How Immune Aging Drives Parkinson's Disease and What We Can Do About It

Parkinson's disease (PD) is the second most common neurodegenerative disorder, yet its underlying drivers remain incompletely understood. This comprehensive review from Nanchang University and Henan University of Science and Technology synthesizes current evidence linking immunosenescence — the age-related decline of immune function — to the progressive neurodegeneration characteristic of PD. The authors argue that aging-immune dysfunction is not a passive bystander but an active driver of dopaminergic neuron loss, operating through multiple converging pathways.

The review distinguishes between primary senescence, driven by intrinsic aging processes such as telomere attrition and genomic instability, and secondary senescence, induced by chronic neuroinflammation, oxidative stress, and alpha-synuclein aggregation. Both converge on the senescence-associated secretory phenotype (SASP), a pro-inflammatory secretome including IL-6, IL-1β, TNF-α, CCL2, CXCL8, VEGF, and matrix metalloproteinases. The SASP creates a self-reinforcing cycle: SASP factors from primarily senescent cells drive secondary senescence in neighboring cells, amplifying neuroinflammation and impairing clearance of pathological proteins. SASP regulation is governed primarily by NF-κB and p38 MAPK pathways, further potentiated by the cGAS-STING pathway sensing cytoplasmic chromatin fragments.

A critical focus is the interface between peripheral immunosenescence and CNS inflammation. Systemic immunosenescence is characterized by thymic involution, contraction of the naïve T-cell repertoire, and accumulation of terminally differentiated CD28⁻/CD57⁺ memory T cells. This inflammaging state compromises blood-brain barrier integrity through downregulation of tight junction proteins like Claudin-5 and upregulation of endothelial adhesion molecules, allowing peripheral immune cells and cytokines to infiltrate the CNS. Elevated activated T cells and monocytes have been detected in the cerebrospinal fluid of PD patients. Chronic viral exposures — notably CMV, HSV-1, and SARS-CoV-2 — are highlighted as accelerants of immunosenescence, promoting clonal T-cell expansion and reducing T-cell repertoire diversity.

Within the CNS, senescent microglia exhibit reduced phagocytic capacity, impairing alpha-synuclein clearance. Aggregated alpha-synuclein activates microglial pattern recognition receptors (TLRs) and the NLRP3 inflammasome, initiating pro-inflammatory cascades that further promote protein misfolding — a vicious cycle. The gut-brain axis emerges as another critical pathway: intestinal dysbiosis and increased gut permeability elevate circulating LPS and cytokines, which activate afferent vagal nerve fibers via TLR4 receptors, relaying neuroinflammatory signals to the brainstem and substantia nigra. Epidemiological data and vagotomy studies cited in the review support the clinical relevance of this pathway.

On the therapeutic front, the review evaluates several emerging strategies targeting the immunosenescence-neuroinflammation axis. Senolytic agents (such as dasatinib plus quercetin) aim to selectively eliminate senescent cells and reduce SASP burden. Adoptive regulatory T-cell (Treg) therapy seeks to restore immune tolerance and dampen microglial hyperactivation. Cytokine-targeted immunomodulation — blocking TNF-α or IL-1β signaling — and immune rejuvenation approaches (thymic regeneration, NAD+ supplementation) round out the therapeutic landscape. The authors acknowledge significant translational challenges, including the inadequacy of rodent models to fully recapitulate human aging or sporadic PD, the lack of validated biomarkers for immunosenescence in the CNS, and the need for longitudinal human studies to establish causal relationships. They call for AI-driven personalized medicine frameworks and advanced organoid or humanized model systems to bridge these gaps.