To examine whether changes in CXCL8 transcription could also be detected at the protein level, we measured IL-8 and other inflammatory cytokines (IL-6, TNF-α and IL-1β) in the substantia nigra and Brodmann’s area 24 and 25 in a separate cohort of patients with PD but found no differences compared to control samples (Extended Data Fig. 5d–f). Here, IL6 is linked to Parkinson disease.