This study investigates the autoimmune response in individuals with Parkinson's Disease (PD) compared to those without or with fewer PD-related proteins. Parkinson's Disease is a condition where certain proteins, like alpha-synuclein, are present in the brain and may trigger an immune response leading to neuronal damage. The purpose of this study is to analyze how the immune system reacts to these proteins in both groups.

Participants will be required to attend a one-time visit where they will complete brief questionnaires and provide a blood sample of 30 mL, which is about 2 tablespoons. This sample will be used to study the presence of antigens and the activity of immune cells, such as T-cells, which may contribute to the degeneration of neurons in PD.

• Who can participate: Individuals aged 50 to 90 years with moderate to advanced Parkinson's Disease, showing two of the following: rest tremor, rigidity, or bradykinesia, and who have seen benefits from dopaminergic medication, are eligible. Diagnosis must have occurred after age 47 and PD duration must exceed 3 years.
• Study details: Participants will complete questionnaires and provide a blood sample for analysis. The study will investigate immune responses to PD-related proteins.
• Study Visits: The study requires 1 visit.