Variation in susceptibility to avian sarcoma viruses and expression of endogenous avian leukosis virus antigens in specific pathogen-free chicken lines.

Five lines of chickens maintained as specific pathogen-free flocks in Australia were characterized in relation to endogenous antigens and endogenous avian leukosis virus expression. Embryos of line N were predominantly of C/E phenotype, uniformly positive for group-specific antigen and chick helper factor (gs+chf+) and 38% expressed endogenous virus at a very low titre. Embryos of line M4 were uniformly of C/ABE phenotype and were either gs+chf+ or gs-chf+. Line W19 embryos segregated for susceptibility to viruses of subgroup A, B and D and were either of C/E or C/ABE phenotype. The majority of W19 embryos were gs+chf+ with a small proportion being gs+chf-. Line I13 embryos were either of C/0 or C/ABE phenotype, uniformly gs-chf- and 44% of embryos expressed endogenous virus at a low titre. Line S segregated for susceptibility to subgroup E virus and embryos were either of C/E or C/0 phenotype, while the majority of embryos from line S were gs-chf- with some embryos being gs+chf+ or gs-chf+. The degree of interference of gs+chf+ and gs-chf+ phenotypes with subgroup E virus infection was identical with the interference patterns of classical gs+chf+ and gs-chf+ phenotypes. The resistance to infection with avian sarcoma viruses of subgroups E in lines N and M4, and to a degree in line W19, was highly associated with the presence of chf. Resistance to subgroup E virus was independent of chf in lines S and I13, probably being under the control of an independent locus. Cellular restriction of endogenous virus replication existed in all subgroup E virus-susceptible cells of line I13 in contrast to cells of line S which supported replication of endogenous virus. The phenotype of chicken cells for the expression of endogenous gs antigen and chf could accurately be predicted from the test performed on whole blood cells.