Expression and immunohistochemical localization of laminin and type IV collagen in developing human fetal tracheal glands.

The expression and distribution of laminin and type IV collagen, two major components of the basement membrane, were investigated at the epithelio-mesenchymal interface of the human developing tracheal glands from 10 to 37 weeks of gestation. The localization of these molecules was assessed by indirect immunoperoxidase and indirect immunofluorescence staining and correlated to morphogenesis and epithelial cell differentiation. Laminin and type IV collagen were detected as early as 10 weeks of gestation in a continuous, linear pattern in the basement membrane surrounding the epithelial tracheal tube. By 12 weeks of gestation the basement membrane developed large openings at the tips of the budding glands beneath poorly differentiated cells, concomitant with the onset of morphogenetic movements. The remodeling of the basement membrane led to branching epithelial morphogenesis. The maturation and the functional differentiation of the secretory cells appeared later in the epithelium, when the basement membrane was strongly labeled with both anti-laminin and anti-type IV collagen antibodies, after 24 weeks of gestation. At this time the basement membrane became regular and thick and the maturation of serous cells increased progressively. These results suggest that the remodeling of the basement membrane takes place very early during gestation and that the morphogenesis and the maturation of the tracheal glands are rapidly achieved in humans.