Circulating immunoglobulin E (IgE) antibodies to L-thyroxine in a euthyroid patient with multinodular goiter and...

A 30-yr-old woman with allergic rhinitis and multinodular goiter developed atopic manifestations on different desiccated thyroid extract treatment. Urticaria was observed when the patient was on L-T4 treatment; no atopy was experienced during L-T3 regimen. Serum total immunoglobulin E (IgE) concentration was 390 +/- 7kU/liter (mean +/- SD) prior to any treatment and rose to 850 +/- 7.5 kU/liter when the patient developed urticaria, but declined to baseline figures while she was on L-T3. Intracutaneous testing was positive for desiccated pork thyroid powder, L-T4 and D-T4, but negative for L-T3, DIT and L-tyrosine. Immunoradioligand analyses of mixtures of patient's serum or precipitated immunoglobulin fraction and of 125I-T4 or of 125I-T3 revealed binding of radiolabeled thyroxine to the patient's serum IgE, in turn bound to anti-human-IgE serum covalently coupled to paper discs. This binding was completely inhibited by the preincubation of immunoglobulin fraction with excess unlabeled L-T4 and D-T4, but not with excess nonradioactive L-T3, thus proving the specificity of the binding. Preadsorption experiments performed with desiccated pork thyroid powder solution mixed with the patient's immunoglobulin fraction suggested binding of some unknown component(s) of desiccated thyroid which was apparently not thyroglobulin. This study provides evidence of IgE antibodies to L-T4 cross reacting with D-T4 and capable of binding 125I-T4 in serum. It also suggests a model for the detection of circulating IgE antibodies to thyroid hormones.