A 28-year-old asthmatic woman has recurrent wheezing episodes, brownish plugs in her sputum, and fleeting upper lobe infiltrates on chest radiograph. Total serum IgE is markedly elevated and Aspergillus fumigatus specific IgE is positive. Sputum microscopy shows eosinophils with Charcot-Leyden crystals. Which immunopathological mechanism best explains this condition?
- A Type I hypersensitivity alone to inhaled conidia
- B Combined type I and type III hypersensitivity to fungal antigens growing within the airway lumen ✓
- C Tissue invasion by hyphae in a neutropenic host
- D Granulomatous delayed-type hypersensitivity to a fungus ball within a pre-existing cavity
Explanation
Allergic bronchopulmonary aspergillosis results from hypersensitivity to A. fumigatus growing non-invasively within the bronchial lumen. Type I (IgE mediated) responses cause wheeze and immediate skin reactivity while type III (IgG immune complex) responses contribute to pulmonary infiltrates and proximal bronchiectasis. Markedly raised total IgE and specific IgE support the diagnosis. Option C describes invasive aspergillosis of neutropenic patients, option D describes chronic cavitary disease with an aspergilloma, and type I hypersensitivity alone does not account for the infiltrates and bronchiectasis.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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