Fine structural identification of organoid mouse lung cells cultured on a pigskin substrate.

Mouse full-term embryonic lung tissue was cultured as organ bits using dead, sterile pigskin dermal collagen as a substrate. Explanted organ bits grew on the surface of, and into, the pigskin dermal collagen for at least 9 weeks after the initiation of culture. The outgrowth consisted of a thick cellular sheet containing various sizes of ductular structures within a cellular matrix that did not show any particular structure. Electron microscopic observation revealed that the larger ductular structures consisted largely of ciliated cells. The smaller ductular structure consisted largely of Type II pneumocytes containing lamellar bodies. The cellular matrix consisted of Type II pneumonocytes and other cell types including fibroblasts and macrophages in the early stage of cultivation. Macrophages invaded the pigskin dermal collagen. An intermediate cell type, which has never been observed in vivo, possessing both cilia and lamellar bodies was identified in the larger ductular structures. Upon comparison of the ultrastructure of the organoid in vitro cultures in pigskin with the original fetal lung, it was apparent that cytodifferentiation had occurred. The organoid components and structure of the cultured cells more closely resembled adult lung than the fetal lung used to initiate the cultures.