Bronchial exudation of bulk plasma at allergen challenge in allergic asthma

Well-controlled mucosal exudation of plasma proteins in airways with intact and regenerating epithelium

Superficial, systemic microcirculations, distinct from the pulmonary circulation, supply the mucosae of human nasal and conducting airways. Non-injurious, inflammatory challenges of the airway mucosa cause extravasation without overt mucosal oedema. Instead, likely reflecting minimal increases in basolateral hydrostatic pressure, circulating proteins/peptides of all sizes are transmitted paracellularly across the juxtaposed epithelial barrier. Thus, small volumes of extravasated, unfiltered bulk plasma appear on the mucosal surface at nasal and bronchial sites of challenge. Importantly, the plasma-exuding mucosa maintains barrier integrity against penetrability of inhaled molecules. Thus, one-way epithelial penetrability, strict localization, and well-controlled magnitude and duration are basic characteristics of the plasma exudation response in human intact airways. In vivo experiments in human-like airways demonstrate that local plasma exudation is also induced by non-sanguineous removal of epithelium over an intact basement membrane. This humoral response results in a protective, repair-promoting barrier kept together by a fibrin-fibronectin net. Plasma exudation stops once the provisional barrier is substituted by a new cellular cover consisting of speedily migrating repair cells, which may emanate from all types of epithelial cells bordering the denuded patch. Exuded plasma on the surface of human airways reflects physiological microvascular-epithelial cooperation in first line mucosal defense at sites of intact and regenerating epithelium.

Early humoral defence: Contributing to confining COVID-19 to conducting airways?

Early airway responses to severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2) infection are of interest since they could decide whether coronavirus disease‐19 (COVID‐19) will proceed to life‐threatening pulmonary disease stages. Here I discuss endothelial‐epithelial co‐operative in vivo responses producing first‐line, humoral innate defence opportunities in human airways. The pseudostratified epithelium of human nasal and tracheobronchial airways are prime sites of exposure and infection by SARS‐CoV‐2. Just beneath the epithelium runs a profuse systemic microcirculation. Its post‐capillary venules respond conspicuously to mucosal challenges with autacoids, allergens and microbes, and to mere loss of epithelium. By active venular endothelial gap formation, followed by transient yielding of epithelial junctions, non‐sieved plasma macromolecules move from the microcirculation to the mucosal surface. Hence, plasma‐derived protein cascade systems and antimicrobial peptides would have opportunity to operate jointly on an unperturbed mucosal lining. Similarly, a plasma‐derived, dynamic gel protects sites of epithelial sloughing‐regeneration. Precision for this indiscriminate humoral molecular response lies in restricted location and well‐regulated duration of plasma exudation. Importantly, the endothelial responsiveness of the airway microcirculation differs distinctly from the relatively non‐responsive, low‐pressure pulmonary microcirculation that non‐specifically, almost irreversibly, leaks plasma in life‐threatening COVID‐19. Observations in humans of infections with rhinovirus, coronavirus 229E, and influenza A and B support a general but individually variable early occurrence of plasma exudation in human infected nasal and tracheobronchial airways. Investigations are warranted to elucidate roles of host‐ and drug‐induced airway plasma exudation in restriction of viral infection and, specifically, whether it contributes to variable disease responses following exposure to SARS‐CoV‐2.

Humoral First-Line Mucosal Innate Defence in vivo

Based on observations in vivo in guinea-pig and human airways, this review presents plasma exudation as non-sieved transmission of bulk plasma across an unperturbed mucosa that maintains its normal barrier functions. Several steps have led to the present understanding of plasma exudation as a non-injurious response to mucosal challenges. The implication of a swift appearance of all circulating multipotent protein systems (also including antimicrobial peptides that now are viewed as being exclusively produced by local cells) on challenged, but intact, mucosal surfaces cannot be trivial. Yet, involvement of early plasma exudation responses in innate mucosal immunology has dwelled below the radar. Admittedly, exploration of physiological plasma exudation mechanisms requires in vivo approaches beyond mouse studies. Plasma exudation also lacks the specificity that is a hallmark of biological revelations. These aspects separate plasma exudation from mainstream progress in immunology. The whole idea, presented here, thus competes with strong paradigms currently entertained in the accepted research front. The present focus on humoral innate immunity in vivo further deviates from most discussions, which concern cell-mediated innate defence. Indeed, plasma exudation has emerged as sole in vivo source of major mucosal defence proteins that now are viewed as local cell produce. In conclusion, this review highlights opportunities for complex actions and interactions provided by non-sieved plasma proteins/peptides on the surface of intact mucosal barriers in vivo.

Airways exudation of plasma macromolecules: Innate defense, epithelial regeneration, and asthma

This review discusses in vivo airway aspects of plasma exudation in relation to current views on epithelial permeability and epithelial regeneration in health and disease. Microvascular-epithelial exudation of bulk plasma proteins characteristically occurs in asthmatic patients, being especially pronounced in those with severe and exacerbating asthma. Healthy human and guinea pig airways challenged by noninjurious histamine-leukotriene–type autacoids also respond through prompt mucosal exudation of nonsieved plasma macromolecules. Contrary to current beliefs, epithelial permeability in the opposite direction (ie, absorption of inhaled molecules) has not been increased in patients with asthma and allergic rhinitis or in acutely exuding healthy airways. A slightly increased subepithelial hydrostatic pressure produces such unidirectional outward perviousness to macromolecules. Lack of increased absorption permeability in asthmatic patients can further be reconciled with occurrence of epithelial shedding, leaving small patches of denuded basement membrane. Counteracting escalating barrier breaks, plasma exudation promptly covers the denuded patches. Here it creates and sustains a biologically active barrier involving a neutrophil-rich, fibrin-fibronectin net. Furthermore, in the plasma-derived milieu, all epithelial cell types bordering the denuded patch dedifferentiate and migrate from all sides to cover the denuded basement membrane. However, this speedy epithelial regeneration can come at a cost. Guinea pig in vivo studies demonstrate that patches of epithelial denudation regeneration are exudation hot spots evoking asthma-like features, including recruitment/activation of granulocytes, proliferation of fibrocytes/smooth muscle cells, and basement membrane thickening. In conclusion, nonsieved plasma macromolecules can operate on the intact airway mucosa as potent components of first-line innate immunity responses. Exuded plasma also takes center stage in epithelial regeneration. When exaggerated, epithelial regeneration can contribute to the inception and development of asthma.

Increased vascular permeability precedes cellular inflammation as asthma control deteriorates

BACKGROUND

Airway microcirculation is abnormal in asthma but the role of vascular changes in asthma deteriorations remains poorly defined. We prospectively assessed the vascular changes accompanying worsening of asthma control by using an inhaled corticosteroid (ICS) dose-reduction model.

OBJECTIVES

To evaluate airway vascularity, vascular permeability and expression of vascular endothelial growth factor (VEGF) in early asthma deterioration induced by ICS back-titration.

METHODS

Twenty mild-to-moderate persistent symptomatic asthmatics on low-to-moderate ICS were recruited and treated with 4 weeks of high-dose fluticasone propionate (1000 microg/day) to achieve symptom control. This was followed by dose reduction to half of the pre-study doses for 4-8 weeks until the symptoms began to return. Endobronchial biopsy and bronchoalveolar lavage (BAL) samples were obtained after both treatment periods.

RESULTS

Vascularity as measured by the number and size of blood vessels, as well as VEGF expression did not change following ICS reduction. Even on high-dose ICS, perivascular albumin staining and BAL microalbumin levels in asthmatic subjects, as markers of permeability, were elevated when compared with normal subjects and both further increased significantly after ICS reduction. There was a significant association between changes in vascular leakiness and clinical deterioration. Increases in airway albumin correlated with previously reported increases in airway wall infiltration with T lymphocytes.

CONCLUSIONS

Our results suggest that airway vascular leakage is a major pathophysiologic feature of early asthma deterioration, occurring before recrudescence of cellular inflammation.

Experimental activation of mast cells and their pharmacological modulation

The activation of mast cells is of pivotal importance in the pathogenesis of allergic conditions. Mast cell activation can provoke rapid increases in microvascular permeability, induce bronchoconstriction after blood flow, stimulate the recruitment and activation of other inflammatory cells, and has come to be associated with the processes of tissue remodeling and fibrosis. Such changes may be mediated by the release of a range of potent mediators of inflammation: preformed in secretory granules, or newly generated, or both. There are major differences in the responsiveness to various stimuli and to pharmacological agents for mast cells from different body compartments. A method is presented here for the purification of mast cells from enzymatically dispersed human tissues. The methods described for the experimental activation of mast cells can be readily adapted to studies with cell lines or mast cells obtained through long-term culture.

Allergen-induced changes in airway responsiveness are not related to indices of airway edema

BACKGROUND

The mechanisms behind airway hyperresponsiveness in asthma are unknown. Airway wall edema has been proposed as one possible culprit of this phenomenon.

OBJECTIVE

To test the hypothesis that airway edema may be the cause of allergen-induced increases in airway responsiveness in asthma, this trial aimed at determining the relationship between allergen-induced changes in airway responsiveness to inhaled methacholine and indirect indices of edema, namely peripheral airway resistance and the levels of the plasma protein fibrinogen in bronchoalveolar lavage (BAL) fluids.

METHODS

Twenty-six atopic individuals with mild asthma were subjected to bronchoscopy at baseline and 28 hours after allergen inhalation. Before each bronchoscopy, methacholine bronchoprovocation was performed. During bronchoscopy, peripheral airway resistance measurements were obtained by wedged bronchoscopy. BAL fluids were analyzed for fibrinogen, as well as for eosinophilic cationic protein. Cytology was performed, and cytokine gene expression was assessed with competitive reverse transcriptase PCR from cell pellets.

RESULTS

A significant increase in airway responsiveness to methacholine was recorded after allergen, but this did not correlate with changes in peripheral airway resistance (which was not affected) or with BAL fibrinogen (which decreased after allergen). Other BAL outcomes confirmed that airway inflammation was produced and was characterized by a T(H)2 cytokine pattern.

CONCLUSIONS

Airway responsiveness in asthma increases after exposure to allergen in the absence of increased indirect indices of edema. The role of edema in this phenomenon should therefore be tested more vigorously.

Exudation of plasma and production of thromboxane in human bronchi after local bradykinin challenge

Plasma exudation has been suggested to be an important component of the inflammatory response in asthma. Bradykinin elicits many of the features of asthma, including bronchoconstriction, cough, plasma exudation and mucus secretion. In an attempt to quantify local plasma exudation, we have employed a novel low-trauma technique with the aim of challenging and lavaging a central part of the bronchial tree, by selecting a medium sized bronchus. A fibreoptic bronchoscopy was performed in non-smoking healthy volunteers. The instrument was placed proximally in the right upper lobe bronchus. A plastic catheter, equipped with an inflatable latex balloon, was inflated with air (2-4 cmH2O). A solution (100 microl of either two different concentrations of bradykinin: 0.09 and 0.9 mg ml(-1) or normal saline) was instilled through the catheter and distal to the balloon. Eight minutes later a lavage procedure with 10 ml of saline was performed through the catheter. The procedure was then repeated twice, with the other solutions, but from the lingular and middle lobe bronchi. All solutions were given in a blinded fashion, and two different studies were performed. Lavage concentrations of albumin and IgG were quantified as measurements of plasma exudation. In our first study we found that bradykinin challenge significantly increased concentrations of albumin and IgG. In study two, there was no numeric increase in plasma proteins after local bradykinin challenge, but the concentration of thromboxane was significantly increased in lavages from bradykinin-challenged bronchi. Thus, local bronchial administration of bradykinin has the capacity to induce exudation of large plasma macromolecules into the bronchial lumen, as well as local thromboxane production.

Antigen-specific IgE and IgA antibodies in bronchoalveolar lavage fluid are associated with stronger antigen-induced late phase reactions

The mechanism(s) leading to the development of late phase allergic reactions is (are) unknown. Previous studies have indicated that a relationship between serum IgE and the late phase exists. To explore the relationships between allergen-specific immunoglobulins in bronchoalveolar lavage (BAL) fluids and the magnitude of airflow limitation during the late phase response to inhaled allergen. Ragweed-specific IgE, IgA, secretory IgA (sIgA) and IgG were measured in BAL fluid and in the serum 1-5 weeks before whole lung antigen challenge with ragweed extract, in 16 ragweed allergic asthmatics. In addition, BAL and serum eosinophil cationic protein (ECP) and BAL fibrinogen levels were determined and BAL cells counted and differentiated. The latter procedures were repeated in a second BAL performed 24 h after the end of the ragweed challenge. After the challenge, lung function was monitored hourly for 8 h, to record the magnitude of airflow limitation. Ragweed-specific immunoglobulins were detected in 25% to 37.5% of BAL samples. Compared to the subjects with undetectable BAL fluid ragweed-specific IgE levels at baseline, those with detectable antibodies had stronger late phase reactions as determined by the nadir of FEV1 between hours 4 and 8 after the ragweed inhalation challenge (P = 0.0007). Allergen-induced changes in BAL ECP and fibrinogen levels were also higher in those subjects with detectable ragweed-specific IgE in baseline fluids (P = 0.03 and P = 0.005, respectively). Significant relationships between BAL antigen-specific IgA, serum ragweed-specific IgE and IgA and the late phase reaction were also found. The results of this study point towards the possibility that allergen-specific IgE and IgA may be independently involved in the pathogenesis of the late phase reaction. This notion merits further exploration.

Virus- and bradykinin-induced airway hyperresponsiveness in guinea pigs

The involvement of bradykinin in virus-induced airway hyperresponsiveness (AHR) in guinea pig airways in vivo was determined with the B(2)-receptor antagonist Hoe 140. The efficacy of Hoe 140 treatment was assessed through its effect on the bradykinin-induced (up to 2.5 microgram/100 g B.W. administered intravenously) decrease in blood pressure (BP). Hoe 140 (0.1 micromol/kg), administered subcutaneously twice a day for 5 d almost completely blocked bradykinin-induced changes in BP. Four days after parainfluenza-3 (PI-3) virus infection, guinea pigs showed AHR; excessive airway contraction was found with histamine-receptor stimulation. This hyperresponsiveness was completely inhibited by pretreatment with Hoe 140 (0.1 micromol/kg) administered subcutaneously twice a day for five consecutive days, starting 1 d before virus inoculation. Interestingly, nebulized delivery of bradykinin itself to captopril-treated animals induced an AHR comparable to that observed in virus-treated guinea pigs. Viral infection also caused influx of bronchoalveolar cells into the lungs. Both histologic examinations and lung lavage experiments showed that this cell influx could not be inhibited by pretreatment with Hoe 140. In summary, the results of the study show that bradykinin is involved in a cascade of events leading to AHR after a viral infection in guinea pigs, without affecting bronchoalveolar cell influx.

Allergen provocation augments endotoxin-induced nasal inflammation in subjects with atopic asthma

BACKGROUND

Recent epidemiologic and in vivo studies have suggested that inhaled endotoxin plays an important role in asthma pathogenesis.

OBJECTIVE

The present study examines the effect of nasal allergen provocation on subsequent endotoxin challenge in subjects with atopic asthma.

METHODS

By using a split-nose randomized crossover design, individual nares of 12 asthmatic subjects underwent challenge and lavage as follows. Immediately after a baseline nasal lavage, one nares received normal saline, and the other received dust mite antigen. Four hours later, both nares were exposed to either saline or endotoxin. Dust mite antigen (Dermatophagoides farinae) and endotoxin (Escherichia coli 026:B6) doses were 100 AU and 1000 ng, respectively. Postchallenge lavages were done at 8 and 24 hours after the initial challenge. The subjects then returned a minimum of 3 weeks later for crossover to the study arm. Nasal lavage fluid was analyzed for total and differential cell counts, IL-8, IL-6, intercellular adhesion molecule 1, GM-CSF, eosinophil cationic protein, myeloperoxidase, and soluble CD14.

RESULTS

A significant increase in the total inflammatory cell count was seen at 8 hours for the dust mite/endotoxin exposure compared with the saline/saline and saline/endotoxin exposures. Differential cell counts revealed a similar neutrophilic and eosinophilic inflammation for the dust mite/endotoxin exposure at 8 hours.

CONCLUSIONS

These data demonstrate an interaction between allergen and endotoxin exposure in asthmatic subjects, suggesting that a prior allergen challenge significantly augments the endotoxin-induced inflammation. Moreover, these data provide further evidence that concomitant exposure to allergen and endotoxin may be an important factor in asthma pathogenesis.

Segmental allergen challenge induces plasma protein leakage into the airways of asthmatic subjects at 4 hours but not at 5 minutes after challenge

We have investigated whether increased plasma protein leakage is present early after segmental allergen challenge in allergic asthma. Seven asthmatic subjects with mild allergy (AA group) and 5 non-asthmatic subjects with allergy (ANA group) were challenged with allergen doses based on similar early skin reactions; 5 healthy control subjects without allergy (C group) were challenged with the highest dose applied in the subjects with allergy. Bronchoalveolar lavage (BAL) fluid was obtained before, at 5 minutes after, and at 4 hours after challenge from different segments. Levels of albumin (Alb) and alpha2-macroglobulin (A2M) were measured in BAL fluid and serum. In addition, we calculated the relative coefficient of excretion as follows: RCE = ((A2M in BAL fluid)/(A2M in serum))/((Alb in BAL fluid)/(Alb in serum)). Also, levels of tryptase as a marker of mast cell activation and tumor necrosis factor-alpha (TNF-alpha), a possible inducer of plasma protein leakage, were determined. At 5 minutes after challenge, in none of the groups was a significant change found in the parameters for protein leakage. Levels of tryptase were increased in the subjects with allergy at 5 minutes after challenge only (P = .004). At 4 hours after challenge, levels of Alb (P = .03) and A2M (P = .04) and the RCE (P = .04) were increased in the AA group only. At 4 hours, levels of TNF-alpha were increased, with no significant differences among the three groups. In the asthmatic subjects with allergy, levels of TNF-alpha correlated with levels of Alb (r = 0.85, P = .02). In conclusion, at 4 hours after segmental allergen challenge, plasma protein leakage was increased in the asthmatic subjects only. The increase in levels of TNF-alpha in all groups indicates that the presence of TNF-alpha alone was not sufficient to cause plasma protein leakage within 4 hours after allergen challenge. Our results confirm the concept that plasma exudation after allergen exposure is a pathophysiologic event associated with asthma.

A double-blind study on the effect of inhaled corticosteroids on plasma protein exudation in asthma

Plasma protein exudation into the airways is an important pathophysiological event in asthma. The effect of 12 wk of treatment with inhaled fluticasone propionate (FP; 250 microgram twice a day) or salbutamol (Sb; 400 microgram twice a day) on plasma protein leakage was compared in a double-blind, randomized parallel-group study of 30 patients with asthma. Primary outcomes were plasma protein leakage and size selectivity of the blood-airway lumen barrier, cell differentials in BAL fluid, and bronchial responsiveness to histamine (PC20histamine). Two independent procedures to account for the effect of variable dilution of BAL on the levels of albumin (Alb) and alpha2-macroglobulin (A2M) in BAL fluid consisted of correction based on urea levels and on the application of the relative coefficient of excretion [RCE = ([A2M] in BAL fluid/[A2M] in serum)/([Alb] in BAL fluid/[Alb] in serum)]. In the FP group a significant decrease was found in the A2M level and the RCE, and in the percentage of eosinophils in BAL fluid. The PC20histamine increased significantly (mean increase, 2.4 doubling doses), whereas PC20histamine decreased in the Sb group. Differences between groups were significant except for the decrease in eosinophils. We conclude that 12 wk of FP (250 microgram twice a day) decreased the permeability of the blood-airway lumen barrier, in particular for high molecular weight proteins.

Contribution of plasma-derived molecules to mucosal immune defence, disease and repair in the airways

This review discusses recent observations, in health and disease, on the release and distribution of plasma-derived molecules in the airway mucosa. Briefly, the new data on airway mucosal exudation mechanisms suggest that the protein systems of plasma contribute significantly to the mucosal biology, not only in injured airways but also in such mildly inflamed airways that lack oedema and exhibit no sign of epithelial derangement. Plasma as a source of pluripotent growth factor, adhesive, leucocyte-activating, etc., molecules may deserve a prominent position in schemes that claim to illustrate immunological and inflammatory mechanisms of the airway mucosa in vivo.

Effects of inhaled histamine, methacholine and capsaicin on sputum levels of alpha 2-macroglobulin

BACKGROUND

Plasma exudation-derived proteins and peptides contribute significantly to inflammation in the airway mucosa in vivo. In the guinea pig trachea both histamine and the neurogenic stimulant capsaicin produce acute mucosal tissue distribution and luminal entry of bulk plasma, whereas cholinergic agonists fail to produce this effect. Of these agents, only histamine induces mucosal exudation of plasma in human nasal airways. The exudative effect of the above agents on human bronchi remains unknown.

METHODS

The bronchial exudative responses to inhalation of histamine, methacholine, and capsaicin were examined in two groups of healthy volunteers. Sputum was induced on three occasions in each study group by inhalation of hypertonic saline (4.5%) given as an aerosol for 40 minutes using an ultrasonic nebuliser. The second and third occasions were preceded by histamine and capsaicin challenges in the first study group, and by histamine and methacholine challenges in the second study group. Histamine and methacholine were given in cumulative doses (total doses 3160 micrograms, respectively) or until a 20% reduction in forced expiratory volume in one second (FEV1) was achieved. Cumulative doses of capsaicin were inhaled until coughing prevented the subjects from drawing a full breath. Sputum levels of alpha 2-macroglobulin (729 kDa) were measured as an index of mucosal exudation of bulk plasma.

RESULTS

Histamine increased mean (SE) sputum levels of alpha 2-macroglobulin from 2.72 (1.01) micrograms/ml (95% confidence interval (CI) 0.49 to 4.94) to 18.38 (8.03) micrograms/ml (95% CI 0.49 to 36.27) in the first group, and from 1.66 (0.84) micrograms/ml (95% CI -0.18 to 3.49) to 9.43 (3.63) micrograms/ml (95% CI 1.59 to 17.27) in the second group. In contrast, capsaicin evoked no exudation (sputum levels of alpha 2-macroglobulin 1.21 (0.28) micrograms/ml (95% CI 0.59 to 1.83)) and methacholine produced a minor increase in sputum levels of alpha 2-macroglobulin (2.90 (0.92) micrograms/ml (95% CI 0.90 to 4.89)).

CONCLUSIONS

These results indicate that histamine is a useful agent for studying bronchial exudative responsiveness in man and that exudative effects are only of marginal importance in the cough and bronchoconstriction produced by capsaicin and methacholine.

Lactoferrin, a potent tryptase inhibitor, abolishes late-phase airway responses in allergic sheep

Tryptase, a serine protease released exclusively from activated mast cells, has been implicated as a potential causative agent in asthma. Enzymatically active tryptase is comprised of four subunits, and heparin stabilizes the associated tetramer. Lactoferrin, a cationic protein released from activated neutrophils, binds tightly to heparin, therefore we investigated lactoferrin as an inhibitor of tryptase and found that it is both a potent (Ki' is 24 nM) and selective inhibitor. Size exclusion chromatography studies revealed that lactoferrin disrupted the quaternary structure of active tryptase. Lactoferrin was tested in an allergic sheep model of asthma; aerosolized lactoferrin (10 mg in 3 ml phosphate-buffered saline, 0.5 h before as well as 4 and 24 h after inhalation challenge by Ascaris suum) abolished both late-phase bronchoconstriction (no significant increase in specific lung resistance 4 to 8 h following provocation, p < 0.05 versus vehicle treatment) and airway hyperresponsiveness (no detectable increase in airway sensitivity to carbachol challenge 24 h after antigen challenge, p < 0.05 versus vehicle). These data suggest tryptase involvement in both late-phase bronchoconstriction and airway hyperreactivity and furthermore suggest that a physiological function of neutrophil lactoferrin is the inhibition of tryptase released from mast cells.

Binding of Aspergillus fumigatus spores to lung epithelial cells and basement membrane proteins: relevance to the asthmatic lung

BACKGROUND

Aspergillus fumigatus is an opportunistic pathogen to which asthmatic subjects are particularly susceptible. The ability of spores of A fumigatus to bind to pulmonary cells and basement membrane proteins was investigated to determine the mechanisms involved in this susceptibility.

METHODS

Cells of the A549 pulmonary epithelial cell line or purified basement membrane proteins were immobilised on the wells of microtitre plates. They were then exposed to spores of A fumigatus in suspension, with or without various pretreatments of the spores, cells, and proteins. Adherent spores were counted by light microscopy.

RESULTS

Spores of A fumigatus bound in a concentration dependent manner to A549 epithelial cells and pretreatment of cells with interferon gamma (2500 units/ml) caused a significant doubling of spore binding. Binding of spores to A549 cells was inhibited by about a third by pre-incubation of the spores with fibrinogen (100 micrograms/ml). Spores bound specifically to extracellular matrix (ECM) components laid down by A549 cells, and pretreatment of the ECM components with hydrogen peroxide (25-80 microM) enhanced spore binding by approximately one third. They also bound specifically and in a saturable manner to purified fibrinogen, fibronectin, laminin, type I collagen, and type IV collagen. Pre-incubation of spores with Arg-Gly-Asp tripeptide (RGD; 50-200 micrograms/ ml) inhibited binding to fibronectin and type I collagen by 50%.

CONCLUSIONS

This study suggests that the presence of activated epithelial cells and the exposure of basement membrane that occurs in asthma, together with oxidant stress, may facilitate the colonisation of the asthmatic lung by A fumigatus. The RGD sequence may be involved in spore binding to some ECM proteins. Free fibrinogen may protect against binding of A fumigatus spores to the pulmonary epithelium.

Effect of eosinophil peroxidase on airway epithelial permeability in the guinea pig

Increased numbers of eosinophils and increased concentrations of plasma proteins have been found in the airways of patients with mild asthma. We used an intact guinea pig trachea model to investigate the role of eosinophil peroxidase (EPO) in altering the function of the airway epithelial barrier. EPO in the presence of hydrogen peroxide (H(2)O(2)) and bromide (Br(-)) catalyzes the production of hypobromous acid (HOBr), which is felt to have a toxic effect on airway epithelial cells. An intact guinea pig trachea was mounted on an apparatus in a way that would allow the tracheal epithelium to be exposed to different solutions. Following these exposures, a test solution containing (14)C-sucrose (S), (3)H-inulin (I), and FITC-dextran-20 (D) was placed in the tracheal lumen and positioned in the center of the segment for 90 minutes. Flux of these molecules across the epithelial barrier into a bath was measured, and the permeability (P) was calculated for each molecule to quantify epithelial barrier function. Light and electron micrographic studies were performed to assess cellular damage. We found that there was a dose response to EPO (in the presence of fixed amounts of H(2)(O)(2) and Br(-)). EPO at 7.3 x 10(-7) M caused no increase in P over controls (Ringer's solution alone) for S, I, or D (P> 0.05), whereas EPO at 2.7 x 10(-6) M caused a significant increase in P over controls (P = 0.008) for all test molecules. Light and electron micrographs of the latter tracheas showed no evidence of microscopic changes despite the increased P. Further testing verified that the increase in permeability was caused by the EPO catalyzed reaction and not the individual substrates themselves, and that the reaction was inhibited by a peroxidase inhibitor. We conclude that EPO can alter the barrier function of the airway epithelium before gross cellular damage becomes visible. We hypothesize that changes in the tight junctions are responsible for the alteration in the barrier function of the airway epithelium and that this may play an important role in the pathophysiology of mild asthma.

Bronchoconstriction and airway hyperresponsiveness after ovalbumin inhalation in sensitized mice

To investigate the mechanisms underlying airway hyperresponsiveness a murine model was developed with several important characteristics of human allergic asthma. Mice were intraperitoneally sensitized with ovalbumin and after 4 weeks challenge via an ovalbumin aerosol. After aerosol, lung function was evaluated with a non-invasive forced oscillation technique. The amount of mucosal exudation into the airway lumen and the presence of mast cell degranulation was determined. Tracheal responsiveness was measured at several time points after challenge. At these time points also bronchoalveolar lavage and histology were performed. Sensitization induced high antigen-specific IgE levels in serum. Inhalation of ovalbumin in sensitized mice induced an immediate but no late bronchoconstrictive response. During this immediate phase, respiratory resistance was increased (54%). Within the first hour after ovalbumin inhalation increased mucosal exudation and mast cell degranulation were observed. At 12 and 24 h after ovalbumin challenge, mice showed tracheal hyperresponsiveness (29% and 34%, respectively). However, no apparent inflammation was found in the lungs or bronchoalveolar lavage. From these results it can be concluded that hyperresponsiveness can develop via mechanisms independent of an inflammatory infiltrate. Since mast cell degranulation occurred after ovalbumin exposure, we hypothesize that mast cells are involved in the induction of airway hyperresponsiveness in this model.

Exudative hyperresponsiveness of the airway microcirculation in seasonal allergic rhinitis

BACKGROUND

Mucosal exudation of plasma is a non-injurious, physiological response of the airway microcirculation to different inflammatory processes. The exudative response is similar in the nose and bronchi and exudation occurs in both allergic asthma and rhinitis. The exudative response is a specific end-organ function of the mucosal microcirculation that may be altered in airway diseases.

OBJECTIVE

This study examines the hypothesis of altered responsiveness of the superficial airway microcirculation to vascular permeability-increasing challenges in sustained allergic inflammation.

METHODS

Fourteen patients with birch-pollen induced allergic rhinitis were studied for 7 weeks during a Swedish birch-pollen season. Nasal symptoms (itching, sneezing, blockage, and discharge) were recorded and the occurrence of pollen was determined. The plasma exudation response was examined by topical histamine challenges at the end (May) and well out of (December) the season. Challenge and lavage were carried out concomitantly using a 'nasal pool'-device. The unilateral nasal cavity was filled for consecutive 10 minute periods with saline and two concentrations of histamine (80 micrograms/mL and 400 micrograms/mL). The lavage fluid levels of different-sized plasma proteins (albumin-66,000 D, fibrinogen-340,000 D, and alpha 2-macroglobulin-725,000 D) were determined.

RESULTS

The pollen season was mild resulting in only minor nasal symptoms. Histamine produced exudation of all plasma proteins across the microvascular epithelial barriers with particularly strong correlation between the levels of albumin and alpha 2-macroglobulin (r = 0.98; P < 0.001). The exudative response to histamine was concentration-dependent (P < 0.05) and, furthermore, it was significantly greater late into the season compared with outside the pollen season (albumin: P < 0.05, fibrinogen; P < 0.05, alpha 2-macroglobulin: P < 0.01).

CONCLUSION

We conclude that histamine produced concentration-dependent nasal airway exudation of bulk plasma in subjects with seasonal rhinitis and that this response is abnormally great during the pollen season. Whether angiogenesis or increased responsiveness of the microvascular endothelium may explain this phenomenon now remains unknown. We suggest that a microvascular exudative hyperresponsiveness may characterize allergic airway disease.

Topical nitroprusside may reduce histamine-induced plasma exudation in human nasal airways

Mucosal exudation of nonsieved bulk plasma is a key feature of airway defense and inflammation. We have previously observed in guinea pig tracheobronchial airways that endogenous nitric oxide (NO) of the mucosa may tonically suppress the permeability of the subepithelial microcirculation, and that topical administration of the NO donor nitroprusside may reduce plasma exudation responses. The present study examines whether nitroprusside affects histamine-induced mucosal exudation of plasma in the human nasal airway. In a dose-finding tolerability experiment, using changes in nasal patency as response, placebo and nitroprusside (1.2 and 3.6 mg per nasal cavity) were applied on the mucosal surface with a nasal-spray device. Nasal peak expiratory flow (PEF) rates were measured before the application and thereafter every third minute for 15 min. Nitroprusside produced a dose-dependent decrease in nasal PEF rates compared to placebo. Placebo or nitroprusside (7.2 mg) was then given to the right nasal cavity, followed 3 min later by challenge with saline or histamine (600 micrograms). The drug and the challenge were both applied with a nasal-spray device. With a nasal pool-device, the same large part of the nasal mucosal surface was lavaged before and after the treatment/challenge. The lavage fluid levels of alpha 2-macroglobulin were measured as an index of mucosal exudation of bulk plasma. The histamine-induced lavage fluid level of alpha 2-macroglobulin was significantly higher after treatment with placebo than with nitroprusside. The present data indicate that nitroprusside may have antiexudative effects in human airways. Hence, unlike other microvascular permeability active agents, this pharmacologic principle may be active in both guinea pig and human airways.

Airway wall liquid. Sources and role as an amplifier of bronchoconstriction

Airway liquid balance in asthma is largely determined by active plasma exudation from tracheobronchial microvessels into the interstitial spaces of the mucosa, submucosa, and/or adventitia, and from there into the luminal space. This exuded plasma is rich in proteins and cell mediators capable of initiating several events, including activation of sensory neural pathways, plasma protein cleavage, inflammatory cell recruitment, and inhibition of surfactant function. It can act to amplify the bronchoconstrictor response by increasing mucosal and/or submucosal thickness, altering mechanical properties of airway wall compartments, decoupling the airway wall from parenchymal attachments, filling airway interstices, and by creating an additional inward force because of surface tension, resulting in further airway constriction and possibly closure and thereby significantly increasing airways resistance.

Effects of topical capsaicin in seasonal allergic rhinitis

BACKGROUND

Mucosal exudation (luminal entry) of bulk plasma is a key feature of airway defence and inflammation. In guinea pig and rat airways this response is readily produced by neurogenic irritants, notably capsaicin. Thus "neurogenic airway inflammation" has become an established concept. The present study examines whether capsaicin also produces mucosal exudation of plasma in human nasal airways both in health and disease (seasonal allergic rhinitis).

METHODS

Pain-producing concentrations of capsaicin (30-300 ng/ml) were applied to the nasal mucosal surface both before and late into the pollen season. Levels of albumin in nasal lavage fluid were measured as an index of mucosal exudation of plasma. In a separate group of patients with seasonal allergic rhinitis nasal challenge with an exudative concentration of histamine was carried out before the birch pollen season and concentrations of albumin in lavage fluid were measured.

RESULTS

Pollen counts and symptom scores revealed a mild pollen season. Capsaicin produced considerable nasal pain and this response was augmented late into the season when capsaicin also produced nasal blockage. However, capsaicin failed to produce any mucosal exudation of plasma either before or late into the pollen season. The exudative effect of histamine was confirmed.

CONCLUSIONS

The augmented pain response to capsaicin suggests that a sensory nerve hyperresponsiveness may characterise allergic airways disease. In contrast to the effects on animal airways, capsaicin failed to produce mucosal exudation of plasma in the human nasal airway. The animal based neurogenic inflammation concept is therefore not valid for the human nasal airway, not even in inflamed airways when a neural hyperresponsiveness has developed.

Mechanisms of nasal hyper-reactivity

Hyper-reactivity to non-specific challenges has been considered a hallmark of asthma and is defined as an abnormal responsiveness of the bronchial airways to a variety of provocative agents. The mechanisms underlying hyper-reactivity in the upper and lower airways are not known. By using the nose to study the inflammatory response possible abnormalities can be investigated carefully and pathophysiology of specific airway hyper-reactivities can be better understood. Other factors than merely constriction of the bronchial smooth muscles can cause narrowing of the free lumen to airflow. Functionally different and very distinct mucosal end-organ reactivities may also be increased. If these reactivities can be well assessed, specific airway hyper-reactivity can be defined. In the present report, specific mucosal end-organ hyper-reactivities in the allergic nasal mucosa are presented. Certain widespread hypotheses, such as the role of the eosinophil and the "increased absorption permeability theory", are disputed.

Analysis of cellular and biochemical constituents of induced sputum after allergen challenge: a method for studying allergic airway inflammation

To determine whether analysis of the constituents of induced sputum permits detection of changes provoked by aerosolized antigen challenge, we performed sputum induction (20-minute inhalation of aerosolized 3% saline solution) before and after aerosolized allergen challenge in eight subjects with asthma. Total cell counts and cell differentials of nonsquamous cells in induced sputum samples were determined after the samples were homogenized in dithiothreitol. Centrifugation of the entire homogenized sputum sample yielded supernatant that could be analyzed for biochemical constituents. We found that the median percentage of eosinophils and neutrophils in induced sputum samples was significantly higher 4 hours after allergen challenge neutrophils in induced sputum samples was significantly higher 4 hours after allergen challenge than at baseline (12% vs 0.5%, p < 0.05; 30.5% vs 7.5%, p < 0.05) and remained high 24 hours after challenge. Median levels of eosinophil cationic protein and histamine in induced sputum supernatants were significantly higher 4 hours after challenge than at baseline (151.3 vs 39.8 ng/ml, p < 0.05; 19.4 vs 8.8 micrograms, p < 0.05) and remained significantly higher 24 hours after challenge. Tryptase was detectable in sputum from seven of the subjects, and in these subjects, we found a trend toward an increase in median tryptase levels 4 hours after allergen challenge (4.4 vs 2.2 U/L, p = 0.09). We conclude that analysis of induced sputum after aerosolized allergen challenge reveals changes in inflammatory cells and markers similar to those reported in bronchoalveolar lavage fluid and that sputum induction is a useful noninvasive method for studying allergic airway inflammation in asthma.

Glucocorticoid-induced attenuation of mucosal exudation of fibrinogen and bradykinins in seasonal allergic rhinitis

The mucosal plasma exudate with its proteins, enzymes, derived peptides, and matrix molecules is an important factor in inflammatory airway diseases. This study investigated whether topical glucocorticosteroid treatment influences mucosal exudation of bulk plasma (fibrinogen) and the generation of plasma-derived mediators (bradykinins) in seasonal allergic rhinitis. Twenty-two patients with birch-pollen-induced allergic rhinitis participated in a double-blind, randomized, placebo-controlled study during the birch pollen season in 1989. After a 2-week run-in period, the participants received treatment with budesonide (200 micrograms per nasal cavity and day) or placebo. The patients kept a diary to record their daily nasal symptoms (itching, sneezing, nasal blockage, and secretion). The amount of birch pollen in the air was determined with the aid of a Burkhard pollen trap. A nasal lavage was performed once a week, and the levels of bradykinins and fibrinogen were determined in the lavage fluid samples. The birch pollen season was very mild, resulting in only minor nasal symptoms. In spite of the low pollen exposure, treatment with budesonide reduced the lavage fluid levels of both bradykinins and fibrinogen. The present results show that topical glucocorticosteroid treatment attenuates plasma exudation and the generation of plasma-derived mediators in seasonal allergic rhinitis. This action may not result from simple vascular antipermeability effects of the drug but may rather reflect the anti-inflammatory efficacy of topical glucocorticoids in the airway mucosa.

Microvascular exudative hyperresponsiveness in human coronavirus-induced common cold

BACKGROUND

The inflammatory response of the airway microcirculation in rhinitis and asthma may be recorded as luminal entry of plasma macromolecules (mucosal exudation). This study examines the exudative responsiveness of the subepithelial microvessels in subjects with and without common cold after inoculation with coronavirus.

METHODS

The airway mucosa was exposed to exudative concentrations of histamine (40 and 400 micrograms/ml) before and six days after inoculation. To assess whether mucosal penetration of a topically applied agent was altered, nasal absorption of chromium-51 labelled ethylene diamine tetraacetic acid (51Cr-EDTA, MW 372) was also examined. A nasal pool technique kept the challenge and tracer solutes in contact with the same ipsilateral mucosal surface. Concentrations of albumin in lavage fluids were measured as an index of mucosal exudation of plasma. Nasal absorption of 51Cr-EDTA was determined by the cumulated 24 hour urinary excretion of radioactivity.

RESULTS

Nine subjects developed common cold after coronavirus inoculation and 10 remained healthy. Histamine produced concentration dependent mucosal exudation of plasma in all subjects before and after coronavirus inoculation. In subjects with common cold, however, the histamine-induced mucosal exudation was significantly augmented compared with the group without common cold. This exudative hyperresponsiveness is not explained by an increased baseline exudation because the lavage regimen used produced comparably low baseline exudation in both groups of subjects, nor is it explained by an increased penetration of topical histamine because the ability of the nasal mucosa to absorb 51Cr-EDTA was not significantly increased in the subjects with common cold.

CONCLUSIONS

An increased proclivity of the airway subepithelial microcirculation to respond with plasma exudation develops during coronavirus-induced common cold. This specific exudative hyperresponsiveness may be a feature of inflammatory airway diseases.

Histamine-induced airway mucosal exudation of bulk plasma and plasma-derived mediators is not inhibited by intravenous bronchodilators

Experimental data suggest the possibility that common bronchodilators, such as the xanthines and beta 2-adrenoceptor agonists, may produce microvascular anti-permeability effects in the subepithelial microcirculation of the airways. In this study, we have examined the effect of bronchodilators given intravenously on exudation of different-sized plasma proteins (albumin and fibrinogen) and the generation of plasma-derived peptides (bradykinins) in human nasal airways challenged with histamine. In a double-blind, crossover, placebo-controlled and randomised trial, 12 normal volunteers were given i.v.infusions of terbutaline sulphate, theophylline and enprofylline to produce therapeutic drug levels. The effect of topical nasal provocation with histamine was closely followed by frequently nasal lavage with saline. The lavage fluid levels of albumin, fibrinogen and bradykinins increased significantly after each histamine provocation. The ratio of albumin-to-fibrinogen in plasma and the lavage fluid was 24 and 56, respectively, indicating that topical histamine provocation induced a largely non-sieved flux of macromolecules across the endothelial-epithelial barriers. The systemically administered drugs did not affect the nasal symptoms (sneezing, secretion and blockage), nor did they significantly reduce the levels of plasma proteins and plasma-derived mediators in the nasal lavage fluids. The present data suggest that systemic xanthines and beta 2-adrenoceptor agonists, at clinically employed plasma levels, may not affect the microvascular (and epithelial) exudative permeability and the bradykinin forming capacity of human airways.

Mucosal exudation of fibrinogen in coronavirus-induced common colds

We studied the mucosal exudation of plasma in relation to pathophysiological events during an induced common cold. Coronavirus 229E was inoculated nasally in 20 healthy volunteers under controlled conditions. Ten volunteers developed the common cold, determined by symptom scores and serology. The bulk plasma exudate was monitored, using fibrinogen (MW 340 kD) in nasal lavage fluids as an endogenous marker. Following inoculation, anterior rhinoscopy and objective registrations of nasal mucosal temperature, nasal discharge weight, and nasal blockage index by peak expiratory air flow, were followed twice daily for 6 days. Mucosal plasma exudation, as assessed by fibrinogen in lavage fluids, increased hundredfold after virus inoculation, concomitantly with the subjective symptoms and objective physiological changes. We propose that this exudation reflects the degree of subepithelial inflammation, and suggests that plasma bulk exudate, including all potent plasma protein systems may be involved in the resolution of acute viral rhinitis--common cold.

Effects of nicotine on the human nasal mucosa

BACKGROUND

Topical application of nicotine and stimulation of tachykinin containing sensory nerves have been shown to produce mucosal exudation of plasma and derangement of the epithelial lining in guinea pig and rat airways. If this occurred in man these effects might contribute to the pathogenesis of airway disease. This study, performed in healthy volunteers without atopy, examined whether nicotine affects the plasma exudation response and the mucosal absorption permeability of the human nasal airway.

METHODS

The acute effects of increasing topical doses of nicotine (0.08-2.0 mg) were examined (n = 8) on nasal symptoms (pain), mucosal exudation of plasma (albumin), mucosal secretion of mucin (fucose), and mucosal exudative responsiveness (histamine induced mucosal exudation of albumin). A separate placebo controlled study was carried out to determine whether frequent applications of the high dose of nicotine (2.0 mg given eight times daily for nine days) had any deleterious effects on the airway mucosa detectable as altered responses to histamine challenge. Both mucosal exudation of plasma (n = 12) and mucosal absorption of chromium-51 labelled EDTA (n = 8) were thus examined in nasal airways exposed to both nicotine and histamine.

RESULTS

Nicotine caused nasal pain and produced dose dependent mucosal secretion of fucose but failed to produce any mucosal exudation of albumin. The exudative responsiveness to histamine was, indeed, decreased when the challenge was performed immediately after administration of acute doses of nicotine, whereas the responsiveness was unaffected when histamine challenges were carried out during prolonged treatment with nicotine. The nasal mucosal absorption of 51Cr-EDTA in the presence of histamine did not differ between subjects receiving either placebo or nicotine treatment for nine days.

CONCLUSIONS

The results indicate that nicotine applied to the human airway mucosa produces pain and secretion of mucin, but inflammatory changes such as mucosal exudation of plasma and epithelial disruption may not be produced. Neurogenic inflammatory responses, which are so readily produced in guinea pig and rat airways, may not occur in human airways.

Plasma exudation and solute absorption across the airway mucosa

The airway mucosa responds to inflammatory provocations with bulk exudation of plasma into the airway tissue (vascular exudation) and lumen (mucosal exudation). The intensity and time course of the exudative response can be relevantly examined by sampling and analysing airway surface liquids, because the luminal entry of plasma proteins/tracers promptly and quantitatively reflects the exudative response of the airways. The process of mucosal exudation of plasma is a prominent feature of airway inflammation and has been demonstrated in rhinitis, asthma, and bronchitis. Inflammatory mediators and allergen produce mucosal exudation of plasma into the airway lumen (outward permeability) whereas the solute absorption across the mucosa (inward permeability) is unaffected. Hence, in contrast to current views, we have demonstrated that in airway inflammation the solute absorption across the airway mucosa is not increased. The findings suggest the plasma exudation response also as a first line respiratory mucosal defence, allowing potent plasma protein systems to appear on an airway mucosa functionally intact as a barrier toward undue luminal material. Our data on plasma exudation and solute absorption across the mucosa of upper and lower airways further suggest the human nasal airways as a model relevant also for the tracheobronchial airways.

The action of beta-receptors on microvascular endothelium or: is airways plasma exudation inhibited by beta-agonists?

The connections between airway inflammation, plasma exudation and a possible anti-exudative action of beta-agonists are discussed. Asthma involves a response to inflammatory mediators which results in increased microvascular leakage with exudation of plasma into the airways. This plasma exudation is a specific inflammatory response and also a general response in the sense that it is independent of the mechanism sustaining the inflammation. Thus, mucosal exudation of plasma may reflect the subepithelial airway inflammatory process, irrespective of its genesis. In addition, the exudate itself contains many substances which may themselves promote inflammation and be major factors in producing and sustaining acute and chronic airway inflammation. This suggests that drug therapies should be aimed at reducing plasma exudation. Studies in guinea pigs have shown that a number of drugs such as xanthines, cromoglycates, glucocorticoids and beta-agonists may inhibit this exudation, but the effect seems to be attenuated in human mucosal tissue. beta-Agonists appear promising in this respect, but if an anti-exudative effect is confirmed for them, it will be necessary to determine whether this is a direct effect or secondary to their effects on cellular inflammatory processes in the airways.