Cellular immune aspects of the human fetal-maternal relationship. III. Mixed lymphocyte reactivity between related maternal and cord blood lymphocytes

Fetal allostimulation of maternal cells: a potential mechanism for perinatal HIV transmission following obstetrical hemorrhage

Our aim was to elucidate the mechanism by which HIV transmission is increased following obstetrical hemorrhage. We investigated whether fetal allostimulation of maternal cells, which could occur following fetal-to-maternal hemorrhage, increases proliferation, HIV replication, and cellular activation. Peripheral blood mononuclear cells (PBMCs) were collected from HIV-infected mothers and their infants to assess maternal-fetal allostimulation. Responses were compared to allostimulation with unrelated donors. Maternal and fetal cells were cocultured to assess allogeneic stimulation. Cell proliferation was measured by [(3)H]thymidine incorporation and cell activation was assessed via fluorochrome-labeled antibody staining and flow cytometric analysis. Virus production from HIV-infected maternal cells was quantitated by p24 enzyme-linked immunosorbent assay or by branched chain DNA assay. Allostimulation with fetal cells led to maternal cell proliferation. In women with unsuppressed viral loads, virus release was also enhanced following allostimulation of maternal cells with fetal cells. Fetal cells are capable of allogeneically stimulating maternal cells, with responses comparable to those seen following allostimulation with unrelated donors. Allostimulation of maternal cells by fetal cells results in statistically significant increases in proliferation and enhanced HIV replication, suggesting a possible physiological mechanism for mother-to-child transmission of HIV in women with obstetrical hemorrhage.

The increased lysis of fetal cells in the mother after pregnancies complicated by pre-eclampsia or HELLP syndrome is not the result of a specific anti-fetal cytotoxicity of the mother

PROBLEM

In pregnancies complicated by pre-eclampsia or hemolytisis elevated liver enzymes, low platelets (HELLP) syndrome, an increase of fetal DNA in the maternal serum indicates an increased lysis of fetal cells. Whether this cytolysis is the cause or the result of an increased specific cytotoxicity against the fetal cells is not yet known.

METHODS

Ten mothers after healthy pregnancy, eight mothers after pregnancy complicated by prematurity (GA < 37 weeks), and eight mothers with pregnancies complicated by pre-eclampsia or HELLP syndrome and their male children were enrolled in the study. Fetally derived DNA in the maternal serum and the specific anti-fetal cytotoxicity of the maternal lymphocytes were measured.

RESULTS

Detection of fetal DNA in maternal serum was significantly associated with pre-eclampsia/HELLP syndrome but not with anti-fetal cytotoxicity of the maternal lymphocytes.

CONCLUSION

The cytolysis of fetal cells in mothers after pregnancies complicated by pre-eclampsia/HELLP syndrome is neither the reason for nor the result of an increased specific anti-fetal cytotoxicity.

Specific immune tolerance during pregnancy after renal transplantation

Pregnancy is associated with specific immunological tolerance to fetal antigens suggesting that immunoregulatory processes during pregnancy can induce specific immunological unresponsiveness. We report a case of a female renal transplant recipient who stopped immunosuppressive therapy during first pregnancy. Despite histologically proven acute renal allograft rejection during the early course of transplantation, no immunological response was observed for 9 years after withdrawal of immunosuppression. Two further pregnancies within that time period did not evoke any renal complications, but were complicated by premature rupture of the amnion and by the development of preeclampsia. To our knowledge, there are no reports of such a long-term specific unresponsiveness to a renal allograft without immunosuppressive therapy. Natural and active immunoregulatory mechanism can be related for the development of specific immune tolerance to renal allograft in this case.

Immunology of pregnancy: towards a unifying hypothesis

The variable findings of hormonal-immunoregulation and the variable cellular and humoral immune responses in pregnancy have been considered in relationship to the physiological response. From such considerations it appears that the peripheral blood lymphocyte/leukocyte response in pregnancy is not important, but rather the local uterine immune response at implantation and throughout pregnancy. It is proposed, and evidence is presented, that a normal allogeneic immune response is initiated at the time of implantation of the blastocyst. This immune response regulates the invasive nature of the trophoblast and initiates the first stage of parturition. The initiation and maintenance of this immune response is based on an interplay between maternal and paternal HLA and trophoblast antigens. In the case of HLA-incompatible donor-recipient blastocyst transplants, a more pivotal role for immunoregulation by trophoblast antigens is proposed. This is because it is considered that the local uterine immune response suppresses the expression of allogeneic HLA. This concept is further developed in terms of haploid HLA suppression on maternal and fetal lymphocytes that cross the placenta. This is considered to allow the interaction of these lymphocytes with each other and explains maternal transfer of cell-mediated immunity.

Changes in maternal and newborn lymphocyte reactivity in reciprocal mixed lymphocyte cultures during the postpartum period

Reciprocal one-way mixed mother-newborn lymphocyte cultures (MMNLC) containing alternatively maternal or newborn responding (R) or stimulating (S) cells were investigated in both directions in primiparae at three different times: a few hours after delivery, and at 4 and at 16 weeks. Cultures were grown in the presence of maternal and pooled control serum prepared from the blood of five to eight unrelated healthy donors. Four weeks after delivery in maternal and in control serum a significant increase in MMNLC reactivity could be observed, which disappeared at 16 weeks when a pronounced decline in MMNLC values in both directions was found. The suppressive effect of maternal serum was more pronounced at delivery, still evident 4 weeks later, and insignificant after 16 weeks. The results of this study suggest that 4 weeks after delivery, maternal sensitization to fetal histocompatibility antigens can be detected in primiparae with MMNLC; and that 16 weeks later, this was no longer detectable with the same test.

Maternal cell-mediated immunity to the fetus in human pregnancy

Cell-mediated sensitisation of the mother to her fetus is not a regular event in human pregnancy, and the role of suppressor cells and blocking antibodies in preventing this sensitisation is unresolved. There is as yet little evidence to support the hypothesis that maternal immune recognition of the fetus is essential for the success of the pregnancy. Further progress in this area will depend on systematic investigations of the development of specific maternal humoral and cell-mediated responses to the fetus throughout gestation, and whether a deficiency of these responses results in the failure of the pregnancy.

Monocyte chemotactic factor production in mixed cultures of maternal and neonatal human lymphocytes

The immunological interaction between related maternal and neonatal human lymphocytes was investigated by assaying monocyte chemotactic factor production in mixed cell culture. Lymphokine was detected in a significantly lower proportion of maternal-neonatal cell cultures compared to mixed cultures of cells from unrelated adults and/or neonates. It is possible that a reduced inflammatory mediator production at the feto-maternal interface may contribute to the survival of the fetal allograft.

T-lymphocyte subsets during pregnancy and the menstrual cycle

Many observations suggest that cellular immunity is depressed during gestation. To define alterations in subsets of circulating lymphocytes during pregnancy, we compared the percentages of total T cells, T helper cells, and T suppressor cells in the peripheral blood of 31 pregnant women at various stages of gestation with those in that of nonpregnant controls. Control studies consisted of five women ingesting oral contraceptives and five women menstruating spontaneously. Isolated peripheral blood mononuclear cells were reacted with fluoresceinated monoclonal antibodies that were specific for Leu-2 cells, Leu-3 cells, and Leu-4 cells and that were subsequently analyzed on a fluorescence-activated cell sorter. No variation in the percentage of Leu-2, Leu-3, or Leu-4 cells was observed during the menstrual cycle or oral contraceptive cycle. No differences were seen when T-cell subsets at various stages of gestation were compared with the corresponding T-cell subset in nonpregnant controls. The data suggest that pregnancy does not alter the percentage of T-cell subsets in the peripheral blood.

The alloreactivity of human colostral T lymphocytes. II. Specific control of maternal anti-fetal mixed lymphocyte reactivity

Lymphocytes in human colostrum were examined for evidence of alloreactivity specifically directed against the paternal HLA haplotype. Such reactivity was detected using umbilical cord blood leukocytes as stimulator cells in the mixed lymphocyte reaction, but the responses were reduced when compared to those of the same patient's blood lymphocytes. Analysis of this defect determined that only colostral lymphocyte responses to neonatal alloantigens were impaired and that the phenomenon apparently depended on a non-adherent fetal leukocyte for its expression. Attempts to demonstrate directly colostrum or cord blood-derived cell-mediated suppression failed, and the results suggest that a classical T suppressor cell is probably not involved. These findings indicate that human colostrum contains anti-paternal T cell clones but their reactivity is specifically abrogated when cultured with fetal leukocytes.

Immunologic regulation in pregnancy

Theories to explain the failure of rejection of the fetus by the mother during pregnancy include immunologic privilege of the uterus as a graft site, lack of transplantation antigen expression on the trophoblast, weakening of maternal cellular immunity during pregnancy, and separation of maternal and fetal circulations. Evidence for and against each of these theories is discussed. Local concentration of a variety of hormones, including human chorionic gonadotropin (HCG), sex steroids, alpha-fetoprotein, and immunoglobulins, could provide a blocking mechanism to prevent maternal cellular immune attack. Possibly, progesterone, antibodies, and immune complexes are important in protecting the placenta and ultimately the fetus from rejection. Elucidation of regulatory mechanisms in pregnancy may be applicable to other problems in immunology.

Cell-mediated immunity in human pregnancy: Changes in lymphocyte reactivity during pregnancy and postpartum

The function of thymus-dependent lymphocytes (T lymphocytes) was studied in women during pregnancy and labor and postpartum by evaluating the blastogenesis of peripheral lymphocytes, which were stimulated with phytohemagglutin-P (PHA-P) in both whole-blood semimicroculture and purifed lymphocyte culture. Data from 353 random samples (203 women) and 50 serial specimens from 10 women revealed that PHA-P induced-lymphocyte blastogenesis was significantly (p less than 0.005) reduced during pregnancy and labor but rapidly returned to normal several days after artificial termination in the early stage of pregnancy as well as after full-term delivery. These results indicate that the T-lymphocyte function in maternal peripheral blood is depressed by causes related to pregnancy. It seems very likely that depressed T-lymphocyte function during pregnancy is caused by inhibitory factors in the blood plasma derived from the feto-placental unit. Questions relating to the inhibitory factors in maternal plasma are discussed.

Relationship between the responsiveness of maternal and foetal lymphocytes to phytohaemagglutinin and to microbial antigens

The response of 105 maternal-foetal lymphocyte pairs to specific and non-specific stimulation were evaluated using a newly defined method of analysis. There were no significant differences in the responses of maternal or foetal lymphocytes to phytohaemogglutinin (PHA) or the various antigens as a function of concentration over the ranges tested. The maternal lymphocytes were stimulated by all of the antigens and responded to PHA three--five times more strongly than to the antigens. The foetal lymphocytes were stimulated by PHA and tetanus toxoid only and were suppressed by streptokinase-streptodornase (SKSD). They responded to stimulation by antigens at a lower level than did the maternal lymphocytes, but they responded at a much higher level to PHA. Unstimulated cultures of foetal lymphocytes incorporated more isotope than did those of maternal lymphocytes in both autologous and AB plasma. The data were cross-classified to determine whether the responses of the foetal lymphocytes varied concordantly with the responses of the maternal lymphocytes in both autologous and AB plasma by the Chi-square test for independence and by rank correlation analysis. There was no significant correlation in either plasma to stimulation with the antigens. Thus, the presence of antigen reactive lymphocytes in the circulation of the mother does not mean that the foetus is sensitized to that antigen. Comparison of the lymphocyte responses in autologous plasma with those in AB plasma provided evidence for the presence of circulating immunoregulatory substances. Autologous maternal plasma suppressed the lymphocyte responses to high concentrations of candida and SKSD and stimulated the response to mumps, varicella and tetanus toxoid. Autologous fetal plasma suppressed the lymphocyte responses to candida, varicella and SKSD and stimulated the response to PHA. The responsiveness of maternal lymphocytes to PHA was less in foetal plasma than in autologous maternal or AB plasma.

Immunosuppressive characteristics of human AFP: effect on tests of cell mediated immunity and induction of human suppressor cells

Murine AFP has been reported to be immunosuppressive in a variety of systems. However, the extent and degree of inhibition has varied in different species and laboratories. Therefore, we have examined the potential suppressive effect of purified human AFP on several in vitro tests of cellular immunity and the potential mechanism of its action. AFP purified from fetal and liver cancer sera significantly inhibited mitogen and antigen-induced proliferative responses but had no effect on lymphocyte E rosetting, MIF production or mitogen induced T cell cytotoxicity to Chang target cells. Purified human AFP induced human suppressor cell activity, capable of suppressing a one-way mixed lymphocyte reaction (MLC). In contrast to Con A induced suppressor cells, AFP induced suppressor cell activity was overcome by mitogen augmentation of the proliferative response in MLC. These data suggest that the inhibition of lymphocyte proliferation by human AFP may be mediated by the induction of a subpopulation of human suppressor cells. Furthermore, mitogen induced cell mediated cytotoxicity was partially inhibited by primary liver cancer serum and completely inhibited by newborn cord serum, in contrast to purified fetal or tumor AFP which had no effect. These data suggest that there are other immunosuppressive factors in fetal and tumor serum which require further characterization. These other serum factors may be responsible for some of the immunosuppressive effects attributed to AFP. Although AFP is unlikely to play a major immunosuppressive role physiologically in vivo, its selective effect on proliferative responses, apparently mediated by suppressor cells, may prove to be a useful pharmacologic probe of the mechanism of these in vitro lymphocyte responses and biological interactions.

Feto-maternal bidirectional mixed lymphocyte reaction and survival of fetal allograft

Maternal and fetal lymphocytes were tolerant of each other in the bidirectional mixed lymphocyte reaction. This seems to be the principal reason why the mother does not reject the fetal allograft. Tolerance between maternal and fetal cells must be largely due to a genetic mechanism, because the bidirectional mixed lymphocyte reaction between parents and older children was much reduced compared with that between randomly selected pairs of controls. This weak reaction disappeared when immunosuppressive agents were given to one member of the parent/child pair, whereas the mixed lymphocyte reaction between unrelated individuals was not abolished by similar immunosuppression. It is suggested that this genetic mechanism is distinct from the HLA system. Tolerance between maternal and fetal cells was not demonstrated in the unidirectional mixed lymphocyte reaction, suggesting that this tolerance requires the viability of the two cell populations.

Mixed lymphocyte culture reactions at delivery and in the puerperium: effects of parity, HLA antigens and maternal serum

Mixed lymphocyte culture reactions between maternal and related neonatal cells at delivery, and maternal and paternal cells about a week after delivery, and the effect of maternal serum and HLA antigens on these reactions were studied in 11 families with primiparous or secundiparous mothers and in 13 families with multiparous mothers (six or more pregnancies). Weak or absent MLC response of the mother to her infant was observed in one-third of primiparous and secundiparous mothers and in one-half of multiparous mothers. In some cases the non-reactivity could be due to genetic similarity, i.e. HLA or HLA-D identity between the mother and her infant. In other cases, this was obviously not a valid explanation and no apparent reason for the non-reactivity was found. The MLC suppressing effect of maternal serum on MLC reactions at delivery and about a week later was not correlated with the strength of maternal-neonatal MLC reaction. Four of the ten sera from multiparous mothers studied a week after delivery had an inhibitory effect of 50% or more on MLC reactions involving stimulatory paternal cells. Responding paternal cells and other MLC combinations were also inhibited to varying degrees. None of the sera of primiparous and secundiparous mothers had an equally strong MLC inhibiting effect.

The modulating effect of human chorionic gonadotropin on lymphocyte blastogenesis

Human chorionic gonadotropin (HCG) produced by fetal trophoblastic cells was suggested to play a role in the suppression of maternal lymphocyte response against the fetal allograft. Reports supporting this concept have demonstrated a suppressive effect of crude HCG on lymphocyte blastogenesis. However, similar doses of purified hormone preparations were unable to inhibit lymphocyte stimulation with mitogens. A modulating influence of phenol-free and immunoglobulin-free HCG preparation on lymphocyte blastogenesis is presented. Enhanced lymphocyte stimulation with various mitogens occurred in cultures supplemented with HCG at low doses. On the other hand, higher hormone concentration exerted an inhibitory effect on lymphocyte blastogenesis. An increase in lymphoid cell concentrations was demonostrated in cultures supplemented with the hormone preparation. These observations are compatible with the suggested role of HCG in the maternal tolerance toward a histoincompatible fetus.

Mixed lymphocyte culture reactions between parental cells in pregnancy and puerperium

Mixed lymphocyte culture (MLC) reactions of maternal cells with paternal and control cells, inhibition of these reactions with maternal serum, and cytotoxic antibodies in maternal serum were studied in 36 couples through pregnancy and puerperium. Average MLC reactions of maternal cells with paternal and control cells were not significantly different, nor did the MLC responses of maternal cells clearly differ from those of other cells in their time-course kinetics. However, the response of maternal cells to paternal cells was weaker than to control cells in 15 of 18 couples studied during the first week postpartum; this may suggest some specific alteration in maternal immunity to paternal antigens. The sera of pregnant women suppressed MLC reactions. This suppressive effect disappeared during the first week postpartum, whereafter only about 20% of the sera studied caused clear inhibition of MLC reactions. Nine per cent of the postpartum sera studied contained cytotoxic antibodies against paternal cells.

Feto-maternal relationship in normal pregnancy in mixed lymphocyte cultures

In eight wife-husband pairs during the whole pregnancy the reactivity of lymphocytes to PHA, to lymphocytes of unrelated donor and to lymphocytes of husband was studied. No statistically significant differences were found in reactivity of wife's and husband's lymphocytes. In eleven women at delivery a statistically significant decline of MLC reaction to lymphocytes of own and unrelated newborn was found, while the reactivity to PHA and to lymphocytes of unrelated adult donor remained unchanged. Similarly, the lymphocytes of eleven newborn infants reacted statistical significantly less to lymphocytes of own mother and unrelated mother, while the reaction to PHA and to lymphocytes of unrelated donor was well expressed.