Lymphocytic thyroiditis in dogs; induction with a local graft-versus-host reaction.

Fifty million allogeneic canine lymphocytes were injected in the left lobe of the thyroid gland of 10 dogs. The left lobe of the gland was surgically removed at 1 and 4 weeks after injection. The intrathyroidal injection of immunocompetent cells resulted in local graft vs host reaction within the thyroid gland. Multifocal infiltration of lymphocytes, plasma cells, and macrophages associated with scattered, isolated, or small groups of degenerated follicular cells were present in the follicular wall and colloid on day 7. Thyroidal lesions at 1 month after injection were characterized by extensive destruction of follicular cells, disseminated foci of mononuclear cell infiltration, and electrondense deposits between follicular cells and the basement membrane. The contralateral (noninjected) lobe of the thyroid gland at 4 weeks after injection was infiltrated by lymphocytes, macrophages, and many plasma cells. The inflammatory lesions were associated with multifocal areas of degeneration of follicular cells and focal electron-dense thickenings of the basement membrane. The noninjected lobe, following hemithyroidectomy at 1 week after injection of the thyroid gland undergoing graft-vs-host reaction, either had a focal infiltration of polymorphonuclear leukocytes, lymphocytes, macrophages, and mast cells or had no significant lesions.