Pathophysiology of Pulmonary Alveolar Proteinosis Impaired alveolar macrophage processing of surfactant due to abnormal granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling is thought to contribute to the disorder, perhaps due to reduced or absent function of the common beta chain of the GM-CSF / interleukin (IL) - 13/IL-5 receptor on mononuclear cells (present in some children but not in adults with the disorder).