Differential expression of complement regulatory proteins on subpopulations of human trophoblast cells.

Trophoblast cells forming the reactive interface between the mother and her semiallogeneic fetus risk attack by cellular and humoral elements of the maternal immune system. Biochemical, molecular, and immunohistologic studies have identified membrane cofactor protein (MCP) and decay accelerating factor (DAF) on trophoblast cells, which could assist in preventing lysis of the cells by complement-activating maternal antibodies. In this immunocytochemical study, differential expression of these two members of the family of complement regulatory proteins on subpopulations of human trophoblast cells and other types of cells in first and third trimester placentas was demonstrated. Staining with anti-MCP was particularly strong on villous cytotrophoblast cells and giant cells in first trimester tissues in comparison with other types of cells. In contrast, staining with anti-DAF was strong on proliferating cytotrophoblast in first trimester tissues, and on basal plate cytotrophoblast and decidual cells in term tissues. Placental villous mesenchymal cells but not trophoblast cells expressed a third regulatory protein, complement receptor 1. These observations support the postulate that complement regulatory proteins are critical to protection of the fetal allograft, and suggest specific requirements for trophoblast cells according to stage of differentiation and anatomic location.