Abstracts

Rationale: Suitable animal models of viral encephalitis-induced epilepsies are needed to understand the mechanisms involved in post-encephalitis epilepsy development. Because animal models of viral encephalitis are associated with high mortality, most of them are not appropriate to study long-term consequences such as epilepsy. Recently a model has been described, in which C57BL/6J (B6) mice show acute as well as chronic epileptic seizures after intracerebral infection with Theiler's murine encephalomyelitis virus (TMEV). Our and other research with this model suggests, that phagocytic cells play a key role on the seizure generation (Cusick et al. 2013, J Virol, 87, 1849-60; Br_x005F_xDE57__x005F_xDCA0_et al. 2016, Exp Neurol, 279, 57-74), which prompted us to further examine the role of infiltrating macrophages and activated microglia in the development of acute seizures. Methods: We infected B6 mice intracerebrally with the Daniel's strain of TMEV or mock solution. Mice were clinically examined and, flow cytometric analysis of immune cells isolated from brain was performed at 2 and 7 days after infection (dpi). CD45 and CD11b were used to differentiate between macrophages, microglia and other immune cells. In addition, CX3CR1, Ly6C, CD86, and CD206 were used as markers for further characterisation. Results: Two-thirds of B6 mice developed acute seizures within the first week post infection. Flow cytometry revealed accumulation of activated CD45highCD11b+ cells in the brain as early as 2 dpi. Among the activated CD45highCD11b+ cells, CX3CR1 and Ly6C single positive cells were present suggesting this population consisted of microglia and infiltrating monocytes. Staining cells with phenotypic markers (M1-like phenotype: CD86, M2-like phenotype: CD206) revealed a population of macrophages with a mixed M1/M2-phenotype. Conclusions: While the presence and importance of phagocytic cells following TMEV-infection has been described previously, we have further characterized the constituent cell types and cell phenotypes during the early stages of epilepsy development after TMEV-infection. Although differentiation of infiltrating macrophages and activated microglia using flow cytometry (CD45low/hiCD11b+) is common practice, recent research has proven that this method is not fully trustworthy. Hence, microglia reporter mice (Cx3cr1CreER-TdTomato) will be used in upcoming experiments to ensure verisimilitude of current data. Funding: Supported by the N-RENNT network (Lower Saxony Ministry of Science and Culture and Volkswagen Stiftung) and the Studienstiftung des Deutschen Volkes.