<prompt> Hypersensitivity pneumonitis is classically described as aType I hypersensitivity reactionType II Hypersensitivity reactionType IIIimmune complexe hypersensitivityType IV cell mediated hypersensitivity  <response>: 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 