In the PD cohort, associations included IL‐6 with higher UPDRS‐III motor scores (P < 0.05), TNF‐α and CRP with faster rates of motor decline (change in UPDRS‐III per year), and IL‐13 with slower rate of motor decline (all P < 0.005); IFN‐γ, P < 0.005; TNF‐α, P < 0.005; IL‐6, P < 0.05; and CRP, P < 0.05 with lower MMSE scores and IL‐1β and IL‐2 with faster rate of cognitive decline (change in MMSE per year; both, P < 0.005). Here, IL2 is linked to Parkinson disease.