Tear Thyrotropin Receptor Stimulator in Normal Smokers and Thyroid Eye Disease Patients

Abstract

Abstract: : Purpose: Stimulating thyrotropin receptor (TSHR) antibodies (TSAb) are the cause of thyrotoxicosis in Graves’ disease (GD) and may be an orbital antigen in thyroid eye disease (TED). The single most important environmental factor exacerbating TED is cigarette smoking. Suggested mechanisms have included nicotine induced HLA-DR expression, increased glycosaminoglycan production by hypoxic fibroblasts and mast cells cytokine release. We have recently reported the presence of IgE antibodies that recognise the (TSHR) in the sera of GD patients and have therefore investigated conjunctival secretions for their capacity to stimulate TSHR. Methods: Non-smokers, smokers and TED patients sera, tears (reflex schirmer strip collection) and TED data were collected in accordance with Bro Taf ethical approval. Tears and sera were examined in a TSAb assay comprising a CHO cell line stably expressing human TSHR linked to a cAMP luciferase reporter. Incubations were carried out in serum free and salt free (enhances antibody stimulation) conditions. Stimulation indicies were calculated, tear stimulation is considered positive when >97^th centile of non-smokers and against euthyroid sera (positive at >1.5). Results: Overall 4/6 smokers and 10/30 TED patients had a TSHR stimulator in their tears in serum free conditions (p=0.18). When incubated in salt free conditions the smokers decreased from 4/6 to 1/6 (McNemar’s test, p=0.25), and the TED patients from 6/20 to 5/20 (NS). In contrast, the serum TSAb increased from 4/30 to 22/30 in TED patients (p<0.001). Serum TSAB was not detected in smokers in either condition. Serum TSAB was not correlated with tear TSHR stimulator (rho=0.1, NS). Serum TSAB was positively correlated with clinical activity score (rho=0.5 p=0.005) but tear stimulator was not (rho=0.1, NS). (Note: Tears positive in serum free conditions when assayed on cells lacking the TSHR show reduced stimulation indicating the effect is via the TSHR) Conclusion: Within the tears of normal smokers and patients with TED there is a factor capable of specifically stimulating the TSHR but it does not behave like TSAB and is not linked to serum TSAB levels. It’s presence in normal smokers may go some way to explain the higher incidence of symptomatic ophthalmopathy in patients with GD given the previously identified orbital expression of TSHR on preadipocytes and adipocytes in TED.

Keywords: autoimmune disease • orbit