Allergy to laboratory animals : risk factors for development of allergy and methods for measuring airborne rodent allergens

Abstract

Between 10-50% of workers exposed to laboratory animals, mainly rats or mice, develop laboratory animal allergy (LAA) with symptoms of rhinitis, conjuctivitis, asthma, or urticaria, and IgE against animal allergens. Symptoms often arise within the first years of animal work. Up to half of the symptomatic subjects develop asthma. One aim of the thesis was to determine risk factors for LAA, especially in environments with low exposures. A second aim was to develop methods to quantify aeroallergen exposure.

In a prospective study, 225 laboratory technician students were investigated. Two years after graduation, those who were laboratory animal exposed (median exposure 18 months) were re-examined (n=38). We found indications of selection by atopy, away from animal work. Seven exposed (18%) had developed skin prick test positivity (sensitisation) to laboratory rodents and 8 (21%) had experienced allergic symptoms at animal work. Those sensitised and/or symptomatic (n=9) against laboratory animals had an increased bronchial responsiveness compared to pre-exposure (P<0.01), and compared to exposed without sensitisation or symptoms (P<0.05). Elevated total IgE (P<0.01) and hours/month of exposure (P<0.05), but not number of months, were both risk factors for LAA.

The risk of developing LAA in research departments with low exposure was investigated in a cross-sectional study (n=80). A fourth of those with <4 years of rodent exposure were sensitised or symptomatic whereas half of those with >4 years of exposure were sensitised or symptomatic. Risk factors for LAA were Phadiatop positivity, elevated total IgE, allergy to other fur animals and exposure to mainly male rodents. For subjects with both exposure to male rodents and elevated total IgE or positive Phadiatop, sensitisation was 11-fold higher compared to subjects with neither risk factor. Thus, exposure to male rodents, who excrete up to hundreds of times higher levels of urinary allergen than females, may constitute an overlooked risk factor. Even a low allergen exposure seems to maintain allergic symptoms and specific IgE.

To measure airborne rat urinary allergens (RUA), a two-monoclonal sandwich ELISA was developed, specific for the potent Rat n 1 isoallergens. An amplification method was developed, which increased sensitivity tenfold, to 0.1 ng/m3 in one-hour air samples collected at 2 I/min. A polyclonal sandwich ELISA for mouse urinary allergen (MUA) measurement was developed against the main allergen complex Mus m 1, with detection limit 1 ng/m3.

The ELISA RUA method was compared with a RAST inhibition method used in the UK. Samples were collected in each country, and analysed in both laboratories. The values were correlated (r2 of log values =0.72, P<0.001) but the RAST inhibition values were about 300 fold higher than the sandwich ELISA values.

In a European Community study, methods to measure rat and mouse aeroallergens used in laboratories in the Netherlands (NL), UK, and Sweden were compared. Samples were collected in triplicate and were divided between the laboratories, where they were eluted and analysed. RAST inhibition using patient serum gave RUA values several orders of magnitude higher than those obtained using the sandwich ELISA methods. Polyclonal rabbit antibodies against MUA used in an inhibition RIA gave values 5-6 times higher than in the sandwich ELISAs. The NL polyclonal ELISAs were the least sensitive and the inhibition assays were the least specific of the assays. Use of polyclonal antibodies gave higher values than monoclonal antibodies. Addition of Tween and BSA increased elution efficiency and storage stability. A major difference between the assays was the reaction to rodent room extracts: whereas the RUA RAST inhibition detected rat room ventilator dust similarly to concentrated urine, dust was detected with 700-800-fold less sensitivity in the ELISA assays. The polyclonal MUA assays all detected mouse room dust with 30-50-fold less sensitivity than mouse urine.

We concluded that assay set-up and antibody specificity are the most important factors influencing antigen binding. A thorough standardisation of methods to measure airborne allergen is necessary and may be achieved using a sandwich ELISA assay with defined and purified antibodies and standard antigens.