Subepithelial superficial lymph vessels in the airway: a histological study using human fetuses and elderly cadavers

Airways are lined by the stratified squamous or ciliated columnar epithelia.

Using D2-40 immunohistochemistry of airway specimens from 20 donated cadavers, we aimed to find an epithelia-dependent morphology of lymph vessels (LVs).

LVs tended to run along and around the hair follicle in the vestibular skin, while they tended to run along the anteroposterior axis in the other nasal walls. They tended to run circularly in the bronchus and both circularly and longitudinally in the upper pharynx. LVs density (mm² per 1 mm length of the epithelium) was highest in the upper pharynx (0.087 ± 0.043 mm²) and lowest in the mucocutaneous junction of nose (0.022 ± 0.006 mm²) although both were covered by squamous epithelia. In the nose, the ciliated epithelia accompanied significantly dense network of LVs relative to the squamous epithelial parts (p < 0.01). The nasal ciliated epithelia (0.052 ± 0.014 mm²) often showed higher density than the bronchial ciliated epithelia (0.032 ± 0.014 mm²), but we found no statistical significance. Therefore, a site-dependent specificity of the pharynx was so evident that it seemed to mask an epithelial type-dependent difference. Histological observations of 10 human fetuses exhibited distinct site-dependent features in airway subepithelial vessels: 1) a well-developed venous plexus occupied the nasal wall and palate and it might interfere with development of LVs; 2) subepithelial LVs appeared abundantly beneath the tracheal and laryngeal epithelia before the epithelial differentiation.

Site-dependent differences in subepithelial LVs appeared in fetuses and, after birth, they seemed to drastically change depending on the functional demand. Accordingly, epithelia-dependent differences tended to became unclear.