Accordingly, absence of PPARγ, GM-CSF, or 1 of the 2 GM-CSF receptor subunits (CSF2R α and β) in mice results in abrogated alveolar macrophage development and pulmonary alveolar proteinosis (PAP) (5, 6, 9–11). Here, CSF2 is linked to pulmonary alveolar proteinosis.