MTOR and pulmonary alveolar proteinosis: Immunosuppression has also been assigned a pathogenic role in cases of symptomatic PAP among solid-organ transplant recipients,2, 5, 6 most commonly in those receiving mammalian target of rapamycin (mTOR) inhibitors.2, 7 The actual mechanism by which PAP may occur de novo with the use of these drugs is not clear.8