Basement membrane pores in human bronchial epithelium - A conduit for infiltrating cells?

This study reports the presence of oval-shaped pores in the basement membra ne of the human bronchial airway that may be used as conduits for immune ce lls to traffic between the epithelial and mesenchymal compartments. Human b ronchial mucosa collected after surgery was stripped of epithelial cells wi thout damaging the basement membrane. Both scanning and transmission electr on microscopy showed oval-shaped pores 0.75 to 3.85 mum in diameter in the bronchial basement membrane at a density of 863 pores/ mm(2). Transmission electron microscopy showed that the pores spanned the full depth of the bas ement membrane, with a concentration of collagen-like fibers at the lateral edges of the pore. Infiltrating cells apparently moved through the pores, both in the presence and absence of the epithelium. Taken together, these r esults suggest that immune cells use basement membrane pores as predefined routes to move between the epithelial and mesenchymal compartments without disruption of the basement membrane. As a persistent feature of the basemen t membrane, pores could facilitate inflammatory cell access to the epitheli um and greatly increase the frequency of intercellular contact between traf ficking cells.