Murine leukemia virus envelope protein in transgenic-mouse serum blocks infection in vitro

Transgenic mice bearing a murine retroviral envelope transgene (Fv4) have Fv4 gp70env (SU) in their serum in amounts sufficient to block infection by ecotropic virus in vitro. Fv4 Env in serum is derived largely but not exclusively from hematopoietic cells. Tail cells from Fv4 mice and cell lines transduced with the Fv4 env transgene synthesize both components of the envelope protein (gp70 SU and p15E TM) but secrete the gp70 moiety, in the absence of retroviral particles. Blocking of the ecotropic viral receptor by secreted gp70 SU may contribute to resistance to retroviral infection in these mice. Natural resistance to various subgroups of retroviruses in two experimental animals, mice and chickens, is well described. In these systems, resistance is due to inheritance of expressed retroviral envelope (env) genes (13, 34). Resistance is thought to be due to viral interference, a phenomenon first described in vitro in which cells chronically infected by one virus are resis-tant to superinfection with viruses that use the same receptor (36). Interference involves blocking of the viral receptor by the viral envelope protein (Env)