HLA-DM and invariant chain are expressed by thyroid follicular cells, enabling the expression of compact DR molecules

Thyroid follicular cells (TFC) in Graves' disease (GD) hyperexpress HLA cla ss I and express ectopic HLA class II molecules, probably as a consequence of cytokines produced by infiltrating T cells. This finding led us to postu late that TFC could act as antigen-presenting cells, and in this way be res ponsible for the induction and/or maintenance of the in situ autoimmune T c ell response. Invariant chain (li) and HLA-DM molecules are implicated in t he antigen processing and presentation by HLA class II molecules. We have i nvestigated the expression of these molecules by TFC from Go glands. The re sults demonstrate that class II+ TFC from GD patients also express Ii and H LA-DM, and this expression is increased after IFN-gamma stimulation. The le vel of HLA-DM expression by TFC was low but sufficient to catalyze peptide loading into the HLA class II molecules and form stable HLA class II-peptid e complexes expressed at the surface of TFC, These results have implication s for the understanding of the possible role of HLA class II+ TFC in thyroi d autoimmune disease.