ADHERENCE OF RFD-1 POSITIVE DENDRITIC CELLS TO THE BASAL SURFACE OF THYROID FOLLICULAR CELLS IN GRAVES-DISEASE

HLA-DR positive cells infiltrating Graves' thyroid tissue were examine d for their expression of cell-specific immunological markers using li ght and electron microscopic immunostaining of frozen sections and iso lated open thyroid follicles. Graves' glands (n = 21) were enriched of CD68 and Leu-M5/CD11c positive monocytes/macrophages as well as CD4 a nd CD8 lymphocytes. These cell types were distributed juxtafollicular as well as in other tissue areas. Only the RFD-1 antibody, considered to label antigen-presenting cells including dendritic cells, identifie d cells invariably located close to the interstitial follicular surfac e. After follicle isolation, RFD-1 cells were enriched compared to Leu -M5 cells and exclusively adherent to the follicular epithelium. The p lasma membrane of RFD-1 positive cells were in intimate contact with t he basolateral membrane of the thyrocytes, sometimes extending deeply into the intercellular space of the epithelium. Parallel labelling exp eriments suggested that the follicle-adhering RFD-1 cells also express ed HLA-DR. Our findings show that in human thyroid glands with Graves' disease RFD-1 positive cells with a dendritic morphology establish di rect contact with the follicular epithelium. In view of the fact that both HLA-DR and RFD-1 are associated with antigen-presenting functions it is suggested that a direct interaction of dendritic cells with thy rocytes might be an important component of the autoimmune reaction in Graves' disease.