EXPRESSION OF MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-II ANTIGEN IN NOD MOUSE THYROID

Non obese diabetic (NOD) mice spontaneously develop thyroiditis in add ition to diabetes. Mononuclear cells begin to infiltrate the thyroid o f these animals in the first month of life. The expression of major hi stocompatibility complex (MHC) class II (Ia) antigens by cells in the thyroid from NOD mice of various ages with and without thyroiditis was examined. We found that only 1 of the 9 infiltrated thyroids from 18 8-33 day old NOD mice surveyed expressed MHC class II antigens. Theref ore Ia antigen expression appears to be secondary to infiltration and does not initiate the autoimmune process. Fourteen of 17 (82.2%) infil trated and 7 of 11 (63.6%) uninfiltrated thyroids from NOD mice aged 5 1-73 days contained cells expressing Ia antigens. Sixteen of 18 (88.9% ) infiltrated and all 7 of the uninfiltrated thyroids from mice aged > 89 days contained Ia positive cells. These MHC class II expressing cel ls included thyroid epithelial cells (TEC), as well as interstitial ce lls such as macrophages. Ia positive cells in the thyroid have the pot ential of presenting thyroid specific antigen to infiltrating T cells and thereby maintaining or potentiating thyroid autoimmune destruction . Macrophages were observed in thyroid tissue from 9 of 11 (81.8%) inf iltrated and 12 of 15 (80%) uninfiltrated 8-33 day old NOD mice, thyro ids from 11 of 16 (68.7%) infiltrated and 6 of 9 (66.7%) uninfiltrated 51-73 day old NOD mice, as well as 28 of 29 (96.5%) uninfiltrated and all 9 of the uninfiltrated thyroid from NOD mice aged >89 days. Thyro ids from control age matched non autoimmune BALB/c mice were consisten tly Ia antigen negative while macrophages were seen in some of the ani mals aged > 60 days.