Interferon-alpha causes neuronal dysfunction in encephalitis

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".

Increased IFNα activity and differential antibody response in patients with a history of Lyme disease and persistent cognitive deficits

Following antibiotic treatment for Lyme disease, some patients report persistent or relapsing symptoms of pain, fatigue, and/or cognitive deficits. Factors other than active infection, including immune abnormalities, have been suggested, but few clues regarding mechanism have emerged. Furthermore, the effect of antibiotic treatment on immune response in affected individuals remains unknown. In this study, a longitudinal analysis of specific immune markers of interest was carried out in patients with a history of Lyme disease and persistent objective memory impairment, prior to and following treatment with either ceftriaxone or placebo. IFNα activity was measured by detection of serum-induced changes in specific target genes, using a functional cell-based assay and quantitative real-time PCR. Level and pattern of antibody reactivity to brain antigens and to Borrelia burgdorferi proteins were analyzed by ELISA and immunoblotting. Sera from the patient cohort induced significantly higher expression of IFIT1 and IFI44 target genes than those from healthy controls, indicating increased IFNα activity. Antibody reactivity to specific brain and borrelial proteins was significantly elevated in affected patients. IFNα activity and antibody profile did not change significantly in response to ceftriaxone. The heightened antibody response implies enhanced immune stimulation, possibly due to prolonged exposure to the organism prior to the initial diagnosis and antibiotic treatment of Lyme disease. The increase in IFNα activity is suggestive of a mechanism contributing to the ongoing neuropsychiatric symptoms.

Morphine exposure during HIV encephalitis in SCID mice

HIV encephalitis (HIVE) is often complicated by opiate abuse. Based on human pathological, animal and in vitro studies, opiates are thought to exacerbate HIVE. To test this hypothesis we exposed 10 week old SCID mice with HIVE to morphine and examined histopathological parameters. Mice inoculated intracerebrally with either HIV-infected or uninfected (control mice) human macrophages were immediately implanted subcutaneously with pellets containing saline, morphine or morphine plus naltrexone. They were sacrificed after 10 days. Immunostaining for astrocytes (GFAP), mouse mononuclear phagocytes (CD45) and neuronal dendrites (MAP2) was analyzed by densitometry. HIVE mice exposed to either saline, morphine or morphine plus naltrexone also had brain sections counted for HIV+ human macrophages. Typical HIVE pathology was present, consistent with previously published studies. Surprisingly, there were no effects on astrogliosis, microgliosis and MAP2 decreases in the HIVE, morphine treated group. There was also no effect of morphine exposure on numbers of p24+ human macrophages. These results emphasize the complexities of modeling opiate effects in HIVE and the potential significance of opiate abuse on HIVE in humans.

Environmental enrichment attenuates hippocampal neuroinflammation and improves cognitive function during influenza infection

Recent findings from our lab have shown that peripheral infection of adult mice with influenza A/PR/8/34 (H1N1) virus induces a neuroinflammatory response that is paralleled by loss of neurotrophic and glial regulatory factors in the hippocampus, and deficits in cognitive function. Environmental enrichment has been shown to exert beneficial effects on the brain and behavior in many central nervous system (CNS) disorders, but its therapeutic potential during peripheral viral infection remains unknown. Therefore, the objective of the present study was to determine if long-term continuous exposure to environmental enrichment could prevent and/or attenuate the negative effects of influenza infection on the hippocampus and spatial cognition. Mice were housed in enriched or standard conditions for 4 months, and continued to live in their respective environments throughout influenza infection. Cognitive function was assessed in a reversal learning version of the Morris water maze, and changes in hippocampal expression of proinflammatory cytokines (IL-1β, IL-6, TNF-α, IFN-α), neurotrophic (BDNF, NGF), and immunomodulatory (CD200, CX3CL1) factors were determined. We found that environmental enrichment reduced neuroinflammation and helped prevent the influenza-induced reduction in hippocampal CD200. These changes were paralleled by improved cognitive performance of enriched mice infected with influenza when compared to infected mice in standard housing conditions. Collectively, these data are the first to demonstrate the positive impact of environmental enrichment on the brain and cognition during peripheral viral infection, and suggest that enhanced modulation of the neuroimmune response may underlie these beneficial effects.

Negative regulation of human astrocytes by interferon (IFN) α in relation to growth inhibition and impaired glucose utilization

The present study assessed the direct effects of IFNs on human astrocytes. Human astrocytes were exposed to human recombinant IFNs, and the proliferation of cells was measured. Type I IFN receptor mRNA and protein expression, the phosphoprotein levels of signaling molecules including JNK, ERK1/2, IκB, p38MAPK, Stat3, and the expression of cytokines were determined respectively. In addition, cellular glucose consumption was measured as well as Glut-1 protein and activation of GSK-3β/mTOR signal were determined. The expression of Type I IFN receptor was detected in cultured human astrocytes. 2 IU/ml IFNα2a and IFNα2b significantly decreased the proliferation of human astrocytes respectively, compared to control. IFNβ had no significant effect on the proliferation of the cells. The phosphorylation of JNK stimulated by all IFNs detected was more pronounced and sustained than ERK1/2 and IκB. No effects were observed on the activation of p38MAPK and Stat3. Moreover, Treatment with IFNα, especially with IFNα2b, decreased glucose consumption and stimulated phosphorylation of GSK-3β and mTOR, but decreased the expression of Glut-1. In contrast, IFNβ had no significant effect on either glucose consumption or activation of GSK-3β/mTOR signals. INFα2b significantly decreased the levels of IL-8 whereas the levels of GM-CSF were increased. The present study demonstrates direct inhibitory effects of IFNα on cell proliferation, cell signaling and glucose utilization in human astrocytes.

Influenza infection induces neuroinflammation, alters hippocampal neuron morphology, and impairs cognition in adult mice

Influenza is a common and highly contagious viral pathogen, yet its effects on the structure and function of the CNS remain largely unknown. Although there is evidence that influenza strains that infect the brain can lead to altered cognitive and emotional behaviors, it is unknown whether a viral strain that is not neurotropic (A/PR/8/34) can result in a central inflammatory response, neuronal damage, and neurobehavioral effects. We hypothesized that neuroinflammation and alterations in hippocampal neuron morphology may parallel cognitive dysfunction following peripheral infection with live influenza virus. Here, we show that influenza-infected mice exhibited cognitive deficits in a reversal learning version of the Morris water maze. At the same time point in which cognitive impairment was evident, proinflammatory cytokines (IL-1β, IL-6, TNF-α, IFN-α) and microglial reactivity were increased, while neurotrophic (BDNF, NGF) and immunomodulatory (CD200, CX3CL1) factors were decreased in the hippocampus of infected mice. In addition, influenza induced architectural changes to hippocampal neurons in the CA1 and dentate gyrus, with the most profound effects on dentate granule cells in the innermost portion of the granule cell layer. Overall, these data provide the first evidence that neuroinflammation and changes in hippocampal structural plasticity may underlie cognitive dysfunction associated with influenza infection. In addition, the heightened inflammatory state concurrent with reduced neurotrophic support could leave the brain vulnerable to subsequent insult following influenza infection. A better understanding of how influenza impacts the brain and behavior may provide insight for preventing inflammation and neuronal damage during peripheral viral infection.

Prefrontal dopaminergic and enkephalinergic synaptic accommodation in HIV-associated neurocognitive disorders and encephalitis

Changes in synapse structure occur in frontal neocortex with HIV encephalitis (HIVE) and may contribute to HIV-associated neurocognitive disorders (HAND). A postmortem survey was conducted to determine if mRNAs involved in synaptic transmission are perturbed in dorsolateral prefrontal cortex (DLPFC) in subjects with HIVE or HAND. Expression of the opioid neurotransmitter preproenkephalin mRNA (PENK) was significantly decreased in a sampling of 446 brain specimens from HIV-1 infected people compared to 67 HIV negative subjects. Decreased DLPFC PENK was most evident in subjects with HIVE and/or increased expression of interferon regulatory factor 1 mRNA (IRF1). Type 2 dopamine receptor mRNA (DRD2L) was decreased significantly, but not in the same set of subjects with PENK dysregulation. DRD2L downregulation occurred primarily in the subjects without HIVE or neurocognitive impairment. Subjects with neurocognitive impairment often failed to significantly downregulate DRD2L and had abnormally high IRF1 expression. Conclusion: Dysregulation of synaptic preproenkephalin and DRD2L in frontal neocortex can occur with and without neurocognitive impairment in HIV-infected people. Downregulation of DRD2L in the prefrontal cortex was associated with more favorable neuropsychological and neuropathological outcomes; the failure to downregulate DRD2L was significantly less favorable. PENK downregulation was related neuropathologically to HIVE, but was not related to neuropsychological outcome independently. Emulating endogenous synaptic plasticity pharmacodynamically could enhance synaptic accommodation and improve neuropsychological and neuropathological outcomes in HIV/AIDS.

Rodent models for HIV-associated neurocognitive disorders

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) reflect the spectrum of neural impairments seen during chronic viral infection. Current research efforts focus on improving antiretroviral and adjunctive therapies, defining disease onset and progression, facilitating drug delivery, and halting neurodegeneration and viral resistance. Because HIV is species-specific, generating disease in small-animal models has proved challenging. After two decades of research, rodent HAND models now include those containing a human immune system. Antiviral responses, neuroinflammation and immunocyte blood-brain barrier (BBB) trafficking follow HIV infection in these rodent models. We review these and other rodent models of HAND and discuss their unmet potential in reflecting human pathobiology and in facilitating disease monitoring and therapeutic discoveries.

Aicardi-Goutieres syndrome: from patients to genes and beyond

Aicardi-Goutières syndrome (AGS) is a hereditary neurodegenerative disorder characterized mainly by early onset progressive encephalopathy, concomitant with an increase in interferon-α levels in the cerebrospinal fluid. Although it was initially mistaken for intrauterine viral infections, AGS has now been genetically attributed to a lack of adequate processing of cellular nucleic acid debris, which culminates in the perpetual trigger of the innate and acquired immune responses. Although the exact mechanisms governing AGS are not fully understood, significant strides have been recently achieved in better characterizing the disorder and the molecular functions of the five known proteins found mutated in AGS. Studies have now uncovered that AGS is tightly linked with the predisposition to other autoimmune disorders such as familial chilblain lupus and systemic lupus erythematosus. Moreover, at least two of the proteins mutated in AGS, namely TREX1 and SAMHD1, also seem to have antagonistic roles in safeguarding humans from human immunodeficiency virus (HIV) infections. We hereby synthesize the current developments into the greater framework of AGS and suggest that a better understanding of AGS might help usher a better treatment not only for some autoimmune disorders but also possibly for patients suffering from HIV infections, too.

Significant effects of antiretroviral therapy on global gene expression in brain tissues of patients with HIV-1-associated neurocognitive disorders

Antiretroviral therapy (ART) has reduced morbidity and mortality in HIV-1 infection; however HIV-1-associated neurocognitive disorders (HAND) persist despite treatment. The reasons for the limited efficacy of ART in the brain are unknown. Here we used functional genomics to determine ART effectiveness in the brain and to identify molecular signatures of HAND under ART. We performed genome-wide microarray analysis using Affymetrix U133 Plus 2.0 Arrays, real-time PCR, and immunohistochemistry in brain tissues from seven treated and eight untreated HAND patients and six uninfected controls. We also determined brain virus burdens by real-time PCR. Treated and untreated HAND brains had distinct gene expression profiles with ART transcriptomes clustering with HIV-1-negative controls. The molecular disease profile of untreated HAND showed dysregulated expression of 1470 genes at p<0.05, with activation of antiviral and immune responses and suppression of synaptic transmission and neurogenesis. The overall brain transcriptome changes in these patients were independent of histological manifestation of HIV-1 encephalitis and brain virus burdens. Depending on treatment compliance, brain transcriptomes from patients on ART had 83% to 93% fewer dysregulated genes and significantly lower dysregulation of biological pathways compared to untreated patients, with particular improvement indicated for nervous system functions. However a core of about 100 genes remained similarly dysregulated in both treated and untreated patient brain tissues. These genes participate in adaptive immune responses, and in interferon, cell cycle, and myelin pathways. Fluctuations of cellular gene expression in the brain correlated in Pearson's formula analysis with plasma but not brain virus burden. Our results define for the first time an aberrant genome-wide brain transcriptome of untreated HAND and they suggest that antiretroviral treatment can be broadly effective in reducing pathophysiological changes in the brain associated with HAND. Aberrantly expressed transcripts common to untreated and treated HAND may contribute to neurocognitive changes defying ART.

[A 38-year old HIV infected male with neurological focality during treatment of hepatitis]

A 38-year old HIV infected male (with adequate immunologic and virologic control) and HCV who, after starting treatment with interferon, experienced loss of strength in the left hemisphere and parenthesis in 4th and 5th fingers of the left hand along with walking instability. Imaging and microbiological tests were performed, brain biopsy finally being necessary for the diagnosis.

Interactions between human immunodeficiency virus (HIV)-1 Vpr expression and innate immunity influence neurovirulence

BACKGROUND

Viral diversity and abundance are defining properties of human immunodeficiency virus (HIV)-1's biology and pathogenicity. Despite the increasing availability of antiretroviral therapy, HIV-associated dementia (HAD) continues to be a devastating consequence of HIV-1 infection of the brain although the underlying disease mechanisms remain uncertain. Herein, molecular diversity within the HIV-1 non-structural gene, Vpr, was examined in RNA sequences derived from brain and blood of HIV/AIDS patients with or without HIV-associated dementia (HAD) together with the ensuing pathobiological effects.

RESULTS

Cloned brain- and blood-derived full length vpr alleles revealed that amino acid residue 77 within the brain-derived alleles distinguished HAD (77Q) from non-demented (ND) HIV/AIDS patients (77R) (p < 0.05) although vpr transcripts were more frequently detected in HAD brains (p < 0.05). Full length HIV-1 clones encoding the 77R-ND residue induced higher IFN-α, MX1 and BST-2 transcript levels in human glia relative to the 77Q-HAD encoding virus (p < 0.05) but both viruses exhibited similar levels of gene expression and replication. Myeloid cells transfected with 77Q-(pVpr77Q-HAD), 77R (pVpr77R-ND) or Vpr null (pVpr(-))-containing vectors showed that the pVpr77R-ND vector induced higher levels of immune gene expression (p < 0.05) and increased neurotoxicity (p < 0.05). Vpr peptides (amino acids 70-96) containing the 77Q-HAD or 77R-ND motifs induced similar levels of cytosolic calcium activation when exposed to human neurons. Human glia exposed to the 77R-ND peptide activated higher transcript levels of IFN-α, MX1, PRKRA and BST-2 relative to 77Q-HAD peptide (p < 0.05). The Vpr 77R-ND peptide was also more neurotoxic in a concentration-dependent manner when exposed to human neurons (p < 0.05). Stereotaxic implantation of full length Vpr, 77Q-HAD or 77R-ND peptides into the basal ganglia of mice revealed that full length Vpr and the 77R-ND peptide caused greater neurobehavioral deficits and neuronal injury compared with 77Q-HAD peptide-implanted animals (p < 0.05).

CONCLUSIONS

These observations underscored the potent neuropathogenic properties of Vpr but also indicated viral diversity modulates innate neuroimmunity and neurodegeneration.

Plasma cytokine concentrations associated with HIV/hepatitis C coinfection are related to attention, executive and psychomotor functioning

Cytokine disturbances have been linked to brain dysfunction among HIV-infected people. Past studies have not simultaneously examined a large set of cytokine measures and their relationships to HIV-associated neurocognitive deficits. We hypothesized that performance on measures of attention and executive and psychomotor functions would be associated with plasma cytokine concentrations in HIV-infected individuals. Plasma samples drawn from 30 HIV-infected and 37 HIV seronegative individuals were analyzed via xMAP multiplexed bead array immunoassay to determine concentrations of 13 cytokines. Performance on Trail Making A/B, Stroop Test, Letter-Number Sequencing, Digit Symbol Coding, Symbol Search, and Grooved Pegboard tests was assessed. Statistical analyses were performed to examine group differences in cytokine concentrations, and associations between cytokine and HIV clinical variables and neurocognitive performance. Significant HIV effects were found on 7 of the 13 cytokines, primarily with respect to interleukins. HIV clinical factors (CD4 and HIV RNA levels, duration of illness, antiretroviral treatment) and hepatitis C status were associated with specific plasma cytokine concentrations. Neurocognitive measures were associated with cytokine concentrations, most consistently among the interleukins and IP-10. Generally, cytokine concentrations were among the strongest predictors of neurocognitive function relative to other clinical factors, which reinforces their potential importance in examining the neuropathological processes of HIV. The findings also point to the potential value of simultaneously examining a panel of biomarkers. The current results suggest that a complex relationship likely exists among cytokines [how?] and that these relationships are mediated not only by HIV infection but also by antiretroviral treatment and other comorbid conditions.

Immune reconstitution of acquired immune deficiency syndrome

Acquired immune deficiency syndrome (AIDS) is a chronic infectious disease, which the patients are infected with human immunodeficiency virus (HIV). HIV damages the human's immune function and causes CD4 cell decline in the number and function. Immune reconstitution is an important treatment to AIDS. Bone marrow transplantation, adoptive immune cell therapy and cytokines infusion can all assist the immune reconstitution; highly active antiretroviral therapy (HAART) can effectively control the virus replication and benefit the immune reconstitution. HAART combined with immunotherapy is an important method of immune reconstitution in AIDS patients. Chinese medicine is playing a more and more important role in immune reconstitution. Immune reconstitution has always been effective in the whole treatment of AIDS.

Links between progressive HIV-1 infection of humanized mice and viral neuropathogenesis

Few rodent models of human immunodeficiency virus type one (HIV-1) infection can reflect the course of viral infection in humans. To this end, we investigated the relationships between progressive HIV-1 infection, immune compromise, and neuroinflammatory responses in NOD/scid-IL-2Rγ(c)(null) mice reconstituted with human hematopoietic CD34(+) stem cells. Human blood-borne macrophages repopulated the meninges and perivascular spaces of chimeric animals. Viral infection in lymphoid tissue led to the accelerated entry of human cells into the brain, marked neuroinflammation, and HIV-1 replication in human mononuclear phagocytes. A meningitis and less commonly an encephalitis followed cM-T807 antibody-mediated CD8(+) cell depletion. We conclude that HIV-1-infected NOD/scid-IL-2Rγ(c)(null) humanized mice can, at least in part, recapitulate lentiviral neuropathobiology. This model of neuroAIDS reflects the virological, immunological, and early disease-associated neuropathological components of human disease.

Systemic challenge with the TLR3 agonist poly I:C induces amplified IFNalpha/beta and IL-1beta responses in the diseased brain and exacerbates chronic neurodegeneration

The role of inflammation in the progression of neurodegenerative disease remains unclear. We have shown that systemic bacterial insults accelerate disease progression in animals and in patients with Alzheimer's disease. Disease exacerbation is associated with exaggerated CNS inflammatory responses to systemic inflammation mediated by microglia that become 'primed' by the underlying neurodegeneration. The impact of systemic viral insults on existing neurodegenerative disease has not been investigated. Polyinosinic:polycytidylic acid (poly I:C) is a toll-like receptor-3 (TLR3) agonist and induces type I interferons, thus mimicking inflammatory responses to systemic viral infection. In the current study we hypothesized that systemic challenge with poly I:C, during chronic neurodegenerative disease, would amplify CNS inflammation and exacerbate disease. Using the ME7 model of prion disease and systemic challenge with poly I:C (12 mg/kg i.p.) we have shown an amplified expression of IFN-alpha and beta and of the pro-inflammatory genes IL-1beta and IL-6. Similarly amplified expression of specific IFN-dependent genes confirmed that type I IFNs were secreted and active in the brain and this appeared to have anti-inflammatory consequences. However, prion-diseased animals were susceptible to heightened acute sickness behaviour and acute neurological impairments in response to poly I:C and this treatment also accelerated disease progression in diseased animals without effect in normal animals. Increased apoptosis coupled with double-stranded RNA-dependent protein kinase (PKR) and Fas transcription suggested activation of interferon-dependent, pro-apoptotic pathways in the brain of ME7+poly I:C animals. That systemic poly I:C accelerates neurodegeneration has implications for the control of systemic viral infection during chronic neurodegeneration and indicates that type I interferon responses in the brain merit further study.

Brain dysfunction in the era of combination antiretroviral therapy: implications for the treatment of the aging population of HIV-infected individuals

Improvements in the treatment of HIV infection and in the advancement of combination antiretroviral therapy (cART) have led to an increase in the number of individuals with HIV who are surviving to an older age. Preventing the development of neurocognitive abnormalities has become an increasingly important issue in this aging patient population, which is already at risk for cognitive impairment as a result of the neuropathological effects of HIV. cART has been critical in reducing the overall severity of HIV-associated neurocognitive disorders (HAND), but numerous challenges remain, as the prevalence of HAND continues to be high. There are several key areas in which treatment could be improved to reduce the incidence and severity of HAND. The use of well-tolerated cART medications that are able to penetrate the blood-brain barrier hold particular promise, as these agents may enable increased viral suppression in the parenchyma and may reduce neurocognitive dysfunction. In addition, the improved treatment of comorbid medical conditions that are common in patient populations with HIV (eg, HCV, liver failure and metabolic syndrome) is critical, as several of these conditions are known to have a significant effect on neural functions. Various research approaches indicate that the development of agents that control free radicals, neurotoxicity, proinflammatory processes and apoptosis may also have substantial potential in this field.

HIV-1 viral protein R causes peripheral nervous system injury associated with in vivo neuropathic pain

Painful peripheral neuropathy has become the principal neurological disorder in HIV/AIDS patients. Herein, we investigated the effects of a cytotoxic HIV-1 accessory protein, viral protein R (Vpr), on the peripheral nervous system (PNS). Host and viral gene expression was investigated in peripheral nerves from HIV-infected individuals and in HIV-infected human dorsal root ganglion (DRG) cultures by RT-PCR and immunocytochemistry. Cytosolic calcium ([Ca(2+)]) fluxes and neuronal membrane responses were analyzed in cultured DRGs. Neurobehavioral responses and cytokine levels were assessed in a transgenic mouse model in which the vpr transgene was expressed in an immunodeficient background (vpr/RAG1(-/-)). Vpr transcripts and proteins were detected in peripheral nerves and DRGs from HIV-infected patients. Exposure of rat or human cultured DRG neurons to Vpr rapidly increased [Ca(2+)] and action potential frequency while increasing input resistance. HIV infection of human DRG cultures caused neurite retraction (P<0.05), accompanied by induction of interferon-α (IFN-α) transcripts (P<0.05). vpr/RAG1(-/-) mice expressed Vpr together with increased IFN-α (P<0.05) in the PNS and also exhibited mechanical allodynia, unlike their vpr/RAG1(-/-) littermates (P<0.05). Herein, Vpr caused DRG neuronal damage, likely through cytosolic calcium activation and cytokine perturbation, highlighting Vpr's contribution to HIV-associated peripheral neuropathy and ensuing neuropathic pain.

Molecular mechanisms of neuroinvasion by monocytes-macrophages in HIV-1 infection

HIV associated neurocognitive disorders and their histopathological correlates largely depend on the continuous seeding of the central nervous system with immune activated leukocytes, mainly monocytes/macrophages from the periphery. The blood-brain-barrier plays a critical role in this never stopping neuroinvasion, although it appears unaltered until the late stage of HIV encephalitis. HIV flux that moves toward the brain thus relies on hijacking and exacerbating the physiological mechanisms that govern blood brain barrier crossing rather than barrier disruption. This review will summarize the recent data describing neuroinvasion by HIV with a focus on the molecular mechanisms involved.

Effect of type-I interferon on retroviruses

Type-I interferons (IFN-I) play an important role in the innate immune response to several retroviruses. They seem to be effective in controlling the in vivo infection, though many of the clinical signs of retroviral infection may be due to their continual presence which over-stimulates the immune system and activates apoptosis. IFN-I not only affect the immune system, but also operate directly on virus replication. Most data suggest that the in vitro treatment with IFN-I of retrovirus infected cells inhibits the final stages of virogenesis, avoiding the correct assembly of viral particles and their budding, even though the mechanism is not well understood. However, in some retroviruses IFN-I may also act at a previous stage as some retroviral LTRs posses sequences homologous to the IFN-stimulated response element (ISRE). When stimulated, ISREs control viral transcription. HIV-1 displays several mechanisms for evading IFN-I, such as through Tat and Nef. Besides IFN-α and IFN-β, some other type I IFN, such as IFN-τ and IFN-ω, have potent antiviral activity and are promising treatment drugs.