How can bird proteins cause pigeon breeder's lung?

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Medical illustration of the human chest showing the lungs, diaphragm, ribs, trachea, bronchus, and bronchioles, with one lung cut away to reveal internal structures. — respiratory disease The bronchioles of the lungs are the site where oxygen is exchanged for carbon dioxide during the process of respiration. Inflammation, infection, or obstruction of the bronchioles is often associated with acute or chronic respiratory disease, including bronchiectasis, pneumonia, and lung abscesses.

Pigeon breeder’s lung, also known as bird fancier’s lung, is a form of hypersensitivity pneumonitis triggered by an allergic reaction to specific proteins found in birds.12

These proteins are primarily present in the excreta of birds, such as pigeons, parakeets, and canaries. When individuals with close contact to these birds inhale dust containing these proteins, their lungs can become sensitized.1

Upon reexposure, this sensitivity leads to an acute inflammatory response in the smaller bronchioles and alveolar walls. If the condition remains untreated or exposure continues, it can progress to chronic forms characterized by the formation of granulomas, widespread lung fibrosis, and permanent respiratory impairment.1