Bd. Uhal, CELL-CYCLE KINETICS IN THE ALVEOLAR EPITHELIUM, American journal of physiology. Lung cellular and molecular physiology, 16(6), 1997, pp. 1031-1045
The type II alveolar epithelial cell has important metabolic and biosy
nthetic functions but also sen es as the stem cell of the alveolar epi
thelium. Much of the evidence underlying this premise was obtained bef
ore 1980 and provided the basis for a working model that has not been
reconsidered for more than fifteen years. With the exceptions to be di
scussed below, little evidence has accumulated in the interim to sugge
st that the model requires significant alteration. Important questions
remain unanswered, however, and some components of the model need to
be supplemented, particularly in light of recent investigations that h
ave provided insights not possible in earlier work. In particular, in
vitro studies have suggested that the relationship between the parent
type II cell and its progeny may not be as straightforward as original
ly thought. In addition, the rate of epithelial cell loss was recogniz
ed long ago to be an important factor in the regulation of this system
, but its kinetics and mechanisms have received little attention. Thes
e and other unresolved issues are critical to our understanding of the
homeostasis of the alveolar epithelium under normal and pathological
conditions.