While the numbers of CD4+ and CD8+ T lymphocytes found in postmortem tissue of PD patients are quite low (0.3 CD4+ cells/mm2 and 1.2 CD8+ cells/mm2 [56]), up to 142 CD3+ T cells were found in the hippocampus of AD patients with an increased number of CD8+ cells compared to CD4+ cells [59]. Here, CD8A is linked to Parkinson disease.