Thyroid epithelial cells in autoimmune thyroid disease may interact with pathogenic T cells in the gland, as suggested by the co-occurrence of MHCII expression and previously identified pathogenic T-cell populations, though this interaction has not been directly demonstrated.

Thyroid cells start displaying a molecular signal called MHCII that normally only immune cells use to show foreign proteins to T cells. These thyroid cells also turn on genes that change the local environment, making it easier for harmful T cells to stay active and attack the gland. The presence of both the signal and the harmful T cells in the same tissue suggests they are directly communicating.