Inhibitory effect of FK506 on intercellular adhesion molecule-1 (ICAM-1) expression on cultured thyroid cells

The effect of FK506, an immunosuppressive agent, on phytohemagglutinin (PHA) or interferon gamma (IFN gamma)-induced intercellular adhesion molecule-1 (ICAM-1) expression on cultured human thyroid cells from patients with Graves' disease was investigated. Primary cultured thyroid cells were incubated for three days with IFN gamma (10 to 800 U/ml) or PHA (1 to 50 micrograms/ml) in the presence of FK506. The surface expression of ICAM-1 was measured by flow cytometry. In some experiments, polyclonal anti-IFN gamma antibody was added to the culture to determine whether ICAM-1 expression was blocked. FK506 inhibited the PHA-induced ICAM-1 expression in thyroid cells, but not the induction by IFN gamma. PHA-induced ICAM-1 expression was not inhibited by the polyclonal anti-IFN gamma antibody. FK506 did not affect the proliferation of thyroid cells. This data indicates that the inhibitory effect of FK506 on ICAM-1 expression in primary cultured thyroid cells may be due to actions on infiltrating lymphocytes in the thyroid gland. Further studies are necessary to elucidate whether the inhibition of ICAM-1 by FK506 results in the suppression of autoimmune reactions in the thyroid gland.