Background Allergy to rats is an important occupational health problem. The allergens of rat urine have been well defined but those in rat room dust, a potentially important source of inhalant exposure, have not.
Objective To describe the allergens present in rat room dust and to identify a suitable marker protein which may be used to quantify airborne rat allergen. Methods Dust collected from the air-conditioning system (bulk dust, ‘bd’) and with an air sampler (airborne dust, ‘ad’) were analysed by radioallergosorbent test (RAST) inhibition, immunoblotting and immunoblot inhibition techniques and comparisons made with hair and urine extracts prepared from adult male Wistar rats. Results Extensive crossreactivity was found between the extracts by RAST inhibition under different experimental conditions. Dust was more potent as an inhibitor than other extracts. The immunoblotting patterns of both dusts were similar although ‘ad’ contained an allergen at 29kDa not found in ‘bd’. Forty-two sera from rat allergic subjects were used to identify 18 allergens in ‘bd’. Three ‘major’ allergens were found; 100% of subjects had immunoglobulin (Ig)E to a 44 kDa allergen and 74% and 88% of subjects had IgE with bound to the 20.5 and 17 kDa allergens respectively. Immunoblot inhibition experiments identified the 17 kDa dust allergen as α2u-globulin (Rat nI). Conclusions Rat dust is a complex allergenic source. The 17 kDa dust allergen has immunological identity with Rat nl and is a suitable marker protein for the quantitation of airborne rat allergen.