4.2. T cells and Parkinson’s disease
PD is the second most prevalent neurodegenerative disorder that affects the motor system and causes symptoms like tremors, stiffness, bradykinesia, gait impairment and many non-motor symptoms. The symptoms are linked to α-synuclein inclusions and the loss of dopaminergic neurons. Inflammation in the brain, specifically the role of T-lymphocytes, can trigger a type 1 pro-inflammatory response, which may initially have a protective effect, but eventually, the inflammation becomes harmful and suppresses the type 2 anti-inflammatory response, leading to a dysregulated state of neuroinflammation and consequent dopaminergic neurodegeneration. Regulating the immune response is a promising approach for managing the disease’s pathogenicity and improving the response to treatments (Baird, Bourdette, Meshul & Quinn, 2019).
In both AD and PD, it is important to identify an early immune response in peripheral blood, as this can be used as a diagnostic and prognostic tool, and even as a means to regulate the progression of both diseases through the use of immunomodulators., Increased levels of activated lymphocytes, apoptosis susceptible lymphocytes, central memory T cells, regulatory T and B cells have been found in both diseases. Characteristic immune cells in AD and PD include CD4+CD38+ and CD8+CD38+ T lymphocytes, and CD4+CD69+ and CD8+CD69+ T cells in PD. Regulatory T cells, such as CD19+ CD5+ IL10+in PD and AD, and CD19+ CD5+IL10+ FoxP3+, CD4+FoxP3+ CD25+CD45RO+ in PD, are also found to play a role in both diseases. In AD, an increase of effector CD4+lymphocytes have been found in the early stages of the disease, while a decrease of CD4+ CD38+CD38+ lymphocytes occur as the disease progresses (Garfias et al., 2019).