Microglial localization of alpha-interferon receptor in human brain tissues

Role of microglia in stroke

Microglia play key roles in the post-ischemic inflammatory response and damaged tissue removal reacting rapidly to the disturbances caused by ischemia and working to restore the lost homeostasis. However, the modified environment, encompassing ionic imbalances, disruption of crucial neuron-microglia interactions, spreading depolarization, and generation of danger signals from necrotic neurons, induce morphological and phenotypic shifts in microglia. This leads them to adopt a proinflammatory profile and heighten their phagocytic activity. From day three post-ischemia, macrophages infiltrate the necrotic core while microglia amass at the periphery. Further, inflammation prompts a metabolic shift favoring glycolysis, the pentose-phosphate shunt, and lipid synthesis. These shifts, combined with phagocytic lipid intake, drive lipid droplet biogenesis, fuel anabolism, and enable microglia proliferation. Proliferating microglia release trophic factors contributing to protection and repair. However, some microglia accumulate lipids persistently and transform into dysfunctional and potentially harmful foam cells. Studies also showed microglia that either display impaired apoptotic cell clearance, or eliminate synapses, viable neurons, or endothelial cells. Yet, it will be essential to elucidate the viability of engulfed cells, the features of the local environment, the extent of tissue damage, and the temporal sequence. Ischemia provides a rich variety of region- and injury-dependent stimuli for microglia, evolving with time and generating distinct microglia phenotypes including those exhibiting proinflammatory or dysfunctional traits and others showing pro-repair features. Accurate profiling of microglia phenotypes, alongside with a more precise understanding of the associated post-ischemic tissue conditions, is a necessary step to serve as the potential foundation for focused interventions in human stroke.

Receptors on Microglia

Microglial cells are the most receptive cells in the central nervous system (CNS), expressing several classes of receptors reflecting their immune heritage and newly acquired neural specialisation. Microglia possess, depending on the particular context, receptors to neurotransmitters and neuromodulators as well as immunocompetent receptors. This rich complement allows microglial cells to monitor the functional status of the nervous system, contribute actively to the regulation of neural activity and plasticity and homeostasis, and guard against pathogens as well as other challenges to the CNS's integrity and function.

Emerging Roles of Type-I Interferons in Neuroinflammation, Neurological Diseases, and Long-Haul COVID

Interferons (IFNs) are pleiotropic cytokines originally identified for their antiviral activity. IFN-α and IFN-β are both type I IFNs that have been used to treat neurological diseases such as multiple sclerosis. Microglia, astrocytes, as well as neurons in the central and peripheral nervous systems, including spinal cord neurons and dorsal root ganglion neurons, express type I IFN receptors (IFNARs). Type I IFNs play an active role in regulating cognition, aging, depression, and neurodegenerative diseases. Notably, by suppressing neuronal activity and synaptic transmission, IFN-α and IFN-β produced potent analgesia. In this article, we discuss the role of type I IFNs in cognition, neurodegenerative diseases, and pain with a focus on neuroinflammation and neuro-glial interactions and their effects on cognition, neurodegenerative diseases, and pain. The role of type I IFNs in long-haul COVID-associated neurological disorders is also discussed. Insights into type I IFN signaling in neurons and non-neuronal cells will improve our treatments of neurological disorders in various disease conditions.

Type-I-interferon signaling drives microglial dysfunction and senescence in human iPSC models of Down syndrome and Alzheimer's disease

Microglia are critical in brain development and Alzheimer's disease (AD) etiology. Down syndrome (DS) is the most common genetic developmental disorder and risk factor for AD. Surprisingly, little information is available on the impact of trisomy of human chromosome 21 (Hsa21) on microglial functions during DS brain development and in AD in DS. Using induced pluripotent stem cell (iPSC)-based organoid and chimeric mouse models, we report that DS microglia exhibit an enhanced synaptic pruning function, which alters neuronal synaptic functions. In response to human brain tissue-derived pathological tau, DS microglia undergo cellular senescence and exhibit elevated type-I-interferon signaling. Mechanistically, knockdown of Hsa21-encoded type I interferon receptors, IFNARs, rescues the DS microglial phenotypes both during brain development and in response to pathological tau. Our findings provide in vivo evidence that human microglia respond to pathological tau by exhibiting dystrophic phenotypes. Targeting IFNARs may improve DS microglial functions and prevent senescence.

Microglia responses to interleukin-6 and type I interferons in neuroinflammatory disease

Microglia are the resident macrophages of the central nervous system (CNS). They are a heterogenous, exquisitely responsive, and highly plastic cell population, which enables them to perform diverse roles. They sense and respond to the local production of many different signals, including an assorted range of cytokines. Microglia respond strongly to interleukin-6 (IL-6) and members of the type I interferon (IFN-I) family, IFN-alpha (IFN-α), and IFN-beta (IFN-β). Although these cytokines are essential in maintaining homeostasis and for activating and regulating immune responses, their chronic production has been linked to the development of distinct human neurological diseases, termed "cerebral cytokinopathies." IL-6 and IFN-α have been identified as key mediators in the pathogenesis of neuroinflammatory disorders including neuromyelitis optica and Aicardi-Goutières syndrome, respectively, whereas IFN-β has an emerging role as a causal factor in age-associated cognitive decline. One of the key features that unites these diseases is the presence of highly reactive microglia. The current understanding is that microglia contribute to the development of cerebral cytokinopathies and represent an important therapeutic target. However, it remains to be resolved whether microglia have beneficial or detrimental effects. Here we review and discuss what is currently known about the microglial response to IL-6 and IFN-I, based on both animal models and clinical studies. Foundational knowledge regarding the microglial response to IL-6 and IFN-I is now being used to devise therapeutic strategies to ameliorate neuroinflammation and promote repair: either through targeting microglia, or by targeting the reduction of CNS levels or downstream biological pathways of IL-6 or IFN-I.

Markers of microglia in post-mortem brain samples from patients with Alzheimer's disease: a systematic review

Neuroinflammation is proposed as one of the mechanisms by which Alzheimer's disease pathology, including amyloid-β plaques, leads to neuronal death and dysfunction. Increases in the expression of markers of microglia, the main neuroinmmune cell, are widely reported in brains from patients with Alzheimer's disease, but the literature has not yet been systematically reviewed to determine whether this is a consistent pathological feature. A systematic search was conducted in Medline, Embase and PsychINFO for articles published up to 23 February 2017. Papers were included if they quantitatively compared microglia markers in post-mortem brain samples from patients with Alzheimer's disease and aged controls without neurological disease. A total of 113 relevant articles were identified. Consistent increases in markers related to activation, such as major histocompatibility complex II (36/43 studies) and cluster of differentiation 68 (17/21 studies), were identified relative to nonneurological aged controls, whereas other common markers that stain both resting and activated microglia, such as ionized calcium-binding adaptor molecule 1 (10/20 studies) and cluster of differentiation 11b (2/5 studies), were not consistently elevated. Studies of ionized calcium-binding adaptor molecule 1 that used cell counts almost uniformly identified no difference relative to control, indicating that increases in activation occurred without an expansion of the total number of microglia. White matter and cerebellum appeared to be more resistant to these increases than other brain regions. Nine studies were identified that included high pathology controls, patients who remained free of dementia despite Alzheimer's disease pathology. The majority (5/9) of these studies reported higher levels of microglial markers in Alzheimer's disease relative to controls, suggesting that these increases are not solely a consequence of Alzheimer's disease pathology. These results show that increased markers of microglia are a consistent feature of Alzheimer's disease, though this seems to be driven primarily by increases in activation-associated markers, as opposed to markers of all microglia.

Antidepressant therapies inhibit inflammation and microglial M1-polarization

Macrophages and their counterparts in the central nervous system, the microglia, detect and subsequently clear microbial pathogens and injured tissue. These phagocytic cells alter and adapt their phenotype depending on their prime activity, i.e., whether they participate in acute defence against pathogenic organisms ('M1'-phenotype) or in clearing damaged tissues and performing repair activities ('M2'-phenotype). Stimulation of pattern recognition receptors by viruses (vaccines), bacterial membrane components (e.g., LPS), alcohol, or long-chain saturated fatty acids promotes M1-polarization. Vaccine or LPS administration to healthy human subjects can result in sickness symptoms and low mood. Alcohol abuse and abdominal obesity are recognized as risk factors for depression. In the M1-polarized form, microglia and macrophages generate reactive oxygen and nitrogen radicals to eradicate microbial pathogens. Inadvertently, also tetrahydrobiopterin (BH4) may become oxidized. This is an irreversible reaction that generates neopterin, a recognized biomarker for depression. BH4 is a critical cofactor for the synthesis of dopamine, noradrenaline, and serotonin, and its loss could explain some of the symptoms of depression. Based on these aspects, the suppression of M1-polarization would limit the inadvertent catabolism of BH4. In the current review, we evaluate the evidence that antidepressant treatments (monoamine reuptake inhibitors, PDE4 inhibitors, lithium, valproate, agomelatine, tianeptine, electroconvulsive shock, and vagus nerve stimulation) inhibit LPS-induced microglia/macrophage M1-polarization. Consequently, we propose that supplementation with BH4 could limit the reduction in central monoamine synthesis and might represent an effective treatment for depressed mood.

Interferons, signal transduction pathways, and the central nervous system

The interferon (IFN) family of cytokines participates in the development of innate and acquired immune defenses against various pathogens and pathogenic stimuli. Discovered originally as a proteinaceous substance secreted from virus-infected cells that afforded immunity to neighboring cells from virus infection, these cytokines are now implicated in various human pathologies, including control of tumor development, cell differentiation, and autoimmunity. It is now believed that the IFN system (IFN genes and the genes induced by them, and the factors that regulate these processes) is a generalized alarm of cellular stress, including DNA damage. IFNs exert both beneficial and deleterious effects on the central nervous system (CNS). Our knowledge of the IFN-regulated processes in the CNS is far from being clear. In this article, we reviewed the current understanding of IFN signal transduction pathways and gene products that might have potential relevance to diseases of the CNS.

Type-1 interferons contribute to oxygen glucose deprivation induced neuro-inflammation in BE(2)M17 human neuroblastoma cells

BACKGROUND

Hypoxic-ischaemic injuries such as stroke and traumatic brain injury exhibit features of a distinct neuro-inflammatory response in the hours and days post-injury. Microglial activation, elevated pro-inflammatory cytokines and macrophage infiltration contribute to core tissue damage and contribute to secondary injury within a region termed the penumbra. Type-1 interferons (IFNs) are a super-family of pleiotropic cytokines that regulate pro-inflammatory gene transcription via the classical Jak/Stat pathway; however their role in hypoxia-ischaemia and central nervous system neuro-inflammation remains unknown. Using an in vitro approach, this study investigated the role of type-1 IFN signalling in an inflammatory setting induced by oxygen glucose deprivation (OGD).

METHODS

Human BE(2)M17 neuroblastoma cells or cells expressing a type-1 interferon-α receptor 1 (IFNAR1) shRNA or negative control shRNA knockdown construct were subjected to 4.5 h OGD and a time-course reperfusion period (0 to 24 h). Q-PCR was used to evaluate IFNα, IFNβ, IL-1β, IL-6 and TNF-α cytokine expression levels. Phosphorylation of signal transducers and activators of transcription (STAT)-1, STAT-3 and cleavage of caspase-3 was detected by western blot analysis. Post-OGD cellular viability was measured using a MTT assay.

RESULTS

Elevated IFNα and IFNβ expression was detected during reperfusion post-OGD in parental M17 cells. This correlated with enhanced phosphorylation of STAT-1, a downstream type-1 IFN signalling mediator. Significantly, ablation of type-1 IFN signalling, through IFNAR1 knockdown, reduced IFNα, IFNβ, IL-6 and TNF-α expression in response to OGD. In addition, MTT assay confirmed the IFNAR1 knockdown cells were protected against OGD compared to negative control cells with reduced pro-apoptotic cleaved caspase-3 levels.

CONCLUSIONS

This study confirms a role for type-1 IFN signalling in the neuro-inflammatory response following OGD in vitro and suggests its modulation through therapeutic blockade of IFNAR1 may be beneficial in reducing hypoxia-induced neuro-inflammation.

Central administration of murine interferon-α induces depressive-like behavioral, brain cytokine and neurochemical alterations in mice: a mini-review and original experiments

A role for pro-inflammatory cytokines and their neuroinflammatory signaling cascades in depressive pathology has increasingly gained acceptance. In this regard, several lines of evidence suggested that interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) can provoke neurochemical and hormonal changes akin to those associated with psychological stressors, and that these cytokines also induce sickness behaviors that resemble some of the neurovegetative features of depression. Similarly, human depressed patients often display marked changes of pro-inflammatory cytokine levels and immune cell activity. Perhaps more germane in the analysis of the cytokine-depression connection, reports of humans undergoing interferon-α (IFN-α) treatment for certain cancers or viral infections have indicated that the pro-inflammatory cytokine caused signs of major depression in a substantial subset of those treated. In the present investigation, we demonstrated that acute or repeated infusion of IFN-α into the lateral ventricles provoked depressive-like behavior and concomitant changes in serotonin (5-HT) and mRNA expression of particular 5-HT receptors and pro-inflammatory cytokines. These actions were less evident following administration directly into the prefrontal cortex and not apparent at all when administered to the dorsal raphe nucleus. The data are discussed in relation to the induction of depression elicited by IFN-α, and are presented in the context of a mini-review that highlights potential mechanisms through which the cytokine might act to promote psychomotor and affective disturbances and interact with stressors.

Type I interferon in neurological disease-the devil from within

The members of the type I interferon (IFN-I) family of cytokines are pleiotropic factors that have seminal roles in host defence, acting as antimicrobial and antitumor mediators as well as potent immunomodulatory factors that bridge the innate and adaptive immune responses. Despite these beneficial actions there is mounting evidence that link inappropriate or chronic production of IFN-I in the CNS to the development of a number of severe neuroinflammatory disorders. The most persuasive example is the genetically determined inflammatory encephalopathy, Aicardi-Goutières syndrome (AGS) in which patients have chronically elevated IFN-α production in the CNS. The presentation of AGS can often mimic congenital viral infection, however, molecular genetic studies have identified mutations in six genes that can cause AGS, most likely via dysregulated nucleic acid metabolism and activation of the innate immune response leading to increased intrathecal production of IFN-α. The role of IFN-α as a pathogenic factor in AGS and other neurological disorders has gained considerable support from experimental studies. In particular, a transgenic mouse model with CNS-restricted production of IFN-α replicates many of the cardinal neuropathologic features of AGS and reveal IFN-I to be the "devil from within", mediating molecular and cellular damage within the CNS. Thus, targeting IFN-I may be an effective strategy for the treatment of AGS as well as some other autoimmune and infectious neurological "interferonopathies".

Comparative pharmacokinetics of a tumour-targeting therapy candidate rh-IFNα2a-NGR with rh-IFNα2a administered intravenously in mice and rats

OBJECTIVES

rh-IFNα2a-NGR is a promising anti-tumor candidate. The aim of present study was to compare pharmacokinetics of rh-IFNα2a-NGR with rh-IFNα2a.

METHODS

Pharmacokinetics and elimination were investigated after intravenous administration to mice and rats. Compared tumor and tissue distribution profiles between rh-IFNα2a-NGR and rh-IFNα2a were illustrated in the tumor transplanted mice of SP2/0 myeloma. Double antibody sandwich ELISA method was used to assess the level of both rh-IFNα2a-NGR and rh-IFNα2a in serum, tissue, bile and urine.

KEY FINDINGS

After a single intravenous administration, the pharmacokinetic characters of rh-IFNα2a-NGR and rh-IFNα2a were described using a two-compartment model. No significant differences were observed between the two drugs in pharmacokinetic and elimination data. However, the concentration of rh-IFNα2a-NGR in tumor was 5.34 times and 1.52 times as high as that of rh-IFNα2a at 0.5 h (P < 0.01) and 1 h. In addition, immunohistochemical stain displayed rh-IFNα2a-NGR was predominantly located in tumor vascular tissues.

CONCLUSIONS

rh-IFNα2a-NGR could be an agent for tumor vascular-targeting therapy and these findings provided references for further clinical study.

Viral etiology of Parkinson's disease: Focus on influenza A virus

Some clinical reports and epidemiological data suggest that a virus may play a role in the etiology of Parkinson's disease (PD). Following intracerebral injection of a neurovirululent strain of influenza A virus into mice, the virus was found to be particularly localized in neurons of the substantia nigra and hippocampus. Although efforts to detect virus particles in the brains, or antibodies in the serum or CSF of patients with PD have been generally unsuccessful, recent immunohistochemical work has revealed the presence of complement proteins and the interferon-induced MxA in association with Lewy bodies and swollen neuronal processes. Although a viral etiology for PD is not now widely accepted, we proposed such an hypothesis. Neurovirulent influenza A virus is a candidate, but some other viruses or complex infection of these viruses may be responsible for the formation of Lewy bodies and the later death of nigral neurons.

Short small-interfering RNAs produce interferon-α-mediated analgesia

BACKGROUND

There is increasing interest in RNA interference in pain research using the intrathecal route to deliver small-interfering RNA (siRNA). An interferon (IFN) response is a common side-effect of siRNA. However, the IFN response in the spinal cord after intrathecal administration of siRNA remains unknown. We hypothesized that high doses of siRNAs can elicit off-target analgesia via releasing IFN-α. We investigated the IFN response and its role in regulating pain sensitivity in the spinal cords after intrathecal administration of siRNAs.

METHODS

Male Sprague-Dawley rats were given intrathecal injections of non-targeting (NT) siRNAs or IFN-α and tested for complete Freund's adjuvant (CFA)-induced mechanical allodynia and heat hyperalgesia. IFN-α in the spinal cord after injection of NT siRNAs was measured by western blotting and immunohistochemical staining.

RESULTS

IFN-α was up-regulated in the spinal cord after intrathecal treatment of NT siRNAs. Intrathecal injection of NT siRNAs, at high doses of 10 or 20 μg, reduced CFA-induced inflammatory pain (P<0.05). Intrathecal application of IFN-α inhibited pain hypersensitivity in inflamed rats and produced analgesia in naïve rats (P<0.05). Notably, the anti-nociceptive effects elicited by NT siRNAs and IFN-α were reversed by IFN-α neutralizing antibody and naloxone.

CONCLUSIONS

Our data suggest that (i) intrathecal administration of high doses of siRNA (≥ 10 μg) induced up-regulation of IFN-α in the spinal cord and produced analgesic effects through IFN-α, and (ii) IFN-α's analgesic effect is mediated via opioid receptors. Caution must be taken to avoid IFN-α-mediated analgesic effects of siRNAs in pain research.

Activation of central nervous system inflammatory pathways by interferon-alpha: relationship to monoamines and depression

BACKGROUND

Interferon (IFN)-alpha has been used to study the effects of innate immune cytokines on the brain and behavior in humans. The degree to which peripheral administration of IFN-alpha accesses the brain and is associated with a central nervous system (CNS) inflammatory response is unknown. Moreover, the relationship among IFN-alpha-associated CNS inflammatory responses, neurotransmitter metabolism, and behavior has yet to be established.

METHODS

Twenty-four patients with hepatitis C underwent lumbar puncture and blood sampling after approximately 12 weeks of either no treatment (n = 12) or treatment with pegylated IFN-alpha 2b (n = 12). Cerebrospinal fluid (CSF) and blood samples were analyzed for proinflammatory cytokines and their receptors as well as the chemokine, monocyte chemoattractant protein-1 (MCP-1), and IFN-alpha. Cerebrospinal fluid samples were additionally analyzed for monoamine metabolites and corticotropin releasing hormone. Depressive symptoms were assessed using the Montgomery Asberg Depression Rating Scale.

RESULTS

Interferon-alpha was detected in the CSF of all IFN-alpha-treated patients and only one control subject. Despite no increases in plasma IL-6, IFN-alpha-treated patients exhibited significant elevations in CSF IL-6 and MCP-1, both of which were highly correlated with CSF IFN-alpha concentrations. Of the immunologic and neurotransmitter variables, log-transformed CSF concentrations of the serotonin metabolite, 5-hydroxyindoleacetic acid (5-HIAA), were the strongest predictor of depressive symptoms. Log-transformed CSF concentrations of IL-6, but not IFN-alpha or MCP-1, were negatively correlated with log-transformed CSF 5-HIAA (r(2) = -.25, p < .05).

CONCLUSIONS

These data indicate that a peripherally administered cytokine can activate a CNS inflammatory response in humans that interacts with monoamine (serotonin) metabolism, which is associated with depression.

Norman Cousins Lecture. Mechanisms of cytokine-induced behavioral changes: psychoneuroimmunology at the translational interface

Work in our laboratory has focused on the mechanisms by which cytokines can influence the brain and behavior in humans and non-human primates. Using administration of interferon (IFN)-alpha as a tool to unravel these mechanisms, we have expanded upon findings from the basic science literature implicating cytokine-induced changes in monoamine metabolism as a primary pathway to depression. More specifically, a role for serotonin metabolism has been supported by the clinical efficacy of serotonin reuptake inhibitors in blocking the development of IFN-alpha-induced depression, and the capacity of IFN-alpha to activate metabolic enzymes (indolamine 2,3 dioxygenase) and cytokine signaling pathways (p38 mitogen activated protein kinase) that can influence the synthesis and reuptake of serotonin. Our data also support a role for dopamine depletion as reflected by IFN-alpha-induced changes in behavior (psychomotor slowing and fatigue) and regional brain activity, which implicate the involvement of the basal ganglia, as well as the association of IFN-alpha-induced depressive-like behavior in rhesus monkeys with decreased cerebrospinal fluid concentrations of the dopamine metabolite, homovanillic acid. Neuroimaging data in IFN-alpha-treated patients also suggest that activation of neural circuits (dorsal anterior cingulate cortex) associated with anxiety and alarm may contribute to cytokine-induced behavioral changes. Taken together, these effects of cytokines on the brain and behavior appear to subserve competing evolutionary survival priorities that promote reduced activity to allow healing, and hypervigilance to protect against future attack. Depending on the relative balance between these behavioral accoutrements of an activated innate immune response, clinical presentations may be distinct and warrant individualized therapeutic approaches.

Basal ganglia hypermetabolism and symptoms of fatigue during interferon-alpha therapy

Interferon (IFN)-alpha is a cytokine of the innate immune response that is well known for inducing behavioral alterations and has been used to study effects of cytokines on the nervous system. Limited data, however, are available on the sites of action of IFN-alpha within the brain and their relationship with specific IFN-alpha-induced symptoms. Using a longitudinal design, whole-brain metabolic activity as assessed by fluorine-18-labeled fluorodeoxyglucose uptake and positron emission tomography was examined before and 4 weeks after IFN-alpha administration in patients with malignant melanoma. Changes in metabolic activity in relevant brain regions were then correlated with IFN-alpha-induced behavioral changes. IFN-alpha administration was associated with widespread bilateral increases in glucose metabolism in subcortical regions including the basal ganglia and cerebellum. Decreases in dorsal prefrontal cortex glucose metabolism were also observed. Prominent IFN-alpha-induced behavioral changes included lassitude, inability to feel, and fatigue. Correlational analyses revealed that self-reported fatigue (specifically as assessed by the 'energy' subscale of the Visual Analog Scale of Fatigue) was associated with increased glucose metabolism in the left nucleus accumbens and putamen. These data indicate that IFN-alpha as well as other cytokines of the innate immune response may target basal ganglia nuclei, thereby contributing to fatigue-related symptoms in medically ill patients.

Type I interferon response in the central nervous system

This review is dedicated to the influence of type I IFNs (also called IFN-alpha/beta) in the central nervous system (CNS). Studies in mice with type I IFN receptor or IFN-beta gene deficiency have highlighted the importance of the type I IFN system against CNS viral infections and non-viral autoimmune disorders. Direct antiviral effects of type I IFNs appear to be crucial in limiting early spread of a number of viruses in CNS tissues. Type I IFNs have also proved to be beneficial in autoimmune disorders like multiple sclerosis or experimental autoimmune encephalitis, probably through immunomodulatory effects. Increasing efforts are done to characterize IFN expression and response in the CNS: to identify type I IFN producing cells, to decipher pathways leading to type I IFN expression in those cells, and to identify responding cells. However, reversible and irreversible damages consecutive to chronic exposure of the CNS to type I IFNs underline the importance of a tightly regulated type I IFN homeostasis in this organ.

Neurons produce type I interferon during viral encephalitis

Type I interferons, also referred to as IFN-alpha/beta, form the first line of defense against viral infections. Major IFN-alpha/beta producers in the periphery are the plasmacytoid dendritic cells (pDCs). Constitutive expression of the IFN regulatory factor (IRF)-7 enables pDCs to rapidly synthesize large amounts of IFN-alpha/beta after viral infection. In the central nervous system (CNS), pDCs are considered to be absent from the parenchyma, and little is known about the cells producing IFN-alpha/beta. The study presented here aimed to identify the cells producing IFN-alpha/beta in the CNS in vivo after infection by neurotropic viruses such as Theiler's virus and La Crosse virus. No cells with high constitutive expression of IRF-7 were detected in the CNS of uninfected mice, suggesting the absence of cells equivalent to pDCs. Upon viral infection, IFN-beta and some subtypes of IFN-alpha, but not IFN-epsilon or IFN-kappa, were transcriptionally up-regulated. IFN-alpha/beta was predominantly produced by scattered parenchymal cells and much less by cells of inflammatory foci. Interestingly, in addition to some macrophages and ependymal cells, neurons turned out to be important producers of both IFN-alpha and IFN-beta. However, only 3% of the infected neurons produced IFN-alpha/beta, suggesting that some restriction to IFN-alpha/beta production existed in these cells. All CNS cell types analyzed, including neurons, were able to respond to type I IFN by producing Mx or IRF-7. Our data show that, in vivo, neurons take an active part to the antiviral defense by being both IFN-alpha/beta producers and responders.

Immune modulation of the hypothalamic-pituitary-adrenal (HPA) axis during viral infection

Compelling data has been amassed indicating that soluble factors, or cytokines, emanating from the immune system can have profound effects on the neuroendocrine system, in particular the hypothalamic- pituitary-adrenal (HPA) axis. HPA activation by cytokines (via the release of glucocorticoids), in turn, has been found to play a critical role in restraining and shaping immune responses. Thus, cytokine-HPA interactions represent a fundamental consideration regarding the maintenance of homeostasis and the development of disease during viral infection. Although reviews exist that focus on the bi-directional communication between the immune system and the HPA axis during viral infection (188,235), others have focused on the immunomodulatory effects of glucocorticoids during viral infection (14,225). This review, however, concentrates on the other side of the bi-directional loop of neuroendocrine-immune interactions, namely, the characterization of HPA axis activity during viral infection and the mechanisms employed by cytokines to stimulate glucocorticoid release.

Effect of interferon-alpha on cognitive functioning in patients with chronic hepatitis C

Treatment with interferon-alpha (IFN-alpha) has been shown to adversely affect cognitive functioning in patients with a variety of medical disorders, but information about the effects of IFN-alpha on cognitive functioning in patients with chronic hepatitis C (CHC) is limited. The purpose of this study was to examine the effects of IFN-alpha on neuropsychological test performance in CHC patients. Participants were 30 patients with CHC, 11 who underwent IFN-alpha therapy and 19 who did not. All participants were tested at baseline (i.e., pretreatment) and approximately 6 months later with the Symbol Digit Modalities Test and Trail Making Test. Results revealed that the treatment group performed significantly worse than untreated CHC patients on Part B of the Trail Making Test after approximately 6 months of treatment. No significant group differences were found on Part A of the Trail Making Test or Symbol Digit Modalities Test. Findings suggest that CHC patients undergoing treatment with IFN-alpha may experience reduced abilities to benefit from practice but suffer no decrements in performance after 6 months of treatment. Additional research is needed to replicate these findings and to explore risk factors for susceptibility to IFN-alpha-induced effects.

Mice deficient in the interferon type I receptor have reduced REM sleep and altered hypothalamic hypocretin, prolactin and 2′,5′-oligoadenylate synthetase expression

We report that mice with a targeted null mutation in the interferon type I receptor (IFN-RI), which cannot respond to such IFNs as IFNalpha and IFNbeta, have a 30% reduction in time spent in spontaneous rapid eye movement sleep (REMS) as a consequence of a reduced number of REMS episodes. Time spent in nonrapid eye movement sleep (NREMS) was essentially unaltered in IFN-RI knockouts (KOs) compared to 129 SvEv controls. Body temperature and locomotor activity were similar in both strains of mice. Hypothalamic expression of mRNAs for molecules previously linked to sleep-wake regulation and an IFN-inducible antiviral gene, 2',5'-oligoadenylate synthetase 1a (OAS), were determined by real-time reverse-transcriptase polymerase chain reaction (RT2-PCR). The level of hypocretin A mRNA was elevated in IFN-RI KO mice compared to 129 SvEv mice, while prolactin mRNA and OAS mRNA levels were suppressed. Vasoactive intestinal peptide (VIP) and corticotropin-releasing hormone (CRH) mRNA levels were unchanged relative to controls. Serum prolactin levels were similar in both strains. Results are consistent with the hypothesis that increased hypocretin and reduced prolactin in the hypothalamus of IFN-RI KO mice are responsible for their reduced REMS. In addition, the reduced OAS expression may result in modulation of prolactin receptor signaling and thus contribute to suppression of REMS.

Association Between Apolipoprotein E ɛ4 and Neuropsychiatric Symptoms During Interferon α Treatment for Chronic Hepatitis C

Neuropsychiatric complications are common in patients with chronic hepatitis C undergoing treatment with interferon alpha. These side effects include alterations of mood, cognition, and neuroendocrine function and are unpredictable. In a number of neurological disorders characterized by neuropsychiatric symptoms and cognitive dysfunction, inheritance of an apolipoprotein E (APOE) epsilon4 allele is associated with adverse neuropsychiatric outcomes. The authors present evidence that the APOE genotype may influence a patient's neuropsychiatric response to interferon alpha treatment. The inheritance of APOE genotypes was examined in 110 patients with chronic hepatitis C treated with interferon alpha. A retrospective investigation was conducted by assessing the rates of psychiatric referral and neuropsychiatric symptoms experienced during treatment along with other complaints indicating psychological distress. A highly statistically significant association was seen between APOE genotypes and interferon-induced neuropsychiatric symptoms. Patients with an epsilon4 allele were more likely to be referred to a psychiatrist and had more neuropsychiatric symptoms during antiviral treatment than those without an epsilon4 allele. Additionally, patients with an epsilon4 allele were more likely to experience irritability or anger and anxiety or other mood symptoms. These data demonstrate that an individual's APOE genotype may influence the neuropsychiatric response to antiviral therapy with interferon alpha. Prospective studies evaluating the importance of APOE in susceptibility to interferon alpha-induced neuropsychiatric complications are needed. Moreover, pathways involving APOE should be considered in understanding the pathophysiology of interferon alpha-induced neuropsychiatric complications.

Protein levels of genes encoded on chromosome 21 in fetal Down syndrome brain: Challenging the gene dosage effect hypothesis (Part IV)

Down syndrome (DS) is the most frequent genetic disorder with mental retardation and caused by trisomy 21. Although the molecular mechanisms of the various phenotypes of DS could be due to overexpression of gene(s) on chromosome 21, several groups have challenged this gene dosage effect hypothesis. The near completion of the sequencing of human chromosome 21 provides unprecedented opportunities to understand the molecular pathology of DS, however, functional information on gene products is limited so far. We therefore evaluated the levels of six proteins whose genes are encoded on chromosome 21 (trefoil factor 1, trefoil factor 2, trefoil factor 3, coxsackie virus and adenovirus receptor, carbonyl reductase 1 and interferon- alpha receptor) in fetal cerebral cortex from DS and controls at the early second trimester using Western blot analysis. None of the investigated proteins showed overexpression in DS compared to controls suggesting that these proteins are not involved in abnormal development of fetal DS brain and that DS phenotype can not be simply explained by the gene dosage effect hypothesis. We are systematically quantifying all proteins whose genes are encoded on chromosome 21 and these studies may provide a better understanding of genotype-phenotype correlation in DS.

Depression induced by treatment with interferon-alpha in patients affected by hepatitis C virus

BACKGROUND

Several studies found a high incidence rate of neuro-psychiatric complications during long-term therapy with interferon alpha (IFNalpha), e.g. slowness, severe fatigue, hypersomnia, lethargy, depressed mood, mnemonic troubles, irritability, short temper, emotional lability, social withdrawal, and lack of concentration. The aim of this study was to examine the incidence of depressed mood and major depression in patients who were treated with IFNalpha.

METHODS

30 patients, affected by chronic active C-hepatitis, have been evaluated at baseline and 3 months after IFNalpha treatment. The evaluation consisted of psychometric assessments employing the DSM-IV criteria and the Montgomery Asberg Depression Rating Scale (MADRS).

RESULTS

At end-point, 40.7% of the patients suffered from a full blown major depression, according to the DSM-IV criteria for major depression. IFNalpha treatment induced a significant increase in the MADRS score from baseline to 3 months later. The MADRS items which were significantly increased at end-point were: expressed and unexpressed sadness; irritability; insomnia; loss of appetite; and asthenia.

DISCUSSION

The results show that prolonged IFNalpha treatment may induce depressive symptoms and major depression in a considerable number of subjects.

Interferons: potential roles in affect

A review of the literature on interferons was conducted and possible roles in neuropsychiatric disorders with affective disturbances are assessed. Interferons and interferon receptors are present in the limbic system where they appear to exert physiological effects pertinent to affect, most potently when levels rise during CNS infections. Interferons interact closely with cytokines and nitric oxide, signaling molecules implicated in depression. Results from knock-out mice suggest a role for interferon-gamma in moderating fear and anxiety, while other lines of evidence point to a role in arousal and circadian rhythms. The interferon-alpha receptor deploys an arginine methyltransferase affecting RNA editing and splicing, which seem to be disrupted in schizophrenia and bipolar disorder. S-Adenosylmethionine (SAMe), an effective antidepressant, may owe its effects in the latter disorders in part to variations in the strength of interferon-alpha signaling impacting RNA processing. Antiviral effects of interferons are of interest in lieu of viral theories of affective disorders. Finally, the relative levels of interferons gamma and alpha might play important roles in neural, and glial, development, as well as the dialog between the CNS and the immune system.

Mood disorders associated with interferon treatment: theoretical and practical considerations

OBJECTIVE

To review the theoretical and clinical aspects of mood disorders associated with interferon treatment and discuss their management.

DATA SOURCES

Pertinent and selected laboratory/clinical studies, review articles, letters, abstracts, and book chapters on behavioral and mood-related adverse effects of interferons published in English-language journals in the past two decades were identified by MEDLINE (June 1980-June 2000) and manual searches. DATA SELECTION AND DATA EXTRACTION: All of the publications identified were reviewed, and the relevant data were included. Studies not using criteria for psychiatric diagnosis or instruments for psychiatnc monitoring were excluded.

DATA SYNTHESIS

Clinical observations and limited research data suggest that interferon treatment may be associated with mood disorders. Mood-related symptoms induced by interferons emerge in a few days or weeks and tend to be dose dependent. Their severity may necessitate discontinuation of interferon therapy and/or the use of antidepressant or antimanic agents. The mechanisms responsible for inducing or exacerbating mood disorders in interferon-treated patients have not been elucidated. There is limited evidence implicating alterations in the serotonin system.

CONCLUSIONS

While interferon therapy may trigger or induce mood-related symptoms, preexisting or stable concurrent mood disorders in remission do not necessarily constitute a contraindication to treatment with interferons. Mood disorders associated with interferon treatment can present clinical challenges. However, they may promote our understanding of mood disorders in the context of the current biologic theories of depression and mania.

Microglia and Alzheimer's disease

Microglia play a major role in the cellular response associated with the pathological lesions of Alzheimer's disease. As brain-resident macrophages, microglia elaborate and operate under several guises that seem reminiscent of circulating and tissue monocytes of the leucocyte repertoire. Although microglia bear the capacity to synthesize amyloid beta, current evidence is most consistent with their phagocytic role. This largely involves the removal of cerebral amyloid and possibly the transformation of amyloid beta into fibrils. The phagocytic functions also encompass the generation of cytokines, reactive oxygen and nitrogen species, and various proteolytic enzymes, events that may exacerbate neuronal damage rather than incite outgrowth or repair mechanisms. Microglia do not appear to function as true antigen-presenting cells. However, there is circumstantial evidence that suggests functional heterogeneity within microglia. Pharmacological agents that suppress microglial activation or reduce microglial-mediated oxidative damage may prove useful strategies to slow the progression of Alzheimer's disease.

Regulation of the hypothalamic-pituitary-adrenal axis by cytokines: actions and mechanisms of action

Glucocorticoids are hormone products of the adrenal gland, which have long been recognized to have a profound impact on immunologic processes. The communication between immune and neuroendocrine systems is, however, bidirectional. The endocrine and immune systems share a common "chemical language," with both systems possessing ligands and receptors of "classical" hormones and immunoregulatory mediators. Studies in the early to mid 1980s demonstrated that monocyte-derived or recombinant interleukin-1 (IL-1) causes secretion of hormones of the hypothalamic-pituitary-adrenal (HPA) axis, establishing that immunoregulators, known as cytokines, play a pivotal role in this bidirectional communication between the immune and neuroendocrine systems. The subsequent 10-15 years have witnessed demonstrations that numerous members of several cytokine families increase the secretory activity of the HPA axis. Because this neuroendocrine action of cytokines is mediated primarily at the level of the central nervous system, studies investigating the mechanisms of HPA activation produced by cytokines take on a more broad significance, with findings relevant to the more fundamental question of how cytokines signal the brain. This article reviews published findings that have documented which cytokines have been shown to influence hormone secretion from the HPA axis, determined under what physiological/pathophysiological circumstances endogenous cytokines regulate HPA axis activity, established the possible sites of cytokine action on HPA axis hormone secretion, and identified the potential neuroanatomic and pharmacological mechanisms by which cytokines signal the neuroendocrine hypothalamus.

Permeability of the blood-brain and blood-spinal cord barriers to interferons

Interferons (IFNs) are cytokines that produce effects in the CNS even though their production occurs mainly in the periphery. Direct passage of IFNs from blood to CNS could be an important route by which circulating IFNs exert their central effects. In this report, we characterize the pharmacokinetics of the passage of IFNs through the blood-brain and blood-spinal cord barriers in four separate regions: whole brain and the cervical, thoracic and lumbosacral segments of the spinal cord. We found that the spinal cord had greater permeability to IFNs than did the brain. For each corresponding region, the permeability to IFN alpha was higher than that to IFN gamma. Capillary depletion after cardiac perfusion showed that most of the injected IFN was not entrapped by the vasculature but entered the parenchyma of the brain. HPLC showed that most of the IFN gamma entered in intact form. The passage of radioactively labeled IFN gamma into the brain and cervical spinal cord was saturated by a low dose of unlabeled IFN gamma, while passage into the thoracic and lumbosacral spinal cord was not saturated. In contrast, for another cytokine, tumor necrosis factor alpha (TNF alpha), a saturable transport system was present in distal spinal cord as well as the brain. The results show that IFNs and TNF alpha can enter the CNS from the periphery but with regional differences.

Enhancement of immunoreactivity for NF-kappa B in human cerebral infarctions

The distribution of the nuclear factor-kappa B (NF-kappa B) was investigated immunohistochemically in recently infarcted areas of postmortem human brain. Previously we reported that immunoreactivity for NF-kappa B was enhanced in neurons of Alzheimer disease brain in comparison with control cases. In the present study, a similar enhancement of immunoreactivity was observed in glial cells of infarcted areas, but not in the unaffected surround. Prominent staining for NF-kappa B was seen in some astrocytes, particularly in the penumbra or border zone between ischemic and non-ischemic areas. In some cases, positively stained macrophages were also observed in affected areas. Capillary staining for NF-kappa B was weak and did not differ significantly between affected and unaffected areas. These results suggest that enhanced expression of astrocytic NF-kappa B occurs in cerebral infarcted areas.