Obstructive airways diseases, smoking and use of inhaled corticosteroids in southern Sweden in 1992 and 2000.

OBJECTIVE: To examine the prevalence of obstructive pulmonary diseases, respiratory symptoms, smoking habits and pulmonary medication in an adult population, and to compare the results with a study performed in the same geographical area in 1992. DESIGN: In 2000, a postal questionnaire was sent to a randomly selected population of 5179 subjects aged 20-59 years living in southern Sweden. RESULTS: The participation rate was 71.3%. Self-reported asthma was reported by 8.5% of all respondents (vs. 5.5% in 1992, P < 0.001) and 14.5% of females aged 20-29 years. Self-reported chronic bronchitis and/or emphysema and/or chronic obstructive pulmonary disease (CBE/COPD) was reported by 3.6% (vs. 4.6% in 1992, non-significant) with the highest prevalence (5.7%) in the 50-59 year cohort. Smoking decreased from 33.3% in 1992 to 28.4% in 2000 (P < 0.05). About 46% of asthmatics reported nocturnal respiratory symptoms, and 69% reported having had asthma symptoms in the last 12 months. Use of inhaled steroids increased in subjects with asthma and CBE/COPD from 19.4% to 36.5% (P < 0.05) and from 8.6% to 30.0% (P < 0.05), respectively. CONCLUSIONS: Self-reported asthma increased significantly between 1992 and 2000, but the prevalence of CBE/COPD was unchanged. The high proportion of reported symptoms in asthmatics despite an increased use of steroids suggests that further efforts are needed to improve asthma treatment.

Effects of steroid treatment on lung CC chemokines, apoptosis and transepithelial cell clearance during development and resolution of allergic airway inflammation.

BACKGROUND: Steroid treatment of allergic eosinophilic airway diseases is considered to attenuate cell recruitment by inhibiting several chemokines and to cause eosinophil clearance through inducement of apoptosis of these cells. However, roles of these mechanisms in the actions of steroids in vivo have not been fully established. Also, as regards clearance of tissue eosinophils other mechanisms than apoptosis may operate in vivo. OBJECTIVE: This study explores anti-inflammatory effects of steroids instituted during either development or resolution of airway allergic inflammation. METHODS: Immunized mice were subjected to week-long daily allergen challenges (ovalbumin). Steroid treatment was instituted either amidst the challenges or exclusively post-allergen challenge. CC chemokines, goblet cell hyperplasia, occurrence of eosinophil apoptosis, and airway tissue as well as lumen eosinophilia were examined at different time-points. RESULTS: Daily steroids instituted amid the allergen challenges non-selectively attenuated a range of chemokines, permitted egression of tissue eosinophils into airway lumen to increase, and reduced development of lung tissue eosinophilia. Steroid treatment instituted post-challenge selectively inhibited the CC-chemokine regulation upon activation, normal T cell expressed and secrted (RANTES), permitted continued egression of eosinophils into airway lumen, and resolved the tissue eosinophilia. Eosinophil apoptosis rarely occurred at development and resolution of the allergic eosinophilic inflammation whether the animals were steroid treated or not. However, anti-Fas monoclonal antibodies given to mice with established eosinophilia post-challenge produced apoptosis of the tissue eosinophils indicating that apoptotic eosinophils, if they occur, are well detectible in vivo. CONCLUSION: Airway tissue eosinophils are likely eliminated through egression into airway lumen with little involvement of apoptosis and phagocytosis. Our data further suggest that therapeutic steroids may resolve airway inflammation by permitting clearance of tissue eosinophils through egression and inhibiting RANTES-dependent cell recruitment to lung tissues.

Blockade of CTLA-4 promotes airway inflammation in naive mice exposed to aerosolized allergen but fails to prevent inhalation tolerance.

In subjects not developing allergy, inhalation of nonpathogenic protein antigens causes no harm and is associated with tolerance induction. Repeated exposure to aerosolized ovalbumin (OVA) likewise does not evoke airway inflammation and induces inhalation tolerance in experimental animals. The present study explored the role of the inhibitory T-cell receptor CTLA-4, in preventing inflammation and in establishing inhalation tolerance in response to a protein antigen. Naive BALB/c mice were injected intraperitoneally with anti-CTLA-4 monoclonal antibody or control immunoglobulin G (IgG) and exposed daily to aerosolized saline or OVA over 10 or 20 consecutive days. OVA-specific IgE levels and the inflammatory response in airway tissues were assessed 2 days after last exposure. The OVA-specific IgE response was also evaluated in mice subjected to a subsequent immunogenic OVA challenge 18 days after last aerosol exposure. Additional mice were made tolerant by 10 days of OVA aerosol exposure and were then subjected to an immunogenic OVA challenge combined with CTLA-4 blockade or control IgG treatment. Repeated inhalation of aerosolized OVA alone did not cause a pulmonary inflammatory response. In contrast, 10 days of OVA exposure combined with blockade of CTLA-4 led to development of eosinophilic lung infiltrates, BAL fluid eosinophilia, goblet cell hyperplasia and increased OVA-specific IgE. By 20 days of OVA exposure and blockade of CTLA-4, the inflammatory response remained. Mice exposed to aerosolized OVA for 10 days exhibited greatly reduced OVA-specific IgE responses to subsequent immunogenic OVA challenge. Blockade of CTLA-4 during the period of OVA aerosol exposure did not prevent this suppression of the OVA-specific IgE response. Neither did blockade of CTLA-4 during immunogenic OVA challenge alter the allergen-specific IgE response. Our results indicate that in vivo blockade of CTLA-4 modulates the initial immune response to a protein antigen allowing the development of allergen-induced airway inflammation in naive mice. However, this initial exaggerated immune response is followed by the induction of inhalation tolerance, demonstrating that CTLA-4 signalling is not decisive in this process. Our findings also show that once inhalation tolerance is established it may not be disrupted by blockade of CTLA-4.

Circulating eosinophils in asthma, allergic rhinitis, and atopic dermatitis lack morphological signs of degranulation.

BACKGROUND: In allergic diseases, eosinophils in affected tissues release granule proteins with cytotoxic, immunoregulatory, and remodelling-promoting properties. From recent observations, it may be assumed that eosinophils degranulate already in circulating blood. If degranulation occurs in the circulation, this could contribute to widespread systemic effects and provide an important marker of disease. OBJECTIVE: To determine the degranulation status of circulating eosinophils in common allergic diseases. METHODS: Using a novel approach of whole blood fixation and leucocyte preparation, the granule morphology of blood eosinophils from healthy subjects, non-symptomatic patients, symptomatic patients with asthma, asthma and Churg-Strauss syndrome, allergic rhinitis, and atopic dermatitis was evaluated by transmission electron microscopy (TEM) and eosinophil peroxidase (TEM) histochemistry. Plasma and serum levels of eosinophil cationic protein were measured by fluoroenzymeimmunoassay. Selected tissue biopsies were examined by TEM. RESULTS: Regardless of symptoms, circulating eosinophils from allergic patients showed the same granule morphology as cells from healthy subjects. The majority of eosinophil-specific granules had preserved intact electron-density (96%; range: 89-98%), while the remaining granules typically exhibited marginal coarsening or mild lucency of the matrix structure. Abnormalities of the crystalline granule core were rarely detected. Furthermore, granule matrix alterations were not associated with any re-localization of intracellular EPO or increase in plasma eosinophil cationic protein. By contrast, eosinophils in diseased tissues exhibited cytolysis (granule release through membrane rupture) and piecemeal degranulation (loss of granule matrix and core structures). CONCLUSION: In symptomatic eosinophilic diseases, circulating blood eosinophils retain their granule contents until they have reached their target organ.

Secretoneurin is released into human airways by topical histamine but not capsaicin.

BACKGROUND: The neuropeptide secretoneurin, with potential relevance to leukocyte trafficking, is present in nerves of the nasal mucosa in allergic rhinitis and may be released in response to allergen and histamine exposure. There is no information on the occurrence and mechanisms of release of secretoneurin in healthy human airways. METHODS: The presence of secretoneurin in nasal biopsies and its release in response to nasal capsaicin and histamine challenges were examined. Symptoms and lavage fluid levels of fucose were recorded as markers of effects in part produced by neural activity. Bronchial histamine challenges followed by sputum induction and analysis of secretoneurin were also carried out. RESULTS: Nerves displaying secretoneurin immunoreactivity abounded in the nasal mucosa. Nasal capsaicin challenge produced local pain (P <0.05) and increased the levels of fucose (P <0.05), but failed to affect the levels of secretoneurin. Nasal histamine challenge produced symptoms (P <0.05) and increased the mucosal output of secretoneurin (P <0.05) and fucose (P <0.05). Bronchial histamine challenge increased the sputum levels of secretoneurin (P <0.05). CONCLUSIONS: We conclude that secretoneurin is present in healthy human airways and that histamine evokes its release in both nasal and bronchial mucosae. The present observations support the possibility that secretoneurin is involved in histamine-dependent responses of the human airway mucosa.

Eosinophil degranulation status in allergic rhinitis: observations before and during seasonal allergen exposure.

Despite the fact that extensive degranulation is a likely prerequisite for a pathogenic role of eosinophils, little is known about the degranulation status of these cells in eosinophilic conditions. The present study of the ultrastructure of tissue eosinophils explores eosinophil degranulation in allergic rhinitis before and during seasonal allergen exposure. A total of 23 patients scored symptoms q.d., prior to and during the pollen season. The numbers of mucosal eosinophils and their degranulation status were determined in nasal biopsies. Furthermore, nasal lavage fluid levels of eosinophil cationic protein (ECP) and alpha2-macroglobulin were assessed as indices of eosinophil activity and plasma exudation, respectively. Seasonal allergen exposure was associated with increased nasal symptoms, increased lavage fluid levels of ECP and alpha2-macroglobulin, and increased numbers of tissue eosinophils. In the tissue, transmission electron microscopy revealed a moderate piecemeal degranulation already prior to the season (mean+/-sd 37+/-2.7% altered granules). Seasonal allergen exposure increased this degranulation (87+/-1.8%), and produced local areas with extensive deposition of granule proteins. The degree of eosinophil degranulation correlated with levels of ECP in lavage fluids obtained at histamine challenge. In conclusion, this study demonstrated that the nasal mucosa in allergic rhinitis features moderately degranulated eosinophils already at nonsymptomatic baseline conditions. In association with the development of symptomatic seasonal allergic rhinitis, the tissue deposition of eosinophil granule proteins is dramatically elevated through increased eosinophil numbers, together with markedly augmented degranulation of individual cells.

Rapid and efficient clearance of airway tissue granulocytes through transepithelial migration.

BACKGROUND: Clearance of tissue granulocytes is central to the resolution of airway inflammation. To date the focus has been on apoptotic mechanisms of cell removal and little attention has been given to alternative processes. The present study explores transepithelial migration as a mechanism of cell clearance. METHOD: Guinea pig tracheobronchial airways where eosinophils are constitutively present in the mucosal tissue were studied. A complex topical stimulus (allergen challenge) was applied and the fate of the eosinophils was determined by selective tracheobronchial lavage and histological examination of the tissue. RESULTS: Within 10 minutes of the allergen challenge, massive migration of eosinophils into the airway lumen occurred together with a reduction in tissue eosinophil numbers. Cell clearance into the lumen continued at high speed and by 30 and 60 minutes the tissue eosinophilia had been reduced by 63% and 73%, respectively. The marked transepithelial migration (estimated maximal speed 35,000 cells/min x cm2 mucosal surface) took place ubiquitously between epithelial cells without affecting epithelial integrity as assessed by transmission and scanning electron microscopy. Eosinophil apoptosis was not detected but occasional cytolytic eosinophils occurred. CONCLUSION: This study shows that luminal entry has a remarkably high capacity as a granulocyte elimination process. The data also suggest that an appropriate stimulus of transepithelial migration may be used therapeutically to increase the resolution of inflammatory conditions of airway tissues.

Influence of heavy traffic, city dwelling and socio-economic status on nasal symptoms assessed in a postal population survey.

BACKGROUND: The association between social position, living environment and nasal symptoms is inconsistent. We wanted to test how living environment, occupation and social position were associated with nasal symptoms. METHODS: In a postal survey study of a random sample of 12,079 adults, aged 20-59 years living in the southern part of Sweden the relationship between nasal symptoms, socio-economic status and environmental factors was analysed. RESULTS: The response rate was 70% (n = 8469) of whom 33% reported significant nasal symptoms. Nasal discharge, thick yellow discharge, a blocked nose, sneezing and itching were strongly associated with living close to heavy traffic or living in cities. Most of the nasal symptoms provoked by extrinsic factors were more frequently reported among subjects who lived close to heavy traffic and in cities. Apart from thick yellow discharge and nasal symptoms provoked by damp/cold air which were more common in the socio-economic position "low" no relation to the socio-economic group was found. The prevalence of self-reported hay fever was neither affected by site of living nor by socio-economic status. Nasal symptoms evoked by "allergic" factors were linked to asthma but symptoms evoked by non-allergic factors were linked to chronic bronchitis/emphysema CBE. CONCLUSIONS: To conclude, we found a strong relation between geographical site and the prevalence of self-reported nasal symptoms which emphasizes the environment as a risk factor for nasal symptoms. Only by merging the socio-economic groups into "low" and "middle/high" an association to nasal symptoms was apparent. Nasal symptoms evoked by "allergic" factors were linked to asthma but symptoms evoked by "non allergic factors" were linked to CBE.

Hypertonic saline increases secretory and exudative responsiveness of human nasal airway in vivo.

Hypertonic saline (HS) is used in sputum induction studies. However, little is known about the physiological effects of HS on human airways in vivo. The present study takes advantage of the fact that the airway effects of topical challenges may be accurately examined in the readily accessible nasal airway. The present study specifically examines whether exposure to HS affects histamine challenge-induced exudation of plasma (alpha2-macroglobulin) and methacholine-induced secretion of mucin (fucose). Isotonic saline and HS (27 and 45 g x L(-1)), with and without concomitant histamine challenges, and with and without preceding methacholine challenges, were administered onto the nasal mucosa in 16 healthy subjects. Lavage fluid levels of alpha2-macroglobulin and fucose were analysed. Histamine produced a significant mucosal output of plasma (alpha2-macroglobulin). HS itself did not evoke exudation of alpha2-macroglobulin, but it significantly increased the plasma exudation effect of histamine. Methacholine produced a significant nasal mucosal output of fucose. HS also increased the mucin secretion (fucose), and it enhanced the secretory effect of methacholine. The authors concluded that hypertonic saline alone evokes mucinous secretion in human nasal airways in vivo and that it also enhances the exudative and secretory effects of histamine and methacholine, respectively. Through different mechanisms the HS exposure may also improve the recovery of soluble indices in human nasal airways. Whether or not the present findings are translatable to human bronchial airways remains to be examined.

Effects of rhinovirus-induced common colds on granulocyte activity in allergic rhinitis.

OBJECTIVE: To explore the activities of mast cells, eosinophils, and neutrophils in patients with allergic rhinitis developing common colds and increased responsiveness to allergen following nasal rhinovirus inoculation. METHODS: We have revisited a nasal lavage material obtained from 17 patients who were successfully inoculated with rhinovirus outside the pollen season and received nasal allergen challenges before and after inoculation. We have examined indices of mast cell activity (tryptase), eosinophil degranulation (eosinophil peroxidase; EPO), and neutrophil activation (myeloperoxidase; MPO). RESULTS: Allergen challenges performed before rhinovirus inoculation increased the nasal output of EPO. Notably, this response was significantly greater after rhinovirus inoculation (cf. before inoculation). The output of MPO was also increased following allergen challenge after, but not before, rhinovirus inoculation. Nasal lavage fluid levels of tryptase were increased following allergen challenge similarly before and after rhinovirus inoculation. Also, the viral infection did not affect the baseline levels of tryptase. CONCLUSIONS: The present data demonstrate that rhinovirus infections activate both eosinophils and neutrophils, but that they may not affect mast cell activity. We suggest that common colds in part through stimulation of granulocyte activity potentiate the airway inflammation in allergic diseases.

Gut mucosal uptake and retention characteristics contribute to the high intestinal selectivity of budesonide compared with prednisolone in the rat.

BACKGROUND: Budesonide and prednisolone are both effective for the treatment of inflammatory bowel disease, but budesonide produces fewer adverse systemic effects. High first-pass hepatic inactivation of budesonide partially explains its favourable ratio between topical and systemic activity, but it is probable that its uptake and retention in intestinal target tissues are also contributory. AIM: To compare the uptake and retention of radio-labelled budesonide and prednisolone in rat ileal mucosa in vivo. METHODS: 3H-Budesonide and 3H-prednisolone were applied for 10 min directly to a perfused segment of rat ileum in vivo, followed by saline lavage every 10 min. Steroid uptake into the mucosa and submucosa was assessed at 20 min and 4 h. The uptake of budesonide was also measured in allergen-challenged animals vs. saline-challenged controls to assess whether inflammation of the mucosa with ongoing plasma exudation would impair its uptake. RESULTS: Budesonide was better absorbed into ileal tissue (15-fold at 20 min) than prednisolone and better retained (50-fold at 4 h) after topical administration. The uptake of budesonide was not impaired by exudation processes following allergen challenge. CONCLUSIONS: The higher uptake and retention characteristics of budesonide in gut mucosa should contribute to its greater intestinal selectivity compared with that of prednisolone.

Lung tissue eosinophils may be cleared through luminal entry rather than apoptosis: effects of steroid treatment.

Spontaneous or steroid-induced eosinophil apoptosis occurring in vitro has not been demonstrated in lung tissues in vivo. This study examines cell apoptosis in rat lungs using the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (dUTP) nick end labeling (TUNEL) technique and transmission electron microscopy (TEM). After establishing sustained lung edema and eosinophilia by challenge with Sephadex beads intratracheally, budesonide treatment was started intratracheally. Sephadex alone increased the total number of apoptotic cells, which were not efficiently engulfed by macrophages or other cells, in vivo. Yet apoptotic tissue eosinophils were exceedingly rare (1 of 360 TEM-analyzed eosinophils). By contrast, approximately 20% of eosinophils in the airway lumen were apoptotic, and unengulfed. Budesonide promptly inhibited edema but 3 d of steroid treatment were required to reduce the established tissue eosinophilia. Not at any time point did budesonide induce eosinophil apoptosis (0 of 318 TEM-analyzed tissue eosinophils). We conclude that (1) eosinophil apoptosis can occur but is a rare event in vivo in respiratory tract tissues; (2) airway tissue eosinophils, rather than undergoing apoptosis, are eliminated by migration into airway lumen followed by apoptosis and mucociliary clearance; (3) anti-inflammatory steroid treatment may not increase eosinophil apoptosis in vivo nor may it affect the luminal entry of eosinophils; (4) steroids permit elimination of eosinophils into airway lumen and slowly resolve established lung eosinophilia.

Topical and oral anti-inflammatory activity of budesonide compared with oral prednisolone in an animal model using allergen-induced gut mucosal exudation of plasma as a marker.

BACKGROUND: Development of topically active glucocorticosteroids with minimal systemic effects is paramount in improving therapy in inflammatory bowel disease. Our experimental model in the rat has proved useful for assessing topical versus systemic anti-inflammatory potency of glucocorticosteroids on the inflamed gut. METHODS: Experiments were performed on allergen-sensitized perfused rat ileum in vivo. Mucosal exudation of plasma, induced by local allergen perfusion, was measured as the appearance of circulating 125I-labelled albumin in the gut lumen. Experiments compared the anti-exudative effects of oral budesonide (0.1 mg/kg) with oral prednisolone (1, 3.3 or 10 mg/kg) and saline, given by oral gavage 24 h prior to allergen challenge, and of topical budesonide (3 x 10(-5) mol/L) with saline, administered in the perfusate 4 h prior to allergen challenge. Systemic glucocorticosteroid activity was assessed by weighing thymus glands after sacrifice. RESULTS: Allergen-induced plasma exudation was significantly reduced by oral budesonide, oral prednisolone (dose-dependently) and topically applied budesonide; topical budesonide was effective within 4 h. While prednisolone significantly reduced the relative thymus weight at both 3.3 and 10 mg/kg, budesonide given orally, 0.1 mg/kg, or topically, 3 x 10(-5) mol/L, had no significant effect. CONCLUSION: Budesonide, administered orally or topically, shows higher selectivity for the gut mucosa than prednisolone and produces local anti-inflammatory responses comparable to prednisolone, without the accompanying systemic effects.

Mucosal output of eotaxin in allergic rhinitis and its attenuation by topical glucocorticosteroid treatment.

BACKGROUND: Eotaxin is a chemokine that attracts and activates eosinophils. The present study examines the occurrence of eotaxin in nasal mucosal surface liquids in patients with seasonal allergic rhinitis without allergen exposure and during repeat allergen challenge with and without topical glucocorticosteroid treatment. The number of subepithelial eosinophils and mucosal outputs of bulk plasma (alpha2-macroglobulin) and eosinophil cationic protein (ECP) are also examined. METHODS: Twelve patients underwent daily allergen challenges for 6 days. Separately, 14 patients, who were receiving budesonide and placebo in a parallel group design, also underwent allergen challenge for 6 days. Nasal biopsies were obtained before and 24 h after the allergen challenge series, and lavages were carried out before and 15 min after selected allergen challenges. RESULTS: At baseline nasal lavage fluid levels of eotaxin correlated to levels of alpha2-macroglobulin and ECP. After the first allergen challenge there was a correlation between nasal lavage fluid levels of eotaxin and ECP. Repeat allergen exposure increased the mucosal output of eotaxin (P <0.05) and ECP (P <0.01) as well as eosinophil numbers (P <0.01), but no correlation was found between increased eosinophil numbers and eotaxin. Budesonide reduced eotaxin levels during repeat allergen challenge (P <0.05). CONCLUSIONS: Repeat allergen exposure in allergic rhinitis is associated with increased mucosal output of eotaxin. Topical budesonide attenuates this effect, suggesting the possibility that inhibitory effects on mucosal eotaxin may contribute to anti-eosinophilic actions of topical glucocorticosteroids.

Prevalence of nasal symptoms and their relation to self-reported asthma and chronic bronchitis/emphysema.

Little information is available on associations between rhinitis and chronic bronchitis/emphysema (CBE). Self-reported upper airway symptoms, asthma, and CBE were examined in 12,079 adults living in southern Sweden. The response rate was 70% (n=8,469), of whom 33% reported significant nasal symptoms: a blocked nose was reported by 21%; sneezing by 18%; nasal discharge by 17%; and thick yellow nasal discharge by 5.7%. Nasal symptoms and combined nasal and self-reported bronchial disease were generally more common among smokers than nonsmokers. There was little overlap between asthma and CBE, but 46% of those with asthma and 40% of those with CBE had significant nasal symptoms. Best predicting factors (odds ratios >3) for asthma and CBE were nasal symptoms due to exposure to animals and damp/cold air, respectively. One-third of an adult, southern Swedish population, had significant allergic and/or nonallergic nasal symptoms. Nasal symptoms were frequently found to coexist with both asthma and chronic bronchitis/emphysema, suggesting that pan-airway engagement is common in both diseases. Differing associations between types of nasal symptoms and allergic and irritant triggers of nasal symptoms, with regard to asthma and chronic bronchitis/emphysema, emphasize the different natures of these bronchial diseases.

Degranulation patterns of eosinophil granulocytes as determinants of eosinophil driven disease.

BACKGROUND: Degranulation of eosinophils in target tissues is considered a key pathogenic event in major chronic eosinophilic diseases. However, because of a lack of appropriate methods, little is known about degranulation of eosinophils in common eosinophilic diseases. METHODS: Using transmission electron microscopic (TEM) analysis, a novel approach has been devised and validated to quantify eosinophil degranulation in human tissues (assessed in individual cells as percentage granules with structural signs of protein release). Biopsy specimens from patients with inflammatory bowel disease, allergic rhinitis, asthma, and nasal polyposis were evaluated. RESULTS: All conditions displayed a similar degree of local tissue eosinophilia, with no differences being observed in eosinophil numbers in the airway mucosa of patients with airway diseases and the colonic mucosa of those with inflammatory bowel disease (IBD). In contrast, marked differences in the mean (SE) extent of eosinophil degranulation were observed between the patient groups; IBD 9.3 (1.4)% altered granules, artificial and natural allergen challenge induced allergic rhinitis 67.8 (6.8)% and 86.6 (3.0)%, respectively, asthma 18.1 (2)%, and nasal polyposis 46.6 (7.6)%. CONCLUSIONS: This study provides the first quantitative data which show that different eosinophilic conditions, despite having similar numbers of tissue eosinophils, may exhibit markedly different degranulation patterns. The present assessment of piecemeal degranulation would thus make it possible to delineate the conditions under which eosinophils are likely to contribute to disease processes. This novel type of analysis may also guide and validate anti-eosinophilic treatment options.

Degranulation status of airway tissue eosinophils in mouse models of allergic airway inflammation.

Eosinophil degranulation is a characteristic feature of asthma and allergic rhinitis. However, degranulated eosinophils have not been convincingly demonstrated in the common mouse models of these airway diseases. This study uses eosinophil peroxidase (EPO) histochemistry and transmission electron microscopy (TEM) analysis to assess eosinophil degranulation in the airways of ovalbumin (OVA)-sensitized and challenged BALB/c and C57BL/6 mice. Using TEM we also examined mouse and human blood eosinophils after in vitro incubation with formyl-Met-Leu-Phe (fMLP) or phorbol myristate acetate (PMA). Although OVA exposure induced significant nasal and lung eosinophilia, we did not observe any of the known cellular processes by which eosinophils release their granule products, i.e., eosinophil cytolysis, piecemeal degranulation, and exocytosis. The occurrence of other allergen-induced degranulation events was ruled out because no difference in granule morphology was observed between lung-tissue eosinophils and blood or bone-marrow eosinophils from control animals. Accordingly, there was no detectable extracellular EPO in lung tissues of allergic mice. Similarly, mouse blood eosinophils remained nondegranulated in vitro in the presence of fMLP and PMA, whereas the same treatment of human eosinophils resulted in extensive degranulation. This investigation indicates that OVA-induced airway inflammation in the present mouse strains does not involve significant eosinophil degranulation. It is speculated that this dissimilarity from the human disease may be due to a fundamental difference in the regulation of mouse and human eosinophils.