Thyroid-stimulating autoantibodies in Graves disease preferentially recognize the free A subunit, not the thyrotropin holoreceptor.
Graves disease is directly caused by thyroid-stimulating autoantibodies (TSAb's) that activate the thyrotropin receptor (TSHR). We observed upon flow cytometry using intact cells that a mouse mAb (3BD10) recognized the TSHR ectodomain with a glycosidylphosphatidylinositol (ECD-GPI) anchor approximately tenfold better than the same ectodomain on the wild-type TSHR, despite the far higher level of expression of the latter. The 3BD10 epitope contains the N-terminal cysteine cluster critical for TSAb action. Consequently, we hypothesized and confirmed that TSAb (but not thyrotropin-blocking autoantibodies [TBAb's]) also poorly recognize the wild-type TSHR relative to the ECD-GPI. Despite poor recognition by TSAb of the holoreceptor, soluble TSHR A subunits (known to be shed from surface TSHR) fully neutralized autoantibody-binding activity. These data indicate that the epitope(s) for TSAb's, but not for TBAb's, are partially sterically hindered on the holoreceptor by the plasma membrane, the serpentine region of the TSHR, or by TSHR dimerization. However, the TSAb epitope on the soluble A subunit is freely accessible. This observation, as well as other evidence, supports the concept that A subunit shedding either initiates or amplifies the autoimmune response to the TSHR, thereby causing Graves disease in genetically susceptible individuals.
Autoimmune Disease Unit, Cedars-Sinai Research Institute and School of Medicine, University of California, Los Angeles, Los Angeles, California, USA.
Gregorio D
GD
Chazenbalk
Pavel
P
Pichurin
Chun-Rong
CR
Chen
Francesco
F
Latrofa
Alan P
AP
Johnstone
Sandra M
SM
McLachlan
Basil
B
Rapoport
D000818:Animals; D000911:Antibodies, Monoclonal; D000918:Antibody Specificity; D001323:Autoantibodies / Q000378:metabolism*; D016466:CHO Cells; D006224:Cricetinae; D003432:Cross-Linking Reagents; D006111:Graves Disease / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D018828:Immunoglobulins, Thyroid-Stimulating; D051379:Mice; D009500:Neutralization Tests; D021122:Protein Subunits; D011989:Receptors, Thyrotropin / Q000737:chemistry / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D013972:Thyrotropin / Q000378:metabolism
D000911:Antibodies, Monoclonal; D001323:Autoantibodies; D003432:Cross-Linking Reagents; D018828:Immunoglobulins, Thyroid-Stimulating; D021122:Protein Subunits; D011989:Receptors, Thyrotropin; D011994:Recombinant Proteins; C094372:thyrotropin-binding inhibitory immunoglobulin; D013972:Thyrotropin