Dust mite allergens are carried on not only large particles

The major obstacle for the successful measurement of airborne mite allergen is its very low concentration in the absence of vigorous disturbance. The aim of this study was to investigate the particle size distribution of grou p 2 dust mite allergen using an amplified ELISA system. Air sampling was pe rformed using an Andersen sampler placed in the centre of the room, 1.2 m a bove floor level (airflow rate 28.7 l/min). This is a multistage, multiorif ice cascade impactor that is comprised of six stages. Any particle greater that 4.7 mu m should impact on stages 1 and 2, whilst stages 3-6 measure th e predominantly respiratory range. The sampling was carried out for 30 min after 15 min of vigorous disturbance (vacuum cleaning without bag and filte r). Der p 2 was measured using mAb-based ELISA with the AmpliQ amplificatio n kit (Dako Ltd, Cambridgeshire, UK). The sensitivity was increased 15-fold as compared with standard assay, bringing the level of detection to 300 pg /ml. The majority of airborne Der p 2 (79.4%) was carried on large particle s (> 4.7 mu m). However, a small but important proportion of airborne Der p 2 (20.6%) was associated with small particles (1.1-4.7 mu m) It is worth n oting that all the levels measured were below the detection limit of standa rd assay. In conclusion, we have shown that using an amplification system, airborne mite allergen previously undetectable owing to its low concentrati on can be quantified. Group 2 dust mite allergen is carried not only on lar ge particles. A small, but potentially significant proportion of this airbo rne allergen is associated with small particles which, when inhaled, may pe netrate deep into the human respiratory tract.