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.