Abstract

Innate defenses in the lung Microanatomy of the airway surfaceWith the advent of the capacity to fix airway surface liquid (ASL) in vivo, using the perfluorocarbon/osmium technique pioneered by Sims et al. ( 12), and the development of well-differentiated (WD) human airway epithelial cultures that exhibit mucus transport in vitro (13), it is now possible to investigate the microanatomy of mucus transport on airway surfaces at high resolution.Representative images depicting the range of morphologic techniques that can be applied to this culture system are shown in Figure 2.Analysis of photomicrographs of this preparation, combined with immunocytochemical studies, have revealed several key features of the microanatomy of the ASL compartment (13,14).The ASL consists of at least two layers, a mucus layer and a periciliary liquid layer (PCL; Figure 2).The mucus layer consists of high-molecular weight, heavily glycosylated macromolecules, products of at least two distinct genes (MUC5AC and MUC5B), that behave as a tangled network of polymers Mucus clearance as a primary innate defense mechanism for mammalian airways