THYROID-CELL INJURY IS AN INITIAL EVENT IN THE INDUCTION OF AUTOIMMUNE-THYROIDITIS BY IODINE IN OBESE STRAIN CHICKENS

The present study examines the role of thyroid cell injury in the initiation of autoimmune thyroiditis by iodine in Obese strain (OS) chickens, a strain genetically susceptible to spontaneous autoimmune thyroiditis. OS and normal strain chickens were placed on an iodine depletion regimen started in ovo. This regimen is known to prevent thyroiditis in OS chickens. The chickens were injected with NaI every 24 h for up to 7 days starting at 3 weeks of age. Both strains showed evidence of mild thyrocyte injury 12 h after NaI. However, significant and sustained infiltration, beginning 24 h after NaI, was seen only in the OS. The infiltrating cells were primarily mononuclear. Polymorphonuclear cells were not observed. Immunohistological analysis showed the infiltrate to be composed of CD8 T cells, CD4 T cells, B cells, and macrophages in the ratio 40:20:22:17. The infiltration was sustained and progressive for at least 7 days. Thyroid infiltration after NaI repletion was significantly reduced in OS chickens tolerized to thyroglobulin at hatching. Prior treatment with the antioxidant drug ethoxyquin completely prevented both the thyrocyte injury and the infiltration induced by iodine. Treatment with antioxidant drugs had no effect on the uptake and incorporation of iodine by the thyroid. In summary, 1) iodine caused thyrocyte injury in both OS and normal chickens. 2) The injury was followed by cellular infiltration in the OS, but not in normal chickens. 3) The infiltration appeared to be immune mediated in being primarily lymphocytic and at least partially thyroglobulin sensitive. 4) Prevention of thyroid injury by antioxidant drug treatment also prevented infiltration. We conclude that thyroid cell injury may be an initial event in the induction of autoimmune thyroiditis by iodine.