Abstracts

Rationale: Temporal lobe epilepsy (TLE) is the most prevalent form of acquired epilepsy and also the most difficult form of epilepsy to treat with the current anti-seizure drugs. Therefore, new disease modifying therapies are needed to treat and prevent seizures in high risk groups. Although the precise mechanisms that lead to epilepsy remain unclear, evidence from experimental and clinical work suggests that inflammation is an important contributor. Several viruses have been implicated in the development of TLE. Brain inflammation, induced by viral infection of the central nervous system (CNS), alters the excitatory and inhibitory balance among neurons and is a significant cause of acute seizures. In our mouse model of infection-driven epilepsy, mice intra-cranially (i.c.) infected with Theiler’s murine encephalomyelitis virus (TMEV) develop behavioral seizures between 3-10 days post infection (d.p.i.). We previously found that infiltrating macrophages play a key role in seizure development. We recently isolated infiltrating macrophages and resident microglia from the CNS of mice following TMEV infection and performed RNA-sequencing to determine the expression profiles of genes relating to CNS infection/inflammation. We identified a population of infiltrating macrophages that express high levels of TREM-1 (Triggering Receptor Expressed on Myeloid cells 1). Activation of this receptor has been shown to lead to the initiation and amplification of the inflammatory response, by increasing the production and secretion of inflammatory cytokines by these macrophages. Therefore, we hypothesized that inhibition of TREM-1 activation could alter seizure development by modulating inflammation. Methods: C57BL/6J mice were i.c. infected with 4x105plaque-forming units of TMEV. TREM-1 peptide inhibitor (300 µg) or control peptide were administered daily, via intra-peritoneal (i.p.) injections, for 6 days (n=17 mice/group). Handling-induced seizures were determined daily, from 3-7 d.p.i., and seizure severity was scored based on the Racine scale. At 7 d.p.i. mice were euthanized and brains and serum were obtained. Cells were isolated from the brains and microglia, macrophage and lymphocyte populations were determined via flow cytometry. Quantification of cytokine and chemokine levels were performed via LEGENDplex bead-based immunoassay. Results: We found that mice treated with TREM-1 inhibitor showed delayed seizure onset (p=0.06), decreased seizure severity (p=0.006) and the CNS-infiltrating macrophages had significantly diminished activation towards an inflammatory reactive state (p<=0.03), as shown by lower major histocompatibility complex-II expression. We also found that TREM-1-treated mice had significantly decreased secretion of CCL22 (p=0.02) and IL-12p70 (p=0.04). Conclusions: Our studies indicate that TREM-1 activation in macrophages is playing a central role in the development of acute seizures after viral infection of the CNS. We are continuing to explore the role of macrophages and how modulation of TREM-1 signaling affects inflammation and seizures. Funding: T32A1055434/National Institute of Allergy and Infectious DiseasesR01NS065714/National Institute of Neurological Disorders and Stroke