Towards an Antigenic Map of Human Thyroglobulin: Identification of Ten Epitope-bearing Sequences Within the Primary Structure of Thyroglobulin

The aim of this study was to define, at the molecular level, epitopes of thyroglobulin recognized by heterologous antibodies and autoantisera. One hundred thousand clones from a lambda gt 11 human thyroid cDNA library were screened using a rabbit antibody to human thyroglobulin at a 1:2000 dilution. Twenty clones were plaque-purified to homogeneity, and characterization and sequencing of their cDNA inserts showed that they represented four distinct regions of the thyroglobulin molecule, one of them being the 22 carboxyl-terminal amino acids. Rescreening of the library with the same rabbit antibody to human thyroglobulin absorbed with peptides encoded by the carboxyl-terminal clone, led to the definition of six further epitope-bearing fragments of thyroglobulin. The ten regions that we have identified were recognized by ten further rabbit antibodies to human thyroglobulin, showing that they are representative of the repertoire of heterologous epitopes. In contrast, none of the ten heteroepitope-bearing fragments was recognized by sera from ten patients with autoimmune thyroid disease with various titres of thyroglobulin antibodies. Screening of 2 x 10(6) clones from the library using a pool of ten autoantisera (individual sera diluted to 1:1000), and of 1 x 10(6) clones using a single autoantiserum of very high antithyroglobulin titre (diluted 1:400) resulted in no thyroglobulin clones being isolated. The significance of these results to the immune process is discussed.