Cellular immune aspects of the human fetal maternal relationship. II. In vitro response of gravida lymphocytes to phytohemagglutinin

Immunoregulatory mechanisms present in the maternal circulation during pregnancy

Systemic alterations of the maternal inflammatory and immune system occur during pregnancy. These changes alone are unlikely to be responsible for the acceptance of the fetal semiallograft. Numerous local events at the maternal-fetal interface appear to be more important. The alterations of the maternal inflammatory and immune systems are subtle enough for no significant increase of infections or malignancy to be apparent. However, 75% of women with rheumatoid arthritis are clinically improved during pregnancy. The effects of pregnancy on polymorphonuclear cells are not likely to be responsible because cell function actually appears enhanced in vivo, despite the fact that pregnancy serum is suppressive in vitro. There is no clear evidence for reduction of monocyte/macrophage function during pregnancy, either in vivo or in vitro. It is unlikely that modulation of B cell phenotype or function is responsible because no suppression is noted, either in vivo or in vitro. Selected products of B cells, immune complexes, appear to be reduced during pregnancy. In patients, the reduction in the concentration of complexes may be due to adsorption by the placenta. The importance of this reduction as a causative factor in the improvement of women with rheumatoid arthritis during pregnancy remains to be determined. Natural killer cell cytotoxicity is decreased during pregnancy. This may in part be due to the release of progesterone induced blocking factor. It is also possible that circulating factors, capable of inhibiting IL-2 release or IL-2 function in vivo, might be responsible. Natural killer cytotoxicity can be normalized by incubation with IL-2. It is unclear how the reduction of natural killer cell activity might systematically affect inflammation or immunity in vivo during pregnancy. In vivo delayed type hypersensitivity appears somewhat reduced during pregnancy. This observation appears consistent with the improvement of rheumatoid synovitis, which is also thought to be T cell mediated. T cell function, measured in vitro, generally appears normal. However, most recent studies have employed mitogens, such as PHA, which is not physiological. Subtle defects involving antigen processing or antigen presentation might be missed in this system. These observations suggest that circulating factors might be important in modulating the cell mediated immune system, in vivo, during pregnancy. While anti-HLA-DR antibodies eluted from the human placenta may be effective therapy in patients with rheumatoid arthritis, their occurrence is too infrequent to account for the improvement seen in afflicted patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Responses to mitogenic stimulation of lymphocytes taken during and after pregnancy

Serial blood samples were collected during pregnancy, after delivery and several months postnatally from 28 women. The blastogenic responses of lymphocytes to varying concentrations of phytohaemagglutinin (PHA) were tested using autologous plasma or fetal calf serum (FCS) to support the lymphocyte cultures. Using FCS, the blastogenic response decreased as pregnancy progressed and remained depressed months after delivery. In contrast, when autologous plasma was used a 10-fold higher concentration of PHA was required to give optimal stimulation. Blastogenic responses were still suppressed during pregnancy but had returned to initial values by the time of delivery and were greater still in the post-partum and postnatal periods. We conclude that the inherent ability of lymphocytes to undergo blastogenesis is suppressed during pregnancy but that this is over-shadowed by a humoral effect of pregnancy plasma. The significance of these results is discussed.

Increased rate of E-rosette formation by T lymphocytes of pregnant women who drink ethanol

Ethanol use by pregnant women increased, in a dose-dependent manner, the rate of sheep erythrocyte rosette (E-rosette) formation with T lymphocytes. The time curve for E-rosette formation by T cells from nondrinking subjects was biphasic, with a rapid formation of half the E-rosettes within the first 16 min, followed by a much slower rate for E-rosette formation until the maximal T-cell percentage was reached overnight. For pregnant drinkers, greater than 85% of the E-rosettes formed during the initial rate period, with a concomitant smaller number forming during the overnight incubation. Despite the faster initial rate of E-rosette formation in the drinking subjects, the total percentage T cells was the same for both groups. Other demographic factors, like tobacco or marijuana use, or trimester, did not significantly contribute to the observed differences. An increase in the rate of E rosetting was also obtained by incubating lymphocytes from nondrinkers overnight in physiologically attainable concentrations of ethanol (less than or equal to 0.1%). These results demonstrate that drinking by pregnant women, even at relatively moderate levels (2 oz/week absolute ethanol), causes alterations in their cellular immune systems. With the ability of ethanol to cross the placental barrier and persist in utero, it is apparent that these levels of ethanol have the potential to affect the developing fetal immune system.

Mid-trimester pregnancy--a time of tranquility or activity?

A number of compounds in pregnancy blood reach a maximum or minimum concentration at around 20-24 weeks of pregnancy, a period of conspicuous clinical tranquility. The compounds mostly derive from either fetal tissue or decidua and it is suggested that they may be part of an elaborate mechanism which controls invasion of the uterine wall by trophoblast.

Is pregnancy immunosuppressive? Humoral immunity against viruses

Serum samples were obtained during the first trimester, second trimester, third trimester, at delivery and 6 weeks postpartum from each of 50 pregnant women. All 250 sera were tested for their content of antibodies specific for herpes simplex, measles, rubella and influenza A viruses. The geometric mean titres of antiviral antibody were shown to decline by 18-48% between the times of booking and delivery, and to return to initial values by the end of the puerperium. By means of two-way analysis of variance, the major confounding variable of differences between individuals was identified and controlled for, so that the progression of pregnancy was shown significantly to decrease titres of antiviral antibody. After allowance was made for haemodilution, antibody levels against two viruses (herpes simplex, measles) still declined significantly while those for rubella and influenza viruses actually increased significantly, so that no consistent effect of pregnancy was demonstrable. We conclude that the declining titres of antiviral antibodies seen in pregnant women are predominantly a manifestation of haemodilution and discuss the reasons for believing that humoral immunity remains intact during pregnancy.

Depression of the lymphocyte transformation response to microbial antigens and to phytohemagglutinin during pregnancy

Lymphocyte transformation (LT) responses to Chlamydia trachomatis, to four other microbial antigens, and to phytohemagglutinin (PHA) were studied in 201 women during pregnancy and/or 3-18 wk postpartum. The LT responses to all stimulants tested were significantly depressed during pregnancy when compared with postpartum LT responses. This difference occurred whether LT assays were performed in autologous or pooled heterologous plasma collected from nonpregnant donors. Among women studied in the third trimester and again postpartum, the autologous LT stimulation index (LTSI) rose from 1.7 to 3.4 (P less than 0.001) with C. trachomatis elementary body antigen, from 3.7 to 7.9 (P less than 0.001) with Candida albicans cell wall extract, from 4.5 to 7.8 (P = 0.008) with streptokinase-streptodornase, from 1.7 to 3.0 (P = 0.007) with fluid tetanus toxoid, from 1.7 to 2.8 (P = 0.046) with mumps virus skin test antigen, from 35.5 to 87.0 (P less than 0.001) with PHA (2 micrograms/ml), and from 107.2 to 181.9 (P = 0.007) with PHA (10 micrograms/ml). LT responses to C. trachomatis were compared in 52 pregnant women and 58 nonpregnant women; all the women had C. trachomatis isolated at the time of LT assay. Using either plasma supplement, the mean LTSI with C. trachomatis antigen was significantly higher in nonpregnant women than in pregnant women, regardless of trimester (P less than 0.001). Among 12 women who were serially tested and remained culture positive for C. trachomatis throughout pregnancy and the postpartum period, the mean autologous LTSI rose from 1.9 in the third trimester to 7.8 postpartum (P = 0.0004). These data are the first to show that the immune response to an ongoing bacterial infection is depressed during pregnancy and to definitively document the depressed LT responses during human pregnancy.

Binding of progestins to the glucocorticoid receptor. Correlation to their glucocorticoid-like effects on in vitro functions of human mononuclear leukocytes

A number of physiological and synthetic progestins were tested for their ability to compete with [3H]dexamethasone for the binding to the glucocorticoid receptor of human mononuclear leukocytes and their ability to elicit glucocorticoid-like effects on the same cells. As compared to the reference compound dexamethasone (relative receptor binding affinity defined as 100%), two potent synthetic progestins with a pregnane-type structure, megestrol acetate and medroxyprogesterone acetate, were found to display a considerable binding affinity towards the receptor (46 and 42%, respectively). The relative binding affinity of the naturally occurring ligand, cortisol, to the receptor was clearly lower (25%). The effective binding of medroxyprogesterone acetate to the glucocorticoid receptor was confirmed by direct binding studies utilizing a tritiated derivative of this steroid. No evidence for the existence of a specific progesterone receptor in human mononuclear leukocytes was obtained as judged by the results of competition experiments where a progesterone receptor-specific ligand [3H]Org 2058 was used. Medroxyprogesterone acetate and megestrol acetate also induced glucocorticoid-like effects on the lymphocyte functions. These included inhibition of the proliferative responses to the T-cell mitogens concanavalin A and phytohaemagglutinin and an enhanced accumulation of immunoglobulin secreting cells in pokeweed mitogen-stimulated cultures. The progestin effect appears to be mediated through a radiosensitive (suppressor) subpopulation of T lymphocytes. In contrast, the synthetic progestins related structurally to 19-nortestosterone, norethisterone and d-norgestrel, were virtually devoid of binding affinity towards the glucocorticoid receptor nor did they measurably influence the in vitro lymphocyte functions. These studies demonstrate that certain progestins in common clinical use probably possess inherent glucocorticoid activity and suggest that side effects attributable to this character (e.g. suppression of the pituitary-adrenal axis) might be expected when these compounds are used in pharmacological doses.

A longitudinal analysis of lymphocyte proliferative responses to mitogens and antigens during human pregnancy

T-cell number and mitogen- and antigen-induced lymphocyte proliferative were assessed longitudinally in 18 normal human pregnancies to examine the effects of pregnancy on cellular immunity. The T-cell percentage and mitogen-induced responses did not change significantly in pregnant women as compared to nonpregnant, non-postpartum control adults. However, cell-mediated immune responses to three antigens were dramatically depressed during the third trimester and then returned to early pregnancy levels by 90 days post partum. This reduction in antigen-specific cellular immunity may be necessary to prevent rejection of the histoincompatible fetus by the mother and at the same time may render women in late gestation more susceptible to infection.

Polyamine-polyamine oxidase interaction: part of maternal protective mechanism against fetal rejection

Human retroplacental blood serum significantly (p less than 0.01) suppresses the in-vitro uptake of 3H-thymidine--that is, synthesis of deoxyribonucleic acid--by spontaneously growing human lymphocytes in the presence of exogenous spermine, but only in concentrations with a higher polyamine oxidase activity than that found in maternal peripheral blood serum during pregnancy. These findings together with observations that the placenta is rich in spermine and that interaction of polyamine oxidase and substrate arrests cell proliferation suggest that such interaction might represent a localised immunoregulatory mechanism in the placental bed, which might contribute to the protection of the fetoplacental unit from possible maternal immune rejection.

Suppression by progesterone of nonspecific in vitro lymphocyte stimulation in mice as a mechanism for the enhancement of herpes simplex virus type 2 vaginal infection

The role of antibody, interferon, and cell-mediated immunity (CMI) were studied to determine the mechanisms for progesterone enhancement of vaginal herpes simplex virus type 2 (HSV 2) infection in mice. Three groups of mice were studied: nonpregnant control, pregnant, and nonpregnant progesterone-treated mice. Vaginal infection with HSV 2 did not elicit a neutralizing antibody or a systemic interferon response in any of the groups tested. Splenic lymphocytes from noninfected and infected mice were stimulated in vitro with a nonspecific T-cell mitogen concanavalin (Con A) to measure the proliferative phase of CMI in these groups of mice. No suppression of (3H) thymidine (3HTdR) uptake was found in the pregnant or nonpregnant, progesterone-treated animals as compared to nonpregnant control mice. When progesterone was added directly to the splenic lymphocytes and continuously present during Con A stimulation a statistically significant depression of 3HTdR incorporation was found. We concluded that progesterone depresses Con A stimulation of murine lymphocytes, but progesterone must be continuously present to do so.

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.

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.

Immunologic and medical considerations in tuberculin-sensitized pregnant patients

One-hundred and seventy-two pregnant patients were identified as tuberculin sensitive in the first trimester. These patients were followed throughout pregnancy for any signs or symptoms of active tuberculosis which were discovered only in the index case. Post partum, patients were again re-evaluated for tuberculosis and prophylactically treated with isoniazid if they met established criteria. The tuberculous host also represented a model for the study of cell-mediated immunity, which presumably is altered in pregnancy. This investigation revealed a progressive depression of lymphocyte function to a specific antigen, purified protein derivative, obtaining significance at 36 weeks' gestation and continuing through delivery (p is less than 0.001). Nonspecific cell-mediated immunity, however, was not depressed when monitored throughout the gestation by the mitogen, phytohemagglutinin, which would stimulate all lymphocyte clones. This discrepancy in the alteration of specific clones of lymphocytes compared to all noncommitted lymphocytes may account for varying reports of the immune status of the pregnant woman.

Studies of lymphocyte populations in pre-eclampsia-eclampsia

The possibility that the etiology of toxemia might be immunologic has been held for over 70 years. In the past decade, numerous studies have been instituted in attempts to verify the possible role of the immune system in this disease. The present study was undertaken as a probe to determine if a gross difference in the numbers of T and B cell lymphocyte populations might exist between pre-eclamptic and normally pregnant women. Twenty-five normally pregnant women in the third trimester were compared to 25 pre-eclamptic women, and significant differences were noted. If, indeed, there is an immunologic basis for pre-eclampsia, it is more subtle than the methodology used in this study is capable of detecting.

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.

Changes in lymphocyte function during pregnancy

A gradual increase in spontaneous lymphocyte DNA synthesis was demonstrated in each trimester of pregnancy. Autoradiographic studies indicated that lymphocytes were primarily responsible for this activity. PHA-induced lymphocyte transformation in both fetal calf serum and autologous serum was significantly reduced in the second and third trimesters of pregnancy. Spontaneous lymphocyte DNA synthesis was significantly reduced in patients with mild pre-eclampsia. However, no significant differences were seen in patients with severe pre-eclampsia in the third trimester of pregnancy compared with the normal control subjects. No evidence was adduced to implicate inhibitory humoral factors affecting the peripheral blood lymphocytes in pregnany patients in experiments in which washed lymphocytes were cultured in medium containing heterologous serum. In vitro experiments demonstrated that cortisol, progesterone and HPL caused a significant reduction in lymphocyte DNA synthesis, and HGH and HCG had a variable effect. However, only cortisol was regularly inhibitory at physiological concentrations. The progesterone effect was dose-related, producing 90 per cent inhibition of activity at a concentration of 10 mug/ml. No synergism could be shown between HPL and progesterone on lymphocyte transformation. The increase in activity of circulating immunoreactive cells during pregnancy and its depression with the onset of pre-eclampsia is discussed.

Complement-fixing and lymphocytotoxic antibodies in serum of pregnant women at delivery II. Clinical observations I

Sera from 2,008 pregnant women were examined for the presence of complement-fixing platelet antibodies (CFPAb) and lymphocytotoxic antibodies (LCTAb). Women with antibodies in their serum were compared with women without antibodies. No clinical significance of CFPAb or LCTAb was found as regards pre-eclampsia, arterial hypertension, albuminuria, oedema, glucosuria, premature delivery, spontaneous onset of labor and abortion.

Inhibitory effect of progesterone on the phytohaemagglutinin- induced transformation of human peripheral lymphocytes

Effect of sex steroids, progesterone and estradiol-17beta, on transformation of human lymphocytes induced by PHA was investigated. Responses of peripheral lymphocytes from non-pregnant women to PHA was markedly reduced in the presence of progesterone at a concentration of 10(3) or 10(4) ng/ml. Estradiol-17beta, on the other hand, had no effects on the PHA-induced transformation under the present experimental conditions. The immunosuppressive property of progesterone may contribute to depression of maternal cell-mediated immunity against fetus during pregnancy.