Fig. 1

PAS staining. a-d PAS staining of respiratory epithelial cells seeded onto pure fibrin gel after 7, 14, 21, 33 days, respectively; Cells seeded onto fibrin gel without fibroblasts built up a monolayer of cells by day 7 (a). On day 14, we observed multiple cell layers (b). On day 33 (d) increasing numbers of cell layers were observed, resulting in hyperproliferation compared to native trachea (i). Morphologically, cells grown on pure fibrin gel did not show clear differences between cell types. Respiratory epithelial cells grown upon pure fibrin gel lose organization into pseudostratified epithelium over time, possibly due to dedifferentiation. e-h PAS staining of respiratory epithelial cells seeded onto fibrin gel with embedded fibroblasts after 7, 14, 21 and 33 days. Cells did not show hyperproliferation. Instead, after 14 days of cultivation cells were organized in pseudostratified cell layers (f), almost resembling the organization of epithelium in native trachea (i). A continuous surface of ciliated cells in samples with embedded fibroblasts persists until day 33 (h). i, j Different magnifications of PAS-staining of native porcine trachea, a pseudostratified epithelium with PAS-positive goblet cells, in the submucosa vasculature structures can be found. Scale: 50 μm