Allergic inflammation after allergen challenge – insights from
the tissue
To the Editor,
Limited data exist on the infiltration of eosinophils in direct response
to allergen exposure in asthmatic patients. The experimental procedure
of segmental allergen provocation (SAP) in mild asthmatic subjects is an
extremely valuable study tool to investigate mechanisms of bronchial
asthma in patients in general and in particular for the role of
eosinophils. In this procedure, BAL and bronchial mucosa can be analysed
simultaneously after the induction of allergic inflammation. Older
studies yielded data on different time points after the challenge with
contradictory results. Eosinophils were studied in mucosa and airway
lumen of mild asthmatics undergoing segmental allergen provocation1,2. Here, eosinophils and their release products were
investigated in thick sections of the bronchial biopsies. Subject data,
methods and detailed results are given in the supplement. All subjects
showed a clear eosinophilic response in the airway lumen and mucosa 24
hours after the challenge (Figure 1, S1). The data on neutrophils were
inconclusive (Figure 1, S2). There was an increase of eosinophils in the
mucosa and in the BAL. In the BAL the concentrations of IL‑5 and ECP
were elevated (supplement). In the mucosa ECP stained areas were found
elevated as well as signs of eosinophil activation and degranulation
(Figure 2). ECP staining was associated with cellular structures, small
granules or dispersed over a large area beneath the epithelium. The
degree of released mediators into the tissue is an important parameter
investigating new drugs for asthma. In the presented study not cell
associated, free ECP positive granules were seen at baseline but only to
a small extent. However, after allergen challenge the ECP volume was
significantly increased and only few distinct cells could be detected
being positive for ECP. These results suggest that in human tissue
eosinophils degranulate to a significant amount after a single allergen
challenge and therefore release all their toxic content into the
surrounding tissue. This is in contrast to animal models of asthma where
eosinophilic degranulation after allergen challenge does not occur
extensively 3,4. In the present study, subjects with a
strong IL-5 reaction in BAL showed a strong eosinophilic response in the
lumen. However, BAL IL-5 levels did not correlate with eosinophil
numbers in the mucosa or volume of ECP positive surfaces in the mucosa
(Figure S3). It is a long known fact that IL-5 levels in the BAL
correlate highly with absolute numbers of eosinophils in the same
compartment 5. In the present study the allergic
reaction is comparable to those of other studies. The missing
correlation between IL-5 in the BAL and numbers of tissue eosinophils
showed that the relationship between both compartments is not as simple
as assumed. Here, the data for the volume of ECP positive surfaces may
give an important hint. Interestingly, the volume of ECP positive
surfaces was inversely correlated with TNF-α and IL-8. TNF-α enhances
migration of eosinophils from mucosa to lumen shown in an in vitro cell
culture model 6. Therefore, one possible explanation
is the more TNF-α is found in the BAL the less activated eosinophils are
found in the mucosa. In conclusion, the findings in subjects with mild
asthma are in alignment with other published results and suggest that 1)
human tissue eosinophils release their granules in non-provoked state,
and 2) toxic content of these cells is significantly released into the
surrounding tissue after a single allergen challenge whereas the
distribution and the degree of activation and degranulation of
eosinophils differs widely between subjects. Many eosinophils in the
airways indicate many eosinophils in the mucosa. Three-dimensional
analysis in thick tissue sections using confocal microscopy is a
valuable tool in the investigation of bronchial biopsies from patients
suffering from bronchial asthma.
(Abbreviations: BAL=bronchoalveolar lavage, ECP=eosinophilic cation
protein, IL=interleukin, MBP=major basic protein, NE=neutrophilic
elastase, SAP=segmental allergen provocation, TNF=tumor necrosis factor)
References
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3. Denzler KL, Borchers MT, Crosby JR, et al. Extensive eosinophil
degranulation and peroxidase-mediated oxidation of airway proteins do
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Frauke Prenzler1, Thomas Tschernig2,
Katherina Sewald1,5, Tibor Z
Veres1,3, Susanne Rittinghausen1,
Norbert Krug1,5, Jens M.
Hohlfeld1,4,5, Armin Braun1,4,5
1Fraunhofer Institute for Toxicology and Experimental
Medicine
2Institute for Cell Biology and Anatomy, Saarland
University, Homburg/Saar, Germany
3Lymphocyte Biology Section, Laboratory of Immune
System Biology, National Institute of Allergy and Infectious Diseases,
National Institutes of Health, Bethesda, MD 20892, USA
4 Institute of Immunology, Hannover Medical School,
Hannover, Germany
5 Member of the German Center for Lung Research (DZL),
Biomedical Research in Endstage and Obstructive Lung Disease (BREATH)
research network, Hannover, Germany
Correspondence: Armin Braun
Preclinical Pharmacology and Toxicology
Fraunhofer Institute for Toxicology and Experimental Medicine (ITEM)
Nikolai-Fuchs-Str. 1, 30625 Hannover, Germany
email: armin.braun@item.fraunhofer.de
Phone: +49(0)511/5350-263
Acknowledgements: We would like to thank Isabelle Bleeker for processing
the biopsy samples of the classical immunohistology.
Funding: Supported by Deutsche Forschungsgemeinschaft (SFB587/ B8 und
B4)
Conflict of Interest: None of the authors has any financial interest.
Contributions: AB, JH and NK planned and conducted the study. FP, AB and
TT wrote the manuscript, all other authors read, corrected and approved
the manuscript. TZV, KS, SR and FP established and performed the
morphology and made the evaluation of tissue data.