Thyroid glands affected by Graves' disease (GD) show striking lymphocytic infiltration, mainly by CD45RO(+) T cells. The mechanisms by which the various lymphocytic subsets are recruited and maintained in the thyroid are unknown. RANTES (regulated on activation, normal T cells expressed and secreted) in interaction with its receptors (CCR1, CCR3, CCR4 and CCR5) may be one of the favorite chemokines involved in the cell trafficking and maintenance. RANTES messenger RNA (mRNA) was quantified in the thyroid tissue of 16 patients with GD and 7 patients with thyroid autonomy (TA), using competitive RT-PCR. We found a clear correlation between the RANTES mRNA level and 1) the degree of T-cell infiltration (r = 0.68), and 2) the level of serum antibodies to thyroid peroxidase (r = 0.76) in GD but not in TA patients. There was no difference between the autonomous nodules and the quiescent surrounding tissue in TA patients. To define the cellular source of RANTES mRNA and protein, we examined various thyroid-derived cells. Lymphocytes showed a markedly higher basal RANTES mRNA and protein level (mean +/- SEM; pg/mL, n = 3; 140 +/- 30) than thyrocytes (12 +/- 5) and fibroblasts (9 +/- 2). Lymphocyte stimulation with PMA enhanced RANTES secretion significantly (4490 +/- 200). Fibroblasts responded to stimulation with interleukin 1 (530 +/- 220) and tumor necrosis factor alpha (2780 +/- 1790), whereas thyrocytes did not. However, some thyroid carcinoma cell lines showed very high basal and stimulated RANTES expression. Lymphocytes expressed the mRNA of all chemokine receptors that bind RANTES. The number of CCR3(+) and CCR5(+) T cells was significantly higher in thyroid-derived leukocytes than in those in the peripheral blood stream. We conclude that RANTES expression, mainly by lymphocytes, is perhaps involved in the maintenance of lymphocytic infiltration and, therefore, in the autoimmune responses in GD.