Allelic complementation between MHC haplotypes B-Q and B-17 increases regression of Rous sarcomas

Major histocompatibility (B) complex haplotypes B-Q and B-17 were examined for their effect on Rous sarcoma outcome. Pedigree matings of (BB17)-B-Q ch ickens from the second backcross generation (BC2) of Line UCD 001 ((BBQ)-B- Q) mated to Line UCD 003 ((BB17)-B-17) produced progeny with genotypes (BBQ )-B-Q, (BB17)-B-Q, and (BB17)-B-17. Six-week-old chickens were injected wit h 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 ino culated with 30 pock-forming units (pfu) RSV. There was no significant B ge notype effect on tumor growth over time or TPI among the 70 chickens that d eveloped tumors. Chickens (n = 141) were injected with 15 PFU RSV in Experi ment 2. The B genotype significantly affected tumor growth pattern over tim e in the 79 chickens with sarcomas. The (BB17)-B-Q chickens had the lowest TPI, which was significantly different from (BB17)-B-17 but not (BBQ)-B-Q. The data indicate complementation because more tumor regression occurs in t he (BB17)-B-Q heterozygote than in either (BBQ)-B-Q or (BB17)-B-17 genotype s at a 15 pfu RSV dose and significantly so compared to (BB17)-B-17. By con trast, the 30 pfu RSV dose utilized in the first experiment overwhelmed all genotypic combinations of the B-Q and B-17 haplotypes, suggesting that cer tain MHC genotypes affect the immune response under modest levels of viral challenge.