T lymphocyte senescence is attenuated in Parkinson's disease.

Background: Immune involvement is well-described in Parkinson's disease (PD), including an adaptive T lymphocyte response. Given the increasing prevalence of Parkinson's disease in older age, age-related dysregulation of T lymphocytes may be relevant in this disorder, and we have previously observed changes in age-associated CD8 ⁺ T cell subsets in mid-stage PD. This study aimed to further characterise T cell immunosenescence in newly diagnosed PD patients, including shifts in CD4 ⁺ and CD8 ⁺ subpopulations, and changes in markers of cellular ageing in CD8 ⁺ T lymphocytes.
Methods: Peripheral blood mononuclear cells were extracted from the blood of 61 newly diagnosed PD patients and 63 age- and sex-matched controls. Flow cytometric analysis was used for immunophenotyping of CD8 ⁺ and CD4 ⁺ lymphocyte subsets, and analysis of recent thymic emigrant cells. Telomere length within CD8 ⁺ T lymphocytes was assessed, as well as the expression of the telomerase reverse transcriptase enzyme (hTERT), and the cell-ageing markers p16 ^INK4a and p21 ^CIP1/Waf1 .
Results: The number of CD8 ⁺ TEMRA T cells was found to be significantly reduced in PD patients compared to controls. The expression of p16 ^INK4a in CD8 ⁺ lymphocytes was also lower in patients versus controls. Chronic latent CMV infection was associated with increased senescent CD8 ⁺ lymphocytes in healthy controls, but this shift was less apparent in PD patients.
Conclusions: Taken together, our data demonstrate a reduction in CD8 ⁺ T cell replicative senescence which is present at the earliest stages of Parkinson's disease.
(© 2021. The Author(s).)