High titers of neutralizing auto-Abs against GM-CSF have been reported in patients with idiopathic PAP worldwide since 1999 (Kitamura et al., 1999; Seymour and Presneill, 2002), in about 90% of the more than 400 PAP cases reported (Trapnell et al., 2019). Here, CSF2 is linked to pulmonary alveolar proteinosis.