Human tracheobronchial epithelial cells direct migration of lung fibroblasts in three-dimensional collagen gels

Normal airway morphogenesis and repair after injury depend in part on the interaction between the mesenchymal and epithelial cells in the tracheobronchial tree. We cultured human lung fibroblasts between layers of type I collagen gel and examined sections through these three-dimensional matrices to assess fibroblast migration. The migration assay used in these experiments allowed simultaneous assessment of directed and random fibroblast migration as well as cell number. We tested the hypothesis that human tracheobronchial epithelial (HTBE) cells direct the migration of fibroblasts. When fibroblasts were cultured alone, migration was nearly equivalent in the upper and lower collagen layers. When HTBE cells were plated on the upper collagen lattice, there was a net migration of fibroblasts toward the HTBE cells. The differential migration was evident early in culture but became maximal after 1 wk. Differences increased at higher HTBE cell inoculation densities. No epithelial chemokinetic or mitogenic influence was evident: total cell migration and total fibroblast number were not significantly different between the control and coculture sections. HTBE fibronectin production may contribute to directed migration because fibronectin, added to the upper lattice, reproduced a portion of the directed migration seen in coculture. Our data support the hypothesis that epithelial cells direct fibroblast migration.