Immunohistology of clotting factor V in human extraembryonic membranes

Blood clotting Factor V was studied on fixed and unfixed cryostat sections of term human placentae, basal plates, amniochorions, and first-trimester placentae by using one- and two-colour immunofluorescence. A monoclonal antibody (GB36) which reacts with cytotrophoblast was used to identify cytotrophoblast. Factor V was identified in villous cytotrophoblast of term chorionic villi and very weakly or not at all in first-trimester chorionic villi. Other extra-embryonic tissues were non-reactive with anti-Factor V. These data show that Factor V is a useful marker of term villous cytotrophoblast. Immunopathological consequences of this are considered.