IN-VIVO RESTITUTION OF AIRWAY EPITHELIUM

Epithelial shedding occurs in health and, extensively, in inflammatory airway diseases. This study describes deepithelialisation, reepitheli alisation and associated events in guinea-pig trachea after shedding-l ike epithelial denudation in vivo. Mechanical deepithelialisation of a n 800-mu m wide tracheal zone was carried out using an orotracheal ste el probe without bleeding or damage to the basement membrane. Reepithe lialisation was studied by scanning- and transmission electron microsc opy and light microscopy. Nerve fibres were examined by immunostaining . Cell proliferation was analysed by [H-3]-thymidine autoradiography. Immediately after epithelial removal secretory and ciliated (and presu mably basal) epithelial cells at the wound margin dedifferentiated, fl attened and migrated rapidly (2-3 mu m/min) over the denuded basement membrane. Within 8-15 h a new, flattened epithelium covered the entire deepithelialised zone. At 30 h a tight epithelial barrier was establi shed and after 5 days the epithelium was fully redifferentiated. After completed migration an increased mitotic activity occurred in the epi thelium and in fibroblasts/smooth muscle beneath the restitution zone. Reinnervating intraepithelial calcitonin gene-related peptide-contain ing nerve fibres appeared within 30 h. We conclude that (1) reproducib le shedding-like denudation, without bleeding or damage to the basemen t membrane, can be produced in vivo; (2) secretory and ciliated cells participate in reepithelialisation by dedifferentiation and migration; (3) the initial migration is very fast in vivo; (4) shedding-like den udation may cause strong secretory and exudative responses as well as proliferation of epithelium, and fibroblasts/smooth muscle. Rapid rest itution of airway epithelium may depend on contributions from the micr ocirculation and innervation.