Rhinovirus disrupts the barrier function of polarized airway epithelial cells

Transcellular passage of Neisseria meningitidis across a polarized respiratory epithelium

Neisseria meningitidis is a major cause of sepsis and meningitis but is also a common commensal, present in the nasopharynx of between 8 and 20% of healthy individuals. During carriage, the bacterium is found on the surface of the nasopharyngeal epithelium and in deeper tissues, while to develop disease the meningococcus must spread across the respiratory epithelium and enter the systemic circulation. Therefore, investigating the pathways by which N. meningitidis crosses the epithelial barrier is relevant for understanding carriage and disease but has been hindered by the lack of appropriate models. Here, we have established a physiologically relevant model of the upper respiratory epithelial cell barrier to investigate the mechanisms responsible for traversal of N. meningitidis. Calu-3 human respiratory epithelial cells were grown on permeable cell culture membranes to form polarized monolayers of cells joined by tight junctions. We show that the meningococcus crosses the epithelial cell barrier by a transcellular route; traversal of the layer did not disrupt its integrity, and bacteria were detected within the cells of the monolayer. We demonstrate that successful traversal of the epithelial cell barrier by N. meningitidis requires expression of its type 4 pili (Tfp) and capsule and is dependent on the host cell microtubule network. The Calu-3 model should be suitable for dissecting the pathogenesis of infections caused by other respiratory pathogens, as well as the meningococcus.

COPD and the response of the lung to tobacco smoke exposure

Chronic Obstructive Pulmonary Disease (COPD) is a major cause of death in the western world and increasing in prevalence in developing countries. COPD is characterised by irreversible airflow obstruction, loss of lung tissue, reduced quality of life and high rates of mortality. The major cause of COPD is tobacco smoke. The changes in the innate immune system directed by tobacco smoke exposure lead to a pronounced and chronic inflammation in the lung. This in turn leads to other pathological changes including remodelling and destruction of lung tissue. Tobacco smoke exposure also leads to infection of the lung by bacteria and viruses. These, bacteria, viruses and co-infection are key triggers of acute worsening's of COPD termed exacerbations. COPD exacerbations are an additional major factor in the morbidity and mortality within COPD and are also the major healthcare costs associated with the disease. Within this review we discuss the response of the immune system to cigarette smoke exposure and inappropriate harmful responses. Successful treatment strategies will need to balance the positive effects of reducing inflammatory aspects of the disease whilst retaining some of the needed immune responses triggered by tobacco smoke exposure.

Do soluble mediators cause ventilator-induced lung injury and multi-organ failure?

BACKGROUND

Significant advances in the management of patients with acute respiratory distress syndrome have been few in the recent past despite considerable efforts in clinical testing and experimental work. The biotrauma hypothesis of ventilator-associated lung injury (VALI), suggesting that mechanical ventilation induces the release of injurious mediators from the lung, implies that pharmaceutical interventions targeting these circulating pathogenic mediators would be clinically beneficial. Among the commonly reported classes of ventilation-associated mediators are cytokines, coagulation factors, hormones (e.g., angiotensin-II), lipid-derived mediators and oxidants, yet proof of their pathogenicity is lacking.

DISCUSSION

This review discusses evidence surrounding the roles of these mediators in VALI and describes how definitive proof could be provided based on Koch's postulates, using an isolated perfused lung model. According to this experimental concept, candidate mediators would fulfill certain criteria, including increased accumulation in perfusate during injurious ventilation and induction of injury during non-injurious ventilation. Accumulation of mediators in the perfusate would facilitate isolation and characterization by standard biochemical means, from broad determination of physical and chemical properties to precise identification of individual molecules (e.g., by modern "omic" approaches such as mass spectrometry). Finally, confirmation by exogenous administration of mediators or antagonists can assess effects on injury and its mechanisms such as cell permeability or cytotoxicity.

CONCLUSIONS

Adaptation of Koch's postulates to the biotrauma hypothesis of VALI could provide important insights. Translation of the acquired knowledge into clinical testing is challenged by the heterogeneity of the patient population (e.g., etiology, co-morbidity, genetics or concomitant therapy) and the specificity and efficacy of the therapeutic intervention on the cellular/molecular level.

Controller medications and their effects on asthma exacerbations temporally associated with upper respiratory infections

BACKGROUND

Exacerbations are a major risk and a cause of asthma morbidity and healthcare utilization. Viral-induced upper respiratory tract infections are the most frequent trigger of asthma-related exacerbations. Studies have traditionally assessed exacerbations without documentation regarding exacerbation etiology. Therefore, it remains unknown whether asthma medications can alter exacerbation susceptibility based on a specific etiology.

OBJECTIVE

To examine whether treatment with inhaled corticosteroids plus long-acting beta(2)-agonists reduced the number of exacerbations associated with upper respiratory tract infections versus inhaled corticosteroids alone.

METHODS

Two large datasets comparing treatment with fluticasone propionate and fluticasone propionate plus salmeterol were analyzed, including the number of clinically reported upper respiratory tract infections, asthma-related exacerbations, and the presence of an exacerbation and concurrent report of an upper respiratory tract infection.

RESULTS

Both treatment groups had similar incidences of upper respiratory tract infections. Of those reporting an upper respiratory tract infection, statistically significantly fewer reported an asthma-related exacerbation comparing fluticasone propionate plus salmeterol with fluticasone propionate (p=0.0057).

DISCUSSION

This retrospective analysis suggests that therapy with fluticasone propionate plus salmeterol provides protection against asthma exacerbations temporally associated with upper respiratory tract infections. This retrospective analysis supports the hypothesis that specific therapeutic approaches to mitigate virus-associated exacerbations may benefit asthma care. Well-controlled prospective studies are warranted.

Rhinovirus infection-induced alteration of tight junction and adherens junction components in human nasal epithelial cells

OBJECTIVES/HYPOTHESIS

Manifestations of rhinovirus (RV) infections include mucus overproduction, increased vascular permeability, and secondary bacterial infection. These effects may reflect disrupted epithelial barrier functions, which are mainly regulated by intercellular junctions, referred to as tight junctions (TJs) and adherens junctions (AJs). The objective of this study was to investigate changes in the components of TJs (ZO-1, occluding, and claudin-1) and AJs (E-cadherin) after RV infection in cultured nasal epithelial cells.

METHODS

Primary human nasal epithelial cells grown at an air-liquid interface were infected apically with RV. RV-induced changes in the expression of epithelial TJ and AJ proteins were determined using real-time reverse transcriptase-polymerase chain reaction, confocal microscopy, and Western blot analyses. Functional changes in the integrity of junctional proteins were assessed by measuring transepithelial resistance (TER) using a voltmeter.

RESULTS

RV infection decreased mRNA levels of ZO-1, occludin, claudin-1, and E-cadherin to 64.2%, 51.8%, 56.2%, and 56.3%, respectively, of those in controls (P < .05). Decreases in ZO-1, occludin, claudin-1, and E-cadherin protein levels in RV-infected cells were evident in immunofluorescent confocal microscopic images. Expression levels of these proteins were also lower in the RV-infected group in Western blot analyses. RV infection reduced the mean TER from 143.1 Omega/cm(2) (controls) to 122.6 Omega/cm(2).

CONCLUSIONS

RV infection decreased the expression of TJ and AJ components and reduced TER in primary cultured human nasal epithelial cells, indicating that RV infection may exert a harmful effect on nasal epithelial barrier function.

A new look at the pathogenesis of asthma

Asthma is an inflammatory disorder of the conducting airways that has strong association with allergic sensitization. The disease is characterized by a polarized Th-2 (T-helper-2)-type T-cell response, but in general targeting this component of the disease with selective therapies has been disappointing and most therapy still relies on bronchodilators and corticosteroids rather than treating underlying disease mechanisms. With the disappointing outcomes of targeting individual Th-2 cytokines or manipulating T-cells, the time has come to re-evaluate the direction of research in this disease. A case is made that asthma has its origins in the airways themselves involving defective structural and functional behaviour of the epithelium in relation to environmental insults. Specifically, a defect in barrier function and an impaired innate immune response to viral infection may provide the substrate upon which allergic sensitization takes place. Once sensitized, the repeated allergen exposure will lead to disease persistence. These mechanisms could also be used to explain airway wall remodelling and the susceptibility of the asthmatic lung to exacerbations provoked by respiratory viruses, air pollution episodes and exposure to biologically active allergens. Variable activation of this epithelial-mesenchymal trophic unit could also lead to the emergence of different asthma phenotypes and a more targeted approach to the treatment of these. It also raises the possibility of developing treatments that increase the lung's resistance to the inhaled environment rather than concentrating all efforts on trying to suppress inflammation once it has become established.

Breakdown in epithelial barrier function in patients with asthma: identification of novel therapeutic approaches

The bronchial epithelium is pivotally involved in the provision of chemical, physical, and immunologic barriers to the inhaled environment. These barriers serve to maintain normal homeostasis, but when compromised, the immunologic barrier becomes activated to protect the internal milieu of the lung. We discuss what is currently understood about abnormalities in these barrier functions in patients with asthma and consider novel therapeutic opportunities that target this key structure.

Toluene diisocyanate enhances human bronchial epithelial cells' permeability partly through the vascular endothelial growth factor pathway

BACKGROUND

Toluene diisocyanate (TDI) is a recognized chemical asthmogen; yet, the mechanisms of its toxicity have not been elucidated.

OBJECTIVE

To investigate the influence of TDI on the permeability of human bronchial epithelial cell (HBE; HBE135-E6E7) monolayers in vitro, and the expression of vascular endothelial growth factor (VEGF) in these cells.

METHODS

TDI-human serum albumin (HSA) conjugates were prepared by a modification of Son's method. Fluorescein isothiocyanate-labelled dextran and transmission electron microscopy were used to evaluate the effects of TDI-HSA on HBE135-E6E7 permeability. RT-PCR and ELISA were used to evaluate VEGF gene expression and protein release from HBE135-E6E7 cells stimulated by TDI-HSA. A VEGF-neutralizing antibody was used in monolayer permeability experiments to determine the role of the VEGF pathway in this process.

RESULTS

TDI-HSA significantly increased the permeability coefficients of HBE135-E6E7 monolayers (P<0.01). TDI-HSA treatment significantly increased the expression of VEGF165 and VEGF189 genes (P<0.01). ELISA showed that TDI significantly induces VEGF release from HBE135-E6E7 cells. Cells treated with TDI-HSA and VEGF-neutralizing antibody had significantly lower permeability coefficients than cells treated with TDI-HSA only (P<0.01), but still significantly higher than control cells (P<0.01). Cells treated with TDI-HSA had fewer tight junctions (TJs) than control and HSA-treated cells, and addition of the anti-VEGF antibody did not restore the original number of TJs.

CONCLUSION

TDI increases the permeability of HBE cell monolayers, partly through a VEGF-mediated pathway. This suggests the importance of VEGF in TDI-induced pulmonary diseases, but shows that other pathways may be involved in the pathogenic process.