Hematoxylin and eosin (H&E) staining of alveolar progenitor clone makes lipid droplets indicative of alveolar differentiation. (A) Alveolar progenitor-derived outgrowths following hormonal stimulation using pituitary isografts show the formation of lipid droplets inside the lumen. (B) Ductal progenitor outgrowths, shown for comparison, are incapable of alveolar differentiation, and the ducts lack the ability to form lipid droplets. (C to E) Intraductal papillary hyperplasia (IDH) generated by the ductal progenitors. Arrows indicate IDH lesions. H&E images taken at ×20 original magnification.