[Anti-triiodothyronine antibodies in patients with rheumatoid arthritis associated with Hashimoto's thyroiditis].

: Anti-triiodothyronine antibody was found in a case of rheumatoid arthritis associated with Hashimoto's thyroiditis. The patient was a 40 year-old woman who had complained of polyarthralgia, joint-swelling and stiffness for seven years. She had a rheumatoid nodule and showed a positive RA test. Radiographic changes of hands and wrists showed osteoporosis, erosions and narrowing of joint space. Nonsteroidal anti-inflammatory drugs had been used for seven years. The diagnosis of Hashimoto's thyroiditis had been made by open biopsy of the thyroid gland seven years before. Serum T4, TSH, TBG, free T4, free T3 and r-T3 were all normal. On the other hand, serum T3 level was almost unmeasurable by radioimmunoassay. Binding of 125I-T3 to the patient's serum was studied by using polyethylene glycol (PEG) and column chromatography. By using the PEG method, the binding of 125I-T3 to the patient's serum was tenfold compared to control serum. Sephadex G-25 column chromatography (0.9 X 1.5 cm) of 125I-T3 with the patient's serum in the presence of 0.1% ANS showed an early radioactive peak, while control serum did not show an early peak. In the next experiments, the patient's serum was labelled with 125I-T3, mixed with human anti-IgG, IgM, IgA, lambda, kappa, incubated at 4 degrees C for 20 hours and centrifuged for 20 min. Strong binding to the anti-IgG and anti-lambda was detected. The presence of this abnormal T3-binding globulin in the patient's serum may have produced an undetectable T3 level.