Genetic nature of regression of Rous sarcoma virusinduced tumors in crosses of Regional Poultry Research

F 2, and reciprocal backcross progenies of these lines were used to investigate host-gene effects upon the regression of Rous sarcoma virus (RSV)-induced tumors. Lines 6t and 63 were suscepti-ble to subgroup A and C lymphoid leukosis (LL) viruses and line 72 was resistant to subgroup A but was segregating for susceptibility to subgroup C LL virus. Viruses of RSV subgroups A and C were used. Lines 6, , 6 3, and 72 were homozygous for shared blood group alleles B2, Cs, L1, and r. The incidence of tumor regression was higher in line 63 than in 7 2, and in reciprocal F [ crosses of these lines was of the same order of magnitude as in line 6 3. Progeny from F, generation par-ents mated to line 63 had a higher frequency of regression than offspring from F, generation parents mated to line 7 2. The frequency of regression in F2 generation offspring was intermediate between the two backcrosses. The data suggest that either a locus (or loci) other than L and B has a role in Rous tumor regres-sion in this species or the immune response region of the B blood group-major histocompatibility complex differs in the two lines even though the serological and/or graft vs. host regions have not been shown to differ