Fig. 3.

Inflammatory factors that regulate T cell–mediated immunity in PD progression. Primarily originating from the gut, various mechanisms such as α-synuclein, gut microbiota, dopamine, and short-chain fatty acids (SCFAs) can result in the activation of T cells that can then bypass a leaky blood–brain barrier (BBB) and travel into the brain. Infiltrated T cells induce neuroinflammation through the secretion of pro-inflammatory cytokines and activation of microglia, leading to the pathogenesis of neurodegenerative diseases like PD