Carrier-induced epitope-specific regulation and its bypass in a protein-protein conjugate

In the course of clinical trials on a birth control vaccine, it was found that some of the immunized women responded poorly to booster immunizations. This vaccine consists of a dimer of the beta chain of human chorionic gonadotropin (beta hCG) and the alpha chain of ovine luteinizing hormone (alpha oLH), linked to tetanus toxoid (TT) as a carrier. Changing this carrier to diphtheria toxoid resulted in reversion to high anti-hCG antibody titers, indicating the extent to which the carrier influences anti-ligand responses in this system. The suppression of anti-hCG responses after booster immunizations was reminiscent of the phenomenon of carrier-induced, epitope-specific regulation. In a mouse model designed to test the effects of preimmunization with TT on anti-hCG responses, we found that a single preimmunization with TT causes reduced anti-hCG antibody responses in two out of four mouse strains, while anti-alpha oLH antibody responses were not affected by the preimmunization with TT. This is particularly interesting considering that beta hCG and alpha oLH were not presented when linked separately to TT. In an effort to devise a strategy to circumvent this carrier-induced, ligand-specific hyporesponsiveness, we investigated the effectiveness of a synthetic T helper epitope from TT as carrier. We show that preimmunization with TT causes a less profound reduction in anti-hCG titers if the preimmunized mice are subsequently injected with alpha oLH-beta hCG conjugated to a synthetic tetanus toxin peptide recognized by TT-induced and peptide-induced T cells.

IL-10 prevents naturally occurring fetal loss in the CBA x DBA/2 mating combination, and local defect in IL-10 production in this abortion-prone combination is corrected by in vivo injection of IFN-tau

CBA x DBA/2 placentae are quantitatively or qualitatively deficient in their production of the anti-inflammatory Th2-type cytokines IL-4 and IL-10 compared with the nonresorption-prone CBA x BALB/c mating combination. Wastage in this mating combination is accompanied by increased levels of local inflammatory cytokines. In addition, alloimmunization enhances the placental production of IL-4 and IL-10 in CBA x DBA/2 matings. Furthermore, rIL-10 by itself completely reverses the high incidence of fetal resorption after i.p. injection. Conversely, anti-IL-10 increases the resorption rate, but only in CBA x DBA/2 matings. On the other hand, injecting either anti-IFN-gamma or pentoxifillin (an anti-TNF agent) partially reduces the resorption. When given together, they produce a synergistic remission of fetal loss. Finally, we report that recombinant ovine trophoblast protein, an IFN-tau which is known to influence reproductive outcome in ruminants, can also counteract increased CBA x DBA/2 fetal resorption. It simultaneously induces increased placental IL-4 and IL-10 production in this mating combination. These results indicate that the placentally produced anti-inflammatory cytokines can play a vital role in the survival to term of the fetal allograft, by counteracting deleterious inflammatory cytokines.

Characterization of an immunosuppressive factor secreted by a human trophoblast-derived choriocarcinoma cell line

Factors and cells of placental origin have been considered to be important in mediating local active immunosuppression that regulates maternal immune reactivity to aid fetal survival. In this context, we investigated the immunosuppressive capabilities of supernatants from human trophoblast-derived choriocarcinoma cell lines (HCS). We have previously reported the inhibitory effects of HCS on proliferative responses of T-lymphocytes both in vitro and in vivo (L. Krishnan, E. Menu, G. Chaouat, G. P. Talwar, and R. Raghupathy, Cell. Immunol. 138, 113, 1991; L. Krishnan, R. Kinsky, G. Chaouat, G.P. Talwar, and R. Raghupathy, Cell. Immunol. 150, 376, 1993). We now show that HCS also suppresses LPS-induced proliferation of murine lymphocytes but does not inhibit the constitutive proliferation of lymphoma cell lines and B cell hybridomas indicating that HCS has no inhibitory effects on terminally differentiated or transformed cells. Furthermore, we have succeeded in isolating and partially characterizing the HCS-derived suppressor factor (HCSf) from culture supernatants of a human choriocarcinoma cell line JEG-3. Purification of the factor has been accomplished by sequential fractionation on anion-exchange, gel filtration, and reverse-phase HPLC columns. The suppressor factor is a low-molecular-weight compound in the range of 5-6 kDa, composed predominantly of hydrophilic amino acids. Protease digestion of the factor revealed that the peptide moiety in HCSf is important for its inhibitory activity. HCSf mediates a dose-dependent suppression of proliferative responses of both human and murine lymphocytes.

IL-10 prevents naturally occurring fetal loss in the CBA x DBA/2 mating combination, and local defect in IL-10 production in this abortion-prone combination is corrected by in vivo injection of IFN-tau

CBA x DBA/2 placentae are quantitatively or qualitatively deficient in their production of the anti-inflammatory Th2-type cytokines IL-4 and IL-10 compared with the nonresorption-prone CBA x BALB/c mating combination. Wastage in this mating combination is accompanied by increased levels of local inflammatory cytokines. In addition, alloimmunization enhances the placental production of IL-4 and IL-10 in CBA x DBA/2 matings. Furthermore, rIL-10 by itself completely reverses the high incidence of fetal resorption after i.p. injection. Conversely, anti-IL-10 increases the resorption rate, but only in CBA x DBA/2 matings. On the other hand, injecting either anti-IFN-gamma or pentoxifillin (an anti-TNF agent) partially reduces the resorption. When given together, they produce a synergistic remission of fetal loss. Finally, we report that recombinant ovine trophoblast protein, an IFN-tau which is known to influence reproductive outcome in ruminants, can also counteract increased CBA x DBA/2 fetal resorption. It simultaneously induces increased placental IL-4 and IL-10 production in this mating combination. These results indicate that the placentally produced anti-inflammatory cytokines can play a vital role in the survival to term of the fetal allograft, by counteracting deleterious inflammatory cytokines.

Maternal anti-placental reactivity in natural, immunologically-mediated fetal resorptions

Observations on maternal recognition of the fetus and the demonstration of the effects of cytokines on reproductive events led to the "immunotrophism" model, which suggests that maternal immune recognition of fetally-derived Ags results in the release of cytokines that promote the growth of the placenta; any disturbance in this balance of cytokines could result in deleterious consequences for the placenta and, in turn, the fetus. We have focused our attention on the murine CBA/J x DBA/2 model of spontaneous abortions and compared them with normal CBA x BALB/c pregnancies. Our results indicate that the extent of stimulation of maternal strain lymphocytes in response to stimulator placental cells in mixed lymphocyte-placenta reactions (MLPR) was much higher in the normal mating combination compared with the abortion-prone mating combination. Cytokine analysis of the supernatants from MLPR indicates that there is significantly higher production of TNF-alpha, IFN-gamma, and IL-2 in supernatants from the abortion-prone combination than in supernatants from the normal combination. Furthermore, MLPR-stimulated cells induce resorptions in normal pregnant mice; maternal strain lymphocytes stimulated by placentas from the abortion-prone combination induce high rates of fetal resorptions, but lymphocytes stimulated with placentas from the normal combination do not. Together, these results suggest that immunologically mediated fetal resorptions probably result from improper or inappropriate maternal responses to placental Ags. Our observations also suggest that such effects are probably mediated by cytokines.

Maternal anti-placental reactivity in natural, immunologically-mediated fetal resorptions

Observations on maternal recognition of the fetus and the demonstration of the effects of cytokines on reproductive events led to the "immunotrophism" model, which suggests that maternal immune recognition of fetally-derived Ags results in the release of cytokines that promote the growth of the placenta; any disturbance in this balance of cytokines could result in deleterious consequences for the placenta and, in turn, the fetus. We have focused our attention on the murine CBA/J x DBA/2 model of spontaneous abortions and compared them with normal CBA x BALB/c pregnancies. Our results indicate that the extent of stimulation of maternal strain lymphocytes in response to stimulator placental cells in mixed lymphocyte-placenta reactions (MLPR) was much higher in the normal mating combination compared with the abortion-prone mating combination. Cytokine analysis of the supernatants from MLPR indicates that there is significantly higher production of TNF-alpha, IFN-gamma, and IL-2 in supernatants from the abortion-prone combination than in supernatants from the normal combination. Furthermore, MLPR-stimulated cells induce resorptions in normal pregnant mice; maternal strain lymphocytes stimulated by placentas from the abortion-prone combination induce high rates of fetal resorptions, but lymphocytes stimulated with placentas from the normal combination do not. Together, these results suggest that immunologically mediated fetal resorptions probably result from improper or inappropriate maternal responses to placental Ags. Our observations also suggest that such effects are probably mediated by cytokines.

Expression of cytokines in placentas of mice undergoing immunologically mediated spontaneous fetal resorptions

It is clear that the immune system and the reproductive system interact with and influence each other and that the immune system can have positive and negative regulatory effects on the outcome of pregnancy. The discovery of murine models of immunologically mediated spontaneous fetal resorptions has proved to be very useful for the study of immunological influences on pregnancy. In an attempt to elucidate the mechanisms underlying pregnancy impairment in one such "natural" model of pregnancy loss, we compared the expression of the cytokines tumor necrosis factor alpha, interferon tau, and interleukin-2 in placental tissue from a resorption-prone strain combination with the expression from a normal combination. We found significantly enhanced expression of these three cytokines in placentas from the resorption-prone combination using dot-blot hybridization and Northern hybridizations. Since these cytokines are abortifacients in vivo and have detrimental effects on the placenta, and hence on fetal development and survival, our demonstration of enhanced expression of these deleterious cytokines may give insight into the mechanisms involved in immunologically mediated spontaneous abortions.

Suppression of local and systemic GVHR by supernatants from human choriocarcinoma cell lines

Graft versus host reaction (GVHR) and host versus graft reactivity during pregnancy share at least some cellular pathways. Immunosuppression mediated by placental suppressor factors may actively contribute to the survival of the conceptus in the immunocompetent mother. We have previously reported that supernatants from human choriocarcinoma cell lines inhibit mitogen-activated and antigen-activated proliferation of lymphoid cells. From this perspective, we investigated the capacity of supernatants from human choriocarcinoma cell lines (HCS) to suppress in vivo graft versus host reactions in mice. HCS was tested for its ability to block both local as well as systemic GVHR induced by the injection of parental cells into F1 mice. HCS mediates profound suppression of acute and chronic GVHR. These results confirm that human choriocarcinoma cell lines secrete a potent immunosuppressive factor(s) which can efficiently modulate immune responses in vivo.

Synthetic gonadotrophin-releasing hormone (GnRH) vaccines incorporating GnRH and synthetic T-helper epitopes

A vaccine against the gonadotrophin-releasing hormone (GnRH) is being developed as an immunological method for treatment of prostatic hypertrophy, based on the observation that active immunization against GnRH leads to the production of anti-GnRH antibodies which results in the shrinkage of the prostate gland. We have been investigating the regulation of anti-GnRH antibody responses by carrier molecules. In previous studies we showed that the use of large protein molecules as carriers limits the use of such a vaccine owing to potential problems of carrier-induced anti-haptenic suppression. In this report we show that synthetic T-helper epitopes can be used as carriers for the generation of anti-GnRH antibody responses.

Vaccines against fertility

The first evidence for the efficacy of a birth control vaccine in humans is now available from the Phase II trials on the human chorionic gonadotrophin vaccine in India. Several sperm antigens have been identified as potential contraceptive immunogens and zona pellucida antigens have been reported that reversibly control fertility.

Bypass of carrier-induced epitope-specific suppression using a T-helper epitope

A gonadotropin-releasing hormone (GnRH)-based vaccine is being developed as a method for non-surgical immunotherapy as immunization with this vaccine results in atrophy of the prostate. This vaccine, a conjugate of GnRH and diphtheria toxoid (DT), provides a unique hapten-carrier system for investigating the influence of carrier presensitization on antibody responses to self haptens. In a recent communication we showed that preimmunization with carriers diphtheria toxoid and tetanus toxoid results in a strain-dependent inhibition of anti-GnRH responses in mice and that T cells from carrier-presensitized mice are responsible for anti-haptenic suppression. In the present report we describe a strategy for bypassing DT-induced epitopic suppression using a T-helper epitope from DT.

A single human monoclonal antibody that confers total protection from tetanus

Protective human monoclonal antibodies (HuMAbs) are superior to hyperimmune sera and murine monoclonal antibodies as far as human immunotherapy is concerned. In this report, we describe the successful generation of triomas secreting HuMAbs to tetanus toxin (tt). Lymphoblastoid cell lines secreting anti-tt antibodies were stabilized by back-fusion with a mouse x human heterohybrid myeloma partner, SBC-H20. One of the antibodies so produced, confers total protection of mice from tetanus, unlike a few recent reports where only partial protection (delay in the onset of tetanus) was achieved with single HuMAbs. Experiments to localize the neutralizing epitope(s) of the toxin using the protective monoclonal antibodies revealed that the antibody recognizes a conformational determinant that is destroyed on SDS-treatment. Preliminary studies show that Fab preparations of the protective antibody are capable of neutralizing tetanus toxin, suggesting that it might be possible to clone and express the Fab in a stable vector for large scale production.

Binding of sperm to somatic cells via HLA-DR. Modulation by sulfated carbohydrates

We have shown previously that human sperm bind and enter leukocytes expressing surface HLA class II molecules. In the present study, mutant B lymphoblastoid cells and HLA-DR-transfected murine 3T3 fibroblasts are used to confirm that HLA class II molecules are somatic cell receptors for sperm. Further, for isolated HLA-DR expressed on murine cells, we show that sperm receptor activity requires the presence of sulfated carbohydrates. As carriers of multiple HLA-DR binding ligands, sperm may 1) mimic the target cell-activating effects of anti-DR antibody and 2) bind HIV through CD4-like or alternate receptors. By these or other mechanisms, sperm/somatic cell interactions in the female reproductive tract may affect fertility and potentiate the sexual transmission of AIDS.

Binding of sperm to somatic cells via HLA-DR. Modulation by sulfated carbohydrates

We have shown previously that human sperm bind and enter leukocytes expressing surface HLA class II molecules. In the present study, mutant B lymphoblastoid cells and HLA-DR-transfected murine 3T3 fibroblasts are used to confirm that HLA class II molecules are somatic cell receptors for sperm. Further, for isolated HLA-DR expressed on murine cells, we show that sperm receptor activity requires the presence of sulfated carbohydrates. As carriers of multiple HLA-DR binding ligands, sperm may 1) mimic the target cell-activating effects of anti-DR antibody and 2) bind HIV through CD4-like or alternate receptors. By these or other mechanisms, sperm/somatic cell interactions in the female reproductive tract may affect fertility and potentiate the sexual transmission of AIDS.

In vitro and in vivo immunosuppressive effects of supernatants from human choriocarcinoma cell lines

Local immunosuppression mediated by placental suppressor factors may contribute to the absence of consistently demonstrable cellular immunity against the fetus. In this context, we have investigated the immunosuppressive capabilities of supernatants from human trophoblastic choriocarcinoma cell lines (HCS) by testing the effects of HCS on immune responses in vitro and in vivo in the human and murine systems. HCS suppresses mitogen-induced proliferation and mixed lymphocyte reactions in humans and in mice, as well as antigen-induced T cell proliferation in mice. HCS also suppresses the in vivo response of mice to allogeneic cells. Furthermore, HCS when injected intraperitoneally causes the induction of suppressor cells in mice which in turn prevent the mounting of an allogeneic response in other strains of mice. These results indicate that human choriocarcinoma cell lines secrete a suppressor factor(s) which induces suppression in vitro as well as in vivo through the generation of suppressor cells.

Carrier-induced suppression of the antibody response to a 'self' hapten

Immunization of male rats and monkeys with gonadotropin-releasing hormone (GnRH) conjugated to a carrier results in a dramatic atrophy of the prostate. GnRH, linked to either diphtheria toxoid or tetanus toxoid as carrier, is now being evaluated for its use in the immunotherapy of hormone-dependent prostate enlargement in men. This report deals with the phenomenon of carrier-induced, epitope-specific regulation in the GnRH-carrier system. In experiments designed to assess the influence of the carrier on antibody responses to the 'self' hapten GnRH, we show that preimmunization with carriers diphtheria toxoid and tetanus toxoid results in a strain-dependent inhibition of anti-GnRH responses in mice. Results of adoptive transfer experiments indicate that T cells from carrier-presensitized mice are responsible for suppression of anti-haptenic antibodies and that T cells from conjugate-immunized mice, on the other hand, can actually help overcome hyporesponsiveness.

Hyporesponsiveness to a GnRH vaccine in a non-responder mouse strain is T-cell mediated

Immunization of rats and monkeys with the decapeptide gonadotropin releasing hormone (GnRH) linked to carriers such as diphtheria toxoid (DT) or tetanus toxoid (TT) results in a marked atrophy of the prostate. This vaccine is now being explored for its potential in the "immunosurgery" of prostatic hypertrophy in men and is currently undergoing Phase I/II clinical trials. We have been investigating immunogenetic aspects of immune responses to this hapten-carrier conjugate, and in a recent communication we described the responses of different strains of mice to GnRH conjugated to DT (GnRH-DT). Mice of the 129 (H-2b) strain were found to be non-responders to GnRH. However, further immunization of GnRH-DT-immunized 129 mice with GnRH linked to an alternate carrier, TT, resulted in the production of high levels of anti-GnRH antibodies. This showed that 129 mice are not deficient in GnRH-specific B cells and that the lack of response to GnRH in 129 mice is possibly due to (i) the lack of appropriate helper T-cells or (ii) the presence of suppressor cells. In this report we present evidence to support the existence of suppressor cells in GnRH-DT-immunized 129 mice.

Influence of the genetic background and carrier protein on the antibody response to GnRH

A vaccine against the gonadotropin releasing hormone (GnRH) is being developed as an immunological method for the treatment of prostatic enlargement. The work described here was aimed at investigating the influence of the genetic background on immune responses to GnRH conjugated to diphtheria toxoid (DT). Mice of different strains were injected with the conjugate and the antibody levels against GnRH and DT quantitated in order to examine the effect of genetic background on immune responses to the hapten and the carrier. All immunized animals produced antibodies to DT. Anti-GnRH antibodies were generated by all strains of mice except 129. The low anti-GnRH response in the 129 strain mice did not appear to be MHC-linked, as C57BL/6 mice, which bear the same MHC haplotype as 129 mice, were able to generate a strong anti-GnRH response. The non-responsiveness to the hapten (GnRH) in 129 strain mice was overcome by the use of an 'alternate carrier' approach.

A simplified cellular ELISA (CELISA) for the detection of antibodies reacting with cell-surface antigens

This paper describes the adaptation of a cellular enzyme-linked immunosorbent assay (CELISA) for the detection of antibodies to cell-surface antigens. This CELISA has the advantages of convenience and rapidity and is therefore ideally suited for the screening of a large number of hybridoma culture supernatants. The basic procedure involves the direct drying of cell suspensions onto the wells of enzyme immunoassay (EIA) plates and a subsequent EIA with appropriate blocking reagents. In order to overcome high background binding of primary antibodies to Fc receptors and of secondary antibodies to surface Ig (sIg), this method involves a blocking step consisting of unlabelled secondary antibodies. Once CELISA plates are prepared, they can be stored for a period of at least 6 months and hence this assay does not rely on the availability of fresh, viable cells for each assay. This assay is simple, reproducible and sensitive. The results can be assessed in an objective manner and can also be adapted for the detection of cellular antigens. This paper describes a CELISA for the detection of antibodies to blood group antigens and human leukocyte (HLA) antigens.

Anti-fertility vaccines

Vaccines are under development for the control of fertility in males and females. This review discusses developments in anti-fertility vaccines at the National Institute of Immunology, New Delhi, India. A single injection procedure for the sterilization or castration of male animals depending on the site at which the injection is given, has passed through field testing and is expected to be on the market in the near future. Vaccines inducing antibodies against the human chorionic gonadotropin have gone through phase I trials with satisfactory results. A vaccine producing a consistently bioeffective antibody response against gonadotropin-releasing hormone is ready for phase I/II clinical trials in patients of carcinoma of prostate after due experimentation in animals and toxicology studies. Research to identify sperm antigens for incorporation into second generation vaccines is in progress.

Purification and characterization of class II histocompatibility antigens from a homozygous human B cell line

Human class II histocompatibility antigens were purified from the Epstein-Barr virus-transformed human B lymphoblastoid cell line LG-2 by immunoaffinity chromatography. This is the first time all three subsets have been prepared as nonradioactive materials on a milligram scale. The yields of DR, DQ, and DP from 10 g of cells were approximately 12, 2, and 0.2 mg, respectively. Cross-contamination of the subsets was found to be less than 2% when assayed by measuring the binding of antigen-specific monoclonal antibodies to antigen immobilized on fixed erythrocytes. The three purified subsets were extensively characterized. They contained no detectable invariant chain. The three proteins were distinguished by their migration on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing. The denatured antigens were susceptible to partial removal of carbohydrate by endoglycosidase H and apparently complete removal of carbohydrate by endoglycosidase F. The isolated, denatured chains differed in their affinities for radiolabeled lectins, suggesting differences in carbohydrate structures. A water-soluble form of each antigen was prepared by a controlled papain digestion of the native antigen. Both native and denatured antigens were analyzed for their reactivities with a panel of class II antigen-specific monoclonal antibodies, allowing a precise definition of the specificities of the antibodies.

Transfected human B lymphoblastoid cells express the mouse Ad beta-chain in association with DR alpha

The human EBV-transformed cell line TOM was transfected with plasmid DNA containing a complete genomic copy of the murine class II Ad beta gene. Drug resistant transfectant clones showed cell surface expression of the Ad beta gene product, as detected by flow microfluorimetry when using a mouse monoclonal antibody (MKD6) specific for Ad beta. Immunoprecipitation and two-dimensional gel electrophoretic analysis of the Ad beta-containing molecules from the transfected cells revealed that the mouse beta-chain was expressed in noncovalent association with the human DR alpha-chain rather than with DQ alpha, the human A alpha homologue. The implications of this unexpected pairing for our understanding of the processes controlling the association of class II alpha and beta gene products and of the roles of Ia molecules in normal and pathologic immune function are discussed.

Transfected human B lymphoblastoid cells express the mouse Ad beta-chain in association with DR alpha

The human EBV-transformed cell line TOM was transfected with plasmid DNA containing a complete genomic copy of the murine class II Ad beta gene. Drug resistant transfectant clones showed cell surface expression of the Ad beta gene product, as detected by flow microfluorimetry when using a mouse monoclonal antibody (MKD6) specific for Ad beta. Immunoprecipitation and two-dimensional gel electrophoretic analysis of the Ad beta-containing molecules from the transfected cells revealed that the mouse beta-chain was expressed in noncovalent association with the human DR alpha-chain rather than with DQ alpha, the human A alpha homologue. The implications of this unexpected pairing for our understanding of the processes controlling the association of class II alpha and beta gene products and of the roles of Ia molecules in normal and pathologic immune function are discussed.

SB subregion of the human major histocompatibility complex: gene organization, allelic polymorphism and expression in transformed cells

The SB region of the human major histocompatibility complex (MHC) has been cloned from cosmid and lambda phage libraries made from the human B-lymphoblastoid cell line Priess (DR4/4, DC4/4, SB3/4). Two alpha genes and two beta genes are encoded in the 100 kb long SB region in the order SB alpha-SB beta-SX alpha-SX beta. The SB alpha and SB beta genes encode the alpha and beta subunits of the SB subset of class II MHC molecules. Both the SX alpha and the SX beta genes are pseudogenes in the haplotype examined. From the isolated clones, the two haplotypes of the Priess cell line, SB3 and SB4, are distinguished by nucleotide sequencing and blot hybridization analyses. Restriction site polymorphisms between the SB3 and SB4 clones were observed only in relatively small regions of the SB beta and SX beta genes. A mouse macrophage cell line was transfected with one of the cosmid clones containing both SB alpha and SB beta genes. Expression of the alpha and beta genes was detected by fluorescene-activated cell sorting (FACS) and two-dimensional gel electrophoresis using SB-specific monoclonal antibodies.

Fate of antipaternal H-2 antibodies bound to the placenta in vivo

We have previously demonstrated that the placental spongiotrophoblast and yolk sac venous plexus express paternally derived H-2K and D (class I) antigens in a manner accessible to maternal circulation, and that the placenta serves to prevent antipaternal antibodies from reaching the fetus. Kinetic studies indicated that the placenta is capable of reexpressing its H-2 antigens after having been bound by anti-H-2 antibodies, suggesting that the placental cells somehow have the ability to eliminate the bound antibodies. In order to investigate the fate of the antibodies, we have followed the uptake and fate of radiolabeled anti-H-2Kk monoclonal antibody in the placentas of target allogeneic and control syngeneic pregnancies. Chromatographic analyses indicate that most of the intercellular radiolabel is associated with fragments smaller than IgG, and similar degradation was not observed with syngeneic control placentas. We conclude that the placenta is capable of binding, ingesting, and then digesting antipaternal H-2 antibodies, further substantiating the immunoabsorbent barrier hypothesis of allogeneic fetal survival.

Characterization and cross-reactivity of human and mouse oncofetal antigens. Use of a new solid phase assay for detection of cell surface antigens

Oncofetal (OF) antigens have been isolated from mouse F9 teratocarcinoma cells, mouse testicular cells, and human molar tissue by detergent extraction followed by dialysis. The soluble antigens have been used in solid phase radioimmunoassay (SPRIA) and enzyme-linked immunosorbent (ELISA) assay. Specific antibodies have been raised to these antigens in mice. By using these antisera, extensive cross-reactivity was found between mouse and human OF antigens. A human trophoblastic tumor cell line BEWO absorbed out mouse anti-F9 reactivity. Patients with tumors of germinal origin were found to have antibodies which cross-react with mouse and human OF antigens. This new assay is a rapid and sensitive method for the screening of monoclonal antibodies against these antigens as well as for detecting antibodies to tumors bearing these antigens in patients.

The ontogeny and turnover kinetics of paternal H-2K antigenic determinants on the allogeneic murine placenta

In previous reports we provided evidence for the expression of paternal H-2Kk antigens on the placenta, accessible to maternal circulation. We have now examined the ontogeny of paternal H-2Kk antigens in the placenta from day 10 to day 17 of gestation and find a steady increase per gram placenta. In order to substantiate the proposal that the placenta functions as an immunoabsorbent barrier preventing the entry of anti-paternal antibodies to the fetus, we monitored the uptake of monoclonal anti-paternal H-2Kk antibody by target (antigen-bearing) and control fetuses and placentas at various intervals after injection. We have previously shown that F(ab')2 anti-H-2Kk behaves like intact immunoglobulin in placental immunoabsorption studies, and demonstrate here that the peak placental uptake of the antibody is not affected by the removal of the Fc portion, whereas its rate of clearance is increased. In contrast to the anti-H-2Kk antibody, monoclonal anti-I-Ak (specificity 17) antibody (IgG2a) shows no placental immunoabsorption.

The ontogeny and turnover kinetics of paternal H-2K antigenic determinants on the allogeneic murine placenta

In previous reports we provided evidence for the expression of paternal H-2Kk antigens on the placenta, accessible to maternal circulation. We have now examined the ontogeny of paternal H-2Kk antigens in the placenta from day 10 to day 17 of gestation and find a steady increase per gram placenta. In order to substantiate the proposal that the placenta functions as an immunoabsorbent barrier preventing the entry of anti-paternal antibodies to the fetus, we monitored the uptake of monoclonal anti-paternal H-2Kk antibody by target (antigen-bearing) and control fetuses and placentas at various intervals after injection. We have previously shown that F(ab')2 anti-H-2Kk behaves like intact immunoglobulin in placental immunoabsorption studies, and demonstrate here that the peak placental uptake of the antibody is not affected by the removal of the Fc portion, whereas its rate of clearance is increased. In contrast to the anti-H-2Kk antibody, monoclonal anti-I-Ak (specificity 17) antibody (IgG2a) shows no placental immunoabsorption.