Increased abundance of myeloid-derived suppressor cells and Th17 cells in peripheral blood of newly-diagnosed Parkinson's disease patients

The interrelationship between intestinal immune cells and enteric α-synuclein in the progression of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder primarily characterized by motor impairment, resulting from the accumulation of α-synuclein and neuronal cell death in the substantia nigra of the midbrain. Emerging evidence suggests that α-synuclein aggregation may originate in the enteric nervous system (ENS) and subsequently propagate to the brain via the vagus nerve. Clinical observations, such as prodromal gastrointestinal dysfunction in PD patients and the increased incidence of PD among individuals with inflammatory bowel disease, support the hypothesis that abnormal intestinal inflammation may contribute to the onset of motor dysfunction and neuropathology in PD. This review examines recent findings on the interplay between intestinal immune cells and α-synuclein aggregation within the framework of gut-originated PD pathogenesis. It begins by discussing evidence linking dysbiosis and intestinal inflammation to α-synuclein aggregation in the ENS. Additionally, it explores the potential role of intestinal immune cells in influencing enteric neurons and α-synuclein aggregation, furthering the understanding of PD development.

Beyond plaques and tangles: The role of immune cell dysfunction in Alzheimer's disease

The interplay between immune cell dysfunction and associated neuroinflammation plays a critical role in the pathogenesis of Alzheimer's disease. Neuroinflammation, orchestrated by microglia and peripheral immune cells, exacerbates synaptic dysfunction and neurodegeneration in AD. Emerging evidence suggests a systemic immune response in AD, challenging traditional views of neurocentric pathology. Therapeutic strategies targeting neuroinflammation hold promise, yet translating preclinical findings into clinical success remains elusive. This article presents recent advances in AD scientific studies, highlighting the pivotal role of immune cell dysfunction and signaling pathways in disease progression. We also discussed therapeutic studies targeting immune cell dysregulation, as treatment methods. This advocates for a paradigm shift towards holistic approaches that integrate peripheral and central immune responses, fostering a comprehensive understanding of AD pathophysiology and paving the way for transformative interventions.

The role of the immune system in Parkinson's disease pathogenesis: A focus on Th17 cells - A systematic review and meta-analysis

BACKGROUND

Parkinson's disease (PD) has been linked to T helper 17 (Th17) cells in prior investigations, but the evidence remains inconclusive. To gain a deeper understanding of this potential connection, we conducted a systematic review and meta-analysis.

METHODS

A comprehensive search for relevant studies published up to July 8, 2023, was performed across PubMed, EMBASE, and Cochrane Library databases. A random-effect model was employed to synthesize effect sizes and their corresponding 95 % confidence intervals (CIs). Leave-one-out sensitivity analysis and funnel plots with trim-and-fill were utilized to assess the combined results' robustness.

RESULTS

Thirteen studies were ultimately included in the meta-analysis. Pooled effect sizes indicated a significantly higher percentage of Th17 cells in PD patients (Standardized Mean Difference [SMD] = 1.00, 95 % CI 0.30-1.71). Notably, Th17 cell levels were more elevated in Asian PD patients (SMD = 1.33, 95 % CI 0.31-2.35). Additionally, the percentage of Th17 cells positively correlated with Movement Disorder Society Unified Parkinson's Disease Rating Scale-III (UPDRS-III) scores (r = 0.22, 95 % CI 0.01-0.41), indicating a link to motor dysfunction. Conversely, a negative correlation was observed with Cognitive function scale scores (r = - 0.27, 95 % CI -0.47--0.04), suggesting a potential association with cognitive decline.

CONCLUSIONS

This study revealed a positive association between Th17 cells and PD, with PD patients exhibiting elevated Th17 levels. Furthermore, the percentage of Th17 cells correlated with motor and cognitive impairments in PD patients.

Potential hypothesis for the increased risk of Parkinson´s disease following COVID-19

Patients with severe COVID-19 may be more likely to develop PD as a result of shared biological pathways including a great expansion of MDSCs and an imbalance in Th17/Tregs ratio. We think that these shared pathogenic features may mechanistically explain the COVID-19 - PD axis. Thus, we assume that patients who recovered from critical COVID-19 should be selected based upon a potential higher risk of developing PD. Further studies are needed to better define the possible relationship between COVID-19 and neuroinflammation and identify whether some people are more likely to develop PD after contracting COVID-19 than others with special emphasis to ascertain possible vulnerable genetic backgrounds or epigenetic factors acting on brain which may promote PD during SARS COV-2 infection. Finally, we think that regular physical activity should be performed and encouraged in patients with PD.

Systemic knockout of Tmem175 results in aberrant differentiation but no effect on hematopoietic reconstitution

Lysosomes play crucial roles in regulating cell metabolism, and K+ channels are critical for controlling various aspects of lysosomal function. Additionally, lysosomal activity is essential for maintaining the quiescence of hematopoietic stem cells (HSCs) under both steady-state and stress conditions. Tmem175 is a lysosomal potassium channel protein. To further investigate the role of K+ channels in HSCs, our study employed knockout mice to examine the function of Tmem175. Our research findings demonstrate that the deletion of Tmem175 does not disrupt the functionality of HSCs in both stable and stressed conditions, including irradiation and intraperitoneal 5-FU injections. However, we did observe that the absence of Tmem175 impairs the long-term differentiation capacity of HSCs into myeloid differentiated subpopulation cells（In this paper, it is referred to simply as M cells）in HSC transplantation test, while promoting their differentiation into T cells. This suggests that Tmem175 plays a role in the lineage differentiation of HSCs without being essential for their self-renewal or long-term regenerative capabilities.

The autoimmune response induced by α-synuclein peptides drives neuronal cell death and glial cell activation

Parkinson's disease (PD) is a progressive neurodegenerative disorder associated with the loss of dopaminergic neurons and neuroinflammation. Recent studies have identified a role of T cells in the pathogenesis of PD. Additionally, these studies suggested that α-synuclein (α-Syn) is related to abnormal T-cell responses and may act as an epitope and trigger autoimmune T-cell responses. However, it is unclear whether the α-Syn-mediated autoimmune response occurs and whether it is related to neuronal cell death and glial cell activation. In this study, we investigated the autoimmune T-cell response induced by α-Syn peptides and evaluated the neurotoxic effect of the α-Syn peptide-mediated autoimmune response. The immunization of mice with α-Syn peptides resulted in enhanced autoimmune responses, such as the peptide recall response, polarization toward Th1/Th17 cells, and regulatory T cell imbalance. Furthermore, the α-Syn autoimmune response led to the death of primary neurons cocultured with splenocytes. Treatment with conditioned media from α-Syn peptide-immunized splenocytes induced microglia and toxic A1-type astrocyte activation. Taken together, our results provide evidence of the potential role of the α-Syn-initiated autoimmune response and its contribution to neuronal cell death and glial cell activation.

Causal role of myeloid cells in Parkinson's disease: Mendelian randomization study

BACKGROUND

Previous studies have observed elevated myeloid cells in the peripheral blood of patients with Parkinson's disease (PD), but the causal relationship between them remains to be elucidated. We investigated whether there is a causal relationship between different subtypes of peripheral blood myeloid cells and PD using Mendelian randomization (MR) combined with bioinformatics analysis. Exploring the etiology of PD from the perspective of genetics can remove confounding factors and provide a more reliable theoretical basis for elucidating the pathogenesis of PD.

METHODS

Comprehensive two-sample MR analysis and sensitivity analyses were conducted to explore the causal associations between 64 myeloid cell signatures and PD risk. The Venn diagram and protein-protein interaction network analysis of instrumental variables (IV) corresponding genes were used to further investigate the potential mechanism of myeloid cells influencing the pathogenesis of PD.

RESULTS

We investigated the impact of four immunophenotypes on the risk of PD, including Im MDSC% CD33dim HLA DR- CD66b- (relative count), CD33dim HLA DR+ CD11b+% CD33dim HLA DR+ (relative count), and CD11b on Mo MDSC (MFI) and CD11b on CD33br HLA DR+ CD14dim (MFI), while an immunophenotype's protective effect on PD was observed CD45 on Im MDSC (MFI). The results of bioinformatics analysis showed that CD33, NTRK2, PLD2, GRIK2 and RELN had protein interactions with the risk genes of PD.

CONCLUSIONS

Our study has demonstrated a close genetic correlation between different subtypes of myeloid cells and PD, providing guidance for early identification and immunotherapeutic development in patients with PD.

The Influence of Myeloid-Derived Suppressor Cell Expansion in Neuroinflammation and Neurodegenerative Diseases

The neuro-immune axis has a crucial function both during physiological and pathological conditions. Among the immune cells, myeloid-derived suppressor cells (MDSCs) exert a pivotal role in regulating the immune response in many pathological conditions, influencing neuroinflammation and neurodegenerative disease progression. In chronic neuroinflammation, MDSCs could lead to exacerbation of the inflammatory state and eventually participate in the impairment of cognitive functions. To have a complete overview of the role of MDSCs in neurodegenerative diseases, research on PubMed for articles using a combination of terms made with Boolean operators was performed. According to the search strategy, 80 papers were retrieved. Among these, 44 papers met the eligibility criteria. The two subtypes of MDSCs, monocytic and polymorphonuclear MDSCs, behave differently in these diseases. The initial MDSC proliferation is fundamental for attenuating inflammation in Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS), but not in amyotrophic lateral sclerosis (ALS), where MDSC expansion leads to exacerbation of the disease. Moreover, the accumulation of MDSC subtypes in distinct organs changes during the disease. The proliferation of MDSC subtypes occurs at different disease stages and can influence the progression of each neurodegenerative disorder differently.

The role of T-lymphocytes in central nervous system diseases

The central nervous system (CNS) has been considered an immunologically privileged site. In the past few decades, research on inflammation in CNS diseases has mostly focused on microglia, innate immune cells that respond rapidly to injury and infection to maintain CNS homeostasis. Discoveries of lymphatic vessels within the dura mater and peripheral immune cells in the meningeal layer indicate that the peripheral immune system can monitor and intervene in the CNS. This review summarizes recent advances in the involvement of T lymphocytes in multiple CNS diseases, including brain injury, neurodegenerative diseases, and psychiatric disorders. It emphasizes that a deep understanding of the pathogenesis of CNS diseases requires intimate knowledge of T lymphocytes. Aiming to promote a better understanding of the relationship between the immune system and CNS and facilitate the development of therapeutic strategies targeting T lymphocytes in neurological diseases.

Causal role of immune cells on risk of Parkinson's disease: a Mendelian randomization study

Background

Previous observational studies have suggested a correlation between immune cells and Parkinson's disease (PD), yet specific investigations into the causal relationship between the two remain limited. This study aims to explore this potential causal relationship.

Methods

We utilized genome-wide association study (GWAS) data on immune cells and Parkinson's Disease, conducting a two-sample Mendelian randomization (MR) analysis using single nucleotide polymorphisms (SNPs). To estimate causality, we employed inverse variance weighting (IVW), MR-Egger, and weighted median (WM) methods. For sensitivity analysis, we used Cochran's Q-test, MR-Egger intercept, leave-one-out analysis, and funnel plots.

Results

After false discovery rate (FDR) correction, the effects of PD on immune cells, and vice versa, were not statistically significant. These include CX3CR1 on CD14+ CD16-monocyte (OR = 0.91, 95% CI = 0.86-0.96, p = 0.0003 PFDR = 0.152), CD62L-CD86+ myeloid DC AC (OR = 0.93, 95% CI = 0.89-0.97, p = 0.0005, PFDR = 0.152),CD11b on Mo (OR = 1.08, 95% CI = 1.03-1.13, p = 0.001, PFDR = 0.152), CD38 on igd+ cd24- (OR = 1.14, 95% CI = 1.06-1.23, p = 0.001, PFDR = 0.152), D14+ cd16+ monocyte %monocyte (OR = 1.10, 95% CI = 1.04-1.17, p = 0.001, PFDR = 0.159). Additionally, PD may be causally related to the immune phenotype of CM CD8br %T cell (beta = 0.10, 95% CI = 1.14-1.16, p = 0.0004, PFDR = 0.151), SSC-A on monocyte (beta = 0.11, 95% CI = 1.15-1.18, p = 0.0004, PFDR = 0.1 SSC-A on monocyte). No pleiotropy was determined.

Conclusion

This study suggested a potential causal link between immune cells and Parkinson's Disease through the MR method, which could provide a new direction for the mechanistic research and clinical treatment of PD.

Comparison of metabolic and neurological comorbidities in Asian patients with psoriasis and atopic dermatitis

Although various comorbidities have been noted to be associated with atopic dermatitis (AD) and psoriasis, few studies have compared comorbidities between the two diseases, and little is known about whether these comorbidities vary by the subtypes of psoriasis. In this study of 1:1 age- and sex-matched pair analysis between patients diagnosed with either psoriasis or AD at Asan Medical Center between 1991 and 2020, comorbidities, as determined by the International Classification of Diseases-10 codes, and likelihood ratios of metabolic and neurologic comorbidities in psoriasis compared with AD were studied using a logistic regression model. Among a total of 14,128 patients, the psoriasis group had higher odds of obesity (odds ratio [95% confidence interval]: 1.49 [1.34-1.66]), hypertension (1.14 [1.03-1.26]), diabetes mellitus (1.46 [1.29-1.66]), chronic kidney disease (1.59 [1.22-2.08]), and Parkinson's disease (2.1 [1.15-3.83]) than the AD group. Subgroup analysis revealed that patients with plaque psoriasis had higher odds of obesity (1.18 [1.05-1.33]), hypertension (1.18 [1.06-1.32]), diabetes mellitus (1.53 [1.34-1.75]), chronic kidney disease (1.66 [1.26-2.17]), and Parkinson's disease (2.12 [1.16-3.88]) compared with AD. Meanwhile, guttate psoriasis was associated with higher odds of dementia (3.63 [1.06-12.40]) and patients with generalized pustular psoriasis showed higher odds of diabetes mellitus (5.42 [1.56-18.83]) compared with AD. In conclusion, Asian patients with all types of psoriasis should be closely monitored for the development of metabolic and neurologic diseases, especially men and those aged ≥ 40 years.

CCL5 promotes LFA-1 expression in Th17 cells and induces LCK and ZAP70 activation in a mouse model of Parkinson's disease

Background

Parkinson's disease (PD), which is associated to autoimmune disorders, is characterized by the pathological deposition of alpha-synuclein (α-Syn) and loss of dopaminergic (DA) neurons. Th17 cells are thought to be responsible for the direct loss of DA neurons. C-C chemokine ligand 5 (CCL5) specifically induces Th17 cell infiltration into the SN. However, the specific effect of CCL5 on Th17 cells in PD and the relationship between CCL5 and lymphocyte function-associated antigen-1 (LFA-1) expression in Th17 cells are unknown.

Methods

We evaluated the effects of CCL5 on LFA-1 expression in Th17 cells in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and examined Th17 cell differentiation upon CCL5 stimulation in vitro. Furthermore, we assessed the effects of CCL5 on tyrosine kinase zeta-chain-associated protein kinase 70 (ZAP70) and lymphocyte-specific protein tyrosine kinase (LCK) activity in CCL5-stimulated Th17 cells in vivo and in vitro.

Results

CCL5 increased the proportion of peripheral Th17 cells in MPTP-treated mice, LFA-1 expression on Th17 cells, and Th17 cell levels in the SN of MPTP-treated mice. CCL5 promoted Th17 cell differentiation and LFA-1 expression in naive T cells in vitro. Moreover, CCL5 increased Th17 cell differentiation and LFA-1 expression by stimulating LCK and ZAP70 activation in naive CD4+ T cells. Inhibiting LCK and ZAP70 activation reduced the proportion of peripheral Th17 cells and LFA-1 surface expression in MPTP-treated mice, and Th17 cell levels in the SN also significantly decreased.

Conclusion

CCL5, which increased Th17 cell differentiation and LFA-1 protein expression by activating LCK and ZAP70, could increase the Th17 cell number in the SN, induce DA neuron death and aggravate PD.

Longitudinal Changes in Mitochondrial DNA Copy Number and Telomere Length in Patients with Parkinson's Disease

Parkinson's disease (PD) pathophysiology includes mitochondrial dysfunction, neuroinflammation, and aging as its biggest risk factors. Mitochondrial DNA copy number (mtDNA-CN) and telomere length (TL) are biological aging markers with inconclusive results regarding their association with PD. A case-control study was used to measure TL and mtDNA-CN using qPCR in PBMCs. PD patients were naive at baseline (T0) and followed-up at one (T1) and two (T2) years after the dopaminergic treatment (DRT). Plasmatic cytokines were determined by ELISA in all participants, along with clinical parameters of patients at T0. While TL was shorter in patients vs. controls at all time points evaluated (p < 0.01), mtDNA-CN showed no differences. An increase in mtDNA-CN and TL was observed in treated patients vs. naive ones (p < 0.001). Our statistical model analyzed both aging markers with covariates, showing a strong correlation between them (r = 0.57, p < 0.01), and IL-17A levels positively correlating with mtDNA-CN only in untreated patients (r = 0.45, p < 0.05). TL and mtDNA-CN could be useful markers for monitoring inflammation progression or treatment response in PD. DRT might modulate TL and mtDNA-CN, reflecting a compensatory mechanism to counteract mitochondrial dysfunction in PD, but this needs further investigation.

Impact of Sex on Neuroimmune contributions to Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. Inflammation has been observed in both the idiopathic and familial forms of PD. Importantly, PD is reported more often in men than in women, men having at least 1.5- fold higher risk to develop PD than women. This review summarizes the impact of biological sex and sex hormones on the neuroimmune contributions to PD and its investigation in animal models of PD. Innate and peripheral immune systems participate in the brain neuroinflammation of PD patients and is reproduced in neurotoxin, genetic and alpha-synuclein based models of PD. Microglia and astrocytes are the main cells of the innate immune system in the central nervous system and are the first to react to restore homeostasis in the brain. Analysis of serum immunoprofiles in female and male control and PD patients show that a great proportion of these markers differ between male and female. The relationship between CSF inflammatory markers and PD clinical characteristics or PD biomarkers shows sex differences. Conversely, in animal models of PD, sex differences in inflammation are well documented and the beneficial effects of endogenous and exogenous estrogenic modulation in inflammation have been reported. Targeting neuroinflammation in PD is an emerging therapeutic option but gonadal drugs have not yet been investigated in this respect, thus offering new opportunities for sex specific treatments.

Disease mechanisms as subtypes: Lysosomal dysfunction in the endolysosomal Parkinson's disease subtype

Parkinson's disease (PD) remains one of the most prevalent neurodegenerative disorders. It has become increasingly recognized that PD is not one disease but a constellation of many, with distinct cellular mechanisms driving pathology and neuronal loss in each given subtype. Endolysosomal trafficking and lysosomal degradation are crucial to maintain neuronal homeostasis and vesicular trafficking. It is clear that deficits in endolysosomal signaling data support the existence of an endolysosomal PD subtype. This chapter describes how cellular pathways involved in endolysosomal vesicular trafficking and lysosomal degradation in neurons and immune cells can contribute to PD. Last, as inflammatory processes including phagocytosis and cytokine release are central in glia-neuron interactions, a spotlight on the role of neuroinflammation plays in the pathogenesis of this PD subtype is also explored.

Disease mechanisms as subtypes: Immune dysfunction in Parkinson's disease

In recent years, the contraposition between inflammatory and neurodegenerative processes has been increasingly challenged. Inflammation has been emphasized as a key player in the onset and progression of Parkinson disease (PD) and other neurodegenerative disorders. The strongest indicators of the involvement of the immune system derived from evidence of microglial activation, profound imbalance in phenotype and composition of peripheral immune cells, and impaired humoral immune responses. Moreover, peripheral inflammatory mechanisms (e.g., involving the gut-brain axis) and immunogenetic factors are likely to be implicated. Even though several lines of preclinical and clinical studies are supporting and defining the complex relationship between the immune system and PD, the exact mechanisms are currently unknown. Similarly, the temporal and causal connections between innate and adaptive immune responses and neurodegeneration are unsettled, challenging our ambition to define an integrated and holistic model of the disease. Despite these difficulties, current evidence is providing the unique opportunity to develop immune-targeted approaches for PD, thus enriching our therapeutic armamentarium. This chapter aims to provide an extensive overview of past and present studies that explored the implication of the immune system in neurodegeneration, thus paving the road for the concept of disease modification in PD.

α-Synuclein induces Th17 differentiation and impairs the function and stability of Tregs by promoting RORC transcription in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons (DA) and the accumulation of Lewy body deposits composed of alpha-Synuclein (α-Syn), which act as antigenic epitopes to drive cytotoxic T-cell responses in PD. Increased T helper 17 (Th17) cells and dysfunctional regulatory T cells (Tregs) have been reported to be associated with the loss of DA in PD. However, the mechanism underlying the Th17/Treg imbalance remains unknown.

METHODS

Here, we examined the percentage of Th17 cells, the percentage of Tregs and the α-Syn level and analysed their correlations in the peripheral blood of PD patients and in the substantia nigra pars compacta (SNpc) and spleen of MPTP-treated mice and A53 transgenic mice. We assessed the effect of α-Syn on the stability and function of Tregs and the differentiation of Th17 cells and evaluated the role of retinoid-related orphan nuclear receptor (RORγt) upregulation in α-Syn stimulation in vivo and in vitro.

RESULTS

We found that the α-Syn level and severity of motor symptoms were positively correlated with the increase in Th17 cells and decrease in Tregs in PD patients. Moreover, α-Syn stimulation led to the loss of Forkhead box protein P3 (FOXP3) expression in Tregs, accompanied by the acquisition of IL-17A expression. Increased Th17 differentiation was detected upon α-Syn stimulation when naïve CD4⁺ T cells were cultured under Th17-polarizing conditions. Mechanistically, α-Syn promotes the transcription of RORC, encoding RORγt, in Tregs and Th17 cells, leading to increased Th17 differentiation and loss of Treg function. Intriguingly, the increase in Th17 cells, decrease in Tregs and apoptosis of DA were suppressed by a RORγt inhibitor (GSK805) in MPTP-treated mice.

CONCLUSION

Together, our data suggest that α-Syn promotes the transcription of RORC in circulating CD4⁺ T cells, including Tregs and Th17 cells, to impair the stability of Tregs and promote the differentiation of Th17 cells in PD. Inhibition of RORγt attenuated the apoptosis of DA and alleviated the increase in Th17 cells and decrease in Tregs in PD.

The role of the adaptive immune system and T cell dysfunction in neurodegenerative diseases

The adaptive immune system and associated inflammation are vital in surveillance and host protection against internal and external threats, but can secondarily damage host tissues. The central nervous system is immune-privileged and largely protected from the circulating inflammatory pathways. However, T cell involvement and the disruption of the blood-brain barriers have been linked to several neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, and multiple sclerosis. Under normal physiological conditions, regulatory T cells (Treg cells) dampen the inflammatory response of effector T cells. In the pathological states of many neurodegenerative disorders, the ability of Treg cells to mitigate inflammation is reduced, and a pro-inflammatory environment persists. This perspective review provides current knowledge on the roles of T cell subsets (e.g., effector T cells, Treg cells) in neurodegenerative and ocular diseases, including uveitis, diabetic retinopathy, age-related macular degeneration, and glaucoma. Many neurodegenerative and ocular diseases have been linked to immune dysregulation, but the cellular events and molecular mechanisms involved in such processes remain largely unknown. Moreover, the role of T cells in ocular pathologies remains poorly defined and limited literature is available in this area of research. Adoptive transfer of Treg cells appears to be a vital immunological approach to control ocular pathologies. Similarities in T cell dysfunction seen among non-ocular neurodegenerative diseases suggest that this area of research has a great potential to develop better therapeutic agents for ocular diseases and warrants further studies. Overall, this perspective review article provides significant information on the roles of T cells in numerous ocular and non-ocular neurodegenerative diseases.

The Innate and Adaptive Immune Cells in Alzheimer’s and Parkinson’s Diseases

Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common neurodegenerative disorders of the central nervous system (CNS). Increasing evidence supports the view that dysfunction of innate immune cells initiated by accumulated and misfolded proteins plays essential roles in the pathogenesis and progression of these diseases. The TLR family was found to be involved in the regulation of microglial function in the pathogenesis and progression of AD or PD, making it as double-edged sword in these diseases. Altered function of peripheral innate immune cells was found in AD and PD and thus contributed to the development and progression of AD and PD. Alteration of different subsets of T cells was found in the peripheral blood and CNS in AD and PD. The CNS-infiltrating T cells can exert both neuroprotective and neurotoxic effects in the pathogenesis and progression. Here, we review recent evidences for the roles of innate and adaptive immune cells in the pathogenesis and progression of AD and PD.

Identification of Immune-Related Hub Genes in Parkinson’s Disease

Background: Parkinson’s disease (PD) is a common, age-related, and progressive neurodegenerative disease. Growing evidence indicates that immune dysfunction plays an essential role in the pathogenic process of PD. The objective of this study was to explore potential immune-related hub genes and immune infiltration patterns of PD.

Method: The microarray expression data of human postmortem substantia nigra samples were downloaded from GSE7621, GSE20141, and GSE49036. Key module genes were screened via weighted gene coexpression network analysis, and immune-related genes were intersected to obtain immune-key genes. Functional enrichment analysis was performed on immune-key genes of PD. In addition to, immune infiltration analysis was applied by a single-sample gene set enrichment analysis algorithm to detect differential immune cell types in the substantia nigra between PD samples and control samples. Least absolute shrinkage and selection operator analysis was performed to further identify immune-related hub genes for PD. Receiver operating characteristic curve analysis of the immune-related hub genes was used to differentiate PD patients from healthy controls. Correlations between immune-related hub genes and differential immune cell types were assessed.

Result: Our findings identified four hub genes (SLC18A2, L1CAM, S100A12, and CXCR4) and seven immune cell types (neutrophils, T follicular helper cells, myeloid-derived suppressor cells, type 1 helper cells, immature B cells, immature dendritic cells, and CD56 bright natural killer cells). The area under the curve (AUC) value of the four-gene-combined model was 0.92. The AUC values of each immune-related hub gene (SLC18A2, L1CAM, S100A12, and CXCR4) were 0.81, 0.78, 0.78, and 0.76, respectively.

Conclusion: In conclusion, SLC18A2, L1CAM, S100A12, and CXCR4 were identified as being associated with the pathogenesis of PD and should be further researched.

Emerging Roles of T Helper Cells in Non-Infectious Neuroinflammation: Savior or Sinner

CD4⁺ T cells, also known as T helper (Th) cells, contribute to the adaptive immunity both in the periphery and in the central nervous system (CNS). At least seven subsets of Th cells along with their signature cytokines have been identified nowadays. Neuroinflammation denotes the brain’s immune response to inflammatory conditions. In recent years, various CNS disorders have been related to the dysregulation of adaptive immunity, especially the process concerning Th cells and their cytokines. However, as the functions of Th cells are being discovered, it’s also found that their roles in different neuroinflammatory conditions, or even the participation of a specific Th subset in one CNS disorder may differ, and sometimes contrast. Based on those recent and contradictory evidence, the conflicting roles of Th cells in multiple sclerosis, Alzheimer’s disease, Parkinson’s disease, epilepsy, traumatic brain injury as well as some typical mental disorders will be reviewed herein. Research progress, limitations and novel approaches concerning different neuroinflammatory conditions will also be mentioned and compared.

Neuroinflammation in Parkinson's Disease - Putative Pathomechanisms and Targets for Disease-Modification

Parkinson’s disease (PD) is a progressive and debilitating chronic disease that affects more than six million people worldwide, with rising prevalence. The hallmarks of PD are motor deficits, the spreading of pathological α-synuclein clusters in the central nervous system, and neuroinflammatory processes. PD is treated symptomatically, as no causally-acting drug or procedure has been successfully established for clinical use. Various pathways contributing to dopaminergic neuron loss in PD have been investigated and described to interact with the innate and adaptive immune system. We discuss the possible contribution of interconnected pathways related to the immune response, focusing on the pathophysiology and neurodegeneration of PD. In addition, we provide an overview of clinical trials targeting neuroinflammation in PD.

Changes of T lymphocyte subpopulations and their roles in predicting the risk of Parkinson's disease

T lymphocytes are involved in the pathogenesis of Parkinson's disease (PD), while the heterogeneity of T-cell subpopulations remains elusive. In this study, we analyzed up to 22 subpopulations of T lymphocytes in 115 PD patients and 60 matched healthy controls (HC) using flow cytometry. We found that PD patients exhibited decreased naïve CD8⁺ T cells (CD3⁺ CD8⁺ CD45RA⁺ CD45RO^-) and increased late-differentiated CD4⁺ T cells (CD3⁺ CD4⁺ CD28^- CD27^-), compared to HC, which were not affected by anti-parkinsonism medication administration. The proportion of naïve CD8⁺ T cells in PD patients was positively correlated with their severity of autonomic dysfunction and psychiatric complications, but negatively associated with the severity of rapid eye movement and sleep behavior disorder. The proportion of late-differentiated CD4⁺ T cells was negatively correlated with the onset age of the disease. We further developed individualized PD risk prediction models with high reliability and accuracy on the base of the T lymphocyte subpopulations. These data suggest that peripheral cellular immunity is disturbed in PD patients, and changes in CD8⁺ T cells and late-differentiated CD4⁺ T cells are representative and significant. Therefore, we recommend naïve CD8 + and late-differentiated CD4⁺ T cells as candidates for multicentric clinical study and pathomechanism study of PD.

T Lymphocytes in Parkinson's Disease

T cells are key mediators of both humoral and cellular adaptive immune responses, and their role in Parkinson’s disease (PD) is being increasingly recognized. Several lines of evidence have highlighted how T cells are involved in both the central nervous system and the periphery, leading to a profound imbalance in the immune network in PD patients. This review discusses the involvement of T cells in both preclinical and clinical studies, their importance as feasible biomarkers of motor and non-motor progression of the disease, and recent therapeutic strategies addressing the modulation of T cell response.

T cells, α-synuclein and Parkinson disease

The notion that autoimmune responses to α-synuclein may be involved in the pathogenesis of this disorder stems from reports that mutations in α-synuclein or certain alleles of the major histocompatibility complex (MHC) are associated with the disease and that dopaminergic and norepinephrinergic neurons in the midbrain can present antigenic epitopes. Here, we discuss recent evidence that a defined set of peptides derived from α-synuclein act as antigenic epitopes displayed by specific MHC alleles and drive helper and cytotoxic T cell responses in patients with PD. Moreover, phosphorylated α-synuclein may activate T cell responses in a less restricted manner in PD. While the roles for the acquired immune system in disease pathogenesis remain unknown, preclinical animal models and in vitro studies indicate that T cells may interact with neurons and exert effects related to neuronal death and neuroprotection. These findings suggest that therapeutics that target T cells and ameliorate the incidence or disease severity of inflammatory bowel disorders or CNS autoimmune diseases such as multiple sclerosis may be useful in PD.

Immunotherapeutic interventions in Parkinson's disease: Focus on α-Synuclein

Parkinson's disease (PD) is a neurodegenerative disorder characterized classically by motor manifestations. However, nonmotor symptoms appear early in the course of the disease progression, making both diagnosis and treatment difficult. The pathology of PD is complicated by the accumulation and aggregation of misfolded proteins in intracellular cytoplasmic inclusions called Lewy bodies (LBs). The main toxic component of LBs is the protein α-Synuclein which plays a pivotal role in PD pathogenesis. α-Synuclein can propagate from cell-to-cell exhibiting prion-like properties and spread PD pathology throughout the central nervous system. Immunotherapeutic interventions in PD, both active and passive immunization, have targeted α-Synuclein in both experimental models and clinical trials. In addition, targeting the hyperactive inflammation in PD also holds promise in designing potential immunotherapeutics. The inflammatory and proteotoxic pathways are interlinked and contribute immensely to the disease pathology. In this chapter, we critically review the targets of immunotherapeutic interventions in PD, focusing on the pathogenetic mechanisms of PD, particularly neuroinflammation and α-Synuclein misfolding, aggregation, and propagation. We thoroughly summarized the various immunotherapeutic strategies designed to treat PD-in vitro, in vivo, and clinical trials. The development of these targeted immunotherapies could open a new avenue in the treatment of patients with PD.

Neuro-Immunity and Gut Dysbiosis Drive Parkinson's Disease-Induced Pain

Parkinson's disease (PD) is the second most common neurodegenerative disorder, affecting 1-2% of the population aged 65 and over. Additionally, non-motor symptoms such as pain and gastrointestinal dysregulation are also common in PD. These impairments might stem from a dysregulation within the gut-brain axis that alters immunity and the inflammatory state and subsequently drives neurodegeneration. There is increasing evidence linking gut dysbiosis to the severity of PD's motor symptoms as well as to somatosensory hypersensitivities. Altogether, these interdependent features highlight the urgency of reviewing the links between the onset of PD's non-motor symptoms and gut immunity and whether such interplays drive the progression of PD. This review will shed light on maladaptive neuro-immune crosstalk in the context of gut dysbiosis and will posit that such deleterious interplays lead to PD-induced pain hypersensitivity.

Regulation of common neurological disorders by gut microbial metabolites

The gut is connected to the CNS by immunological mediators, lymphocytes, neurotransmitters, microbes and microbial metabolites. A mounting body of evidence indicates that the microbiome exerts significant effects on immune cells and CNS cells. These effects frequently result in the suppression or exacerbation of inflammatory responses, the latter of which can lead to severe tissue damage, altered synapse formation and disrupted maintenance of the CNS. Herein, we review recent progress in research on the microbial regulation of CNS diseases with a focus on major gut microbial metabolites, such as short-chain fatty acids, tryptophan metabolites, and secondary bile acids. Pathological changes in the CNS are associated with dysbiosis and altered levels of microbial metabolites, which can further exacerbate various neurological disorders. The cellular and molecular mechanisms by which these gut microbial metabolites regulate inflammatory diseases in the CNS are discussed. We highlight the similarities and differences in the impact on four major CNS diseases, i.e., multiple sclerosis, Parkinson's disease, Alzheimer's disease, and autism spectrum disorder, to identify common cellular and molecular networks governing the regulation of cellular constituents and pathogenesis in the CNS by microbial metabolites.

Alpha-Synuclein Induced Immune Cells Activation and Associated Therapy in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder closely related to immunity. An important aspect of the pathogenesis of PD is the interaction between α-synuclein and a series of immune cells. Studies have shown that accumulation of α-synuclein can induce an autoimmune response that accelerates the progression of PD. This study discusses the mechanisms underlying the interaction between α-synuclein and the immune system. During the development of PD, abnormally accumulated α-synuclein becomes an autoimmune antigen that binds to Toll-like receptors (TLRs) that activate microglia, which differentiate into the microglia type 1 (M1) subtype. The microglia activate intracellular inflammatory pathways, induce the release of proinflammatory cytokines, and promote the differentiation of cluster of differentiation 4 + (CD4 +) T cells into proinflammatory T helper type 1 (Th1) and T helper type 17 (Th17) subtypes. Given the important role of α-synuclein in the immune system of the patients with PD, identifying potential targets of immunotherapy related to α-synuclein is critical for slowing disease progression. An enhanced understanding of immune-associated mechanisms in PD can guide the development of associated therapeutic strategies in the future.

T-cell dysregulation is associated with disease severity in Parkinson's Disease

The dysregulation of peripheral immunity in Parkinson’s Disease (PD) includes changes in both the relative numbers and gene expression of T cells. The presence of peripheral T-cell abnormalities in PD is well-documented, but less is known about their association to clinical parameters, such as age, age of onset, progression rate or severity of the disease. We took a detailed look at T-cell numbers, gene expression and activation in cross-sectional cohorts of PD patients and age-matched healthy controls by means of flow cytometry and NanoString gene expression assay. We show that the well-pronounced decrease in relative T-cell numbers in PD blood is mostly driven by a decrease of CD8⁺ cytotoxic T cells and is primarily associated with the severity of the disease. In addition, we demonstrate that the expression of inflammatory genes in T cells from PD patients is also associated with disease severity. PD T cells presented with increased activation upon stimulation with phytohemagglutinin that also correlated with disease severity. In summary, our data suggest that the consequences of disease severity account for the changes in PD T cells, rather than age, age of onset, duration or the disease progression rate.

Platelet Behavior Contributes to Neuropathologies: A Focus on Alzheimer's and Parkinson's Disease

The functions of platelets are broad. Platelets function in hemostasis and thrombosis, inflammation and immune responses, vascular regulation, and host defense against invading pathogens, among others. These actions are achieved through the release of a wide set of coagulative, vascular, inflammatory, and other factors as well as diverse cell surface receptors involved in the same activities. As active participants in these physiological processes, platelets become involved in signaling pathways and pathological reactions that contribute to diseases that are defined by inflammation (including by pathogen-derived stimuli), vascular dysfunction, and coagulation. These diseases include Alzheimer's and Parkinson's disease, the two most common neurodegenerative diseases. Despite their unique pathological and clinical features, significant shared pathological processes exist between these two conditions, particularly relating to a central inflammatory mechanism involving both neuroinflammation and inflammation in the systemic environment, but also neurovascular dysfunction and coagulopathy, processes which also share initiation factors and receptors. This triad of dysfunction-(neuro)inflammation, neurovascular dysfunction, and hypercoagulation-illustrates the important roles platelets play in neuropathology. Although some mechanisms are understudied in Alzheimer's and Parkinson's disease, a strong case can be made for the relevance of platelets in neurodegeneration-related processes.

Interleukin-17 and Th17 Lymphocytes Directly Impair Motoneuron Survival of Wildtype and FUS-ALS Mutant Human iPSCs

Amyotrophic lateral sclerosis (ALS) is a progressive disease leading to the degeneration of motor neurons (MNs). Neuroinflammation is involved in the pathogenesis of ALS; however, interactions of specific immune cell types and MNs are not well studied. We recently found a shift toward T helper (Th)1/Th17 cell-mediated, pro-inflammatory immune responses in the peripheral immune system of ALS patients, which positively correlated with disease severity and progression. Whether Th17 cells or their central mediator, Interleukin-17 (IL-17), directly affects human motor neuron survival is currently unknown. Here, we evaluated the contribution of Th17 cells and IL-17 on MN degeneration using the co-culture of iPSC-derived MNs of fused in sarcoma (FUS)-ALS patients and isogenic controls with Th17 lymphocytes derived from ALS patients, healthy controls, and multiple sclerosis (MS) patients (positive control). Only Th17 cells from MS patients induced severe MN degeneration in FUS-ALS as well as in wildtype MNs. Their main effector, IL-17A, yielded in a dose-dependent decline of the viability and neurite length of MNs. Surprisingly, IL-17F did not influence MNs. Importantly, neutralizing IL-17A and anti-IL-17 receptor A treatment reverted all effects of IL-17A. Our results offer compelling evidence that Th17 cells and IL-17A do directly contribute to MN degeneration.

Dysregulation of the Adaptive Immune System in Patients With Early-Stage Parkinson Disease

Objective

To determine the activation status and cytokine profiles of CD4⁺ T cells, CD8⁺ T cells, and CD19⁺ B cells from patients with early-stage Parkinson disease (PD) compared with healthy controls (HCs).

Methods

Peripheral blood samples from 41 patients with early-stage PD and 40 HCs were evaluated. Peripheral blood mononuclear cells were analyzed by flow cytometry for surface markers and intracellular cytokine production. Correlations of immunologic changes and clinical parameters were analyzed.

Results

Adaptive immunity plays a role in the pathogenesis of PD, yet the contribution of T cells and B cells, especially cytokine production by these cells, is poorly understood. We demonstrate that naive CD4⁺ and naive CD8⁺ T cells are significantly decreased in patients with PD, whereas central memory CD4⁺ T cells are significantly increased in patients with PD. Furthermore, IL-17–producing CD4⁺ Th17 cells, IL-4–producing CD4⁺ Th2 cells, and IFN-γ–producing CD8⁺ T cells are significantly increased in patients with PD. Regarding B cells, we observed a decrease in naive B cells and an increase in nonswitched memory and double-negative B cells. As well, TNF-α–producing CD19⁺ B cells were significantly increased in patients with PD. Notably, some of the changes observed in CD4⁺ T cells and B cells were associated with clinical motor disease severity.

Conclusions

These findings suggest that alterations in the adaptive immune system may promote clinical disease in PD by skewing to a more proinflammatory state in the early-stage PD patient cohort. Our study may shed light on potential immunotherapies targeting dysregulated CD4⁺ T cells, CD8⁺ T cells, and CD19⁺ B cells in patients with PD.

Perinatal Inflammation Reprograms Neuroendocrine, Immune, and Reproductive Functions: Profile of Cytokine Biomarkers

Viral and bacterial infections causing systemic inflammation are significant risk factors for developing body. Inflammatory processes can alter physiological levels of regulatory factors and interfere with developmental mechanisms. The brain is the main target for the negative impact of inflammatory products during critical ontogenetic periods. Subsequently, the risks of various neuropsychiatric diseases such as Alzheimer's and Parkinson's diseases, schizophrenia, and depression are increased in the offspring. Inflammation-induced physiological disturbances can cause immune and behavioral disorders, reproductive deficiencies, and infertility. The influence of maternal immune stress is mediated by the regulation of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, monocyte chemotactic protein 1, leukemia-inhibiting factor, and tumor necrosis factor-alpha secretion in the maternal-fetal system. The increasing number of patients with neuronal and reproductive disorders substantiates the identification of biomarkers for these disorders targeted at their therapy.

Ex vivo expansion of dysfunctional regulatory T lymphocytes restores suppressive function in Parkinson's disease

Inflammation is a pathological hallmark of Parkinson's disease (PD). Chronic pro-inflammatory responses contribute to the loss of neurons in the neurodegenerative process. The present study was undertaken to define the peripheral innate and adaptive immune contributions to inflammation in patients with PD. Immunophenotyping revealed a shift of peripheral myeloid and lymphoid cells towards a pro-inflammatory phenotype. Regulatory T cells (Tregs) were reduced in number, and their suppression of T responder proliferation decreased. The PD Tregs did not suppress activated pro-inflammatory myeloid cells. Ex vivo expansion of Tregs from patients with PD restored and enhanced their suppressive functions while expanded Tregs displayed increased expression of foxp3, il2ra (CD25), nt5e (CD73), il10, il13, ctla4, pdcd1 (PD1), and gzmb. Collectively, these findings documented a shift towards a pro-inflammatory peripheral immune response in patients with PD; the loss of Treg suppressive functions may contribute significantly to this response, supporting PD as a disorder with extensive systemic pro-inflammatory responses. The restoration and enhancement of Treg suppressive functions following ex vivo expansion may provide a potential cell therapeutic approach for patients with PD.

MDSCs, ageing and inflammageing

The challenge of distinguishing between changes attributable to ageing and those attributable to pathology is even greater for the immune system than for many other organs, and this is especially true for myeloid-derived suppressor cells (MDSCs). Hematopoiesis is different in older adults with a bias towards myelopoiesis, and older adults also manifest "inflammageing" exacerbated by disease and contributing to MDSC induction. Hence, at least in humans, one can only investigate MDSCs in the context of ageing and disease states, and not in the context of ageing processes per se. This contribution provides a brief overview of the literature on MDSCs and ageing in humans.

Progress in the molecular pathogenesis and nucleic acid therapeutics for Parkinson's disease in the precision medicine era

Parkinson's disease (PD) is one of the most common neurodegenerative disorders that manifest various motor and nonmotor symptoms. Although currently available therapies can alleviate some of the symptoms, the disease continues to progress, leading eventually to severe motor and cognitive decline and reduced life expectancy. The past two decades have witnessed rapid progress in our understanding of the molecular and genetic pathogenesis of the disease, paving the way for the development of new therapeutic approaches to arrest or delay the neurodegenerative process. As a result of these advances, biomarker‐driven subtyping is making it possible to stratify PD patients into more homogeneous subgroups that may better respond to potential genetic‐molecular pathway targeted disease‐modifying therapies. Therapeutic nucleic acid oligomers can bind to target gene sequences with very high specificity in a base‐pairing manner and precisely modulate downstream molecular events. Recently, nucleic acid therapeutics have proven effective in the treatment of a number of severe neurological and neuromuscular disorders, drawing increasing attention to the possibility of developing novel molecular therapies for PD. In this review, we update the molecular pathogenesis of PD and discuss progress in the use of antisense oligonucleotides, small interfering RNAs, short hairpin RNAs, aptamers, and microRNA‐based therapeutics to target critical elements in the pathogenesis of PD that could have the potential to modify disease progression. In addition, recent advances in the delivery of nucleic acid compounds across the blood–brain barrier and challenges facing PD clinical trials are also reviewed.

Circulating immune cell phenotype dynamics reflect the strength of tumor-immune cell interactions in patients during immunotherapy

The extent to which immune cell phenotypes in the peripheral blood reflect within-tumor immune activity prior to and early in cancer therapy is unclear. To address this question, we studied the population dynamics of tumor and immune cells, and immune phenotypic changes, using clinical tumor and immune cell measurements and single-cell genomic analyses. These samples were serially obtained from a cohort of advanced gastrointestinal cancer patients enrolled in a trial with chemotherapy and immunotherapy. Using an ecological population model, fitted to clinical tumor burden and immune cell abundance data from each patient, we find evidence of a strong tumor-circulating immune cell interaction in responder patients but not in those patients that progress on treatment. Upon initiation of therapy, immune cell abundance increased rapidly in responsive patients, and once the peak level is reached tumor burden decreases, similar to models of predator-prey interactions; these dynamic patterns were absent in nonresponder patients. To interrogate phenotype dynamics of circulating immune cells, we performed single-cell RNA sequencing at serial time points during treatment. These data show that peripheral immune cell phenotypes were linked to the increased strength of patients' tumor-immune cell interaction, including increased cytotoxic differentiation and strong activation of interferon signaling in peripheral T cells in responder patients. Joint modeling of clinical and genomic data highlights the interactions between tumor and immune cell populations and reveals how variation in patient responsiveness can be explained by differences in peripheral immune cell signaling and differentiation soon after the initiation of immunotherapy.

Reduction of Peripheral Blood iNKT and γδT Cells in Patients With Parkinson's Disease: An Observational Study

Objective: To investigate the frequencies and numbers of invariant natural killer T (iNKT) cells and γδT cells in the peripheral blood of patients with the Parkinson's disease (PD), and to examine their association with the PD severity.

Methods: Peripheral blood samples from 47 PD patients (PD group) and 47 age-matched healthy control subjects (HC group) were collected. The frequencies and the absolute cell numbers were analyzed by flow cytometry. Mann-Whitney U-test was used to test the difference between two groups, where P < 0.05 was considered as significant. An ordered probit regression method was used to examine the association of the iNKT and γδT cells with severity of PD.

Results: Patients in the PD group showed significantly lower frequencies (0.039 vs. 0.139%; P = 0) and cell counts (308/mL vs. 1,371/mL; P = 0) of iNKT cells compared to the HC group. Moreover, the percentages and absolute numbers of γδT cells were significantly decreased in the PD group compared to the HC group (3.69 vs. 7.95% and 30/μL vs. 66/μL; P = 0). The iNKT cells were significantly reduced in PD patients with higher Unified Parkinson's Disease Rating Scale (UPDRS) scores or cognitive decline.

Conclusions: Cell frequencies and absolute numbers of iNKT cells and γδT cells are significantly reduced in the peripheral blood samples of PD patients. Patients with high UPDRS scores or cognitive decline also showed significant reduction of iNKT cells. Our results suggest that iNKT cells and γδT cells may contribute to the development of PD.

Harnessing regulatory T cell neuroprotective activities for treatment of neurodegenerative disorders

Emerging evidence demonstrates that adaptive immunity influences the pathobiology of neurodegenerative disorders. Misfolded aggregated self-proteins can break immune tolerance leading to the induction of autoreactive effector T cells (Teffs) with associated decreases in anti-inflammatory neuroprotective regulatory T cells (Tregs). An imbalance between Teffs and Tregs leads to microglial activation, inflammation and neuronal injury. The cascade of such a disordered immunity includes the drainage of the aggregated protein antigens into cervical lymph nodes serving to amplify effector immune responses. Both preclinical and clinical studies demonstrate transformation of this altered immunity for therapeutic gain. We posit that the signs and symptoms of common neurodegenerative disorders such as Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, and stroke can be attenuated by boosting Treg activities.

LRRK2 at the Interface Between Peripheral and Central Immune Function in Parkinson's

It is becoming increasingly accepted that there is an interplay between the peripheral immune response and neuroinflammation in the pathophysiology of Parkinson's disease (PD). Mutations in the leucine-rich-repeat kinase 2 (LRRK2) gene are associated with familial and sporadic cases of PD but are also found in immune-related disorders, such as inflammatory bowel disease (IBD) and leprosy. Furthermore, LRRK2 has been associated with bacterial infections such as Mycobacterium tuberculosis and Salmonella typhimurium. Recent evidence suggests a role of LRRK2 in the regulation of the immune system and modulation of inflammatory responses, at a systemic level, with LRRK2 functionally implicated in both the immune system of the central nervous system (CNS) and the periphery. It has therefore been suggested that peripheral immune signaling may play an important role in the regulation of neurodegeneration in LRRK2 as well as non-LRRK2-associated PD. This review will discuss the current evidence for this hypothesis and will provide compelling rationale for placing LRRK2 at the interface between peripheral immune responses and neuroinflammation.

Astrocytes have the capacity to act as antigen-presenting cells in the Parkinson's disease brain

Background

Many lines of evidence suggest that accumulation of aggregated alpha-synuclein (αSYN) in the Parkinson’s disease (PD) brain causes infiltration of T cells. However, in which ways the stationary brain cells interact with the T cells remain elusive. Here, we identify astrocytes as potential antigen-presenting cells capable of activating T cells in the PD brain. Astrocytes are a major component of the nervous system, and accumulating data indicate that astrocytes can play a central role during PD progression.

Methods

To investigate the role of astrocytes in antigen presentation and T-cell activation in the PD brain, we analyzed post mortem brain tissue from PD patients and controls. Moreover, we studied the capacity of cultured human astrocytes and adult human microglia to act as professional antigen-presenting cells following exposure to preformed αSYN fibrils.

Results

Our analysis of post mortem brain tissue demonstrated that PD patients express high levels of MHC-II, which correlated with the load of pathological, phosphorylated αSYN. Interestingly, a very high proportion of the MHC-II co-localized with astrocytic markers. Importantly, we found both perivascular and infiltrated CD4⁺ T cells to be surrounded by MHC-II expressing astrocytes, confirming an astrocyte T cell cross-talk in the PD brain. Moreover, we showed that αSYN accumulation in cultured human astrocytes triggered surface expression of co-stimulatory molecules critical for T-cell activation, while cultured human microglia displayed very poor antigen presentation capacity. Notably, intercellular transfer of αSYN/MHC-II deposits occurred between astrocytes via tunneling nanotubes, indicating spreading of inflammation in addition to toxic protein aggregates.

Conclusions

In conclusion, our data from histology and cell culture studies suggest an important role for astrocytes in antigen presentation and T-cell activation in the PD brain, highlighting astrocytes as a promising therapeutic target in the context of chronic inflammation.

Regulatory impairment in untreated Parkinson's disease is not restricted to Tregs: other regulatory populations are also involved

BACKGROUND

Parkinson's disease (PD) is the second most common neurodegenerative disease in the world. Various studies have suggested that the immune response plays a key role in this pathology. While a predominantly pro-inflammatory peripheral immune response has been reported in treated and untreated PD patients, the study of the role of the regulatory immune response has been restricted to regulatory T cells. Other immune suppressive populations have been described recently, but their role in PD is still unknown. This study was designed to analyze the pro and anti-inflammatory immune response in untreated PD patients, with emphasis on the regulatory response.

METHODS

Thirty-two PD untreated patients and 20 healthy individuals were included in this study. Peripheral regulatory cells (CD4+Tregs, Bregs, CD8+Tregs, and tolerogenic dendritic cells), pro-inflammatory cells (Th1, Th2, and Th17 cells; active dendritic cells), and classical, intermediate, and non-classical monocytes were characterized by flow cytometry. Plasmatic levels of TNF-α, IFN-γ, IL-6, GM-CSF, IL-12p70, IL-4, IL-13, IL-17α, IL-1β, IL-10, TGF-β, and IL-35 were determined by ELISA.

RESULTS

Decreased levels of suppressor Tregs, active Tregs, Tr1 cells, IL-10-producer CD8regs, and tolerogenic PD-L1+ dendritic cells were observed. With respect to the pro-inflammatory response, a decrease in IL-17-α and an increase in IL-13 levels were observed.

CONCLUSION

A decrease in the levels of regulatory cell subpopulations in untreated PD patients is reported for the first time in this work. These results suggest that PD patients may exhibit a deficient suppression of the pro-inflammatory response, which could contribute to the pathophysiology of the disease.

The incidence rates and risk factors of Parkinson disease in patients with psoriasis: A nationwide population-based cohort study

BACKGROUND

The association between psoriasis and Parkinson disease has not been established.

OBJECTIVE

To determine the incidence rates and risk factors of Parkinson disease in patients with psoriasis.

METHODS

We conducted a nationwide population-based cohort study. The data from patients with psoriasis (N = 548,327, ≥20 years of age, 53.32% men and 46.68% women) and age- and sex-matched control patients (N = 2,741,635) without psoriasis were analyzed in this study.

RESULTS

The incidence rates of Parkinson disease per 1000 person-years were 0.673 and 0.768 in the control and psoriasis groups, respectively. The psoriasis group showed a significantly increased risk of developing Parkinson disease (hazard ratio [HR] 1.091, 95% confidence interval [CI] 1.029-1.115). The risk of Parkinson disease was significantly higher among the psoriasis patients who were not receiving systemic therapy (HR 1.093, 95% CI 1.031-1.159) and lower among the psoriasis patients on systemic therapy (HR 1.04, 95% CI 0.806-1.316).

LIMITATIONS

The limitations of this study included the retrospective design, patient inclusion solely on the basis of diagnostic codes, and unavailability of data on confounding factors.

CONCLUSION

Systemic anti-inflammatory agents might mitigate the risk of Parkinson disease in psoriasis patients.

Myeloid-Derived Suppressor Cells: Not Only in Tumor Immunity

Since the realization that immature myeloid cells are powerful modulators of the immune response, many studies on “myeloid-derived suppressor cells” (MDSCs) have documented their ability to promote tumor progression in melanoma and other cancers. Whether MDSCs are induced solely pathologically in tumorigenesis, or whether they also represent physiological immune control mechanisms, is not well-understood, but is particularly important in the light of ongoing attempts to block their activities in order to enhance anti-tumor immunity. Here, we briefly review studies which explore (1) how best to identify MDSCs in the context of cancer and how this compares to other conditions in humans; (2) what the suppressive mechanisms of MDSCs are and how to target them pharmacologically; (3) whether levels of MDSCs with various phenotypes are informative for clinical outcome not only in cancer but also other diseases, and (4) whether MDSCs are only found under pathological conditions or whether they also represent a physiological regulatory mechanism for the feedback control of immunity. Studies unequivocally document that MDSCs strongly influence cancer outcomes, but are less informative regarding their relevance to infection, autoimmunity, transplantation and aging, especially in humans. So far, the results of clinical interventions to reverse their negative effects in cancer have been disappointing; thus, developing differential approaches to modulate MSDCs in cancer and other diseases without unduly comprising any normal physiological function requires further exploration.

Th17 cells: a promising therapeutic target for Parkinson's disease?

INTRODUCTION

Parkinson's disease (PD) is the most common neurodegenerative movement disorder caused by the progressive loss of neurons in the midbrain and other brain regions. Only symptomatic treatment is currently available. Mounting evidence suggests that T cells are a key contributor to PD pathogenesis and neurodegeneration by a mechanism that requires further elucidation. Areas covered: We discuss the evidence of imbalanced activation of effector T cell populations in PD and summarize the data of Th17 involvement and Th17-regulated mechanisms in PD pathology. Moreover, possible Th17-related molecular targets as possible neuroprotective immunomodulatory therapeutic targets for PD are examined. Expert Opinion: Existing data show that Th17 cells, their effector molecules, and signaling pathways are potentially effective therapeutic targets for neuroprotective immunomodulation in PD treatment. However, specificity of action within Th17-mediated signaling pathways for PD requires careful consideration.

Autoimmunity in Parkinson's Disease: The Role of α-Synuclein-Specific T Cells

Evidence from a variety of studies implicates a role for the adaptive immune system in Parkinson's disease (PD). Similar to multiple sclerosis (MS) patients who display a high number of T cells in the brain attacking oligodendrocytes, PD patients show higher numbers of T cells in the ventral midbrain than healthy, age-matched controls. Mouse models of the disease also show the presence of T cells in the brain. The role of these infiltrating T cells in the propagation of disease is controversial; however, recent studies indicate that they may be autoreactive in nature, recognizing disease-altered self-proteins as foreign antigens. T cells of PD patients can generate an autoimmune response to α-synuclein, a protein that is aggregated in PD. α-Synuclein and other proteins are post-translationally modified in an environment in which protein processing is altered, possibly leading to the generation of neo-epitopes, or self-peptides that have not been identified by the host immune system as non-foreign. Infiltrating T cells may also be responding to such modified proteins. Genome-wide association studies (GWAS) have shown associations of PD with haplotypes of major histocompatibility complex (MHC) class II genes, and a polymorphism in a non-coding region that may increase MHC class II in PD patients. We speculate that the inflammation observed in PD may play both pathogenic and protective roles. Future studies on the adaptive immune system in neurodegenerative disorders may elucidate steps in disease pathogenesis and assist with the development of both biomarkers and treatments.

T-Cell-Driven Inflammation as a Mediator of the Gut-Brain Axis Involved in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder affecting mainly the dopaminergic neurons of the nigrostriatal pathway, a neuronal circuit involved in the control of movements, thereby the main manifestations correspond to motor impairments. The major molecular hallmark of this disease corresponds to the presence of pathological protein inclusions called Lewy bodies in the midbrain of patients, which have been extensively associated with neurotoxic effects. Importantly, different research groups have demonstrated that CD4⁺ T-cells infiltrate into the substantia nigra of PD patients and animal models. Moreover, several studies have consistently demonstrated that T-cell deficiency results in a strong attenuation of dopaminergic neurodegeneration in animal models of PD, thus indicating a key role of adaptive immunity in the neurodegenerative process. Recent evidence has shown that CD4⁺ T-cell response involved in PD patients is directed to oxidised forms of α-synuclein, one of the main constituents of Lewy bodies. On the other hand, most PD patients present a number of non-motor manifestations. Among non-motor manifestations, gastrointestinal dysfunctions result especially important as potential early biomarkers of PD, since they are ubiquitously found among confirmed patients and occur much earlier than motor symptoms. These gastrointestinal dysfunctions include constipation and inflammation of the gut mucosa and the most distinctive pathologic features associated are the loss of neurons of the enteric nervous system and the generation of Lewy bodies in the gut. Moreover, emerging evidence has recently shown a pivotal role of gut microbiota in triggering the development of PD in genetically predisposed individuals. Of note, PD has been positively correlated with inflammatory bowel diseases, a group of disorders involving a T-cell driven inflammation of gut mucosa, which is strongly dependent in the composition of gut microbiota. Here we raised the hypothesis that T-cell driven inflammation, which mediates dopaminergic neurodegeneration in PD, is triggered in the gut mucosa. Accordingly, we discuss how structural components of commensal bacteria or how different mediators produced by gut-microbiota, including short-chain fatty acids and dopamine, may affect the behaviour of T-cells, triggering the development of T-cell responses against Lewy bodies, initially confined to the gut mucosa but later extended to the brain.

Do Th17 Lymphocytes and IL-17 Contribute to Parkinson's Disease? A Systematic Review of Available Evidence

Parkinson's disease (PD) is a neurodegenerative disease characterized by progressive loss of dopaminergic neurons, appearance of Lewy bodies and presence of neuroinflammation. No treatments currently exist to prevent PD or delay its progression, and dopaminergic substitution treatments just relieve the consequences of dopaminergic neuron loss. Increasing evidence points to peripheral T lymphocytes as key players in PD, and recently there has been growing interest into the specific role of T helper (Th) 17 lymphocytes. Th17 are a proinflammatory CD4+ T cell lineage named after interleukin (IL)-17, the main cytokine produced by these cells. Th17 are involved in immune-related disease such as psoriasis, rheumatoid arthritis and inflammatory bowel disease, and drugs targeting Th17/IL-17 are currently approved for clinical use in such disease. In the present paper, we first summarized current knowledge about contribution of the peripheral immune system in PD, as well as about the physiopharmacology of Th17 and IL-17 together with its therapeutic relevance. Thereafter, we systematically retrieved and evaluated published evidence about Th17 and IL-17 in PD, to help assessing Th17/IL-17-targeting drugs as potentially novel antiparkinson agents. Critical appraisal of the evidence did not allow to reach definite conclusions: both animal as well as clinical studies are limited, just a few provide mechanistic evidence and none of them investigates the eventual relationship between Th17/IL-17 and clinically relevant endpoints such as disease progression, disability scores, intensity of dopaminergic substitution treatment. Careful assessment of Th17 in PD is anyway a priority, as Th17/IL-17-targeting therapeutics might represent a straightforward opportunity for the unmet needs of PD patients.

The Yin and Yang of Myeloid Derived Suppressor Cells

In recent years, most of our knowledge about myeloid derived suppressor cells (MDSCs) has come from cancer studies, which depicts Yin side of MDSCs. In cancer, inherent immunosuppressive action of MDSCs favors tumor progression by inhibiting antitumor immune response. However, recently Yang side of MDSCs has also been worked out and suggests the role in maintenance of homeostasis during non-cancer situations like pregnancy, obesity, diabetes, and autoimmune disorders. Continued work in this area has armored the biological importance of these cells as master regulators of immune system and prompted scientists all over the world to look from a different perspective. Therefore, explicating Yin and Yang arms of MDSCs is obligatory to use it as a double edged sword in a much smarter way. This review is an attempt toward presenting a synergistic coalition of all the facts and controversies that exist in understanding MDSCs, bring them on the same platform and approach their "Yin and Yang" nature in a more comprehensive and coherent manner.