.0%]; n=14) did not differ significantly from that in normal controls (4.7% [0.0% to 20.0%]; n=11); however, in subjects with severe asthma, epithelial STAT-6 expression (13.7% [4.8% to 25.7%]; n=9) was increased in comparison with subjects with mild asthma and normal controls ( P Conclusion: These data demonstrate expression and activation of STAT-6 in normal and asthmatic bronchial epithelium. The activity of this transcription factor is likely to play a key role in mediating the responses of the bronchial epithelium to T H 2 cytokines that are characteristic of the asthmatic phenotype. (J Allergy Clin Immunol 2001;108:832-8.)

Asthmatic Bronchial Epithelium is More Susceptible to Oxidant — Induced Apoptosis (Introduced by ST Holgate)

Abstract: Abnormal apoptotic mechanisms are associated with disease pathogenesis. Because the asthmatic bronchial epithelium is characteristically damaged with loss of columnar epithelial cells, we postulated that this is due to unscheduled apoptosis. Using an antibody directed toward the caspase cleavage product of poly(ADP-ribose) polymerase, immunohistochemistry applied to endobronchial biopsies showed higher levels of staining in the bronchial epithelium of subjects with asthma as compared with normal control subjects (% epithelial staining [median (range) = 10.5 (1.4-24.5) versus 0.4 (0.0-9.7)]; P < 0.001). Because we were unable to determine whether this difference was due to ongoing inflammation in vivo, cultures of normal and asthmatic bronchial epithelial cells were used to study apoptosis in vitro. In complete growth medium, these cells showed no difference in their rate of proliferation or viability. However, cells from subjects with asthma were more susceptible to the apoptotic effects of H2O2 than cells from normal control subjects (% apoptotic cells = 32.2 [8.8-54.9] versus 14.3 [6.4-24.7]; P < 0.05), even though both were similarly affected by treatment with actinomycin D. These data indicate that the susceptibility of asthmatic bronchial epithelium to oxidants is greater than normal. This susceptibility may contribute to the rising trends in asthma associated with air pollution and diets low in antioxidants.

Invited lecture: activation of the epithelial mesenchymal trophic unit in the pathogenesis of asthma.

Abstract: Background: A recent NIH Workshop and an ERS Task Force concluded that more work was needed to understand mechanisms of severe and chronic asthma. This report describes a series of

The bronchial epithelium in asthma--much more than a passive barrier.

Abstract: The bronchial epithelium has a multifunctional role in the airway. It is actively engaged in communicating with cells of the immune and inflammatory systems, as well as secreting cytoprotective molecules and acting as a physical barrier between the internal and external milieu of the lungs. In asthma, the bronchial epithelium is often damaged, with shedding of the columnar cells into the airway lumen. This damage and ensuing repair responses are proposed to orchestrate airway remodelling via activation of myofibroblasts in the underlying lamina reticularis. This allows the two cell types to work as a trophic unit, propagating and amplifying the response at the cell surface into the submucosa. In addition to structural damage, the epithelium displays an "activated" phenotype evident by activation of transcription factors such as nuclear factor kappa B (NF kappa B), and expression of mediators which directly or indirectly lead to a chronic cycle of inflammation and injury. A diverse number of innocuous stimuli trigger asthma. It is likely that interactions between genetic and environmental factors converge on common intracellular signalling pathways that regulate epithelial stress and repair. Of particular relevance is the NF kappa B signalling pathway and the mitogen activated protein kinase pathways (MAPKs), of which the mitogen activated extracellular regulated kinases (ERKs), and the stress activated P38 and c-Jun NH2 terminal kinase (JNKs) are best known. This review aims to highlight the importance of these signalling pathways in coordinating the response to diverse stimuli at the surface of the bronchial epithelium which leads to development and maintenance of the asthmatic state.

The role of CD28-B7 costimulation in allergen-induced cytokine release by bronchial mucosa from patients with moderately severe asthma.

Abstract: Background: T cells play an important role in airway inflammation in asthma through the release of T H 2 cytokines. Optimal T-cell activation by antigen-presenting cells requires co-stimulatory signaling, such as the interaction of CD80, CD86, or both with CD28. In patients with mild allergic asthma, the fusion protein cytotoxic T-lymphocyte antigen 4Ig (CTLA-4Ig), which inhibits CD28-mediated signaling, blocks the release of IL-5 and IL-13 from bronchial explant cultures exposed to the allergen Dermatophagoides pteronyssinus . Objectives: To assess costimulation in more severe forms of atopic asthma, we have compared the ability of CTLA-4Ig to block allergen-induced cytokine responses of bronchial explants and PBMCs from patients with moderately severe asthma. Methods: Bronchial explants and PBMCs were cultured in vitro, and cytokine expression was measured by means of quantitative RT-PCR and ELISA. Results: Constitutive mRNA transcripts for IL-5, IL-13, and GM-CSF were detected in the tissue explants, but only IL-5 mRNA increased significantly with allergen stimulation. Consistent with increased transcription, allergen-stimulated IL-5 protein release into explant supernatants, but this was not blocked by CTLA-4Ig. Allergen did not induce GM-CSF release, and IL-13 protein could not be detected in the explant supernatants under any condition. In contrast, allergen enhanced production of IL-5 and IL-13 by PBMC cultures from the same subjects, and this was inhibited effectively by CTLA-4Ig. Conclusions: These data suggest that IL-5 production in the airways of subjects with moderately severe asthma is largely independent of CD28-mediated costimulation. The different requirements for CD28-mediated costimulation in PBMC cultures and bronchial tissue cultures emphasizes the importance of the tissue microenvironment in pulmonary inflammatory responses in severe asthma. (J Allergy Clin Immunol 2001;108:976-81.)

The bronchial epithelium: translating gene and environment interactions in asthma.

Abstract: The rising trends in asthma over the past 30 years are likely to be a consequence of changes in the environment acting on a susceptible genotype. Recognising that environmental agents impact on the bronchial epithelium, this structure is in a key position to translate and coordinate these gene-environment interactions. In asthma, the bronchial epithelium is stressed and damaged, with shedding of the columnar cells into the airway lumen. The aim of this review is to consider recent advances in our understanding of why the epithelium is damaged and how the ensuing repair responses orchestrate airway inflammation and remodelling leading to the development and maintenance of the asthmatic state.

The bronchial epithelium in chronic and severe asthma

Abstract: Although patients with severe, steroid-refractory asthma represent a minor proportion of the asthmatic population, they consume a disproportionate amount of healthcare costs and have a greatly impaired quality of life. They respond poorly to conventional anti-inflammatory therapy and frequently exhibit a component of fixed airflow obstruction that has been linked to airway wall remodeling. In addition to its classic barrier function, the bronchial epithelium responds to changes in the external environment by secreting cytoprotective molecules and mediators that signal to cells of the immune system. In asthma, the bronchial epithelium is stressed and damaged, with shedding of the columnar cells into the airway lumen. This damage and ensuing repair responses are proposed to orchestrate airway inflammation and remodeling via activation of myofibroblasts in the underlying lamina reticularis. This allows the two cell types to work as a trophic unit, propagating and amplifying the response at the cell surface into the submucosa. Because wound healing involves inflammation, repair, and remodeling processes, this review considers the evidence that exaggerated inflammation and remodeling of the airways arise as a consequence of abnormal injury and repair responses coordinated by the bronchial epithelium, highlighting, where possible, steroid-insensitive components.

Solution structure of the mEGF/TGFalpha44-50 chimeric growth factor.

Abstract: The solution structure of the growth factor chimera mEGF/TGF ?(44-50) has been determined using an extended version of the DYANA procedure for calculating structures from NMR data. The backbone fold and preferred orientation of the domains of the chimera are similar to those found in previous studies of EGF structures, and several H-bonds used as input constraints in those studies were found independently in the chimera. This shows that the modified activity of the chimera does not result from a major structural change. However, the improved precision of the structure presented here allows the origin of some unusual chemical shifts found in all of these compounds to be explained, as well as the results obtained from some site-specific mutants. Further studies of the properties of this chimeric growth factor should help to elucidate the mechanism(s) of hetero- and homodimerization of the c-erbB receptors.