Hypersensitivity pneumonitis.

Hypersensitivity pneumonitis is a syndrome caused by sensitization to any of a wide variety of environmental antigens and results in a pulmonary immunologic inflammatory process. The clinical syndrome occurs in a temporal relationship to exposure to the offending agent with resultant systemic or respiratory symptoms with defined chest radiographic and pulmonary function abnormalities. Definitive immune responses include those of the humoral and cellular system. Avoidance of exposure as treatment results in reversal of the clinical abnormalities.