Mediators of lymphocyte infiltration in inflammatory thyroid disease have yet to be identified. Here we examine the ability of IL-1beta to enhance the production of chemoattractants by human thyrocytes. Primary cultures, when treated with the cytokine, release T lymphocyte chemotactic activity. The effect of IL-1beta is time dependent, and the chemoattraction activity can be partially attenuated by the addition of either anti-IL-16 or anti-regulated upon activation, normal T cell expressed, and secreted (RANTES) neutralizing antibodies. IL-16 is a CD4(+)-specific ligand, and RANTES is a C-C type chemokine that targets monocytes and lymphocytes. These chemoattractants could be detected by specific ELISAs in conditioned medium from IL-1beta treated thyrocytes. Northern analysis revealed that thyrocytes express high constitutive levels of IL-16 mRNA, which were invariant with regard to IL-1beta (10 ng/ml) or glucocorticoid treatment. RANTES mRNA was not detected in control cultures but was strongly induced by the cytokine. IL-16 but not RANTES expression was dependent on the activity of caspase-3. Pro-IL-16 protein could be detected in homogenates of thyroid tissue from patients with multinodular goiter and Graves' disease. Thus, human thyrocytes, through the expression of chemoattractants, may participate in the recruitment of lymphocytes to the thyroid in inflammatory states.