Because ABCA1 and ABCG1 are involved in cholesterol clearance in macrophages and expression of both is abnormal in alveolar macrophages in humans and mice with PAP caused by disruption of GM-CSF mediated PPARγ signaling, we determined if the changes in expression were primary (i.e., due to the loss of GM-CSF signaling) or secondary (i.e., due to exposure to surfactant). Here, ABCA1 is linked to pulmonary alveolar proteinosis.