THYROID PEROXIDASE AUTOANTIBODY FINGERPRINTS IN HYPOTHYROID AND EUTHYROID INDIVIDUALS .1. CROSS-SECTIONAL STUDY IN ELDERLY WOMEN

Human monoclonal immunoglobulin G-class autoantibodies to thyroid pero xidase (TPO), expressed as recombinant F(ab), are powerful tools for a nalyzing the individual components of polyclonal serum TPO autoantibod ies. Four TPO-specific F(ab) interact with epitopes in two closely rel ated domains (A and B) in the immunodominant region on TPO. In the pre sent study, these TPO F(ab) were used to compete for serum autoantibod y binding to [I-125]TPO to determine the ''epitopic fingerprints'' in two groups of carefully controlled individuals. All individuals (14 hy pothyroid and 32 euthyroid) were elderly women (60-71 yr old) with sim ilar genetic and environmental backgrounds as well as comparable level s of serum TPO autoantibodies. Using the pool of four F(ab), serum TPO autoantibody binding was inhibited to the same extent (similar to 90% ) in hypothyroid and euthyroid individuals, demonstrating that the maj ority of TPO autoantibodies in both groups recognize the TPO immunodom inant 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 r atio of inhibition by domain A F(ab) to inhibition by domain B F(ab) w as similar in hypothyroid (0.11-1.39) and euthyroid (0.21-1.79) women. In conclusion, no difference in TPO autoantibody epitopes was observe d in this cross-sectional study of hypothyroid and euthyroid individua ls. Longitudinal studies are required to address the question of wheth er TPO autoantibody epitopic fingerprints are stable over time.