Lines of chickens selected from a common ancestral population for either resistance or susceptibility to Marek's disease developed contrasting frequencies of particular B alloalleles. Comparison of inoculated sibs in backcross-families revealed that the B alloalleles characterizing the two lines accounted for an eightfold difference in tumor incidence. This genetic difference in tumorigenesis associated with the alloalleles of the major histocompatibility complex is probably expressed through the cell-mediated immune system.

No abstract

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.