Farmer's lung pathophysiology

The pathogenesis of the Farmer’s lung disease is type 3 or type 4 hypersensitivity reaction.

Hypersensitivity reaction because of the many immunologic phenomenon present and antibodies of organism invasion into tissues.

• Type 3 hypersensitivity
• When moldy hay antigens complex with antibodies, to bind complements and attract neutrophils, causing inflammation by release of their toxic enzymes and radicals.^[1]

• Type 4 hypersensitivity
• mononuclear cell inflammation and granuloma.

Sensitized pulmonary alveolar macrophages activated by antigen attract neutrophils and also modulate T cell activity leading to appearance of mononuclear cells and granuloma.^[2]

There are no established genetic predispositions.

There are no associated conditions.

• Pulmonary alveolar wall and interstitial accumulation of neutrophils, mononuclear cells and edema.
• Obstructive bronchiolitis and capillary inflammation is present.

• mononuclear cell predominant
• presence of noncaseating granuloma