ANALYSIS OF ORBITAL T-CELLS IN THYROID-ASSOCIATED OPHTHALMOPATHY

Thyroid-associated ophthalmopathy (TAO) has a major effect on the two compartments of the retroorbital (RO) space, leading to enlargement of the extraocular muscles and other RO tissues. T lymphocyte infiltrati on of RO tissue is a characteristic feature of TAO and there is curren t interest in whether these T cells are specifically and selectively r eactive to RO tissue itself. We recently established 18 T cell lines ( TCL) from RO adipose/connective tissue of six patients with severe TAO by using IL-2, anti-CD3 antibodies and irradiated autologous peripher al blood mononuclear cells (PBMC) to maintain the growth of T cells re active to autologous RO tissue protein fractions. Here we report on th e phenotype characteristics and cytokine gene expression profiles of t hese orbital TCL and on their immunoreactivity to the organ-specific t hyroid antigens thyrotropin receptor (TSH-R), thyroidal peroxidase (TP O) and thyroglobulin (TG). Flow cytometry revealed that 10 TCL were pr edominantly of CD4(+) phenotype, three being mostly CD8(+) and five ne ither CD4(+) nor CD8(+). Analysis with reverse transcriptase polymeras e chain reaction (RT-PCR) of cytokine gene expression revealed both Th 1- and Th2-like products in all TCL: IL-2 product (in 17 TCL), interfe ron-gamma (IFN-gamma) (n = 10), tumour necrosis factor-beta (TNF-beta) (n = 15), IL-4 (n = 12), IL-5 (n = 17), IL-6 (n = 13), TNF-alpha (n = 12) and IL-10 (n=4). Reactivity to thyroid antigens was observed only in two TCL, the other 16 being uniformly unreactive. Although 10 out of 18 RO tissue-reactive TCL were predominantly CD4(+) there were no s ignificant relationships between TCL phenotype, cytokine gene profile, magnitude of reactivity to RO tissue protein or the (rare) occurrence of thyroid reactivity. The findings of both Th1- and Th2-like cytokin e gene expression in all RO tissue-reactive TCL support the concept th at TAO is a tissue-specific autoimmune disease, distinct immunological ly from the thyroid, and involving both T cell and B cell autoimmune m echanisms in disease pathogenesis.