The appearance in thyroidectomized mice of immunoglobulins that bind TSH and stimulate FRTL-5 thyrocytes

Abstract

The purpose of these studies was to examine whether thyroid stimulating antibodies in Graves' patients could arise as auto-antiidiotypic antibodies to endogenous anti-TSH antibodies. The model system chosen was the thyroidectomized mouse, exhibiting an elevated level of endogenous, circulating TSH. Mice were thyroidectomized by 131I administration. Sera samples were drawn 1 to 14 months later. The following activities were measured in the immunoglobulin (Ig) fractions prepared: (a) TSH binding by elisa techniques, (b) iodide pump activity (as measured by 99mTcO4 uptake) and (c) increased [3H]thymidine incorporation into the DNA of FRTL-5 cells. TSH binding Igs were detected in 29/98 mice thyroidectomized for 7\p=n-\14 months. Stimulation of technetium uptake was observed in 59/110 mice and stimulated labeled thymidine uptake in 37/102 mice, beginning eight and nine months after thyroidectomy, respectively. Of the positive animals, 51 showed a single stimulating activity. The incidence and the serum titers of Igs that stimulate technetium uptake increased significantly with time.Indeed, in the group tested 14 months post-thyroidectomy, 75% of the sera were positive for this antibody with a mean titer eightfold higher than the controls. Hybridomas were prepared from the spleen lymphocytes of thyroidectomized mice. Of these, 18 produced 99mTcO4 uptake stimulating Igs,12 [3H]thymidine-uptake stimulating Igs and 18 TSH binding Igs. Most of the hybridomas secreted Igs with a single bioactivity. One monoclonal antibody was isolated which neutralized the bioactivity of bTSH on FRTL-5 cells. 99mTcO4 uptake was decreased by 50% and [3H]thymidine uptake was virtually abolished. These results suggest that the hypothyroid mouse can develop anti-TSH antibodies and thyroid-stimulating antiidiotypic antibodies by an autoimmune process. Several pathological syndromes of the thyroid gland in the human are associated with the appearance of TSH receptor-recognizing immunoglobulins. These could be elicited as primary idiotypes against determinants on the TSH receptor ( 1 ) or as antiidiotypes to previously formed anti-TSH antibodies (abs), in accordance with the immune regulation theory of Jeme (2). The presence of both anti-bovine and anti-human bTSH abs was shown in the sera of some of the thyrotoxic patients, as reviewed by Noh et al. ( 3 ). However, the sequence of appearance of the antibodies could not be shown, neither could their idiotype-antiidiotype relationship be confirmed (4). Several experimental models were set up to examine the possibility that circulating TSH might be recognized by the immune system as nonself, and trigger thyrotoxicosis.Farid and Lo (5) immunized rats with bovine or human TSH and isolated and purified the anti-TSH antibodies which they then injected into rabbits. Some of the antiidiotypic antibodies obtained activated the TSH receptor. Costagliola et al. (6) isolated antiidiotypic abs to a mono¬ clonal anti-hTSH ab, which reacted in various ways with human TSH receptor preparations. Beall et al. (7) ...