Using a bead-based cytokine array, we detected no significant differences in cytokine (IL-2, IL-4, IL-5, IL-6, IL-9, IL-10, IL-13, IL-17A, IL-17F, IL-21, IL-22, IFNy, TNFa) and chemokine (CCL11, CCL17, CCL20, CXCL1, CXCL5, CXCL9, CXCL11, IL-8, IP-10, MCP-1, MIP-1a, MIP-1b, RANTES) levels in the serum (data not shown) of PD. Here, IL21 is linked to Parkinson disease.