Objective: Atypical expression of human leukocyte antigen histocompatibility molecules or complement regulatory proteins by placental trophoblast has been hypothesized as a mechanism for spontaneous abortion. The purpose of this study was to determine expression of these proteins by placental villous trophoblast and to identify leukocyte populations within uteroplacental tissues from women with their first spontaneous abortion, their fourth or more recurrent spontaneous abortion, and from women having elective pregnancy termination.
Study design: Fresh uteroplacental tissues were obtained at 6 to 9 weeks' gestation from eight 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 histocompatibility 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 expression of class I and II human leukocyte antigen molecules but strong trophoblast expression of complement regulatory proteins in all villous placental samples. Leukocyte infiltration was noted in all decidual specimens. The predominant decidual leukocyte population was CD3-negative, CD56-positive cells, except in four cases of recurrent abortion where the normal ratio (< or = 2:3) of CD14-positive macrophages to CD56-positive leukocytes was > 2:1. There was an unusual retention of maternal class II major histocompatibility complex-positive leukocytes within intervillous spaces attached to the apical surface of syncytiotrophoblast from one individual with recurrent abortion.
Conclusion: Our data do not support the hypothesis that some cases of recurrent spontaneous abortion result from atypical expression of human leukocyte antigen histocompatibility molecules or lack of complement regulatory protein expression by placental villous trophoblast. These data suggest that occasional cases of recurrent spontaneous abortion could be associated with an impaired CD56-positive leukocyte response in the early decidualized endometrium.