Uptake and transport of exogenous proteins by respiratory epithelium.

The tracer proteins, horseradish peroxidase and ferritin, placed in the trachea of guinea pigs were taken up by epithelial cells and transported to the extracellular space. The interval between the introduction of the tracer proteins into the lumen of the trachea and the morphologic demonstration of the porteins in the extracellular space or within the basal portion of the cells was between 30 and 60 minutes. The proteins were transported in vesicles and no penetration of the epithelial intercellular tight junctions was found. The intercellular tight junctions were made permeable to horseradish peroxidase by anesthetic ether and this permeable epithelium was compared to the vesicle type transport. Transepithelial transport of proteins is a possible mechanism for the introduction of antigenic material into the subepithelial lymphoid tissue and this transport may also be of importance in the late onset type of asthma.