In healthy lungs, type II alveolar epithelial cells produce GM-CSF to aid in alveolar epithelial cell repair and restoration and to maintain surfactant homeostasis via alveolar macrophage cholesterol clearance (discussed in Autoimmune Pulmonary Alveolar Proteinosis (aPAP): a GM-CSF deficiency state and in the setting of checkpoint-induced pneumonitis in Anti-cancer potential and mitigation of immune checkpoint inhibitor immune-related adverse events and risk of GM-CSF insufficiency) (7, 11, 118, 125). This evidence concerns the gene CSF2 and pneumonitis.