Immunological reactivity of antibodies produced by Pr-beta-HCG-TT with different hormones

Regulation of progesterone secretion in human syncytiotrophoblast in culture by human chorionic gonadotropin

In the present investigation we sought to define the specific sites in the pathway of placental progesterone biosynthesis that underlie the action of human chorionic gonadotropin (hCG). When the cells were challenged with dibutryl cAMP (dbcAMP), forskolin or isobutylmethylxanthine, they produced significantly higher amounts of progesterone which in the presence of the hCG antibody was reduced to the level of the control set of cells. Trophoblast cells cultured in serum free medium with 25-hydroxycholesterol (25-OHC) produced increased amounts of progesterone. In the presence of hCG antibody at a concentration which neutralized the secreted hCG, the steroid production was completely blocked, even when the 25-OHC was added to the medium. Also, direct quantitation of the cytochrome P450 SCC enzyme in the absence of hCG indicated a significant decrease. The exogenous addition of low density lipoproteins (LDL) increased the progesterone secretion by the trophoblast cells in culture. Neutralization of hCG by the antibodies, however, drastically reduced the LDL induced progesterone secretion, which was restored by the addition of dbcAMP to the medium. Based on these findings, we suggest a stimulatory effect of hCG on normal trophoblast cells at the level of LDL utilization and cytochrome P450 SCC enzyme. Since dbcAMP could mimic these actions of hCG, the data suggest a possible autocrine/paracrine role of hCG on the trophoblast cells. An additive effect of hCG and cAMP on progesterone secretion observed in our studies, indicate that apart from hCG, adenylate cyclase activity may also be regulated by other factors.

Expression of biologically active human chorionic gonadotropin and its subunits by recombinant vaccinia virus

Vaccinia virus (VV) expression vector was used to clone the genes for coding alpha and beta subunits of human chorionic gonadotropin (hCG). Recombinant viruses VSL3 and VSS1 containing these genes were selected as blue coloured plaques on the basis of co-expression of Escherichia coli beta-galactosidase in the infected cells. CV-1 cells when infected with VSL3 or VSS1 secreted 2.4 and 1.8 micrograms of alpha and beta hCG subunits, respectively, per 3 x 10(6) cells after 24 h of infection. The subunit proteins expressed individually had immunoreactivity with monoclonal and polyclonal antibodies specific to hCG. The subunit hormonal peptides associated with each other during co-infection to form the complete hCG dimer, which was biologically active as evident from the induction of steroidogenesis in a mouse Leydig cell system.

A potential anti-pregnancy vaccine built by conjugation of the beta-subunit of human chorionic gonadotropin to adjuvant-active muramyl peptide

The beta-subunit of human chorionic gonadotropin (hCG) conjugated to tetanus toxoid is being investigated as a vaccine for human fertility control. Initial clinical trials indicated that the level of antibody response induced by such an immunogen was not always sufficient to prevent pregnancy. Therefore, efforts are being made to evaluate new carriers for the beta-subunit and to select adjuvants to yield a more efficient vaccine. In the present report, we demonstrate that conjugates of the beta-subunit of hCG with muramyl dipeptide (MDP), or its nonpyrogenic derivative murabutide, may have potential as an effective antipregnancy vaccine. The copolymer of beta hCG and MDP administered with Al(OH)3 to mice induced a high anti-beta hCG response, better than that induced by the conjugate of beta hCG to tetanus toxoid given with Al(OH)3. Moreover, the antibodies induced by such an immunogen were competent for neutralizing the biological activity of hCG in vivo. Even more interesting, a copolymer of beta hCG and of murabutide induced high levels of biologically active antibodies. This immunogen may represent a promising candidate for the development of an efficient vaccine for human fertility control.

A candidate carrier protein for beta-human chorionic gonadotropin: 54,000-molecular-weight fragment of tetanus toxin

As an alternative to intact tetanus toxoid as a carrier for beta-human chorionic gonadotropin (beta-hCG), a fragment of tetanus toxin was sought that had a relatively low molecular weight, yet was highly immunogenic. Purified culture filtrate tetanus toxin was subjected to limited enzymatic digestion with papain, and the resulting fragments separated by column chromatography on Sephadex G-150. Four fractions were thus identified. Fraction II was found to have a molecular weight of 54,000 by SDS-polyacrylamide gel electrophoresis. This fragment was covalently linked to the beta-subunit of hCG (beta-hCG-TTII) using carbodiimide hydrochloride. The ability of beta-hCG-TTII to stimulate production of anti-hCG sera in rabbits was measured by 125I-hCG radioimmunoassay. At sera dilutions of 1:40,000, an average 125I-hCG binding capacity of 34.7 +/- 5.86% (mean +/- SD) was observed 8 weeks after the final immunization. Tetanus toxin Fragment II has the potential for future application in active immunization studies involving hormone-carrier conjugates.

Comparison of Corynebacterium parvum with Freund's complete adjuvant as a potentiator of the immune response to beta-human chorionic gonadotropin linked to tetanus toxoid

Corynebacterium parvum was compared with Freund's complete adjuvant (FCA) for potentiation of the rabbit immune response to beta-human chorionic gonadotropin linked to tetanus toxoid (beta-hCG-TT). With each adjuvant, antibodies to hCG were detected using passive hemagglutination. Higher antibody titers were produced by FCA-treated animals. The ability of antisera to beta-hCG-TT to neutralize the biological action of native hCG was determined by the rat uterine weight assay. Anti-beta-hCG-TT sera from C. parvum-treated rabbits were not significantly different (p greater than 0.10) from FCA potentiated anti-beta-hCG-TT sera in neutralizing hCG-induced uterine weight gain. C. parvum has potential for future application in active immunization studies of fertility regulation.

Effect of carrier preimmunization on neutralizing antibody response of rabbits immunized with beta-human chorionic gonadotropin coupled to tetanus toxoid

Antisera to the conjugate of beta-human chorionic gonadotropin and tetanus toxoid (beta hCG-TT) generated in rabbits receiving TT carrier preimmunization were characterized and compared with antisera from rabbits receiving the conjugate without preimmunization. Double immunodiffusion and immunoelectrophoresis were used to identify individual antisera components to the conjugate and its substructures. 125IhCG radioimmunoassay indicated similar antibody titers (P = 0.447) regardless of whether the rabbits were preimmunized with TT. However, bioneutralization of native hCG as measured by inhibition of prepubertal rat uterine weight increase was significantly more effective (P = 0.025) with antisera from rabbits which received carrier presensitization. These results demonstrate that carrier preimmunization provides a method for increasing the efficacy of neutralizing antibody produced against haptenic beta hCG.

Immunobiological properties of a carboxy-terminal 53-amino acid peptide of the beta subunit of human chorionic gonadotropin

Lengthening of the carboxy terminus unique region of beta-hCG from 30 to 45 amino acids was found in previous studies to improve immunogenicity and hormone neutralization capacity. The present study was carried out to determine whether further elongation of the peptide to 53 amino acids enhances to hormone neutralization capacity without loss of specificity characteristics. The peptide 93--145 of beta-hCG with substitution of cysteines at 93, 100 and 110 by alpha-aminobutyric acid was synthesized by solid phase and conjugated to tetanus toxoid by an active ester method. Rabbit antibodies against this conjugate reacted with CTP-53 and CTP-45 with a parallel slope in anti-CTP-53-[125I]Tyr-CTP--53 radioimmunoassay system. Other CTPs, e.g. CTP-26, CTP-31 and CTP-35 competed with lower efficiency; 50% inhibition of binding was obtained with 10-100 pmol/tube with these peptides instead of 0.5 pmol/tube for the homologous CTP-53. Anti-CTP-53 reacted with both beta-hCG and hCG but around twenty times greater amount of hCG was required to give 50% inhibition of binding as compared to CTP-53. The antigen binding capacity of anti-CTP-53 was around 4000 ng/ml for CTP-53 and 25 ng/ml for hCG. The anti-CTP-53 sera retained non-cross-reactivity with hLH as determined by direct binding with [125I]hLH and by competitive inhibition of CTP-53 binding with anti-CTP-53. Anti-CTP-53 neutralized the bioactivity of hCG in the Leydig cell bioassay and in the mouse uterine weight gain assay. Anti-CTP-53 antibodies were about three times more effective than anti-CTP-45 in their capacity to neutralize the bioactivity of hCG, though still substantially poorer than anti-beta-hCG sera in this respect.

Effect of anti-HCG sera on purified syncytiotrophoblast from full-term human placenta

Heterologous anti-HCG and anti-beta-HCG sera failed to effect complement-dependent lysis of purified 51chromium-labeled syncytiotrophoblast in vitro. The progesterone synthetic activity of syncytiotrophoblast was also preserved in the presence of the anti-HCG sera. Binding of the anti-HCG antibodies to the syncytiotrophoblast was demonstrated in an immunofluorescence test. The potential of the anti-HCG sera to participate in complement dependent lysis of other HCG-bearing cell types was revealed using BeWo cells as the targets; 53%-68% of the latter were killed by exposure to anti-HCG sera and complement. The possible mechanism(s) whereby syncytiotrophoblast resists damage by the anti-HCG sera are considered.

Monoclonal antibodies against immunodeterminants associated with the alpha and beta subunits of human chorionic gonadotropin

Spleen cells of BALB/c mice immunized with human chorionic gonadotropin (HCG), a glycopeptide hormone composed of two nonidentical alpha and beta subunits, were fused with NS-1 mouse myeloma cells. Two hybrid cell lines, cone PC2 and clone PD3 secreting monoclonal antibodies (McAb) to HCG were isolated. With the aid of a double antibody radioimmunoassay it was established that PC2-McAb recognizes an immunodeterminant associated with beta-HCG subunit, whereas, PD3-McAb recognizes an epitope present on the alpha-HCG subunit. Both monoclonal antibodies showed an affinity constant of approximately 5 X 10(10) L/M. Because of these immunological characteristics, only PC2-McAb specifically reacts with HCG and shows cross-reactivities of less than 0.1% to other related human glycopeptide hormones. On the other hand, using a hemagglutination test based on antibody induced agglutination of sheep red blood cells coated with HCG, it was shown that only PD3-McAb is capable of inducing a positive reaction, although both monoclonal antibodies have a similar binding capacity to the coated cells. The potential of these two new monoclonal reagents for the qualitative detection and quantitative determination of HCG in human biological fluids is discussed.

Immunogenicity of three C-terminal synthetic peptides of the beta subunit of human chorionic gonadotropin and properties of the antibodies raised against 45-amino acid C-terminal peptide

Immunological studies were carried out in rhesus monkeys and rabbits on three C-terminal synthetic peptides of beta-hCG (115-145; 111-145 and 101-145) after conjugating these to tetanus toxoid (TT). The immunogenicity of the peptide conjugates was comparatively poorer with reference to Pr-beta-hCG-TT conjugates at similar doses and immunization schedule. Amongst the three peptides, the best response was obtained with the 45-amino acid c-terminal peptide (45-CTP; 101-145). The anti-45-CTP recognized native hCG and was devoid of cross-reaction with hLH. hCG-induced testosterone production by mouse Leydig cells was inhibited by anti-45-CTP antiserum, although its neutralization capacity decreased more rapidly upon dilution than anti-beta-hCG sera of comparable titres. Immune complexes formed by the anti-45-CTP with hCG had a lower sedimentation value than those formed by anti-beta-hCG antisera with hCG, suggesting the presence of a limited number of immuno-determinant regions in the 45-amino acid C-terminal synthetic peptide.