PURPOSE: Fibrocytes (FC) are bone marrow-derived progenitor cells that are more 
abundant and infiltrate the thyroid and orbit in Graves orbitopathy (GO). FCs 
express high levels of thyrotropin receptor (TSHR) and insulin-like growth 
factor-1 receptor (IGF-1R). These receptors are physically and functionally 
associated, but their role in GO pathogenesis is not fully delineated. Treatment 
of FCs with thyroid stimulating hormone (TSH) or M22 (activating antibody to 
TSHR) induces the production of numerous cytokines, including tumor necrosis 
factor α (TNFα). Teprotumumab (TMB) is a human monoclonal IGF-1R blocking 
antibody currently in clinical trial for GO and inhibits TSHR-mediated actions 
in FCs.
AIM: To characterize the molecular mechanisms underlying TSH-induced TNFα 
production by FCs, and the role of IGF-1R blockade by TMB.
DESIGN: FCs from healthy and GD patients were treated with combinations of TSH, 
M22, MG132 and AKTi (inhibitors of NF-κB and Akt, respectively), and TMB. TNFα 
protein production was measured by Luminex and flow cytometry. Messenger RNA 
expression was quantified by real time PCR.
RESULTS: Treatment with TSH/M22 induced TNFα protein and mRNA production by FCs, 
both of which were reduced when FCs were pretreated with MG132 and AKTi 
(p<0.0001). TMB decreased TSH-induced TNFα protein production in circulating FCs 
from mean fluorescent index (MFI) value of 2.92 to 1.91, and mRNA expression in 
cultured FCs from 141- to 52-fold expression (p<0.0001). TMB also decreased 
M22-induced TNFα protein production from MFI of 1.67 to 1.12, and mRNA 
expression from 6- to 3-fold expression (p<0.0001).
CONCLUSION: TSH/M22 stimulates FC production of TNFα mRNA and protein. This 
process involves the transcription factor NF-κB and its regulator Akt. Blocking 
IGF-1R attenuates TSH/M22-induced TNFα production. This further delineates the 
interaction of TSHR and IGF1-R signaling pathways. By modulating the 
proinflammatory properties of FCs such as TNFα production, TMB may be a 
promising therapeutic agent for GO.