title: Affinity-enrichment of thyrotropin receptor autoantibodies from Graves' patients and normal individuals provides insight into their properties and possible origin from natural antibodies.
abstract: We used purified recombinant TSH receptor (TSHR) antigen prepared in mammalian cells to affinity-enrich TSHR autoantibodies from Graves' patients' IgG. Autoantibody enrichment, assayed by TSH binding inhibitory activity, was 20- to 1000-fold. Thyroid-stimulating antibody activity enrichment, although more difficult to quantitate, was comparable. TSHR-autoantibody approximate affinities for the holoreceptor assessed indirectly by TSH binding inhibition were 4-27 x 10(-9) m, an underestimate because 100% TSHR autoantibody purity was not attained. Consistent with previous data for serum, highly enriched TSHR autoantibodies in three of four patients showed lambda light chain bias. However, in contrast to expectations, antigen-enriched IgG was skewed primarily toward IgG2 and IgG3, subclasses associated with polysaccharides and microorganisms, respectively. Subclass depletion studies on antigen-enriched IgG indicated that TSHR autoantibodies were predominantly IgG1 and, surprisingly, IgG4. As controls, we affinity-enriched pooled IgG from normal individuals on TSHR antigen. This enriched IgG had detectable TSH binding inhibitory activity, although with lower specific activity than, and lacking the thyroid stimulatory activity of, Graves' IgG. Moreover, these natural IgG class autoantibodies largely recognized the same conformational variation in the TSHR N-terminal region as disease-associated TSHR autoantibodies. These studies suggest that TSHR autoantibodies may arise from natural autoantibodies, possibly by class switching from cross-reacting antibodies to microorganisms.
authors.affiliation: Cedars-Sinai Medical Center, 8700 Beverly Boulevard, Suite B-131, Los Angeles, California 90048, USA.
authors.forename: Francesco
authors.initials: F
authors.lastname: Latrofa
authors.forename: Gregorio D
authors.initials: GD
authors.lastname: Chazenbalk
authors.forename: Pavel
authors.initials: P
authors.lastname: Pichurin
authors.forename: Chun-Rong
authors.initials: CR
authors.lastname: Chen
authors.forename: Sandra M
authors.initials: SM
authors.lastname: McLachlan
authors.forename: Basil
authors.initials: B
authors.lastname: Rapoport
mesh_terms: D000906:Antibodies / Q000276:immunology*; D000915:Antibody Affinity; D001323:Autoantibodies / Q000276:immunology*; D006111:Graves Disease / Q000276:immunology*; D006801:Humans; D017578:Immunoglobulin Class Switching; D007074:Immunoglobulin G / Q000145:classification / Q000276:immunology; D018828:Immunoglobulins, Thyroid-Stimulating; D011989:Receptors, Thyrotropin / Q000276:immunology*
chemical_list: D000906:Antibodies; D001323:Autoantibodies; D007074:Immunoglobulin G; D018828:Immunoglobulins, Thyroid-Stimulating; D011989:Receptors, Thyrotropin; C094372:thyrotropin-binding inhibitory immunoglobulin