Identification of novel sites in the ovine growth hormone receptor involved in binding hormone and conferring species specificity.

Using site-directed mutagenesis we mutated the extracellular domain of the ovine growth hormone receptor (oGHR) to the corresponding amino acids in the rat GHR at two different sites: site A is between Thr28 and Leu34 and represents a major immunogenic epitope, while site B is between Ser121 and Asp124 and is involved in the interaction of the human GHR with growth hormone (GH). Native and mutant receptors were bacterially expressed and refolded, and then RIA and GH-binding assays were carried out on the purified recombinant proteins. Mutations at the N-terminal site A of oGHR led to greatly reduced binding to bovine GH and, in addition, to significant loss of recognition by a polyclonal antiserum to bovine GHR which recognizes site A as a major epitope. The crystal structure of human GH bound to human GHR did not resolve this extreme N-terminal region of the receptor but our data indicate that the N-terminal loop undertakes a 180 degrees turn bringing it into close proximity to the hormone-binding domain in a fashion analogous to the prolactin receptor. A fourfold decrease in affinity for binding bovine GH was also observed after mutation of site B. However, this change from the ovine sequence to the equivalent sequence in the rat GHR at site B caused a 2.4-fold increase in the affinity of binding to rat GH. Taken together, the changes in binding affinity of the site-B mutant for rat and bovine GH demonstrate that this site is involved in conferring species specificity for binding GH.     

Evidence from the use of monoclonal antibody probes for structural heterogeneity of the growth hormone receptor.

We describe the use of four monoclonal antibodies (MAbs) to the rabbit liver growth hormone (GH) receptor and one raised against purified rat liver GH receptor to characterize liver receptor subtypes which differ in their hormone-binding regions. The anti-(rat liver GH receptor) MAb both inhibited and precipitated rat and rabbit GH receptors, but only one-half of 125I-oGH (ovine GH) binding to liver microsomes could be inhibited by excess antibody. Conversely, only one-half of 125I-anti-(rat GH receptor) MAb binding was inhibited by excess oGH and Scatchard plots for this MAb exhibited two components. Although only 50% of 125I-oGH binding to membranes was inhibited by this MAb, all solubilized receptor could be immunoprecipitated. We postulate two epitopes for the anti-(rat GH receptor) MAb, one located at the hormone-binding site (inhibitory site) and one elsewhere (immunoprecipitating site). A second, rabbit-specific antibody (MAb 7) inhibited 85% of hormone binding but only 30% of 125I-anti-(rat GH receptor) MAb binding to rabbit liver microsomes. A combination of this MAb with the anti-(rat GH receptor) MAb totally inhibited 125I-oGH binding. MAb 7 alone totally inhibited 125I-rat GH binding to rabbit liver microsomes, as it did with 125I-oGH binding to purified receptor. On the basis of these results and others we postulate three types of GH receptor in rabbit liver membranes and ascribe approximate extents of 125I-oGH binding to each. A cytosolic 'GH receptor' which is not poly(ethylene glycol)-precipitable is shown to share five epitopes with 'type 2' microsomal receptors. Purified plasma membrane and endoplasmic reticulum fractions derived from a rabbit liver microsomal preparation have identical antigenic characteristics with respect to the GH-binding region, indicating that the heterogeneity we describe is not related to receptor processing. Of the three types of GH receptor in the plasma membrane of the rabbit (and possibly rat) we postulate that one (type 1) corresponds to the GH receptor involved in stimulating growth and possesses all of the epitopes studied here. A second (type 2) appears to be identical with the cytosolic 'GH receptor' and lacks the epitope for the anti-(rat GH receptor) MAb in the hormone binding site region. A third (type 3) does not possess the epitope for the inhibitory anti-(rabbit GH receptor) MAb, appears not to bind rat GH and is lost during purification. The availability of type-specific MAbs will facilitate assignment of specific functions to liver receptor subtypes which mediate the multiple functions of GH.     

Immune escape by human immunodeficiency virus type 1 from neutralizing antibodies: evidence for multiple pathways.

Sera from many HIV-1-infected individuals contain broadly reactive, specific neutralizing antibodies. Despite their broad reactivity, variant viruses, resistant to neutralization, can be selected in vitro in the presence of such antisera. We have previously shown that neutralization resistance of an escape mutant with an amino acid substitution in the transmembrane protein (A582T) occurs because of alteration of a conformational epitope that is recognized by neutralizing antibodies directed against the CD4 binding site. In this report we demonstrate that immune escape via a single-amino-acid substitution (A281V) within a conserved region of the envelope glycoprotein gp120 confers neutralization resistance against a broadly reactive neutralizing antiserum from a seropositive individual. We show this alteration affects V3 and additional regions unrelated to V3 or the CD4 binding site. Together with previous studies on escape mutants selected in vitro, our findings suggest that immune-selective pressure can arise by multiple pathways.     

An immunodominant domain in adenovirus type 2 early region 1A proteins.

Six independent rat hybridoma cell lines producing monoclonal antibodies to human subgroup C adenovirus early region 1A (E1A) proteins were isolated. Competition binding experiments revealed that each of the monoclonal antibodies was directed against the same epitope or overlapping cluster of epitopes on the E1A proteins. Viral E1A deletion mutants and deleted forms of E1A proteins expressed in Escherichia coli were used to localize the antibody recognition sites to sequences between amino acids 23 and 120, encoded within the first exon of the E1A gene. Similarly, polyclonal antisera raised against the trpE-E1A fusion protein, as well as against the native, biologically active E1A protein, were also directed primarily against this immunodominant region.     

Immunological crossreactivity of the antisera to purified hormones

Antisera to ovine follicle stimulating hormone free of ovine lutinising hormone contamination has been obtained in monkeys. These antisera have been shown to be able to crossreact with ovine lutinising hormone. Quantitation of the binding data for ovine follicle stimulating hormone and ovine lutinising hormone show that 10–40% of the total antibody population to ovine follicle stimulating hormone can bind to ovine lutinising hormone and the affinity constant for ovine lutinising hormone is about 2–20 times lesser than for ovine follicle stimulating hormone. These binding data indicate that there are common epitopes exposed in ovine follicle stimulating hormone and ovine lutinising hormone through the α-subunit. Results are obtained which match with the above conclusions when ovine lutinising hormone antisera is analysed for ovine follicle stimulating hormone binding. These results show that the α-subunit when combined with different β-subunits will have common epitopes exposed, but would be sterically disposed differently in the two hormones.     

Highly efficient selection of epitope specific antibody through competitive yeast display library sorting

Combinatory antibody library display technologies have been invented and successfully implemented for the selection and engineering of therapeutic antibodies. Precise targeting of important epitopes on the protein of interest is essential for such isolated antibodies to serve as effective modulators of molecular interactions. We developed a strategy to efficiently isolate antibodies against a specific epitope on a target protein from a yeast display antibody library using dengue virus envelope protein domain III as a model target. A domain III mutant protein with a key mutation inside a cross-reactive neutralizing epitope was designed, expressed, and used in the competitive panning of a yeast display naïve antibody library. All the yeast display antibodies that bound to the wild type domain III but not to the mutant were selectively sorted and characterized. Two unique clones were identified and showed cross-reactive binding to envelope protein domain IIIs from different serotypes. Epitope mapping of one of the antibodies confirmed that its epitope overlapped with the intended neutralizing epitope. This novel approach has implications for many areas of research where the isolation of epitope-specific antibodies is desired, such as selecting antibodies against conserved epitope(s) of viral envelope proteins from a library containing high titer, high affinity non-neutralizing antibodies, and targeting unique epitopes on cancer-related proteins.     

Comparing antigenicity and immunogenicity of engineered gp120

We have engineered monomeric gp120 in such a way as to favorably present the conserved epitope for the broadly neutralizing antibody b12 while lowering the exposure of epitopes recognized by some weakly neutralizing and nonneutralizing antibodies. The work presented here describes the immune response in rabbits immunized with two prototype, engineered gp120s to explore the relationship between antigenicity and immunogenicity for these mutants. The GDMR gp120 mutant (residues 473 to 476 on gp120 altered from GDMR to AAAA) has a series of substitutions on the edge of the CD4 binding site (CD4bs), and the mCHO gp120 mutant has seven extra glycans relative to the wild-type protein. Importantly, serum mapping showed that both mutants did not elicit antibodies against a number of epitopes that had been targeted for dampening. The sera from rabbits immunized with the GDMR gp120 mutant neutralized some primary viruses at levels somewhat better than the wild-type gp120 immune sera as a result of an increased elicitation of anti-V3 antibodies. Unlike wild-type gp120 immune sera, GDMR gp120 immune sera failed to neutralize HXBc2, a T-cell line adapted (TCLA) virus. This was associated with loss of CD4bs/CD4-induced antibodies that neutralize TCLA but not primary viruses. The mCHO gp120 immune sera did not neutralize primary viruses to any significant degree, reflecting the masking of epitopes of even weakly neutralizing antibodies without eliciting b12-like antibodies. These results show that antibody responses to multiple epitopes on gp120 can be dampened. More precise focusing to a neutralizing epitope will likely require several iterations comparing antigenicity and immunogenicity of engineered proteins.     

Immunolocalization of intermediate filament proteins using antibodies to synthetic peptides.

Synthetic peptides corresponding to amino acid sequences of amino terminal non-alpha helical domains of human cytokeratin 18 and to low molecular weight human neurofilament subunit were used to obtain monospecific antisera. The results of our immunohistochemical investigations confirmed in general the data previously published on the distribution of cytokeratin 18 in human, rat, and calf tissues. The reactivity of the antiserum was abolished after formalin fixation of specimens. Immunolocalization of the neurofilament subunit using our monospecific antiserum was quite variable from species to species in cells of the central and peripheral nervous systems, and also varied as the result of the tissue fixation procedures. In particular, formalin fixation destroyed the immunoreactivity of the recognized epitope. We discuss the advantages and limits of the use of synthetic peptides as immunogens to produce polyclonal antibodies against intermediate filament proteins, with particular attention to the epitope masking phenomena in cytokeratin polypeptides and the phosphorylation of epitopes in neurofilament subunits.     

Investigation of the solid- and solution-phase binding reactivities of continuous epitopes recognized by polyclonal guinea-pig anti-recombinant bovine growth hormone antisera.

We have used the technique of multiple pin peptide synthesis to identify three major continuous epitopes in the recombinant bovine (rb) GH molecule. We have synthesized these peptides, residues 24-40, 139-152 and 179-189, as N-terminally acetylated, C-terminal amides and confirmed their reactivity in a standard solid-phase ELISA. Subsequently, for epitope 139-152, we have synthesized a peptide affinity column and used this to isolate antibodies with this epitope specificity from whole antiserum. In addition, we demonstrate that under native conditions in a liquid phase RIA, these antibodies will precipitate [125I]rbGH. Further, peptide 139-152 itself also cross-reacts in an rbGH RIA inhibiting binding by up to 20%. Our data suggest that during the immune response to rbGH in guinea-pigs a substantial part of the B-cell response is directed to the 139-152 region and that this part of the protein is a native epitope.     

Monoclonal antimyogenin antibodies define epitopes outside the bHLH domain where binding interferes with protein-protein and protein-DNA interactions

We have developed a panel of monoclonal antibodies against rat myogenin, a skeletal muscle regulatory protein of the bHLH family. Some of these monoclonals have been widely used by others, and details of their production are presented. Mapping the epitopes by immunoprecipitation of myogenin deletion mutants demonstrates that this panel recognizes epitopes spanning the entire molecule outside the HLH region. Four antibodies against epitopes outside the bHLH region interfere with the binding of myogenin/E-protein heterodimers to DNA sequences containing the myogenin heterodimer consensus recognition site. Three of these epitopes are partially masked in the heterodimers; antibody binding to these epitopes reduces the interactions between myogenin and E12. This suggests that surfaces outside the HLH dimerization domain may contribute to the stability of myogenin/E12 complexes. The binding of one antibody to its epitope did not appear to affect the myogenin/E12 interaction but nonetheless interfered with the binding of the complex to DNA, suggesting that this epitope lies near to a surface occupied by DNA. © 1996 Wiley-Liss, Inc.     

Expression of meningococcal epitopes in LamB of Escherichia coli and the stimulation of serosubtype-specific antibody responses

The class 1 outer membrane protein (OMP), a major variable surface antigen of Neisseria meningitidis, is a component of novel meningococcal vaccines currently in field trials. Serological variants of the protein are also used to serosubtype meningococci. Most of the amino acid changes that give rise to antigenic variants of the protein occur in two variable regions (VR1 and VR2) that are thought to form loops on the cell surface. The polymerase chain reaction (PCR) was used to amplify the nucleotide sequences encoding VR1 and VR2 from the chromosomal DNA of N. meningitidis strain M1080. These were cloned in frame into the lamB gene of the Escherichia coli expression vector pAJC264. Whole-cell enzyme-linked immunosorbent assays (ELISAs), using monoclonal antibodies, and SDS PAGE confirmed that, upon induction, strains of E. coli carrying these constructs expressed hybrid LamB proteins containing the N. meningitidis surface loops. These strains were used to immunize rabbits and the resultant polyclonal antisera reacted specifically with the class 1 OMP of reference strain M1080 (P1.7). Immunogold labelling of meningococcal cells and whole-cell dot-blot analyses with these antisera showed that the variable epitopes were exposed on the cell surface and confirmed that this approach could be used to obtain serosubtype-specific antisera. The binding profiles of the antisera were determined from their reactions with overlapping synthetic peptides and their reactivity compared with that of relevant serosubtype-specific monoclonal antibodies. This approach was used successfully to raise antisera against two other class 1 OMP VR2s. A fourth antiserum raised against a VR2, including the P1.1 epitope, was not subtype specific.     

Antigenic determinants of vesicular stomatitis virus: analysis with antigenic variants

Antigenic variants of vesicular stomatitis virus (VSV) serotypes New Jersey and Indiana (VSV-NJ, VSV-Ind) were selected by using a panel of monoclonal antibodies (MAb) specific for the major surface glycoprotein (G-protein). The reactivity of antigenic variants with the panel of MAb confirmed observations made by competitive binding assays that four distinct antigenic sites (A-D)NJ on the VSV-NJ G-protein and four partially overlapping sites (A, B1, B2, C)Ind on the VSV-Ind G-protein are involved in virus neutralization. Furthermore, subregions within the A epitopes of both serotypes were detected by variant analysis. The frequency of variation at most epitopes was 1 in 10(5) for VSV-NJ and 1 in 10(6) for VSV-Ind. The A3 and C determinants of VSV-Ind, however, defined by MAb that exhibited overlap in binding to other epitopes, appeared to be relatively invariant. Multiple mutations may be necessary to abolish antibody binding at these sites. Overlap of the C group of anti-VSV-Ind MAb with the A epitopes was assigned to the A2 subregion, because variants selected with A2 MAb show reduced binding of C MAb. Heterogeneous antisera from a primary immune response could detect differences in reactivity between variants at the A epitopes and wild-type VSV-NJ or VSV-Ind, suggesting the A epitope is immunodominant. Hyperimmune sera could detect a small difference between ANJ and BNJ variants compared to wild-type VSV-NJ, but could not distinguish between VSV-Ind variants and wild-type VSV-Ind.     

Production and characteristics of human tissue plasminogen-activator antibodies with region-oriented synthetic peptides.

We selected six peptide sequences as belonging to potential epitopes of tissue plasminogen activator (tPA) using, as the main criterion for their choice, the location of the peptide sequences on the surface of the protein molecule. The six peptides (corresponding to amino acids 4-8, 11-16, 96-101, 272-277, 371-376 and 514-519) were synthesized, coupled to carrier proteins and injected into rabbits. All of these peptides elicited antibodies and 15-75% binding of the corresponding iodinated peptide was obtained with a 1:100 dilution of antiserum. Only two anti-(peptide) sera [anti-(tPA96-101) and anti-(tPA272-277)] reacted with intact tPA and its heavy chain in Western immunoblotting analysis. These two peptides sequences and fragment tPA11-16 appear to be involved in the structure of native antigenic epitopes of tPA, since they were recognized and antibodies present in antisera raised against native tPA. There was no interaction between anti-(tPA4-8) and anti-(tPA371-376) sera with intact one-chain or two-chain tPA. In the case of anti-(tPA4-8) cleavage of one-chain tPA to two-chain tPA and reduction of disulfide bonds exposed this epitope.     

Distribution of corticotropin releasing factor-like immunoreactivity in the rat brain by immunohistochemistry and radioimmunoassay: comparison and characterization of ovine and rat/human CRF antisera

The distribution of corticotropin releasing factor (CRF)-like immunoreactivity in the rat brain has been demonstrated by immunohistochemistry and radioimmunoassay using 4 different antisera. Two antisera were directed against synthetic ovine CRF, two antisera were directed against synthetic rat/human CRF. Immunohistochemistry revealed that there are discrete regions where CRF immunoreactive cell bodies are seen with all 4 antisera (e.g., the paraventricular nucleus, the dorsolateral tegmental nucleus) whereas there are cells observed only with one rat CRF antiserum (e.g., in the cortex) or terminal fields observed only with ovine CRF antisera (e.g., the spinal trigeminal tract, the substantia gelatinosa, the spinal cord). Radioimmunoassay showed different cross reactivity of the antisera with synthetic ovine or rat/human CRF and sauvagine, however, there was no cross reactivity with a variety of other peptides. Tissue values of CRF obtained by RIA of micropunched brain nuclei with the 4 antisera were frequently dissimilar suggesting that different antisera recognize different substances. High performance liquid chromatography and radioimmunoassay of brain tissue samples, revealed that there is more than one form of CRF-like immunoreactivity present. There is indirect evidence that there exists at least one peptide in the rat brain, prominent in the medulla and the spinal cord, which cross reacts with antisera directed to ovine CRF only.     

Relative ability of ovine follicle stimulating hormone and itsβ-subunit to generate antibodies having bioneutralization potential in nonhuman primates

The relative ability of ovine follicle stimulating hormone and itsβ-subunit, two potential candidates for male contraceptive vaccine, to generate antibodies in monkeys capable of bioneutralizing follicle stimulating hormone was assessed usingin vitro model systems. Antiserum against native ovine follicle stimulating hormone was found to be highly specific to the intact form with no cross-reactivity with either of the two subunits while the antiserum againstβ-subunit of follicle stimulating hormone could bind to theβ-subunit in its free form as well as when it is combined withα-subunit to form the intact hormone. Both antisera could block the binding of the hormone to the receptor if the hormone was preincubated with the antibody. However, the follicle stimulating hormoneβ-antisera could only inhibit the binding of the hormone partially (33% inhibition) if the antibody and receptor were mixed prior to the addition of the hormone, while antisera to the native follicle stimulating hormone could block the binding completely (100% inhibition) in the same experiment. Similarly antisera to the native follicle stimulating hormone was significantly effective in blocking (100%) response to follicle stimulating hormone but not theβ-subunit antisera (0%) as checked using anin vitro granulosa cell system. Thus the probability of obtaining antibodies of greater bioneutralization potential is much higher if intact hormone is used as an antigen rather than itsβ-subunit as a vaccine. Majority of the work reported here was carried out during the tenure of Visiting Scientist fellowship awarded by the MRC Canada to the first author.     

Site-Specific Anti-C-ERB A Antibodies Recognizing Native Thyroid Hormone Receptors: Their use to Detect the Expression and Localization of α and β C-ERB A Proteins in Rat Liver

Abstract

The cell-specific expression and tissue distribution of c-erbA proteins α and β is still unknown. To address this problem, we prepared anti-peptide antibodies directed against epitopes of human (h) c-erbA, specific for the α or β form of thyroid hormone receptors. The cDNAs coding for h c-erbA β1, α1 and α2 were transcribed and the mRNAs were translated in vitro in the presence of 35S-methionine, and then their reactivity with the antisera was evaluated. The antiserum anti-β 62–81 immunoprecipitated only the β1 receptor. The antiserum anti-α 144–162 determined precipitation of both α1 and α2 proteins but not of the β1 receptor. Anti-α2 431–451 produced a selective precipitation of α2, and had no effect on α1 or β1 receptor. In order to study the interaction of the antibodies with native T3 receptor we evaluated the binding of antibodies to rat liver T3 receptors by Sephacryl S300 chromatography: both antisera anti-β 62–81 and anti-α 144–162 caused a partial shift of the labeled T3–receptor complex to a higher molecular form, while the antibody directed against c-erbA α2 did not produce any significant shift. The anti-peptide antibodies were then immunopurified by affinity chromatography and used to immunolocalize the different forms of c-erb A proteins in adult and fetal rat liver, by a sensitive immunohistochemical technique. All 3 antibodies stained mainly the nuclei of the majority of adult liver cells. No staining was detectable when the original antiserum was deprived of anti-peptide antibodies by running through the affinity columns or when the antibodies were pre-absorbed with the homologous peptide. No significant staining was present in the liver from rat fetus.     

Epitope mapping of the Syrian hamster prion protein utilizing chimeric and mutant genes in a vaccinia virus expression system.

The cellular prion protein (PrPc) is a host-encoded sialoglycoprotein bound to the external surface of the cell membrane by a glycosyl phosphatidylinositol anchor. A posttranslationally modified PrP isoform (PrPSc) is a component of the infectious particle causing scrapie and the other prion diseases. mAb have been raised against the protease-resistant core of Syrian hamster (SHa) PrPSc designated PrP 27-30. To map the epitopes within PrP reacting to these antibodies, we have expressed wild-type, chimeric mouse (Mo)/SHa and mutant MoPrP genes using recombinant vaccinia virus systems. The fidelity of the expression of recombinant PrPC was examined using vaccinia viruses expressing SHa-PrPC. It is full length, possesses Asn-linked carbohydrates and is attached to the external surface of the cell membrane by a glycosyl phosphatidylinositol anchor that is sensitive to cleavage by phosphatidylinositol-specific phospholipase C. We have tested 18 mAb for their ability to bind to chimeric prion proteins on immunoblots. Three distinct epitopes were identified that mapped to amino acid differences between SHa and MoPrP sequences. The first epitope, recognized by three of the antibodies tested, was defined by methionines at amino acids 108 and 111 in the mouse protein. The second epitope was dependent upon the presence of asparagines at positions 154 and 174 in MoPrP and was recognized by four of the antibodies tested. The third epitope mapped to a single amino acid substitution at residue 138 in MoPrP. mAb raised against SHaPrP 27-30 specific for this epitope are able to bind MoPrPC which has a single amino acid change (Ile to Met) at position 138. Eleven of the 18 antibodies tested mapped to this immunodominant epitope. It is located within a postulated amphipathic helix, a structure associated with immunodominant Ag. Inasmuch as PrPC, in its native form on the cell surface, is detected by the mAb 13A5 (a prototypic antibody of the immunodominant third epitope class), it is likely that this epitope is accessible in the native conformation of this protein.     

Expression,purification, and characterization of minimized chicken riboflavin carrier protein from a synthetic gene in Escherichia coli

Minimized proteins have long been used to elicit immune response to particular regions of a protein antigen. Most efforts to derive minimized proteins have employed synthetic peptide fragments. Here we describe molecular cloning and production of a minimized chicken riboflavin carrier protein (mini-RCP) sequence that harbours all the four neutralizing epitopes but lacks the sequences that otherwise elicit undesirable antibodies. The gene encoding mini-RCP is engineered by contiguous alignment of nucleotide sequences coding for selected epitopes of chicken RCP separated by leucyl alanine residues. The gene has been constructed from eight oligonucleotides by employing overlapping PCR strategy and expressed in Escherichia coli, using the T7 promoter system. The recombinant protein could be purified to homogeneity by a single step Ni2+ affinity chromatography. Western blot experiments using epitope specific antisera confirm that the corresponding linear amino acid sequences are available for immunorecognition in the engineered protein. This methodology enables continuous production and purification in bulk amounts of the minimized RCP as a source of candidate immunocontraceptive vaccine in mammals.     

Application of an immune-tolerizing procedure to generate monoclonal antibodies specific to an alternate protein isoform of bovine growth hormone.

An immune-tolerizing protocol was employed to generate monoclonal antibodies to a variant protein isoform of bovine growth hormone arising from alternative pre-mRNA processing. Variant bovine growth hormone used for immunization was obtained by expression in bacteria and electroelution of the protein from preparative sodium dodecyl sulfate-polyacrylamide gels. Balb/c mice were first immunized with wild-type bovine growth hormone in the presence of the cytotoxic drug cyclophosphamide, thereby tolerizing the mouse to common epitopes shared among the two proteins. Subsequently, the mice were immunized with variant bovine growth hormone to produce antibodies specific to variant epitopes. Comparisons of fusions resulting from standard and tolerizing immunization protocols resulted in a significantly enhanced production of variant bovine growth hormone-specific antibodies as a result of the immunotolerizing protocol. The specificity of the antibodies to the variant growth hormone was substantiated by differential enzyme-linked immunosorbent assay and Western blot. Nearly all hybridomas positive for variant growth hormone were negative for wild-type growth hormone. Finally, the antibodies were used to demonstrate intracytoplasmic staining of COS I cells transiently transfected with a variant growth hormone-producing plasmid. Given the power of the polymerase chain reaction to conveniently clone alternatively processed mRNA species, followed by expression in bacteria to provide antigen, the immunotolerizing protocol provides a convenient general method for producing antibodies specific to desired protein isoforms.