Detection of human anti-thyroxine and anti-triiodothyronine antibodies in different thyroid conditions.

Abstract

Anti-thyroxine (T4) and anti-triiodothyronine (T3) antibodies have been demonstrated in man. It was assumed that antibodies were at least partially saturated in vivo by the hormones. The initial step of the method therefore consisted in a dissociation of the postulated antigen-antibody complex by a 45% ammonium sulfate precipitation. The second part of the method consisted in incubating the euglobulins with trace amounts of 125I-T3 and 131I-T4. The hormones bound to the gammaglobulins were then separated from the free hormones by a column of DEAE Sephadex A-50 in ammonium acetate 0.05 M pH 7.6. The amounts of 125I and 131I bound to the gammaglobulin fraction were then measured. The results in any unknown sample were compared to those obtained when an equal amount of standard serum was identically treated, and the results were expressed as unknown/standard ratios of bound 125I and bound 131I, respectively. The mean binding ratios for T3 and T4 found in sera obtained from 42 normal subjects were 0.7 +/- 0.4 SD and 0.8 +/- 0.5, respectively. Elevated binding ratios for both T3 and T4 were found in sera obtained from 5 out of 43 cases of primary hypothyroidism and in 2 out of 34 cases of hyperthyroidism. The binding ratios were elevated for only T3 in 10 cases of primary hypothyroidism and in 5 cases of hyperthyroidism. Antibodies against T4 were detected in one case of primary hypothyroidism. High binding ratios for T3 were also observed in one patient with secondary hypothyroidism who had received treatment with dessicated thyroid for several years. In most of the positive sera, anti-thyroglobulin antibodies, as measured by passive hemagglutination, could also be detected. For one serum containing anti-T3 antibody and another containing anti-T4 antibody, the binding affinity and capacity were estimated by Scatchard plot analysis; affinity constants were 5.4 x 10(8) L/mol and 1.3 x 10(9) L-mol, respectively; capacities 1.4 ng/ml and 1.2 ng/ml, respectively. The presence of anti-T3 and anti-T4 antibodies in serum may result in an apparent lowering of the serum T3 and T4 concentrations, respectively.