Allergic fungal airways disease (AFAD): an under-recognised asthma endotype
Catherine H Pashley1, Andrew J Wardlaw2
1Department of Respiratory Sciences, Institute for Lung Health, University of Leicester, University Road, Leicester, LE1 7RH, UK. chp5@le.ac.uk.
Abstract:
The term allergic fungal airways disease has a liberal definition based on IgE sensitisation to thermotolerant fungi and evidence of fungal-related lung damage. It arose from a body of work looking into the role of fungi in asthma. Historically fungi were considered a rare complication of asthma, exemplified by allergic bronchopulmonary aspergillosis; however, there is a significant proportion of individuals with Aspergillus fumigatus sensitisation who do not meet these criteria, who are at high risk for the development of lung damage. The fungi that play a role in asthma can be divided into two groups; those that can grow at body temperature referred to as thermotolerant, which are capable of both infection and allergy, and those that cannot but can still act as allergens in IgE sensitised individuals. Sensitisation to thermotolerant filamentous fungi (Aspergillus and Penicillium), and not non-thermotolerant fungi (Alternaria and Cladosporium) is associated with lower lung function and radiological abnormalities (bronchiectasis, tree-in-bud, fleeting shadows, collapse/consolidation and fibrosis). For antifungals to play a role in treatment, the focus should be on fungi capable of growing in the airways thereby causing a persistent chronic allergenic stimulus and releasing tissue damaging proteases and other enzymes which may disrupt the airway epithelial barrier and cause mucosal damage and airway remodelling. All patients with IgE sensitisation to thermotolerant fungi in the context of asthma and other airway disease are at risk of progressive lung damage, and as such should be monitored closely.
Insights
Allergic fungal airways disease involves IgE sensitization to fungi that grow at body temperature, leading to lung damage. Monitoring is crucial for asthma patients with this sensitization to prevent progressive respiratory issues.
Area of Science:
- Pulmonology
- Allergology
- Mycology
Background:
- Allergic fungal airways disease (AFAD) is defined by IgE sensitization to thermotolerant fungi and fungal-related lung damage.
- Historically, fungal complications in asthma, like allergic bronchopulmonary aspergillosis, were considered rare.
- A significant number of individuals with Aspergillus fumigatus sensitization, not meeting AFAD criteria, are at high risk for lung damage.
Purpose of the Study:
- To investigate the role of fungi in asthma and identify risk factors for lung damage.
- To differentiate between thermotolerant and non-thermotolerant fungi in the context of allergic airway diseases.
- To highlight the importance of monitoring patients with IgE sensitization to thermotolerant fungi.
Main Methods:
- Review of existing literature on fungal sensitization and airway diseases.
- Classification of fungi based on their ability to grow at body temperature (thermotolerant vs. non-thermotolerant).
- Analysis of the association between fungal sensitization and lung function/radiological abnormalities.
Main Results:
- Sensitization to thermotolerant fungi (Aspergillus, Penicillium) is linked to reduced lung function and radiological abnormalities (e.g., bronchiectasis, fibrosis).
- Non-thermotolerant fungi (Alternaria, Cladosporium) sensitization is not associated with these adverse outcomes.
- Thermotolerant fungi cause persistent allergenic stimulus and release enzymes that damage airway tissues.
Conclusions:
- All patients with IgE sensitization to thermotolerant fungi and existing airway disease are at risk of progressive lung damage.
- Focusing on fungi capable of growing in airways is crucial for effective antifungal treatment strategies.
- Close monitoring of at-risk patients is essential for managing allergic fungal airways disease.
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