TLR4 and Parkinson disease: Brain samples from Parkinson’s disease patients analyzed after the fact have demonstrated increased Toll-like receptor 2 expression in neurons and microglia in various regions of the brain, including the substantia nigra and putamen (129), as well as increased expression of the substantia nigra striatum Toll-like receptor 2-related signaling pathways [including cluster 14 (CD14), a coreceptor for Toll-like receptor 4] (130).