Moreover, it has been reported that the amount of CD4(+) CD25(+) regulatory T cells was decreased in the spleen of AQP4-deficient mice, which may be, at least in part, responsible for the lack of suppression of hyperactive uncontrolled microglial and immune responses that exacerbate neurodegeneration in an MPTP-induced PD model in mice [161]. Here, AQP4 is linked to Parkinson disease.