Schematic diagram showing the relationship between peripheral inflammation and neuronal loss in PD. Neurodegenerative diseases present microglial activation as the main hallmark, which can change its morphology from resting (ramified) towards an activated round shape (ameboidal). The intermediate stage, “primed microglia”, describes the atypical microglial stage, which precedes a further neurotoxic microglial activation as a consequence of a secondary pro-inflammatory stimulus. This stimulus can come from the periphery, either through neural or humoral pathways. Activated microglia release pro-inflammatory cytokines which can act on neuronal integrity. In addition, acute brain injury induces early hepatic expression of chemokines, which in turn produce recruitment of leukocytes into the blood and subsequently brain and liver inflammation via a chemokines and cytokines web.
