Abstract

The lymphoid cells infiltrating the thyroid in three examples of Hashimoto's disease and three examples of focal lymphocytic thyroiditis have been studied by light and electron microscopy. The cell types found were small lymphocytes, plasma cells and plasmablasts, immunoblasts, and cells morphologically intermediate between immunoblasts and small lymphocytes. The infiltrate was similar in the two conditions studied and resembled the cell response found in other conditions thought to be due to delayed hypersensitivity. It is considered that these similarities support the views that focal lymphocytic thyroiditis is a focal form of Hashimoto's disease and that delayed hypersensitivity is important in the pathogenesis of these conditions.