Epithelium, microcirculation, and eosinophils--new aspects of the allergic airway in vivo

In vivo observations provide insight into roles of eosinophils and epithelial cells in asthma

Observations in vivo in patients, supported by guinea-pig in vivo data, take centre stage in this perspective. Its objective is to highlight dichotomies between asthma features observed in vivo and accepted views involving cell/molecular biology research paradigms. For example, increased bronchial epithelial permeability is now considered a major paradigm and trait of asthma, yet, absorption of inhaled tracers has not been increased in vivo in asthma. Such maintained barrier function in exudative asthma reflects in vivo asymmetry of the epithelial lining as barrier between outside and inside world of molecules and cells. In desquamatory asthma, maintained epithelial tightness may be explained by in vivo demonstrations of exceedingly patchy epithelial loss, prompt creation of plasma-derived provisional barriers, and high-speed epithelial regeneration. Acknowledged protein/peptide secretion by epithelial cells in vitro is contrasted here with a dominant, unidirectional movement in vivo of plasma-derived proteins/peptides (including antimicrobial peptides) to the surface of an intact epithelial lining. Furthermore, longstanding claims that epithelium-produced adenosine is a mediator of asthma are eroded by observations in vivo in asthmatics. Notions concerning activation/fate of mucosal tissue eosinophils illustrate additional distinctions between accepted views and in vivo patient observations. Finally, in vitro-based paradigms preaching defect epithelial regeneration and increased permeability in pathogenesis of asthma are contrasted with experimental in vivo observations of exaggerated epithelial regeneration, which is multipathogenic in its own right. In conclusion, unexpected and challenging in vivo observations in recent decades underpin novel insights into mucosal mechanisms in asthma.

Asthma

Asthma has been recognized as a disease since the earliest times. In the Corpus Hippocraticum, Hippocrates used the term “ασθμα” to indicate any form of breathing difficulty manifesting itself by panting. Aretaeus of Cappadocia, a well-known Greek physician (second century A.D.), is credited with providing the first detailed description of an asthma attack [13], and to Celsus it was a disease with wheezing and noisy, violent breathing. In the history of Rome, we find many members of the Julio-Claudian family affected with probable atopic respiratory disorders: Caesar Augustus suffered from bronchoconstriction, seasonal rhinitis as well as a highly pruritic skin disease. Claudius suffered from rhinoconjunctivitis and Britannicus was allergic to horse dander [529]. Maimonides (1136–1204) warned that to neglect treatment of asthma could prove fatal, whereas until the 19th century, European scholars defined it as “nervous asthma,” a term that was given to mean a defect of conductivity of the ninth pair of cranial nerves.

Pathogenesis of chronic rhinosinusitis

Chronic rhinosinusitis (CRS) is a heterogenous disorder and represents a major public health problem. Although insights into the pathophysiology of CRS have largely expanded over the last two decades, the exact etiology and mechanism of persistence is still unrevealed. CRS is a multifactorial disease, and, with variable evidence, impaired ostial patency, mucociliary impairment, allergy, bacterial or fungal infection (or triggering), immunocompromised state, and environmental and genetic factors have been suggested to be associated or risk factors. Pathomechanisms in CRS are better understood currently, allowing us to characterize and differentiate the heterogeneous pathology of chronic sinonasal inflammation based on histopathology, inflammatory pattern, cytokine profile, and remodeling processes. In nasal polyposis (NP), but not CRS without NP, an abundant eosinophilic inflammation and local immunoglobulin E production could be demonstrated, and Staphylococcus-derived superantigens may at least modulate disease severity and expression. These findings question the current assumption that NP is a subgroup of CRS, but suggest that CRS and NP should probably be considered as distinct disease entities.

Allergen exposure of mouse airways evokes remodeling of both bronchi and large pulmonary vessels

Remodeling of airway structures is a well-documented feature of allergic airway inflammation. To investigate whether bronchial remodeling is associated with remodeling of adjacent pulmonary vessels, sensitized mice were subjected to repeated ovalbumin inhalations, and bronchi and pulmonary vessels were subjected to histologic analysis. Allergen challenges induced peribronchial as well as perivascular eosinophilia. Remodeling of systemic airway microcirculation, as studied in tracheal whole-mount preparations, revealed an allergen-induced increase in both the diameter and length of the airway microvessels. Immunostaining for alpha-smooth muscle actin disclosed an increase in smooth muscle mass in both bronchi and large pulmonary vessels. Both bronchi and pulmonary vessels also displayed increased expression of procollagen I and procollagen III. Staining for proliferating cell nuclear antigen revealed increased proliferation of bronchial epithelial and smooth muscle cells as well as pulmonary vascular endothelial and smooth muscle cells. We conclude that central features of remodeling that take place in allergen-exposed airways are present also in the pulmonary vessels. The significance of this finding with respect to occurrence in disease, pathophysiologic importance, and involved mechanisms warrants further investigation.

Allergic rhinitis: past, present and the future

Allergic rhinitis represents a global health issue affecting between 10% to 25% of the world population, with increasing prevalence over the last decade. Although often trivialized by patients and doctors, allergic rhinitis is a significant cause of morbidity, in addition to its substantial economic impact. While allergic rhinitis is an inflammatory disorder of the upper airways, inflammation alone is insufficient to explain the chronic nature of the disease. An exciting concept which has recently emerged in asthma concerns the role of the bronchial epithelium as a key regulator of airway inflammatory and remodelling responses in asthma. It has been shown by our group that the disruption and alteration in the function of the lower airway epithelium in asthma leads to the generation of a variety of stimuli that lead to the restructuring of the airway wall. This raises interesting questions regarding a similar role for the upper airway epithelium in allergic rhinitis. This review aims to interpret past and current research into allergic rhinitis, and to address specific areas where future research is warranted, particularly in relation to the possibility of an altered upper airway epithelial phenotype in allergic rhinitis.

Subset-specific reductions in lung lymphocyte accumulation following intratracheal antigen challenge in endothelial selectin-deficient mice

We previously demonstrated induction and expression of CD62E and CD62P in the lungs of mice primed and then challenged with intratracheal (i.t.) SRBC. The current study examined accumulation of endogenous lymphocytes in the lungs of endothelial E- and P-selectin-deficient (E(-)P(-)) mice after i.t. SRBC challenge. Compared with syngeneic wild-type (wt) mice, E(-)P(-) mice showed an 85-95% decrease in CD8(+) T cells and B cells in the lungs at both early and late time points. In contrast, CD4(+) T cell accumulation was reduced by approximately 60% early, but equivalent to wt levels later. Surprisingly, many gammadelta T cells were found in lungs and blood of E(-)P(-) mice but were undetectable in the lungs and blood of wt mice. Absolute numbers of peripheral blood CD4, CD8, and B lymphocytes in E(-)P(-) mice equaled or exceeded the levels in wt mice, particularly after challenge. Trafficking studies using alphabeta T lymphoblasts confirmed that the recruitment of circulating cells after challenge was markedly reduced in E(-)P(-) mice. Furthermore, Ag priming occurred normally in both the selectin-deficient and wt mice, because primed lymphocytes from both groups transferred Ag sensitivity into naive wt mice. Lung production of mRNA for six CC and two CXC chemokines after challenge was equivalent by RT-PCR analysis in wt and E(-)P(-) mice. Therefore, reduced lung accumulation of alphabeta T cells and B cells in E(-)P(-) mice did not result from reduced delivery of circulating lymphocytes to the lungs, unsuccessful Ag priming, or defective pulmonary chemokine production. Selectin-dependent lymphocyte recruitment into the lungs following i.t.-SRBC challenge is subset specific and time dependent.

Absorption across the nasal airway mucosa in house dust mite perennial allergic rhinitis

House dust mite allergens express protease activity and it has been suggested that this property has pathogenic effects by increasing airway absorption. In accordance, house dust mite allergens may increase mucosal permeability in vitro. The objective of the present study was to examine nasal absorption of desmopressin (1-deamino-8-D-arginine vasopressin) in patients with perennial house dust mite allergic rhinitis and in healthy subjects in vivo. Patients with perennial allergic rhinitis were examined after a 4-week treatment withdrawal period, when symptoms of allergic rhinitis occurred, and healthy subjects were examined together with the patients. Desmopressin (20 microg ml(-1)) was moved into the nasal cavity using a nasal pool-device that contained 15 ml fluid. The fluid was kept in the nasal cavity for 15 min and then recovered. Urine was collected for 24 h after the nasal administration and the urinary excretion of desmopressin was determined as an index of nasal absorption. The urinary excretion of desmopressin was 1148+/-535 pmol 24 h(-1) in patients with perennial house dust mite allergic rhinitis and 1012+/-291 pmol 24 h(-1) in healthy subjects. We conclude that nasal airway absorption of the 1067 Da peptide desmopressin is unaffected in perennial house dust mite allergic rhinitis compared with healthy subjects.

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.

Transepithelial migration of activated eosinophils induces a decrease of E-cadherin expression in cultured human nasal epithelial cells

BACKGROUND

The damage of respiratory epithelium in allergic diseases has a close correlation with the extent of eosinophil infiltration. It seems to be a good possibility that eosinophil infiltration could induce the changes in the expression of the epithelial cell adhesion molecules, which play a key role in the maintenance of structural and functional rigidity of epithelium.

OBJECTIVE

We observed the expression of E-cadherin in cultured human nasal epithelial cells (HNECs) to study whether could it be affected by transepithelial migration of inflammatory cells, especially eosinophils.

METHODS

In vitro study of the transmigration assay was designed using various types of inflammatory cells and HNEC monolayers. Various assays of each experimental group were done under the stimulation of interleukin-5 (IL-5) and/or platelet activating factor (PAF). Subsequently immunohistochemistry for E-cadherin was performed in the HNECs. The intensity of immunofluorescence of E-cadherin was quantified using confocal laser scanning microscopy (CLSM) system and compared before and after the transmigration.

RESULTS

The mean intensity of immunofluorescence for E-cadherin decreased significantly after the transmigration of any types of inflammatory cells. Above all, the migration of eosinophils treated with IL-5 and PAF had an eminent effect on the decrease, whereas the degranulation extracts derived from eosinophils activated by IL-5 and secretory IgA (sIgA) did not affect the intensity.

CONCLUSION

This work suggests that transepithelial migration of inflammatory cells can directly induce the decrease in epithelial E-cadherin expression. Furthermore, the most prominent change was induced by transmigration of activated eosinophils, which might be caused by some mechanisms independent of the eosinophil contents. The decrease in E-cadherin expression may trigger the damage of epithelial barrier, which contributes to the pathogenesis of allergic diseases.

Innervation of nasal turbinate blood vessels in rhinitic and nonrhinitic children

An immunohistochemical study of the nasal mucosa was done in pediatric patients attending an otorhinolaringology (ORL) clinic. The goal was a comparison between vascular innervation in patients with or without symptoms of chronic rhinitis. All patients had an indication for tonsillectomy prior to their inclusion in this study. Samples were obtained under general anesthesia at the time of programmed surgery and fixed in a paraformaldehyde-picric acid mixture. Cryostat sections were immunostained for the following neuronal markers: protein-gene product 9.5 (PGP), calcitonin gene- related peptide (CGRP), substance P (SP), and C-terminal peptide of neuropeptide Y (CPON). The following classes of vessels were identified: arteries, sinusoids, veins, and arteriovenous anastomoses (AVAs). As shown by immunostaining with the general neuronal marker PGP, each vessel type had a characteristic innervation pattern, differing in the amount of fibers and their distribution within the adventitial and muscle layers. Evaluation of PGP, CPON, and CGRP immunoreactivity patterns indicated that rhinitic arteries and AVAs displayed a richer innervation than did nonrhinitic blood vessels. Quantification of vascular PGP immunostaining confirmed the difference of vascular innervation between nonrhinitic and rhinitic patients. Fibers immunostained by CPON partially accounted for the rhinitic arterial hyperinnervation.

Generation of clusters of free eosinophil granules (Cfegs) in seasonal allergic rhinitis

Generation of clusters of free eosinophil granules (Cfegs), through lysis of eosinophils, has recently been proposed as a major paradigm for ultimate activation of airway mucosal eosinophils. In the present study involving patients with seasonal allergic rhinitis, we have investigated whether generation of Cfegs in the nasal mucosa is a feature of allergic rhinitis. Nasal mucosal biopsies were obtained before and late in a birch-pollen season, and were subjected to histochemical staining of eosinophil peroxidase. In biopsies obtained before the pollen season, a few, intact eosinophils were observed, and Cfegs were scarce. In biopsies taken during the pollen season, the numbers of eosinophils were increased about 10-fold (P < 0.05) and the Cfegs about 25-fold (P < 0.05). We conclude that generation of Cfegs is a significant feature of seasonal allergic rhinitis and that this process represents the ultimate activation of mucosal eosinophils in this disease.

The mouse trap

Mouse models of asthma are now being used extensively in drug research. However, the successful unravelling of combinatorial interplays of cells and molecules in the murine airways may not be matched by equally successful demonstrations of an asthma-like pathophysiology. Here, Carl Persson, Jonas Erjefält, Magnus Korsgren and Frank Sundler discuss the fact that major features of asthma may still need to be demonstrated in the airways of allergic mice.

Allergic eosinophil-rich inflammation develops in lungs and airways of B cell-deficient mice

Immunoglobulins (Ig), particularly IgE, are believed to be crucially involved in the pathogenesis of asthma and, equally, in allergic models of the disease. To validate this paradigm we examined homozygous mutant C57BL/6 mice, which are B cell deficient, lacking all Ig. Mice were immunized intraperitoneally with 10 micrograms ovalbumin (OVA) plus alum, followed by daily (day 14-20) 30 min exposures to OVA aerosol (OVA/OVA group). Three control groups were run: OVA intraperitoneally plus saline (SAL) aerosol (OVA/SAL group); saline intraperitoneally plus saline aerosol; saline intraperitoneally plus OVA aerosol (n = 6-7). Lung and large airway tissues obtained 24 h after the last OVA or SAL exposure were examined by light microscopy and transmission electron microscopy (TEM). The Ig-deficient mice receiving OVA/ OVA treatment had swollen and discolored lungs and exhibited marked eosinophilia both in large airway subepithelial tissue (49.2 +/- 12.0 cells/mm basement membrane [BM] versus OVA/ SAL control 1.2 +/- 0.3 cells/mm BM; P < 0.001), and perivascularly and peribronchially in the lung (49.3 +/- 9.0 cells/unit area versus OVA/SAL control 2.6 +/- 0.6 cells/unit area; P < 0.001). The eosinophilia extended to the regional lymph nodes. TEM confirmed the subepithelial and perivascular localization of eosinophils. Mucus cells in large airway epithelium increased from 1.5 +/- 0.8 (OVA/SAL mice) to 39.5 +/- 5.7 cells/mm BM in OVA/OVA treated mice (P < 0.001). OVA/SAL mice never differed from the other control groups. Corresponding experiments in wild-type mice (n = 6-7 in each group) showed qualitatively similar but less pronounced eosinophil and mucus cell changes. Macrophages and CD4+ T cells increased in lungs of all OVA/OVA-treated mice. Mast cell number did not differ but degranulation was detected only in OVA/OVA-treated wild-type mice. Immunization to OVA followed by OVA challenges thus cause eosinophil-rich inflammation in airways and lungs of mice without involvement of B cells and Ig.