Lipopolysaccharide, Tumor Necrosis Factor Alpha, or Interleukin-1β Triggers Reactivation of Latent Cytomegalovirus in Immunocompetent Mice

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Abstract
We have previously shown that cytomegalovirus (CMV) can reactivate in lungs of nonimmunosuppressed patients during critical illness. Our recent work has shown that polymicrobial bacterial sepsis can trigger reactivation of latent murine CMV (MCMV). We hypothesize that MCMV reactivation following bacterial sepsis may be caused by inflammatory mediators. To test this hypothesis, BALB/c mice latently infected with Smith strain MCMV received sublethal intraperitoneal doses of lipopolysaccharide (LPS), tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), or saline. Lung tissue homogenates were evaluated for viral reactivation 3 weeks after mediator injection. Because LPS is known to signal via Toll-like receptor 4 (TLR-4) in mice, further studies blocking this signaling mechanism were performed using monoclonal MTS510. Finally, mice were tested with intravenous TNF-alpha to determine whether this would cause reactivation. All mice receiving sublethal intraperitoneal doses of LPS, TNF-alpha, or IL-1beta had pulmonary reactivation of latent MCMV 3 weeks following injection, and LPS caused MCMV reactivation with kinetics similar to those for sepsis. When TLR-4 signaling was blocked, exogenous LPS did not reactivate latent MCMV. Intravenous TNF-alpha administration at near-lethal doses did not reactivate MCMV. Exogenous intraperitoneal LPS, TNF-alpha, and IL-1beta are all capable of reactivating CMV from latency in lungs of previously healthy mice. LPS reactivation of MCMV appears dependent on TLR-4 signaling. Interestingly, intravenous TNF-alpha did not trigger reactivation, suggesting possible mechanistic differences that are discussed. We conclude that inflammatory disease states besides sepsis may be capable of reactivating CMV from latency.