Characterization of a bioeffective monoclonal antibody against thyrotropin beta-subunit

Increased receptor binding by bovine (b) TSH bound to monoclonal antibody to bTSHbeta-subunit

TSH receptor (R) binding and cAMP production by bovine (b) TSH-bound to a monoclonal antibody (MoAb) or polyclonal antibody (Ab) to bTSH were examined, using TSH receptor (R) coating tube and porcine thyroid cells. (125) I-bTSH bound-to MoAbs to bTSH(alpha) or discontinuous type MoAb showed TSHR binding (10%) similar to intact (125) I-bTSH. TSHR binding was completely decreased (<2%) when (125) I-bTSH was bound by polyclonal Abs to bTSH(alpha) in Graves' patient or rabbit polyclonal Abs to bTSH. When either of the two MoAb (No. 1 and 2) to bTSH(beta) was bound to (125) I-bTSH, TSHR binding was 4 times higher (40%) compared to intact (125) I-bTSH. Binding of another MoAb (No. 3) caused no increased binding. TSHR binding of intact (125) I-bTSH was decreased from 10% to 2% by excess amounts of bTSH. Binding of (125) I-bTSH bound to MoAb to bTSH(beta) (No. 1 and 2) decreased from 40% to 30% by excess amounts of bTSH. When (125) I-bTSH bound-Fab of MoAb was used, the binding was reduced from 30 to 10% (No. 1) and from 25 to 6% (No. 2), respectively. In contrast, cAMP production by bTSH was decreased by pre-binding of all MoAbs and polyclonal Abs. Binding of (125) I-MoAb to bTSH (beta) to a synthetic peptide array of bTSH (beta) sequence was examined by the radioautography. The epitope of MoAb to bTSH(beta) was suggested to be LPK (beta 42-44) for No. 1, KLF (beta 39-41) for No. 2 and PKYA (beta 43-46) for No. 3, respectively, although the existence of discontinuous epitope could not be ruled out. The increased TSHR binding and the decreased cAMP production by bTSH bound to MoAbs may be due to the conformational change of TSH molecule or TSHR by binding of both bTSH and MoAb.

Production and characterization of specific monoclonal antibodies of the human thyroid stimulating hormone

Spleen cells from BALB/c mice immunized with human thyroid stimulating hormone (beta-subunit) were fused with mouse myeloma cells (P3/X63-Ag8) and five hybridomas secreting monoclonal antibodies (MAbs) were obtained. These hybridomas specifically recognize (hTSH) and do not cross-react with the other human glycoprotein hormones such as: luteinizing hormone (LH), follicle-stimulating hormone (FSH) and human chorionic gonadotropin (hcG). The MAbs were of the IgG1 subclass and ascitic fluid from these hybridomas was purified by affinity chromatography on Protein A-sepharose CL-4B column to isolate the IgG1 active fraction. The affinity constant of these MAbs ranged from 3.2 x 10(10) to 1.5 x 10(11) M(-1).

Contribution of Specific Disulphide Bonds to Two Epitopes of Thyrotropin beta-Subunit Associated with Receptor Recognition

In previous studies, we have shown that two epitopes of bovine thyrotropin beta-subunit that are recognised by the monoclonal antibodies designated mAb 279 and mAb 299 are also associated with the receptor-binding site of bovine thyrotropin. The present investigation has examined the role of the six disulphide bonds of bovine thyrotropin beta-subunit in the conformational stabilisation of these two epitopes, and hence assessed the relative contribution that these disulphide bonds make to the stabilisation of the receptor-binding region of the beta-subunit. The experimental procedure involved the production of several bovine thyrotropin beta-subunit-related derivatives in which an increasing number of the disulphide bonds were selectively reduced with dithiothreitol and alkylated with iodoacetic acid. Antibody-binding properties of these derivatives were then evaluated in thyrotropin beta-subunit-specific immunoassays based on the use of the well characterised mAb 279 and mAb 299, to determine the effect of disulphide bond reduction and alkylation on each epitopic specificity. In separate experiments, the residual disulphide bonds that remained intact following these selective partial reductive alkylation procedures were then fully reduced and alkylated with the fluorescent reagent 5-N-[(iodoacetamidoethyl)amino]naphthalene 1-sulphonic acid. The relative contribution of individual disulphide bonds in the stabilisation of each epitope could then be assessed after application of reverse-phase HPLC peptide mapping methods. Epitope recognition by mAb 279 was not dependent on the preservation of the so-called determinant loop Cys88-Cys95 disulphide bond nor directly involved binding interactions via the Cys2-Cys52, Cys27-Cys83, and Cys31-Cys85 disulphide bonds. However, the experimental results indicated that the mAb 279 epitope was stabilised by the Cys19-Cys105 and Cys16-Cys67 disulphide bonds, which is consistent with other data on the role of the C-terminal region of the thyrotropin beta-subunit in this epitope. In contrast, the presence of an intact Cys88-Cys95 disulphide bond was required for the stabilisation of the mAb 299 epitope, although the location of this disulphide bond is distal to the hairpin loop structure that constitutes the mAb 299 epitope. These results on the relative contribution of these disulphide bonds are also discussed in terms of their relationship to the stabilisation of the predicted region of bovine thyrotropin beta-subunit involved in receptor binding.

Immunochemical characterization of two thyroid-stimulating hormone beta-subunit epitopes

The epitopes of human thyroid-stimulating hormone (hTSH) recognized by two murine monoclonal antibodies (MAbs), designated MAb 279 and MAb 299, have been characterized. These MAbs are highly specific for the beta-subunit of TSH. The epitope recognized by MAb 279 appears to be completely conserved between bovine and human TSH and partially conserved in the porcine species. The TSH beta-subunit epitope recognized by MAb 299 is only partially conserved between the human, bovine and porcine species. Both MAbs are capable of inhibiting the binding of TSH to its receptor in a TSH radioreceptor assay, indicating that the epitopes either coincide or are located close to the TSH beta-subunit receptor-binding sites. The carbohydrate moieties of the TSH beta-subunit appear to play little or no role in the epitope recognition by MAb 279 or MAb 299 while the integrity of the disulphide bonds are essential. The epitopic recognition may also involve lysine residues, as determined by the immunoreactivity with both MAbs following citraconylation of TSH. In addition, the amino acid sequence region between residues bTSH beta 34-44 could be excised by trypsin digestion of bovine TSH beta (bTSH beta) without eliminating epitopic recognition by either MAb. These results provide further insight into the relationship between the structure of the TSH beta-subunit epitopes and location of the receptor-binding sites.

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.

Subunit interaction of human chorionic gonadotropin (hCG) with rat ovarian luteinizing hormone (LH)/CG receptor

The subunit interaction of hCG with its rat ovarian LH/CG receptor was studied by cross-linking the solubilized receptor-hormone complex with glutaraldehyde (GA), disuccinimidyl suberate (DSS) or dithiobis(succinimidyl propionate) (DSP) and analyzing the complexes by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and autoradiography. The hormone was labeled either in its alpha-subunit (125I-hCG) or in its beta-subunit (3H-hCG) or the label (3H) was introduced into the receptor molecule instead of the hormone. All of the labeling procedures led to the detection of only the receptor-(alpha,beta)hCG and receptor-(alpha)hCG complexes on the autoradiograms. The sizes of these complexes were 137,000 and 106,000, respectively, under reducing conditions. These results suggest that the receptor binds one hormone molecule, and that hCG interacts with the receptor mainly through its alpha-subunit. In addition, polyclonal antibodies directed against the LH/CG receptor and the alpha- and beta-subunits of hCG were used to detect the non-reduced receptor-(alpha,beta)hCG complex in immunoblotting. As antibodies directed against both the alpha-subunit and the beta-subunit were able to detect the Mr 130,000 complex, it is conceivable that both of the subunits are at least partially exposed on the receptor-hormone complex. 125I-hCG was also cross-linked to the membrane-bound receptor. The membrane-bound complex had an Mr of 144,000 under reducing conditions, i.e. approximately 7000 higher than that of the solubilized complex (Mr 137,000). This may indicate that the membrane-bound receptor is covalently modified or differs in conformation from the solubilized receptor.