Thyroid peroxidase autoantibody fingerprints in hypothyroid and euthyroid individuals. I. Cross-sectional study in elderly women.

Human monoclonal immunoglobulin G-class autoantibodies to thyroid peroxidase (TPO), expressed as recombinant F(ab), are powerful tools for analyzing the individual components of polyclonal serum TPO autoantibodies. Four TPO-specific F(ab) interact with epitopes in two closely related domains (A and B) in the immunodominant region on TPO. In the present study, these TPO F(ab) were used to compete for serum autoantibody binding to [125I]TPO to determine the "epitopic fingerprints" in two groups of carefully controlled individuals. All individuals (14 hypothyroid and 32 euthyroid) were elderly women (60-71 yr old) with similar genetic and environmental backgrounds as well as comparable levels of serum TPO autoantibodies. Using the pool of four F(ab), serum TPO autoantibody binding was inhibited to the same extent (approximately 90%) in hypothyroid and euthyroid individuals, demonstrating that the majority of TPO autoantibodies in both groups recognize the TPO immunodominant domain. When tested individually, the F(ab) produced a spectrum of inhibition patterns, ranging from sera preferentially inhibited by domain A F(ab) to sera preferential inhibited by domain B F(ab). The ratio of inhibition by domain A F(ab) to inhibition by domain B F(ab) was similar in hypothyroid (0.11-1.39) and euthyroid (0.21-1.79) women. In conclusion, no difference in TPO autoantibody epitopes was observed in this cross-sectional study of hypothyroid and euthyroid individuals. Longitudinal studies are required to address the question of whether TPO autoantibody epitopic fingerprints are stable over time.