Pulmonary alveolar proteinosis (PAP) is a rare lung disease characterized by the accumulation of a lipoproteinaceous substance in the distal air spaces which positively stains with periodic acid-Schiff (PAS). The disease is autoimmune pulmonary alveolar proteinosis (MONDO_0012579, a Monarch Disease Ontology id). Also known as: APAP, Pulmonary Alveolar Proteinosis, autoimmune PAP, iPAP, idiopathic PAP, idiopathic pulmonary alveolar proteinosis.