• Fetal thymus;
  • epithelial cells;
  • macrophages;
  • ciliated cells;
  • epidermal/fibroblast growth factors;
  • ultrastructure

ABSTRACT: Fourteen-day fetal thymus was grown in organ culture under conditions reportedly optimizing epidermal/epithelial cell growth. While the fibroblastoid component is stimulated by epidermal growth factor and fibroblastoid growth factor, embryonic thymic epithelial cells do not grow significantly under any conditions, although they persist in organ explants. The major cell types cultured are fibroblastoid and macrophage. In organ explant cultures, epithelial cells appear to be oriented by the presence of a cell coat demonstrated by electron microscopy. This coat is absent from certain ciliated cells consistently found in deeper regions of the explant. Using amniotic fluid as a growth factor, almost pure cultures of thymic macrophages can be obtained.