Quantitative immunohistochemical analysis of the expression of CD31 during lung development in the rat

The CD31 antigen, known also as the platelet/endothelial cell adhesion molecule 1, has been shown to be a good marker for monitoring the formation of the vasculature in mammals. Available evidence suggests that the expression of CD31 is regulated during embryonal and fetal development. The aim of the present study was to evaluate the changes in the expression of CD31 during the development of the rat lung. We studied samples of lung tissue from rat fetuses (17, 19 and 21 days after conception), newborns (1, 3, 5, 7, 14 and 21 days after birth) and adult animals. The tissue samples from rats in the various age groups were divided into sets, with all age groups being represented in every set. After immunohistochemical localization of the antigen, the amount of chromogen deposited after the immunoreaction (defined in terms of optical density; OD) was evaluated by image analysis in the various sets. Measurements were obtained twice from each set, and the results were reproducible (paired t test, alpha = 0.05). We subjected the results of measurements from all sets to an analysis of variance (ANOVA). The amount of chromogen (OD) decreased from fetal day 19 to 5 days after delivery and then increased again. The decrease in the level of expression of CD31 on days 3 and 5 after delivery was significant (p < 0.0001).