Hypersensitivity pneumonitis.

Hypersensitivity pneumonitis (HP) is a disease of immunemediated inflammation of the lungs after exposure to specific antigens. Patients are often exposed at work or at home to antigens that lead acutely to symptoms of cough, fever, and dyspnea. If the patient is no longer exposed to these antigens, there is usually a recovery without any long-term sequelae. However, chronic exposure can lead to chronic dyspnea and irreversible lung disease. Recent studies have shown the importance of T helper 1 cells and other inflammatory mediators like interleukin-17 in driving the acute inflammatory process. A transition to chronic stages of HP seems to be secondary to T helper 2-mediated inflammation. Symptoms of HP can be acutely controlled with steroids but the definitive treatment involves considering the diagnosis and identifying and stopping continued antigen exposure.