Regulation of intercellular adhesion molecule-1 expression in human thyroid cells in vitro and human thyroid tissue transplanted to the nude mouse in vivo: role of Graves' immunoglobulins and human thyrotropin receptor.

Abstract

To further explore a potential role for the human TSH receptor (hTSHR) in the propagation of thyroid autoimmune disease, we examined immunomodulatory effects in response to its stimulation by Graves' Igs both in human thyroid tissue transplanted to the nude mouse and in primary cultures of human thyrocytes. We injected nude mice bearing transplants derived from normal human thyroid with protein A-Sepharose-purified Graves' IgGs (0.05-1 mg) on 2 days and assessed, in addition to functional stimulation, the expression of intercellular adhesion molecule-1 (ICAM-1) by transplant thyrocytes. In parallel to functional stimulation, as demonstrated by thyroid follicular cell hypertrophy in the transplants and increased T4 production, Graves' IgGs induced a marked dose-dependent expression of ICAM-1 by transplanted thyrocytes, which exceeded that of a continuous interferon-gamma infusion (200 IU/24 h) for 2 days. Normal IgGs were ineffective. Bovine TSH (bTSH) had little effect by itself, but did enhance interferon-gamma-induced ICAM-1 expression. To assess the specificity of their effects, experiments with Graves' IgGs were conducted in the presence and absence of a selective hTSHR antagonist (asialoagalacto-hCG). Asialoagalacto-hCG nearly completely abolished the stimulatory effect of Graves' IgGs on ICAM-1 expression and significantly reduced the combined bTSH/interferon-gamma effect. It failed, however, to affect interferon-gamma action. In vitro studies using human thyroid cells in primary culture confirmed the in vivo observations, treatment with saline resulted in 14% of cells expressing ICAM-1, with pooled normal IgGs (500 mg/L) in 18% and with Graves' IgGs (patient A, 448 mg/L; patient B, 260 mg/L) in 78% and 51%, respectively. Upon exposure to Graves' IgGs (90 mg/L) plus asialo-hCG(350 mg/L), 25% of the cells stained positively for ICAM-1, 29% to bTSH (10 IU/L), 31% to recombinant human TSH (10 IU/L), and 84% to interferon-gamma (10 IU/mL). In conclusion, stimulation of human thyroid cells, either transplanted to the nude mouse in vivo or studied under in vitro conditions, with Igs derived from patients with Graves' disease increased the expression of ICAM-1 on the surface of the cells. The action appears to be specific and mediated by the hTSHR. This particular property of TSHR autoantibodies may be of pathophysiological relevance in Graves' disease, as it may assist in targeting the autoimmune attack and in promoting lymphocyte recruitment to the thyroid gland.