Immunopathological studies on thyroid immunity. IX. Thyroid and renal amyloidosis in thyroglobulin immunized rabbits

In serial studies of immunopathologic changes in an animal model of thyroiditis 52 rabbits were immunized with either bovine, porcine or human thyroglobulin (Tg) in Freund's complete adjuvant, while another 47 animals served as noninjected or adjuvant injected controls. The immunized animals were divided into two groups, one receiving an initial series of only three Tg injections while the other received, in addition, challenging injections over an 8-week period. The immunized animals were killed over a period of 6-34 months after the last Tg injection, and untreated controls were killed at comparable ages. In Tg immunized animals, lymphocytic thyroiditis was encountered in 25 per cent and thyroid amyloid in 17 per cent; glomerular amyloid was encountered in 44 per cent with diffuse lesions in 8 per cent, nodular lesions in 17 per cent and a mixture of the two in 19 per cent. That the thyroid and glomerular hyaline deposits contained amyloid was shown by various histochemical criteria, as well as by the presence of typical fibrils on electron microscopy. Immunohistochemical studies indicated that the amyloid was predominantly of the AA type. Rabbits receiving challenging Tg injections, in addition to the initial series, showed only thyroiditis and nodular glomerular lesions most of which were amyloid. Whilst the vast majority of rabbits with lymphocytic or amyloidotic responses showed both thyroid and renal lesions, a small percentage of animals showed only a lesion of one or the other of these two organs. It is of interest that the thyroid and renal amyloid lesions, described for the first time with induced thyroglobulin immunity, were not detected in other earlier short term investigations.