ANIMAL-MODELS OF OCCUPATIONAL ASTHMA

Occupational asthma is characterized by variable airflow obstruction o ccurring in the workplace. The presence of airways inflammation and hy perreactivity provides further evidence for the disease. Since its pat hogenic mechanism(s) are unknown, animal models have been developed to investigate the various disease processes, as well as to enable study of environmental and genetic factors which may contribute to disease development. Numerous parameters can be measured in animal systems, in cluding specific and total immunoglobulin E (IgE), pulmonary eosinophi lia, diaphragm contractions and airflow muscle hypertrophy. It is reco gnized that no single factor is sufficient to lead to a conclusion of occupational asthma, but rather that a selected combination of paramet ers is most fitting. Animal species selected for study have included: mice, rats, guinea-pigs, rabbits, sheep, horses and nonhuman primates. A guinea-pig system has been utilized for more than 90 yrs and has co ntributed to the basic understanding of physiological and immunologica l processes involved in allergic respiratory sensitization. The benefi ts as well as the disadvantages to be derived from each of the animal systems have been enumerated in this review. Certain caveats must be r ecognized in using animal systems. Attention must always be given to i dentifying differences which exist between animal and human systems, i ncluding morphological, physiological and immunological factors. The e xtent of bronchus-associated lymphoid tissue (BALT) differs greatly am ong animal species and probably plays a major role in development of a llergic responsiveness in animals. In using animal systems, it must be appreciated that animals are only surrogates. Results from such studi es must be compared with information obtained from clinical evaluation in order to avoid faulty extrapolations. Prudent employment of animal models is expected to advance the recognition, treatment and preventi on of occupationally-based asthma.