The role of the immune response in Parkinson's disease (PD) is controversial. Recent studies show that neurons can present MHC-I (major histocompatibility complex - class 1) molecules and therefore may be susceptible to an attack by immune cells. The investigators anticipate that the results of this study will improve our understanding of the mechanisms of immune mediated neuronal degeneration in PD. Initial results suggest that antigens are presented by neuronal MHC-I in PD, and that this could lead to T-cell mediated neuronal death. The most obvious antigen that could be differentially expressed in PD patients and controls would be alpha-synuclein (-syn): -syn oligomers appear in all Lewy bodies and Lewy neurites and are the hallmark of PD changes in the brain. This study will offer the opportunity to further characterize the immune mediated component of PD, and to continue elucidating the biology that underlies antigen presentation and T-cell cytolytic activity.