Mononuclear cell thyroiditis in rats with graft-versus-host disease.

Rats with graft-versus-host disease (GVHD), induced by injecting spleen cells of parental strain rats (Brown Norway) into non-irradiated (Brown Norway x Lewis) F1 hybrid rats, develop thyroiditis. This is characterized by mononuclear cell infiltration with destruction of the epithelium and a significant reduction in serum thyroid hormone levels. Immunohistochemically, the mononuclear cells consisted mainly of CD8-positive cells and macrophages. These findings provide evidence that the thyroid gland can now be enumerated as one of the target organs during GVHD. The CD8-positive cells may serve as important effector cells in lesion development, either by direct cytotoxicity or by supporting the cytotoxic potential of macrophages.