Animal models of occupational asthma

Occupational asthma is characterized by variable airflow obstruction occurring in the workplace. The presence of airways inflammation and hyperreactivity provides further evidence for the disease. Since its pathogenic 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, including specific and total immunoglobulin E (IgE), pulmonary eosinophilia, diaphragm contractions and airflow muscle hypertrophy. It is recognized that no single factor is sufficient to lead to a conclusion of occupational asthma, but rather that a selected combination of parameters 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 contributed to the basic understanding of physiological and immunological processes involved in allergic respiratory sensitization. The benefits as well as the disadvantages to be derived from each of the animal systems have been enumerated in this review. Certain caveats must be recognized in using animal systems. Attention must always be given to identifying differences which exist between animal and human systems, including morphological, physiological and immunological factors. The extent of bronchus-associated lymphoid tissue (BALT) differs greatly among animal species and probably plays a major role in development of allergic responsiveness in animals. In using animal systems, it must be appreciated that animals are only surrogates. Results from such studies 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 prevention of occupationally-based asthma.