AQP4−/− mice studies have also suggested that AQP4 could be contributing to the production of CD4+ and CD25+ T regulator cells; and lack of AQP4 may be disrupting the immunosuppressive regulators in Parkinson’s disease, leading to increased microglial activation and a worse outcome due to more dopaminergic neuronal loss after induction of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine [5]. This evidence concerns the gene AQP4 and Parkinson disease.