Comparative effects of immunization of rabbits with human thyroglobulin and human and rabbit thyroid microsomal fractions

Dutch rabbits were immunized with human thyroglobulin and human and rabbit thyroid microsomal fractions. The animals were bled at intervals and their serum was assayed for thyroid-stimulating activity, thyroglobulin haemagglutinins, and total and free thyroxine (T 4 ). Their thyroidal radio-iodine uptake and thyroid histology was also studied. Five out of ten animals immunized with human thyroglobulin developed histological evidence of thyroiditis but none had thyroid-stimulating activity in the serum. Only one out of twenty-six animals immunized with rabbit or human thyroid microsomal fractions had any histological abnormality in the thyroid, but eight had significant amounts of thyroid-stimulating activity in their serum. Although the frequency of the latter response was no greater after immunization with rabbit as compared to human thyroid microsomal fraction, there was a significant increase in serum free T 4 in the group immunized with rabbit tissue. Thyroiditis and rabbit immunologic thyroid stimulator (RITS) formation appear to be completely separable phenomena, and RITS is not a by-product of thyroiditis. The absence of thyroid-stimulating activity in the serum of rabbits immunized with thyroglobulin is further evidence that thyroglobulin is not the important antigen leading to the production of this thyroid-stimulating globulin.