CCL2 and Parkinson disease: IL-8 correlated with YKL-40 in the cohort as a whole (p < 0.001, β = 0.253) as well as in PD and controls (p ≤ 0.020, β ≥ 0.219) whereas IL-8 only correlated with MCP-1 in the cohort as a whole (p = 0.014, β = 0.158).