Enhancer dependence of polyomavirus persistence in mouse kidneys

We previously showed that alterations in the enhancer sequence of polyomavirus DNA can alter both the level and the organ specificity of viral DNA replication during the acute phase of infection of newborn mice (R. Rochford, B. A. Campbell, and L. P. Villarreal, J. Virol. 64:476-485, 1990). In this study, we examined whether these enhancer sequence alterations can also affect polyomavirus replication during the persistent phase of infection in vivo. After infection of newborn mice with a mixture of three enhancer variants, the individual organs could select for enhancer-specific viral DNA replication during both the acute and the persistent phases of infection. Contrary to expectations, the ability of some variants to establish a high-level acute infection in some organs (e.g., the pancreas) did not necessarily lead to a persistent infection in those organs. Thus, enhancers can affect acute and persistent infections differently. In addition, some enhancer variants tended to establish a high-level persistent infection in the kidneys immediately following an acute infection; however, in all cases considerable histopathology was associated with these elevated long-term infections, and these mice were always runty. A persistent infection in the kidneys thus appears able to exist in two distinguishable states, a high-level pathological state and a low-level nonpathological state, which can be affected by the viral enhancer sequence.