There is considerable neuropathological evidence of inflammation in the substantia nigra pars compacta (SNc) of PD patients, including reactive, HLA-DR+ microglia (McGeer et al., 1988) and the presence of CD8 + and CD4 + T cells near the pigmented SNc dopaminergic (DA) neurons and noradrenergic neurons of the locus coeruleus (Brochard et al., 2009; Cebrián et al., 2014; Gate et al., 2021; Sommer et al., 2018), neurons that are killed in PD. Here, CD4 is linked to Parkinson disease.