On P7 and P14, rat pups were anesthetized, and their lungs were harvested and prepared for immunohistochemistry and histological analyses, as previously described (14 (link),33 (link)). For immunohistochemical evaluation of von Willebrand factor (vWF), the deparaffinized lung sections were incubated with polyclonal rabbit antihuman vWF antibody (DakoCytomation, Glostrup, Denmark) and a biotin-labeled donkey antimouse secondary antibody (Jackson ImmunoResearch Laboratories, West Grove, PA). Immune complexes were visualized using diaminobenzidine (Vector Laboratories, Burlingame, CA). Light hematoxylin and eosin was applied as a counterstain.