Mite allergen (Der p 1) is not only carried on mite feces.

Exposure to allergens derived from house dust mites (eg, Dermatophagoides pteronyssinus) is considered an important factor in the development and exacerbation of asthma. In cultures, more than 95% of mite allergen Der p 1 was associated with mite feces (mean diameter of 22 ± 6 µm; range, 10 to 40 µm). 1 Domestic air sampling in bedrooms during dust disturbance showed that greater than 80% of detectable Der p 1 was associated with particles larger than 10 µm and only a small proportion with particles smaller than 5 µm, 2,3 the identity of which is not known. To explain how exposure to such large particles (>10 µm) could cause asthma, it was proposed that a low proportion of these large fecal particles would enter the lower airways, and the effects of high local allergen concentrations from each particle, on chronic exposure, might provide sufficient stimulus to maintain or produce hyperreactivity. 2 There is also some direct evidence of mite allergen, albeit in low concentrations, in the lungs of asthmatic subjects. 4 We investigated the sources of Der p 1 aeroallergen by using a new technique, which enables individual particles containing allergen to be visualized. METHODS Airborne particles were sampled with intranasal air samplers (Institute of Respiratory Medicine, Sydney, Australia), which collect particles larger than 5 µm. Samples were collected in parallel with a lapel-mounted filter (Institute of Occupational Medicine [IOM], Edinburgh, UK) and a vacuum pump, which achieved a flow rate of 1.8 L/min with the filter in place. Each sample was collected for 10-minute periods, and 4 nasal samplers and 6 filter samples were collected while brushing the carpet once every 30 seconds. Within the nasal sampler, particles were collected onto a polyvinylidene difluoride membrane and coated with a thin film of an aqueous-based adhesive that was later over-layed with a thin layer of agarose to fix captured particles in position. In the IOM sampler, particles were collected by suction onto a dry polyvinylidene difluoride membrane (pore size, 0.45 µm), which was later overlayed with transparent adhesive tape to prevent particle movement. Particles captured for both IOM and nasal air samplers were immunostained with Der p 1–specific mAb (Indoor Biotechnologies , University of Virginia) followed by an anti-mouse alkaline phosphatase conjugate and developed by using 5 bromo-4 chloro-3 indolyl phosphate/nitro blue tetrazolium substrate. The total number of particles and those containing Der p 1 were counted, and their sizes …