Promotion of animal growth with a monoclonal anti-idiotype specific to anti-porcine growth hormone antibody

Development and Characterization of a Novel Anti-idiotypic Monoclonal Antibody to Growth Hormone, Which Can Mimic Physiological Functions of Growth Hormone in Primary Porcine Hepatocytes

B-32 is one of a panel of monoclonal anti-idiotypic antibodies to growth hormone (GH) that we developed. To characterize and identify its potential role as a novel growth hormone receptor (GHR) agonist, we determined that B-32 behaved as a typical Ab2β based on a series of enzyme-linked immunosorbent assay assays. The results of fluorescence-activated cell sorting, indirect immunofluorescence and competitive receptor binding assays demonstrated that B-32 specifically binds to the GHR expressed on target cells. Next, we examined the resulting signal transduction pathways triggered by this antibody in primary porcine hepatocytes. We found that B-32 can activate the GHR and Janus kinase (2)/signal transducers and activators of transcription (JAK2/STAT5) signalling pathways. The phosphorylation kinetics of JAK2/STAT5 induced by either GH or B-32 were analysed in dose-response and time course experiments. In addition, B32 could also stimulate porcine hepatocytes to secrete insulin-like growth factors-1. Our work indicates that a monoclonal anti-idiotypic antibody to GH (B-32) can serve as a GHR agonist or GH mimic and has application potential in domestic animal (pig) production.

The activation and differential signalling of the growth hormone receptor induced by pGH or anti-idiotypic monoclonal antibodies in primary rat hepatocytes

In this report, we have developed a panel of monoclonal anti-idiotypic antibodies to pGH by immunising BALB/c mice with a purified monoclonal anti-pGH antibody (1A3), among which one mAb, termed CG-8F, was selected for further characterisation. We found that CG-8F behaved as a typical Ab2β, not only conformationally competing with pGH for 1A3 but also exhibiting recognition for GHR in a rat hepatocyte model. We next examined the resulting signal transduction pathways triggered by this antibody in rat hepatocytes and found that both pGH and CG-8F could trigger the JAK2-STAT1/3/5-mediated signal transduction pathway. Furthermore, the phosphorylation kinetics of pSTAT1/3/5 induced by either pGH or CG-8F were remarkably similar in the dose-response and time course rat hepatocyte experiments. In contrast, only pGH, but not CG-8F, was capable of inducing ERK phosphorylation. Further experimental studies indicated that the two functional binding sites on CG-8F are required for GHR activation. This study partially reveals the mechanism of action of GH anti-idiotypic antibodies and also indicates that monoclonal anti-idiotypic antibodies represent an effective way to produce GH mimics, suggesting that it is possible to produce signal-specific cytokine agonists using an anti-idiotypic antibody approach.

Immunomanipulation of appetite and body temperature through the functional mimicry of leptin

OBJECTIVE

Although current obesity therapies produce some benefits, there is a need for new strategies to treat obesity. A novel proposal is the use of anti-idiotypic antibodies as surrogate ligands or hormones. These anti-idiotypic antibodies carry an internal motif that imitates or mimics an epitope in the antigen (i.e., hormone or ligand). Thus, anti-idiotypic antibodies to several ligands may mimic them in transducing signals when binding to their receptors.

RESEARCH METHODS AND PROCEDURES

We developed an anti-idiotypic polyclonal antibody against the region of a leptin monoclonal antibody that competitively binds leptin, mimicking the active site structure of leptin. To test whether our anti-idiotype could also reproduce leptin functions, we examined food intake, body weight, and colonic temperature in male Wistar rats (n = 9) in response to intracerebroventricular administration of the leptin anti-idiotype.

RESULTS

Our leptin anti-idiotype induced a significant reduction in food intake coupled with an increase in body temperature comparable to that of leptin. That is, the intracerebroventricular administration of 8.0 microg of leptin anti-idiotype or 5.0 microg leptin significantly increased colonic temperature (Delta 1.9 +/- 0.11 degrees C and Delta 1.7 +/- 0.12 degrees C, respectively). In addition, both decreased 24-hour food intake (-26.4 +/- 2.4% and -21.9 +/- 2.2%) compared with the control. The gain in body weight was also decreased by acute administration of the anti-idiotype (-1.4 +/- 0.28%) and leptin (-1.1 +/- 0.17%) vs. the phosphate-buffered saline control (1.3 +/- 0.15%).

DISCUSSION

These studies revealed that the leptin anti-idiotype inhibited food intake and enhanced heat production, mimicking leptin's central actions.

An anti-idiotypic antibody with an internal image of human interferon-gamma and human interferon-gamma-like antiviral activity

D9D10, a monoclonal antibody that inhibits the biological activity of human interferon-gamma (IFN-gamma), was used to generate monoclonal anti-idiotypic antibodies. After a first selection, the monoclonal anti-idiotypic antibody AA1E5 was chosen to be fully characterized. To the best of our knowledge this is the first description of a monoclonal antibody with an IFN-gamma-like antiviral activity; AA1E5 competed with IFN-gamma for binding to D9D10 indicating its anti-idiotypic character. However, AA1E5 also fully mimics HuIFN-gamma as it not only binds to the HuIFN-gamma-receptor, where it competes with HuIFN-gamma, but more importantly AA1E5 and its Fv fragment, cloned and expressed in Escherichia coli, mimic the antiviral activity of HuIFN-gamma. Indeed, 15 microg of AA1E5 and 2.5 microg of its Fv fragment had an effect comparable to that of 10 IU of HuIFN-gamma in an antiviral assay on A549 cells. Sequence comparison between the complementarity determination regions of the antibody and the sequence of HuIFN-gamma revealed that both the heavy chain variable domain, VH, and the kappa light chain variable domain, Vkappa, have epitopes of 3-4 amino acids that are present in the HuIFN-gamma sequence, some of which contribute to receptor binding, as identified by Walter et al. [M. R. Walter, W. T. Windsor, T. L. Nagabhushan, D. J. Lundell, C. A. Lunn, P. J. Zauodny & S. K. Narula (1995) Nature 376, 230-235].

Anti-idiotypic sera against monoclonal anti-porcine growth hormone antibodies: production in rabbits and characterization of specificity

Antisera were raised in rabbits against two mouse monoclonal anti-porcine growth hormone (pGH) antibodies. Anti-idiotypic antibodies were isolated from rabbit sera by successive passage over immunoadsorbent columns of normal mouse Ig (mIg), followed by the specific immunizing monoclonal and elution from the latter. Enzyme linked immunoadsorbent assay (ELISA) for anti-idiotype and free idiotype were established. While showing specificity for their respective inducing monoclonals, anti-idiotypes also cross reacted in varying degrees with other anti-pGH monoclonals regardless of specificity differences between the antibodies, demonstrating the presence of a cross-reactive idiotype.

Immunological manipulation of body composition

Hormonal growth promoters (e.g., growth hormone [GH], beta-adrenergic agonists, steroids), which improve growth rate and/or lean:fat ratios in the carcass, have received considerable adverse publicity and are either banned or have no licence for their use in the EC. This has led to the development of a number of techniques, involving the use of antibodies, aimed at regulating metabolic processes involved in determining growth and body composition. A different approach to the problem of excess fat deposition involves the use of antibodies directed against the plasma membranes of adipocytes in order to elicit their destruction and thereby limit the capacity for fat storage. This technique has been demonstrated in rats, sheep and pigs in both passive and active immunisation techniques. This promising approach is, however, limited by the lack of a commercially suitable vaccine. The identification of individual membrane proteins that are antigenic has been achieved and this affords the prospect of producing recombinant DNA-derived vaccines. Whether these new approaches will be perceived as acceptable to the general public remains a serious concern and a potential limitation to their development as many would-be sponsors withdraw their support for research in these areas.

Augmentation of hormonal activities with antibodies from cattle immunized with a combination of synthetic and recombinant growth hormone peptide

Antibodies generated against a synthetic growth hormone (GH) peptide in a number of animal species were shown to enhance the efficacy of GH. However, the ability to produce the effective antibodies diminished over time and repeated boosters failed to overcome the hurdle. Therefore, this study was designed to address the issue on the failed antibody responses by employing different GH peptide antigen preparations in cattle. Holstein steers were repeatedly immunized with a synthetic peptide corresponding to an amino acid sequence 54-95 of porcine GH (pGH). The peptide was conjugated to ovalbumin (OVA) as a carrier. Animals initially responded to the antigen well and elicited antibodies specific to the peptide. However, the 4th challenge with the same OVA-peptide antigen rendered animals unresponsive, resulting in a decline in antibody production. This unresponsiveness was overcome by switching the antigen at the 5th immunization from OVA-peptide to a recombinant peptide preparation which was composed of maltose binding protein (MBP) as a carrier. Antibodies generated in cattle after the 5th immunization recognized not only the pGH(54-95) peptide, but also bovine GH (bGH) and pGH. These antibodies were not immunoreactive with an unrelated control peptide. Hypophysectomized (hypox) rats were used for functional analysis and bGH was active in promoting the growth of these GH-deficient rats. The growth-promoting effect of bGH was significantly enhanced by mixing it with bovine anti-peptide antibodies prior to administration. Therefore, the present findings suggest that peptide 54-95 induces cattle to elicit antibodies capable of not only recognizing bGH but also augmenting the somatogenic effectiveness of bGH in hypox rats.

Augmentation of hormonal activities with antibodies from cattle immunized with a combination of synthetic and recombinant growth hormone peptide

Antibodies generated against a synthetic growth hormone (GH) peptide in a number of animal species were shown to enhance the efficacy of GH. However, the ability to produce the effective antibodies diminished over the time and repeated boosters failed to overcome the hurdle. Therefore, this study was designed to address the issue on the fallen antibody responses by employing different GH peptide antigen preparations in cattle. Holstein steers were repeatedly immunized with a synthetic peptide corresponding to an amino acid sequence 54-95 of porcine GH (pGH). The peptide was conjugated to ovalbumin (OVA) as a carrier. Animals initially responded to the antigen well and elicited antibodies specific to the peptide. However, the 4th challenge with the same OVA-peptide antigen rendered animals unresponsive, resulting in a decline in antibody production. This unresponsiveness was overcome by switching the antigen at the 5th immunization from OVA-peptide to a recombinant peptide preparation which was composed of maltose binding protein (MBP) as a carrier. Antibodies generated in cattle after the 5th immunization recognized not only the pGH(54-95) peptide, but also bovine GH (bGH) and pGH. These antibodies were not immunoreactive with an unrelated control peptide. Hypophysectomized (hypox) rats were used for functional analysis and bGH was active in promoting the growth of these GH-deficient rats. The growth-promoting effect of bGH was significantly enhanced by mixing with bovine anti-peptide antibodies prior to administration. Therefore, the present findings suggest that peptide 54-95 induces cattle to elicit antibodies capable of not only recognizing bGH but also augmenting the somatogenic effectiveness of bGH in hypox rats.

Neurite outgrowth is enhanced by anti-idiotypic monoclonal antibodies to the ganglioside GM1

Exogenously added gangliosides enhance sprouting, neurite outgrowth, and other neuronal activities; this effect may be initiated when a ganglioside binds to a membrane protein or when a ganglioside intercalates into the plasma membrane. To test whether binding to membrane proteins is sufficient for ganglioside-mediated activity, anti-idiotypic antibodies were generated that mimic the functional binding sites of the ganglioside GM1 as described by M. J. Riggott and W. D. Matthew (1996, Glycobiology, 6, 581-589). These anti-idiotypic antibodies are proteinaceous probes that model the biochemical and biological effects of gangliosides. Those anti-idiotypic ganglioside (AIG) monoclonal antibodies (mAb's) were selected based on their ability to bind a known GM1 binding protein, the beta-subunit of cholera toxin. These studies described neuronal cell surface proteins that were identified by immunocytochemistry and Western blotting using these AIG mAb's. Here we show that AIG mAb's mimic the functional properties of GM1 in that they facilitate neurite outgrowth from central and peripheral nervous system neurons in in vitro bioassays. In addition, AIG mAb binding modulates second messenger activity, suggesting that membrane protein binding alone is sufficient to invoke intracellular activation. The similarity in the pattern of protein tyrosine phosphorylation evoked by GM1 and the anti-idiotypic ganglioside antibodies suggests that the AIG mAb's modulate neurite outgrowth in a manner similar to that of GM1. Because antibodies cannot intercalate into the plasma membrane, these results suggest that the ganglioside GM1 can mediate neuronal cellular activity by binding to cell surface proteins.

Molecular interaction of growth hormone with two monoclonal antibodies recognizing distinct epitopes

Two monoclonal antibodies (mAb), designated PS-7.6 and PS-11.2, were generated against recombinant porcine growth hormone (pGH) and shown to enhance the hormonal activity in promoting the growth of animals. The mAb were compared and their functional relationship investigated. It was demonstrated by radioimmunoassay that PS-11.2 did not compete, but rather enhanced binding of 125I-pGH tracer to PS-7.6, suggesting that both mAb recognized distinct epitopes and also were additive in their antigen bindings. Surface plasmon resonance analysis using optical BIAcore technology (Pharmacia Biosensor, Piscataway NJ, USA) provided additional data to support this idea because pGH, after being captured by PS-11.2, remained capable of interacting with PS-7.6. An anti-idiotypic mAb was employed and shown to interact with PS-7.6 but not PS-11.2, implying that the differences in the Fab variable regions of these two mAb might contribute to their epitope specificity. Binding kinetics were determined by the BIAcore and the individual affinities of PS-7.6 and PS-11.2 to pGH were 6.8 x 10(-8) and 1.2 x 10(-9) mol/L, respectively. When these mAb were sequentially subjected to the BIAcore, however, their affinities decreased by approximately 100-fold. Therefore, binding of pGH with one mAb significantly impaired a subsequent interaction with another mAb despite the fact that both mAb targeted different epitopes. Hypophysectomized rats were used for functional analysis and pGH was active in promoting growth of these GH-deficient animals. The hormonal effect was further improved by incubating pGH with either PS-7.6 or PS-11.2 prior to administration. However, enhancement by individual mAb was completely abolished when pGH was treated with both mAb together, indicating their unpredictable biological interference with each other. Therefore, the present findings clearly demonstrate that although PS-7.6 and PS-11.2 recognize separate epitopes, their individual interactions with pGH are closely interrelated both immunologically and biologically.

Enhancement of the insulin antagonistic effect of porcine somatotropin in swine using a monoclonal antibody

A monoclonal antibody (mAb), PS-7.6, to porcine somatotropin (pST) significantly enhanced the growth responses to pST injections in hypophysectomized (hypox) rats but could not be tested in pigs because of the large quantity of antibody required for a growth trial. Because pST inhibits the hypoglycemic effects of insulin, an insulin tolerance test procedure was established to measure pST activity in jugular-catheterized pigs. Doses of 0, 30, 100, and 300 micrograms/kg per day of pST were split and administered subcutaneously (sc) in equal portions twice daily for 2 d. After a 17-hr fast, plasma samples were obtained at 10-min intervals for 30 min before an intravenous injection of insulin (0.08 IU/kg) and then for an additional 50 min. Because pST increased fasting plasma glucose concentrations, preinsulin glucose values were used as a covariate to adjust the postinsulin concentrations. pST caused a dose-dependent increase in resistance to the insulin injection in these pigs. The areas under the curves (AUC), for plasma glucose were 22.1, 29.0, 39.0, and 47.2 mg/dl per min for the 0, 30, 100, and 300 micrograms/kg pST doses, respectively. Because different doses of pST could be detected, the PS-7.6 enhancement of pST treatment was evaluated. In the first experiment, five pigs/group each received sc injections of either vehicle, pST (75 micrograms/kg; approximately 3.0 mg/d), pST (75 micrograms/kg) + PS-7.6 at 3.75 mg/kg, or pST (75 micrograms/kg) + PS-7.6 at 15 mg/kg for 2 d before the insulin test. The pST and PS-7.6 were combined and incubated for at least 1 hr at room temperature before being injected. The injection of pST alone did not significantly change insulin tolerance activity (23.1 vs. 21.1, AUC), but insulin resistance was enhanced when this dose of pST also included PS-7.6 (27.4 and 29.5, AUC, respectively; P < 0.05). In a second experiment, the effects of PS-7.6 and PS-4.2, a mAb that did not potentiate the pST-stimulated growth of hypox rats, were compared. The five pigs/treatment received either vehicle, pST (75 micrograms/kg), pST (75 micrograms/kg) + PS-7.6 (3.75 mg/kg), or pST (75 micrograms/kg) + PS-4.2 (3.75 mg/kg) for 2 d. The administration of pST increased the resistance to insulin (26.7 vs. 18.8, AUC; P < 0.01), which was markedly potentiated by PS-7.6 (54.3, AUC, P < 0.001) but not affected by PS-4.2 (27.6 AUC). The injection of PS-7.6 at 7.5 mg/kg without exogenous pST did not alter the sensitivity to insulin. These results indicate that PS-7.6, but not PS-4.2, enhanced the insulin antagonistic activity of pST in swine, suggesting that an enhancement of pST-stimulated growth would also occur in PS-7.6-treated pigs.

Functional characterization of monoclonal antibodies specific to growth hormone receptor

Upon engagement with appropriate ligands, receptors can be activated to initiate various metabolic and morphological changes in living cells. An attempt was made in this study to generate monoclonal antibodies (mAb) specific to recombinant rat growth hormone receptor (GHR) and subsequently to investigate their ability to act as biologically active ligands. Three mAbs, designated 1A9, 1H2 and 2C3, were produced and all were highly reactive with GHR in an enzyme-linked immunosorbent assay. In contrast to 1H2, 1A9 and 2C3 competed with radioactive growth hormone (GH) tracer for the binding to GHR in a radioreceptor assay, suggesting that the GH-binding sites of GHR were identical, or very close to its epitopes recognized by 1A9 and 2C3. The molecular interaction evaluated by the BIAcore technology further demonstrated the separate GHR epitopes for 1A9 and 2C3. 2C3 apparently targeted the precise GH-binding sites of GHR, while the antigenic determinants for 1A9 were not at the site, but adjacent to it. Functional analysis showed that 2C3 promoted the growth of hypophysectomized rats, whereas others failed to do so. Therefore, findings from the present study suggest that these mAbs recognize distinct GHR epitopes and are useful for investigating the structure-function relationship of GHR. Furthermore, 2C3 may prove important as a biologically active agonist for better understanding of the process of GHR activation relevant to growth.