Distribution of annexin I and II in term human fetal membranes, decidua and placenta.

Annexin I and II are calcium binding proteins implicated in the regulation of a number of cellular functions, including secretory processes, prolactin release and prostaglandin formation. The cellular distribution of these proteins was examined in human term placenta, fetal membranes (amnion and chorion laeve) and decidua using immunohistochemistry. Annexin I was found in amnion epithelial cells and chorion laeve trophoblast but not in decidua, and was located in the syncytiotrophoblast cells of placenta. Annexin II and annexin II light-chain were located in the amnion epithelial cells, the cells of the mesenchymal layer between the amnion and chorion laeve trophoblast and endothelial cells lining the blood vessels in the decidua. In contrast to annexin I, annexin II was located in the villous core and not the syncytiotrophoblast cells in the placenta. There was no apparent change in the distribution of these annexins during labour. These findings indicate that the cellular distribution of these annexins is different, and may be an important consideration when examining their synthesis or action in tissues and in vitro with mixed cell populations and tissue homogenates.