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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.

The hypothesis that replication-competent mouse cytomegalovirus (MCMV) is detectable in severe combined immunodeficient (scid) mice after implantation of latently infected tissue was examined. Sections of latently infected salivary gland from 5 BALB/c mice were implanted into 20 C.B-17 scid mice. Recipient scid mice were sacrificed weekly for 5 weeks, and MCMV infection was detected in target organs using culture and DNA polymerase chain reaction (PCR). All donors were negative by standard culture but positive by DNA PCR. Replicating MCMV was recovered from 9 of 15 recipient scid mouse salivary gland, lung, liver, or spleen samples at postoperative weeks 2-5. No virus was recovered from recipient scid mice at weeks 1 or 12. Transplantation of latently infected tissues into scid mice resulted in rapid reactivation and dissemination of the virus. Further study of this model promises insight into the mechanisms of CMV latency and reactivation.

The spleens of mice latently infected with murine cytomegalovirus were examined by reverse transcription followed by the polymerase chain reaction to assay for transcriptional activity of the viral immediate early 1 gene. Transcripts were detected in 6 of 8 animals at a level between 50 and 500 copies in 200 ng of total cellular RNA. This level appears to be roughly 10-fold higher than that of viral genome even though viral DNA is more readily detectable. These data suggest that a significant fraction of latent murine cytomegalovirus is transcriptionally active in the spleen, which may be indicative of an abortive infection or possibly low-level persistence or a transient reactivation.

The polymerase chain reaction (PCR) was used to detect human immunodeficiency virus type 1 (HIV-1) proviral sequences (gag and env) in nucleated cells from the cerebrospinal fluid (CSF) of 31 HIV-1-positive patients, and the results were compared with clinical and radiologic evidence of neurologic disease. Provirus was detected in 21 patients, of whom 20 had neurologic abnormalities. Provirus was not detected in another 6, all of whom were neurologically normal. No neurologic disease has developed in 4 of these 6 patients for whom 12.8 months of follow-up is available. PCR of CSF nucleated cells from HIV-positive patients provides early, rapid, direct evidence of neurologic involvement.

Transmission of human and murine cytomegalovirus (CMV) with transfusions and organ transplantation suggests that the latent virus is located in multiple organs and perhaps multiple cell types. The direct identification and localization of the latent virus in the normal host has been difficult using standard culture and hybridization techniques. In vitro amplification using the polymerase chain reaction followed by oligonucleotide hybridization can be used to detect murine CMV DNA. When this method was applied to DNA extracted from latently infected mice, it allowed detection of viral nucleic acid not detected by standard Southern hybridization. The results of these studies support the presence of latent murine CMV in multiple organs including the salivary gland, spleen, and kidney. Amplification and detection of viral DNA in purified renal tubule preparations suggest that this may be a site of viral latency and potential source of the virus during renal transplantation.