The epithelial barrier and immunoglobulin A system in allergy.

Airway and intestinal epithelial layers represent first-line physical barriers, playing a key role in mucosal immunity. Barrier dysfunction, characterized by alterations such as disruption of cell-cell apical junctions and aberrant epithelial responses, probably constitutes early and key events for chronic immune responses to environmental antigens in the skin and in the gut. For instance, barrier dysfunction drives Th2 responses in atopic disorders or eosinophilic esophagitis. Such epithelial impairment is also a salient feature of allergic asthma and growing evidence indicates that barrier alterations probably play a driving role in this disease. IgA has been identified as the most abundant immunoglobulin in mucosa, where it acts as an active barrier through immune exclusion of inhaled or ingested antigens or pathogens. Historically, it has been thought to represent the serum factor underlying reaginic activity before IgE was discovered. Despite several studies about regulation and major functions of IgA at mucosal surfaces, its role in allergy remains largely unclear. This review aims at summarizing findings about epithelial functions and IgA biology that are relevant to allergy, and to integrate the emerging concepts and the recent developments in mucosal immunology, and how these could translate to clinical observations in allergy.

Invasive pulmonary aspergillosis in patients with chronic obstructive pulmonary disease.

Aspergillus spp. cultured in specimens from the airways of chronic obstructive pulmonary disease (COPD) patients are frequently considered as a contaminant. However, growing evidence suggests that severe COPD patients are at higher risk of developing invasive pulmonary aspergillosis (IPA), although IPA incidence in this population is poorly documented. Some data report that COPD is the underlying disease in 1% of patients with IPA. Definitive diagnosis of IPA in COPD patients is often difficult as tissue samples are rarely obtained before death. Diagnosis is therefore usually based on a combination of clinical features, radiological findings (mostly thoracic computed tomography scans), microbiological results and, sometimes, serological information. Of 56 patients with IPA reported in the literature, 43 (77%) were receiving corticosteroids on admission to hospital. Breathlessness was always a feature of disease and excess wheezing was present in 79% of patients. Fever (>38 degrees C) was present in only 38.5%. Chest pain and haemoptysis were uncommon. Six out of 33 (18%) patients had tracheobronchitis observed during bronchoscopy. The median delay between symptoms and diagnosis was 8.5 days. The mortality rate was high: 53 out of 56 (95%) patients died despite invasive ventilation and antifungal treatment in 43 (77%) of them. In chronic obstructive pulmonary disease patients, invasive pulmonary aspergillosis currently carries a very poor prognosis. Outcome could perhaps be improved by more rapid diagnosis and prompt therapy with voriconazole.

Increased galectin-3 expression and intra-epithelial neutrophils in small airways in severe COPD.

Galectins-1 and -3 regulate epithelial proliferation/apoptosis and neutrophil activation, and are implicated in lung cancer and asthma. The role of galectins in chronic obstructive pulmonary disease (COPD), characterised by epithelial changes and neutrophil infiltration, remains unknown. In the present study, galectin-1 and -3 expression was assessed by immunohistology in the bronchial epithelium of lung specimens from eight severe COPD patients and compared with nine nonsmokers and six smokers without COPD. Findings were related to epithelial proliferation (Ki-67), tissue inflammation and lung function. Epithelial galectin-3 immunostaining was increased only in the small airways of COPD patients when compared with nonsmokers and smokers. In contrast, galectin-1 was only significantly increased in the small airways of the group of smokers. Ki-67+ epithelial cells and neutrophils were increased in the small airways of COPD patients when compared with smokers. Furthermore, intra-epithelial neutrophils correlated in the small airways with Ki-67+ epithelial cells and with the forced expiratory volume in one second/forced vital capacity ratio. However, no correlation was observed with galectin expression. The present study supports the hypothesis that distal airways represent an important site for detecting changes in chronic obstructive pulmonary disease. In patients with severe disease, an increased galectin-3 expression and neutrophil accumulation in the small airway epithelium was demonstrated, correlating with epithelial proliferation and airway obstruction.

[Secretory immunity of the airways]. / Immunité sécrétoire des voies respiratoires.

INTRODUCTION: Continuous exposure of the respiratory tract to inhaled particles and microbes implies the presence of effective defence mechanisms at a bronchial and alveolar level. STATE OF ART: Among the mechanisms involved secretory mucosal immunity contributes considerably to the defence of the bronchial tree. This immunity depends essentially on the active trans-epithelial transport of IgA involved in both innate non-specific and acquired specific immunity. Recently an IgA receptor has been identified on the surface of phagocytes including alveolar macrophages, establishing a link between alveolar and bronchial defences. PERSPECTIVES: The respiratory mucosa represents a crucial interface between the host and its environment, and should provide in the future a new target for the development of diagnostic and therapeutic tools. CONCLUSIONS: Beyond its function as an anatomical barrier the bronchial epithelium possesses a secretory activity that is essential for the protection of the lung. Despite a better understanding of mucosal immunity this secretory activity and in particular the part played by IgA remains to be elucidated.

Oxidative burst in lipopolysaccharide-activated human alveolar macrophages is inhibited by interleukin-9.

Interleukin (IL)-9 is known to regulate many cell types involved in T-helper type 2 responses classically associated with asthma, including B- and T-lymphocytes, mast cells, eosinophils and epithelial cells. In contrast, target cells mediating the effects of IL-9 in the lower respiratory tract remain to be identified. Therefore, the authors evaluated the activity of IL-9 on human alveolar macrophages (AM) from healthy volunteers. AM preincubated with IL-9 before lipopolysaccharide (LPS) stimulation exhibited a decreased oxidative burst, as previously shown with IL-4. The inhibitory effect of IL-9 was abolished by anti-hIL-9R alpha monoclonal antibody, and presence of IL-9 receptors on AM was demonstrated by immunofluorescence. Both IL-4 and IL-9 failed to modulate tumour necrosis factor-alpha, IL-8 and IL-10 release by LPS-stimulated AM. However, several observations suggested that IL-9 and IL-4 act through different mechanisms: 1) interferon-gamma antagonised the IL4- but not the IL-9-mediated inhibition of AM oxidative burst; 2) expression of CD14 was downregulated by IL-4 but not by IL-9 and 3) production of tumour growth factor-beta by activated AM was potentiated by IL-9 and not by IL4, and was required for the IL-9-mediated inhibition of AM oxidative burst. These observations provide additional information concerning the activity of interleukin-9 in the lung, related to inflammatory or fibrosing lung processes.

Acute exacerbation of chronic obstructive pulmonary disease and antibiotics: what studies are still needed?

The use of antibiotics in acute exacerbations of chronic bronchitis (AECBs) remains the subject of controversy despite considerable medical and socioeconomic implications. First, the contribution of bacterial infection to AECBs is difficult to assess in patients with chronic obstructive pulmonary disease (COPD) who are chronically colonized with respiratory pathogens. In addition, several studies suggest a major role of viral infections in AECBs. Secondly, it is unlikely that all COPD patients will benefit from antibiotics during AECBs. In particular, the benefit in mild COPD remains uncertain. Unfortunately, the number of studies complying with evidence-based medicine requirements is too small for definite recommendations in AECBs to be drawn up. Considering the impact of acute exacerbations of chronic bronchitis on chronic obstructive pulmonary disease patients, as well as the community, and the impact of antibiotic therapy on the development of bacterial resistance, there is an urgent need for the design of appropriate multicentric studies to define the usefulness of this type of treatment in acute exacerbations of chronic bronchitis.

Lung mucosal immunity: immunoglobulin-A revisited.

Mucosal defence mechanisms are critical in preventing colonization of the respiratory tract by pathogens and penetration of antigens through the epithelial barrier. Recent research has now illustrated the active contribution of the respiratory epithelium to the exclusion of microbes and particles, but also to the control of the inflammatory and immune responses in the airways and in the alveoli. Epithelial cells also mediate the active transport of polymeric immunoglobulin-A from the lamina propria to the airway lumen through the polymeric immunoglobulin receptor. The role of IgA in the defence of mucosal surfaces has now expanded from a limited role of scavenger of exogenous material to a broader protective function with potential applications in immunotherapy. In addition, the recent identification of receptors for IgA on the surface of blood leukocytes and alveolar macrophages provides an additional mechanism of interaction between the cellular and humoral immune systems at the level of the respiratory tract.

Reduced epithelial expression of secretory component in small airways correlates with airflow obstruction in chronic obstructive pulmonary disease.

The epithelial polymeric immunoglobulin receptor/transmembrane secretory component (pIgR/SC) transports into secretions polymeric immunoglobulin A (pIgA), which is considered the first line of defense of the respiratory tract. The present study, done with quantitative immunohistochemistry, evaluated epithelial expression of secretory component (SC) and Clara cell protein (CC16) and neutrophil infiltration into the airways of eight patients with severe chronic obstructive pulmonary disease (COPD) who were undergoing lung transplantation, as compared with these processes in six nonsmoking patients with pulmonary hypertension who were used as controls and in lung specimens from five smokers without chronic bronchitis. Staining for SC was significantly decreased in the COPD patients as compared with the controls, both in large (mean optical density [MOD]: 23.4 [range: 21.1 to 27.8] versus 42.2 [range: 28.2 to 49.3], p = 0.003) and in small airways (MOD: 30.8 [range: 20.3 to 39.4] versus 41.5 [range: 39.2 to 46.2], p = 0.003). SC expression in small airways correlated strongly with functional parameters such as FEV1 (Kendall's tau (K) = 0.76, p = 0.008), FVC (K = 0.64, p = 0.03), and midexpiratory flow at 50% of VC (MEF50) (K = 0.74, p = 0.01). The reduced expression of SC in large airways correlated with neutrophil infiltration in submucosal glands (K = -0.47, p = 0.03). Expression of CC16 in the bronchial epithelium of COPD patients was also significantly decreased as compared with that of controls, especially in small airways (MOD: 28.3 [range: 26.8 to 32.4] versus 45.8 [range: 40.7 to 56.0], p = 0.002), but no correlation was observed with lung function tests. In conclusion, this study shows that reduced expression of SC in airway epithelium is associated with airflow obstruction and neutrophil infiltration in severe COPD.

Secretory mucosal immune mechanisms.

Mucosal immune mechanisms in the airways are the first specific line of defense, protecting the body from pathogens. The respiratory epithelium actively transports locally produced dimeric IgA in the respiratory secretions by transcytosis, through the pIgR. S-IgA production therefore requires epithelial integrity. S-IgA at the epithelial level is active in several non-inflammatory pathways including intracellular neutralization of virus, antigen excretion, binding to bacterial adhesins. Local IgA production is regulated by various growth factors and cytokines of both epithelial and non-epithelial origin. The respiratory epithelium is thought to play a crucial role in this process. In addition, in chronic airway inflammation, IgA production demonstrates a correlation with eosinophil activation both in vitro and in vivo. While increased IgA and S-IgA production is reported in asthmatics, decreased SC production has been documented in CF and COPD patients, further impairing their local defense mechanisms.

Modulation of intracellular growth of Listeria monocytogenes in human enterocyte Caco-2 cells by interferon-gamma and interleukin-6: role of nitric oxide and cooperation with antibiotics.

The influence of interferon (IFN)-gamma and interleukin (IL)-6 on the intracellular growth of Listeria monocytogenes phagocytosed from the apical pole was examined in polarized Caco-2 cells. IFN-gamma (from the apical pole) and IL-6 (from the basolateral pole) considerably reduced the bacterial intracellular growth, an effect largely abolished by l-monomethyl arginine. Both cytokines caused overexpression of inducible nitric oxide synthase. IL-6, but not IFN-gamma, caused a partial restriction of L. monocytogenes in phagosomes and largely prevented the cytosolic forms from being surrounded by actin. Ampicillin was bacteriostatic in unstimulated cells but modestly bactericidal in cells treated with IFN-gamma and IL-6. Azithromycin (a macrolide) was fairly bactericidal and sparfloxacin (a fluoroquinolone) highly bactericidal in all situations. IFN-gamma and IL-6 may therefore be important determinants in the protection of epithelial cells from intracellular multiplication of L. monocytogenes. Ampicillin may fail in their absence, requiring the use of other antibiotics such as the fluoroquinolones.

Pulmonary effects of short-term exposure to low levels of toluene diisocyanate in asymptomatic subjects.

Isocyanates may be involved in the development of chronic obstructive airway disease among exposed workers. A short-term exposure to toluene diisocyanate (TDI) at concentrations near the permissible levels was investigated to examine whether there was an association with changes in pulmonary function tests and in potential markers of airway injury and inflammation in bronchial lavage (BL) and bronchoalveolar lavage (BAL). Seventeen subjects without respiratory symptoms (eight smokers and nine nonsmokers) were exposed once to ambient air and once to TDI (5 parts per billion (ppb) for 6 h followed by 20 ppb for 20 min) in a randomized, single-blind sequence. Pulmonary function tests were repeatedly assessed during exposure and BAL was performed 1 h after each exposure. Biochemical studies on lavage fluids included albumin, immunoglobulins, antiproteases (alpha2-macroglobulin and alpha1-proteinase inhibitor), potential indicators of epithelial cell function (secretory component and Clara cell protein), and cytokines (tumour necrosis factor-alpha, interleukin (IL)-4, IL-5, IL-6, and IL-8). Exposure to TDI caused a modest decrease in specific airway conductance (sGaw) (p=0.053) and in maximal expiratory flow at 25% of forced vital capacity (MEF25%) (p=0.015) when compared with ambient air. Exposure to TDI resulted in a slight increase in BAL albumin level (TDI: 26.4+/-12.5 versus air: 21.8+/-8.6 microg x mL(-1), p=0.044) and in BL alpha2-macroglobulin concentration (TDI: 0.07+/-0.061 versus air: 0.05+/-0.04 microg x mL(-1), p=0.021). This study suggests that exposure to low toluene disocyanate concentrations is associated with minimal but detectable changes in airway calibre and in epithelial barrier permeability. The pulmonary effects of long-term exposure to low levels of isocyanates require further investigation.

Mechanism of the intracellular killing and modulation of antibiotic susceptibility of Listeria monocytogenes in THP-1 macrophages activated by gamma interferon.

Listeria monocytogenes, a facultative intracellular pathogen, readily enters cells and multiplies in the cytosol after escaping from phagosomal vacuoles. Macrophages exposed to gamma interferon, one of the main cellular host defenses against Listeria, become nonpermissive for bacterial growth while containing Listeria in the phagosomes. Using the human myelomonocytic cell line THP-1, we show that the combination of L-monomethyl arginine and catalase restores bacterial growth without affecting the phagosomal containment of Listeria. A previous report (B. Scorneaux, Y. Ouadrhiri, G. Anzalone, and P. M. Tulkens, Antimicrob. Agents Chemother. 40:1225-1230, 1996) showed that intracellular Listeria was almost equally sensitive to ampicillin, azithromycin, and sparfloxacin in control cells but became insensitive to ampicillin and more sensitive to azithromycin and sparfloxacin in gamma interferon-treated cells. We show here that these modulations of antibiotic activity are largely counteracted by L-monomethyl arginine and catalase. In parallel, we show that gamma interferon enhances the cellular accumulation of azithromycin and sparfloxacin, an effect which is not reversed by addition of L-monomethyl arginine and catalase and which therefore cannot account for the increased activity of these antibiotics in gamma interferon-treated cells. We conclude that (i) the control exerted by gamma interferon on intracellular multiplication of Listeria in THP-1 macrophages is dependent on the production of nitric oxide and hydrogen peroxide; (ii) intracellular Listeria may become insensitive to ampicillin in macrophages exposed to gamma interferon because the increase in reactive oxygen and nitrogen intermediates already controls bacterial growth; and (iii) azithromycin and still more sparfloxacin cooperate efficiently with gamma interferon, one of the main cellular host defenses in Listeria infection.