[Clinical and immunopathological aspects of hypersensitivity pneumonitis]

Hypersensitivity pneumonitis (HP) is a pulmonary disease with symptoms of dyspnoea and cough resulting from the inhalation of an antigen to which the patient has been previously sensitized.

Acute and subacute HP represent the most active forms of the disease which may become chronic while remaining progressive. HP may also evolve to end-stage lung disease. Clinical symptoms and signs tend to be non-specific and the diagnosis of HP often relies on the clinical context. The immune response is initiated when the alveolar macrophage phagocytoses the antigen, provoking the expansion of lymphocytes T and B that reach the pulmonary parenchyma through the systemic circulation. This reaction is amplified by the expression of a number of inflammatory mediators.

This article summarizes our current understanding of the diagnostic approach and immunological mechanisms related to HP.