TNF and Parkinson disease: The pattern of CSF TNF (p = 0.02), CRP (p = 0.03), IL-8 (p = 0.02), and Aβ42 (p = 0.006) levels across the day were best fit by a parabolic (not linear) relationship in PD subjects, but not in HCs (p = 0.07, p = 0.25, p = 0.31, p = 0.06, respectively), indicating that the levels of these CNS proteins rise and fall across the day more in PD subjects versus HC.