MURINE CYTOMEGALOVIRUS IS PRESENT IN BOTH CHRONIC ACTIVE AND LATENT STATES IN PERSISTENTLY INFECTED MICE

Cytomegalovirus induces serious disease in immunosuppressed individual s, often from an ''activated'' persistent infection. Whether the infec tion is chronically active or latent is unknown. Using murine cytomega lovirus (MCMV) in mice as a model system, we examined persistent infec tions in spleen, lung, and bone marrow of infected animals. At 28 days after infection, no virus could be recovered from any organs tested e xcept salivary glands, and here, virus was cleared by 48 days, Virus c ould be retrieved at all times by cocultivation of spleen or lung with permissive cells. In addition, MCMV DNA was always present in spleen, lung, and bone marrow. After acute infection, RNA from the MCMV immed iate early-1 (ie-1) gene was routinely found only in the lung. In sple en and bone marrow, only one sample from each organ examined at these times contained ie-1 RNA, and the RNA in these two samples was present at levels comparable to that found in acute infection. This suggests that the virus had reactivated. The ie-1 RNA found in the lung was pre sent at a much lower RNA:DNA ratio than that found at early times. Tak en together, these results indicate that persistent MCMV exists simult aneously in both chronic active and latent states. (C) 1994 Academic P ress, Inc.