Hypersensitivity pneumonitis: experimental production in calves with antigens of Micropolyspora faeni.

Pneumonitis was induced in calves by exposure to aerosols of Micropolyspora faeni with or without prior sensitization of the animals by subcutaneous injection of antigen. The pneumonitis primarily involved centrolobular areas and was characterized by alveolar septal thickening and loss of air space by cellular infiltration. Vasculitis and focal haemorrhage occurred in certain individuals and haemoproteinaceous exudate appeared within septa and alveolar lumina. The pneumonitis was compared with human farmer's lung, pneumonitis of housed cattle and other experimental hypersensitivity pneumonitides.