Furthermore, neuroimaging studies have reported that in individuals with prodromal or early-stage PD, elevated peripheral levels of chemokines such as C–C motif chemokine ligand (CCL)22 and CCL26, as well as cytokines including IFN-γ, IL-1β, and IL-6, correlate with increased TSPO-PET signals indicative of microglial activation [17, 29]. This evidence concerns the gene TSPO and Parkinson disease.