In addition to microglia, lymphocytes are involved in the pathology of brain diseases. Lymphocytes in the brain are discriminated into brain-resident lymphocytes and peripheral lymphocytes infiltrating into the brain. Recently, the function of the meningeal lymphatic vessels was revealed as an infiltrating route for lymphocytes into the brain. The presenter is clarifying the pathological role of peripheral lymphocytes infiltrating into the brain in the disease by surgical blocking of the meningeal lymphatic route and by pharmacological intervention. Here, our recent findings from such study on the function of peripheral lymphocytes in the brain disease are introduced.