Immunologic Aspects of Granulomatous and Interstitial Lung Diseases

HYPERSENSITIVITY pneumonitis, also known as extrinsic allergic alveolitis, is a hypersensitivity reaction involving the lung interstitium and terminal bronchioles due to hypersensitivity to antigenic organic dusts. These dusts are most often encountered in occupations or hobbies (see Table 11-1). HYPERSENSITIVITY PNEUMONITIS—EXTRINSIC ALLERGIC PNEUMONITIS Prevalence and Etiology The true prevalence of the disease is unknown. Farmer's lung, pigeon breeder's disease, and disease from contaminated air-conditioning systems 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 10% of persons who raise pigeons for a hobby become ill. In some industries up to 10% of exposed individuals have been affected by contaminated air conditioners. Since not everyone exposed equally to these dusts manifests the disease, there are obviously host factors that predispose to this illness, but these have not been defined. Symptoms and Signs