THE HUMAN PLACENTA - A MODEL FOR TENASCIN EXPRESSION

Tenascin is a large glycoprotein of the extracellular matrix. Previous reports have demonstrated that it is associated with epithelial-mesenchymal interfaces and is expressed during embryonic and tumour development, wound healing, cell proliferation and it may be involved in immunomodulation. The human placenta shows numerous features related to these aspects. We have investigated the presence of tenascin in the human placenta throughout pregnancy by immunohistochemistry. We used monoclonal (mAb) and polyclonal (pAb) antibodies to tenascin, a mAb to fibrin, a pAb to fibrinogen, and the mAb Ki-67 as proliferation marker. Tenascin was highly expressed in the mesenchymal villi which are considered the basis of growth and differentiation of the villous trees. Moreover, fibrinoid deposits at the surfaces of the villous trees were always separated from the fetal stroma by tenascin. The stroma of villi encased in fibrinoid was also positive for tenascin. This glycoprotein was also expressed in the villous stroma directly apposed to cell islands and cell columns. In the proximal portions of both epithelial structures, cytotrophoblast was Ki-67 positive. These data show that tenascin is expressed during the development of the placenta, particularly in the mesenchymal villi, cell islands and cell columns. These structures are considered to be the proliferating units of the villous trees. Tenascin underlying fibrinoid deposits suggests that it also participates in repair mechanisms. Thus, in the human placenta tenascin expression can be correlated with villous growth, cell proliferation, and fibrinoid deposition. Its role in immunoprotection of fetal tissues in areas where syncytiotrophoblast as barrier is missing or damaged is discussed.