Thyroid glands affected by Graves' disease (GD) show striking leukocytic infiltration, mainly by T-cells. The mechanisms by which the various leukocytes are maintained in the thyroid are unknown. Growth-regulated oncogene-(GRO-) in interaction with its receptor CXCR2 is a chemoattractant for both T-cells and neutrophils and may be one of the chemokines involved in the cell maintenance. GRO-and CD18 mRNA as a marker of leukocytic infiltration were quantified in thyroid tissue using competitive

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... -PCR. We found very high GRO-mRNA levels in all thyroid tissues. In GD patients (n=16), the GRO-mRNA did not correlate with the CD18 mRNA level or thyroid peroxidase and TSH-receptor antibodies in patients' sera. In thyroid autonomy (n=10), the GRO-mRNA levels were significantly lower in autonomous single adenomas compared with the corresponding normal tissue. In order to define the cellular source of GRO-mRNA and protein, we examined various thyroidderived cells. Thyrocytes, thyroid-derived leukocytes and fibroblasts showed basal GRO-mRNA and protein expression, which was remarkably upregulated by different stimuli in vitro. The expression of GRO-by thyroid carcinoma cell lines confirms that thyrocytes may actually produce GRO-. As shown by flow cytometry and immunohistology, CD68 + monocytes/macrophages are the only cell population strongly expressing CXCR2 in the thyroid.