Exogenous MMTV RNA Loads Are Higher in the Presence of Endogenous <i>Mtv</i> Proviruses

<div><p>(A) RT-PCR indicates higher levels of C3H MMTV RNA in spleens derived from infected BALB/c mice compared to those from infected <i>Mtv</i>-null mice. The numbers above each lane represent separate BALB/c or <i>Mtv</i>-null animals as indicated. Mice injected with cloned HYB-MTV-producing cells are designated HM, whereas mice infected by foster-nursing are designated F. Organs were harvested between 6–15 mo post-infection in BALB/c mice at the time of tumor development, whereas organs from <i>Mtv</i>-null mice were harvested between 10–15 mo post-infection. MT, mammary tumor</p><p>(B) RT-PCR analysis shows lower TBLV levels in <i>Mtv</i>-null versus <i>Mtv</i>-positive strains. Organs were harvested between 4–10 mo post-infection in BALB/c mice at the time of tumor development; organs from <i>Mtv</i>-negative mice were obtained at 10 mo post-infection.</p>