Abstracts

Rationale: The goal of this project is to determine the role of immune responses in mediating childhood epilepsy. Proinflammatory conditions have been detected preceding the onset of epilepsy in both patients and animal models. Recurrent or prolonged seizures lead to activation of immune responses, which further increase seizure susceptibility. We therefore characterized different populations of brain-resident and -infiltrating immune cells in resections of brain tissues from pediatric patients with epilepsy and determined their differentiation and activation statuses. We then adopted a two-hit murine model to recapitulate the clinical findings by inducing status epilepticus. We used this rodent model delineate the specific roles of innate versus adaptive immunity in the process of epileptogenesis.Methods: Freshly resected human brain tissues were processed to generate single cell suspensions suitable for flow cytometric analyses. The cell preparation was then stained with fluorescently labeled cell markers for identification of different cell populations. Similar analyses were performed in brain samples of inbred mice that were induced to develop status epilepticus with two hits. The first hit was either kainic acid delivered peritoneally or hyperthermia at post-natal day 14. The second hit was another dose of kainic acid at post-natal day 28.Results: We detected brain-infiltrating monocytes, macrophages, T cells, T cells, and T regulatory cells in the resected brain of patients and inbred mice subjected to two-hit induced status epilepticus. About 25 percent of the brain-infiltrating T cells were of lineage. These T cells are thought to be activated by alarm signals such as heat shock proteins following stress. This cell subset is considered to be a bridge between innate and adaptive responses as it permits rapid immune responses to a variety of invariant foreign antigens, and yet displaying limited T-cell receptor rearrangement. They may also serve as antigen-presenting cells to activated conventional T cells. The remaining 75 percent of infiltrating T cells were stained positive for the T-cell receptor. Interestingly, majority of these T cells were memory cells that are capable of homing to peripheral secondary lymphoid organs, as indicated by their surface expression of CD45RO and CCR7. Furthermore, these memory cells are capable of undergoing antigen-independent and homeostatic self-renewal, as they express CD127, the interleukin-7 receptor subunit.Conclusions: Our preliminary human studies demonstrated for the first time that peripheral leukocytes infiltrate pediatric epileptic cortical tissues. Most importantly, we developed a two-hit murine model to recapitulate the clinical findings by inducing status epilepticus in post-natal day 14 mice pups followed by a kainic acid-induced secondary seizure. We have shown marked increase of peripheral lymphocytes, specifically activated and memory T lymphocytes, in the mouse brain, consistent with our human data.