By contrast, autoimmune PAP has an essentially adult onset, with more than 90% of cases due to high serum levels of neutralizing anti-GM-CSF auto-Abs [34], whereas about 5 to 10% of the remaining adult PAP cases may be secondary to underlying conditions, such as hematological disorders, cancers, chronic inflammatory syndrome, and chronic infections [21]. Here, CSF2 is linked to pulmonary alveolar proteinosis.