Occupational asthma due to spores of Pleurotus ostreatus

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  • A case of occupational asthma due to Pleurotus ostreatus’ spores inhalation, and the environmental study is reported

Basidiomycetes, the most morphologically advanced of the fungi, include mushrooms, puffballs, bracket fungi and toadstools. Exposure to basidiospores is known to give rise to allergic rhinoconjunctivitis, asthma, and hypersensitivity pneumonitis (1–4). Pleurotus ostreatus is one of the most important basidiomycetes.

A 49-year-old man, a nonatopic, had worked as a seller of fruits and vegetables for the last 30 years at one of the biggest market in Spain. In the last 3 years he had experienced dyspnea, cough, and wheezing 1 or 2 h after large quantities of different mushrooms were unload at the market. He had never had cutaneous or rhinoconjunctival symptoms. He had not experienced constitutional symptoms, such as fever, weight loss, or myalgia. He related his respiratory symptoms to environmental exposure to the mushroom P. ostreatus, being symptom-free during holidays and when mushrooms were not available. He could eat all foodstuffs without any ill effect.

The blood tests revealed eosinophilia (547 eosinophils/mm3). Chest radiography and spirometry were normal. The patient was still working during the study. Skin prick tests to common aeroallergens were negative (including common environmental molds like Aspergillus fumigatus, Alternaria alternata, Penicillium notatum, and Cladosporium herbarum). Skin prick tests were positive to commercial P. ostreatus extract (10 mg/ml) (Bial-Aristegui, Bilbao, Spain) and to home-made P. ostreatus spore extract (10% w/v). Prick-prick with fresh P. ostreatus was also positive.

The methacholine inhalation test revealed bronchial hyperresponsiveness (PC20 0.39 mg/ml). Specific inhalation challenge was carried out by the tidal breathing method as previously described (5) with nebulized P. ostreatus spores extract. At a concentration of 1.25 mg/ml it elicited an early asthmatic response (maximum fall in FEV1 from baseline of 31%) and an incipient late asthmatic reaction (16% fall in FEV1) 9 h later.

Induced sputum when he was at work showed marked eosinophilia (56%). The sputum obtained 24 h after the specific inhalation challenge showed a further increase in airway eosinophilia (70% eosinophils). Bronchial hyperresponsiveness to methacholine increased 24 h after the challenge (PC20 < 0.125 mg/ml).

To verify the existence of airborne allergens that could be triggering the symptoms of our patient, environmental sampling was performed using a volumetric air sampler (Air Sentinel) located inside the cold chamber used to store the mushrooms during a regular working day. Airborne particles were collected onto polytetrafluoroethylene filters (6) and an extract was prepared for the in vitro study (immunoblotting and immunoblotting-inhibition assays).

Total serum IgE was 514 IU/ml. Determination of specific IgE measured by EAST (Enzyme AllergoSorbent Test) technique was positive to Pleurotus spores extract (2.1 kU/l) and to the workplace air sample extract (0.6 kU/l). Specific IgE was negative for several molds (A. fumigatus, A. alternata, P. notatum, and C. herbarum).

Immunoblotting performed with the Pleurotus spores extract (Fig. 1A) showed several IgE-binding bands, ranging from 17 to 85 kDa. Immunoblotting-inhibition studies were carried out using the air sample extract as the solid phase (Fig. 1B). When the patient's serum was preincubated with the Pleurotus spores extract, a wide IgE-binding band disappeared (around 66 kDa), whereas it was present when the patient's serum was preincubated with a nonrelated extract (lamb, as negative control).

Figure 1.

 (A) SDS-PAGE immunoblotting for Pleurotus spores extract. P: Patient's serum. C: Control's serum. M: Molecular mass marker. (−): Non-reducing conditions. (+): Reducing conditions. (B) SDS-PAGE immunoblotting inhibition using the filter extract as the solid phase. Nonreducing conditions. S: Patient's serum pre-incubated with the Pleurotus spores extract. C: Patient's serum preincubated with lamb extract, as negative control. M: Molecular mass marker.

In conclusion, the clinical history and the results of the allergologic work-up including the specific inhalation challenge, the variation of airway hyperresponsiveness and sputum eosinophilia post-challenge point out that this patient had developed occupational asthma caused by P. ostreatus spores. The environmental study demonstrated that airborne allergens from Pleurotus are present in the workplace.

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