This CD8+ T-cell infiltration preceded both α-synuclein aggregation and neuronal cell death, where patients with incidental Lewy body disease (iLBD), which is considered to be an early, pre-symptomatic stage of PD, also demonstrated CD8+ T-cell infiltration in the SNpc and colocalization with midbrain DA neurons. This evidence concerns the gene CD8A and Lewy body dementia.