Effect of pretreatment with toll-like receptor agonists in a mouse model of herpes simplex virus type 1 encephalitis.

Background. We evaluated the effect of pretreatment with Toll-like receptor (TLR) agonists in a mouse model of herpes simplex virus type 1 ( HSV-1) encephalitis. Methods. BALB/c mice received a single intraperitoneal or intranasal injection of polyinosinic: polycytidylic acid ( poly I: C), a TLR3 agonist; lipopolysaccharide (LPS), a TLR4 agonist; oligodeoxynucleotide (ODN), a TLR9 agonist; or control vehicle. Twenty-four hours later, animals were infected with 5000 plaque-forming units of HSV-1. Results. Mice that received intraperitoneal pretreatment with vehicle, LPS, and poly I: C had survival rates of 7%, 13%, and 56%, respectively, and mean life expectancies of 156.80 +/- 9.56, 176.00 +/- 9.24, and 213.00 +/- 7.71 h, respectively (P < .05, poly I: C group vs. other groups). Similarly, intranasal pretreatment with vehicle, LPS, ODN, and poly I: C were associated with survival rates of 20%, 47%, 60%, and 94%, respectively, and mean life expectancies of 153.60 +/- 11.71, 188.80 +/- 12.97, 204.80 +/- 11.73, and 234.00 +/- 5.81 h, respectively (P < .05, ODN and poly I: C groups vs. vehicle group). Pretreatment with intranasal poly I: C induced early expression of several immune genes in the brain and resulted in a significantly lower virus load. Conclusion. TLR3 stimulation by poly I: C 24 h before infection reinforces a natural innate immune mechanism of neuroprotection against HSV-1.