Parkinson's disease patients have a complex phenotypic and functional Th1 bias: cross-sectional studies of CD4+ Th1/Th2/T17 and Treg in drug-naïve and drug-treated patients

Abstract

Background: Parkinson's disease (PD) affects an estimated 7 to 10 million people worldwide, and only symptomatic treatments are presently available to relieve the consequences of brain dopaminergic neurons loss. Neuronal degeneration in PD is the consequence of neuroinflammation in turn influenced by peripheral adaptive immunity, with CD4+ T lymphocytes playing a key role. CD4+ T cells may however acquire proinflammatory phenotypes, such as T helper (Th) 1 and Th17, as well as anti-inflammatory phenotypes, such as Th2 and the T regulatory (Treg) one, and to what extent the different CD4+ T cell subsets are imbalanced and their functions dysregulated in PD remains largely an unresolved issue.

Methods: We performed two cross-sectional studies in antiparkinson drug-treated and drug-naïve PD patients, and in age- and sex-matched healthy subjects. In the first one, we examined circulating Th1, Th2, Th17, and in the second one circulating Treg. Number and frequency of CD4+ T cell subsets in peripheral blood were assessed by flow cytometry and their functions were studied in ex vivo assays. In both studies, complete clinical assessment, blood count and lineage-specific transcription factors mRNA levels in CD4+ T cells were independently assessed and thereafter compared for their consistency.

Results: PD patients have reduced circulating CD4+ T lymphocytes, due to reduced Th2, Th17, and Treg. Naïve CD4+ T cells from peripheral blood of PD patients preferentially differentiate towards the Th1 lineage. Production of interferon-γ and tumor necrosis factor-α by CD4+ T cells from PD patients is increased and maintained in the presence of homologous Treg. This Th1-biased immune signature occurs in both drug-naïve patients and in patients on dopaminergic drugs, suggesting that current antiparkinson drugs do not affect peripheral adaptive immunity.

Conclusions: The complex phenotypic and functional profile of CD4+ T cell subsets in PD patients strengthen the evidence that peripheral adaptive immunity is involved in PD, and represents a target for the preclinical and clinical assessment of novel immunomodulating therapeutics.

Keywords: CD4+ T lymphocytes; Parkinson’s disease; Th1; Th17; Th2; Treg.

Conflict of interest statement

Ethics approval and consent to participate

The Ethics Committees of Ospedale di Circolo of Varese (I) and Neurological Institute “C. Mondino” of Pavia (I) approved the protocol and all the participants signed a written informed consent before enrollment.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1

CD4+ T cells in HS and PD patients. Cells are shown as absolute numbers (left panel) and as percentage of total lymphocytes (right panel). Data are medians with 25°–75° percentiles (boxes) and min–max values (whiskers)

Fig. 2

Th subsets in HS and PD patients. Cells are shown as absolute numbers (upper panels) and as percentage of total lymphocytes (lower panels). Th1/Th2 ratio and Th1/Th17 ratio are also shown (middle panels). Data are medians with 25°–75° percentiles (boxes) and min–max values (whiskers)

Fig. 3

Transcription factors mRNA levels in CD4+ T cells of HS and PD patients. Data are medians with 25°–75° percentiles (boxes) and min–max values (whiskers)

Fig. 4

Polarization of naïve CD4+ T cells towards Th1, Th2, and Th17 in HS and PD patients. Data are means ± SD of n = 5–6 subjects tested in triplicate. * = P < 0.05 and ** = P < 0.01 vs HS; # = P < 0.05 and ## = P < 0.01 vs standard conditions (Th0)

Fig. 5

Treg cells in HS and PD patients. Cells are shown as absolute numbers (upper panels) and as percentage of total CD4+ T cells and of total Treg, respectively (lower panels). Data are medians with 25°–75° percentiles (boxes) and min–max values (whiskers)

Fig. 6

Treg-induced inhibition of Teff proliferation in HS and PD patients. Teff from HS and PD patients proliferated to a similar extent in the presence of PHA (a) and were concentration-dependently inhibited by Treg (b). Treg inhibition of Teff proliferation was reduced by DA 1 μM in cells from HS and PD-dn patients but not from PD-dt patients (c). Data are means ± SD of n = 9–17 subjects. *P < 0.05 and **P < 0.01 vs respective Teff alone; #P < 0.05 vs respective Teff:Treg 1:1; §P < 0.05 vs both HS and PD-dn

Fig. 7

Cytokine production by Teff cells in HS and PD patients. Cytokines were measured in supernatants of resting cells (white columns) and of cells stimulated with PHA (black columns). Data are means ± SD of n = 4–9 subjects. *P < 0.05 and **P < 0.01 vs resting cells; # = P < 0.05 and ##P < 0.01 vs HS

Fig. 8

Teff production of IFN-γ and TNF-α and inhibition by Treg in HS and PD patients. Teff were stimulated with PHA alone (white columns) or in the presence of Treg 1:1 (hatched columns). Data are means ± SD of n = 6–10 subjects. *P < 0.05 and **P < 0.01 vs Teff alone; #P < 0.01 vs HS

Fig. 9

The Th1 bias in PD. Circulating CD4+ T naive cells in PD patients are reduced by about 30%; however, the proportion of IFN-γ-positive cells is increased (1). Differentiation towards the Th1 lineage is increased (2), while differentiation towards Th17 is impaired (3), and both Th2 and Th17 cells in blood are reduced on average by 20–30% (4). Production of IFN-γ and TNF-α by Th1 cells is strongly increased (5) and not impaired in the presence of Treg, which are also reduced by 30% in the circulation (6). Reduced production of IL-10 by CD4+ effector T cells, which likely contributes to amplify the Th1 bias, is not represented