Immunohistochemical localization of laminin and fibronectin isoforms in human placental villi

We studied the localization of laminin alpha1, alpha2, alpha3, alpha5, beta 1, beta2, and gamma1 chains and extradomain A- (EDA), EDB-, and oncofetal f ibronectin by immunohistochemistry in human placental villi during placenta l development. The laminin alpha2, alpha5, beta1, beta2, and gamma1 chains were detected in the trophoblastic basement membrane (BM) at all stages of gestation, suggesting the presence of laminin-2, -4, -10 and -11 trimers. T he laminin al chain was selectively found at sites where the villous BM was in contact with proliferating cells in trophoblastic islands or columns. E DA-Fn, but not other Fn isoforms, was found in the trophoblastic BM during the first trimester. The laminin alpha2, beta1, beta2, and gamma1 chains we re detected in the villous stroma and capillaries throughout placental deve lopment, while the laminin alpha5 chain emerged distinctly during developme nt. Extensive EDA-Fn immunoreactivity was found in first-trimester villous stroma, but distinctly fewer Fn isoforms were seen in the villous stroma du ring the later stages of gestation. Our results also suggest that, during t he formation of new villi, laminins are not found in trophoblastic sprouts before the ingrowth of the villous mesenchyme. Rather, laminins may be depo sited at the villous epithelial-mesenchymal interface. Furthermore, the res ults show that distinct changes occur in the localization of various lamini n and Fn isoforms during the maturation of villous trophoblastic and capill ary BMs.