Abstracts

Rationale: Virus infections of the central nervous system (CNS) can result in acute seizures. About 20% of patients who have had viral encephalitis go on to develop epilepsy. We have established a mouse model where about 50% of infected mice have behavioral seizures and recover. After a variable latent period mice go on to develop recurrent spontaneous seizures. We have been exploring how the innate immune response to viral infection can lead to seizures and epilepsy.Methods: C57BL/6 (B6) mice infected with 2x105 plaque forming units of the DA strain of Theiler s murine encephalomyelitis virus (TMEV) develop acute seizures between day 3 and day 10 post infection. By flow cytometry and intracellular cytokine staining we can identify infiltrating macrophages, differentiate them from resident microglia, and determine which cells are producing interleukin (IL)-6. This can be confirmed using chimeric mice where resident cells such as microglial cells are deficient in IL-6 or, conversely, where the macrophages are deficient in IL-6 and the resident cells are wild-type. We are also able to quantify tumor necrosis factor (TNF)-alpha ( )-producing cells in the CNS. Viral titers are determined via viral plaque assays on CNS tissue using BHK cells.Results: We find that following TMEV infection, B6 mice experiencing seizures have enhanced numbers of IL-6-producing infiltrating macrophages in the brains versus control infected animals that are not experiencing seizures. In addition, resident microglial cells produce significantly more TNF- in mice with seizures versus control animals without seizures. When mice were treated with wogonin (an O-methylated flavone), a natural compound from Scutellaria baicalensis, fewer mice developed seizures and there was about a 2-fold reduction in the numbers of infiltrating macrophages. Upon titering virus in the CNS, wogonin did not appear to have anti-viral activity but likely acts to regulate IL-6 and TNF- production.Conclusions: In an animal model for epilepsy, IL-6 produced by infiltrating macrophages and TNF- produced by microglia are involved in the development of seizures. Treating animals with wogonin ameliorates proinflammatory cytokine production resulting in fewer animals developing seizures. Anti-cytokine treatment may prove to be an additional way to modulate seizures.