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 antic at 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 <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 < 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 < -3.04 (median - 2.74) log FDA units Cat-1. These measurements of Cat-1 exposure in the room correlated (p < 0.01) with the doses of cat extract (-1.18 to -3.15 [median -2.26] log FDA units Cat-I equivalents) required to induce a 20% fall in FEV₁ in the conventional bronchoprovocation tests.