A human monoclonal autoantibody to the thyrotropin receptor with thyroid-stimulating blocking activity.
BACKGROUND
Human monoclonal autoantibodies (MAbs) are valuable tools to study autoimmune responses. To date only one human MAb to the thyrotropin (TSH) receptor (TSHR) with stimulating activity has been available. We now describe the detailed characterization of a blocking type human MAb to the TSHR.


METHODS
A single heterohybridoma cell line was isolated from the peripheral blood lymphocytes of a patient with severe hypothyroidism (TSH 278 mU/L) using standard techniques. The line stably expresses a TSHR autoantibody (5C9; IgG1/kappa). Ability of 5C9 to bind and compete with 125I-TSH or TSHR antibodies binding to the TSHR was tested using tubes coated with solubilized TSHR. Furthermore, the blocking effects of 5C9 on stimulation of cyclic AMP production was assessed using Chinese hamster ovary (CHO) cells expressing the wild-type human TSHR or TSHRs with amino acid mutations.


RESULTS
5C9 IgG bound to the TSHR with high affinity (4 x 10(10) L/mol) and inhibited binding of TSH and a thyroid-stimulating human monoclonal autoantibody (M22) to the receptor. 5C9 IgG preparations inhibited the cyclic AMP-stimulating activities of TSH, M22, serum TSHR autoantibodies and thyroid-stimulating mouse monoclonal antibodies. Furthermore 5C9 reduced the constitutive activity of wild-type TSHR and TSHR with some activating mutations. The effect of different amino acid mutations in the TSHR on 5C9 biological activity was studied and TSHR Lys129Ala or Asp203Ala completely abolished the ability of 5C9 to block TSH-mediated stimulation of cyclic AMP production.


CONCLUSIONS
The availability of 5C9 provides new opportunities to investigate the binding and biological activity of TSHR blocking type autoantibodies including studies at the molecular level. Furthermore, monoclonal antibodies such as 5C9 may well provide the basis of new drugs to control TSHR activity including applications in thyroid cancer and Graves' ophthalmopathy.
Sanders
Jane
J
FIRS Laboratories, RSR Ltd, Llanishen, Cardiff, United Kingdom.
Evans
Michele
M
Betterle
Corrado
C
Sanders
Paul
P
Bhardwaja
Anshu
A
Young
Stuart
S
Roberts
Emma
E
Wilmot
Jane
J
Richards
Tonya
T
Kiddie
Angela
A
Small
Kasemsri
K
Platt
Hayley
H
Summerhayes
Sara
S
Harris
Rebecca
R
Reeve
Magnus
M
Coco
Graziella
G
Zanchetta
Renato
R
Chen
Shu
S
Furmaniak
Jadwiga
J
Smith
Bernard Rees
BR
D000328:Adult; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology* / Q000494:pharmacology* / Q000627:therapeutic use; D001323:Autoantibodies / Q000097:blood; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D049970:Graves Ophthalmopathy / Q000188:drug therapy; D006801:Humans; D007037:Hypothyroidism / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010053:Ovary / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D011989:Receptors, Thyrotropin / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D013961:Thyroid Gland / Q000187:drug effects* / Q000378:metabolism; D013964:Thyroid Neoplasms / Q000188:drug therapy
D000911:Antibodies, Monoclonal; D001323:Autoantibodies; D011989:Receptors, Thyrotropin; D000242:Cyclic AMP