Genetically-controlled severity of autoimmune thyroiditis in Obese strains (OS) chickens is expressed at both the humoral and cellular effector mechanism levels.

Two lines of Obese strain (OS) chickens of identical MHC (B) genotype, B5B5, bred over 10 years with different selection parameters, differ in their severity of spontaneous autoimmune thyroiditis. To determine whether alterations in immune responsiveness underly this discrepancy, the two lines were compared for their thyroiditis effector mechanisms. The OS B5B5 chickens, selected for high levels of serum thyroglobulin autoantibody, had correspondingly 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. These results thus emphasize the importance of the non-MHC locus controlling immune responsiveness, in the 3 locus-model for this autoimmune disorder.