Monoclonal thyroglobulin autoantibodies: variable region analysis and epitope recognition.

Abstract

A panel of human monoclonal thyroglobulin (Tg) autoantibodies (TgAAb) has been used to analyze autoantigenic determinants on human Tg and to investigate the relationship between variable (V) region gene sequences and epitope specificity. Two monoclonal TgAAb bound to the same (or closely related) epitope on Tg, and these were defined as type I TgAAb. Three other monoclonals bound to a different site and were defined as type II TgAAb. Inhibition studies with mixtures of type I and type II monoclonal TgAAb (Fab)2 preparations indicated that a mixture of the (Fab)2s almost completely inhibited (> 75%) labeled Tg binding to intact TgAAb in the sera of apparently healthy blood donors and patients with autoimmune thyroid disease (AITD). Type I TgAAb predominated in apparently healthy blood donors' sera, whereas type II TgAAb predominated in AITD sera. Analysis of V region gene sequences of the TgAAb indicated that a range of light chain and heavy chain genes from different gene families was used. Furthermore, the same germline genes that are used by TgAAb are also well represented in the genes coding for other self- and nonself-reactive antibodies. No homology in terms of light chain and heavy chain gene families, germline gene usage, or complementarity determining region sequences was observed in TgAAb directed to the same or closely related epitopes. Our studies show that TgAAb are directed to two major conformational epitopes on the Tg molecule and that the proportion of TgAAb directed to these epitopes in apparently healthy blood donors and that in patients with AITD appear to be different. TgAAb derived from different germline genes and with different complementarity determining region sequences can display similar epitope specificity, and this indicates that AAb directed to the same or a closely related epitope show considerable heterogeneity at the molecular level.

Thyroglobulin autoantibodies switch to immunoglobulin (Ig)G1 and IgG3 subclasses and preserve their restricted epitope pattern after 131I treatment for Graves' hyperthyroidism: the activity of autoimmune disease influences subclass distribution but not epitope pattern of autoantibodies

“…The epitope pattern of TgAb has long been reported as restricted . Using four human recombinant monoclonal TgAb‐Fab (A, B, C and D), which recognize four different, partially overlapping Tg regions , we confirmed this restriction, particularly in AITD patients .…”

“…The epitope pattern of TgAb has long been reported to be restricted, particularly in AITD . Neither age nor the genetic background influences the epitope pattern of TgAb from HT patients .…”

Iodine, Thyroid Autoimmunity and Cancer

“…We have previously characterized 4 human recombinant monoclonal TgAb-Fab (A, B, C and D) [27,28]. In agreement with the well-known restriction of TgAb epitope pattern [29,30], the 4 TgAb-Fab recognize 4 different but partially overlapping epitopes, A epitope lying at one pole, B epitope at the other pole and epitopes C and D being on the fringe of the immunodominant region of Tg [28]. By inhibiting TgAb binding to Tg with human recombinant monoclonal TgAb-Fab (fig.…”

Thyroid Autoimmunity: Role of Anti-thyroid Antibodies in Thyroid and Extra-Thyroidal Diseases

“…Antibodies against Tg differ between healthy subjects and AITD patients in that polyclonal antibodies are seen in normal subjects and oligoclonal antibodies in AITD patients (4). Antibodies in healthy subjects and AITD patients differentially recognize mainly two conformational epitopes of the molecule (32). Pattern of anti-Tg antibodies are similar in GD and HT patients and similar in healthy individuals and patients with TC (33).…”