CSF2 and pulmonary alveolar proteinosis: For example, autoimmune pulmonary alveolar proteinosis (aPAP), the most common form of PAP (>90% of patients), is caused by the inappropriate production of IgG class autoAbs against granulocyte-macrophage colony-stimulating factor (GM-CSF), a 23-kDa hematopoietic cytokine.