Autoimmune PAP (APAP), which accounts for 89% of PAP cases, occurs when anti-GM-CSF antibodies (GMAb) reduce the phagocytic ability of alveolar macrophages, resulting in an inability to process old surfactants in the alveoli and induce surfactant accumulation. This evidence concerns the gene CSF2 and autoimmune pulmonary alveolar proteinosis.