ABCG1 and pulmonary alveolar proteinosis: Because PPARγ is a master transcriptional regulator of alveolar macrophage phenotype specification34, 35 and stimulates expression of both ABCA1 and ABCG1, molecules important in cholesterol export from macrophages26, 36, we tested the hypothesis that pioglitazone, a thiazolidinedione capable of binding and activating PPARγ37, would increase the expression of Abca1 and Abcg1 in Csf2−/− macrophages and reduce the PAP disease severity after oral administration in Csf2rb−/− mice.