Introduction: 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.
State of art: 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.
Perspective and conclusion: This article summarizes our current understanding of the diagnostic approach and immunological mechanisms related to HP.