Pulmonary alveolar epithelial cells (PAEpiC), comprised of alveolar type I and type II epithelial cells, line more than 99% of the internal surface area of the lung. Type I cells are large squamous cells whose thin cytoplasmic extensions cover >95% of the internal surface area. They contain aquaporins and exhibit the highest osmotic water permeability of any mammalian cell type. Type II cells, which cover 2-5% of the surface area, produce, secrete, and recycle pulmonary surfactant. Type II cells contain Na+-, K+-ATPase and amiloride-sensitive epithelial Na+ channels. The currently accepted hypothesis is that Type II cells maintain pulmonary fluid homeostasis by regulating active Na+ transport in the lungs, whereas Type I cells are "inert" cells that provide solely a barrier function, rather than having active functions. Recent studies indicate that Type I cells are also important in regulating ion and fluid transport. HPAEpiC from ScienCell Research Laboratories are isolated from human lung tissue. HPAEpiC are cryopreserved at passage one and delivered frozen. Each vial contains >1 x 106 cells in 1 ml volume. HPAEpiC are characterized by immunofluorescence with antibodies specific to cytokeratin-18 and/or cytokeratin-19. HPAEpiC are negative for HIV-1, HBV, HCV, mycoplasma, bacteria, yeast and fungi. HPAEpiC are guaranteed to further culture under the conditions provided by ScienCell Research Laboratories; however, HPAEpiC are not recommended for expanding or long-term cultures since the cells differentiate to become type I alveolar epithelial cells immediately after plating and type I alveolar epithelial cells do not proliferate in culture. Recommended Medium It is recommended to use Alveolar Epithelial Cell Medium (AEpiCM, Cat. #3201) for culturing HPAEpiC in vitro.