A 25-year-old man experiences acute onset of fever, cough, dyspnea, headache, and malaise a day after moving into a new apartment. His symptoms subside over 3 days when he visits a friend in another city. On the day of his return, the symptoms recur. There are no remarkable findings on physical examination. A chest radiograph also is unremarkable. Which of the following pathogenic mechanisms is most likely to produce these findings?

Hypersensitivity pneumonitis has acute symptoms that occur soon after exposure to an antigen, often actinomycetes or fungi (molds) growing in contaminated HVAC systems (air conditioner or ventilation ducts). The symptoms improve when the patient leaves the environment where the antigen is located. The pulmonary pathologic changes are usually minimal, with interstitial mononuclear infiltrates. It is mainly a type III hypersensitivity reaction, but with more chronic exposure to the antigen, there may be a component of type IV hypersensitivity with granulomatous inflammation and fibrosis. Attachment of antibody to basement membrane occurs in Goodpasture syndrome. Mycolic acid is a component of the cell wall of mycobacteria, and infections with these organisms are chronic, not episodic. Prostaglandins are produced by the cyclooxygenase pathway of arachidonic acid metabolism during acute inflammation, and they mediate pain and vasodilation. Histamine release is characteristic of a type I hypersensitivity reaction that more typically occurs in allergic disease. A toxic injury is more typical of inhalation of a toxic gas, such as sulfur dioxide (so-called silo filler's disease).