Immunoregulatory pathways in pregnancy

Murine pregnancy is characterized by transient thymic atrophy and splenomegally. Several laboratories are investigating the immunoregulatory mechanisms during pregnancy, and the majority of these studies are primarily focused on the immunological changes either in the uterus or the thymus and not much information is available on the immunological changes in the spleen that result in transient splenomegally. An attempt has been made in this review to understand the significance of thymic atrophy, splenomegally and local immune changes in the uterus to understand the overall immunomodulatory mechanisms in pregnant mother. The most significant change which occurs soon after mating is the infiltration of immune cells such as macrophages and gammadelta-T cells into the uterus indicating that the mother's immune system detects the presence of foreign antigens in the reproductive tract. The sensitized cells appear to migrate to the secondary lymphoid organs including the spleen. The microenvironment in the spleen is conducive for the cell-cell contact and generation of immune response. The major changes that occur in the spleen are, the induction of T-cell dependent B-cell response on day-1 post-coitum (P.C.), generation of antibody producing B-cells on day-3 and also proliferation of CD8+ T-cells that peaks on day-3 of pregnancy. The weight of the spleen reaches a peak on day-10 in mice. Thereafter, on day-15 of pregnancy, lymphocyte apoptosis is seen in the spleen indicating the deletion of peripheral sensitized cells. This results in decrease in spleen weight to that of normal non-pregnant mice. The decrease in thymic weight after day-5 pregnancy was associated with the increased apoptosis of cortical thymocytes. This perhaps is due to negative selection of self-reactive thymocytes. Our studies have demonstrated that the pregnancy associated monoclonal antibodies react with antigens of sperm indicating that the mother's immune system recognizes and responds to the constituents of the semen to produce non-precipitating asymmetric auto antibodies (NPAA) or blocking antibodies which have favourable effects on pregnancy. It is postulated that the mother's immune response could be directed to some antigens of sperm along with some conserved antigens such as heat shock proteins (HSP) that are present both in sperm and in the mother. It may be speculated that after the initial priming to some conserved antigens of sperm and due to the presence of similar antigens in the mother, these activated clones are eliminated both in the primary and secondary lymphoid organs to prevent autoimmunity in the mother during pregnancy.

The role of LFA-1, Mac-1, ICAM-1 and Ia in the induction of Th-2 type of immune response in spleen during murine syngeneic pregnancy

Murine syngeneic pregnancy is characterized by the transient splenomegaly at mid gestation. Recent studies from our laboratory have indicated the initiation of T-cell dependent B-cell response in the spleen during early pregnancy (Hegde and Nainan 1998). Present studies were carried out to understand the role of cell adhesion and MHC class II (Ia) molecules in the induction of Th-2 type of response in the spleen of pregnant mouse. Immunochemical localization of ICAM-1, LFA-1, Mac-1 and Ia in spleen have been carried out at different stages of pregnancy and formation of cell clusters and natural cell adhesion assay with splenocytes were carried out on day 1 (D1) pregnancy and compared with control. Upregulation of ICAM-1, LFA-1, Mac-1 and Ia was observed during early pregnancy. This coincided with the formation of germinal centers (GC) and Th2 type of interleukins in spleen as reported earlier. Increased expression of cell adhesion and Ia molecules during early pregnancy provides additional evidence for the systemic shift to Th2 type of immune response in syngeneic murine pregnancy.

T helper-2 type of interleukins with de novo germinal center formation in the spleen during murine pregnancy

PROBLEM

Murine pregnancy is characterized by transient thymic atrophy and splenomegaly. Although some reports on the thymus are available, little is known about the role of the spleen. In the present study, sequential changes in the spleen have been evaluated during murine syngeneic pregnancy.

METHOD OF STUDY

Formation of germinal centers (GCs), immunoglobulin positive (Ig+) cells and interleukin (IL)-2, IL-4, and IL-6 were immunolocalized in the spleen during pregnancy and compared with a control group of virgin mice.

RESULTS

Initiation of T-cell dependent B-cell response with the induction of peanut agglutinin (PNA+) GCs correlated with decrease in IL-2 and maintenance of IL-4 and IL-6 on day-1 pregnancy followed by an increase in Ig+ cells.

CONCLUSION

The immune response observed in the syngeneically pregnant mother is not directed to paternal major histocompatibility complex antigens. Present studies demonstrate for the first time the role of the spleen in initiating a T-cell dependent B-cell response with a shift of systemic immune response from T helper 1 to T helper 2 type.

Immunochemical characterization and antifertility effect of an androgen independent antigen of spermatozoa identified by a monoclonal antibody (D7G3)

Monoclonal antibody, (mAb) D7G3, directed to human spermatozoa and cross-reactive with mouse and rat spermatozoa was found to be a sperm agglutinating antibody. It reacted with antigen present on the post acrosomal region of human spermatozoa and acrosomal region of mouse spermatozoa. The antigen reacting with mAb D7G3 was localized in mouse testicular germ cells and Sertoli cells. It was also localized in the epithelium and spermatozoa of the caput, corpus and cauda epididymides. In addition, the antigen was detected in the epithelial cells and secretions of the prostate and seminal vesicle. The mAb D7G3 reacted with a band of molecular mass 16 kDa in testicular and epididymal sperm and protein preparations of ventral prostate. In the seminal vesicle, an additional band of molecular mass 36 kDa was also identified. The effect of castration on the expression of proteins was studied in the rat. Immunohistochemical localization and Western blotting experiments showed that the antigens identified by the mAb D7G3 was detectable in the epididymis, ventral prostate and seminal vesicle after two weeks of castration. In the seminal vesicle, three additional bands were identified by mAb D7G3 following castration. The expression of this antigen throughout spermatogenesis and sperm maturation indicated that it may have an important biological function. A polyclonal antiserum directed to the 16 kDa mouse epididymal sperm protein was raised in rabbits. Passive immunization of female mice with this antibody caused a significant reduction in fertility only if administered 24 hours prior to mating, indicating that the antibody inhibited a pre-fertilization event by inhibiting sperm function.

Epididymal sperm maturation proteins

Mammalian spermatozoa are not motile when they leave the testis. They have to undergo a complex maturation process to be able to fertilize in vivo. The maturation changes of mammalian sperm membrane have been extensively studied using lectins and antibodies. Some of these antigens have been purified and cloned. The interaction of secreted proteins with sperm membranes and acquisition of sperm motility as essential steps for spermatozoa to be fertile are well documented. The role of these epididymal maturation proteins in infertility and the possibility of using these antigens for immunocontraception are discussed in this review.

Antigenic stimulation and blocking of pregnancy in mice by an anti-idiotypic antibody to progesterone

PROBLEM

The present study was carried out to see if the anti-idiotypic (anti-Id) antibody (Ab2) to progesterone could mimic the immunogenicity of the steroid hormone by giving rise to antiprogesterone antibodies (Ab3) and whether these antiprogesterone antibodies (Ab3) were biologically active.

METHOD

Twenty virgin female Balb/C mice were actively immunized with the anti-Id antibody (Ab2). The antiprogesterone antibody (Ab3) titres in the serum were determined and the animals were used for fertility studies. In the passive immunization studies Balb/C female mice were injected i.p. with 100 micrograms of anti-Id antibody to see its effect on pregnancy.

RESULTS

The actively immunized animals when mated showed 80% reduction in their fertility rate. The duration of infertility (20-121 days) in these animals could be directly correlated with the concentration of antiprogesterone antibody (Ab3). The anti-Id antibody (Ab2) blocked pregnancy in 80% of the passively immunized mice.

CONCLUSION

The studies show that anti-Id antibody to progesterone could mimic the immunogenicity of progesterone and give rise to antiprogesterone antibodies (Ab3). The anti-Id antibody successfully blocked pregnancy in mice both after active and passive immunization.

Localization and detection of ovarian follicular fluid protein in follicles of human ovaries

Human ovarian follicular fluid protein has been partially purified and the active fraction designated as hGF2. Using specific polyclonal antiserum to hGF2, it was observed to be localized immunohistochemically in the granulosa cells of medium but not large follicles of human ovary. The hGF2 levels were estimated by ELISA in serum and follicular fluid of 10 gonadotropin-stimulated women recruited for IVF-ET programme. The results revealed a 3-fold increase in the concentration of hGF2 in follicular fluid compared to that in serum of these patients. These data indicate that the protein is secreted by granulosa cells and plays an important role in the regulation of follicular maturation and ovulation.

Immunomodulation of the mother during pregnancy

The concept that the immune responsiveness of the mother is reduced during pregnancy arose from studies which appeared to show that immune response to certain antigens is reduced during pregnancy (1, 2). Various substances claimed to have immunosuppressive or immunomodulating effect include alpha fetoprotein, placental proteins, early pregnancy factor (EPF), human chorionic gonadotropin (HCG), corticosteroids, estrogens, androgens and progesterone (2). To summarise a body of literature, there is very little change in the immune competence of the mother during pregnancy. This makes sense, as generalized immunosuppression would be a risky way to ensure the survival of the fetus. Immune enhancement and subsequent immunomodulation of the mother is likely to be the mechanism operative during pregnancy. It is conceivable that the overall immune response in pregnancy could be the net result of an interplay of various interactions that may be operating to ensure non-rejection of the antigenically alien fetus while at the same time preventing a state of excessive immunosuppression. Such a dynamic homeostatic mechanism appears to be important for the successful completion of pregnancy.

Ontogeny of mouse caudal proteins identified by a monoclonal antibody

A monoclonal antibody (mAb) D2G4 directed to human spermatozoa recognized antigens on the acrosomal region of both human and mouse spermatozoa and reacted with two proteins of molecular weights 45 kd and 26 kd. Immunohistochemical staining with this antibody indicated that only the epithelial cells of the cauda epididymis were stained and not the sections of testis, caput or corpus epididymis. These observations suggest that antigens recognized by D2G4 were acquired by the spermatozoa during their passage through the cauda epididymis and appear to have a role in the maturation of spermatozoa. The ontogeny of these antigens in mice was studied during sexual maturation. These antigens could be detected in cauda epididymis from day 50 onwards by immunohistochemistry. The highest concentration of these antigens was observed in the cauda epididymis of 80-day-old mice. SDS-PAGE analysis indicated that the 26 kd protein recognized by D2G4 was visible from day 50 onwards, confirming the immunohistochemical observations. The plasma testosterone levels showed a significant increase from days 40 to 60 followed by a decrease. The fact that these epididymal proteins appear during sexual maturation and at the time of the testosterone surge indicates that they are androgen dependent.

Immunochemical localization and characterization of proteins from mouse cauda epididymis using human sperm specific monoclonal antibody

Monoclonal antibodies (mAbs) to sperm specific antigens were generated by fusion of mouse myeloma cells (SP2/0) with splenocytes of female BALB/c mice hyperimmunized with washed human spermatozoa. The resultant hybridomas producing antisperm antibodies were first screened by ELISA. Out of these, one of the mAbs (D2G4) which recognized target antigens restricted to the acrosomal cap was chosen for these studies. The mAb D2G4 was found to be an agglutinating antibody and was also found to cross-react with mouse epididymal spermatozoa in ELISA and indirect immunofluorescence. The origin of antigens reacting with monoclonal antibody D2G4 was investigated. When frozen sections of murine testis and various regions of epididymis were reacted with mAb D2G4, only the cauda epididymal region was stained. Western blot of proteins from the epididymal spermatozoa and fluid indicated the presence of two bands of mol. wt 45 and 26 kd. These bands were identical under reducing and non-reducing conditions. These observations suggest that the two proteins are structurally similar or at least have a common epitope. These data indicate that the proteins recognized by D2G4 are acquired by spermatozoa during their passage and storage in the cauda epididymis.

Immune response to syngeneic spermatozoa & its effect on target organs in mice

Two groups of adult Swiss mice were immunised with washed syngeneic spermatozoa without any adjuvant for a period of two months or four months respectively. The presence of antibodies to spermatozoa was measured by micro sperm-agglutination and micro sperm-immobilization tests. The development of cell mediated immune response (CMIR) was measured by leucocyte migration inhibition test (LMIT) using spermatozoal antigens solubilized by 3M KCl, Nonidet P-40 or by subjecting the cells to ultrasonication. SDS-PAGE analysis of these proteins indicated that extraction of spermatozoa with 3 M KCl was a better method for solubilization of antigens present on sperm membrane. Almost all immunized mice had varying titers of sperm agglutinating antibodies. Nearly 40-50 per cent of the mice had a titre of 1:128 in both groups whereas only 33 per cent had sperm immobilizing antibodies. CMIR, as assessed by LMIT, was detected in immunized mice. However, this had not resulted in the infiltration of immune cells into the target organs perhaps due to the lower magnitude of immune response.

Production of H-Y antibody in the ascites fluid of mouse and localization of the antigen on cells and tissues

A procedure is described for the production of large amounts of ascites fluid containing specific H-Y antibody. The distribution of H-Y antigen on mouse epididymal spermatozoa, thymocytes, and splenocytes was carried out using this specific antibody in the microcytotoxicity test and ELISA. Employing the indirect immunofluorescent technique, the H-Y antigen was localized on the acrosomal membrane of mouse epididymal and washed ejaculated human spermatozoa and on the entire membrane of mouse splenocytes and thymocytes. Immunohistochemical localization of the antigen in the testicular section indicated its presence in the cytoplasm of Leydig cells and on the membrane of Sertoli cells and sperm heads.

Effect of pregnancy plasma and monoclonal antibodies to HLA and DR antigens on leukocyte migration

We studied the effect of pregnancy plasma and monoclonal antibodies to the histocompatibility antigens HLA and DR on migration of normal leukocytes from capillaries. It was observed that plasma from women in the first trimester of pregnancy significantly enhanced leukocyte migration at a concentration of 10% (mean area of migration = 50.7 +/- 9.2 cm2), as compared with plasma from nonpregnant women (22.8 +/- 7.0 cm2; p less than 0.05). This effect was less during the second trimester (39.5 +/- 3.5 cm2; p less than 0.05) and no enhancement was noted with plasma obtained from the third trimester of pregnancy. Similar results were obtained with a 20% concentration of plasma also. On the other hand, the monoclonal anti-HLA and anti-DR antibodies had an inhibitory effect on migration of leukocytes. These results are discussed in relation to the immunoregulatory role of pregnancy plasma in the nonrejection of the fetal allograft.

Studies on cell-mediated immunity in women using different fertility regulating methods

Cell-mediated immunity (CMI) was assessed in women using fertility regulating methods for 1-5 months, 6-11 months or 12-18 months. The CMI as assessed by phytohaemagglutin in (PHA)-induced lymphocyte transformation of treated groups were compared with that of normal subjects who were not using any contraceptive methods and women on conventional methods of contraception. The data obtained indicates that there is no significant alteration of CMI in women fitted with IUCD or women on estrogen progestogen combination. However, a significant suppression of CMI is observed in women in progestogen pills for 12-18 months. The short term therapy did not affect the CMI. In a prospective study it was found that the CMI in women before and after the use of combination therapy for 1-5 and 6-11 months revealed no change. Estradiol and progesterone at concentration on 1 microgram/ml in culture medium suppressed PHA-induced lymphocyte transformation.

Use of monoclonal antibodies for the detection of HLA and DR antigens on spermatozoa of different species

There are conflicting reports about the presence of HLA and DR antigens on human sperm. The difference may be due to the complexity of anti-sera used by earlier researchers. These limitations have been overcome by using monoclonal antibodies in the present studies. The microcytotoxicity test was used to determine the presence of HLA and DR antigens on sperm of different species. It was observed that about 60% of human spermatozoa express HLA antigens and a slightly lower percentage (48%) express DR antigens. These antigens are highly cross-reactive with that of monkey and, to a lesser extent, with that of buffalo. Histocompatibility antigens expressed on epididymal spermatozoa of rat and mouse are also weakly reactive with monoclonal antibodies directed to human HLA and DR.

Phytohaemagglutinin as a molecular probe to study the membrane constituents of human X- and Y-bearing spermatozoa

Phytohaemagglutinin (PHA) was employed to study the constituents of the cell membrane in X- and Y-bearing human spermatozoa. The presence of certain receptors for PHA was revealed in the equatorial region of about 50% of the spermatozoa. To determine the association of the equatorial staining by PHA with one of the subpopulations of spermatozoa a double staining technique was developed. In this method, the membrane was first stained with PHA employing the indirect immunofluorescence technique and then followed by the conventional quinacrine staining method to demonstrate the F-body. It was shown that spermatozoa which had receptors in the equatorial region for PHA were the ones which exhibited in the F-body. Staining of the membrane with PHA is a better method for the identification of human Y spermatozoa since it does not have the drawbacks of quinacrine staining.

Use of dithiothreitol for improved visibility of the F body in human Y-bearing spermatozoa

Dithiothreitol was used to decondense the nuclear chromatin before staining human spermatozoa with quinacrine for the F body present in Y-bearing spermatozoa. In unseparated fractions and those enriched in X- or Y-bearing spermatozoa, the number of spermatozoa with F bodies increased by 2-9% after dithiothreitol treatment.

A study of Krebs citric acid cycle enzymes in rice moth larvae (Corcyrace phalonica St) during mycotoxicosis

Krebs citric acid cycle enzymes have been studied in rice moth larvae (Corcyra cephalonica St) reared in groundnut meal control and contaminated with A. flavus, wheat bran control and wheat bran contaminated with A. flavus and also wheat bran containing aflatoxin. It was observed that the activity of enzymes other than succinic oxidase, succinic dehydrogenase and isocitric dehydrogenase were reduced significantly in larvae reared in contaminated groundnut meal when compared with the control. In the case of larvae reared in contaminated wheat bran all the enzymes except succinic oxidase were inhibited when compared to the control larvae. It was also observed that the inhibition of these enzymes is greater in the case of larvae reared in contaminated wheat bran than in contaminated groundnut meal. The higher toxicity of wheat bran has been discussed.