Production and characterization of monoclonal antibodies against bovine luteinizing hormone

A novel monoclonal antibody-based enzyme-linked immunosorbent assay to determine luteinizing hormone in bovine plasma

The development of a novel enzyme-linked immunosorbent assay (ELISA) for determining luteinizing hormone (LH) in bovine plasma is described. Anti-bovine LH (bLH) monoclonal antibodies (mAbs) were produced and characterized. One mAb recognizing the bLH β subunit was used for immunoaffinity purification of substantial amounts of biologically active bLH from pituitary glands. The purified bLH in combination with 2 anti-bLH β subunit mAbs was used to develop a sandwich ELISA, which satisfied all the criteria required to investigate LH secretory patterns in the bovine species. The ELISA standard curve was linear over the range 0.05 to 2.5 ng/mL, and the assay proved suitable for measuring bLH in plasma without any prior treatment of samples. Cross-reactivity and recovery tests confirmed the specificity of the method. The intra- and inter-assay coefficients of variation ranged between 3.41% and 9.40%, and 9.29% and 15.84%, respectively. The analytical specificity of the method was validated in vivo by provocative tests for LH in heifers, using the LH releasing peptide gonadotropin-releasing hormone. In conclusion, the adoption of mAbs for this ELISA for coating the wells and labeling, combined with the easy one-step production of reference bLH, ensures long-term continuity in large-scale measurements of LH in the bovine species.

Candidate epitopes for measurement of hCG and related molecules: the second ISOBM TD-7 workshop

Participants of the Second International Workshop (WS) on human chorionic gonadotropin (hCG) of the International Society of Oncology and Biomarkers Tissue Differentiation 7 (ISOBM TD-7) have characterized in detail a panel of 69 antibodies (Abs) directed against hCG and hCG-related variants that were submitted by eight companies and research groups. Specificities of the Abs were determined using the First WHO International Reference Reagents for six hCG variants, i.e., hCG, hCGn, hCGβ, hCGβn, hCGβcf, and hCGα, which are calibrated in SI units, and hLH. Molecular epitope localizations were assigned to the ISOBM-mAbs by comparing ISOBM-Ab specificity, sandwich compatibility, and mutual inhibition profiles, to those of 17 reference monoclonal (m)Abs of known molecular epitope specificities. It appeared that 48 Abs recognized hCGβ-, 8 hCGα-, and 13 αβ-heterodimer-specific epitopes. Twenty-seven mAbs were of pan hCG specificity, two thereof with no (<0.1 %; epitope β₁), 12 with low (<1.0 %; epitopes β_2/4), and 13 with high (>>1 %; epitopes β_3/5) hLH cross-reactivity. The majority of hCGβ epitopes recognized were located in two major antigenic domains, one on the peptide chain of the tips of β-sheet loops 1 and 3 (epitopes β_2–6; 27 mAbs) and the second around the cystine knot (e.g., epitopes β₁, β₇, and β₁₀; 9 mAbs). Four mAbs recognized epitopes on hCGβcf-only (e.g., epitopes β₁₁ and β₁₃) and six mAbs epitopes on the remote hCGβ-carboxyl-terminal peptide (epitopes β₈ and β₉ corresponding to amino acids 135–144 and 111–116, respectively). For routine diagnostic measurements, methods are used that either detect hCG-only, hCGβ-only, or hCG together with hCGβ or hCG together with hCGβ and hCGβcf. Sandwich assays that measure hCG plus hCGβ and eventually hCGβcf should recognize the protein backbone of the analytes preferably on an equimolar basis, should not cross-react with hLH and not be susceptible to blunting of signal by nonmeasured variants like hCGβcf. Such assays can be constructed using pairs of mAbs directed against the cystine knot-associated epitope β₁ (Asp10, Asp60, and Gln89) in combination with epitopes β₂ or β₄ located at the top of β-sheet loops 1 + 3 of hCGβ involving aa hCGβ20-25 + 68-77. In summary, the results of the First and Second ISOBM TD-7 WSs on hCG provide the basis for harmonization of specificities and epitopes of mAbs to be used in multifunctional and selective diagnostic hCG methods for different clinical purposes.

Immunochemical mapping of gonadotropins

As a glycoprotein hormone, human chorionic gonadotropic (hCG) is not a single molecular entity but this term rather comprises an array of molecular variants such as hCG, hCG beta, hCGn, hCG beta n, hCG beta cf, -CTPhCG, hCG beta CTP, deglyhCG, asialohCG, hCGav and the closely related molecules hLH, hLH beta and hLH beta ef. The advent of monoclonal antibodies (MCA), the availability of ultrasensitive detection systems and the recent determination of the crystal structure of hCG, made it possible to design special purpose diagnostic and clinical research immunoassays for hCG-like molecules. For more than a decade we and others have tried to refine epitope maps for hCG and related molecules by means of a large panel of MCA, naturally occurring metabolic variants of hCG (hCGn, hCG beta, hCG alpha, hCG beta cf, hCG beta CTP), homologous hormones and subunits of various species (e.g. hLH, hLH beta, hFSH, hTSH, oLH, rLH beta), chemically modified molecules (deglyhCG, asialohCG, tryptic and chymotryptic hCG beta and hCG alpha fragments) and synthetic peptides (octapeptides and longer). It appeared that all epitopes on molecular hCG-variants recognized by our MCA are determined by the protein backbone. Except for the two major epitopes on hCG beta CTP and parts of two antigenic domains on hCG alpha, epitopes on hCG-derived molecules are determined by the tertiary and quarternary structure. Operationally useful descriptive epitope maps were designed including information on assay suitability of antigenic determinants. On this basis we established ultrasensitive time-resolved fluoroimmuno-assays for hCG, hCG and hCGn, hCG beta and hCG beta n and hCG beta cf, hCG alpha and additional assays recognizing different spectra of hCG-variants. Such assay have been applied by us and others to the detection of pregnancy, early pregnancy loss, choriocarcinoma, testicular cancer, other cancers and prenatal diagnosis. However, as the molecular structure of many epitopes utilized in immunoassays of different laboratories was not resolved, comparability of results was not satisfactory. Consequently, attempts were made to compare schematic epitope maps from different research institutions. The situation has been much improved by solving the three-dimensional (3D) structure of hCG. It has been shown that hCG is a member of the structural superfamily of cystine knot growth factors like NGF, PDGF-B and TGF-beta. Each of its subunits is stabilized in its topology by three disulfide bonds forming a cystine knot. Moreover, it turned out that the disulfide bridges in their majority have previously been wrongly assigned. Computer molecular modeling of crystallographic coordinates of hCG and subsequent selective combined--PCR-based and immunological--mutational analyses of hCG beta expressed via the transmembrane region of a MHC molecule made it possible to more precisely localize epitopes on hCG-derived molecules. Although the entire surface of hCG has to be regarded as potentially immunogenic there seems to be hot spots where epitopes are clustered in antigenic domains. These are located on the first and third loops protuding from the cystine knots of both subunits and are possibly centered around the knot itself. Ultimate answers on epitope localizations will be given by the crystal structure determination of hCG complexed with different Fabs.

Heterologous radioimmunoassay for llama and alpaca luteinizing hormone with a monoclonal antibody, an equine standard and a human tracer

A radioimmunoassay for llama and alpaca LH was developed using a human I125LH tracer from a commercial kit, equine LH diluted in human LH free serum as standard, and a monoclonal antibody (518B7) specific for LH but with low species specificity. A 60-min delay in the addition of the tracer and overnight incubation gave a sensitivity of 0.8 microgram L-1. The intra-assay coefficient of variation was 37% at 1 microgram L-1, declined to 15% at 4 micrograms L-1 and was below 6% for concentrations up to 32 micrograms L-1. The inter-assay coefficients of variation for 3 control samples were 20% (2.8 micrograms L-1), 16% (7.1 micrograms L-1) and 9.8% (19 micrograms L-1). In an attempt to increase sensitivity, all tubes were preincubated for 4 h at room temperature before adding the tracer, and the sample volume was increased from 50 microL to 100 microL (in the standard curve the increased volume was compensated for by human LH free serum). With this protocol, the assay sensitivity was 0.5 microgram L-1. The assay was validated clinically and demonstrated increased concentrations of LH after mating in llamas and alpacas. Furthermore, the assay was used to monitor LH responses to a single dose of GnRH in llamas (adult males and females at different ages).

Twelve of fourteen surface epitopes of receptor-bound human chorionic gonadotropin (hCG) being antibody-inaccessible suggest an extensive involvement of the long extracellular domain of the hCG receptor

On the surface of the free (receptor-unbound) form of hCG, we have previously identified 14 topographically distinct epitopes (Schwarz et al. (1986) Endocrinology 118, 189-197; Berger et al. (1990) J. Endocrinol. 125, 301-309). Here we report that only two of them, i.e. the (adjacent) beta 3 and beta 5 epitopes, can be recognized by 125iodine-labeled monoclonal antibodies when hCG was specifically bound to the rat testis hCG receptor. The exclusive accessibility of precisely these two surface epitopes indicates that hCG assumes a defined rather than a stochastic orientation in its receptor-bound state. The inaccessibility of 12 of 14 epitopes is consistent with the idea that the 341 residues long extracellular domain of the recently cloned hCG receptor (MacFarland et al. (1989) Science 245, 494-499) is the ligand binding domain. It is proposed that the extracellular domain is folded in a way that a cavity is formed large enough to accommodate hCG. Thereby, a considerable portion of the total surface of hCG is covered, as reflected by the masking of most of its epitopes.

Number and topography of epitopes of human chorionic gonadotropin (hCG) are shared by desialylated and deglycosylated hCG

A previously established map of the surface epitopes of human chorionic gonadotropin (hCG) served as template for the present study in which we investigated the antigenic surfaces of two glycosylation variants of hCG, i.e. desialylated hCG (asialo-hCG) and deglycosylated hCG (degly-hCG). This map allocates five epitopes to the alpha subunit, five to the beta subunit and four alpha beta epitopes to structures formed only by the alpha/beta heterodimer holo-hCG (Schwarz et al. (1986) Endocrinology 118, 189-197; Berger et al. (1990) J. Endocrinol. 125, 301-309). Here it is described that both variants complied with this template: each of the 14 distinct monoclonal antibodies with which the epitopes of hCG were defined reacted with radiolabeled asialo-hCG and degly-hCG as well and generally bound degly-hCG with greater affinity than hCG. Moreover, every combination of capture and radiolabeled detection antibody that was either compatible or incompatible on unlabeled hCG was so also on unlabeled asialo-hCG and degly-hCG. It thus appears that alterations of the carbohydrate structure of hCG can be associated with a change in affinity between some antibodies and their respective epitopes but not with a loss of an epitope or with a change in the topographical relationships of the 14 epitopes.

Relationship of orientation with affinity and activity of receptor-bound glycosylation variants of human chorionic gonadotropin (hCG), as visualized by monoclonal antibodies (MCA)

When hCG was receptor-bound, only 2 epitopes (i.e. beta 3 and beta 5) out of its previously mapped total of 14 surface epitopes (10, 11, 12) could be detected by the respective 125I-MCA. Clearly, this indicates a non-random orientation of hCG in this particular state (1). Now we report that on receptor-bound desialylated (asialo-hCG) as well as on receptor-bound deglycosylated hCG (degly-hCG), the beta 3 and beta 5 epitopes were inaccessible for 125I-MCA as were the remaining epitopes, although both variants, when not receptor-bound, were indistinguishable from native hCG with respect to number and topography of epitopes. Thus, the carbohydrate (CHO) units of hCG neither seem to be part of these 14 antigenic sites nor to contribute to the affinity of receptor binding: both variants had even higher affinities than native hCG. However, since the CHO are known to be obligatory for triggering the postreceptor responses of hCG-stimulated target cells, as seen by the 50% reduced or totally abolished biological potency of asialo-hCG and degly-hCG, respectively, the here demonstrated clear-cut differences in epitope accessibility can be related to differences in receptor-bound orientations which reflect signal transduction-competent and incompetent modes of interaction with the receptor. We believe that the CHO, while not contributing to receptor binding per se, function to assure correct positioning of hCG in the ligand recognition domain to allow for proper protein-protein interactions between ligand and receptor and thus optimal activation and hence transduction of the external signal to the cell's interior. In addition, the fact that most of the surface epitopes were masked on receptor-bound hCG, represents the first experimental support for the sofar unproven hypothesis that this unusually long (i.e. 341 amino acid residues) extracellular N' terminal domain of the recently cloned hCG receptor (hCG-R) (23,24), is indeed involved in ligand recognition.

Production and characterisation of monoclonal antibodies directed against different epitopes of human thyroid stimulating hormone

We have produced monoclonal antibodies (mAbs) to human thyroid stimulating hormone (hTSH) and selected five that specifically recognize hTSH and do not cross-react with the other human glycoprotein hormones such as luteinizing hormone (LH), chorionic gonadotropin (CG), follicle stimulating hormone (FSH). All of the antibodies were of the IgG1 subclass with affinities ranging from 5.3 X 10(8) to 1.9 X 10(10) mol-1.l; they could be assigned to two subgroups on the basis of their epitope specificity.

Probing the receptor-interaction of glycoprotein hormones with monoclonal antibodies

Having recently analyzed with monoclonal antibodies (MCA) the immunologic surface of human chorionic gonadotropin (hCG) as consisting of 9 distinct epitopes exposed on the molecule in a characteristic topographical manner (Schwarz, S., Berger, P., and Wick, G., Endocrinology 118, 189-197, 1986) we now attempted to confirm this result on a more general basis, e.g. by incorporating MCA that were just recently obtained and previously not included. What we were, however, interested most was the question whether the tentative model of the epitope map of hCG could represent a "target" with which hCG-related hormones such as LH, FSH, and TSH (the family of glycoprotein hormones, GPH) would (partially) match. Indeed, repeating various immunizations with GPH of human as well as animal origin revealed a remarkable reproducibility in terms of several anticipated epitope specificities of MCA. This indicates that MCA can be regarded as reliable probes for mapping epitopes and, as we have presumed, of receptor interaction domains of GPH as well. Extending the originally used 2-site MCA binding exclusion approach by an interspecies crossreactivity (Xr) analysis we now are able to refine our epitope model of hCG such that 2 additional epitopes were found which were not previously resolvable. Most surprisingly, two of 5 epitopes on the alpha subunit were now also detected on various non-human GPH, which is in striking contrast to a seemingly well established dogma. Yet all five alpha epitopes of hCG are present on hLH, hFSH, and hTSH as well and arranged in the same spatial relationship to each other as on hCG. Even the 2 conformational epitopes and their close topographical relationship to the alpha-epitopes appear to be remarkably conserved on all human GPH. Among the beta-epitopes we have found one that is not shared by hLH and that - surprisingly - is not the C-terminal peptide (CTP) by which hLH differs from hCG. On the basis of this refined epitope map a way was paved along which it should be feasible to elucidate the sterical relationship of the epitopes to the receptor interaction domain(s) of hCG. To this end the MCA were tested in principally two ways: first, as to which of the 11 MCA with different epitope specificities would be able (or not) to inhibit by preincubation the binding of radiolabeled hCG (or hLH, respectively) to rat testis LH/hCG receptors? Secondly (and inversely) which of the 11 epitopes of hCG would still be accessible to binding by radiolabeled MCA when the (unlabeled) hormone is bound to the receptor?(ABSTRACT TRUNCATED AT 400 WORDS)

Epitope masking and immunodominance--complications in the selection of monoclonal antibodies against HCG

Spleen cells from Balb/c mice immunized with HCG were subjected to the normal hybridoma procedures. The resulting MCA's (from 78 clones) were evaluated in radioimmunoassay, haemagglutination and enzyme immunoassay with whole HCG. The RIA analysis was extended to include HCG subunits and intact LH. The alpha-chain of HCG was found to be strongly immunodominant, as shown by the very high frequency (46 of 78) of MCA's directed at the alpha-chain epitopes. These antibodies would bind luteinizing hormone as well as HCG. Only 1 of the 78 clones was specific for the B subunit of HCG, in RIA. This clone was later found to be positive for LH in EIA, thus making the derivation of antibodies specific for this B-epitope extremely difficult. Most MCA's were found to be applicable in the three types of assay systems (48 of 78), but some were compatible in just one or two of the systems. These differences are believed to be due to epitope masking resulting from the way in which the antigen was handled and presented in the different systems.

Chromogranin A, B and C: immunohistochemical localization in ovine pituitary and the relationship with hormone-containing cells

Chromogranins A, B and C, three distinct groups of proteins found in bovine chromaffin granules, were also found to be present in the pituitary using immunoblotting techniques. Their distribution was therefore studied in the normal ram pituitary using an immunoperoxidase technique applied to semithin serial sections and compared with that of some of the hormones of the anterior pituitary. Chromogranin-immunoreactivity was found in gonadotrophs (all three), thyrotrophs (A with some positive for C) and corticotrophs (a fraction with A and fewer with B and C). The mammotrophs and somatotrophs were negative. Chromogranin C was the only one of the three to be located in the pars nervosa, whilst chromogranin B was rarely found in the pars intermedia. The results suggest that chromogranins A, B and C are not always stored together, some hormone-containing cells do not contain immunohistologically detectable levels of the chromogranins.

A monoclonal antibody reacting with a membrane determinant expressed on activated chicken T lymphocytes

A monoclonal antibody (INN-CH-16) was prepared which reacts with a cell surface antigen termed chicken activated T lymphocyte antigen. This antigen is expressed on antigen- or mitogen-activated T lymphocytes and is not present on nonstimulated lymphocytes. It has an apparent molecular mass of 48-50 kDa under reducing conditions. The value of this antibody for the immunohistochemical characterization of infiltrating cells in the thyroid glands from Obese strain chickens with spontaneous thyroiditis is demonstrated.

MHC- and non-MHC-encoded surface antigens of chicken lymphoid cells and erythrocytes recognized by polyclonal xeno-, allo- and monoclonal antibodies

Surface antigens on chicken thymus and bursa cells were analyzed by immunoprecipitation using polyclonal and monoclonal antisera raised against (and specific for) thymus (ATS) or bursa (ABS) cells, respectively. The antigens identified were compared with those governed by the B-F, B-L and B-G regions of the chicken major histocompatibility complex (B complex). Four proteins were precipitated from thymus cells by 2 polyclonal ATS: both antisera recognized molecules of apparent molecular mass of 172-182, 132-135, 75-76 kDa, and one antiserum in addition recognized a protein of 102 kDa. The 172-182 and 102-kDa peaks were still demonstrable under reducing conditions indicating that they are composed of a single polypeptide chain, the other 2 were lost under reducing conditions, therefore, must be composed of smaller subunits. Of the 2 monoclonal ATS tested, one identified a single protein of 186 kDa and the other a 135-kDa protein (in addition to 2 smaller molecules); whether these are the same as those precipitated by the polyclonal antisera remains to be determined as they behaved differently under reducing conditions. Proteins of 162 and 78-84 kDa were revealed by 2 polyclonal ABS under nonreducing conditions but the former may in one case be a polymer (it disappeared under reducing conditions) and in the other a single molecule. In addition molecules of 182 kDa were identified by one antiserum and of 84 and 60 kDa by the other under nonreducing conditions. Of the 4 monoclonal ABS only one identified a 200-kDa protein: molecules of 115-125, 90-100, 48-52 and 40-43 kDa were also precipitated, all of which were reduced to smaller molecules. With 2 specific anti-B-F alloantisera we were able to precipitate the "conventional" B-F antigen from red blood cell lysates of CB-strain chickens resolving into a 40-kDa peak and a light chain of about 12 kDa corresponding to beta 2 microglobulin. Precipitates from peripheral blood lymphocytes, bursa and thymus cells revealed an additional protein of 22 kDa. With 2 specific B-L alloantisera two peaks of 33 kDa and 31 kDa were obtained from peripheral blood lymphocytes. Using anti-B-G alloantisera a double band corresponding to 47 and 42 kDa was seen under reducing conditions. There is no evidence from these data to indicate that the polyclonal and monoclonal antibodies are directed towards major histocompatibility complex antigens.

An immunoperoxidase study of a human pituitary adenoma associated with Cushing's syndrome

A large endocrine active pituitary adenoma causing a Cushing's syndrome was investigated for the presence of subunits of the corticotropin-lipotropin precursor by immunohistology. A quantitative study revealed immunoreactivity (ir) for ACTH in 87.1% of the adenoma cells, beta-lipotropin-ir in 77.1%, beta-endorphin-ir in 75.3%, alpha-MSH-ir in 22.9% and methionine-enkephalin-ir in 7.8%. The adjacent distal pituitary gland showed a six-fold increase of prolactin-ir cells indicating the release of biologically active endogenous opiates. The strong alpha-MSH-ir within the adenoma cells in contrast to those of the distal pituitary may signify that alpha-MSH was being secreted by the adenoma. The proportions of other endocrine cell types within the anterior pituitary were normal (3.1% corticotrophs, 49.4% somatotrophs, 8.2% gonadotrophs and 7.1% thyrotrophs). 0.5% of the cells of the distal pituitary and 0.1% within the adenoma were VIP-ergic, which may be due to a vasoregularitory system and/or be involved in prolactin release.

Characterisation of monoclonal antibodies for human luteinising hormone, and mapping of antigenic determinants on the hormone

Twelve mouse monoclonal antibodies for human luteinising hormone were produced. The affinities varied from 4 X 10(7) to 1 X 10(10) l/mol. The specificity of each antibody was assessed by determining the relative reactivities with luteinising hormone, thyroid stimulating hormone, follicle stimulating hormone and chorionic gonadotrophin. Six antibodies bound to the alpha-subunit as shown by similar reactivity with all hormones, and the remainder to the beta-subunit as shown by specificity for luteinising hormone. This latter group of antibodies cross-reacted only weakly with thyroid stimulating hormone (approximately 10%) and follicle stimulating hormone (approximately 3%). Three of these antibodies also showed low reactivity towards chorionic gonadotrophin (less than 10%), though the others did not (80-300%). The ability of different antibodies to bind simultaneously to luteinising hormone was examined and it was shown that several distinct antigenic determinants existed on both subunits. The characterisation of monoclonal antibody binding sites is discussed in relation to the use of antibodies in two-site immunoradiometric assays.

Monoclonal antibodies against human chorionic gonadotropin (hCG): I. production, specificity, and intramolecular binding sites

Thirty-nine monoclonal antibody (MCA) producing hybridoma cell lines derived from fusions of mouse myeloma cells with spleen cells from mice immunized with human chorionic gonadotropin (hCG) have been established. Their products have been tested in radioimmunoassays using 125I-labeled hCG, luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), the alpha (alpha) and beta (beta) subunits of hCG and LH, and the C-terminal peptide 109-145 (CTP) of CG. All MCA were, in addition, tested in indirect immunofluorescence (IIF) on paraffin sections of human pituitary glands. According to the intramolecular localization of the determinants recognized, three main groups of MCA can be distinguished: 1) MCA directed against epitopes on the alpha-chain(alpha-MCA), 2) MCA directed against beta-chain determinants(beta-MCA), and 3) MCA reacting with a conformational determinant only present on the native hormone and not on either subunit (conformational-MCA). All alpha-MCA cross-react with human LH, FSH, and TSH. The beta-MCA do not react with FSH or TSH, but do react to a varying degree with LH. The conformational-MCA show no binding of labeled FSH or TSH and very little or no cross-reactivity with LH. (Am J Reprod Immunol. 1982; 2:212-216.)