CD4 and Parkinson disease: MR analyses employing a random-effects model with the IVW method yielded the following results: myeloid DC of DC (OR = 0.924, 95%CI: 0.876–0.975, p = 0.004), HVEM on CD45RA− CD4+ T cell (OR = 0.945, 95%CI: 0.907–0.985, p = 0.007), CD62L− CD86+ myeloid DC of DC (OR = 0.945, 95%CI: 0.903–0.989, p = 0.015), and HLA DR on monocyte (OR = 0.951, 95%CI: 0.911–0.992, p = 0.019) indicated a protective effect against reduced PD risk.