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).