GPNMB and Parkinson disease: While P2RY12 is highly abundant in the resting microglia,51 GPNMB,52 HSP90,53 and IL-1β54 are involved in the inflammatory response and have previously been linked to neurodegeneration53,55,56 supporting the notion that the idiopathic Parkinson’s disease-specific upregulation of GPNMB and HSP90AA1 are markers of microglial activation.