Abstract
Two lines of Obese strain (OS) chickens of identical MHC [major histocompatibility complex] (B) genotype, B5B5, bred over 10 yr with different selection parameters, differ in their severity of spontaneous autoimmune thyroiditis. To determine whether alterations in immune responsiveness underly this discrepancy, the 2 lines were compared for their thyroiditis effector mechanisms. The OS B5B5 chickens, selected for high levels of serum thyroglobulin autoantibody, had corresondingly higher levels of thyroid-specific cytotoxic cells and also antibody dependent cellular cytotoxicity (ADCC) than the equivalent B5B5 line selected solely for the phenotypic trait of hypothyroidism. The importance of the non-MHC locus controlling immune responsiveness, in the 3 locus-model for this autoimmune disorder was emphasized.