CSF2 and pulmonary alveolar proteinosis: For example, pulmonary alveolar macrophages require GM-CSF to maintain surfactant homeostasis, which is critical to alveolar stability and lung function5, 6, and disruption of GM-CSF signaling causes pulmonary alveolar proteinosis (PAP) – a syndrome of progressive alveolar surfactant accumulation and resulting hypoxemic respiratory failure that occurs in men, women and children3, 7.