IMMUNOHISTOCHEMICAL STUDIES OF HUMAN UTEROPLACENTAL TISSUES FROM FIRST-TRIMESTER SPONTANEOUS-ABORTION

OBJECTIVE: Atypical expression of human leukocyte antigen histocompati bility molecules or complement regulatory proteins by placental tropho blast has been hypothesized as a mechanism for spontaneous abortion. T he purpose of this study was to determine expression of these proteins by placental villous trophoblast and to identify leukocyte population s within uteroplacental tissues from women with their first spontaneou s abortion, their fourth or more recurrent spontaneous abortion, and f rom women having elective pregnancy termination. STUDY DESIGN: Fresh u teroplacental tissues were obtained at 6 to 9 weeks' gestation from ei ght women with their first spontaneous abortion, 20 women experiencing their fourth or more unexplained recurrent spontaneous abortion, and 20 women having an elective pregnancy termination. These tissues were analyzed immunohistochemically for human leukocyte antigen histocompat ibility molecules (class I and II major histocompatibility complexes), complement regulatory proteins (CD46, CD55), and leukocyte phenotypes (CD45, CD3, CD14, CD56). RESULTS: There was absence of cell surface e xpression of class I and II human leukocyte antigen molecules but stro ng trophoblast expression of complement regulatory proteins in all vil lous placental samples. Leukocyte infiltration was noted in all decidu al specimens. The predominant decidual leukocyte population was CD3-ne gative, CD56-positive cells, except in four cases of recurrent abortio n where the normal ratio (<less than or equal to 2:3) of CD14-positive macrophages to CD56-positive leukocytes was >2:1. There was an unusua l retention of maternal class II major histocompatibility complex-posi tive leukocytes within intervillous spaces attached to the apical surf ace of syncytiotrophoblast from one individual with recurrent abortion . CONCLUSION: Our data do not support the hypothesis that some cases o f recurrent spontaneous abortion result from atypical expression of hu man leukocyte antigen histocompatibility molecules or lack of compleme nt regulatory protein expression by placental villous trophoblast. The se data suggest that occasional cases of recurrent spontaneous abortio n could be associated with an impaired CD56-positive leukocyte respons e in the early decidualized endometrium.