Replication of endogenous avian retrovirus in permissive and nonpermissive chicken embryo fibroblasts

Abstract

Clones of chicken embryo fibroblasts exogenously infected with the endogenous avian retrovirus were analyzed to examine the replication of this virus in permissive (Gr+) and nonpermissive (Gr-) cells. The results demonstrate that the endogenous virus was capable of infecting both Gr+ and Grcells with equal efficiency. Infected clones of Gr+ and Gr-cells differed, however, in two significant ways. At the time of their initial characterization, the Gr+ clones produced 100to 1,000-fold more virus than the Grclones. Further, the amount of virus produced by Gr+ clones did not change significantly during serial passage of the cells. In contrast, continued passage of the infected Gr-clones resulted in a gradual increase in the amount of virus produced. Individual clones of infected Gr-cells produced infectious virus at rates that, initially, differed by a factor of more than 104. The large differences in the production of virus by these