Astrocytes produce IL-19 in response to bacterial challenge and are sensitive to the immunosuppressive effects of this IL-10 family member

Effects of Interleukin-19 overexpression in the medial prefrontal cortex on anxiety-related behaviors, BDNF expression and p38/JNK/ERK pathways

Anxiety is a prevalent mental illness known for its high incidence, comorbidity, and tendency to recur, posing significant societal and individual burdens. Studies have highlighted Interleukin-19 (IL-19) as having potential relevance in neuropsychiatric disorders. Our previous research revealed that IL-19 overexpression in colonies exacerbated anxiety-related behaviors induced by dextran sodium sulfate/stress. However, the precise role and molecular mechanisms of IL-19 in anxiety regulation remain uncertain. In this study, we initiated an acute restraint stress (ARS)-induced anxious mouse model and identified heightened expression of IL-19 and IL-20Rα in the medial prefrontal cortex (mPFC) of ARS mice. Notably, IL-19 and IL-20Rα were predominantly present in the excitatory pyramidal neurons of the mPFC under both basal and ARS conditions. Utilizing the adeno-associated virus (AAV) strategy, we demonstrated that IL-19 overexpression in the mPFC induced anxiety-related behaviors and elevated stress susceptibility. Additionally, we observed decreased protein levels of brain-derived neurotrophic factor (BDNF) and postsynaptic density protein 95 (PSD95) in the mPFC of IL-19 overexpression mice, accompanied by reduced phosphorylation of in the p38, JNK, and Erk signaling pathways. These findings emphasize the role of IL-19 in modulating anxiety-related behaviors within the mPFC and suggest its potential as a pathological gene and therapeutic target for anxiety.

Testosterone Inhibits Secretion of the Pro-Inflammatory Chemokine CXCL1 from Astrocytes

Astrocytes play an important role in the regulation of the inflammatory response in the CNS, e.g., in demyelinating diseases. Since the chemokine CXCL1 is known to be secreted by astrocytes and to have a pro-inflammatory effect on immune cells in the CNS, we verified the effect of testosterone on its secretion in vitro (in the astrocytic cell line DI TNC1). Testosterone reduced the increase in CXCL1 production caused by the pro-inflammatory agent lysophosphatidylcholine and restored the basal production level of CXCL1. The androgen receptor (present and functional in the studied cell line) was strongly suggested to mediate this effect-its non-steroid ligand flutamide exerted an agonist-like effect, mimicking the activity of testosterone itself on CXCL1 secretion. This novel mechanism has important implications for the known immunomodulatory effect of testosterone and potentially other androgenic hormones. It provides a potential explanation on the molecular level and shows that astrocytes are important players in inflammatory homeostasis in the CNS and its hormonal regulation. Therefore, it suggests new directions for the development of the therapeutic intervention.

Spinal interleukin-24 contributes to neuropathic pain after peripheral nerve injury through interleukin-20 receptor2 in mice

Neuroinflammation is critically involved in nerve injury-induced neuropathic pain, characterized by local and systemic increased levels of proinflammatory cytokines. Interleukin-24 (IL-24), a key member of the IL-10 family, has been extensively studied for its therapeutic potential in various diseases, including cancer, autoimmune disorders, and bacterial infections, but whether it is involved in the regulation of neuropathic pain caused by peripheral nerve injury (PNI) has not been well established. In this study, we reported that spared nerve injury (SNI) induced a significant upregulation of IL-24 in fibroblasts, neurons, and oligodendrocyte precursor cells (OPCs, also called NG2-glia) in the affected spinal dorsal horns (SDHs), as well as dorsal root ganglions (DRGs). We also found that tumor necrosis factor α (TNF-α) induced the transcriptional expression of IL-24 in cultured fibroblasts, neurons, and NG2-glia; in addition, astrocytes, microglia, and NG2-glia treated with TNF-α exhibited a prominent increase in interleukin-20 receptor 2 (IL-20R2) expression. Furthermore, we evaluated the ability of IL-24 and IL-20R2 to attenuate pain in preclinical models of neuropathic pain. Intrathecal (i.t.) injection of IL-24 neutralizing antibody or IL-20R2 neutralizing antibody could effectively alleviate mechanical allodynia and thermal hyperalgesia after PNI. Similarly, intrathecal injection of IL-24 siRNA or IL-20R2 siRNA also alleviated mechanical allodynia after SNI. The inhibition of IL-24 reduced SNI-induced proinflammatory cytokine (IL-1β and TNF-α) production and increased anti-inflammatory cytokine (IL-10) production. Meanwhile, the inhibition of IL-20R2 also decreased IL-1β mRNA expression after SNI. Collectively, our findings revealed that IL-24/IL-20R might contribute to neuropathic pain through inflammatory response. Therefore, targeting IL-24 could be a promising strategy for treating neuropathic pain induced by PNI.

Inhibition of IL-17 ameliorates keratinocyte-borne cytokine responses in an in vitro model for house-dust-mite triggered atopic dermatitis

A subgroup of patients suffering from atopic dermatitis (AD) does not respond to biologics therapy targeting the key players of type-2 inflammation, and it is an ongoing discussion whether skin-infiltrating Th17 cells may underlie this phenomenon. This study aimed to investigate the potential of allergen-induced, immune-cell derived IL-17 on the induction of inflammatory processes in keratinocytes. Peripheral blood mononuclear cells derived from respectively sensitized AD patients were stimulated with house dust mite (HDM) extract and cell culture supernatants were applied subsequently in absence or presence of secukinumab to primary human keratinocytes. Hereby we confirm that the immune response of sensitized AD patients to HDM contains aside from type-2 cytokines significant amounts of IL-17. Blocking IL-17 efficiently reduced the stimulation-induced changes in keratinocyte gene expression. IL-17-dependent transcriptional changes included increased expression of the cytokines IL-20 and IL-24 as well as Suppressor of Cytokine Siganling 3 (SOCS3), a negative feedback-regulator of the STAT3/IL-17/IL-24 immune response. We conclude that the immune response to HDM can induce pro-inflammatory cytokines from keratinocytes in AD, which in part is mediated via IL-17. Targeting IL-17 may turn out to be a reasonable alternative therapy in a subgroup of patients with moderate to severe AD and HDM sensitization.

Upregulation of interleukin-19 in saliva of patients with COVID-19

Cytokines are major players in orchestrating inflammation, disease pathogenesis and severity during COVID-19 disease. However, the role of IL-19 in COVID-19 pathogenesis remains elusive. Herein, through the analysis of transcriptomic datasets of SARS-CoV-2 infected lung cells, nasopharyngeal swabs, and lung autopsies of COVID-19 patients, we report that expression levels of IL-19 and its receptor, IL-20R2, were upregulated following SARS-CoV-2 infection. Of 202 adult COVID-19 patients, IL-19 protein level was significantly higher in blood and saliva of asymptomatic patients compared to healthy controls when adjusted for patients’ demographics (P < 0.001). Interestingly, high saliva IL-19 level was also associated with COVID-19 severity (P < 0.0001), need for mechanical ventilation (P = 0.002), and/or death (P = 0.010) within 29 days of admission, after adjusting for patients’ demographics, diabetes mellitus comorbidity, and COVID-19 serum markers of severity such as D-dimer, C-reactive protein, and ferritin. Moreover, patients who received interferon beta during their hospital stay had lower plasma IL-19 concentrations (24 pg mL⁻¹) than those who received tocilizumab (39.2 pg mL⁻¹) or corticosteroids (42.5 pg mL⁻¹). Our findings indicate that high saliva IL-19 level was associated with COVID-19 infectivity and disease severity.

Z-DNA binding protein 1 mediates necroptotic and apoptotic cell death pathways in murine astrocytes following herpes simplex virus-1 infection

Background

The mechanisms by which glia respond to viral central nervous system (CNS) pathogens are now becoming apparent with the demonstration that microglia and astrocytes express an array of pattern recognition receptors that include intracellular RNA and DNA sensors. We have previously demonstrated that glia express Z-DNA binding protein 1 (ZBP1) and showed that this cytosolic nucleic acid sensor contributes to the inflammatory/neurotoxic responses of these cells to herpes simplex virus-1 (HSV-1). However, the relative contribution made by ZBP1- to HSV-1-mediated cell death in glia has not been determined.

Methods

We have investigated the relative contribution made by ZBP1- to HSV-1-mediated cell death in primary astrocytes derived from mice genetically deficient in this sensor. We have used capture ELISAs and immunoblot analysis to assess inflammatory cytokine production and ZBP1 and phosphorylated mixed lineage kinase domain-like protein (MLKL) expression levels, respectively, following HSV-1 challenge. Furthermore, we have used a commercially available cell viability assay to determine the proportion and rate of cell death in cells following infection with laboratory and neuroinvasive clinical strains of HSV-1, and pharmacological inhibitors of necroptotic and apoptotic pathway components to assess the relative role of each.

Results

We show that the loss of ZBP1 in astrocytes results in an increase in the number of viral particles released following HSV-1 infection. Importantly, we have confirmed that HSV-1 induces necroptosis in astrocytes and have established the ability of ZBP1 to mediate this cell death pathway. Interestingly, while ZBP1 is best known for its role in necroptotic signaling, our findings indicate that this sensor can also contribute to virally induced apoptosis in these glia.

Conclusions

Our findings indicate that ZBP1 serves as a restriction factor for HSV-1 infection and is associated with the induction of both necroptotic and apoptotic cell death pathways in primary murine astrocytes. While it remains to be seen whether ZBP1-mediated activation of cell death in astrocytes contributes significantly to host protection or, rather, exacerbates HSV-1 encephalitis pathology, the identification of such a role in resident CNS cells may represent a novel target for therapeutic intervention to reduce HSV encephalitis-associated morbidity and mortality.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02469-z.

Expression of IL-20 Receptor Subunit β Is Linked to EAE Neuropathology and CNS Neuroinflammation

Considerable clinical evidence supports that increased blood-brain barrier (BBB) permeability is linked to immune extravasation of CNS parenchyma during neuroinflammation. Although BBB permeability and immune extravasation are known to be provoked by vascular endothelial growth factor-A (i.e., VEGF-A) and C-X-C motif chemokine ligand 12 (CXCL12), respectively, the mechanisms that link both processes are still elusive. The interleukin-20 (i.e., IL-20) cytokine signaling pathway was previously implicated in VEGF-mediated angiogenesis and is known to induce cellular response by way of signaling through IL-20 receptor subunit β (i.e., IL-20RB). Dysregulated IL-20 signaling is implicated in many inflammatory pathologies, but it's contribution to neuroinflammation has yet to be reported. We hypothesize that the IL-20 cytokine, and the IL cytokine subfamily more broadly, play a key role in CNS neuroinflammation by signaling through IL-20RB, induce VEGF activity, and enhance both BBB-permeability and CXCL12-mediated immune extravasation. To address this hypothesis, we actively immunized IL-20RB^-/- mice and wild-type mice to induce experimental autoimmune encephalomyelitis (EAE) and found that IL-20RB^-/- mice showed amelioration of disease progression compared to wild-type mice. Similarly, we passively immunized IL-20RB^-/- mice and wild-type mice with myelin-reactive Th1 cells from either IL-20RB^-/- and wild-type genotype. Host IL-20RB^-/- mice showed lesser disease progression than wild-type mice, regardless of the myelin-reactive Th1 cells genotype. Using multianalyte bead-based immunoassay and ELISA, we found distinctive changes in levels of pro-inflammatory cytokines between IL-20RB^-/- mice and wild-type mice at peak of EAE. We also found detectable levels of all cytokines of the IL-20 subfamily within CNS tissues and specific alteration to IL-20 subfamily cytokines IL-19, IL-20, and IL-24, expression levels. Immunolabeling of CNS region-specific microvessels confirmed IL-20RB protein at the spinal cord microvasculature and upregulation during EAE. Microvessels isolated from macaques CNS tissues also expressed IL-20RB. Moreover, we identified the expression of all IL-20 receptor subunits: IL-22 receptor subunit α-1 (IL-22RA1), IL-20RB, and IL-20 receptor subunit α (IL-20RA) in human CNS microvessels. Notably, human cerebral microvasculature endothelial cells (HCMEC/D3) treated with IL-1β showed augmented expression of the IL-20 receptor. Lastly, IL-20-treated HCMEC/D3 showed alterations on CXCL12 apicobasal polarity consistent with a neuroinflammatory status. This evidence suggests that IL-20 subfamily cytokines may signal at the BBB via IL-20RB, triggering neuroinflammation.

The Neuroprotective Role of Reactive Astrocytes after Central Nervous System Injury

Reactive astrocytes have traditionally been viewed as a significant contributor to secondary neuronal damage and repair inhibition after central nervous system (CNS) injury attributed, in large part, to their roles in glial scarring. However, more recent transcriptional evidence has uncovered the vast diversity in reactive astrocyte identity and functions that comprises both neuroprotective and -toxic characteristics. Additionally, the capacity of reactive astrocytes to shift between these activation states demonstrates a high level of environment-dependent plasticity that drives the interplay between neuroprotection and -toxicity after CNS injury. These recent findings have spawned a new field of research that seeks to identify and categorize the function of these discrete subpopulations in the context of neurotrauma, as well as identify their regulators. Therefore, this review will discuss the major and most recent advances in this field of research, with a primary emphasis on neuroprotection. This review will also discuss the major pitfalls present in the field, with a particular focus on model species and their impact on the development of novel therapies.

Antimicrobial responses of peripheral and central nervous system glia against Staphylococcus aureus

Staphylococcus aureus infections of the central nervous system are serious and can be fatal. S. aureus is commonly present in the nasal cavity, and after injury to the nasal epithelium it can rapidly invade the brain via the olfactory nerve. The trigeminal nerve constitutes another potential route of brain infection. The glia of these nerves, olfactory ensheathing cells (OECs) and trigeminal nerve Schwann cells (TgSCs), as well as astrocytes populating the glia limitans layer, can phagocytose bacteria. Whilst some glial responses to S. aureus have been studied, the specific responses of different glial types are unknown. Here, we compared how primary mouse OECs, TgSCs, astrocytes and microglia responded to S. aureus. All glial types internalized the bacteria within phagolysosomes, and S. aureus-conjugated BioParticles could be tracked with subtle but significant differences in time-course of phagocytosis between glial types. Live bacteria could be isolated from all glia after 24 h in culture, and microglia, OECs and TgSCs exhibited better protection against intracellular S. aureus survival than astrocytes. All glial types responded to the bacteria by cytokine secretion. Overall, OECs secreted the lowest level of cytokines, suggesting that these cells, despite showing strong capacity for phagocytosis, have immunomodulatory functions that can be relevant for neural repair.

Ablation of interleukin-19 improves motor function in a mouse model of amyotrophic lateral sclerosis

Neuroinflammation by activated microglia and astrocytes plays a critical role in progression of amyotrophic lateral sclerosis (ALS). Interleukin-19 (IL-19) is a negative-feedback regulator that limits pro-inflammatory responses of microglia in an autocrine and paracrine manner, but it remains unclear how IL-19 contributes to ALS pathogenesis. We investigated the role of IL-19 in ALS using transgenic mice carrying human superoxide dismutase 1 with the G93A mutation (SOD1G93A Tg mice). We generated IL-19-deficient SOD1G93A Tg (IL-19-/-/SOD1G93A Tg) mice by crossing SOD1G93A Tg mice with IL-19-/- mice, and then evaluated disease progression, motor function, survival rate, and pathological and biochemical alternations in the resultant mice. In addition, we assessed the effect of IL-19 on glial cells using primary microglia and astrocyte cultures from the embryonic brains of SOD1G93A Tg mice and IL-19-/-/SOD1G93A Tg mice. Expression of IL-19 in primary microglia and lumbar spinal cord was higher in SOD1G93A Tg mice than in wild-type mice. Unexpectedly, IL-19-/-/SOD1G93A Tg mice exhibited significant improvement of motor function. Ablation of IL-19 in SOD1G93A Tg mice increased expression of both neurotoxic and neuroprotective factors, including tumor necrosis factor-α (TNF-α), IL-1β, glial cell line-derived neurotrophic factor (GDNF), and transforming growth factor β1, in lumbar spinal cord. Primary microglia and astrocytes from IL-19-/-/SOD1G93A Tg mice expressed higher levels of TNF-α, resulting in release of GDNF from astrocytes. Inhibition of IL-19 signaling may alleviate ALS symptoms.

Interleukin-19 Abrogates Experimental Autoimmune Encephalomyelitis by Attenuating Antigen-Presenting Cell Activation

Interleukin-19 (IL-19) acts as a negative-feedback regulator to limit proinflammatory response of macrophages and microglia in autocrine/paracrine manners in various inflammatory diseases. Multiple sclerosis (MS) is a major neuroinflammatory disease in the central nervous system (CNS), but it remains uncertain how IL-19 contributes to MS pathogenesis. Here, we demonstrate that IL-19 deficiency aggravates experimental autoimmune encephalomyelitis (EAE), a mouse model of MS, by promoting IL-17-producing helper T cell (Th17 cell) infiltration into the CNS. In addition, IL-19-deficient splenic macrophages expressed elevated levels of major histocompatibility complex (MHC) class II, co-stimulatory molecules, and Th17 cell differentiation-associated cytokines such as IL-1β, IL-6, IL-23, TGF-β1, and TNF-α. These observations indicated that IL-19 plays a critical role in suppression of MS pathogenesis by inhibiting macrophage antigen presentation, Th17 cell expansion, and subsequent inflammatory responses. Furthermore, treatment with IL-19 significantly abrogated EAE. Our data suggest that IL-19 could provide significant therapeutic benefits in patients with MS.

Astrocyte subtype-specific approach to Alzheimer's disease treatment

Astrocytes respond to any pathological condition in the central nervous system (CNS) including Alzheimer's disease (AD), and this response is called astrocyte reactivity. Astrocyte reaction to a CNS insult is a highly heterogeneous phenomenon in which the astrocytes undergo a set of morphological, molecular and functional changes with a characteristic secretome profile. Such astrocytes are termed as 'reactive astrocytes'. Controversies regarding the reactive astrocytes abound. Recently, a continuum of reactive astrocyte profiles with distinct transcriptional states has been identified. Among them, disease-associated astrocytes (DAA) were uniquely present in AD mice and expressed a signature set of genes implicated in complement cascade, endocytosis and aging. Earlier, two stimulus-specific reactive astrocyte subtypes with their unique transcriptomic signatures were identified using mouse models of neuroinflammation and ischemia and termed as A1 astrocytes (detrimental) and A2 astrocytes (beneficial) respectively. Interestingly, although most of the A1 signature genes were also detected in DAA, as opposed to A2 astrocyte signatures, some of the A1 specific genes were expressed in other astrocyte subtypes, indicating that these nomenclature-based signatures are not very specific. In this review, we elaborate the disparate functions and cytokine profiles of reactive astrocyte subtypes in AD and tried to distinguish them by designating neurotoxic astrocytes as A1-like and neuroprotective ones as A2-like without directly referring to the A1/A2 original nomenclature. We have also focused on the dual nature from a functional perspective of some cytokines depending on AD-stage, highlighting a number of them as major candidates in AD therapy. Therefore, we suggest that promoting subtype-specific beneficial roles, inhibiting subtype-specific detrimental roles or targeting subtype-specific cytokines constitute a novel therapeutic approach to AD treatment.

Cryptococcus neoformans-astrocyte interactions: effect on fungal blood brain barrier disruption, brain invasion, and meningitis progression

Cryptococcus neoformans is an opportunistic, neurotropic, and encapsulated fungus that causes life-threatening cryptococcal meningitis (CM), especially in regions of the world where AIDS is endemic. The polysaccharide capsule of C. neoformans is the fungus major virulent factor, being copiously released during infection and causing immunosuppressive defects in the host. Although the capsular material is commonly associated with reactive astrocytes in fatal CM, little is known about the molecular and cellular interactions among astroglia and C. neoformans. As astrocytes also make up the neurovascular unit at the blood-brain barrier (BBB), which C. neoformans must transverse to colonize the central nervous system and cause CM; these cells may play a significant regulatory role in the prevention and progression of infection. For example, astrocytes are implicated in neurological disease including the regulation of cerebral intracranial pressure, immune function, and water homeostasis. Hence, in this review, we provide a general overview of astroglia biology and discuss the current knowledge on C. neoformans-astrocyte interactions including their involvement in the development of CM. This "gliocentric view" of cerebral cryptococcosis suggests that therapeutic interventions particularly targeting at preserving the neuroprotective function of astrocytes may be used in preventing and managing C. neoformans BBB transmigration, brain invasion, colonization, and meningitis.

Resolution of inflammation in immune and nonimmune cells by interleukin-19

The inflammatory response is a complex, tightly regulated process activated by tissue wounding, foreign body invasion, and sterile inflammation. Over the decades, great progress has been made to advance our understanding of this process. One often overlooked aspect of inflammation is its sequel: resolution. We know that dysregulated resolution often results in numerous chronic degenerative diseases such as arthritis, cancer, and asthma. However, identification of components and mechanisms of resolving pathways lags behind those of proinflammatory processes, yet represents overlooked therapeutic opportunities. One approach is identification of endogenous, negative compensatory mechanisms, which are activated in response to inflammation for the purpose of resolution of that inflammatory stimuli. This review will focus on literature that describes expression and function of interleukin-19, a proposed anti-inflammatory cytokine, in numerous inflammatory diseases. The literature concerning IL-19 is complex, context-dependent, and often contradictory. The expression and function of IL-19 in the inflammatory response are in no way settled. We will attempt to clarify the role that this interesting and understudied cytokine plays in resolution of inflammation and discuss its mechanisms of action in different cell types. We will present a hypothesis that endogenous IL-19 expression in response to inflammatory stimuli is a cellular compensatory mechanism to dampen inflammation. We further present studies suggesting that while endogenously expressed IL-19 may be a response to inflammation, pharmacological levels may be necessary to effectively resolve the inflammatory cascade.

Retinoic acid inducible gene-I mediated detection of bacterial nucleic acids in human microglial cells

Background

Bacterial meningitis and meningoencephalitis are associated with devastating neuroinflammation. We and others have demonstrated the importance of glial cells in the initiation of immune responses to pathogens invading the central nervous system (CNS). These cells use a variety of pattern recognition receptors (PRRs) to identify common pathogen motifs and the cytosolic sensor retinoic acid inducible gene-1 (RIG-I) is known to serve as a viral PRR and initiator of interferon (IFN) responses. Intriguingly, recent evidence indicates that RIG-I also has an important role in the detection of bacterial nucleic acids, but such a role has not been investigated in glia.

Methods

In this study, we have assessed whether primary or immortalized human and murine glia express RIG-I either constitutively or following stimulation with bacteria or their products by immunoblot analysis. We have used capture ELISAs and immunoblot analysis to assess human microglial interferon regulatory factor 3 (IRF3) activation and IFN production elicited by bacterial nucleic acids and novel engineered nucleic acid nanoparticles. Furthermore, we have utilized a pharmacological inhibitor of RIG-I signaling and siRNA-mediated knockdown approaches to assess the relative importance of RIG-I in such responses.

Results

We demonstrate that RIG-I is constitutively expressed by human and murine microglia and astrocytes, and is elevated following bacterial infection in a pathogen and cell type-specific manner. Additionally, surface and cytosolic PRR ligands are also sufficient to enhance RIG-I expression. Importantly, our data demonstrate that bacterial RNA and DNA both trigger RIG-I-dependent IRF3 phosphorylation and subsequent type I IFN production in human microglia. This ability has been confirmed using our nucleic acid nanoparticles where we demonstrate that both RNA- and DNA-based nanoparticles can stimulate RIG-I-dependent IFN responses in these cells.

Conclusions

The constitutive and bacteria-induced expression of RIG-I by human glia and its ability to mediate IFN responses to bacterial RNA and DNA and nucleic acid nanoparticles raises the intriguing possibility that RIG-I may be a potential target for therapeutic intervention during bacterial infections of the CNS, and that the use of engineered nucleic acid nanoparticles that engage this sensor might be a method to achieve this goal.

[Recent progress in the pathophysiological role of interleukin-19]

Cytokine signal is essential for the biological function including development, maintenance of homeostasis and progression of disease. There are growing evidences that signaling via pro-inflammatory cytokines underlie a variety of immunological diseases such as psoriasis, atopic dermatitis, inflammatory bowel disease, and metabolic syndromes, in which cytokine signals are known as a potential therapeutic target of antibody drugs. In contrast, anti-inflammatory cytokines, which is represented by IL-10, largely contribute to suppression of inflammation and restoration of injured tissues. IL-19 is a member of IL-10 cytokine family, which comprises IL-20 cytokine subfamily with IL-20, IL-22, IL-24, and IL-26. IL-19 is produced by myeloid and epithelial cells with stimulation of bacterial components and cytokines. Although IL-19 has been originally recognized as a potential Th2-related cytokine, in recent researches, it has been reported that this cytokine upregulates Th17 response to reflect and promote progression of Th17-related disease including psoriasis. On the other hand, IL-19 has anti-inflammatory effects on inflammatory diseases such as infectious skin disease, inflammatory bowel disease, and cardiovascular disease. Therefore, IL-19 may exert pleiotropic effects dependent on the pathological mechanism of inflammatory diseases. In this review, we summarize recent studies about IL-19 and introduce the pathophysiological and therapeutic role of IL-19 in inflammatory diseases.

Murine astrocytes are responsive to the pro-inflammatory effects of IL-20

Glia are key regulators of inflammatory responses within the central nervous system (CNS) following infection or trauma. We have previously demonstrated the ability of activated astrocytes to rapidly produce pro-inflammatory mediators followed by a transition to an anti-inflammatory cytokine production profile that includes the immunosuppressive cytokine interleukin (IL)-10 and the closely related cytokines IL-19 and IL-24. IL-20, another member of the IL-10 family, is known to modulate immune cell activity in the periphery and we have previously demonstrated that astrocytes constitutively express the cognate receptors for this cytokine. However, the ability of glia to produce IL-20 remains unclear and the effects of this pleiotropic cytokine on glial immune functions have not been investigated. In this study, we report that primary murine and human astrocytes are not an appreciable source of IL-20 following challenge with disparate bacterial species or their components. Importantly, we have determined that astrocyte are responsive to the immunomodulatory actions of this cytokine by showing that recombinant IL-20 administration upregulates microbial pattern recognition receptor expression and induces release of the inflammatory mediator IL-6 by these cells. Taken together, these data suggest that IL-20 acts in a dissimilar manner to other IL-10 family members to augment the inflammatory responses of astrocytes.

Past and Current Perspectives in Modeling Bacteria and Blood-Brain Barrier Interactions

The central nervous system (CNS) barriers are highly specialized cellular barriers that promote brain homeostasis while restricting pathogen and toxin entry. The primary cellular constituent regulating pathogen entry in most of these brain barriers is the brain endothelial cell (BEC) that exhibits properties that allow for tight regulation of CNS entry. Bacterial meningoencephalitis is a serious infection of the CNS and occurs when bacteria can cross specialized brain barriers and cause inflammation. Models have been developed to understand the bacterial - BEC interaction that lead to pathogen crossing into the CNS, however, these have been met with challenges due to these highly specialized BEC phenotypes. This perspective provides a brief overview and outlook of the in vivo and in vitro models currently being used to study bacterial brain penetration, and opinion on improved models for the future.

Immunity Against Bacterial Infection of the Central Nervous System: An Astrocyte Perspective

Bacterial infection of the central nervous system (CNS) is a severe and life-threatening condition with high mortality, and it may lead to permanent neurological deficits in survivors. Increasing evidence indicates that astrocytes, as the most abundant CNS glial cell population, regulate innate and adaptive immune responses in the CNS under pathological conditions in addition to their role in the maintenance of CNS homeostasis and neuronal function. Following antigen recognition, astrocytes participate in the initiation of innate immune responses, and prompt an adaptive immune response to recruit peripheral immune cells. Investigations have been conducted to understand the immunological role of astrocytes in CNS disease and injury, however, their part in bacterial infections of the CNS has not been fully evaluated. A better understanding will permit the identification of successful therapeutic targets for an improved prognosis and disease outcome.

Murine astrocytes produce IL-24 and are susceptible to the immunosuppressive effects of this cytokine

Background

Glia are key regulators of inflammatory responses within the central nervous system (CNS) following infection or trauma. We have previously demonstrated the ability of activated glia to rapidly produce pro-inflammatory mediators followed by a transition to an anti-inflammatory cytokine production profile that includes the immunosuppressive cytokine interleukin (IL)-10 and the closely related cytokine IL-19. IL-24, another member of the IL-10 family, has been studied in a number of inflammatory conditions in the periphery and is known to modulate immune cell activity. However, the ability of glia to produce IL-24 remains unclear and the effects of this pleiotropic cytokine on glial immune functions have not been investigated.

Methods

In this study, we have assessed whether primary murine glia produce IL-24 following stimulation and evaluated the effect of this cytokine on the immune responses of such cells. We have utilized RT-PCR and immunoblot analyses to assess the expression of IL-24 and its cognate receptors by astrocytes following challenge with bacteria or their components. Furthermore, we have determined the effect of recombinant IL-24 on astrocyte immune signaling and responses to clinically relevant bacteria using RT-PCR and specific capture ELISAs.

Results

We demonstrate that astrocytes express IL-24 mRNA and release detectable amounts of this cytokine protein in a delayed manner following bacterial challenge. In addition, we have determined that glia constitutively express the cognate receptors for IL-24 and show that such expression can be increased in astrocytes following activation. Importantly, our results indicate that IL-24 exerts an immunosuppressive effect on astrocytes by elevating suppressor of cytokine signaling 3 expression and limiting IL-6 production following challenge. Furthermore, we have demonstrated that IL-24 can also augment the release of IL-10 by bacterially challenged astrocytes and can induce the expression of the potentially neuroprotective mediators, glutamate transporter 1, and cyclooxygenase 2.

Conclusions

The expression of IL-24 and its cognate receptors by astrocytes following bacterial challenge, and the ability of this cytokine to limit inflammatory responses while promoting the expression of immunosuppressive and/or neuroprotective mediators, raises the intriguing possibility that IL-24 functions to regulate or resolve CNS inflammation following bacterial infection in order to limit neuronal damage.

The Interleukin-10 Family of Cytokines and Their Role in the CNS

Resident cells of the central nervous system (CNS) play an important role in detecting insults and initiating protective or sometimes detrimental host immunity. At peripheral sites, immune responses follow a biphasic course with the rapid, but transient, production of inflammatory mediators giving way to the delayed release of factors that promote resolution and repair. Within the CNS, it is well known that glial cells contribute to the onset and progression of neuroinflammation, but it is only now becoming apparent that microglia and astrocytes also play an important role in producing and responding to immunosuppressive factors that serve to limit the detrimental effects of such responses. Interleukin-10 (IL-10) is generally considered to be the quintessential immunosuppressive cytokine, and its ability to resolve inflammation and promote wound repair at peripheral sites is well documented. In the present review article, we discuss the evidence for the production of IL-10 by glia, and describe the ability of CNS cells, including microglia and astrocytes, to respond to this suppressive factor. Furthermore, we review the literature for the expression of other members of the IL-10 cytokine family, IL-19, IL-20, IL-22 and IL-24, within the brain, and discuss the evidence of a role for these poorly understood cytokines in the regulation of infectious and sterile neuroinflammation. In concert, the available data indicate that glia can produce IL-10 and the related cytokines IL-19 and IL-24 in a delayed manner, and these cytokines can limit glial inflammatory responses and/or provide protection against CNS insult. However, the roles of other IL-10 family members within the CNS remain unclear, with IL-20 appearing to act as a pro-inflammatory factor, while IL-22 may play a protective role in some instances and a detrimental role in others, perhaps reflecting the pleiotropic nature of this cytokine family. What is clear is that our current understanding of the role of IL-10 and related cytokines within the CNS is limited at best, and further research is required to define the actions of this understudied family in inflammatory brain disorders.

Staphylococcus aureus Colonization Induces Strain-Specific Suppression of Interleukin-17

Staphylococcus aureus is a pathogen that causes significant morbidity and mortality. Nasal carriage is a major source of transmission and of endogenous infection. Persistent carriage is detected in ∼30% of healthy individuals. While Th17 cells have been shown to play a role in S. aureus infection and clearance, the immune response to carriage is not well understood. Here, we evaluate the Th17 response and its potential inhibitors during S. aureus carriage. We recruited 25 volunteers, of whom 11 were persistent carriers. Volunteers' peripheral blood mononuclear cells (PBMCs) were stimulated with either their endogenous strain (a strain isolated from that carrier) or exogenous ones (strains not carried by that volunteer). Changes in Th17 cell frequency and numbers, interleukin-17 (IL-17) mRNA expression, and IL-17 protein abundance were measured by fluorescence-activated cell sorting, real-time PCR, and enzyme-linked immunosorbent assay. Similarly, responses of IL-17 suppressors (regulatory T cells [FOXP3], IL-10, IL-27, and IL-19) were measured. Th17 and IL-17 levels in response to stimulation with endogenous strains were significantly lower than those in response to stimulation with exogenous ones. Of the suppressive cytokines tested, only IL-19 exhibited a stronger response to endogenous than to exogenous strains. Addition of recombinant IL-19 to exogenous-strain-stimulated PBMCs caused decreased IL-17 expression, whereas addition of IL-19 antibodies to endogenous-strain-stimulated cells resulted in an increased IL-17 response. Together, our results suggest that S. aureus carriage induced a tolerogenic response to a carried strain that could be reproduced through the addition of recombinant IL-19 or prevented by the addition of IL-19 antibodies. This differential immune response may play a role in the determination of S. aureus carriage patterns.

Human microglia and astrocytes constitutively express the neurokinin-1 receptor and functionally respond to substance P

Background

The tachykinin substance P (SP) is recognized to exacerbate inflammation at peripheral sites via its target receptor, neurokinin 1 receptor (NK-1R), expressed by leukocytes. More recently, SP/NK-1R interactions have been associated with severe neuroinflammation and neuronal damage. We have previously demonstrated that NK-1R antagonists can limit neuroinflammatory damage in a mouse model of bacterial meningitis. Furthermore, we have since shown that these agents can attenuate bacteria-induced neuronal and glial inflammatory mediator production in nonhuman primate (NHP) brain explants and isolated neuronal cells, and following in vivo infection.

Methods

In the present study, we have assessed the ability of NHP brain explants, primary human microglia and astrocytes, and immortalized human glial cell lines to express NK-1R isoforms. We have utilized RT-PCR, immunoblot analysis, immunofluorescent microscopy, and/or flow cytometric analysis, to quantify NK-1R expression in each, at rest, or following bacterial challenge. Furthermore, we have assessed the ability of human microglia to respond to SP by immunoblot analysis of NF-kB nuclear translocation and determined the ability of this neuropeptide to augment inflammatory cytokine release and neurotoxic mediator production by human astrocytes using an ELISA and a neuronal cell toxicity assay, respectively.

Results

We demonstrate that human microglial and astrocytic cells as well as NHP brain tissue constitutively express robust levels of the full-length NK-1R isoform. In addition, we demonstrate that the expression of NK-1R by human astrocytes can be further elevated following exposure to disparate bacterial pathogens or their components. Importantly, we have demonstrated that NK-1R is functional in both human microglia and astrocytes and show that SP can augment the inflammatory and/or neurotoxic immune responses of glial cells to disparate and clinically relevant bacterial pathogens.

Conclusions

The robust constitutive and functional expression of the full-length NK-1R isoform by human microglia and astrocytes, and the ability of SP to augment inflammatory signaling pathways and mediator production by these cells, support the contention that SP/NK-1R interactions play a significant role in the damaging neuroinflammation associated with conditions such as bacterial meningitis.

Astrocyte Apoptosis and HIV Replication Are Modulated in Host Cells Coinfected with Trypanosoma cruzi

The protozoan Trypanosoma cruzi is the etiological agent of Chagas disease. In immunosuppressed individuals, as it occurs in the coinfection with human immunodeficiency virus (HIV), the central nervous system may be affected. In this regard, reactivation of Chagas disease is severe and often lethal, and it accounts for meningoencephalitis. Astrocytes play a crucial role in the environment maintenance of healthy neurons; however, they can host HIV and T. cruzi. In this report, human astrocytes were infected in vitro with both genetically modified-pathogens to express alternative fluorophore. As evidenced by fluorescence microscopy and flow cytometry, HIV and T. cruzi coexist in the same astrocyte, likely favoring reciprocal interactions. In this context, lower rates of cell death were observed in both T. cruzi monoinfected-astrocytes and HIV-T. cruzi coinfection in comparison with those infected only with HIV. The level of HIV replication is significantly diminished under T. cruzi coinfection, but without affecting the infectivity of the HIV progeny. This interference with viral replication appears to be related to the T. cruzi multiplication rate or its increased intracellular presence but does not require their intracellular cohabitation or infected cell-to-cell contact. Among several Th1/Th2/Th17 profile-related cytokines, only IL-6 was overexpressed in HIV-T. cruzi coinfection exhibiting its cytoprotective role. This study demonstrates that T. cruzi and HIV are able to coinfect astrocytes thus altering viral replication and apoptosis.

Aprepitant limits in vivo neuroinflammatory responses in a rhesus model of Lyme neuroborreliosis

BACKGROUND

Substance P (SP) is produced at high levels in the central nervous system (CNS), and its target receptor, neurokinin 1 receptor (NK-1R), is expressed by glia and leukocytes. This tachykinin functions to exacerbate inflammatory responses at peripheral sites. Moreover, SP/NK-1R interactions have recently been associated with severe neuroinflammation and neuronal damage. We have previously demonstrated that NK-1R antagonists can limit neuroinflammatory damage in a mouse model of bacterial meningitis. Furthermore, we have since shown that these agents can attenuate Borrelia burgdorferi-induced neuronal and glial inflammatory mediator production in non-human primate brain explants and isolated neuronal cells.

METHODS

In the present study, we have assessed the role played by endogenous SP/NK-1R interactions in damaging CNS inflammation in an established rhesus macaque model that faithfully reproduces the key clinical features of Lyme neuroborreliosis, using the specific NK-1R antagonist, aprepitant. We have utilized multiplex ELISA to quantify immune mediator levels in cerebrospinal fluid, and RT-PCR and immunoblot analyses to quantify cytokine and NK-1R expression, respectively, in brain cortex, dorsal root ganglia, and spinal cord tissues. In addition, we have assessed astrocyte number/activation status in brain cortical tissue by immunofluorescence staining and confocal microscopy.

RESULTS

We demonstrate that aprepitant treatment attenuates B. burgdorferi-induced elevations in CCL2, CXCL13, IL-17A, and IL-6 gene expression in dorsal root ganglia, spinal cord, and/or cerebrospinal fluid of rhesus macaques at 2 to 4 weeks following intrathecal infection. In addition, we demonstrate that this selective NK-1R antagonist also prevents increases in total cortical brain NK-1R expression and decreases in the expression of the astrocyte marker, glial fibrillary acidic protein, associated with B. burgdorferi infection.

CONCLUSIONS

The ability of a centrally acting NK-1R inhibitor to attenuate B. burgdorferi-associated neuroinflammatory responses and sequelae raises the intriguing possibility that such FDA-approved agents could be repurposed for use as an adjunctive therapy for the treatment of bacterial CNS infections.

Infectious immunity in the central nervous system and brain function

Inflammation is emerging as a critical mechanism underlying neurological disorders of various etiologies, yet its role in altering brain function as a consequence of neuroinfectious disease remains unclear. Although acute alterations in mental status due to inflammation are a hallmark of central nervous system (CNS) infections with neurotropic pathogens, post-infectious neurologic dysfunction has traditionally been attributed to irreversible damage caused by the pathogens themselves. More recently, studies indicate that pathogen eradication within the CNS may require immune responses that interfere with neural cell function and communication without affecting their survival. In this Review we explore inflammatory processes underlying neurological impairments caused by CNS infection and discuss their potential links to established mechanisms of psychiatric and neurodegenerative diseases.

Interleukin-19 alleviates brain injury by anti-inflammatory effects in a mice model of focal cerebral ischemia

Stroke causes brain injury with neuroinflammation which exacerbates the neuronal damage. Recent studies show that anti-inflammatory cytokine interleukin-19 (IL-19) plays a critical part in the inflammatory and ischemic vascular diseases, yet its potential role in ischemic stroke is unknown. Here, we tested the hypothesis that IL-19 exerts protective effects against brain ischemia by modulating inflammation after stroke. Mice were injected intraperitoneally with 10ng/g per day recombinant mouse IL-19 starting pre-stroke, and were subjected to transient middle cerebral artery occlusion. Infarct volume was assessed by triphenyltetrazolium chloride and neurobehavioral outcome by neurological scores. Inflammation was measured using real-time quantitative PCR, immunochemistry, and fluorescence-activated cell sorting. Infarct volume at 72h after stroke was significantly smaller in IL-19 treated group and focal neurological score was significantly better. IL-19 treatment markedly attenuated elevation of the expression of TNF-α and IL-6 mRNA, suppressed increases in the number of microglia, macrophages, CD4⁺ T cells, CD8⁺ T cells as well as B cells, and blocked activation of macrophages and neutrophils in the ischemic brain. In peripheral blood, IL-19 injection helped to robustly preserve the reduced immune cells, including macrophages, CD4⁺ T cells, CD8⁺ T cells and B cells, compared to control group. IL-19 reduced brain infarction and attenuated neurological deficits following stroke in mice, probably by inhibiting infiltration and activation of immune cells, and by suppressing increases in gene expression of proinflammatory cytokines. This may identify IL-19 as a new therapeutic to limit neuroinflammation after stroke.

Astrocytes Enhance Streptococcus suis-Glial Cell Interaction in Primary Astrocyte-Microglial Cell Co-Cultures

Streptococcus (S.) suis infections are the most common cause of meningitis in pigs. Moreover, S. suis is a zoonotic pathogen, which can lead to meningitis in humans, mainly in adults. We assume that glial cells may play a crucial role in host-pathogen interactions during S. suis infection of the central nervous system. Glial cells are considered to possess important functions during inflammation and injury of the brain in bacterial meningitis. In the present study, we established primary astrocyte-microglial cell co-cultures to investigate interactions of S. suis with glial cells. For this purpose, microglial cells and astrocytes were isolated from new-born mouse brains and characterized by flow cytometry, followed by the establishment of astrocyte and microglial cell mono-cultures as well as astrocyte-microglial cell co-cultures. In addition, we prepared microglial cell mono-cultures co-incubated with uninfected astrocyte mono-culture supernatants and astrocyte mono-cultures co-incubated with uninfected microglial cell mono-culture supernatants. After infection of the different cell cultures with S. suis, bacteria-cell association was mainly observed with microglial cells and most prominently with a non-encapsulated mutant of S. suis. A time-dependent induction of NO release was found only in the co-cultures and after co-incubation of microglial cells with uninfected supernatants of astrocyte mono-cultures mainly after infection with the capsular mutant. Only moderate cytotoxic effects were found in co-cultured glial cells after infection with S. suis. Taken together, astrocytes and astrocyte supernatants increased interaction of microglial cells with S. suis. Astrocyte-microglial cell co-cultures are suitable to study S. suis infections and bacteria-cell association as well as NO release by microglial cells was enhanced in the presence of astrocytes.

Inflammatory Markers in Recent Onset Psychosis and Chronic Schizophrenia

BACKGROUND

Immune markers have been associated with schizophrenia, but few studies have examined multiple markers in both recent onset and chronic schizophrenia patients.

METHODS

The sample of 588 individuals included 79 with recent onset psychosis, 249 with chronic schizophrenia, and 260 controls. A combined inflammation score was calculated by principal components factor analysis of the levels of C-reactive protein, Pentraxin 3, and IgG antibodies to gliadin, casein, and Saccharomyces cerevisiae measured in blood samples. Inflammation scores among groups were compared by multivariate analyses.

RESULTS

The chronic schizophrenia group showed significant elevations in the combined inflammation score compared with controls. The recent onset group surprisingly showed a reduction in the combined inflammation score. Consistent with these findings, the chronic schizophrenia group had significantly increased odds of a combined inflammation score greater than the 75th and the 90th percentile of that of the controls. The recent onset group had significantly increased odds of a combined inflammation score less than the 10th and the 25th percentile level of the controls.

CONCLUSIONS

The recent onset of psychosis may be associated with inherent deficits in innate immunity. Individuals later in the course of disease may have increased levels of innate immunity. The reasons for these changes are not known with certainty but may be related to compensatory increases as the disease progresses. Longitudinal studies are needed to determine the course of immune abnormalities in schizophrenia and their role in the clinical manifestations of the disorder.

Cytokine and Chemokine Profiles in Patients with Neuromyelitis Optica Spectrum Disorder

OBJECTIVE

To screen cytokines and chemokines and determine their dynamic changes in the serum and cerebrospinal fluid (CSF) of patients with neuromyelitis optica spectrum disorder (NMOSD).

METHODS

Eight NMOSD with seropositive aquaporin-4 antibody (AQP4-IgG) were enrolled, as well as 8 matched patients with multiple sclerosis (MS) and 8 with noninflammatory neurological diseases, who were included as controls. In total, 102 cytokines and 34 chemokines were detected in the CSF and serum of NMOSD patients and controls.

RESULTS

CSF interleukin (IL)-17A levels were significantly higher in NMOSD patients in the relapsing phase (27.15 ± 11.33) than in those in the remitting phase (10.04 ± 3.11, p = 0.0017), and patients with MS (14.72 ± 3.20, p = 0.0283) and other controls (10.39 ± 11.38, p = 0.0021). CSF IL-6 levels were higher in the NMOSD patients in the relapsing phase (12.23 ± 3.47) than in those in the remitting phase (5.87 ± 2.78, p = 0.0001), and MS patients (7.38 ± 2.35, p = 0.0033) and other controls (7.50 ± 0.37, p = 0.0043). CSF CCL19 levels were also significantly higher in NMOSD patients in the relapsing phase (35.87 ± 27.07) than in those in the remitting phase (10.71 ± 3.62, p = 0.0215). Serum IL-19 levels were lower in NMOSD patients in the relapsing phase (6.23 ± 1.95) than in those in the remitting phase (10.72 ± 4.46, p = 0.0092). Further, there was a positive, significant correlation between serum IL-9 concentration and the Expanded Disability Status Scale score in the NMOSD patients in the relapsing phase (p = 0.04).

CONCLUSION

In addition to IL-6 and IL-17A, IL-16 and CCL19 act as proinflammatory cytokines/chemokines, while IL-19 plays a protective role in NMOSD pathogenesis.

HIV-1, methamphetamine and astrocytes at neuroinflammatory Crossroads

As a popular psychostimulant, methamphetamine (METH) use leads to long-lasting, strong euphoric effects. While METH abuse is common in the general population, between 10 and 15% of human immunodeficiency virus-1 (HIV-1) patients report having abused METH. METH exacerbates the severity and onset of HIV-1-associated neurocognitive disorders (HAND) through direct and indirect mechanisms. Repetitive METH use impedes adherence to antiretroviral drug regimens, increasing the likelihood of HIV-1 disease progression toward AIDS. METH exposure also directly affects both innate and adaptive immunity, altering lymphocyte numbers and activity, cytokine signaling, phagocytic function and infiltration through the blood brain barrier. Further, METH triggers the dopamine reward pathway and leads to impaired neuronal activity and direct toxicity. Concurrently, METH and HIV-1 alter the neuroimmune balance and induce neuroinflammation, which modulates a wide range of brain functions including neuronal signaling and activity, glial activation, viral infection, oxidative stress, and excitotoxicity. Pathologically, reactive gliosis is a hallmark of both HIV-1- and METH-associated neuroinflammation. Significant commonality exists in the neurotoxic mechanisms for both METH and HAND; however, the pathways dysregulated in astroglia during METH exposure are less clear. Thus, this review highlights alterations in astrocyte intracellular signaling pathways, gene expression and function during METH and HIV-1 comorbidity, with special emphasis on HAND-associated neuroinflammation. Importantly, this review carefully evaluates interventions targeting astrocytes in HAND and METH as potential novel therapeutic approaches. This comprehensive overview indicates, without a doubt, that during HIV-1 infection and METH abuse, a complex dialog between all neural cells is orchestrated through astrocyte regulated neuroinflammation.

Astrocyte barriers to neurotoxic inflammation

Astrocytes form borders (glia limitans) that separate neural from non-neural tissue along perivascular spaces, meninges and tissue lesions in the CNS. Transgenic loss-of-function studies reveal that astrocyte borders and scars serve as functional barriers that restrict the entry of inflammatory cells into CNS parenchyma in health and disease. Astrocytes also have powerful pro-inflammatory potential. Thus, astrocytes are emerging as pivotal regulators of CNS inflammatory responses. This Review discusses evidence that astrocytes have crucial roles in attracting and restricting CNS inflammation, with important implications for diverse CNS disorders.

Interleukin-19 acts as a negative autocrine regulator of activated microglia

Activated microglia can exert either neurotoxic or neuroprotective effects, and they play pivotal roles in the pathogenesis and progression of various neurological diseases. In this study, we used cDNA microarrays to show that interleukin-19 (IL-19), an IL-10 family cytokine, is markedly upregulated in activated microglia. Furthermore, we found that microglia are the only cells in the nervous system that express the IL-19 receptor, a heterodimer of the IL-20Rα and IL-20Rβ subunits. IL-19 deficiency increased the production of such pro-inflammatory cytokines as IL-6 and tumor necrosis factor-α in activated microglia, and IL-19 treatment suppressed this effect. Moreover, in a mouse model of Alzheimer's disease, we observed upregulation of IL-19 in affected areas in association with disease progression. Our findings demonstrate that IL-19 is an anti-inflammatory cytokine, produced by activated microglia, that acts negatively on microglia in an autocrine manner. Thus, microglia may self-limit their inflammatory response by producing the negative regulator IL-19.

Methamphetamine alters the normal progression by inducing cell cycle arrest in astrocytes

Methamphetamine (MA) is a potent psychostimulant with a high addictive capacity, which induces many deleterious effects on the brain. Chronic MA abuse leads to cognitive dysfunction and motor impairment. MA affects many cells in the brain, but the effects on astrocytes of repeated MA exposure is not well understood. In this report, we used Gene chip array to analyze the changes in the gene expression profile of primary human astrocytes treated with MA for 3 days. Range of genes were found to be differentially regulated, with a large number of genes significantly downregulated, including NEK2, TTK, TOP2A, and CCNE2. Gene ontology and pathway analysis showed a highly significant clustering of genes involved in cell cycle progression and DNA replication. Further pathway analysis showed that the genes downregulated by multiple MA treatment were critical for G2/M phase progression and G1/S transition. Cell cycle analysis of SVG astrocytes showed a significant reduction in the percentage of cell in the G2/M phase with a concomitant increase in G1 percentage. This was consistent with the gene array and validation data, which showed that repeated MA treatment downregulated the genes associated with cell cycle regulation. This is a novel finding, which explains the effect of MA treatment on astrocytes and has clear implication in neuroinflammation among the drug abusers.