An autoimmuno-dominant thyroglobulin epitope characterized by a monoclonal antibody

Hinge-deleted IgG4 blocker therapy for acetylcholine receptor myasthenia gravis in rhesus monkeys

Autoantibodies against ion channels are the cause of numerous neurologic autoimmune disorders. Frequently, such pathogenic autoantibodies have a restricted epitope-specificity. In such cases, competing antibody formats devoid of pathogenic effector functions (blocker antibodies) have the potential to treat disease by displacing autoantibodies from their target. Here, we have used a model of the neuromuscular autoimmune disease myasthenia gravis in rhesus monkeys (Macaca mulatta) to test the therapeutic potential of a new blocker antibody: MG was induced by passive transfer of pathogenic acetylcholine receptor-specific monoclonal antibody IgG1-637. The effect of the blocker antibody (IgG4Δhinge-637, the hinge-deleted IgG4 version of IgG1-637) was assessed using decrement measurements and single-fiber electromyography. Three daily doses of 1.7 mg/kg IgG1-637 (cumulative dose 5 mg/kg) induced impairment of neuromuscular transmission, as demonstrated by significantly increased jitter, synaptic transmission failures (blockings) and a decrease in the amplitude of the compound muscle action potentials during repeated stimulations (decrement), without showing overt symptoms of muscle weakness. Treatment with three daily doses of 10 mg/kg IgG4Δhinge-637 significantly reduced the IgG1-637-induced increase in jitter, blockings and decrement. Together, these results represent proof-of principle data for therapy of acetylcholine receptor-myasthenia gravis with a monovalent antibody format that blocks binding of pathogenic autoantibodies.

A new assay for thyroglobulin concentration in serum using monoclonal antibodies against synthetic peptides

The concentration of thyroglobulin (Tg) measured by radioimmunoassay (RIA) or enzyme-linked immunosorbent assay (ELISA) is greatly affected by the presence of anti-Tg autoantibodies in sera. We developed a new assay for detecting Tg in the presence of high concentrations of anti-Tg autoantibodies. A 48-kDa fragment was purified from Tg after treatment with V8 protease. This fragment did not appear to bind to two types of monoclonal antibodies (57Ab and 28D3) against a peptide in the C-terminus (amino acids 2735-2748) of Tg and intact Tg, respectively, by ELISA and Western blot analysis. In contrast, anti-Tg autoantibody or anti-Tg polyclonal antibody reacted well with this fragment. Our new ELISA used 57Ab as a solid phase antibody and 28D3 as a antibody conjugated to horseradish peroxidase. Buffer containing purified 48-kDa fragment was used to neutralize autoantibodies against Tg. With this assay, the recovery of Tg was 84.0-89.6% in normal healthy donors (n=5) in the presence of immunoglobulin G (IgG) purified from sera positive for anti-Tg autoantibody, and 76.2-104.4% in patient sera Grave's disease (n=15). Furthermore, the Tg concentrations in sera from patients with Grave's disease (n=20) ranged from 25 to 526 ng/ml, even though the Tg concentration, as measured by a commercial RIA did not exceed 55 ng/ml. There was good agreement between Tg concentrations measured by new Tg-ELISA and commercial Tg-RIA in sera that were negative for anti-Tg autoantibody. Overall, our new ELISA containing a Tg fragment to neutralize the presence of autoantibodies, showed good sensitivity and precision, and may be useful for routine use. Further investigations with the new assay should allow wider assessment of the prevalence and pattern of thyroid autoimmunity or thyroid neoplasms.

Tryptic peptides of human thyroglobulin: I. Immunoreactivity with murine monoclonal antibodies

Human thyroglobulin (Tg) was treated with trypsin at different concentrations of trypsin/Tg for various incubation times at 37 degrees C using non-reducing conditions. A ratio of trypsin to Tg of 1:100 (w/w) was optimal to release small peptides that were reactive to murine MoAbs to human Tg. Most peptides were released after only 1 h incubation with trypsin, but these peptides were further degraded at longer incubation times. However, a few small peptides, the largest of which with an apparent molecular weight (MWap) of 40 kD, resisted tryptic digestion up to at least 12 h of incubation. These resistant peptides were further degraded by trypsin at 18-24 h of incubation. Tryptic peptides of Tg, released at 1 h and 4 h of incubation, were analysed for their immunoreactivity to 16 well characterized anti-Tg MoAbs by Western immunoblot. Patterns of peptide recognition of these MoAbs were generally unique. Eight MoAbs reacted with peptides of MWap of 10-25 kD and above. Four other MoAbs reacted with peptides of MWap of 25-43 kD and above, and the remaining four reacted with peptides of MWap > 43 kD. Nine of these MoAbs failed to recognize peptides after reduction, suggesting that the MoAbs bind conformation-dependent epitopes. The above information will promote the development of models relating the structure of Tg to the autoimmune process, and may provide an understanding of those regions of Tg responsible for the induction of autoimmune thyroiditis.

Tryptic peptides of human thyroglobulin: II. Immunoreactivity with sera from patients with thyroid diseases

Tryptic peptides of human thyroglobulin (Tg) were analysed by Western immunoblot for their reactivity to circulating autoantibodies from patients with Hashimoto's thyroiditis (HT), Graves' disease (GD) and thyroid carcinoma, and from normal human controls. Low molecular weight peptides were released after 4 h incubation of Tg with trypsin. The sera of thyroid disease patients reacted with several peptides, but predominantly bound three peptides with apparent molecular weights (MWap) of 25 kD, 20 kD, and 15 kD; the sera of normal individuals did not bind these fragments of Tg. The pattern of tryptic peptides recognized by the majority of sera from GD patients differed from that recognized by sera from most patients with HT. Autoantibodies from both groups of patients recognized a 15-kD peptide with a high frequency, but the sera from 26/43 (60%) GD patients also recognized a peptide with MWap of 25 kD, whereas the sera from 22/35 (63%) of HT patients recognized a 20-kD peptide. A few sera from patients with thyroid carcinoma reacted with peptides with MWap of 15 and 20-kD, and none bound the 25-kD peptide. The immunoreactivity of autoantibodies in HT sera to the 20-kD peptide paralleled the competitive inhibition of the MoAb 137C1 by these sera. In addition, MoAb 137C1 and Hashimoto's sera showed the same Western immunoblot-binding pattern to Tg tryptic peptides, suggesting that a Hashimoto-associated epitope and the 137C1-binding site are found on the same peptide. These findings suggest that distinct peptides are recognized by Tg autoantibodies from patients with different thyroid diseases.

Thyroid autoimmunity

Antigenic structure remains a major focus in thyroid immunology. The genes for three major thyroid antigens--thyroglobulin, thyroid peroxidase and the thyrotropin receptor--were sequenced in the late 1980's, and epitopes for antibody and T cells have been reported within the last year. In addition, new evidence for selective use of T-cell receptor V gene segments in human thyroid infiltrates may point the way to specific immunotherapy.