# Characterization of alveolar epithelial cells type II during postnatal lung development in relation to alveolarization – Stereological studies of rat lungs

## TL;DR

This study examines how alveolar epithelial cells type II develop in rat lungs after birth and their role in surfactant production during alveolarization.

## Contribution

The study provides new insights into how AEII cell numbers and surfactant storage adapt during postnatal lung development.

## Key findings

- The number of AEII cells increases significantly by day 21, but their size and volume remain unchanged.
- The total lamellar body volume increases at the end of alveolarization, but individual lamellar body size remains stable.
- AEII cell number, not size, correlates with alveolar surface area and lung volume.

## Abstract

Rats are born with morphologically immature lungs, but intact surfactant system. The aim of this study was to characterize the surfactant producing alveolar epithelial cells type II (AEII) during alveolarization and find relationships between the intracellular surfactant pool and alveolar surface area, lung volume and body weight.

After exsanguination, lungs of 3, 7, 14, 21 and 90 days old rats were inflated with a pressure of 10 mm H20 and fixed by perfusion and prepared for light and electron microscopy. Using different stereological parameters AEII were characterized.

At day 21, the end of bulk alveolarization, the alveolar surface and the number of AEII increased significantly but their volume and size did not change compared to values before alveolarization. The number of AEII, but not the AEII volume correlated significantly with alveolar surface and lung volume. The size and volume weighted mean volume of lamellar bodies (Lb) as well as the Lb volume per AEII did not change during alveolarization. Total Lb volume was significantly higher at the end of bulk alveolarization compared to values before alveolarization.

The adaptation of the intracellular surfactant during postnatal development occurred predominantly by increasing the number of AEII.