SynopsisPulmonary alveolar proteinosis (PAP) is a rare syndrome characterized by the accumulation of surfactant in alveoli and terminal airways resulting in respiratory failure. PAP comprises part of a spectrum of disorders of surfactant homeostasis (clearance and production). The surfactant clearance disorders are caused by disruption of GM-CSF signaling (primary PAP) or by an underlying disease that impairs alveolar macrophage functions including surfactant catabolism (secondary PAP). Primary PAP is related to alveolar macrophage dysfunction due to the disruption of GM-CSF signaling caused by a high serum level of anti-GM-CSF autoantibody (autoimmune PAP) (∼90%) or by the mutations in the GM-CSF receptor genes (hereditary PAP). The surfactant production disorders are caused by mutations in genes required for normal surfactant production. The PAP syndrome can be identified based on history, radiologic and bronchoalveolar lavage and/or histopathological findings. The diagnosis of PAP-causing diseases in secondary PAP requires further studies. Whole lung lavage is the current standard therapy and promising new pharmacologic therapies are currently in development.
KeywordsPulmonary surfactant; GM-CSF; Alveolar macrophages; GM-CSF autoantibody; CSF2RA; CSF2RB; Whole lung lavage; GM-CSF inhalation therapy
IntroductionPulmonary alveolar proteinosis (PAP) is a rare syndrome characterized by the accumulation of surfactant in alveolar macrophages and alveoli resulting in hypoxemic respiratory failure. In 1958, Rosen et al. first reported PAP as a disorder consisting of filling of alveoli by a PAS-positive proteinaceous material, rich in lipid 1 . The accumulated material is now known Correspondence: Takuji Suzuki, Cincinnati Children's Hospital Medical Center, Room 4030, Location R, Cincinnati, OH, 45229, USA, to be comprised primarily of pulmonary surfactant and smaller amounts of cell debris. PAP is often reported in the medical literature as a disease rather than as a syndrome and by the use of various terms, e.g., as pulmonary alveolar lipoproteinosis, idiopathic PAP, acquired PAP and congenital PAP 2 . However, it should be noted that PAP is not a single disease. These disorders of surfactant homeostasis can be defined in the context of abnormalities of surfactant production or surfactant clearance. Surfactant production disorders are less common, typically occur in neonates and children, and are associated with alveolar wall distortion and varying degrees of accumulation of dysfunctional surfactant. They are caused by genetic mutations in genes that encode surfactant proteins or proteins involved in surfactant lipid metabolism, e.g., mutation in the SFTPB, SFTPC, ABCA3 or Nkx2.1 genes.
HHS Public AccessDisorders of surfactant clearance are caused by disruption of GM-CSF signaling (primary PAP) or by an underlying disease that impairs alveolar macrophage number or functions including surfactant catabolism (secondary PAP) ( Table 1). Among these PAP-causing diseases, autoimmune PAP is most common and will be a foc...