RECOMBINANT THYROTROPIN RECEPTOR AND THE INDUCTION OF AUTOIMMUNE THYROID-DISEASE IN BALB C MICE - A NEW ANIMAL-MODEL/

In a preliminary study, we observed the production of TSH binding-inhi biting (TBII) and thyroid-blocking (TBAb) antibodies accompanied by ly mphocytic infiltration of the thyroid in a pool of male BALB/c mice im munized with the extracellular domain (ECD) of the human TSH receptor (TSHR) expressed as a maltose-binding protein (MBP) fusion in bacteria . In the present study we evaluated the humoral response to the same a ntigenic preparation in a new series of individual male and female BAL B/c mice immunized ip on day 0 with 100 mu g MBP-ECD and days 25, 39, and 53 with 50 mu g MBP-ECD in an adiuvant composed of aluminum oxide, magnesium hydroxide, and Bordetella pertussis vaccine. Mice immunized with MBP served as control. Individual sera and immunoglobulins were tested for TBII, TBAb, and thyroid-stimulating antibodies (TSAb) on da ys 0, 32, 46, and 60, and total circulating T-4 levels were measured b y RIA. Animals were killed on day 120, their thyroids were examined hi stologically, the infiltrates were characterized using monoclonal anti bodies specific for T-cells (total, activated, helper, and suppressor) , B-cells, and macrophages. Sera and immunoglobulins G of the MBP-trea ted control group were all negative for TSAb, TBAb, and TBII activity. The receptor-immunized mice, despite having high titers of antibodies to the immunogen in an enzyme-linked immunosorbent assay, displayed a heterogeneous response in terms of biological activity, with 3 of 7 f emale and 4 of 8 male mice having TBAb/TBII activities that persisted and whose activity increased throughout the experiment. No significant TSAb antibody activity was observed. Total T-4 levels were also heter ogeneous even before immunization, but 9 of 15 MBP-ECD-treated mice ha d levels below the normal range after immunization, and 7 of these als o had TBII/TBAb activities. At the end of the experiment, only 4 of th e MBP-ECD-treated female mice survived, but all of them had a severe l ymphocytic infiltration of their thyroid, composed mostly of activated T-cells, although B-cells and macrophages were also present. A simila r infiltrate was seen in 4 of 8 male MBP-ECD-treated mice. No infiltra te was observed in male or female MBP-treated mice. The model describe d demonstrates the feasibility of using the TSHR as an immunogen to ov ercome tolerance and mimics some characteristics of human autoimmune d isease of the thyroid.