CD9 is expressed in extravillous trophoblasts in association with integrin α3 and integrin α5

The CD9 molecule is a 24-27 kDa cell surface glycoprotein, which may be related to Schwann cell migration and adhesion. In this study, we examined the expression of CD9 in human extravillous trophoblasts, which invade into the endometrium during implantation and placentation, CD9 was detected immunohistochemically on the extravillous trophoblasts in the cell columns of first trimester placentae, but not on villous trophoblasts. In the second and third trimester, CD9 was highly expressed on the extravillous trophoblasts in the basal plate of placentae, and in the chorion laeve in the fetal membrane of term placentae. The molecular mass of CD9 in the chorion laeve was shown to be 27 kDa by Western blotting. The mRNA of CD9 was also detected in the chorion laeve by reverse transcription-polymerase chain reaction (RT-PCR). Proteins were purified from chorion laeve by affinity chromatography with anti-integrin as and as monoclonal antibodies and Western blotting, revealed that CD9 was associated with both integrins, These findings indicate that CD9 is a differentiation-related molecule present in the extravillous trophoblasts. Since it is associated with integrin as which has been proposed to regulate trophoblast invasion, CD9 may be implicated in trophoblast invasion at the fete-maternal interface.