Immunocytochemical identification of cytotrophoblast from other mononuclear cell populations isolated from first-trimester human chorionic villi.

Trophoblast biologists are often uncertain as to what cell types they are investigating because the mononuclear cell populations prepared from trypsinization of human first-trimester chorionic villi are morphologically very similar. In the present study, immunocytochemical and phagocytic markers have been used to distinguish cytotrophoblast populations from cell types derived from the mesenchyme of the chorionic villus. Two anti-trophoblast monoclonal antibodies generated in our own laboratory (18B/A5 and 18A/C4) were found to be very efficient in identifying cytotrophoblast, which made up 35-40% of the cells in a smear. Most cytotrophoblast cells did not stain with a monoclonal anti-HLA-A,B,C antibody but a few cells (5%) were found to express both trophoblast and HLA-A,B,C antigens by a double-labelling technique. Endothelial cells from villous capillaries could be identified by a rabbit anti-factor VIII antibody. These cells formed 28% of the population in a cytospin smear. Macrophages from the villous mesenchyme were less readily separable as neither specific monoclonal antibodies nor localization of enzymes were found to be effective. However, these cells could be identified by their ability to phagocytose carmine. About 15% of the cells in a smear consisted of macrophages. The procedure described should prove useful in judging the efficiency of isolation methods from human placental cells.