Cells of the fetomaternal interface: Their role in the maintenance of viviparous pregnancy

Abstract

An immune system capable of discriminating between self and nonself evolved in nature long before the appearance of the viviparous mode of pregnancy, which brings maternal cells into a direct physical contact with genetically disparate cells of fetal origin. In the hemochorial type of placentation, the former include cells of the maternal immune system. This article briefly reviews the possible mechanisms that may protect the semiallogeneic conceptus in nature, with special reference to the role of the cells at the fetomaternal interface. We also present some new data on the antigenicity of pre- and postimplantation trophoblast cells and the immunobiology of decidual cells. Systemic changes in the maternal immune system appear to represent homeostatic responses to the presence of a semiallogeneic conceptus, unrelated to its protection; mechanisms for this protection must reside locally at the fetomaternal interface. We find that the lack of immunogenicity of the outer (trophoblast) cells of the preimplantation blastocyst can be explained by a transient disappearance of the major histocompatibility (MHC) antigens on their cell surface. However, following implantation and the formation of the placenta, class 1 MHC antigens reappear on certain classes of trophoblast cells, i.e., labyrinthine and spongiotrophoblast cells of the murine placenta. Similarly, cytotrophoblast cells of the early human placenta exhibit the presence of class 1 MHC antigens. An absence of class 2 MHC antigens despite the presence of class 1 antigens cannot entirely explain the lack of trophoblast immunogenicity. A local immunosuppression mediated by trophoblast cells themselves as well as maternal cells of hemopoietic origin in the decidua remain as a strong possibility. Typical decidual cells appear to play a central role in the maintenance of pregnancy because of their numerous functions: nutritive, endocrine, and immunoregulatory. Our studies reveal that they are descendants of bone-marrow-derived precursors, have unique surface markers recognizable with monoclonal antibodies nonreactive with other hemopoietic cell lineages, and have the ability to abrogate mixed lymphocyte reactions in vitro in a genetically unrestricted manner. Further studies directed at the cells of the fetomaternal interface should provide a better insight into the mode of survival of the nature's most commonplace allograft.

Immunolocalization of extracellular matrix proteins and collagen synthesis in first‐trimester human decidua

“…early human decidua incorporates 3H-proline into colla-The immunoprotective role, which is currently emphagen types 1,111, IV, and V in culture. Immunoprecipita-sized (Beer and Sio, 1982;Lala, 1982, 1983; tion of these newly synthesized, radiolabeled collagens Lala et al, 1984), may be performed by the decidual from the medium of cultured decidual explants corre-ECM acting as the groundwork for infiltration and prolates with our immunolocalization of these proteins in liferation of suppressor lymphocytes. In conjunction with the matrix of first-trimester human decidua.…”

The Fetal Allograft Revisited: Does the Study of an Ancient Invertebrate Species Shed Light on the Role of Natural Killer Cells at the Maternal-Fetal Interface?

“…Placental villous syncytiotrophoblast and extravillous cytotrophoblast cells are the fetal cells most intimately contacted by maternal cells (Figure 3). According to mRNA analysis, these cells do not express normal levels of classical MHC I or MHC II molecules [51, 52]. Instead, the extravillous cytotrophoblast cells express two nonclassical MHC I molecules, human leukocyte antigen (HLA)-G and HLA-E, and low levels of the classical MHC I molecule, HLA-C [53, 54].…”

Hemopoietic origin of certain decidual cell precursors in murine pregnancy

“…The morphology o f decidual cells in single cell suspensions was established earlier in this laboratory through extensive comparison of smears or cytocentrifuge preparations with semithin Epon sections of decidualized uteri and decidual capsules (decidua basalis) of pregnant mice (Kearns and Lala, 1982;Lala et al, 1984). Figure 2B illustrates the morphology in a semithin section.…”

“…Nuclei were eccentrically placed, round or ovoid in shape, and contained one or more prominent nucleoli among uniformly distributed chromatin. The size of decidual cells in smears and cytocentrifuge preparations ranged from 12 pm to 20 pm (Kearns and Lala, 1982;Lala et al, 1984). In contrast to macrophages, these cells are nonphagocytic and express distinctive surface markers, e.g., Thy-1 and Dec-1, but few express Mac-1 antigen and none expresses the F4/80 antigen (Lala, unpublished).…”