Pattern of connective tissue development in swine pulmonary vasculature by immunolocalization.

Light microscopic immunolocalization studies were carried out on lung tissue from eight newborn and four adult pigs using antibodies to six extracellular matrix components. Antibodies to fibronectin, collagen type IV, and laminin localized on the same structures in adult and newborn lungs. By contrast, antibodies to the interstitial collagens (types I, III, and V) were less extensively localized in the newborn than in the adult, particularly those to type I because the fibres on which they localized in the newborn were thin and sparse. At all ages, antibodies to collagen types III and V co-localized on type I fibres and also on thin individual fibres which formed networks, more dense in the adult than in the newborn. At all ages, anti-type III collagen antibodies also localized on smooth muscle cells. In the adult, but not in the newborn, anti-type I and type V collagen antibodies localized on the connective tissue around the smooth muscle cells in the pulmonary arterial media and vein wall. The dominance of collagen type III suggests greater plasticity in the newborn pulmonary vasculature, which helps explain the recently described rapid changes in arterial wall structure which constitute adaptation to extrauterine life. The postnatal increase in collagen type I helps explain the documented postnatal increase in structural stiffness of the pulmonary arteries.