IMMUNOCYTOCHEMICAL LOCALIZATION OF ANNEXINS-V AND ANNEXINS-VI IN HUMAN PLACENTAE OF DIFFERENT GESTATIONAL AGES

The cellular and subcellular localization of annexins V and VI, two me mbers of a superfamily of Ca2+-dependent phospholipid- and membrane-bi nding proteins, was investigated in chorionic villi of human placentae of different gestational ages by postembedding immunocytochemistry at the electron microscope level. All cell types of placental villi, i.e ., the syncytiotrophoblast, Langhans cells, Hofbauer cells, fibroblast s, and capillary endothelial cells, appeared to express the two protei ns, irrespective of the gestational age. By immunogold particle counts , annexin V was observed to be 2-3 times as much abundant as annexin V I. Syncytiotrophoblast cells appeared to contain the largest amounts a nd Langhans cells appeared to contain the least amounts of annexins V and VI, as judged by immunocytochemistry. The two proteins were found associated with plasma, Golgi, and vacuolar membranes, and with membra nes of the endoplasmic reticulum, as well as diffusely in the cytoplas m. Annexin V appeared to be distributed in nearly equal proportions be tween cell membranes and the cytoplasm in stromal cells and to be abou t 30% associated with cell membranes in trophoblast cells, whereas ann exin VI appeared almost equally distributed between cell membranes and the cytoplasm in trophoblast and stromal cells. Also, annexins V and VI appeared to be more abundant in trophoblast cells than in stromal c ells. The present data strongly support the idea that placenta is a pr eferential site of annexin-regulated activities, and suggest that anne xins V and VI are actively involved in the Ca2+-dependent regulation o f membrane processes in trophoblast cells.