Resistance to experimental autoimmune encephalomyelitis in mice lacking the CC chemokine receptor (CCR)2

Cenicriviroc, a CCR2/CCR5 antagonist, promotes the generation of type 1 regulatory T cells

Cenicriviroc, a dual CCR2/CCR5 antagonist, initially developed as an anti-HIV drug, has shown promising results in nonalcoholic steatohepatitis phase 2 clinical trials. It inhibits the infiltration and activation of CCR2+/CCR5+ monocytes and macrophages to the site of liver injury, preventing liver fibrosis. However, the role of Cenicriviroc in the modulation of helper T cell differentiation and functions remains to be explored. In inflamed colons of Crohn's disease patients, CCR2+ and CCR5+ CD4+ T cells are enriched. Considering the role of CCR2+ and CCR5+ T cells in IBD pathogenesis, we investigated the potential role of Cenicriviroc in colitis. Our in vitro studies revealed that Cenicriviroc inhibits Th1-, Th2-, and Th17-cell differentiation while promoting the generation of type 1 regulatory T cells (Tr1), known for preventing inflammation through induction of IL-10. This study is the first to report that Cenicriviroc promotes Tr1 cell generation by up-regulating the signature of Tr1 cell transcription factors such as c-Maf, Prdm1, Irf-1, Batf, and EGR-2. Cenicriviroc displayed a protective effect in experimental colitis models by preventing body weight loss and intestinal inflammation and preserving epithelial barrier integrity. We show that Cenicriviroc induced IL-10 and inhibited the generation of pro-inflammatory cytokines IFN-γ, IL-17, IL-6, and IL-1β during colitis. Based on our data, we propose Cenicriviroc as a potential therapeutic in controlling tissue inflammation by inhibiting the generation and functions of effector T cells and promoting the induction of anti-inflammatory Tr1 cells.

ATG5-regulated CCL2/MCP-1 production in myeloid cells selectively modulates anti-malarial CD4+ Th1 responses

Parasite-specific CD4+ Th1 cell responses are the predominant immune effector for controlling malaria infection; however, the underlying regulatory mechanisms remain largely unknown. This study demonstrated that ATG5 deficiency in myeloid cells can significantly inhibit the growth of rodent blood-stage malarial parasites by selectively enhancing parasite-specific CD4+ Th1 cell responses. This effect was independent of ATG5-mediated canonical and non-canonical autophagy. Mechanistically, ATG5 deficiency suppressed FAS-mediated apoptosis of LY6G- ITGAM/CD11b+ ADGRE1/F4/80- cells and subsequently increased CCL2/MCP-1 production in parasite-infected mice. LY6G- ITGAM+ ADGRE1- cell-derived CCL2 selectively interacted with CCR2 on CD4+ Th1 cells for their optimized responses through the JAK2-STAT4 pathway. The administration of recombinant CCL2 significantly promoted parasite-specific CD4+ Th1 responses and suppressed malaria infection. Conclusively, our study highlights the previously unrecognized role of ATG5 in modulating myeloid cells apoptosis and sequentially affecting CCL2 production, which selectively promotes CD4+ Th1 cell responses. Our findings provide new insights into the development of immune interventions and effective anti-malarial vaccines.Abbreviations: ATG5: autophagy related 5; CBA: cytometric bead array; CCL2/MCP-1: C-C motif chemokine ligand 2; IgG: immunoglobulin G; IL6: interleukin 6; IL10: interleukin 10; IL12: interleukin 12; MFI: mean fluorescence intensity; JAK2: Janus kinase 2; LAP: LC3-associated phagocytosis; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; pRBCs: parasitized red blood cells; RUBCN: RUN domain and cysteine-rich domain containing, Beclin 1-interacting protein; STAT4: signal transducer and activator of transcription 4; Th1: T helper 1 cell; Tfh: follicular helper cell; ULK1: unc-51 like kinase 1.

The brain cytokine orchestra in multiple sclerosis: from neuroinflammation to synaptopathology

The central nervous system (CNS) is finely protected by the blood-brain barrier (BBB). Immune soluble factors such as cytokines (CKs) are normally produced in the CNS, contributing to physiological immunosurveillance and homeostatic synaptic scaling. CKs are peptide, pleiotropic molecules involved in a broad range of cellular functions, with a pivotal role in resolving the inflammation and promoting tissue healing. However, pro-inflammatory CKs can exert a detrimental effect in pathological conditions, spreading the damage. In the inflamed CNS, CKs recruit immune cells, stimulate the local production of other inflammatory mediators, and promote synaptic dysfunction. Our understanding of neuroinflammation in humans owes much to the study of multiple sclerosis (MS), the most common autoimmune and demyelinating disease, in which autoreactive T cells migrate from the periphery to the CNS after the encounter with a still unknown antigen. CNS-infiltrating T cells produce pro-inflammatory CKs that aggravate local demyelination and neurodegeneration. This review aims to recapitulate the state of the art about CKs role in the healthy and inflamed CNS, with focus on recent advances bridging the study of adaptive immune system and neurophysiology.

Pharmacologically targeting intracellular allosteric sites of GPCRs for drug discovery

G-protein-coupled receptors (GPCRs) are a family of cell surface proteins that can sense a variety of extracellular stimuli and mediate multiple signaling transduction pathways involved in human physiology. Recent advances in GPCR structural biology have revealed a relatively conserved intracellular allosteric site in multiple GPCRs, which can be utilized to modulate receptors from the inside. This novel intracellular site partially overlaps with the G-protein and β-arrestin coupling sites, providing a novel avenue for biological intervention. Here, we review evidence available for GPCR structures complexed with intracellular small-molecule allosteric modulators, elucidating drug-target interactions and allosteric mechanisms. Moreover, we highlight the potential of intracellular allosteric modulators in achieving biased signaling, which provides insights into biased allosteric mechanisms.

The Role of the Intestinal Microbiome in Multiple Sclerosis-Lessons to Be Learned from Hippocrates

Based on recent advances in research of chronic inflammatory conditions, there is a growing body of evidence that suggests a close correlation between the microbiota of the gastrointestinal tract and the physiologic activity of the immune system. This raises the idea that disturbances of the GI ecosystem contribute to the unfolding of chronic diseases including neurodegenerative pathologies. Here, we overview our current understanding on the putative interaction between the gut microbiota and the immune system from the aspect of multiple sclerosis, one of the autoimmune conditions accompanied by severe chronic neuroinflammation that affects millions of people worldwide.

The role of biogenic amines in the modulation of monocytes in autoimmune neuroinflammation

Multiple sclerosis (MS) is inflammatory demyelinating and neurodegenerative disease of the central nervous system (CNS) with autoimmune mechanism of development. The study of the neuroimmune interactions is one of the most developing directions in the research of the pathogenesis of MS. The influence of biogenic amines on the pathogenesis of experimental autoimmune encephalomyelitis (EAE) and MS was shown by the modulation of subsets of T-helper cells and B-cells, which plays a crucial role in the autoimmunity of the CNS. However, along with T- and B-cells the critical involvement of mononuclear phagocytes such as dendritic cells, macrophages, and monocytes in the development of neuroinflammation also was shown. It was demonstrated that the activation of microglial cells (resident macrophages of the CNS) could initiate the neuroinflammation in the EAE, suggesting their role at an early stage of the disease. In contrast, monocytes, which migrate from the periphery into the CNS through the blood-brain barrier, mediate the effector phase of the disease and cause neurological disability in EAE. In addition, the clinical efficacy of the therapy with depletion of the monocytes in EAE was shown, suggesting their crucial role in the autoimmunity of the CNS. Biogenic amines, such as epinephrine, norepinephrine, dopamine, and serotonin are direct mediators of the neuroimmune interaction and may affect the pathogenesis of EAE and MS by modulating the immune cell activity and cytokine production. The anti-inflammatory effect of targeting the biogenic amines receptors on the pathogenesis of EAE and MS by suppression of Th17- and Th1-cells, which are critical for the CNS autoimmunity, was shown. However, the latest data showed the potential ability of biogenic amines to affect the functions of the mononuclear phagocytes and their involvement in the modulation of neuroinflammation. This article reviews the literature data on the role of monocytes in the pathogenesis of EAE and MS. The data on the effect of targeting of biogenic amine receptors on the function of monocytes are presented.

Fc multimers effectively treat murine models of multiple sclerosis

Multiple Sclerosis (MS) is a chronic neurodegenerative disease with limited therapeutic options. Recombinant Fc multimers (rFc), designed to mirror many of the anti-inflammatory activities of Intravenous Immunoglobulin (IVIG), have been shown to effectively treat numerous immune-mediated diseases in rodents. In this study we used the experimental autoimmune encephalomyelitis (EAE) murine model of MS to test the efficacy of a rFc, M019, that consists of multimers of the Fc portion of IgG2, in inhibiting disease severity. We show that M019 effectively reduced clinical symptoms when given either pre- or post-symptom onset compared to vehicle treated EAE induced mice. M019 was effective in reducing symptoms in both SJL model of relapsing remitting MS as well as the B6 model of chronic disease. M019 binds to FcγR bearing-monocytes both in vivo and in vitro and prevented immune cell infiltration into the CNS of treated mice. The lack of T cell infiltration into the spinal cord was not due to a decrease in T cell priming; there was an equivalent frequency of Th17 cells in the spleens of M019 and vehicle treated EAE induced mice. Surprisingly, there was an increase in chemokines in the sera but not in the CNS of M019 treated mice compared to vehicle treated animals. We postulate that M019 interacts with a FcγR rich monocyte intermediary to prevent T cell migration into the CNS and demyelination.

Dendritic Cells as a Nexus for the Development of Multiple Sclerosis and Models of Disease

Multiple sclerosis (MS) results from an autoimmune attack on the central nervous system (CNS). Dysregulated immune cells invade the CNS, causing demyelination, neuronal and axonal damage, and subsequent neurological disorders. Although antigen-specific T cells mediate the immunopathology of MS, innate myeloid cells have essential contributions to CNS tissue damage. Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that promote inflammation and modulate adaptive immune responses. This review focuses on DCs as critical components of CNS inflammation. Here, evidence from studies is summarized with animal models of MS and MS patients that support the critical role of DCs in orchestrating CNS inflammation.

Chemokine positioning determines mutually exclusive roles for their receptors in extravasation of pathogenic human T cells

Pro-inflammatory T cells co-express multiple chemokine receptors, but the distinct functions of individual receptors on these cells are largely unknown. Human Th17 cells uniformly express the chemokine receptor CCR6, and we discovered that the subgroup of CD4+CCR6+ cells that co-express CCR2 possess a pathogenic Th17 signature, can produce inflammatory cytokines independent of TCR activation, and are unusually efficient at transendothelial migration (TEM). The ligand for CCR6, CCL20, was capable of binding to activated endothelial cells (ECs) and inducing firm arrest of CCR6+CCR2+ cells under conditions of flow - but CCR6 could not mediate TEM. By contrast, CCL2 and other ligands for CCR2, despite being secreted from both luminal and basal sides of ECs, failed to bind to the EC surfaces - and CCR2 could not mediate arrest. Nonetheless, CCR2 was required for TEM. To understand if CCR2's inability to mediate arrest was due solely to an absence of EC-bound ligands, we generated a CCL2-CXCL9 chimeric chemokine that could bind to the EC surface. Although display of CCL2 on the ECs did indeed lead to CCR2-mediated arrest of CCR6+CCR2+ cells, activating CCR2 with surface-bound CCL2 blocked TEM. We conclude that mediating arrest and TEM are mutually exclusive activities of chemokine receptors and/or their ligands that depend, respectively, on chemokines that bind to the EC luminal surfaces versus non-binding chemokines that form transendothelial gradients under conditions of flow. Our findings provide fundamental insights into mechanisms of lymphocyte extravasation and may lead to novel strategies to block or enhance their migration into tissue.

Scale down and optimized automated production of [68Ga]68Ga-DOTA-ECL1i PET tracer targeting CCR2 expression

BACKGROUND

Recently it has been identified a short peptide that showed allosteric antagonism against C-C motif chemokine receptor 2 (CCR2) expressed on inflammatory monocyte and macrophages. A 7-D-amino acid peptidic CCR2 inhibitor called extracellular loop 1 inverso (ECL1i), d(LGTFLKC) has been identified and labeled to obtain a new probe for positron emission tomography in pulmonary fibrosis, heart injury, abdominal aortic aneurysm inflammation, atherosclerosis, head and neck cancer. Our goal was to develop, optimize and validate an automated synthesis method for [68Ga]68Ga-DOTA-ECL1i to make it available for a broader community. The synthesis of [68Ga]68Ga-DOTA-ECL1i was done using the Scintomics GRP^® module with the already estabilished synthesis template for [68Ga]68Ga-DOTATOC/[68Ga]68Ga-PSMA. The radiopharmaceutical production was optimized scaling down the amount of DOTA-ECL1i (from 50 to 10 μg), evaluating synthesis efficiency and relevant quality control parameters in accordance with the European Pharmacopeia.

RESULTS

Best results were yielded with 20 μg DOTA-ECL1i and then the process validation was carried out by producing three different batches on three different days obtaining an optimal radiochemical yield (66.69%) as well as radiochemical purity (100%) and molar activity (45.41 GBq/µmol).

CONCLUSIONS

[68Ga]68Ga-DOTA-ECL1i was successfully synthesized and it is, thus, available for multi-dose application in clinical settings.

GM-CSF-producing CCR2+ CCR6+ Th17 cells are pathogenic in dextran sodium sulfate-induced colitis model in mice

Although excessive immune responses by Th17 cells, a helper T cell subset, are implicated in the pathogenesis of inflammatory bowel disease (IBD), the mechanism by which its localization in an inflamed colon is regulated remains unclear. Chemokines and their receptors are involved in the pathogenesis of IBD, however, the relative significance of each receptor on Th17 cells remains unknown. We generated C-C motif chemokine receptor 2 (CCR2) knockout (KO) and CCR6 KO mice in the syngeneic background using the CRISPR/Cas9 system and found that the phenotypes of experimental colitis worsened in both mutant mice. Surprisingly, the phenotype of colitis in CCR2/CCR6-double knockout (CCR2/6 DKO) mice was opposite to that of the single-deficient mice, with significantly milder experimental colitis (p < .05). The same was true for the symptoms in CCR6 KO mice, but not in wild type mice treated with a CCR2 inhibitor, propagermanium. Colonic CCR2⁺ CCR6⁺ Th17 cells produced a potentially pathogenic cytokine GM-CSF whose levels in the gut were significantly reduced in CCR2/6 DKO mice (p < .05). These results suggest that GM-CSF-producing CCR2⁺ CCR6⁺ Th17 cells are pathogenic and are attracted to the inflamed colon by either CCR2 or CCR6 gradient, which subsequently exacerbates experimental colitis in mice.

ETV3 and ETV6 enable monocyte differentiation into dendritic cells by repressing macrophage fate commitment

In inflamed tissues, monocytes differentiate into macrophages (mo-Macs) or dendritic cells (mo-DCs). In chronic nonresolving inflammation, mo-DCs are major drivers of pathogenic events. Manipulating monocyte differentiation would therefore be an attractive therapeutic strategy. However, how the balance of mo-DC versus mo-Mac fate commitment is regulated is not clear. In the present study, we show that the transcriptional repressors ETV3 and ETV6 control human monocyte differentiation into mo-DCs. ETV3 and ETV6 inhibit interferon (IFN)-stimulated genes; however, their action on monocyte differentiation is independent of IFN signaling. Instead, we find that ETV3 and ETV6 directly repress mo-Mac development by controlling MAFB expression. Mice deficient for Etv6 in monocytes have spontaneous expression of IFN-stimulated genes, confirming that Etv6 regulates IFN responses in vivo. Furthermore, these mice have impaired mo-DC differentiation during inflammation and reduced pathology in an experimental autoimmune encephalomyelitis model. These findings provide information about the molecular control of monocyte fate decision and identify ETV6 as a therapeutic target to redirect monocyte differentiation in inflammatory disorders.

Saturated very long-chain fatty acids regulate macrophage plasticity and invasiveness

Saturated very long-chain fatty acids (VLCFA, ≥ C22), enriched in brain myelin and innate immune cells, accumulate in X-linked adrenoleukodystrophy (X-ALD) due to inherited dysfunction of the peroxisomal VLCFA transporter ABCD1. In its severest form, X-ALD causes cerebral myelin destruction with infiltration of pro-inflammatory skewed monocytes/macrophages. How VLCFA levels relate to macrophage activation is unclear. Here, whole transcriptome sequencing of X-ALD macrophages indicated that VLCFAs prime human macrophage membranes for inflammation and increased expression of factors involved in chemotaxis and invasion. When added externally to mimic lipid release in demyelinating X-ALD lesions, VLCFAs did not activate toll-like receptors in primary macrophages. In contrast, VLCFAs provoked pro-inflammatory responses through scavenger receptor CD36-mediated uptake, cumulating in JNK signalling and expression of matrix-degrading enzymes and chemokine release. Following pro-inflammatory LPS activation, VLCFA levels increased also in healthy macrophages. With the onset of the resolution, VLCFAs were rapidly cleared in control macrophages by increased peroxisomal VLCFA degradation through liver-X-receptor mediated upregulation of ABCD1. ABCD1 deficiency impaired VLCFA homeostasis and prolonged pro-inflammatory gene expression upon LPS treatment. Our study uncovers a pivotal role for ABCD1, a protein linked to neuroinflammation, and associated peroxisomal VLCFA degradation in regulating macrophage plasticity.

The therapeutic potential of bone marrow-derived macrophages in neurological diseases

Circulating monocytes are precursors of both tissue macrophages and dendritic cells, and they can infiltrate the central nervous system (CNS) where they transform into bone marrow-derived macrophages (BMDMs). BMDMs play essential roles in various CNS diseases, thus modulating BMDMs might be a way to treat these disorders because there are currently no efficient therapeutic methods available for most of these neurological diseases. Moreover, BMDMs can serve as promising gene delivery vehicles following bone marrow transplantation for otherwise incurable genetic CNS diseases. Understanding the distinct roles that BMDMs play in CNS diseases and their potential as gene delivery vehicles may provide new insights and opportunities for using BMDMs as therapeutic targets or delivery vehicles. This review attempts to comprehensively summarize the neurological diseases that might be treated by modulating BMDMs or by delivering gene therapies via BMDMs after bone marrow transplantation.

Astrocyte immunometabolic regulation of the tumour microenvironment drives glioblastoma pathogenicity

Malignant brain tumours are the cause of a disproportionate level of morbidity and mortality among cancer patients, an unfortunate statistic that has remained constant for decades. Despite considerable advances in the molecular characterization of these tumours, targeting the cancer cells has yet to produce significant advances in treatment. An alternative strategy is to target cells in the glioblastoma microenvironment, such as tumour-associated astrocytes. Astrocytes control multiple processes in health and disease, ranging from maintaining the brain's metabolic homeostasis, to modulating neuroinflammation. However, their role in glioblastoma pathogenicity is not well understood. Here we report that depletion of reactive astrocytes regresses glioblastoma and prolongs mouse survival. Analysis of the tumour-associated astrocyte translatome revealed astrocytes initiate transcriptional programmes that shape the immune and metabolic compartments in the glioma microenvironment. Specifically, their expression of CCL2 and CSF1 governs the recruitment of tumour-associated macrophages and promotes a pro-tumourigenic macrophage phenotype. Concomitantly, we demonstrate that astrocyte-derived cholesterol is key to glioma cell survival, and that targeting astrocytic cholesterol efflux, via ABCA1, halts tumour progression. In summary, astrocytes control glioblastoma pathogenicity by reprogramming the immunological properties of the tumour microenvironment and supporting the non-oncogenic metabolic dependency of glioblastoma on cholesterol. These findings suggest that targeting astrocyte immunometabolic signalling may be useful in treating this uniformly lethal brain tumour.

Cladribine Treatment for MS Preserves the Differentiative Capacity of Subsequently Generated Monocytes, Whereas Its Administration In Vitro Acutely Influences Monocyte Differentiation but Not Microglial Activation

Cladribine (2-chlorodeoxyadenosine, 2CdA) is one of the most effective disease-modifying drugs for multiple sclerosis (MS). Cladribine is a synthetic purine nucleoside analog that induces cell death of lymphocytes and oral cladribine treatment leads to a long-lasting disease stabilization, potentially attributable to immune reconstitution. In addition to its effects on lymphocytes, cladribine has been shown to have immunomodulatory effects on innate immune cells, including dendritic cells and monocytes, which could also contribute to its therapeutic efficacy. However, whether cladribine can modulate human macrophage/microglial activation or monocyte differentiation is currently unknown. The aim of this study was to determine the immunomodulatory effects of cladribine upon monocytes, monocyte-derived macrophages (MDMs) and microglia. We analyzed the phenotype and differentiation of monocytes from MS patients receiving their first course of oral cladribine both before and three weeks after the start of treatment. Flow cytometric analysis of monocytes from MS patients undergoing cladribine treatment revealed that the number and composition of CD14/CD16 monocyte subsets remained unchanged after treatment. Furthermore, after differentiation with M-CSF, such MDMs from treated MS patients showed no difference in gene expression of the inflammatory markers compared to baseline. We further investigated the direct effects of cladribine in vitro using human adult primary MDMs and microglia. GM-CSF-derived MDMs were more sensitive to cell death than M-CSF-derived MDMs. In addition, MDMs treated with cladribine showed increased expression of costimulatory molecules CD80 and CD40, as well as expression of anti-inflammatory, pro-trophic genes IL10 and MERTK, depending on the differentiation condition. Cladribine treatment in vitro did not modulate the expression of activation markers in human microglia. Our study shows that cladribine treatment in vitro affects the differentiation of monocytes into macrophages by modulating the expression of activation markers, which might occur similarly in tissue after their infiltration in the CNS during MS.

Histone functions as a cell-surface receptor for AGEs

Reducing sugars can covalently react with proteins to generate a heterogeneous and complex group of compounds called advanced glycation end products (AGEs). AGEs are generally considered as pathogenic molecules, mediating a pro-inflammatory response and contributing to the development of a number of human diseases. However, the intrinsic function of AGEs remains to be elucidated. We now provide multiple lines of evidence showing that AGEs can specifically bind histone localized on the cell surface as an AGE-binding protein, regulate the function of histone as a plasminogen receptor, and result in the regulation of monocytes/macrophage recruitment to the site of inflammation. Our finding of histone as a cell-surface receptor for AGEs suggests that, beside our common concept of AGEs as danger-associated molecular patterns mediating a pro-inflammatory response, they may also be involved in the homeostatic response via binding to histone.

Advanced glycation end products (AGEs) are believed to be pathogenic molecules that mediate pro-inflammatory responses. Here the authors identify histone as a cell-surface receptor for AGEs and show that AGEs may also be involved in the homeostatic response via binding to histone.

Chemokine-Driven Migration of Pro-Inflammatory CD4+ T Cells in CNS Autoimmune Disease

Pro-inflammatory CD4⁺ T helper (Th) cells drive the pathogenesis of many autoimmune conditions. Recent advances have modified views of the phenotype of pro-inflammatory Th cells in autoimmunity, extending the breadth of known Th cell subsets that operate as drivers of these responses. Heterogeneity and plasticity within Th1 and Th17 cells, and the discovery of subsets of Th cells dedicated to production of other pro-inflammatory cytokines such as GM-CSF have led to these advances. Here, we review recent progress in this area and focus specifically upon evidence for chemokine receptors that drive recruitment of these various pro-inflammatory Th cell subsets to sites of autoimmune inflammation in the CNS. We discuss expression of specific chemokine receptors by subsets of pro-inflammatory Th cells and highlight which receptors may be tractable targets of therapeutic interventions to limit pathogenic Th cell recruitment in autoimmunity.

Targeting brain lesions of non-small cell lung cancer by enhancing CCL2-mediated CAR-T cell migration

Metastatic non-small cell lung cancer (NSCLC) remains largely incurable and the prognosis is extremely poor once it spreads to the brain. In particular, in patients with brain metastases, the blood brain barrier (BBB) remains a significant obstacle for the biodistribution of antitumor drugs and immune cells. Here we report that chimeric antigen receptor (CAR) T cells targeting B7-H3 (B7-H3.CAR) exhibit antitumor activity in vitro against tumor cell lines and lung cancer organoids, and in vivo in xenotransplant models of orthotopic and metastatic NSCLC. The co-expression of the CCL2 receptor CCR2b in B7-H3.CAR-T cells, significantly improves their capability of passing the BBB, providing enhanced antitumor activity against brain tumor lesions. These findings indicate that leveraging T-cell chemotaxis through CCR2b co-expression represents a strategy to improve the efficacy of adoptive T-cell therapies in patients with solid tumors presenting with brain metastases.

Decreased β-catenin expression contributes to IFNγ-induced chemokine secretion and lymphocyte infiltration in Hashimoto's thyroiditis

Hashimoto's thyroiditis (HT) is a very common organ-specific autoimmune disease characterized by lymphocyte infiltration and the destruction of thyroid follicular cells (TFCs), in which IFN-γ and chemokines play pivotal roles. Moreover, β-catenin has been implicated in the regulation of T cell infiltration. However, whether β-catenin is involved in Hashimoto's thyroiditis is unknown. Here, we examined β-catenin expression in thyroid tissues and investigated its role in the pathogenesis of HT. The results showed that β-catenin expression was markedly reduced in the thyroid tissues of HT patients; more importantly, IFN-γ treatment markedly reduced the expression of β-catenin and was accompanied by the secretion of chemokines such as CCL5, CXCL16, GRO-β, and GRO-γ in TFCs in vitro, which was attributed to GSK-3β/β-catenin signaling pathway activation. Collectively, the decreased expression of β-catenin might contribute to IFNγ-induced chemokine secretion and lymphocyte infiltration in the development of HT.

Effect of Multiple Sclerosis Cerebrospinal Fluid and Oligodendroglia Cell Line Environment on Human Wharton's Jelly Mesenchymal Stem Cells Secretome

Multiple sclerosis (MS) is a neurological disorder of autoimmune aetiology. Experimental therapies with the use of mesenchymal stem cells (MSCs) have emerged as a response to the unmet need for new treatment options. The unique immunomodulatory features of stem cells obtained from Wharton’s jelly (WJ-MSCs) make them an interesting research and therapeutic model. Most WJ-MSCs transplants for multiple sclerosis use intrathecal administration. We studied the effect of cerebrospinal fluid (CSF) obtained from MS patients on the secretory activity of WJ-MSCs and broaden this observation with WJ-MSCs interactions with human oligodendroglia cell line (OLs). Analysis of the WJ-MSCs secretory activity with use of Bio-Plex Pro™ Human Cytokine confirmed significant and diverse immunomodulatory potential. Our data reveal rich WJ-MSCs secretome with markedly increased levels of IL-6, IL-8, IP-10 and MCP-1 synthesis and a favourable profile of growth factors. The addition of MS CSF to the WJ-MSCs culture caused depletion of most proteins measured, only IL-12, RANTES and GM-CSF levels were increased. Most cytokines and chemokines decreased their concentrations in WJ-MSCs co-cultured with OLs, only eotaxin and RANTES levels were slightly increased. These results emphasize the spectrum of the immunomodulatory properties of WJ-MSCs and show how those effects can be modulated depending on the transplantation milieu.

Microglia and monocytes in inflammatory CNS disease: integrating phenotype and function

In neurological diseases, the actions of microglia, the resident myeloid cells of the CNS parenchyma, may diverge from, or intersect with, those of recruited monocytes to drive immune-mediated pathology. However, defining the precise roles of each cell type has historically been impeded by the lack of discriminating markers and experimental systems capable of accurately identifying them. Our ability to distinguish microglia from monocytes in neuroinflammation has advanced with single-cell technologies, new markers and drugs that identify and deplete them, respectively. Nevertheless, the focus of individual studies on particular cell types, diseases or experimental approaches has limited our ability to connect phenotype and function more widely and across diverse CNS pathologies. Here, we critically review, tabulate and integrate the disease-specific functions and immune profiles of microglia and monocytes to provide a comprehensive atlas of myeloid responses in viral encephalitis, demyelination, neurodegeneration and ischemic injury. In emphasizing the differential roles of microglia and monocytes in the severe neuroinflammatory disease of viral encephalitis, we connect inflammatory pathways common to equally incapacitating diseases with less severe inflammation. We examine these findings in the context of human studies and highlight the benefits and inherent limitations of animal models that may impede or facilitate clinical translation. This enables us to highlight common and contrasting, non-redundant and often opposing roles of microglia and monocytes in disease that could be targeted therapeutically.

ASK1 signaling regulates phase-specific glial interactions during neuroinflammation

Neuroinflammation is associated with many neurodegenerative diseases such as Alzheimer’s disease and multiple sclerosis (MS). Thus, decreasing neuroinflammation may be a promising treatment for these diseases. Apoptosis signal-related kinase 1 (ASK1) has been shown to cause neuroinflammation in neurodegenerative disease models, but its mechanism of action has been unclear. Here, we generated conditional knockout mice that lack ASK1 in T cells, dendritic cells, microglia/macrophages, microglia, or astrocytes, to assess the roles of ASK1 during experimental autoimmune encephalomyelitis (EAE), a mouse model of MS. We propose that ASK1 is required in microglia and astrocytes to cause and maintain neuroinflammation by a feedback loop between these two cell types.

Neuroinflammation is well known to be associated with neurodegenerative diseases. Apoptosis signal-regulating kinase 1 (ASK1) is a mitogen-activated protein kinase kinase kinase that has been implicated in neuroinflammation, but its precise cellular and molecular mechanisms remain unknown. In this study, we generated conditional knockout (CKO) mice that lack ASK1 in T cells, dendritic cells, microglia/macrophages, microglia, or astrocytes, to assess the roles of ASK1 during experimental autoimmune encephalomyelitis (EAE). We found that neuroinflammation was reduced in both the early and later stages of EAE in microglia/macrophage-specific ASK1 knockout mice, whereas only the later-stage neuroinflammation was ameliorated in astrocyte-specific ASK1 knockout mice. ASK1 deficiency in T cells and dendritic cells had no significant effects on EAE severity. Further, we found that ASK1 in microglia/macrophages induces a proinflammatory environment, which subsequently activates astrocytes to exacerbate neuroinflammation. Microglia-specific ASK1 deletion was achieved using a CX3CR1^CreER system, and we found that ASK1 signaling in microglia played a major role in generating and maintaining disease. Activated astrocytes produce key inflammatory mediators, including CCL2, that further activated and recruited microglia/macrophages, in an astrocytic ASK1-dependent manner. Astrocyte-specific analysis revealed CCL2 expression was higher in the later stage compared with the early stage, suggesting a greater proinflammatory role of astrocytes in the later stage. Our findings demonstrate cell-type–specific roles of ASK1 and suggest phase-specific ASK1-dependent glial cell interactions in EAE pathophysiology. We propose glial ASK1 as a promising therapeutic target for reducing neuroinflammation.

Tetramerization of STAT5 promotes autoimmune-mediated neuroinflammation

Signal tranducer and activator of transcription 5 (STAT5) plays a critical role in mediating cellular responses following cytokine stimulation. STAT proteins critically signal via the formation of dimers, but additionally, STAT tetramers serve key biological roles, and we previously reported their importance in T and natural killer (NK) cell biology. However, the role of STAT5 tetramerization in autoimmune-mediated neuroinflammation has not been investigated. Using the STAT5 tetramer-deficient Stat5a-Stat5b N-domain double knockin (DKI) mouse strain, we report here that STAT5 tetramers promote the pathogenesis of experimental autoimmune encephalomyelitis (EAE). The mild EAE phenotype observed in DKI mice correlates with the impaired extravasation of pathogenic T-helper 17 (Th17) cells and interactions between Th17 cells and monocyte-derived cells (MDCs) in the meninges. We further demonstrate that granulocyte-macrophage colony-stimulating factor (GM-CSF)-mediated STAT5 tetramerization regulates the production of CCL17 by MDCs. Importantly, CCL17 can partially restore the pathogenicity of DKI Th17 cells, and this is dependent on the activity of the integrin VLA-4. Thus, our study reveals a GM-CSF-STAT5 tetramer-CCL17 pathway in MDCs that promotes autoimmune neuroinflammation.

Chemokines in the Landscape of Cancer Immunotherapy: How They and Their Receptors Can Be Used to Turn Cold Tumors into Hot Ones?

Over the last decade, monoclonal antibodies to immune checkpoint inhibitors (ICI), also known as immune checkpoint blockers (ICB), have been the most successful approach for cancer therapy. Starting with mAb to cytotoxic T lymphocyte antigen 4 (CTLA-4) inhibitors in metastatic melanoma and continuing with blockers of the interactions between program cell death 1 (PD-1) and its ligand program cell death ligand 1 (PDL-1) or program cell death ligand 2 (PDL-2), that have been approved for about 20 different indications. Yet for many cancers, ICI shows limited success. Several lines of evidence imply that the limited success in cancer immunotherapy is associated with attempts to treat patients with "cold tumors" that either lack effector T cells, or in which these cells are markedly suppressed by regulatory T cells (Tregs). Chemokines are a well-defined group of proteins that were so named due to their chemotactic properties. The current review focuses on key chemokines that not only attract leukocytes but also shape their biological properties. CXCR3 is a chemokine receptor with 3 ligands. We suggest using Ig-based fusion proteins of two of them: CXL9 and CXCL10, to enhance anti-tumor immunity and perhaps transform cold tumors into hot tumors. Potential differences between CXCL9 and CXCL10 regarding ICI are discussed. We also discuss the possibility of targeting the function or deleting a key subset of Tregs that are CCR8+ by monoclonal antibodies to CCR8. These cells are preferentially abundant in several tumors and are likely to be the key drivers in suppressing anti-cancer immune reactivity.

The RNA binding protein IMP2 drives a stromal-Th17 cell circuit in autoimmune neuroinflammation

Stromal cells are emerging as key drivers of autoimmunity, partially because they produce inflammatory chemokines that orchestrate inflammation. Chemokine expression is regulated transcriptionally but also through posttranscriptional mechanisms, the specific drivers of which are still incompletely defined. CCL2 (MCP1) is a multifunctional chemokine that drives myeloid cell recruitment. During experimental autoimmune encephalomyelitis (EAE), an IL-17–driven model of multiple sclerosis, CCL2 produced by lymph node (LN) stromal cells was essential for immunopathology. Here, we showed that Ccl2 mRNA upregulation in human stromal fibroblasts in response to IL-17 required the RNA-binding protein IGF-2 mRNA-binding protein 2 (IGF2BP2, IMP2), which is expressed almost exclusively in nonhematopoietic cells. IMP2 binds directly to CCL2 mRNA, markedly extending its transcript half-life, and is thus required for efficient CCL2 secretion. Consistent with this, Imp2^−/− mice showed reduced CCL2 production in LNs during EAE, causing impairments in monocyte recruitment and Th17 cell polarization. Imp2^–/– mice were fully protected from CNS inflammation. Moreover, deletion of IMP2 after EAE onset was sufficient to mitigate disease severity. These data showed that posttranscriptional control of Ccl2 in stromal cells by IMP2 was required to permit IL-17–driven progression of EAE pathogenesis.

JAB1 deletion in oligodendrocytes causes senescence-induced inflammation and neurodegeneration in mice

Oligodendrocytes are the primary target of demyelinating disorders and progressive neurodegenerative changes may evolve in the CNS. DNA damage and oxidative stress are considered key pathogenic events, but the underlying molecular mechanisms remain unclear. Moreover, animal models do not fully recapitulate human diseases, complicating the path to effective treatments. Here we report that mice with cell autonomous deletion of the nuclear COP9 signalosome component CSN5 (JAB1) in oligodendrocytes develop DNA damage and defective DNA repair in myelinating glial cells. Interestingly, oligodendrocytes lacking JAB1 expression underwent a senescence-like phenotype that fostered chronic inflammation and oxidative stress. These mutants developed progressive CNS demyelination, microglia inflammation and neurodegeneration, with severe motor deficits and premature death. Notably, blocking microglia inflammation did not prevent neurodegeneration, whereas the deletion of p21CIP1 but not p16INK4a pathway ameliorated the disease. We suggest that senescence is key to sustaining neurodegeneration in demyelinating disorders and may be considered a potential therapeutic target.

Targeting the CCL2/CCR2 Axis in Cancer Immunotherapy: One Stone, Three Birds?

CCR2 is predominantly expressed by monocytes/macrophages with strong proinflammatory functions, prompting the development of CCR2 antagonists to dampen unwanted immune responses in inflammatory and autoimmune diseases. Paradoxically, CCR2-expressing monocytes/macrophages, particularly in tumor microenvironments, can be strongly immunosuppressive. Thus, targeting the recruitment of immunosuppressive monocytes/macrophages to tumors by CCR2 antagonism has recently been investigated as a strategy to modify the tumor microenvironment and enhance anti-tumor immunity. We present here that beneficial effects of CCR2 antagonism in the tumor setting extend beyond blocking chemotaxis of suppressive myeloid cells. Signaling within the CCL2/CCR2 axis shows underappreciated effects on myeloid cell survival and function polarization. Apart from myeloid cells, T cells are also known to express CCR2. Nevertheless, tissue homing of Treg cells among T cell populations is preferentially affected by CCR2 deficiency. Further, CCR2 signaling also directly enhances Treg functional potency. Thus, although Tregs are not the sole type of T cells expressing CCR2, the net outcome of CCR2 antagonism in T cells favors the anti-tumor arm of immune responses. Finally, the CCL2/CCR2 axis directly contributes to survival/growth and invasion/metastasis of many types of tumors bearing CCR2. Together, CCR2 links to two main types of suppressive immune cells by multiple mechanisms. Such a CCR2-assoicated immunosuppressive network is further entangled with paracrine and autocrine CCR2 signaling of tumor cells. Strategies to target CCL2/CCR2 axis as cancer therapy in the view of three types of CCR2-expessing cells in tumor microenvironment are discussed.

CD47 antibody blockade suppresses microglia-dependent phagocytosis and monocyte transition to macrophages, impairing recovery in EAE

Experimental autoimmune encephalomyelitis (EAE) is a well-characterized animal model of multiple sclerosis. During the early phase of EAE, infiltrating monocytes and monocyte-derived macrophages contribute to T cell recruitment, especially CD4⁺ T cells, into the CNS, resulting in neuronal demyelination; however, in later stages, they promote remyelination and recovery by removal of myelin debris by phagocytosis. Signal regulatory protein α and CD47 are abundantly expressed in the CNS, and deletion of either molecule is protective in myelin oligodendrocyte glycoprotein–induced EAE because of failed effector T cell expansion and trafficking. Here we report that treatment with the function blocking CD47 Ab Miap410 substantially reduced the infiltration of pathogenic immune cells but impaired recovery from paresis. The underlying mechanism was by blocking the emergence of CD11c^hiMHCII^hi microglia at peak disease that expressed receptors for phagocytosis, scavenging, and lipid catabolism, which mediated clearance of myelin debris and the transition of monocytes to macrophages in the CNS. In the recovery phase of EAE, Miap410 Ab–treated mice had worsening paresis with sustained inflammation and limited remyelination as compared with control Ab–treated mice. In summary, Ab blockade of CD47 impaired resolution of CNS inflammation, thus worsening EAE.

Elevated sCD40L in Secondary Progressive Multiple Sclerosis in Comparison to Non-progressive Benign and Relapsing Remitting Multiple Sclerosis

Background

The long-term prognosis of relapsing-remitting multiple sclerosis (RRMS) is usually unfavorable as most patients transition to secondary progressive multiple sclerosis (SPMS) with accumulative disability. A rare form of non-progressive multiple sclerosis (MS) also exists, known as benign MS (BMS or NPMS), which lacks disease progression defined as Expanded Disability Status Scale (EDSS) ≤3 after 15 years of disease onset without treatment.

Purpose

Our study aims to identify soluble plasma factors predicting disease progression in multiple sclerosis (MS).

Research Design and Study Sample

We utilized Luminex multiplex to analyze plasma levels of 33 soluble factors, comparing 32 SPMS patients to age-, sex-, and disease duration-matched non-progressive BMS patients, as well as to RRMS patients and healthy controls.

Results

Plasma levels of EGF, sCD40L, MCP1/CCL2, fractalkine/CX3CL1, IL-13, Eotaxin, TNFβ/LTα, and IL-12p40 were significantly different between the various types of MS. Plasma sCD40L was significantly elevated in SPMS compared to BMS and RRMS. The combination of MCP1/CCL2 and sCD40L discriminated between RRMS and SPMS. MCP1/CCL2 was found to be the most effective classifier between BMS and RRMS, while BMS was most effectively distinguished from SPMS by the combination of sCD40L and IFNγ levels.

Conclusions

These differences may facilitate personalized precision medicine and aid in the discovery of new therapeutic targets for disease progression through the improvement of patient stratification.

Cold exposure protects from neuroinflammation through immunologic reprogramming

Autoimmunity is energetically costly, but the impact of a metabolically active state on immunity and immune-mediated diseases is unclear. Ly6C^hi monocytes are key effectors in CNS autoimmunity with an elusive role in priming naive autoreactive T cells. Here, we provide unbiased analysis of the immune changes in various compartments during cold exposure and show that this energetically costly stimulus markedly ameliorates active experimental autoimmune encephalomyelitis (EAE). Cold exposure decreases MHCII on monocytes at steady state and in various inflammatory mouse models and suppresses T cell priming and pathogenicity through the modulation of monocytes. Genetic or antibody-mediated monocyte depletion or adoptive transfer of Th1- or Th17-polarized cells for EAE abolishes the cold-induced effects on T cells or EAE, respectively. These findings provide a mechanistic link between environmental temperature and neuroinflammation and suggest competition between cold-induced metabolic adaptations and autoimmunity as energetic trade-off beneficial for the immune-mediated diseases.

CCR2 Signaling Promotes Brain Infiltration of Inflammatory Monocytes and Contributes to Neuropathology during Cryptococcal Meningoencephalitis

Cryptococcal meningoencephalitis (CM) is a leading cause of central nervous system (CNS) infection-related mortality worldwide, with surviving patients often developing neurological deficiencies. While CNS inflammation has been implicated in the pathogenesis of CM, little is known about the relative contribution of the specific inflammatory/immune pathways to CNS pathology versus fungal clearance. Increased cerebrospinal fluid level of C-C chemokine receptor 2 (CCR2) ligand CCL2 is associated with disease deterioration in patients with CM. Using a murine model, we investigated the role of the CCR2 pathway in the development of CNS inflammation and pathology during CM. We found that CCR2-deficient mice exhibited improved 28-day survival and alleviated neurological disease scores despite a brain fungal burden higher than that of the WT mice. Reduced CM pathology in CCR2-deficient mice was accompanied by markedly decreased neuronal cell death around cryptococcal microcysts and restored expression of genes involved in neurotransmission, connectivity, and neuronal cell structure in the brains. Results show that CCR2 axis is the major pathway recruiting CD45hiCD11b+Ly6C+ inflammatory monocyte to the brain and indirectly modulates the accumulation of CD4+ T cells and CD8+ T cells. In particular, CCR2 axis promotes recruitment of interferon gamma (IFN-γ)-producing CD4+ T cells and classical activation of myeloid cells. In this context, CCR2 deletion limits the immune network dysregulation we see in CM and attenuates neuropathology. Thus, the CCR2 axis is a potential target for interventions aimed to limit inflammatory CNS pathology in CM patients. IMPORTANCE Cryptococcal meningoencephalitis (CM) causes nearly 200,000 deaths worldwide each year, and survivors frequently develop long-lasting neurological sequelae. The high rate of mortality and neurologic sequelae in CM patients indicate that antifungal therapies alone are often insufficient to control disease progression. Here, we reveal that CM disease progression in mice is accompanied by inflammatory monocytes infiltration at the periphery of the infected foci that overlap locally perturbed neuronal function and death. Importantly, we identified that CCR2 signaling is a critical pathway driving neuroinflammation, especially inflammatory monocyte recruitment, as well as CNS pathology and mortality in CM mice. Our results imply that targeting the CCR2 pathway may be beneficial as a therapy complementary to antifungal drug treatment, helping to reduce CNS damage and mortality in CM patients.

IFN-β Acts on Monocytes to Ameliorate CNS Autoimmunity by Inhibiting Proinflammatory Cross-Talk Between Monocytes and Th Cells

IFN-β has been the treatment for multiple sclerosis (MS) for almost three decades, but understanding the mechanisms underlying its beneficial effects remains incomplete. We have shown that MS patients have increased numbers of GM-CSF+ Th cells in circulation, and that IFN-β therapy reduces their numbers. GM-CSF expression by myelin-specific Th cells is essential for the development of experimental autoimmune encephalomyelitis (EAE), an animal model of MS. These findings suggested that IFN-β therapy may function via suppression of GM-CSF production by Th cells. In the current study, we elucidated a feedback loop between monocytes and Th cells that amplifies autoimmune neuroinflammation, and found that IFN-β therapy ameliorates central nervous system (CNS) autoimmunity by inhibiting this proinflammatory loop. IFN-β suppressed GM-CSF production in Th cells indirectly by acting on monocytes, and IFN-β signaling in monocytes was required for EAE suppression. IFN-β increased IL-10 expression by monocytes, and IL-10 was required for the suppressive effects of IFN-β. IFN-β treatment suppressed IL-1β expression by monocytes in the CNS of mice with EAE. GM-CSF from Th cells induced IL-1β production by monocytes, and, in a positive feedback loop, IL-1β augmented GM-CSF production by Th cells. In addition to GM-CSF, TNF and FASL expression by Th cells was also necessary for IL-1β production by monocyte. IFN-β inhibited GM-CSF, TNF, and FASL expression by Th cells to suppress IL-1β secretion by monocytes. Overall, our study describes a positive feedback loop involving several Th cell- and monocyte-derived molecules, and IFN-β actions on monocytes disrupting this proinflammatory loop.

Macrophage Plasticity and Polarization Are Altered in the Experimental Model of Multiple Sclerosis

Multiple sclerosis (MS) is an immune-mediated demyelinating disease of the central nervous system. MS is characterized by infiltrations of leukocytes such as T and B lymphocytes and macrophages. Macrophages have been identified as major effectors of inflammation and demyelination in both MS and its animal model, experimental autoimmune encephalomyelitis (EAE). However, the activation and heterogeneity of macrophages in MS has been poorly investigated. Thus, in this study, we evaluated M1 and M2 macrophages immunophenotype from EAE and control mice by analyzing over 30 surface and intracellular markers through polychromatic flow cytometry, qRT-PCR, and ELISA assay. We showed that M1 macrophages possessed a higher proinflammatory profile in EAE compared to control mice, since they expressed higher levels of activation/co-stimulatory markers (iNOS, CD40, and CD80) and cytokines/chemokines (IL-6, IL-12, CCL2, and CXCL10), whereas M2 lost their M2-like phenotype by showing a decreased expression of their signature markers CD206 and CCL22, as well as a concomitant upregulation of several M1 makers. Furthermore, immunization of M1 and M2 macrophages with MOG35-55 led to a significant hyperactivation of M1 and a concomitant shift of anti-inflammatory M2 to pro-inflammatory M1 macrophages. Overall, we provide evidence for a phenotypic alteration of M1/M2 balance during MS, which can be of crucial importance not only for a better understanding of the immunopathology of this neurodegenerative disease but also to potentially develop new macrophage-centered therapeutic strategies.

Inflammation in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) that is characterised pathologically by demyelination, gliosis, neuro-axonal damage and inflammation. Despite intense research, the underlying pathomechanisms driving inflammatory demyelination in MS still remain incompletely understood. It is thought to be caused by an autoimmune response towards CNS self-antigens in genetically susceptible individuals, assuming autoreactive T cells as disease-initiating immune cells. Yet, B cells were recognized as crucial immune cells in disease pathology, including antibody-dependent and independent effects. Moreover, myeloid cells are important contributors to MS pathology, and it is becoming increasingly evident that different cell types act in concert during MS immunopathology. This is supported by the finding that the beneficial effects of actual existing disease-modifying therapies cannot be attributed to one single immune cell-type, but rather involve immunological cooperation. The current strategy of MS therapies thus aims to shift the immune cell repertoire from a pro-inflammatory towards an anti-inflammatory phenotype, involving regulatory T and B cells and anti-inflammatory macrophages. Although no existing therapy actually exists that directly induces an enhanced regulatory immune cell pool, numerous studies identified potential net effects on these cell types. This review gives a conceptual overview on T cells, B cells and myeloid cells in the immunopathology of relapsing-remitting MS and discusses potential contributions of actual disease-modifying therapies on these immune cell phenotypes.

Immunopathogenesis of Craniotomy Infection and Niche-Specific Immune Responses to Biofilm

Bacterial infections in the central nervous system (CNS) can be life threatening and often impair neurological function. Biofilm infection is a complication following craniotomy, a neurosurgical procedure that involves the removal and replacement of a skull fragment (bone flap) to access the brain for surgical intervention. The incidence of infection following craniotomy ranges from 1% to 3% with approximately half caused by Staphylococcus aureus (S. aureus). These infections present a significant therapeutic challenge due to the antibiotic tolerance of biofilm and unique immune properties of the CNS. Previous studies have revealed a critical role for innate immune responses during S. aureus craniotomy infection. Experiments using knockout mouse models have highlighted the importance of the pattern recognition receptor Toll-like receptor 2 (TLR2) and its adaptor protein MyD88 for preventing S. aureus outgrowth during craniotomy biofilm infection. However, neither molecule affected bacterial burden in a mouse model of S. aureus brain abscess highlighting the distinctions between immune regulation of biofilm vs. planktonic infection in the CNS. Furthermore, the immune responses elicited during S. aureus craniotomy infection are distinct from biofilm infection in the periphery, emphasizing the critical role for niche-specific factors in dictating S. aureus biofilm-leukocyte crosstalk. In this review, we discuss the current knowledge concerning innate immunity to S. aureus craniotomy biofilm infection, compare this to S. aureus biofilm infection in the periphery, and discuss the importance of anatomical location in dictating how biofilm influences inflammatory responses and its impact on bacterial clearance.

Interferon-γ/Interleukin-27 Axis Induces Programmed Death Ligand 1 Expression in Monocyte-Derived Dendritic Cells and Restores Immune Tolerance in Central Nervous System Autoimmunity

Antigen (Ag)-specific tolerance induction by intravenous (i. v.) injection of high-dose auto-Ags has been explored for therapy of autoimmune diseases, including multiple sclerosis (MS). It is thought that the advantage of such Ag-specific therapy over non-specific immunomodulatory treatments would be selective suppression of a pathogenic immune response without impairing systemic immunity, thus avoiding adverse effects of immunosuppression. Auto-Ag i.v. tolerance induction has been extensively studied in experimental autoimmune encephalomyelitis (EAE), an animal model of MS, and limited clinical trials demonstrated that it is safe and beneficial to a subset of MS patients. Nonetheless, the mechanisms of i.v. tolerance induction are incompletely understood, hampering the development of better approaches and their clinical application. Here, we describe a pathway whereby auto-Ag i.v. injected into mice with ongoing clinical EAE induces interferon-gamma (IFN-γ) secretion by auto-Ag-specific CD4⁺ T cells, triggering interleukin (IL)-27 production by conventional dendritic cells type 1 (cDC1). IL-27 then, via signal transducer and activator of transcription 3 activation, induces programmed death ligand 1 (PD-L1) expression by monocyte-derived dendritic cells (moDCs) in the central nervous system of mice with EAE. PD-L1 interaction with programmed cell death protein 1 on pathogenic CD4⁺ T cells leads to their apoptosis/anergy, resulting in disease amelioration. These findings identify a key role of the IFN-γ/IL-27/PD-L1 axis, involving T cells/cDC1/moDCs in the induction of i.v. tolerance.

Potential for Targeting Myeloid Cells in Controlling CNS Inflammation

Multiple Sclerosis (MS) is characterized by immune cell infiltration to the central nervous system (CNS) as well as loss of myelin. Characterization of the cells in lesions of MS patients revealed an important accumulation of myeloid cells such as macrophages and dendritic cells (DCs). Data from the experimental autoimmune encephalomyelitis (EAE) model of MS supports the importance of peripheral myeloid cells in the disease pathology. However, the majority of MS therapies focus on lymphocytes. As we will discuss in this review, multiple strategies are now in place to target myeloid cells in clinical trials. These strategies have emerged from data in both human and mouse studies. We discuss strategies targeting myeloid cell migration, growth factors and cytokines, biological functions (with a focus on miRNAs), and immunological activities (with a focus on nanoparticles).

Repetitive injury and absence of monocytes promote astrocyte self-renewal and neurological recovery

Unlike microglia and NG2 glia, astrocytes are incapable of migrating to sites of injury in the posttraumatic cerebral cortex, instead relying on proliferation to replenish their numbers and distribution in the affected region. However, neither the spectrum of their proliferative repertoire nor their postinjury distribution has been examined in vivo. Using a combination of different thymidine analogs and clonal analysis in a model of repetitive traumatic brain injury, we show for the first time that astrocytes that are quiescent following an initial injury can be coerced to proliferate after a repeated insult in the cerebral cortex grey matter. Interestingly, this process is promoted by invasion of monocytes to the injury site, as their genetic ablation (using CCR2^-/- mice) increased the number of repetitively dividing astrocytes at the expense of newly proliferating astrocytes in repeatedly injured parenchyma. These differences profoundly affected both the distribution of astrocytes and recovery period for posttraumatic behavior deficits suggesting key roles of astrocyte self-renewal in brain repair after injury.

Cytokines and Chemokines in the Pathogenesis of Experimental Autoimmune Encephalomyelitis

Experimental autoimmune encephalomyelitis is a CD4⁺ T cell-mediated demyelinating disease of the CNS that serves as a model for multiple sclerosis. Cytokines and chemokines shape Th1 and Th17 effector responses as well as regulate migration of leukocytes to the CNS during disease. The CNS cellular infiltrate consists of Ag-specific and nonspecific CD4⁺ and CD8⁺ T cells, neutrophils, B cells, monocytes, macrophages, and dendritic cells. The mechanism of immune-mediated inflammation in experimental autoimmune encephalomyelitis has been extensively studied in an effort to develop therapeutic modalities for multiple sclerosis and, indeed, has provided insight in modern drug discovery. The present Brief Review highlights critical pathogenic aspects of cytokines and chemokines involved in generation of effector T cell responses and migration of inflammatory cells to the CNS. Select cytokines and chemokines are certainly important in the regulatory response, which involves T regulatory, B regulatory, and myeloid-derived suppressor cells. However, that discussion is beyond the scope of this brief review.

Neuroimmune interaction in seizures and epilepsy: focusing on monocyte infiltration

Epilepsy is a major neurological condition that affects millions of people globally. While a number of interventions have been developed to mitigate this condition, a significant number of patients are refractory to these treatments. Consequently, other avenues of research are needed. One such avenue is modulation of the immune system response to this condition, which has mostly focused on microglia, the resident immune cells of the central nervous system (CNS). However, other immune cells can impact neurological conditions, principally blood-borne monocytes that can infiltrate into brain parenchyma after seizures. As such, this review will first discuss how monocytes can be recruited to the CNS and how they can be distinguished from there immunological cousins, microglia. Then, we will explore what is known about the role monocytes have within seizure pathogenesis and epilepsy. Considering how little is known about monocyte function in seizure- and epilepsy-related pathologies, further studies are warranted that investigate infiltrated blood-borne monocytes as a potential therapeutic target for epilepsy treatment.

The Roles of Monocyte and Monocyte-Derived Macrophages in Common Brain Disorders

The brain is the most important and complex organ in most living creatures which serves as the center of the nervous system. The function of human brain includes controlling of the motion of the body and different organs and maintaining basic homeostasis. The disorders of the brain caused by a variety of reasons often severely impact the patients' normal life or lead to death in extreme cases. Monocyte is an important immune cell which is often recruited to the brain in a number of brain disorders. However, the role of monocytes may not be simply described as beneficial or detrimental. It significantly depends on the disease models and the stages of disease progression. In this review, we summarized the current knowledge about the role of monocytes and monocyte-derived macrophages during several common brain disorders. Major focuses include ischemic stroke, Alzheimer's disease, multiple sclerosis, intracerebral hemorrhage, and insomnia. The recruitment, differentiation, and function of monocyte in these diseases are reviewed.

CCL2 Overexpression in the Brain Promotes Glial Activation and Accelerates Tau Pathology in a Mouse Model of Tauopathy

Innate immune activation is a major contributor to Alzheimer's Disease (AD) pathophysiology, although the mechanisms involved are poorly understood. Chemokine C-C motif ligand (CCL) 2 is produced by neurons and glial cells and is upregulated in the AD brain. Transgene expression of CCL2 in mouse models of amyloidosis produces microglia-induced amyloid β oligomerization, a strong indication of the role of these activation pathways in the amyloidogenic processes of AD. We have previously shown that CCL2 polarizes microglia in wild type mice. However, how CCL2 signaling contributes to tau pathogenesis remains unknown. To address this question, CCL2 was delivered via recombinant adeno-associated virus serotype 9 into both cortex and hippocampus of a mouse model with tau pathology (rTg4510). We report that CCL2 overexpression aggravated tau pathology in rTg4510 as shown by the increase in Gallyas stained neurofibrillary tangles as well as phosphorylated tau-positive inclusions. In addition, biochemical analysis showed a reduction in the levels of detergent-soluble tau species followed by increase in the insoluble fraction, indicating a shift toward larger tau aggregates. Indeed, increased levels of high molecular weight species of phosphorylated tau were found in the mice injected with CCL2. We also report that worsening of tau pathology following CCL2 overexpression was accompanied by a distinct inflammatory response. We report an increase in leukocyte common antigen (CD45) and Cluster of differentiation 68 (CD68) expression in the brain of rTg4510 mice without altering the expression levels of a cell-surface protein Transmembrane Protein 119 (Tmem119) and ionized calcium-binding adaptor molecule 1 (Iba-1) in resident microglia. Furthermore, the analysis of cytokines in brain extract showed a significant increase in interleukin (IL)-6 and CCL3, while CCL5 levels were decreased in CCL2 mice. No changes were observed in IL-1α, IL-1β, TNF-α. IL-4, Vascular endothelial growth factor-VEGF, IL-13 and CCL11. Taken together our data report for the first time that overexpression of CCL2 promotes the increase of pathogenic tau species and is associated with glial neuroinflammatory changes that are deleterious. We propose that these events may contribute to the pathogenesis of Alzheimer's disease and other tauopathies.

Neurons promote encephalitogenic CD4+ lymphocyte infiltration in experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system characterized by neuroinflammation, leading to demyelination and axonal degeneration. Neuronal excitotoxity mediated by Ca²⁺/calmodulin-dependent protein kinase IIα (CaMKIIα) results in neuronal damage in experimental autoimmune encephalitis (EAE), an animal model of MS. Here, we define a critical role of excitatory neurons in the pathogenesis of CD4⁺ lymphocyte accumulation in EAE. We silenced the activity of excitatory neurons in a mouse model of targeted EAE using inhibitory designer receptors exclusively activated by designer drugs (DREADD) under a CaMKIIα promoter. Neuronal silencing mitigated clinical disease scores in EAE, reduced the expression of c-fos, Tnfα, Ccl2, and Ccr2 mRNAs in targeted EAE lesions, and prevented the migration of CD4⁺ lymphocytes towards neurons. Ccl2 shRNA treatment of targeted EAE suppressed the migration of CD4⁺ lymphocytes and alleviated the motor deficits of EAE. Our findings indicate that neuronal activation in EAE promotes the migration of CCR2⁺ CD4⁺ lymphocytes and that neuronal silencing with an inhibitory DREADD alleviates clinical and molecular markers of disease. Neuronal CCL2 is thought to be involved in promoting lymphocytes migration.

Sustained exposure to systemic endotoxin triggers chemokine induction in the brain followed by a rapid influx of leukocytes

Background

Recent years have seen an explosion of research pertaining to biological psychiatry, yet despite subsequent advances in our understanding of neuroimmune communication pathways, how the brain senses and responds to peripheral inflammation remains poorly understood. A better understanding of these pathways may be important for generating novel therapeutics to treat many patients with chronic inflammatory diseases who also suffer from neuropsychiatric comorbidities. Here we have systematically assessed the leukocyte infiltrate to the brain following systemic endotoxin exposure to better understand this novel route of neuroimmune communication.

Methods

Mice were injected intraperitoneally with LPS daily for 2, 5 or 7 consecutive days. We systematically interrogated the subsequent induction of chemokine transcription in the brain using TaqMan low-density arrays. A combination of flow cytometry and immunohistochemistry was then used to characterise the accompanying leukocyte infiltrate.

Results

Repeated LPS challenges resulted in prolonged activation of brain-resident microglia, coupled with an increased local transcription of numerous chemokines. After 2 days of administering LPS, there was a marked increase in the expression of the neutrophil chemoattractants CXCL1 and CXCL2; the monocyte chemoattractants CCL2, CCL5, CCL7 and CCL8; and the lymphocyte chemoattractants CXCL9, CXCL10 and CXCL16. In a number of cases, this response was sustained for several days. Chemokine induction was associated with a transient recruitment of neutrophils and monocytes to the brain, coupled with a sustained accumulation of macrophages, CD8+ T cells, NK cells and NKT cells. Strikingly, neutrophils, monocytes and T cells appeared to extravasate from the vasculature and/or CSF to infiltrate the brain parenchyma.

Conclusions

Prolonged exposure to a peripheral inflammatory stimulus triggers the recruitment of myeloid cells and lymphocytes to the brain. By altering the inflammatory or metabolic milieu of the brain, this novel method of immune-to-brain communication may have profound implications for patients with chronic inflammatory diseases, potentially leading to neuropsychiatric comorbidities.

Microglial process convergence on axonal segments in health and disease

Microglia dynamically interact with neurons influencing the development, structure, and function of neuronal networks. Recent studies suggest microglia may also influence neuronal activity by physically interacting with axonal domains responsible for action potential initiation and propagation. However, the nature of these microglial process interactions is not well understood. Microglial-axonal contacts are present early in development and persist through adulthood, implicating microglial interactions in the regulation of axonal integrity in both the developing and mature central nervous system. Moreover, changes in microglial-axonal contact have been described in disease states such as multiple sclerosis (MS) and traumatic brain injury (TBI). Depending on the disease state, there are increased associations with specific axonal segments. In MS, there is enhanced contact with the axon initial segment and node of Ranvier, while, in TBI, microglia alter interactions with axons at the site of injury, as well as at the axon initial segment. In this article, we review the interactions of microglial processes with axonal segments, analyzing their associations with various axonal domains and how these interactions may differ between MS and TBI. Furthermore, we discuss potential functional consequences and molecular mechanisms of these interactions and how these may differ among various types of microglial-axonal interactions.

STAT3 signaling in myeloid cells promotes pathogenic myelin-specific T cell differentiation and autoimmune demyelination

Myeloid lineage cells are suspected of having an integral role in pathophysiological processes of multiple sclerosis (MS), but the molecular mechanism(s) governing their effector function remains incompletely understood. We show that STAT3 is activated in myeloid cells near active MS lesions. Conditional deletion of Stat3 in myeloid cells abolished symptoms of experimental autoimmune encephalomyelitis (EAE) by suppressing the generation of pathogenic T cells. Functional and transcriptomic analyses of myeloid cells from wild-type and conditional knockout mice implicated antigen processing/presentation and inflammatory cytokine production as the mechanism underlying the effects of STAT3 deletion on impaired T cell activation. Our data indicate that targeting STAT3 in myeloid cells might be a viable treatment option for autoimmune demyelinating disease.

Multiple sclerosis (MS) is an autoimmune inflammatory demyelinating disease of the central nervous system. Dysregulation of STAT3, a transcription factor pivotal to various cellular processes including Th17 cell differentiation, has been implicated in MS. Here, we report that STAT3 is activated in infiltrating monocytic cells near active MS lesions and that activation of STAT3 in myeloid cells is essential for leukocyte infiltration, neuroinflammation, and demyelination in experimental autoimmune encephalomyelitis (EAE). Genetic disruption of Stat3 in peripheral myeloid lineage cells abrogated EAE, which was associated with decreased antigen-specific T helper cell responses. Myeloid cells from immunized Stat3 mutant mice exhibited impaired antigen-presenting functions and were ineffective in driving encephalitogenic T cell differentiation. Single-cell transcriptome analyses of myeloid lineage cells from preclinical wild-type and mutant mice revealed that loss of myeloid STAT3 signaling disrupted antigen-dependent cross-activation of myeloid cells and T helper cells. This study identifies a previously unrecognized requisite for myeloid cell STAT3 in the activation of myelin-reactive T cells and suggests myeloid STAT3 as a potential therapeutic target for autoimmune demyelinating disease.

Clozapine reduces infiltration into the CNS by targeting migration in experimental autoimmune encephalomyelitis

Background

Atypical antipsychotic agents, such as clozapine, are used to treat schizophrenia and other psychiatric disorders by a mechanism that is believed to involve modulating the immune system. Multiple sclerosis is an immune-mediated neurological disease, and recently, clozapine was shown to reduce disease severity in an animal model of MS, experimental autoimmune encephalomyelitis (EAE). However, the mode of action by which clozapine reduces disease in this model is poorly understood.

Methods

Because the mode of action by which clozapine reduces neuroinflammation is poorly understood, we used the EAE model to elucidate the in vivo and in vitro effects of clozapine.

Results

In this study, we report that clozapine treatment reduced the infiltration of peripheral immune cells into the central nervous system (CNS) and that this correlated with reduced expression of the chemokines CCL2 and CCL5 transcripts in the brain and spinal cord. We assessed to what extent immune cell populations were affected by clozapine treatment and we found that clozapine targets the expression of chemokines by macrophages and primary microglia. Furthermore, in addition to decreasing CNS infiltration by reducing chemokine expression, we found that clozapine directly inhibits chemokine-induced migration of immune cells. This direct target on the immune cells was not mediated by a change in receptor expression on the immune cell surface but by decreasing downstream signaling via these receptors leading to a reduced migration.

Conclusions

Taken together, our study indicates that clozapine protects against EAE by two different mechanisms; first, by reducing the chemoattractant proteins in the CNS; and second, by direct targeting the migration potential of peripheral immune cells.

Differential expression of genes involved in the acute innate immune response to intracortical microelectrodes

Higher order tasks in development for brain-computer interfacing applications require the invasiveness of intracortical microelectrodes. Unfortunately, the resulting inflammatory response contributes to the decline of detectable neural signal. The major components of the neuroinflammatory response to microelectrodes have been well-documented with histological imaging, leading to the identification of broad pathways of interest for its inhibition such as oxidative stress and innate immunity. To understand how to mitigate the neuroinflammatory response, a more precise understanding is required. Advancements in genotyping have led the development of new tools for developing temporal gene expression profiles. Therefore, we have meticulously characterized the gene expression profiles of the neuroinflammatory response to mice implanted with non-functional intracortical probes. A time course of differential acute expression of genes of the innate immune response were compared to naïve sham mice, identifying significant changes following implantation. Differential gene expression analysis revealed 22 genes that could inform future therapeutic targets. Particular emphasis is placed on the largest changes in gene expression occurring 24 h post-implantation, and in genes that are involved in multiple innate immune sets including Itgam, Cd14, and Irak4. STATEMENT OF SIGNIFICANCE: Current understanding of the cellular response contributing to the failure of intracortical microelectrodes has been limited to the evaluation of cellular presence around the electrode. Minimal research investigating gene expression profiles of these cells has left a knowledge gap identifying their phenotype. This manuscript represents the first robust investigation of the changes in gene expression levels specific to the innate immune response following intracortical microelectrode implantation. To understand the role of the complement system in response to implanted probes, we performed gene expression profiling over acute time points from implanted subjects and compared them to no-surgery controls. This manuscript provides valuable insights into inflammatory mechanisms at the tissue-probe interface, thus having a high impact on those using intracortical microelectrodes to study and treat neurological diseases and injuries.

Monocytes and Monocyte-Derived Antigen-Presenting Cells Have Distinct Gene Signatures in Experimental Model of Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease mediated by a complex interaction between the autoreactive lymphocytes and the effector myeloid cells within the central nervous system (CNS). In a murine model of MS, experimental autoimmune encephalomyelitis (EAE), Ly6Chi monocytes migrate into the CNS and further differentiate into antigen-presenting cells (APCs) during disease progression. Currently, there is no information about gene signatures that can distinguish between monocytes and the monocyte-derived APCs. We developed a surface marker-based strategy to distinguish between these two cell types during the stage of EAE when the clinical symptoms were most severe, and performed transcriptome analysis to compare their gene expression. We report here that the inflammatory CNS environment substantially alters gene expression of monocytes, compared to the monocyte differentiation process within CNS. Monocytes in the CNS express genes that encode proinflammatory cytokines and chemokines, and their expression is mostly maintained when the cells differentiate. Moreover, monocyte-derived APCs express surface markers associated with both dendritic cells and macrophages, and have a significant up-regulation of genes that are critical for antigen presentation. Furthermore, we found that Ccl17, Ccl22, and Ccr7 are expressed in monocyte-derived APCs but not the Ly6Chi monocytes. These findings may shed light on identifying molecular signals that control monocyte differentiation and functions during EAE.