ASTHMA that is mediated by IgE— mast-cell mechanisms is the most common immunologic disease. However, other inflammatory lung diseases are increasingly being recognized as having an immune basis and their pathogenetic mechanisms are beginning to be understood. The granulomatous and interstitial lung diseases are an important part of this group.
Hypersensitivity pneumonitis, or extrinsic allergic alveolitis, is an immunologic inflammatory reaction involving the lung interstitium, terminal bronchioles, and alveoli and is due to hypersensitivity to antigenic organic dusts often encountered in occupations or hobbies.1 Some of the more common antigens causing this reaction are listed in Table 13-1.
Prevalence and Etiology
The prevalence of the disease is unknown. Farmer's lung, pigeon breeder's disease, and ventilation pneumonitis are most frequently encountered in the United States. About 8% of dairy farmers have serum precipitins to thermophilic organisms and about 4% have farmer's lung. About 6% to 15% of persons