Responses of chickens lacking or expressing endogenous avian leukosis virus genes to infection with exogenous virus.

Line 0 chickens that lack endogenous viral (ev) genes and 15I5 X 7 chickens that carry and express ev genes were inoculated with the avian leukosis virus, RAV-1, at 1 day of age or as embryos, and maintained to 70 days of age. Comparable uninoculated controls were also kept. Most of the day-old inoculated chickens developed antibody by 70 days, but as expected, most of the embryo inoculated chickens remained viremic. Major differences in response between the lines were only noted after day-old inoculation. About 40% of Line 0 died of a specific nonneoplastic syndrome (NNS) while none of the 15I5 X 7 chickens did. Line 0 also developed neutralizing antibodies at a much earlier age than 15I5 X 7 and, consequently, virus was cleared from the serum much earlier. Day-old RAV-1 infection of Line 0 also lowered hematocrit more at 14 and 21 days of age than in 15I5 X 7 chickens. Body weight was clearly reduced at all ages in both lines of chickens by both day-old and embryo inoculation. After embryo inoculation, hematocrit was lowered in both lines of chickens between 28 and 42 days of age. Immune response to sheep red blood cells and Brucella abortus was only slightly and inconsistently reduced by inoculation of RAV-1 by both routes in both lines of chickens. It was concluded that the major influences of ev gene expression was to reduce the incidence of NNS and the neutralizing antibody response after RAV-1 inoculation of day-old chicks.