In primary PAP, GM-CSF signaling is disrupted, leading to alveolar macrophage dysfunction and impaired surfactant clearance.5 This may be the result of mutations affecting GM-CSF receptor expression (hereditary PAP) or of autoantibodies against GM-CSF (autoimmune PAP [AI-PAP]). The gene discussed is CSF2; the disease is pulmonary alveolar proteinosis.