Latency versus persistence or intermittent recurrences: evidence for a latent state of murine cytomegalovirus in the lungs

Abstract

The state of cytomegalovirus (CMV) after the resolution of acute infection is an unsolved problem in CMV research. While the term "latency" is in general use to indicate the maintenance of the viral genome, a formal exclusion of low-level persistent productive infection depends on the sensitivity of the assay for detecting infectious virus. We have improved the method for detecting infectivity by combining centrifugal infection of permissive indicator cells in culture, expansion to an infectious focus, and sensitive detection of immediateearly RNA in the infected cells by reverse transcriptase PCR. A limiting-dilution approach defined the sensitivity of this assay. Infectivity was thereby found to require as few as 2 to 9 virion DNA molecules of murine CMV, whereas the standard measure of infectivity, the PFU, is the equivalent of ca. 500 viral genomes. Since murine CMV forms multicapsid virions in most infected tissues, the genome-to-infectivity ratio is necessarily >1. This assay thus sets a new standard for investigating CMV latency. In mice in which acute infection was resolved, the viral DNA load in the lungs, a known organ site of CMV latency and recurrence, was found to be 1 genome per 40 lung cells, or a total of ca. 1 million genomes. Despite this high load of CMV DNA, infectious virus was not detected with the improved assay, but recurrence was inducible. These data provide evidence against a low-level persistent productive infection and also imply that intermittent spontaneous recurrence is not a frequent event in latently infected lungs.

Evolution of diverse antiviral CD8+ T cell populations after murine cytomegalovirus infection

“…“effector” memory) 1, 4. MCMV is believed to undergo continuous low‐level reactivation throughout latency, but only certain genes may be expressed under conditions of normal immune pressure 5–7. These immunological data support a hypothesis initially proposed some years ago 6, 8 that presentation of antigens expressed early during the virus replication cycle is continuous throughout the latent period, resulting in both sustained activation and proliferation of antigen‐specific CD8 + T cells.…”

Control of Cytomegalovirus in Bone Marrow Transplantation Chimeras Lacking the Prevailing Antigen-Presenting Molecule in Recipient Tissues Rests Primarily on Recipient-Derived CD8 T Cells

“…The in vitro depletion of CD8 and CD4 T cells was achieved by two cycles of treatment with the relevant MAbs and complement (47). Recipients were infected with 10 5 PFU of purified murine CMV (25) strain Smith (ATCC VR-194), injected subcutaneously in the left hind footpad about 2 h after BMT or T-cell transfer.…”

Vaccine Vectors Harnessing the Power of Cytomegaloviruses

“…Nevertheless, experiments in animal models infected with the orthologous virus have proven useful in advancing the understanding of HCMV infection, pathogenicity and immunity [4]. Two shared cardinal features of CMV infection are (i) viral persistence in absence of overt replication but associated with reactivation capability defined as "latency" [5,6] and (ii) the induction of a large pool of functional antigen-specific T cells in the periphery that follow expanding kinetics [7][8][9]. This latter phenomenon is referred as "memory inflation" (MI) due to the fact that CMV-specific T cells accumulate over time [10], comprising on average 10% of CD4 and CD8 T-cell memory compartments in humans [2].…”