CD4 and Parkinson disease: To further elucidate the contribution of different classes of immune cells and identify cell-type-specific alterations in gene regulation, we performed epigenome-wide DNA methylation profiling of purified cell populations representing major peripheral cell types of the innate and adaptive immune system, namely CD14+ monocytes, CD19+ B cells, CD4+ T helper cells and CD8+ cytotoxic T cells in 25 patients with early PD and 25 healthy controls.