Dose of cat (Felis domesticus) allergen 1 (Fel d 1) that induces asthma.
In 10 patients with cat asthma and hay fever, we quantified the doses of cat allergen (expressed as cat allergen 1 [Cat-1] in log Food and Drug Administration [FDA] units) inspired from the ambient air of a room containing living cats required to induce a 20% drop in FEV1. These doses were compared with the doses required to cause the same change in FEV1 when the patients were subjected to bronchial challenge with aerosols of cat hair and dander extract in the conventional manner. Patients highly sensitive to cat extract by skin, leukocyte histamine release, and bronchoprovocation tests and with measurable levels of anticat IgE by RAST were exposed for up to 2 hours in a room occupied full-time by two cats. At the same time, room air was sampled by a Durham gravity sampler, by an Andersen sampler, and by lapel fiberglass filters. When hair and dander particles trapped on greased slides by gravity and Andersen samplers were stained, sized, and counted, squamous cell fragments in the less than 10 mm range were abundant. Assays of extracts from the lapel filters for Cat-1 content by radioimmunoassay and for allergenic activity by leukocyte histamine release demonstrated a significant correlation (p less than 0.05) between the results of the two assays. All patients developed rhinitis and asthma during exposure. At the time of a 20% drop in FEV1, when air sampling was stopped, the lapel filters had trapped a total of -1.86 to less than -3.04 (median -2.74) log FDA units Cat-1. These measurements of Cat-1 exposure in the room correlated (p less than 0.01) with the doses of cat extract (-1.18 to -3.15 [median -2.26] log FDA units Cat-1 equivalents) required to induce a 20% fall in FEV1 in the conventional bronchoprovocation tests.