Differentiation of ciliated cells in the terminal bronchioles of neonatal calves

The bronchiolar ciliated cells are exquisitely sensitive to injury caused by infection or irritation of the airways. The mechanism by which bronchiolar ciliated cells are renewed following injury or during the normal course of differentiation is still debated. The present study aimed at recognizing the progenitor cell population for bronchiolar ciliated cells during early neonatal life of calves and to demonstrate the course of events occurs during its differentiation into ciliated cells. Scanning electron microscopy of the terminal bronchiolar epithelium revealed two distinct cell types namely ciliated and non-ciliated cells. Transmission electron microscopy revealed ciliated, non-ciliated (Clara), intermediate and basal cells. At least two categories of intermediate cells could be distinguished: intermediate cells with abundant glycogen and variable numbers of organelles; intermediate cells with little glycogen, large numbers of polyribosomes, and variable numbers of basal bodies. We conclude that: (1) both bronchiolar non-ciliated and basal cells serve as progenitors for the bronchiolar ciliated cells; (2) differentiation of ciliated cell from the non-ciliated one involves a transitional cell in which glycogen is lost, polyribosomes are synthesized before the synthesis of basal bodies and cilia.