Active immunization of baboons (Papio anubis) with the bovine LH receptor

Expression of a recombinant bifunctional protein from a chimera of human lutropin receptor and human chorionic gonadotropin beta-subunit

Human lutropin (hLH) and human chorionic gonadotropin (hCG) are structurally and functionally similar and play important roles in reproduction via a common gonadal receptor (LH-R). However, hormone specific hCG-beta subunit contains 24 additional amino acid carboxyl terminal peptide (CTP), which produce specific antibodies to hCG-beta with little cross-reaction with LH. A chimeric protein containing both hLH-R and hCG-beta would provide a unique bifunctional antigen for immunocontraception. In this study is described the synthesis of a chimeric DNA construct of full-length of hLH-receptor and hCG-beta and its expression in Sf9 cells to produce a bifunctional protein. Recombinant protein was recognized by antibodies to LH-R as well as anti-hCG-beta in Western Blots, thus indicating the preservation of immunological epitopes for both hLH-R and hCG-beta in the chimera. Specific ligand binding of recombinant hLH-R component was demonstrated by the displacement of bound labeled hCG at increasing concentrations of unlabeled hCG, indicating that, the presence of hCG-beta component of the chimera did not interfere with the binding of hCG to LH-R. hCG-beta was also present in the recombinant chimeric protein as shown by a specific hCG-beta chemiluminescence assay. Treatment of transfected Sf9 cells with hCG induced dose-dependent increase in the stimulation of intracellular cAMP production, which showed that the ligand binding had functional activity. These results demonstrate that the chimeric DNA construct of hLHR-hCG-beta expressed a bifunctional protein containing both hLH-R and hCG-beta activities, which could provide a unique potential antigen for immunocontraception in vertebrates.

Effect of immunization with bovine luteinizing hormone receptor on ovarian function in cats

OBJECTIVE

To determine the effect of immunization with bovine luteinizing hormone receptor (LH-R) on ovarian function of cats.

ANIMALS

9 adult female domestic cats.

PROCEDURE

7 cats were immunized with 0.5 mg of LH-R encapsulated in a silastic subdermal implant (3 x 10 mm); 2 served as control cats. Receptors had 80% specific binding to 125I-human chorionic gonadotropin with a binding capacity of 2,682 pM/mg. Cats received booster injections of LH-R. Cats were induced to ovulate with luteinizing hormone (LH) releasing hormone on day 345. Samples of venous blood and vaginal cells were collected through day 395. Observation of estrus behavior continued until day 516. Serum concentrations of estradiol, progesterone, thyroid gland hormones, LH, and LH-R antibody were determined.

RESULTS

LH-R antibody was detected in the sera of immunized cats within 21 days after implantation. Detection of LH-R antibody was associated with suppression of serum progesterone to < or = 0.5 ng/mL during the study period, compared with concentrations of 5 to 10 ng/mL in control cats. Immunized cats did not display signs of estrus. Release of LH after administration of LH-releasing hormone indicated an intact hypothalamic-pituitary axis but poor corpus luteum function. Serum estradiol concentrations remained between 30 to 40 pg/mL in immunized and control cats. With the decrease antibody titers, hormone concentrations returned to a pattern consistent with that during fertility.

CONCLUSIONS AND CLINICAL RELEVANCE

Active immunization with LH-R suppressed corpus luteum function in cats. The effect was reversible. An LH-R-based antifertility vaccine may have clinical application in other vertebrates.

Modulation of ovarian function in female dogs immunized with bovine luteinizing hormone receptor

Adult female dogs were immunized with 0.5 mg bovine luteinizing hormone receptor (LH-R) encapsulated in a silastic subdermal implant and subsequently with four intramuscular booster injections of 0.1 mg LH-R each. Circulating LH-R antibody was detected in the sera 3 weeks post-implant. The appearance of LH-R antibody was associated with a decline in the serum progesterone concentrations to a range of 0-0.5 ng/ml until day 365 in the immunized dogs in comparison with a range of 5-10 ng in the control animals, suggesting a lack of ovulation and corpus luteum function in immunized dogs. The immunized dogs did not show signs of 'standing heat' and failed to ovulate when induced by LH-RH challenge. Serum oestradiol levels, however, remained in the range of 30-40 pg/ml in both the immunized and the control dogs. With the decline in the antibody titres, the hormonal profile and vaginal cytology returned to a fertile state and the dogs exhibited signs of 'standing heat', as well as vaginal bleeding. Dogs immunized with LH-R did not show any serious metabolic, local or systemic adverse effects. The hypothalamic--pituitary gonadal axis remained intact as indicated by little difference in pituitary LH levels between control and immunized animals, and by the release of LH by LH-RH challenge. These studies demonstrate that active immunization of female dogs with LH-R could immunomodulate ovarian function to cause a reversible state of infertility. It may be postulated that, due to extensive interspecies homology, a recombinant LH receptor-based immunocontraceptive vaccine may also be effective in other vertebrates.

Effect of immunization with lutropin-receptor on the ovarian function of rabbits

Three New Zealand white adult female rabbits, designated as A, B, and C, were immunized to produce lutropin receptor antibodies. Antisera inhibited the binding of 125I-hCG to the lutropin receptor and the production of testosterone by hCG stimulated rat Leydig cells. During the study period of, approximately 10 months after the last immunization, rabbits did not ovulate in response to an injection of 75 IU of human chorionic gonadotropin or mating as revealed by laparotomy. As the antibody titers declined, induction of ovulation and laparotomy revealed restoration of ovulation and corpus luteum formation. However, no pregnancy occurred when rabbits A and B were mated and artificially inseminated. These observations indicate that lutropin receptor antibodies can cause infertility in female rabbits.

Immunoregulation of mammalian fertility

Fertility management is a global issue of agricultural, medical, economic, and social consequence. Although many methods have been devised to both inhibit and assist reproduction, more acceptable alternatives are needed. Regulation by immune intervention is a promising technology as applied to livestock, pets, wildlife, and human beings. Outcome is dictated by site within the reproductive axis that is targeted. Fertility is suppressed by immunization against gonadotropin-releasing hormone, gonadotropins, prostaglandin F2 alpha, oxytocin, gonadotropin receptors, and gamete/embryonic antigens. It also is possible to lyse gonadal cells with ligand-antibody hybrid molecules. Ovulation rates are enhanced by vaccination with inhibin. Antibodies to sex steroid hormones have yielded mixed results. Perhaps recombinant viral vectors can be used to deliver reproductive immunogens. A new and simple technique to generate sustained autoimmune reactions to hormones and cellular antigens entails direct gene transfer into somatic cells. Evolving advances in reproductive immunology and biotechnology should furnish us with novel nonsurgical contraceptives and profertility agents that can be efficiently and safely implemented.

Suppression of fertility in male mice by immunization against LH receptor

We have investigated the potential contraceptive effects of immunization against the luteinizing hormone (LH) receptor in male mice at the prepubertal stage. Two N-terminal fragments of the porcine LH receptor encoding amino acids 1-297 and 1-370 were produced in large quantities through the Baculovirus insect cell system. We have immunized three-week-old mice from two Balb/c stocks of differing fecundity with Sf9 insect cells producing the short (1-297) or long (1-370) recombinant LH receptor. A booster injection was performed at six weeks using purified antigens. Ten days later, the immunized male mice were mated over a period of two weeks with adult untreated females. After weaning of the first litters, the same partners were mated once again under the same conditions. There was no decrease in the antiserum titers against the antigens over a two-month period. The circulating testosterone decreased as the anti-LH receptor antibodies increased. The fertility of the treated male mice was reduced up to 75%, depending on the mouse stock, the antigen used and the time separating immunization and mating. The impaired fertility was mostly due to male sterilization (up to 60% of sterile mates). The delay between mating and birth was enhanced by the treatment, reflecting delayed fertility and/or delayed male behaviour acquisition.

Biological actions of monoclonal antibodies to bovine lutropin receptor

Monoclonal antibodies (Mabs) were produced against bovine Lutropin receptor (LH-R). Antibodies were detected by an enzyme linked immunosorbant assay (ELISA). Hybridomas were subcloned to achieve monoclonality. Ascites were developed in Balb/c mice. Hybridoma supernatants were purified by ammonium sulfate precipitation and chromatography on hydroxylapatite columns. LH-R antibodies showed upto 50% inhibition of 125I-labeled hCG binding to bovine luteal cell membranes and up to 80% inhibition of testosterone production by hCG stimulated mouse Leydig cells. LH-R antibodies were predominantly IgM isotype. Purified antibodies showed a 78-kDa band, in SDS-PAGE, as the heavy chain of the immunoglobulin. LH-R antibodies were localized specifically in the thecal and luteal cells of the rat ovaries as well as in the Leydig cell of mouse testes. Injections of the LH-R antibody caused a constant estrus in normal rats. One month after the cessation of the injections the animals returned to normal estrus cycle and fertility. Pregnant mice injected with LH-R antibodies produced only 3 viable pregnancies and 10 pups, as compared to 8 pregnancies and 45 pups born to normal controls. LH-R antibodies also caused, approximately, a 50% reduction in testosterone production in normal male rats. These observations indicate a high degree of specificity of the Mab to LH-R and their potential in studies on gonadal function.