Experimental allergic thyroiditis in the guinea-pig. A light, fluorescence and electron microscopic study, with particular reference to the migration of lymphocytes through the vessel walls.

Abstract

Thyroiditis was induced in guinea-pigs by the injection of (NH4)2S04 purified thyroglobulin in complete Freund's adjuvant, and the development of the disease was studied at intervals between 5 and 40 days after immunization. Inflammatory reactions, varying from small focal to severe, confluent infiltrations, were observed. In inflamed areas the follicular cells were hypertrophied. In perfusion-fixed thyroids focal accumulations of leucocytes adherent to the vessel wall of capillaries and venules could be seen. Studies with fluorescein isothiocyanate conjugated anti-γ-globulin serum revealed that the inflammatory cells contained γ-globulin. In general the intensity of the fluorescence was moderate, but especially in the more severe forms of thyroiditis scattered strongly labelled cells were seen in the interstitium. In the electron microscope the leucocytes adhering to the vessel wall turned out to be almost exclusively lymphocytes in different stages of transformation, from small lymphocytes to immunoblasts. The transformed lymphocytes traversed the vessel wall through the endothelial cell cytoplasm, and not through the intercellular junctions. Most of the inflammatory cells in the interstitium were lymphocytes exhibiting the same continuous picture of transformation as intravascularly. Further differentiated cells, from the plasmablast, through the proplasmacyte to the mature plasma cell were, however, also found. The thyroid follicles and their lumina were invaded by leucocytes, mainly transformed lymphocytes, but also a few granulocytes. Some of the lymphocytes bulged deeply into the cytoplasm of the follicular cell, often indenting its nucleus, but true emperipolesis was not observed. Penetration of the leucocytes into the follicular lumina appeared to take place through the intercellular spaces. The only changes noted in the follicular cells were the hypertrophy and their occasional deformation by the lymphocytes.