Experimental autoimmune thyroiditis. II. An immunocytochemical and ultrastructural study of the lesion.

The early steps of thyroid damage in experimentally induced autoimmune thyroiditis in mice were studied. Mice were immunized with 150 micrograms of rat thyroglobulin followed by 20 micrograms of bacterial LPS 3 h later on day 0 and 7. Thyroid glands were obtained on days 14, 21 and 28 in order to be studied by light microscopy, electron microscopy and immunocytochemical techniques. The initial lesion was a focal inflammatory infiltrate composed of lymphocytes and lymphoblasts, and plasma cells as the damage progressed. In some cases an increase in neutrophils, macrophages and eosinophils was also seen. The infiltrate became multifocal and eventually diffuse and in few cases germinal center-like structures were seen. The cellular infiltrate corresponded to IgG, IgM and IgA bearing B cells and to a lesser degree Thy 1.2, Lyt 1 and Lyt 2 bearing T cells. Follicular alterations corresponded to different degenerative states of the follicular cells that in some cases was seen without the participation of lymphoid cells. Another mechanism observed was the migration of small lymphoid cells and plasma cells between the follicular cells.