Adoptive transfer of T lymphocytes in immunodeficient mice influences epileptogenesis and neurodegeneration in a model of temporal lobe epilepsy

Intra-hippocampal injection of kainic acid (KA) in adult mice causes a focal lesion in the CA1 area and hilus of the dentate gyrus, as well as pronounced granule cell hypertrophy and dispersion. The lesion results in chronic focal seizures, with a two-week delay following KA-induced status epilepticus. Furthermore, seizures are preceded by infiltration of T lymphocytes into the lesioned tissue and of macrophage-like cells, strongly immunopositive for the monocyte marker F4/80, into the dentate gyrus, where they regulate granule cell dispersion and survival. Unexpectedly, depletion of CD4+ and/or CD8+ T lymphocytes by targeted gene deletion results in a marked shortening of the delay prior to seizure onset, suggesting a role of adaptive immunity in epileptogenesis (Zattoni et al. 2011, J. Neurosci. 31, 4037). Here, we investigated the specific role of adaptive immunity in this TLE model by adoptive i.v. transfer of immunopurified T cells in mutant mice lacking either CD4+ T cells (MHCII-knockout), CD8+ T cells (β2-microglobulin-knockout), or both populations (RAG1-knockout mice). EEG analysis in mutants mice injected with KA two days after the T cell transfer revealed that grafting of the missing T cell population had no influence on seizure onset, but strongly influenced F4/80+ macrophage-like cell infiltration in the dentate gyrus. Specifically, CD8+ T cells in β2-microgloblin-knockout mice enhanced macrophage recruitment, whereas CD4+ T cells transferred in MHCII-knockout and in RAG1-knockout mice blocked macrophage infiltration, leading to reduced granule cell dispersion and survival, thereby worsening the KA-induced lesion. These results suggest that intact adaptive immunity is required for delayed seizure onset in this mouse model of TLE and unravel complex interactions between T cells and mononuclear phagocytes for the control of neuronal integrity and survival in the lesioned brain.

► Unilateral intra-hippocampal kainic acid injection in mice induces an epileptic focus
► Ablation of CD4 and/or CD8 T lymphocytes accelerates recurrent seizure onset
► Adoptive transfer of T lymphocytes in mutant mice affects lesion severity
► Adaptive immunity regulates epileptogenesis and neurodegeneration in TLE