CSF2 and pulmonary alveolar proteinosis: Multiple clinical forms of PAP have been described according to the presumed aetiology [11]: (1) idiopathic (primary) PAP, the most common form diagnosed in adults, which may be either congenital (mutations of α or β chains of the receptor for GM-CSF) or acquired (autoimmune PAP with autoantibodies targeting GM-CSF); (2) secondary PAP, resulting from conditions in which AM function is suppressed, such as immunodeficiency states, hematologic malignancies, exposure to inorganic dusts (eg, silica), or pharmacologically induced.