Hypersensitivity pneumonitis is classically described as a: (A) Type I hypersensitivity reaction, (B) Type II Hypersensitivity reaction, (C) Type III(immune complexe) hypersensitivity, (D) Type IV ( cell mediated) hypersensitivity
Answer is C. 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