LRRK2 Affects Vesicle Trafficking,Neurotransmitter Extracellular Level and Membrane Receptor Localization

The leucine-rich repeat kinase 2 (LRRK2) gene was found to play a role in the pathogenesis of both familial and sporadic Parkinson’s disease (PD). LRRK2 encodes a large multi-domain protein that is expressed in different tissues. To date, the physiological and pathological functions of LRRK2 are not clearly defined. In this study we have explored the role of LRRK2 in controlling vesicle trafficking in different cellular or animal models and using various readouts. In neuronal cells, the presence of LRRK2^G2019S pathological mutant determines increased extracellular dopamine levels either under basal conditions or upon nicotine stimulation. Moreover, mutant LRRK2 affects the levels of dopamine receptor D1 on the membrane surface in neuronal cells or animal models. Ultrastructural analysis of PC12-derived cells expressing mutant LRRK2^G2019S shows an altered intracellular vesicle distribution. Taken together, our results point to the key role of LRRK2 to control vesicle trafficking in neuronal cells.     

Non-classical monocytes contribute to innate immune training in cattle

Innate immune training is defined as a property of innate immune cells to react stronger to a secondary contact with pathogens. Induction of innate immune training has been reported for a variety of pathogens and selected pattern recognition receptor-ligands, such as β-glucans (βG). We examined whether Saccharomyces cerevisiae cell wall component βG induces training in bovine monocytes in vitro based on a heightened TNF secretion after stimulation by trained monocyte-derived macrophages with Escherichia coli LPS. Sorted CD14-expressing monocytes (classical and intermediate monocytes), as well as single populations of sorted classical, intermediate and non-classical monocytes could not be trained by βG, whereas macrophages derived from plastic-adherent mononuclear cell preparations displayed features of a trained function. The hypothesis, that non-classical monocytes need to be present in a mixed monocyte population in order to be trained by βG could be verified by a successful training of positively sorted whole monocyte populations (CD14CD16/M) containing all three monocyte subpopulations. The trainability depended on conditions favoring M1 polarization of macrophages. Altogether, innate immune training of bovine monocytes seems to depend on the presence of non-classical monocytes. This adds new information to the role of this monocyte subpopulation in the bovine immune system.     

Apoptosis of peripheral blood lymphocytes in patients with LRRK2-assoctated Parkinson's disease

Mutations in the Leucine Reach Repeat Kinase 2 (LRRK2) gene are the most frequent cause of familial Parkinson's disease (PD). Although the precise physiological and pathological role of LRRK2 is unclear, a direct link between mutant LRRK2 and apoptosis has been suggested. Using flow cytometric analysis (PI+Annexin V(FITC)) we showed increased spontaneous apoptosis of peripheral blood lymphocytes in patients with LRRK.2-associated PD compared to controls after 24 (P < 0.016) and 48 (P < 0.031 ) h of incubation (5 % CO2, 37 degrees C). We found the increased FAS mRNA level in peripheral blood lymphocytes of patients with LRRK2-associated PD compared to controls (P < 0.05) and to sporadic PD (sPD) (P < 0.002). Significant difference in FAS expression between patients with LRRK2-associated PD and controls remained after three years and was detected after 1 and 24 h during lymphocyte incubation (P < 0.03 and 0.05, respectively). Increased spontaneous lymphocytes apoptosis along to increased FAS expression in patients with LRRK2-associated PD suggest that LRRK2 mutations may lead to the activation of extrinsic apoptotic way.     

Leucine-rich repeat kinase 2 induces α-synuclein expression via the extracellular signal-regulated kinase pathway

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most frequent cause of autosomal-dominant Parkinson's disease (PD). The second known autosomal-dominant PD gene (SNCA) encodes α-synuclein, which is deposited in Lewy bodies, the neuropathological hallmark of PD. LRRK2 contains a kinase domain with homology to mitogen-activated protein kinase kinase kinases (MAPKKKs) and its activity has been suggested to be a key factor in LRRK2-associated PD. Here we investigated the role of LRRK2 in signal transduction pathways to identify putative PD-relevant downstream targets. Over-expression of wild-type [wt]LRRK2 in human embryonic kidney HEK293 cells selectively activated the extracellular signal-regulated kinase (ERK) module. PD-associated mutants G2019S and R1441C, but not kinase-dead LRRK2, induced ERK phosphorylation to the same extent as [wt]LRRK2, indicating that this effect is kinase-dependent. However, ERK activation by mutant R1441C and G2019S was significantly slower than that for [wt]LRRK2, despite similar levels of expression. Furthermore, induction of the ERK module by LRRK2 was associated to a small but significant induction of SNCA, which was suppressed by treatment with the selective MAPK/ERK kinase inhibitor U0126. This pathway linking the two dominant PD genes LRRK2 and SNCA may offer an interesting target for drug therapy in both familial and sporadic disease.     

Metabolomic Profiling in LRRK2-Related Parkinson's Disease

Background

Mutations in LRRK2 gene represent the most common known genetic cause of Parkinson''s disease (PD).

Methodology/Principal Findings

We used metabolomic profiling to identify biomarkers that are associated with idiopathic and LRRK2 PD. We compared plasma metabolomic profiles of patients with PD due to the G2019S LRRK2 mutation, to asymptomatic family members of these patients either with or without G2019S LRRK2 mutations, and to patients with idiopathic PD, as well as non-related control subjects. We found that metabolomic profiles of both idiopathic PD and LRRK2 PD subjects were clearly separated from controls. LRRK2 PD patients had metabolomic profiles distinguishable from those with idiopathic PD, and the profiles could predict whether the PD was secondary to LRRK2 mutations or idiopathic. Metabolomic profiles of LRRK2 PD patients were well separated from their family members, but there was a slight overlap between family members with and without LRRK2 mutations. Both LRRK2 and idiopathic PD patients showed significantly reduced uric acid levels. We also found a significant decrease in levels of hypoxanthine and in the ratios of major metabolites of the purine pathway in plasma of PD patients.

Conclusions/Significance

These findings show that LRRK2 patients with the G2019S mutation have unique metabolomic profiles that distinguish them from patients with idiopathic PD. Furthermore, asymptomatic LRRK2 carriers can be separated from gene negative family members, which raises the possibility that metabolomic profiles could be useful in predicting which LRRK2 carriers will eventually develop PD. The results also suggest that there are aberrations in the purine pathway in PD which may occur upstream from uric acid.     

CD56+ monocytes have a dysregulated cytokine response to lipopolysaccharide and accumulate in rheumatoid arthritis and immunosenescence

Introduction

Peripheral blood monocytes are no longer regarded as a homogeneous cell population, but can be differentiated both phenotypically and functionally into various subpopulations. In rheumatoid arthritis, the subpopulation of CD14^bright/CD16+ monocyte is expanded and prone towards generation of Th17 cells. CD56+ monocytes represent a different subpopulation, which is also expanded in conditions associated with autoimmunity like inflammatory bowel diseases. The aim of the study was the quantification and functional characterization of the CD56+ monocyte subset in rheumatoid arthritis (RA).

Methods

Frequencies of peripheral blood monocyte subpopulations were analyzed by flow cytometry in 86 healthy controls and 75 RA patients. In 16 patients, anti-tumor necrosis factor (TNF) therapy was initiated, and the CD56+ monocyte frequency was monitored longitudinally. Lipopolysaccharide (LPS)-induced cytokine production of CD56+ and CD56– monocytes was determined by intracellular staining or cytokine secretion assays.

Results

In healthy individuals, 8.6% ± 0.6 of the monocytes co-expressed CD56, with the majority of CD56+ monocytes being CD14^bright (7.9% ± 0.5), while only a minor population was CD14^dim (0.7% ± 0.1). We found a strong positive correlation between an individual’s age and the frequency of CD56+ monocytes. Upon stimulation with LPS, CD56+ monocytes became more frequently positive for TNF, IL-10 and IL-23 than CD56– monocytes. In addition, CD56+ monocytes spontaneously produced more reactive oxygen intermediates than CD56- monocytes. In RA patients, the frequency of CD56+ monocytes was significantly higher than in healthy controls (12.2% ± 0.9 vs. 7.9% ± 0.5, p = 0.0002), and this difference most pronounced in RA patients below 40 years of age (11.1% ± 1.6 vs. 4.1% ± 0.4, P < 0.0001). Treatment of the patients with an anti-TNF blocking agent significantly reduced CD56+ monocyte frequencies (baseline 12.4% vs. 24 weeks treatment 8.0%, P = 0.0429), and the magnitude of this decrease was found to correlate with the change in disease activity under the therapy.

Conclusion

The CD14^bright/CD56+ monocyte subset is expanded in aging individuals as well as in patients with RA. The pro-inflammatory production of cytokines and reactive oxygen species as well as the elimination of those cells in patients with a good response towards TNF inhibiting agents indicates a possible contribution of those monocytes in the inflammatory response in RA.     

Imbalance of Circulating Monocyte Subsets and PD-1 Dysregulation in Q Fever Endocarditis: The Role of IL-10 in PD-1 Modulation

Q fever endocarditis, a severe complication of Q fever, is associated with a defective immune response, the mechanisms of which are poorly understood. We hypothesized that Q fever immune deficiency is related to altered distribution and activation of circulating monocyte subsets. Monocyte subsets were analyzed by flow cytometry in peripheral blood mononuclear cells from patients with Q fever endocarditis and controls. The proportion of classical monocytes (CD14⁺CD16⁻ monocytes) was similar in patients and controls. In contrast, the patients with Q fever endocarditis exhibited a decrease in the non-classical and intermediate subsets of monocytes (CD16⁺ monocytes). The altered distribution of monocyte subsets in Q fever endocarditis was associated with changes in their activation profile. Indeed, the expression of HLA-DR, a canonical activation molecule, and PD-1, a co-inhibitory molecule, was increased in intermediate monocytes. This profile was not restricted to CD16⁺ monocytes because CD4⁺ T cells also overexpressed PD-1. The mechanism leading to the overexpression of PD-1 did not require the LPS from C. burnetii but involved interleukin-10, an immunosuppressive cytokine. Indeed, the incubation of control monocytes with interleukin-10 led to a higher expression of PD-1 and neutralizing interleukin-10 prevented C. burnetii-stimulated PD-1 expression. Taken together, these results show that the immune suppression of Q fever endocarditis involves a cross-talk between monocytes and CD4⁺ T cells expressing PD-1. The expression of PD-1 may be useful to assess chronic immune alterations in Q fever endocarditis.     

Apoptosis of peripheral blood lymphocytes in patients with <Emphasis Type="Italic">LRRK2</Emphasis>-associated Parkinson’s disease

Mutations in the Leucine Reach Repeat Kinase 2 (LRRK2) gene are the most frequent cause of familial Parkinson’s disease (PD). Although the precise physiological and pathological roles of LRRK2 are unclear, a direct link between mutant LRRK2 and programmed cell death (apoptosis) has been suggested. By using flow cytometry (PI+Annexin V(FITC)), we showed an increased level of spontaneous lymphocyte apoptosis in patients with LRRK2-associated PD compared to controls after 24 h (p < 0.016) and 48 h (p < 0.031) of incubation (5% CO₂, 37°C). We found an increased FAS mRNA level in peripheral blood lymphocytes of patients with LRRK2-associated PD compared to controls (p < 0.05) and to sporadic PD (sPD) (p < 0.002). A significant difference in FAS expression between patients with LRRK2-associated PD and controls remained after 3 years and was detected after 1 and 24 h during lymphocyte incubation (p < 0.03 and 0.05, respectively). Increased spontaneous lymphocyte apoptosis, along with increased FAS expression, in patients with LRRK2-associated PD suggests that LRRK2 mutations may lead to preferable activation of extrinsic apoptotic way.     

Fine-Mapping,Gene Expression and Splicing Analysis of the Disease Associated LRRK2 Locus

Association studies have identified several signals at the LRRK2 locus for Parkinson''s disease (PD), Crohn''s disease (CD) and leprosy. However, little is known about the molecular mechanisms mediating these effects. To further characterize this locus, we fine-mapped the risk association in 5,802 PD and 5,556 controls using a dense genotyping array (ImmunoChip). Using samples from 134 post-mortem control adult human brains (UK Human Brain Expression Consortium), where up to ten brain regions were available per individual, we studied the regional variation, splicing and regulation of LRRK2. We found convincing evidence for a common variant PD association located outside of the LRRK2 protein coding region (rs117762348, A>G, P = 2.56×10⁻⁸, case/control MAF 0.083/0.074, odds ratio 0.86 for the minor allele with 95% confidence interval [0.80–0.91]). We show that mRNA expression levels are highest in cortical regions and lowest in cerebellum. We find an exon quantitative trait locus (QTL) in brain samples that localizes to exons 32–33 and investigate the molecular basis of this eQTL using RNA-Seq data in n = 8 brain samples. The genotype underlying this eQTL is in strong linkage disequilibrium with the CD associated non-synonymous SNP rs3761863 (M2397T). We found two additional QTLs in liver and monocyte samples but none of these explained the common variant PD association at rs117762348. Our results characterize the LRRK2 locus, and highlight the importance and difficulties of fine-mapping and integration of multiple datasets to delineate pathogenic variants and thus develop an understanding of disease mechanisms.     

Dispensable role of Drosophila ortholog of LRRK2 kinase activity in survival of dopaminergic neurons

Background

Parkinson's disease (PD) is the most prevalent incurable neurodegenerative movement disorder. Mutations in LRRK2 are associated with both autosomal dominant familial and sporadic forms of PD. LRRK2 encodes a large putative serine/threonine kinase with GTPase activity. Increased LRRK2 kinase activity plays a critical role in pathogenic LRRK2 mutant-induced neurodegeneration in vitro. Little is known about the physiological function of LRRK2.

Results

We have recently identified a Drosophila line with a P-element insertion in an ortholog gene of human LRRK2 (dLRRK). The insertion results in a truncated Drosophila LRRK variant with N-terminal 1290 amino acids but lacking C-terminal kinase domain. The homozygous mutant fly develops normally with normal life span as well as unchanged number and pattern of dopaminergic neurons. However, dLRRK mutant flies were selectively sensitive to hydrogen peroxide induced stress but not to paraquat, rotenone and β-mercaptoethanol induced stresses.

Conclusion

Our results indicate that inactivation of dLRRK kinase activity is not essential for fly development and suggest that inhibition of LRRK activity may serve as a potential treatment of PD. However, dLRRK kinase activity likely plays a role in protecting against oxidative stress.     

Phosphorylation of 4E-BP1 in the Mammalian Brain Is Not Altered by LRRK2 Expression or Pathogenic Mutations

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are a common cause of autosomal dominant familial Parkinson''s disease (PD). LRRK2 encodes a multi-domain protein containing GTPase and kinase enzymatic domains. Disease-associated mutations in LRRK2 variably influence enzymatic activity with the common G2019S variant leading to enhanced kinase activity. Mutant LRRK2 induces neuronal toxicity through a kinase-dependent mechanism suggesting that kinase activity is important for mediating the pathogenic effects of LRRK2 mutations. A number of LRRK2 kinase substrates have been identified in vitro but whether they represent authentic physiological substrates in mammalian cells or tissues is not yet clear. The eukaryotic initiation factor 4E (eIF4E)-binding protein, 4E-BP1, was recently identified as a potential substrate of LRRK2 kinase activity in vitro and in Drosophila with phosphorylation occurring at Thr37 and Thr46. Here, we explore a potential interaction of LRRK2 and 4E-BP1 in mammalian cells and brain. We find that LRRK2 can weakly phosphorylate 4E-BP1 in vitro but LRRK2 overexpression is not able to alter endogenous 4E-BP1 phosphorylation in mammalian cells. In mammalian neurons LRRK2 and 4E-BP1 display minimal co-localization, whereas the subcellular distribution, protein complex formation and covalent post-translational modification of endogenous 4E-BP1 are not altered in the brains of LRRK2 knockout or mutant LRRK2 transgenic mice. In the brain, the phosphorylation of 4E-BP1 at Thr37 and Thr46 does not change in LRRK2 knockout or mutant LRRK2 transgenic mice, nor is 4E-BP1 phosphorylation altered in idiopathic or G2019S mutant PD brains. Collectively, our results suggest that 4E-BP1 is neither a major nor robust physiological substrate of LRRK2 in mammalian cells or brain.     

Monocyte subset redistribution from blood to kidneys in patients with Puumala virus caused hemorrhagic fever with renal syndrome

Innate immune cells like monocytes patrol the vasculature and mucosal surfaces, recognize pathogens, rapidly redistribute to affected tissues and cause inflammation by secretion of cytokines. We previously showed that monocytes are reduced in blood but accumulate in the airways of patients with Puumala virus (PUUV) caused hemorrhagic fever with renal syndrome (HFRS). However, the dynamics of monocyte infiltration to the kidneys during HFRS, and its impact on disease severity are currently unknown. Here, we examined longitudinal peripheral blood samples and renal biopsies from HFRS patients and performed in vitro experiments to investigate the fate of monocytes during HFRS. During the early stages of HFRS, circulating CD14–CD16+ nonclassical monocytes (NCMs) that patrol the vasculature were reduced in most patients. Instead, CD14+CD16– classical (CMs) and CD14+CD16+ intermediate monocytes (IMs) were increased in blood, in particular in HFRS patients with more severe disease. Blood monocytes from patients with acute HFRS expressed higher levels of HLA-DR, the endothelial adhesion marker CD62L and the chemokine receptors CCR7 and CCR2, as compared to convalescence, suggesting monocyte activation and migration to peripheral tissues during acute HFRS. Supporting this hypothesis, increased numbers of HLA-DR+, CD14+, CD16+ and CD68+ cells were observed in the renal tissues of acute HFRS patients compared to controls. In vitro, blood CD16+ monocytes upregulated CD62L after direct exposure to PUUV whereas CD16– monocytes upregulated CCR7 after contact with PUUV-infected endothelial cells, suggesting differential mechanisms of activation and response between monocyte subsets. Together, our findings suggest that NCMs are reduced in blood, potentially via CD62L-mediated attachment to endothelial cells and monocytes are recruited to the kidneys during HFRS. Monocyte mobilization, activation and functional impairment together may influence the severity of disease in acute PUUV-HFRS.     

Gingival crevicular fluid infiltrating CD14+ monocytes promote inflammation in periodontitis

Periodontitis is a condition that occurs because of inflammation-mediated tissue degeneration. Many studies have been conducted to identify inflammatory molecules in periodontitis, but the well-defined role of cells from the immune system in the progression of periodontitis as well as in gingival tissue degeneration has not been appropriately established. The objective of the present study was to characterize the monocytes isolated from the gingival crevicular fluid (GCF) in patients with periodontitis. GCF was obtained from periodontitis patients and healthy controls. Cytokine levels of CCL2 were evaluated by ELISA in GCF samples. CD14+ monocytes were separated using magnetic sorting from GCF. RT-qPCR was performed to assess the gene expression. Cytometric bead array analysis was performed to analyze the levels of cytokines and chemokines in the secretome of cells. CD14+ monocytes from GCF secreted higher levels of CCL2 and showed elevated expression of genes responsible for monocyte migration. Additionally, upon lipopolysaccharide stimulation, these monocytes secreted higher levels of inflammatory cytokines and chemokines. This investigation aids in understanding the inflammatory microenvironment of periodontitis by characterizing GCF in terms of infiltrated CD14+ monocytes, cytokines, and molecules secreted by these monocytes, which are specific for cellular differentiation.     

HSV-2 Regulates Monocyte Inflammatory Response via the Fas/FasL Pathway

Monocytic cells represent important cellular elements of the innate and adaptive immune responses in viral infections. We assessed the role of Fas/FasL in promoting monocyte apoptosis during HSV-2 infection by using an in vitro model based on the murine RAW 264.7 monocytic cell line and an in vivo murine model of HSV-2 infection applied to C57BL6, MRL-Fas^lpr/J (Fas−/−) and C3-Fasl^gld/J (FasL−/−) mice. HSV-2 infection of the monocytic cell line led to early induction of apoptosis, with no protective expression of anti-apoptotic Bcl-2. HSV-2 infected monocytes up-regulated Fas and FasL expression early during in vitro infection but were susceptible to Fas induced apoptosis. The vaginal monocytes in the HSV-2 murine model of infection up-regulated FasL expression and were susceptible to Fas induced apoptosis. HSV-2 infection of Fas and FasL- deficient mice led to decreased apoptosis of monocytes and impaired recruitment of NK, CD4+ and CD8+ T cells within the infection sites. The vaginal lavages of HSV-2 infected Fas and FasL- deficient showed decreased production of CXCL9, CXCL10 and TNF-α in comparison to HSV-2 infected wild-type mice strain. The decreased recruitment of immune competent cells was accompanied by delayed virus clearance from the infected tissue. Triggering of the Fas receptor on HSV-2 infected monocytes in vitro up-regulated the expression of CXCL9 chemokines and the cytokine TNF-α. Our study provides novel insights on the role of Fas/FasL pathway not only in apoptosis of monocytes but also in regulating local immune response by monocytes during HSV-2 infection.     

Impaired in vitro Interferon-γ production in patients with visceral leishmaniasis is improved by inhibition of PD1/PDL-1 ligation

Visceral leishmaniasis (VL) is a neglected tropical disease that causes substantial morbidity and mortality and is a growing health problem in Ethiopia, where this study took place. Most individuals infected with Leishmania donovani parasites will stay asymptomatic, but some develop VL that, if left untreated, is almost always fatal. This stage of the disease is associated with a profound immunosuppression, characterised by impaired production of Interferonγ (IFNγ), a cytokine that plays a key role in the control of Leishmania parasites, and high expression levels of an inhibitory receptor, programmed cell death 1 (PD1) on CD4⁺ T cells. Here, we tested the contribution of the interaction between the immune checkpoint PD1 and its ligand PDL-1 on the impaired production of IFNγ in VL patients. Our results show that in the blood of VL patients, not only CD4⁺, but also CD8⁺ T cells express high levels of PD1 at the time of VL diagnosis. Next, we identified PDL-1 expression on different monocyte subsets and neutrophils and show that PDL-1 levels were significantly increased in VL patients. PD1/PDL-1 inhibition resulted in significantly increased production of IFNγ, suggesting that therapy using immune checkpoint inhibitors might improve disease control in these patients.     

<Emphasis Type="Italic">Borrelia burgdorferi</Emphasis>stimulation of chemokine secretion by cells of monocyte lineage in patients with Lyme arthritis

Introduction  

Joint fluid in patients with Lyme arthritis often contains high levels of CCL4 and CCL2, which are chemoattractants for monocytes and some T cells, and CXCL9 and CXCL10, which are chemoattractants for CD4+ and CD8+ T effector cells. These chemokines are produced primarily by cells of monocyte lineage in T_H1-type immune responses. Our goal was to begin to learn how infection with Borrelia burgdorferi leads to the secretion of these chemokines, using patient cell samples. We hypothesized that B. burgdorferi stimulates chemokine secretion from monocytes/macrophages in multiple ways, thereby linking innate and adaptive immune responses.     

Elevated Soluble CD163 Plasma Levels Are Associated with Disease Severity in Patients with Hemorrhagic Fever with Renal Syndrome

Background

Hantaan virus is a major zoonotic pathogen that causesing hemorrhagic fever with renal syndrome (HFRS). Although HFRS pathogenesis has not been entirely elucidated, the importance of host-related immune responses in HFRS pathogenesis has been widely recognized. CD163, a monocyte and macrophage-specific scavenger receptor that plays a vital function in the hosts can reduce inflammation, is shed during activation as soluble CD163 (sCD163). The aim of this study was to investigate the pathological significance of sCD163 in patients with HFRS.

Methods

Blood samples were collected from 81 hospitalized patients in Tangdu Hospital from October 2011 to January 2014 and from 15 healthy controls. The sCD163 plasma levels were measured using a sandwich ELISA, and the relationship between sCD163 and disease severity was analyzed. Furthermore, CD163 expression in 3 monocytes subset was analyzed by flow cytometry.

Results

The results demonstrated that sCD163 plasma levels during the HFRS acute phase were significantly higher in patients than during the convalescent stage and the levels in the healthy controls (P<0.0001). The sCD163 plasma levels in the severe/critical group were higher than those in the mild/moderate group during the acute (P<0.0001). A Spearman correlation analysis indicated that the sCD163 levels were positively correlated with white blood cell, serum creatine, blood urea nitrogen levels, while they were negatively correlated with blood platelet levels in the HFRS patients. The monocyte subsets were significantly altered during the acute stage. Though the CD163 expression levels within the monocyte subsets were increased during the acute stage, the highest CD163 expression level was observed in the CD14++CD16+ monocytes when compared with the other monocyte subsets.

Conclusion

sCD163 may be correlated with disease severity and the disease progression in HFRS patients; however, the underlying mechanisms should be explored further.     

Human Monocytes Differentiate into Dendritic Cells Subsets that Induce Anergic and Regulatory T Cells in Sepsis

Background

Sepsis is a multifactorial pathology with high susceptibility to secondary infections. Innate and adaptive immunity are affected in sepsis, including monocyte deactivation.

Methodology/Principal Findings

To better understand the effects of alterations in monocytes on the regulation of immune responses during sepsis, we analyzed their differentiation in dendritic cell (DC). Cells from septic patients differentiated overwhelmingly into CD1a−negative DC, a population that was only a minor subset in controls and that is so far poorly characterized. Analysis of T cell responses induced with purified CD1a−negative and CD1a+ DC indicated that (i) CD1a−negative DC from both healthy individuals and septic patients fail to induce T cell proliferation, (ii) TGFβ and IL-4 were strongly produced in mixed leukocyte reaction (MLR) with control CD1a−negative DC; reduced levels were produced with patients DC together with a slight induction of IFNγ, (iii) compared to controls, CD1a+ DC derived from septic patients induced 3-fold more Foxp3+ T cells.

Conclusion/Significance

Our results indicate a strong shift in DC populations derived from septic patients’ monocytes with expanded cell subsets that induce either T cell anergy or proliferation of T cells with regulatory potential. Lower regulatory cytokines induction on a per cell basis by CD1a−negative dendritic cells from patients points however to a down regulation of immune suppressive abilities in these cells.     

Age-dependent and cell-population-restricted LRRK2 expression in normal mouse spleen

Leucine-rich repeat kinase 2 (LRRK2) is the causal molecule of familial Parkinson’s disease (PD), but its true physiological function remains unknown. In the normal mouse, LRRK2 is expressed in kidney, spleen, and lung at much higher levels than in brain, suggesting that LRRK2 may play an important role in these organs. Analysis of age-related changes in LRRK2 expression demonstrated that expression in kidney, lung, and various brain regions was constant throughout adult life. On the other hand, expression of both LRRK2 mRNA and protein decreased markedly in spleen in an age-dependent manner. Analysis of purified spleen cells indicated that B lymphocytes were the major population expressing LRRK2, and that T lymphocytes showed no expression. Consistently, the B lymphocyte surface marker CD19 exhibited an age-dependent decrease of mRNA expression in spleen. These results suggest a possibly novel function of LRRK2 in the immune system, especially in B lymphocytes.