Immunological studies of human trophoblast: markers, subsets and functions

Allosensitization in tumor therapy and prophylaxis, and in female contraception--a prospect for clinical use

A hypothesis is presented on the possible role of allosensitization in therapy and prophylaxis of human tumors, and in human female contraception. The essence of the proposed treatment of human malignancies is allosensitization with allogeneic white blood cells by means of application of two blood transfusions from normal healthy donors within a certain time interval to patients with invasive or metastasizing cancer. The therapy should be accompanied by immunoglobulins, bacterial toxins and a single dose of cytostatics. In the case of a successful tumor regression a prophylaxis of recurrence should be made with two doses of intradermally injected allogeneic lympho-leucocytic concentrates mixed with bacterial toxins; such treatment might also be effective in tumor prophylaxis, or in long-lasting contraception in women. The hypothesis is supported by recent literature as well as by our recent results in the area of cell-mediated control of tissue proliferation, fetal allograft survival or tumor development. It is concluded that tumor rejection can be mediated not only by the direct effect of anti-tumor drugs but more effectively by the organisms mechanisms responsible for removal of undesirable tissue.

Identification of leucocytes within the human chorion laeve

Occasional macrophages and granulocytes have been detected within the cytotrophoblast layer of the chorion laeve in normal term placentae. It is clearly important to identify these leucocytes in studies of antigen expression by trophoblastic populations within the amniochorion. The relevance of these observations to any immunocompetent interactions between maternal and fetal cells through the chorion laeve remains to be established.

The formation of immune complexes in primiparous and multiparous human pregnancies

Using a recently developed ELISA, antibodies were detected in maternal sera with reactivity directed against determinants present on the plasma membrane of the outer layer of the placenta, the syncytiotrophoblast. The anti-trophoblast antibodies were present in maternal sera in the form of "free" antibodies and "immune complex" antibodies. Examination of the sera throughout gestation and from successive pregnancies revealed that the generation of anti-trophoblast antibodies and the formation of immune complexes was predominantly a first pregnancy and early second pregnancy event, with very little activity detectable in later pregnancies. It is proposed that immune recognition occurs in a first pregnancy, which generates some form of immunosuppression that involves the activation of suppressor memory cells.

Spiral (uteroplacental) arteries of the human placental bed show the presence of amniotic basement membrane antigens

The spiral arteries of the placental bed lose clearly recognizable arterial features early in pregnancy because of their invasion by extravillous trophoblast. Extensive structural alterations take place in the walls of invaded arteries, their walls containing an amorphous acidophilic "fibrinoid" matrix in which endovascular trophoblast is embedded. Such spiral arteries examined by immunofluorescence techniques in placental bed biopsy specimens obtained at cesarean section show a characteristic pattern of reaction with antisera to epithelial basement membrane amniotic antigens. These antisera have been previously demonstrated to react with the basement membrane of human amnion and of ectodermally derived epithelium such as breast ducts and skin. Interstitial trophoblast usually does not contain these antigens, and it is postulated that, following vascular invasion, endovascular trophoblast produces amniotic antigens to establish its presence. This may be of importance in maintaining the structural integrity of spiral arteries and thereby adequate maternal blood flow to the fetal-placental unit.

Class I antigens of the major histocompatibility complex on cytotrophoblast of the human placental basal plate

The lack of class I antigens of the major histocompatibility complex (MHC) on syncytiotrophoblast has been proposed as an explanation for the survival of the allogeneic fetus. These antigens, however, have recently been detected on nonvillous trophoblastic columns of the early human placenta. By using a combination of immunofluorescence techniques to identify trophoblast, we have studied transplantation antigens of the cytotrophoblastic shell present in the basal plate of normal full-term human placentae. With the use of two different monoclonal antibodies to a common determinant of HLA (clones W6/32 and 61D2), it was shown that this subset of trophoblast does express class 1 MHC antigens. However, while these cells reacted uniformly with W6/32, only rare reactivity with 61D2 was found. Reactivity of polyclonal antisera to beta 2-microglobulin correlated with that seen using W6/32. These results are similar to those recently observed in a subset of trophoblast of the amniochorion to which the term "metatrophoblast" has been given.

Circulating antibodies against human chorionic gonadotropin following trophoblastic disease

The presence of antibodies against human chorionic gonadotropin (hCG) is described in a patient who was treated for persistent trophoblastic disease. These antibodies remained detectable over a 14-month period of observation. In 15 other patients, successfully treated for trophoblastic disease, their presence could not be demonstrated. The binding affinity for labeled hCG was investigated by polyethylene glycol precipitation, by complex formation with protein A-Sepharose, and by gel filtration. Circulating antibodies against hCG may interfere with immunological serum hCG estimations.

Sera from women with histories of repeated pregnancy losses cause abnormalities in mouse peri-implantation blastocysts

Incubation of peri-implantation mouse blastocysts in the presence of untreated human sera resulted in destruction of the blastocysts. Heating the serum resulted in deactivation of the non-specific toxic factor. Whereas heat-treated serum from women with normal obstetrical histories, and men, supported normal trophoblast attachment and outgrowth, sera from women with reproductive dysfunction resulted in inhibition of attachment or disruption of the trophoblast cells. The inner cell masses were not adversely affected by the sera which were toxic to trophoblast. Fractionation of a serum sample by affinity chromatography resulted in removal of the toxic factor with the IgG fraction. Absorption of the toxic serum with human trophoblast membranes resulted in serum that supported trophoblast outgrowth indicating that the toxic factor was an antibody directed against trophoblast antigens.

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

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.

Maternal antipaternal immunity in couples predisposed to repeated pregnancy losses

Maternal antipaternal immunity was compared between a group of 12 couples with normal reproductive histories and a group of 13 couples with obstetrical histories of more than one consecutive stillbirth or repeated pregnancy loss subsequent to having had successfully carried to term. Couples were studied for maternal-paternal HLA antigen sharing and for maternal antihusband immunity in tests detecting both complement dependent and independent antibodies as well as in an assay measuring direct cell-mediated cytotoxicity. There was no significant difference in the proportion of HLA antigen sharing between these two groups; however, the women in the pregnancy loss group demonstrated significantly more antipaternal immunity than their normal childbearing counterparts and more than previously described for aborting couples who share HLA antigens. Screening of the cytotoxic sera on a well characterized cell panel failed to reveal alloreactivity patterns consistent with paternal HLA antigen profiles. These data demonstrate that certain women who suffer recurrent pregnancy losses can mount vigorous immune responses to paternal lymphocyte antigens. We propose that the appearance of such lymphocytotoxins represents inappropriate maternal immune responses to fetal extraembryonic antigens that may subsequently result in fetal demise.

Human trophoblast-lymphocyte cross-reactive (TLX) antigens define a new alloantigen system

Antisera to human syncytiotrophoblast microvillous cell surface membranes from different placentas are cytotoxic for lymphocytes from some people but not others, demonstrating the presence of allotypic trophoblast-lymphocyte cross-reactive (TLX) antigens. Exploratory principal components factor analysis, performed on limited data consisting of 300 cytotoxic reactions produced by ten separate trophoblast antisera on a panel of lymphocytes from 30 random donors, suggested the presence of three distinct TLX antigen groupings. It is proposed that such TLX alloantigens are central in establishing maternal recognition and protection of the blastocyst, and that lack of recognition results in implantation failure and spontaneous abortion. These findings are compatible with contemporary results of immunotherapy to prevent recurrent spontaneous abortions, and their implications extend to other conditions of allogeneic coexistence, such as organ transplantation and the tumor-host relationship.