The fetus as an allograft: immunobiologic role of human trophoblasts for fetal survival.

Abstract

The hypothesis of this study is that trophoblasts contribute to the survival of the mammalian fetal allograft. Immunologic and molecular biologic studies were performed with human trophoblasts or trophoblastic tumor cells to investigate the expression of class I human leukocyte antigens, the susceptibility to natural killer and lymphokine-activated cells, the ontogeny of Fc gamma-receptors, and the production of immunosuppressive factors. Heterogeneous expression of class I human leukocyte antigens on trophoblasts was regulated at transcriptional level. Trophoblasts showed low susceptibility to natural killer and lymphokine-activated cells. Trophoblasts expressed natural killer cell-type Fc gamma-receptor III, which mediates phagocytosis. The trophoblast-derived immunosuppressive factor was very similar to transforming growth factor-beta. The trophoblasts, which ultimately form the fetoplacental interface, constitute a major immune barrier for the survival of the allogenic conceptus.