Hypersensitivity pneumonitis is classically described as a
The pathophysiology of HP has not been characterized in depth on an immunologic level, although it has been established that HP is an immune-mediated condition that occurs in response to inhaled antigens that are small enough to deposit in distal airways and alveoli. Ref Harrison 19th edition pg 1681-82
Type I hypersensitivity reaction
Type II Hypersensitivity reaction
Type III(immune complexe) hypersensitivity
Type IV ( cell mediated) hypersensitivity
Respiratory system