CSF2RB and pulmonary alveolar proteinosis: GM-CSF plays a key role in surfactant clearance of AMs, as evidenced by the development of hereditary PAP in patients with deficiencies in either CSF2RA or CSF2RB resulting in a lack of AMs (4, 69), and the development of autoimmune PAP in patients with non-functional AMs due to neutralizing auto-antibodies against GM-CSF (70).