Tumor necrosis factor-alpha and interleukin-1 beta play a critical role in the resistance against lethal herpes...

The innate immune response after herpes simplex type 1 (HSV-1) encephalitis could be protective or, paradoxically, implicated in neuronal damage. We investigated the role of the innate immune response in such infection using a C57BL/6 mouse knockout (KO) model for tumor necrosis factor (TNF)-alpha and/or interleukin (IL)-1beta.

Encephalitis was induced by intranasal infection with a clinical strain of HSV-1 in 1-month-old KO or wild-type (WT) mice. Mice were monitored for survival, brain viral load was quantified by real-time polymerase chain reaction, and the inflammatory response was assessed by in situ hybridization in groups of mice killed on days 3-7.

WT mice had a significantly higher mean life expectancy (P=.0001, log-rank test) than other groups. IL-1beta and TNF-alpha KO mice had a similar mean life expectancy, and encephalitis was lethal to all TNF-alpha /IL-1beta-deficient mice. Brain viral loads were lower in WT than in KO mice that had disseminated viral replication in the pons and medulla. Moreover, TNF- alpha and IL-1beta KO mice failed to initiate an adequate immune response, as shown by the virtual absence of expression of proinflammatory molecules in the brain.

These data clearly demonstrate the importance of TNF-alpha and IL-1beta in protection against HSV-1 encephalitis in this mouse model.