CSF2RB and pulmonary alveolar proteinosis: Moreover, knock-out mice deficient in the GM-CSF receptor β-chain (Csf2rb−/− mice) (40, 41) or GM-CSF receptor α-chain (Csf2ra−/− mice) (42, 43) also developed a lung phenotype similar to PAP caused by CSF2RA or CSF2RB mutations observed in children.