Expression of a murine cytomegalovirus early-late protein in "latently" infected mice.

Monoclonal antibodies were isolated from the spleen of a latently infected mouse to identify possible antigenic markers for latent murine cytomegalovirus infection. One antibody, AM3, was selected for further study. Characterization of the antigen recognized by AM3 confirmed that it is the early-late phosphoprotein pp50. The antigen was readily detected by immunoautoradiography in the spleens of acutely and latently infected mice. Low levels of the AM3/pp50 transcript were also detected in latently infected tissues by in situ hybridization. Presence of AM3/pp50 mRNA, as well as IE-1 transcripts, was confirmed by reverse transcription-polymerase chain reaction in 3 of 5 latently infected spleens. The expression of both immediate-early and early-late classes of viral genes suggests that persistent infection may be a component of the MCMV life cycle operationally defined as latency and that this gene is not specific for latency.