A 33-year-old man suddenly develops severe dyspnea with wheezing. On physical examination, his vital signs are temperature, 37deg C; pulse, 95/min; respirations, 35/min; and blood pressure, 130/80 mm Hg. A chest radiograph shows increased lucency in all lung fields. Arterial blood gas analysis shows PO2, 65 mm Hg; PCO2, 30 mm Hg; and pH, 7.48. A sputum cytologic specimen shows Curschmann spirals, Charcot-Leyden crystals, branching septate hyphae, and eosinophils in a background of abundant mucus. What is the most likely risk factor predisposing him to this illness?

Asthma, particularly extrinsic (atopic) asthma, is driven by a type I hypersensitivity response and is associated with an excessive TH 2 and TH 17 cell-mediated immune response. Genetic factors are important in the pathogenesis of atopic asthma and linkage to cytokine genes that map on 5q are strongly associated with development of asthma and other atopic allergies. The Charcot-Leyden crystals represent the breakdown products of eosinophil granules. The Curschmann spirals represent the whorls of sloughed surface epithelium within the abundant mucin. The septated hyphae are Aspergillus organisms colonizing the tracheobronchial tree (allergic bronchopulmonary aspergillosis). Foreign body aspiration may result in inflammation, but without eosinophils. Inorganic dust inhalation leads to restrictive, not obstructive, lung disease. CFTR mutations with cystic fibrosis lead to chronic widespread bronchiectasis. Inflammation with eosinophils is not a significant component of emphysema related to a1 -antitrypsin deficiency or to smoking.