A dysfunction of CD4+ T lymphocytes in peripheral immune system of Parkinson's disease model mice

Parkinson's disease (PD), a neurodegenerative disorder, has been reported to be associated with brain neuroinflammation in its pathogenesis. Herein, changes in peripheral immune system were determined to better understand PD pathogenesis and provide possible target for treatment of PD through improvement of immune disorder.

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was intraperitoneally injected into mice to prepare PD model. Expression levels of pro-inflammatory and anti-inflammatory cytokines and transcription factors of CD4+ T lymphocyte subsets in spleen and mesenteric lymph nodes and concentrations of the cytokines in serum were examined on day 7 after MPTP injection. Percentages of CD4+ T lymphocyte subsets were measured by flow cytometry.

MPTP induced PD-like changes such as motor and behavioral deficits and nigrostriatal impairment. Expression levels of the pro-inflammatory cytokines including interferon (IFN)-γ, interleukin (IL)-2, IL-17 and IL-22, in spleen and mesenteric lymph nodes were upregulated and their concentrations in serum were elevated in PD progression. But, the concentrations of the anti-inflammatory cytokines including IL-4, IL-10 and transforming growth factor (TGF)-β were not altered in the two lymphoid tissues or serum of PD mice. In addition, expression of T-box in T cells (T-bet), the specific transcription factor of helper T (Th) 1 cells, was downregulated, but expression of transcription factor forkhead box p3 (Foxp3), the transcription factor of regulatory T (Treg) cells, was upregulated. In support of the results, the numbers of IFN-γ-producing CD4+ cells (Th1 cells) were reduced but CD4+CD25+ cells (Treg cells) were elevated in both the lymphoid tissues of PD mice.

PD has a dysfunction of peripheral immune system. It manifests enhancement of proinflammatory response and CD4+ T cell differentiation bias towards Treg cells away from Th1 cells.