Lack of correlation between Marena tumor induction and expression of endogenous avian RNA tumor virus genome.

Infection with Marek's disease virus (MDV) and subsequent tumor development failed to induce the expression of endogenous avian RNA tumor virus genome in Line-15I and Line-7 chickens which lacked such expression at 1 day of age. Titers of avian leukosis virus (ALV) group-specific (gs) antigen detected by the COFAL test and expression of chick helper factor (chf) activity remained relatively constant in birds which expressed these genome functions at hatching time. Endogenous ALV belonging to the E-subgroup was isolated from two of 50 birds; both were controls not exposed to MDV. There was no correlation between expression of ALV genome (gs or chf) at 1 day of age and the rate of tumor development subsequent ot MDV infection. It was concluded that MDV infection can induce tumors without the participation of endogenous ALV genome.