Transplantation--nature's success

Sex hormones and the immune system--Part 2. Animal data

Sex hormones have physiological and pathological (autoimmune conditions) effects on the immune system. Studies in experimental animal models of human autoimmune diseases have clearly shown that sex hormones regulate the expression, severity and course of autoimmune diseases. Sex hormones affect the function of T, B and NK cells, and macrophages. Precisely how sex hormones affect lymphocytes is a highly complex question. Sex hormones can modulate the immune system, perhaps directly (e.g. thymic reticular tissue), or indirectly via host and many oestrogen target tissues, including the central nervous system hypothalamic-pituitary axis (the neuroendocrine tissues). The effects of sex hormones on the immune system (immunosuppression or immunopotentiation) may vary, even with the same hormone. For example, oestrogen can increase IgA levels in the uterus, but decrease IgA levels in the vagina or have no effect in lacrimal tissues (Sullivan, 1989). Therefore the effects of sex hormones on the immune system cannot be generalized but must be evaluated independently. Some of the reasons for variability in results have been reviewed in detail elsewhere (Steinberg et al, 1979; Ansar Ahmed et al, 1985b). These include, dose of hormones, age and sex-hormonal status of animals, route and time of administration, the immunocompetence of the host, stress, the metabolism of hormones (e.g. metabolism of testosterone to oestrogen) resulting in alteration of biological activity, and differential response to various antigens. The initial encounter of sex hormones with the type of target cells, the variability of secondary messengers and gene activation events are other important considerations. The effects of sex hormones on the immune system to modulate immune responses are unequivocal. The burgeoning advances in cellular immunology, endocrinology and molecular biology, should provide a better understanding of: (1) the interactions of hormones with the immune system; (2) how hormones activate specific genes; and (3) how hormones influence intracellular communication. In a clinical situation, it is hoped that androgenic compounds which lack virilizing effects, but possessing the desired immunomodulatory effects, will eventually be synthesized. These hormone analogues, in combination with specific (non-toxic) oestrogen antagonists, may offer new therapeutic avenues.

Maternal-fetal immune relationship: another point of view

Placental transfer of maternal IgG is known to be an active process resulting in a concentration on the fetal side of the circulation--at the apparent expense of that in the mother--at full term. However, when this apparent decrease in maternal IgG is related to the actual hemodilution occurring in parallel, the total inventory of the mother's IgG appears to be constant throughout pregnancy. Therefore, conclusions regarding the variations in IgG concentrations cannot be drawn without simultaneous information about plasma volume fluctuations.

Human placenta-eluted gammaglobulins in immunomodulating treatment of rheumatoid arthritis

Thirty-one patients with severe rheumatoid arthritis were treated with intravenous perfusion of human placenta-eluted gammaglobulins. These gammaglobulins, which are IgG eluted from placental tissue, have strong immunomodulating properties in vitro. Several clinical trials were tested to find the optimal useful dosage. A 50 percent improvement was considered a good result and was obtained in 60 percent of patients with rheumatoid arthritis. The best results were obtained in patients receiving 1,500 mg daily seven days each month. Six subjects had a long remission of their disease after the end of treatment. The side effects were usually minor. In all patients, an immunostimulation of lymphocyte function was shown, even when they had no improvement. A control group of patients underwent perfusion with IgG from placental blood without any clinical or immunologic effect. It is suggested that the in vivo effects of placenta-eluted gammaglobulins might be mediated by polyspecific anti-HLA-DR antibodies.

Histocompatibility antigens in pregnancy, abortions, infertility, preeclampsia, and trophoblast neoplasms

The genetic makeup of an individual may determine the capacity of the individual to combat successfully cancer and other disease states, eg abnormal pregnancies, abortions, infertility, and preeclampsia. These factors appear to be based upon the individual's immunogenetics, as histocompatibility-restricted T-cell cytotoxicity may be deficient in the observed instances of increased histocompatibility between husband and wife found in trophoblast tumor patients and in other instances of abnormal pregnancies.

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.

Do plasma glycoproteins induce lymphocyte hyporesponsiveness and insulin resistance?

Depression of lymphocyte transformation and an increase in insulin resistance are common to pregnancy, oral contraceptive use, widespread malignancy, infection, and tissue destruction. We suggest that these abnormalities are caused by a rise in the plasma-glycoprotein level which is also common to these clinical states. There is evidence that glycoproteins can inhibit cell division, lymphocyte transformation, and the action of hormones on target cells. Because of the increase in plasma glycoprotein the cells in many organs and their hormone receptors may have a thicker coating of glycoproteins which blunts their response to variuos stimuli.

Polymorphonuclear leucocyte function during pregnancy

Polymorphonuclear leucocyte (PMN) function was studied in pregnant women and related to the serum concentration of pregnancy zone protein (PZP) and to mixed lymphocyte culture (MLC) reactivity. Neutrophil chemotaxis was depressed in pregnant women. Pregnancy serum inhibited the MLC-reaction. The serum levels of PZP were inversely related to chemotactic responsiveness (P less than 0.05) and depression of MLC reactivity (P less than 0.01). The capacity to reduce nitroblue tetrazolium was depressed in PMNs from pregnant women, and pregnancy serum inhibited phagocytosis of Escherichia coli by control PMNs. Neutrophils from pregnant women showed increased chemiluminescence during phagocytosis of zymosan. The results may be explained by depression of ingestion by pregnancy serum and increased oxidative metabolism in PMNs from pregnant women.

An investigation of the immune response of patients suffering from anorexia nervosa

Patients suffering from anorexia nervosa rarely appear to develop the common cold or influenza. This study examines the immunological response of fifteen female anorexia nervosa patients of both the vomiting and carbohydrate-abstaining type and compares them with a control population matched for age and occupation. Both anorectics and control populations received the admune influenza vaccine. Initially both groups had similar haemagglutination inhibition titres against the three different viral antigens: A/HK; A/PC; A/Eng. However, the anorectics showed over a 2-month period a higher titre of antibody especially to the Hong Kong virus: this was sigignificant. Cellular immune responses were measured using a tuberculin and a macrophage inhibition test, no significant difference between the two groups was obderved. These results which support the clinical findings are discussed.

Immunosuppression by human placenta lactogen (HPL) and the pregnancy-specific beta 1-glycoprotein (SP-1). Inhibition of mitogen-induced lymphocyte transformation

The in vitro effect of human placental lactogen (HPL) and the gravidity-specific beta1-Glycoprotein (SP-1) on the lymphocyte transformation was investigated in 20 healthy women. It was shown that simultaneous incubation of the lymphocytes with HPL or SP-1 together with PHA has no influence on the incorporation rate of H3-Thymidine. When the fetal calf serum (FCS) in the lymphocyte cultures was substituted by a 3% human albumin-solution, there was a reduction of the incorporation rate of the radioactive nucleic acid precursors to 20%, as compared to the controls with FCS. After addition of HPL and SP-1 to the cultures there was a further dosis dependent decrease of the incorporation rate. When lymphocytes were preincubated with the proteins for 24 h, there was a marked reduction of the blastogenesis after additon of PHA, HPL and SP-1 under these conditions had a immunosuppressive effect on the lymphocyte transformation.

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.

The immunosuppressive role of alpha-fetoprotein during pregnancy

Cell-mediated and humoral immune responses were assessed in mice at mid-term (day 10) in pregnancy. A significant but selective suppression of the primary in vivo antibody (plaque-forming cell) response to SRBC was observed, with the most pronounced effect being on the gammaA response. Similar results were obtained for secondary in vitro antibody synthesis by antigen-primed spleen cells from pregnant mice, demonstrating the intrinsic nature of the inhibition. Pregnant mouse serum (PMS) was shown to suppress primary in vitro antibody synthesis, and the inhibitory effect was abrogated by the selective removal of alpha-fetoprotein (AFP) using affinity chromatography. Normal mouse serum became similarly suppressive in vitro when purified AFP of fetal origin was added to it in concentrations approximating that found in PMS. Spleen cells from pregnant mice showed a suppressed mitogenic response to phytohemagglutinin, a lowered response to concanavalin. A, and a normal response to lipopolysaccharide. In contrast, the allogeneic response of these animals as measured in the one-way mixed lymphocyte culture was enhanced. PMS suppressed both allogeneic and mitogen-induced lymphocyte transformation by spleen cells from nonpregnant mice, and the effect was eliminated by the selective removal of AFP. These findings indicate an important functional role for AFP in normal embryological development.

Depression of blast transformation of peripheral leukocytes by plasma from pregnant women

The blast transformation of peripheral leukocytes from pregnant and nonpregnant women has been studied at different time intervals with graded concentrations of phytohemagglutinin. The transformation is markedly depressed during pregnancy. Leukocytes from nonpregnant women and men show diminished transformation when cultured in a medium containing plasma from pregnant women.

Immunological responses in pregnancy and survival of fetal homograft

Immunological responses were studied in pregnant women and controls using as tests phytohaemagglutinin-induced lymphocyte transformation and the tuberculin reaction. Significantly reduced responses were found to both tests in the pregnant women. These results suggest that a reduction in T-cell activity during pregnancy may help protect the fetus from rejection by its mother's immunological mechanisms.