Allelic complementation between MHC haplotypes B(Q) and B17 increases regression of Rous sarcomas

Major histocompatibility (B) complex haplotypes B(Q) and B17 were examined for their effect on Rous sarcoma outcome. Pedigree matings of B(Q)B17 chickens from the second backcross generation (BC2) of Line UCD 001 (B(Q)B(Q)) mated to Line UCD 003 (B17B17) produced progeny with genotypes B(Q)B(Q), B(Q)B17, and B17B17. Six-week-old chickens were injected with subgroup A Rous sarcoma virus (RSV). The tumors were scored for size at 2, 3, 4, 6, 8, and 10 weeks postinoculation. A tumor profile index (TPI) was assigned to each bird based on the six tumor scores. Two experiments with two trials each were conducted. In Experiment 1, chickens (n = 84) were inoculated with 30 pock-forming units (pfu) RSV. There was no significant B genotype effect on tumor growth over time or TPI among the 70 chickens that developed tumors. Chickens (n = 141) were injected with 15 PFU RSV in Experiment 2. The B genotype significantly affected tumor growth pattern over time in the 79 chickens with sarcomas. The B(Q)B17 chickens had the lowest TPI, which was significantly different from B17B17 but not B(Q)B(Q). The data indicate complementation because more tumor regression occurs in the B(Q)B17 heterozygote than in either B(Q)B(Q) or B17B17 genotypes at a 15 pfu RSV dose and significantly so compared to B17B17. By contrast, the 30 pfu RSV dose utilized in the first experiment overwhelmed all genotypic combinations of the B(Q) and B17 haplotypes, suggesting that certain MHC genotypes affect the immune response under modest levels of viral challenge.