Participation of the spleen in the neuroinflammation after pilocarpine-induced status epilepticus: implications for epileptogenesis and epilepsy

Abstract Epilepsy, a chronic neurological disorder characterized by recurrent seizures, affects millions of individuals worldwide. Despite extensive research, the underlying mechanisms leading to epileptogenesis, the process by which a normal brain develops epilepsy, remain elusive. We, here, explored the immune system and spleen responses triggered by pilocarpine-induced status epilepticus (SE) focusing on their role in the epileptogenesis that follows SE. Initial examination of spleen histopathology revealed transient disorganization of white pulp, in animals subjected to SE. This disorganization, attributed to immune activation, peaked at 1-day post-SE (1DPSE) but returned to control levels at 3DPSE. Alterations in peripheral blood lymphocyte populations, demonstrated a decrease following SE, accompanied by a reduction in CD3+ T-lymphocytes. Further investigations uncovered an increased abundance of T-lymphocytes in the piriform cortex and choroid plexus at 3DPSE, suggesting a specific mobilization toward the Central Nervous System. Notably, splenectomy mitigated brain reactive astrogliosis, neuroinflammation, and macrophage infiltration post-SE, particularly in the hippocampus and piriform cortex. Additionally, splenectomized animals exhibited reduced lymphatic follicle size in the deep cervical lymph nodes. Most significantly, splenectomy correlated with improved neuronal survival, substantiated by decreased neuronal loss and reduced degenerating neurons in the piriform cortex and hippocampal CA2-3 post-SE. Overall, these findings underscore the pivotal role of the spleen in orchestrating immune responses and neuroinflammation following pilocarpine-induced SE, implicating the peripheral immune system as a potential therapeutic target for mitigating neuronal degeneration in epilepsy.