CCL4 and Cognitive impairment: The brain regions, blood, and cells of LRRK2-associated mouse models of PD have shown abnormal expression of LRRK2 kinase and their association with elevated brain and circulatory level of pro-inflammatory cytokines (e.g., IFNγ, TNFα, IL-1α, IL-1β, IL-6, IL-8, IL-10, and IL-12), chemokines (e.g., CCL2, CCL3, CCL4, CCL5, CXCL1, and CXCL10), and growth factors (e.g., GCSF and MCSF), as well as their link to the loss of NCs and the development of cognitive defects (Table 2A).