From the Guidelines
The hypersensitivity reaction associated with farmer's lung is a Type IV hypersensitivity reaction, also known as a T-cell-mediated delayed type hypersensitivity reaction [ 1 ].
Key Characteristics
- This reaction occurs when the immune system responds to repeated inhalation of finely dispersed allergens, such as organic particles like fungi and thermophilic bacteria [ 1 ].
- The immunologic mechanism involves T-cell-mediated responses, which lead to bronchiolocentric granulomatous inflammation [ 1 ].
- Farmer's lung is a form of hypersensitivity pneumonitis (HP), a complex group of syndromes that can be classified by temporal relationship between exposure and symptoms, occupation, or type of antigen [ 1 ].
- Treatment and management of HP typically involve avoidance of exposure to the offending antigen and may include administration of corticosteroids to reduce inflammation [ 1 ].
Clinical Presentation
- HP can present as acute, subacute, or chronic (fibrotic) disease, with cough being a common symptom in all forms [ 1 ].
- The condition is often associated with specific occupations, such as farming, or exposure to certain antigens, like aerosolized water contaminated with microbes [ 1 ].
From the Research
Hypersensitivity Reaction in Farmer's Lung
The type of hypersensitivity reaction associated with farmer's lung, a condition characterized by hypersensitivity pneumonitis (HP), is:
- Type III immune complex hypersensitivity, as initially thought, but more recent evidence suggests that
- Type IV or delayed-type hypersensitivity plays a more important role in the pathogenesis of hypersensitivity pneumonitis 2, 3 Some key points about the hypersensitivity reaction in farmer's lung include:
- The disease is caused by inhaling microorganisms from hay or grain stored in conditions of high humidity in the agricultural workplace 4
- The most common antigens are usually thermophilic actinomycetes and fungi 4, 2
- The clinical presentation may vary, differentiating the chronic and acute forms of the disease 4, 5
- The main treatment is avoidance of the antigen, and corticosteroid treatment may accelerate resolution of the acute forms, but its effectiveness in preventing disease progression in the long-term or reducing mortality is not well established 4, 5, 6