Abstract
Thyroid hormone levels were studied in a euthyroid patient with hepatocellular carcinoma. The thyroid gland was normal at autopsy and both antithyroglobulin and antimicrosomal antibodies were undetectable in serum. Serum triiodothyronine (T3) values as measured by different RIA procedures, showed striking discrepancies suggesting the presence of an endogenous T3 binding antibody. The preincubation of the patient's serum with 125I-T3, followed by a precipitation with polyethyleneglycol showed a 74.8% of binding, confirming the presence of an endogenous factor interfering with T3 assays. Agarose electrophoresis of the patient's serum showed that 125I-T3 migrated mainly with the gammaglobulin fraction (60%). When immunoprecipitation tests with different antihuman antiimmunoglobulins were carried out, a positive binding for immunoglobulin G (11.9%), Fab (8.5%) and lambda chain (9.3%) was noted. Scatchard plot analysis showed a binding affinity of 0.77 X 10(9) liter/mol and a binding capacity of 1.02 nmol/liter. These data suggest that the abnormal serum T3 binding was caused by the presence of a T3 antibody which was shown to be an immunoglobulin G specific only for the lambda chain.
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