CCR5 deficiency is a risk factor for early clinical manifestations of West Nile virus infection but not for viral transmission

Flaviviruses are neurotropic, but how do they invade the CNS?

Flaviruses (FV) are RNA viruses carried by mosquitoes. Neurological signs including acute encephalitis, meningitis and acute flaccid paralysis develop in a small percentage of infected individuals; long term sequlae are, Parkinsonism, dystonias and cognitive changes. FV neuroinfection is neurotropic involving subcortical nuclei (substantia nigra and thalamus) anterior horn neurons and neocortex. Glycosylation of the FV E envelope protein is one determinant of neuroinvasion, increasing both axonal and trans-epithelial transportation. Neutralizing antibodies against the E and NS proteins prevents FV uptake into several cell types, including axons. CD8+ T cells are vital for clearance of WNF infected cells from the CNS, whereas TLR-3 and TLR-7 mediated anti-virus response through increased serum inflammatory cytokines to disrupt the BBB providing infected leucocytes and free virus access to the CNS (so called Trojan horse) Cellular virus attachment factors, promoting FV cell entry are widely distributed and include DC-SIGN (that detects complex carbohydrate molecules); Glycosamino glycans (GAG), Heparan sulphate(HSPG) Semaphorin 7A, Low Density Lipid receptors (LDLR); these are not FV specific virus entry receptors. The FV also crosses epithelial and endothelial barriers by disrupting Tight Junction complexes to increase BBB permeability. This review describes the multiple pathways responsible for the neuroinvasive properties of the Flaviviruses.

Genetic variants associated with susceptibility of Ashkenazi Jews to West Nile virus infection

The epidemiology of West Nile virus (WNV) in Israel is different from other neighbouring countries in the Middle East where disease burden has been minimal. We analysed a cohort of Ashkenazi Jewish patients with symptomatic WNV infection (n = 39), and WNV-negative controls (n = 61), for nine genetic variants that has been suggested to be associated with susceptibility to WNV. Two single nucleotide polymorphisms were significantly more frequent in WNV-infected than non-infected individuals, rs7280422 (MX1) [odds ratio (OR) 4·05, 95% confidence interval (CI) 2·04-8·03, P < 0·001] and rs3213545 (OASL) (OR 1·85, 95% CI 1·03-3·3, P = 0·03). Genetic polymorphism may play a significant role in susceptibility to WNV infection in Ashkenazi Jews.

Systems analysis of West Nile virus infection

•

Emerging/re-emerging mosquito-borne viruses are a significant public health threat.

•

There is a need define the virus–host interactions that govern immunity to infection.

•

Systems biology provides a comprehensive analysis of the host response.

•

High-throughput based assays provide rapid identification of host targets.

Emerging and re-emerging mosquito-borne viruses continue to pose a significant threat to human health throughout the world. Over the past decade, West Nile virus (WNV), Dengue virus (DENV), and Chikungunya virus (CHIKV), have caused annual epidemics of virus-induced encephalitis, hemorrhagic fever\shock syndromes, and arthritis, respectively. Currently, no specific antiviral therapies or vaccines exist for use in humans to combat or prevent these viral infections. Thus, there is a pressing need to define the virus–host interactions that govern immunity and infection outcome. Recent technological breakthroughs in ‘omics’ resources and high-throughput based assays are beginning to accelerate antiviral drug discovery and improve on current strategies for vaccine design. In this review, we highlight studies with WNV and discuss how traditional and systems biological approaches are being used to rapidly identify novel host targets for therapeutic intervention and develop a deeper conceptual understanding of the host response to virus infection.

Gene polymorphisms in CCR5, CCR2, SDF1 and RANTES among Chinese Han population with HIV-1 infection

Chemokines and chemokine receptors are crucial for immune response in HIV-1 infection. Although many studies have been done to investigate the relationship between chemokines and chemokine receptor gene polymorphisms and host's susceptibility to HIV-1 infection, the conclusions are under debate. In the present study, a cohort of 287 HIV-1 seropositive patients, 388 ethnically age-matched healthy controls and 49 intravenous drug users (IDUs) HIV-1 exposed seronegative individuals (HESN) from Chinese Han population were enrolled in order to determine the influence of host genetic factors on HIV-1 infection. Seven polymorphisms on four known chemokines/chemokine receptor genes (CCR5Δ32, CCR5 m303, CCR5 59029A/G, CCR2 64I, RANTES -403A/G, RANTES -28C/G and SDF1 3'-A) were screened. CCR5Δ32 and CCR5 m303 were absent or infrequent in Chinese Han population, which may not be hosts' genetic protective factors for HIV-1 infection. Our results showed the CCR5 59029A/G, CCR2 64I and SDF1 3'-A were not associated with host's resistance to HIV-1 infection. The frequency of RANTES -403A allele was significantly lower in HIV-1 patients than in healthy blood donors (p=0.0005) and HESN group (p=0.035), which implied the association between A allele and reduced HIV-1 infection risk. Different genetic models were assessed to investigate this association (AA vs. GG+AG, OR=0.38 95% CI, 0.22-0.65 p=0.0004; A vs. G, OR=0.66 95% CI, 0.52-0.84 p=0.0006), which supported this association, either. The genotype and allele distribution of RANTES -28 between HIV-1 patients and healthy controls (genotype profile: p=0.072; allele profile: p=0.027) or HIV-1 seronegative group (genotype profile: p=0.036; allele profile: p=0.383) were both at the marginal level of significance, which were not observed after Bonferroni correction. All these results suggest the RANTES -403A may be associated with reduced susceptibility to HIV-1 infection, while the RANTES -28 locus not. By lack of the patients' clinical information, whether these polymorphisms affect AIDS disease progression and their role in different HIV-1 infection routes could not performed in present study and needs to be assessed in ongoing studies.

Primary acute dengue and the deletion in chemokine receptor 5 (CCR5Δ32)

Dengue virus is a significant arboviral pathogen that is continuing to spread due to human travel and invasion of the mosquito vectors into new regions. Chemokine receptor 5 (CCR5) has a truncated 32 base pair deletion form (CCR5Δ32), which has been associated with resistance to HIV but increased severity in some flaviviral diseases. If CCR5Δ32 is associated with dengue, European carriers of this mutation may be at increased risk. In a Western Australian population with the same frequency of CCR5Δ32 (0.08) as that found in southern Europe there was no significant difference in CCR5Δ32 allele frequency between returned travellers with and without dengue (p = 0.82, OR = 0.86, 95% CI = 0.35-2.1).

Neurological and psychiatric adverse effects of antiretroviral drugs

Antiretroviral drugs are associated with a variety of adverse effects on the central and peripheral nervous systems. The frequency and severity of neuropsychiatric adverse events is highly variable, with differences between the antiretroviral classes and amongst the individual drugs in each class. In the developing world, where the nucleoside reverse transcriptase inhibitor (NRTI) stavudine remains a commonly prescribed antiretroviral, peripheral neuropathy is an important complication of treatment. Importantly, this clinical entity is often difficult to distinguish from human immunodeficiency virus (HIV)-induced peripheral neuropathy. Several clinical trials have addressed the efficacy of various agents in the treatment of NRTI-induced neurotoxicity. NRTI-induced neurotoxicity is caused by inhibition of mitochondrial DNA polymerase. This mechanism is also responsible for the mitochondrial myopathy and lactic acidosis that occur with zidovudine. NRTIs, particularly zidovudine and abacavir, may also cause central nervous system (CNS) manifestations, including mania and psychosis. The non-nucleoside reverse transcriptase inhibitor (NNRTI) efavirenz is perhaps the antiretroviral most commonly associated with CNS toxicity, causing insomnia, irritability and vivid dreams. Recent studies have suggested that the risk of developing these adverse effects is increased in patients with various cytochrome P450 2B6 alleles. Protease inhibitors cause perioral paraesthesias and may indirectly increase the relative risk of stroke by promoting atherogenesis. HIV integrase inhibitors, C-C chemokine receptor type 5 (CCR5) inhibitors and fusion inhibitors rarely cause neuropsychiatric manifestations.

Novel approaches and challenges to treatment of central nervous system viral infections

Existing and emerging viral central nervous system (CNS) infections are major sources of human morbidity and mortality. Treatments of proven efficacy are currently limited predominantly to herpesviruses and human immunodeficiency virus (HIV). Development of new therapies has been hampered by the lack of appropriate animal model systems for some important viruses and by the difficulty in conducting human clinical trials for diseases that may be rare, or in the case of arboviral infections, often have variable seasonal and geographic incidence. Nonetheless, many novel approaches to antiviral therapy are available, including candidate thiazolide and pyrazinecarboxamide derivatives with potential broad‐spectrum antiviral efficacy. New herpesvirus drugs include viral helicase‐primase and terminase inhibitors. The use of antisense oligonucleotides and other strategies to interfere with viral RNA translation has shown efficacy in experimental models of CNS viral disease. Identifying specific molecular targets within viral replication cycles has led to many existing antiviral agents and will undoubtedly continue to be the basis of future drug design. A promising new area of research involves therapies based on enhanced understanding of host antiviral immune responses. Toll‐like receptor agonists and drugs that inhibit specific cytokines as well as interferon preparations have all shown potential therapeutic efficacy. Passive transfer of virus‐specific cytotoxic T lymphocytes has been used in humans and may provide an effective therapy for some herpesvirus infections and potentially for progressive multifocal leukoencephalopathy. Humanized monoclonal antibodies directed against specific viral proteins have been developed and in several cases evaluated in humans in settings including West Nile virus and HIV infection and in pre‐exposure prophylaxis for rabies. Ann Neurol 2013;74:412–422

Differential virulence and pathogenesis of West Nile viruses

West Nile virus (WNV) is a neurotropic flavivirus that cycles between mosquitoes and birds but that can also infect humans, horses, and other vertebrate animals. In most humans, WNV infection remains subclinical. However, 20%-40% of those infected may develop WNV disease, with symptoms ranging from fever to meningoencephalitis. A large variety of WNV strains have been described worldwide. Based on their genetic differences, they have been classified into eight lineages; the pathogenic strains belong to lineages 1 and 2. Ten years ago, Beasley et al. (2002) found that dramatic differences exist in the virulence and neuroinvasion properties of lineage 1 and lineage 2 WNV strains. Further insights on how WNV interacts with its hosts have recently been gained; the virus acts either at the periphery or on the central nervous system (CNS), and these observed differences could help explain the differential virulence and neurovirulence of WNV strains. This review aims to summarize the current state of knowledge on factors that trigger WNV dissemination and CNS invasion as well as on the inflammatory response and CNS damage induced by WNV. Moreover, we will discuss how WNV strains differentially interact with the innate immune system and CNS cells, thus influencing WNV pathogenesis.

Role of CC chemokine receptor 1 and two of its ligands in human dengue infection. Three approaches under the Cuban situation

Any of the four dengue serotypes can cause a severe disease, partly due to systemic inflammation orchestrated by mediators like cytokines and chemokines. We addressed the role of CCR1 and its ligands CCL3/MIP-1α and CCL5/RANTES in dengue infection using three different approaches: an ex vivo model exploring memory immune response in subjects with a well characterized dengue immune background, an in vivo study in patients with primary or secondary dengue infection, and an approach in fatal dengue. CCR1 and CCL3/MIP-1α gene expression showed differences after homotypic and heterotypic challenge according to dengue immune background of subjects, in correspondence with previous observations in Cuban dengue outbreaks. CCL5/RANTES gene expression was higher after homotypic challenge. CCR1 and CCL3/MIP-1α gene expression was higher in patients with secondary infection during critical days of the dengue disease, while the increase in RANTES expression started earlier than the observed for CCR1 and CCL3/MIP-1α. CCR1 and CCL3/MIP-1α gene expression was as high in brain as in spleen tissue from necropsy. Our results confirm the strong influence of previous immunity in subsequent dengue infections, and confer a possible pathogenic role to CCR1 and CCL3/MIP-1α in dengue disease and a possible protective role for CCL5/RANTES, probably through CCR5 interaction.

Host genomics in infectious diseases

Understanding mechanisms by which genetic variants predispose to complications of infectious diseases can lead to important benefits including the development of biomarkers to prioritize vaccination or prophylactic therapy. Family studies, candidate genes in animal models, and the absence of well-defined risks where the complications are rare all can point to genetic predisposition. The most common approach to assessing genetic risk is to conduct an association study, which is a case control study using either a candidate gene approach or a genome wide approach. Although candidate gene variants may focus on potentially causal variants, because other variants across the genome are not tested these studies frequently cannot be replicated. Genome wide association studies need a sizable sample and usually do not identify causal variants but variants which may be in linkage disequilibrium to the actual causal variant. There are many pitfalls that can lead to bias in such studies, including misclassification of cases and controls, use of improper phenotypes, and genotyping errors. These studies have been limited to common genes and rare variants may not be detected. As the use of next generation sequencing becomes more common, it can be anticipated that more variants will be confirmed. The purpose of this review article is to address the issue of genomics in infectious diseases with an emphasis on the host. Although there are a plentitude of studies that focus on the molecular characteristics of pathogens, there are far fewer studies that address the role of human genetics in the predisposition to infection or more commonly its complications. This paper will review both the approaches used to study host genetics in humans and the pitfalls associated with some of these methods. The focus will be on human disease and therefore discussion of the use of animal models will be limited to those where there are genes that have been replicated in humans. The paper will focus on common genetic variants that account for complex traits such as infectious diseases using examples from flaviviruses.

CCR5 deficiency and severe polio infection in the 1984 outbreak in Finland

CCR5, a leukocyte chemoattractant receptor for chemokines CCL3, CCL4, and CCL5, promotes innate and adaptive immune responses by mediating leukocyte trafficking within lymph nodes and to peripheral tissues and is also known as a co-receptor for HIV cell entry. Homozygous inheritance of a complete loss-of-function mutation in CCR5 (CCR5Δ32/CCR5Δ32) is associated with symptomatic neuroinflammatory disease in humans with West Nile and Tickborne Encephalitis flavivirus infections. This study sought to establish whether CCR5 deficiency could also be a determinant of clinical outcome after infection by poliovirus which results in central nervous system damage in only a small proportion of cases. We analyzed serum samples from seven patients and 79 controls, collected during the 1984-1985 polio outbreak in Finland, where CCR5Δ32 is relatively common in the general population. The results excluded CCR5 deficiency as the sole determinant of severe neurologic disease after poliovirus infection in this population.

The neuroimmune response to West Nile virus

The recent introduction of highly pathogenic strains of West Nile virus (WNV) into naïve populations in Europe, Israel, and the USA has resulted in a marked increase in both the number of reported cases and the severity of disease compared to previous outbreaks. The impact of the increased virulence of recently emerged strains of WNV is exacerbated by the fact that antiviral therapies and vaccines are not currently available for use in humans. A greater understanding of the viral and host factors involved in WNV-mediated neuropathology is necessary to facilitate the development of novel therapeutic approaches. This review summarizes the current state of knowledge of the role of the cell-intrinsic innate immune responses as well as the cell-mediated innate and adaptive immune responses in promoting the detection and clearance of WNV from the CNS.

CCR5delta32 in systemic lupus erythematosus: implications for disease susceptibility and outcome in a Brazilian population

The aim of this study was to analyze the allelic and genotypic frequencies of the CCR5delta32 polymorphism in systemic lupus erythematosus (SLE) patients and to investigate a possible association of this allele with SLE susceptibility and clinical outcome. A total of 367 SLE patients and 435 healthy controls were genotyped for the CCR5delta32 polymorphism. We observed that, in European-derived individuals, the frequency of the CCR5delta32 allele was smaller in patients than in controls (2.7% vs. 7.5%, OR 0.34, 95% CI 0.17-0.65, p Bonf=0.002), suggesting that this allele could be considered a protective factor for the disease. Regarding clinical manifestations, we observed that CCR5delta32 female African-derived carrier patients presented a higher predisposition to class IV nephritis when compared with absent nephritis/other class group (13.8% vs. 3.8%, OR 37.1, 95% CI 2.8-1854.7, p Bonf=0.030). A multivariate analysis including all female patients and controlling for the presence or absence of anti-dsDNA antibodies, ethnicity and age at diagnosis showed an increased relative risk of 3.9 times for patients carrying the CCR5delta32 allele to develop class IV nephritis as compared with noncarriers. Our data suggest that the CCR5delta32 allele is a protective factor for the disease in European-derived patients and a susceptibility factor to class IV nephritis in African-derived female patients.

Association between regulated upon activation, normal T cells expressed and secreted (RANTES) -28C/G polymorphism and susceptibility to HIV-1 infection: a meta-analysis

BACKGROUND

Many studies have investigated the distributions of RANTES genotypes between HIV-1 infected patients and uninfected individuals. However, no definite results have been put forward about whether the RANTES -28C/G polymorphism can affect HIV-1 susceptibility.

METHODS

We performed a meta-analysis of 12 studies including 7473 subjects for whom the RANTES -28C/G polymorphism was genotyped. Odds ratios (ORs) with 95% confidence intervals (CIs) were employed to assess the association of the polymorphism with HIV-1 susceptibility. By dividing the controls into healthy controls and HIV-1 exposed but seronegative (HESN) controls, we explored the both allelic and dominant genetic models.

RESULTS

By using the healthy controls, we found a marginally significant association between the -28C/G polymorphism and susceptibility to HIV-1 infection in the allelic model (OR = 0.82, 95%CI = 0.70-0.97). But sensitivity analysis suggested that the association was driven by one study. We further performed stratified analysis according to ethnicity. The -28G allele decreased susceptibility to HIV-1 infection in the allelic model among Asians (OR = 0.79, 95%CI = 0.66-0.94). By using the HESN controls, no association between the polymorphism -28C/G and the susceptibility to HIV-1 infection was revealed in either the allelic model (OR = 0.84, 95%CI = 0.60-1.17) or the dominant model (OR = 0.77, 95%CI = 0.54-1.10).

CONCLUSIONS

Our findings suggested that the RANTES -28G allele might play a role in resistance to HIV-1 infection among Asians. Additional well-designed studies were required for the validation of this association.

Staphylococcus aureus and CCR5: unveiling commonalities in host-pathogen interactions and potential treatment strategies

Microbes that have acquired the ability to colonize and/or cause disease in humans must be able to both recognize and respond to host defenses to ensure their survival. For commensal microbes, adaptive strategies generally promote a balance between host immune defenses and bacterial maintenance, allowing asymptomatic colonization. Pathogenic microbes, on the other hand, tilt the balance in favor of the microorganism, leading to symptomatic illness and disease. Some microorganisms that are known to be asymptomatic colonizers of humans can cause serious disease upon gaining access to foreign sites and usurping immunological attack. The Gram-positive bacterium Staphylococcus aureus is one such microorganism.

This article will address recent advances in our understanding of S. aureus immune evasion with an emphasis on immune cell targeting. The prospects of this targeting in terms of understanding the evolution of S. aureus as a pathogen as well as its implications for future anti-S. aureus therapeutics, will be discussed.

Genetic susceptibility to West Nile virus and dengue

This article focuses on the host genetic predisposition to 2 viruses, West Nile virus and dengue virus, which belong to the genus Flavivirus. Although by definition these viruses have shared characteristics (e.g. similar size, single stranded, RNA viruses, both transmitted by the bite from an infected mosquito), they differ greatly in epidemiology and clinical manifestations. The text below not only summarizes the genetic factors that predispose to complications of these 2 important flaviviruses, but also illustrates the challenges in determining the genomic basis for complications to these viruses.

The role of chemokines in the pathogenesis of neurotropic flaviviruses

Neurotropic flaviviruses are important emerging and reemerging arthropod-borne pathogens that cause significant morbidity and mortality in humans and other vertebrates worldwide. Upon entry and infection of the CNS, these viruses can induce a rapid inflammatory response characterized by the infiltration of leukocytes into the brain parenchyma. Chemokines and their receptors are involved in coordinating complex leukocyte trafficking patterns that regulate viral pathogenesis in vivo. In this review, we will summarize the current literature on the role of chemokines in regulating the pathogenesis of West Nile, Japanese encephalitis, and tick-borne encephalitis virus infections in mouse models and humans. Understanding how viral infections trigger chemokines, the key cellular events that occur during the infection process, as well as the immunopathogenic role of these cells, are critical areas of research that may ultimately guide a much needed effort toward developing specific immunomodulators and/or antiviral therapeutics.

West Nile Virus: biology, transmission, and human infection

West Nile Virus was introduced into the Western Hemisphere during the late summer of 1999 and has been causing significant and sometimes severe human diseases since that time. This article briefly touches upon the biology of the virus and provides a comprehensive review regarding recent discoveries about virus transmission, virus acquisition, and human infection and disease.

Molecular pathways: hepatitis C virus, CXCL10, and the inflammatory road to liver cancer

An estimated 170 million people worldwide are chronically infected with the hepatitis C virus (HCV), which is characterized histologically by a persistent immune and inflammatory response that fails to clear HCV from hepatocytes. This response is recruited to the liver, in part, by the chemokine CXCL10, the serum and intrahepatic levels of which have been inversely linked to the outcome of interferon-based therapies for hepatitis C. Bystander tissue damage from this ineffective response is thought to lead to increased hepatocyte turnover and the development of fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). However, CXCL10 is traditionally viewed as an orchestrator of the angiostatic and antitumor immune response. In this review, we will explore this duality and the pathways by which CXCL10 is produced by hepatocytes during HCV infection, its effects on resident and infiltrating immune cells, and how deregulation of these cell populations within the liver may lead to chronic liver inflammation. We will also discuss potential host-directed therapies to slow or reverse HCV-induced inflammation that leads to fibrosis, cirrhosis, and HCCs.

CD22 is required for protection against West Nile virus Infection

West Nile virus (WNV) is a RNA virus of the family Flaviviridae and the leading cause of mosquito-borne encephalitis in the United States. Humoral immunity is essential for protection against WNV infection; however, the requirements for initiating effective antibody responses against WNV infection are still unclear. CD22 (Siglec-2) is expressed on B cells and regulates B cell receptor signaling, cell survival, proliferation, and antibody production. In this study, we investigated how CD22 contributes to protection against WNV infection and found that CD22 knockout (Cd22(-/-)) mice were highly susceptible to WNV infection and had increased viral loads in the serum and central nervous system (CNS) compared to wild-type (WT) mice. This was not due to a defect in humoral immunity, as Cd22(-/-) mice had normal WNV-specific antibody responses. However, Cd22(-/-) mice had decreased WNV-specific CD8(+) T cell responses compared to those of WT mice. These defects were not simply due to reduced cytotoxic activity or increased cell death but, rather, were associated with decreased lymphocyte migration into the draining lymph nodes (dLNs) of infected Cd22(-/-) mice. Cd22(-/-) mice had reduced production of the chemokine CCL3 in the dLNs after infection, suggesting that CD22 affects chemotaxis via controlling chemokine production. CD22 was not restricted to B cells but was also expressed on a subset of splenic DCIR2(+) dendritic cells that rapidly expand early after WNV infection. Thus, CD22 plays an essential role in controlling WNV infection by governing cell migration and CD8(+) T cell responses.

CCR5 antagonism impacts vaccination response and immune profile in HIV-1 infection

Maraviroc (MVC) is the first licensed antiretroviral therapeutic agent to target a host cell surface molecule, and successful HIV-1 entry blockade by this C-C chemokine receptor type 5 (CCR5)-antagonist potentiates immunomodulation. We hypothesized that MVC intensification impacts immunization responses, T-cell phenotype, function and delayed type hypersensitivity (DTH) in HIV-1(+) subjects. A 24-wk, double-blinded, placebo-controlled study of the addition of MVC to suppressive antiretroviral therapy in HIV-1(+) persons was performed. Subjects received DTH tests, intramuscular tetanus, meningococcal and oral cholera immunizations. Antibody titers, T-cell function and phenotype were assessed. Of 157 patients referred, 47 were randomized 1:1; MVC:placebo. MVC enhanced meningococcal neo-immunization, blunted cholera response and expedited lymphoproliferation to tetanus boost, without affecting recall humoral response. Anti-HIV-1 group-specific antigen (Gag) and tetanus toxoid (TTox) function improved significantly, HIV-1-associated CD8 T-cell skewing normalized, and the percentage of late-stage and major histocompatibility complex (MHC) class II expressing CD4 T-cells increased. Activated CD4(+) CD38(+) human leukocyte antigen (HLA)-DR(+) T-cells declined, and costimulation shifted to coinhibition. DTH was unchanged. Maraviroc intensification, through antagonism of the cell surface molecule CCR5, favorably influences immune profiles of HIV-1(+) patients, supporting its immunomodulatory use in HIV-1 infection and potentially in other immunologically relevant settings.

The chemokine receptor CCR5, a therapeutic target for HIV/AIDS antagonists, is critical for recovery in a mouse model of Japanese encephalitis

Japanese encephalitis is a severe central nervous system (CNS) inflammatory disease caused by the mosquito-borne flavivirus, Japanese encephalitis virus (JEV). In the current study we have investigated the immune responses against JEV in mice lacking expression of the chemokine receptor CCR5, which functions in activation and chemotaxis of leukocytes during infection. We show that CCR5 serves as a host antiviral factor against Japanese encephalitis, with CCR5 deficiency markedly increasing mortality, and viral burden in the CNS. Humoral immune responses, which are essential in recovery from JEV infection, were of similar magnitude in CCR5 sufficient and deficient mice. However, absence of CCR5 resulted in a multifaceted deficiency of cellular immune responses characterized by reduced natural killer and CD8⁺ T cell activity, low splenic cellularity, and impaired trafficking of leukocytes to the brain. Interestingly, adoptive transfer of immune spleen cells, depleted of B lymphocytes, increased resistance of CCR5-deficient recipient mice against JEV regardless of whether the cells were obtained from CCR5-deficient or wild-type donor mice, and only when transferred at one but not at three days post-challenge. This result is consistent with a mechanism by which CCR5 expression enhances lymphocyte activation and thereby promotes host survival in Japanese encephalitis.

Controlling the HIV/AIDS epidemic: current status and global challenges

This review provides an overview of the current status of the global HIV pandemic and strategies to bring it under control. It updates numerous preventive approaches including behavioral interventions, male circumcision (MC), pre- and post-exposure prophylaxis (PREP and PEP), vaccines, and microbicides. The manuscript summarizes current anti-retroviral treatment options, their impact in the western world, and difficulties faced by emerging and resource-limited nations in providing and maintaining appropriate treatment regimens. Current clinical and pre-clinical approaches toward a cure for HIV are described, including new drug compounds that target viral reservoirs and gene therapy approaches aimed at altering susceptibility to HIV infection. Recent progress in vaccine development is summarized, including novel approaches and new discoveries.

CD8+ T cells use TRAIL to restrict West Nile virus pathogenesis by controlling infection in neurons

Previous studies of mice have demonstrated that an orchestrated sequence of innate and adaptive immune responses is required to control West Nile virus (WNV) infection in peripheral and central nervous system (CNS) tissues. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL; also known as CD253) has been reported to inhibit infection with dengue virus, a closely related flavivirus, in cell culture. To determine the physiological function of TRAIL in the context of flavivirus infection, we compared the pathogenesis of WNV in wild-type and TRAIL(-/-) mice. Mice lacking TRAIL showed increased vulnerability and death after subcutaneous WNV infection. Although no difference in viral burden was detected in peripheral tissues, greater viral infection was detected in the brain and spinal cord at late times after infection, and this was associated with delayed viral clearance in the few surviving TRAIL(-/-) mice. While priming of adaptive B and T cell responses and trafficking of immune and antigen-specific cells to the brain were undistinguishable from those in normal mice, in TRAIL(-/-) mice, CD8(+) T cells showed qualitative defects in the ability to clear WNV infection. Adoptive transfer of WNV-primed wild-type but not TRAIL(-/-) CD8(+) T cells to recipient CD8(-/-) mice efficiently limited infection in the brain and spinal cord, and analogous results were obtained when wild-type or TRAIL(-/-) CD8(+) T cells were added to WNV-infected primary cortical neuron cultures ex vivo. Collectively, our results suggest that TRAIL produced by CD8(+) T cells contributes to disease resolution by helping to clear WNV infection from neurons in the central nervous system.

Targeted DNA mutagenesis for the cure of chronic viral infections

Human immunodeficiency virus type 1 (HIV-1), hepatitis B virus (HBV), and herpes simplex virus (HSV) have been incurable to date because effective antiviral therapies target only replicating viruses and do not eradicate latently integrated or nonreplicating episomal viral genomes. Endonucleases that can target and cleave critical regions within latent viral genomes are currently in development. These enzymes are being engineered with high specificity such that off-target binding of cellular DNA will be absent or minimal. Imprecise nonhomologous-end-joining (NHEJ) DNA repair following repeated cleavage at the same critical site may permanently disrupt translation of essential viral proteins. We discuss the benefits and drawbacks of three types of DNA cleavage enzymes (zinc finger endonucleases, transcription activator-like [TAL] effector nucleases [TALENs], and homing endonucleases [also called meganucleases]), the development of delivery vectors for these enzymes, and potential obstacles for successful treatment of chronic viral infections. We then review issues regarding persistence of HIV-1, HBV, and HSV that are relevant to eradication with genome-altering approaches.

The contribution of rodent models to the pathological assessment of flaviviral infections of the central nervous system

Members of the genus Flavivirus are responsible for a spectrum of important neurological syndromes in humans and animals. Rodent models have been used extensively to model flavivirus neurological disease, to discover host-pathogen interactions that influence disease outcome, and as surrogates to determine the efficacy and safety of vaccines and therapeutics. In this review, we discuss the current understanding of flavivirus neuroinvasive disease and outline the host, viral and experimental factors that influence the outcome and reliability of virus infection of small-animal models.

Genetic variants and susceptibility to neurological complications following West Nile virus infection

To determine genetic factors predisposing to neurological complications following West Nile virus infection, we analyzed a cohort of 560 neuroinvasive case patients and 950 control patients for 13 371 mostly nonsynonymous single-nucleotide polymorphisms (SNPs). The top 3 SNPs on the basis of statistical significance were also in genes of biological plausibility: rs2066786 in RFC1 (replication factor C1) (P = 1.88 × 10⁻⁵; odds ratio [OR], 0.68 [95% confidence interval {CI}, .56–.81]); rs2298771 in SCN1A (sodium channel, neuronal type I α subunit) (P = 5.87 × 10⁻⁵; OR, 1.47 [95% CI, 1.21–1.77]); and rs25651 in ANPEP (ananyl aminopeptidase) (P = 1.44 × 10⁻⁴; OR, 0.69 [95% CI, .56–.83]). Additional genotyping of these SNPs in a separate sample of 264 case patients and 296 control patients resulted in a lack of significance in the replication cohort; joint significance was as follows: rs2066786, P = .0022; rs2298771, P = .005; rs25651, P = .042. Using mostly nonsynonymous variants, we therefore did not identify genetic variants associated with neuroinvasive disease.

Innate immune control of West Nile virus infection

West Nile virus (WNV), from the Flaviviridae family, is a re-emerging zoonotic pathogen of medical importance. In humans, WNV infection may cause life-threatening meningoencephalitis or long-term neurologic sequelae. WNV is transmitted by Culex spp. mosquitoes and both the arthropod vector and the mammalian host are equipped with antiviral innate immune mechanisms sharing a common phylogeny. As far as the current evidence is able to demonstrate, mosquitoes primarily rely on RNA interference, Toll, Imd and JAK-STAT signalling pathways for limiting viral infection, while mammals are provided with these and other more complex antiviral mechanisms involving antiviral effectors, inflammatory mediators, and cellular responses triggered by highly specialized pathogen detection mechanisms that often resemble their invertebrate ancestry. This mini-review summarizes our current understanding of how the innate immune systems of the vector and the mammalian host react to WNV infection and shape its pathogenesis.

Host genetic risk factors for West Nile virus infection and disease progression

West Nile virus (WNV), a category B pathogen endemic in parts of Africa, Asia and Europe, emerged in North America in 1999, and spread rapidly across the continental U.S. Outcomes of infection with WNV range from asymptomatic to severe neuroinvasive disease manifested as encephalitis, paralysis, and/or death. Neuroinvasive WNV disease occurs in less than one percent of cases, and although host genetic factors are thought to influence risk for symptomatic disease, the identity of these factors remains largely unknown. We tested 360 common haplotype tagging and/or functional SNPs in 86 genes that encode key regulators of immune function in 753 individuals infected with WNV including: 422 symptomatic WNV cases and 331 cases with asymptomatic infections. After applying a Bonferroni correction for multiple tests and controlling for population stratification, SNPs in IRF3 (OR 0.54, p = 0.035) and MX1, (OR 0.19, p = 0.014) were associated with symptomatic WNV infection and a single SNP in OAS1 (OR 9.79, p = 0.003) was associated with increased risk for West Nile encephalitis and paralysis (WNE/P). Together, these results suggest that genetic variation in the interferon response pathway is associated with both risk for symptomatic WNV infection and WNV disease progression.

A role for the chemokine RANTES in regulating CD8 T cell responses during chronic viral infection

RANTES (CCL5) is a chemokine expressed by many hematopoietic and non-hematopoietic cell types that plays an important role in homing and migration of effector and memory T cells during acute infections. The RANTES receptor, CCR5, is a major target of anti-HIV drugs based on blocking viral entry. However, defects in RANTES or RANTES receptors including CCR5 can compromise immunity to acute infections in animal models and lead to more severe disease in humans infected with west Nile virus (WNV). In contrast, the role of the RANTES pathway in regulating T cell responses and immunity during chronic infection remains unclear. In this study, we demonstrate a crucial role for RANTES in the control of systemic chronic LCMV infection. In RANTES^−/− mice, virus-specific CD8 T cells had poor cytokine production. These RANTES^−/− CD8 T cells also expressed higher amounts of inhibitory receptors consistent with more severe exhaustion. Moreover, the cytotoxic ability of CD8 T cells from RANTES^−/− mice was reduced. Consequently, viral load was higher in the absence of RANTES. The dysfunction of T cells in the absence of RANTES was as severe as CD8 T cell responses generated in the absence of CD4 T cell help. Our results demonstrate an important role for RANTES in sustaining CD8 T cell responses during a systemic chronic viral infection.

Chemokines are small proteins that attract cells and play complex roles in coordinating immune responses. RANTES is one such chemokine that attracts many different cell types. The receptor for RANTES, CCR5, is also a coreceptor for HIV and drugs blocking the RANTES∶CCR5 pathway are in clinical use to treat HIV-infected individuals. Despite the importance of CCR5 during HIV infection, the role of RANTES during other chronic infections remains poorly defined. In this study, we found that the absence of RANTES limited the ability of mice to control chronic LCMV infection resulting in higher viral loads and more severe T cell exhaustion. Our data suggest that the impact of blocking the RANTES∶CCR5 pathway on the ability to control other chronic infections should be given careful consideration when treating HIV-infected individuals.

Tissue expression of steroid hormone receptors is associated with differential immune responsiveness

Glucocorticoids have been used as treatments against a number of diseases, especially autoimmune/inflammatory conditions in which the immune system is overactive. These treatments have varying degrees of responsiveness among individuals and in different tissues (including brain); therefore, it is important to determine what could account for these differences. In this study, we evaluated expression of stress hormone receptors in immune cells from lymphoid and non-lymphoid tissues (including brain) as a possible explanation. We analyzed leukocytes (CD45(+)) in kidney, liver, spleen, and thymus tissues from healthy mice for expression of the receptor for stress hormone (glucocorticoid-GR) as well as other steroid hormones (androgen-AR, progesterone-PR) and found that all tissues expressed these steroid hormone receptors but with varying patterns. To determine whether tissue-specific differences were related to immune cell composition, we examined steroid hormone receptor expression in T lymphocytes from each of these tissues and found similar patterns of expression in these cells regardless of tissue source. Because glucocorticoids can also impact brain function, we further examined expression of the stress hormone receptor in brain tissue and found GR expressed in immune cells at this site. In order to investigate the potential impact in an area of neuropathology, we utilized a mouse model of West Nile Virus (WNV). We observed pathological changes in brains of WNV-infected animals and T lymphocytes in the areas of inflammation; however, these cells did not express GR. These data indicate that tissue-specific differences in steroid hormone receptor expression by immune cells could determine responsiveness to steroid hormone treatment.

The CCR5-delta32 polymorphism as a model to study host adaptation against infectious diseases and to develop new treatment strategies

Humans respond differently toward exposure against pathogens and some individuals are completely resistant against transmission due to a genetically determined susceptibility. A rising number of such, so-called, host factors have been described during the last years, but their role for diagnostic or therapeutic application is still to be clarified. Here, we describe the biology of the chemokine receptor CCR5 and its polymorphism in the context of host adaptation and immune system function. Furthermore, the first clinical applications exploiting our knowledge of this chemokine receptor as a host factor are described.

Maximal T cell-mediated antitumor responses rely upon CCR5 expression in both CD4(+) and CD8(+) T cells

Immune responses against cancer rely upon leukocyte trafficking patterns that are coordinated by chemokines. CCR5, the receptor for chemotactic chemokines MIP1alpha, MIP1beta, and RANTES (CCL3, CCL4, CCL5), exerts major regulatory effects on CD4(+)- and CD8(+) T cell-mediated immunity. Although CCR5 and its ligands participate in the response to various pathogens, its relevance to tumoral immune control has been debated. Here, we report that CCR5 has a specific, ligand-dependent role in optimizing antitumor responses. In adoptive transfer studies, efficient tumor rejection required CCR5 expression by both CD4(+) and CD8(+) T cells. CCR5 activation in CD4(+) cells resulted in CD40L upregulation, leading to full maturation of antigen-presenting cells and enhanced CD8(+) T-cell crosspriming and tumor infiltration. CCR5 reduced chemical-induced fibrosarcoma incidence and growth, but did not affect the onset or progression of spontaneous breast cancers in tolerogenic Tg(MMTV-neu) mice. However, CCR5 was required for TLR9-mediated reactivation of antineu responses in these mice. Our results indicate that CCR5 boosts T-cell responses to tumors by modulating helper-dependent CD8(+) T-cell activation.

Chemokine control of West Nile virus infection

West Nile virus (WNV) is a re-emerging pathogen responsible for fatal outbreaks of meningoencephalitis in humans. Recent research using a mouse model of infection has indicated that specific chemokines and chemokine receptors help mediate the host response to WNV acting by at least three mechanisms: control of early neutrophil recruitment to the infection site (Cxcr2), control of monocytosis in blood (Ccr2) and control of leukocyte movement from blood to brain (Cxcr4, Cxcr3, Cxcl10 and possibly Ccr5). CCR5 also appears to be important in human infection, since individuals genetically deficient in this receptor have increased risk of symptomatic disease once infected. These findings provide detailed insight into non-redundant chemokine roles in organ-specific leukocyte recruitment during infection, and emphasize the importance of the balance between pathogen control and immunopathology in determining overall clinical outcome.

Clinical use of CCR5 inhibitors in HIV and beyond

Since the discovery of CCR5 as a coreceptor for HIV entry, there has been interest in blockade of the receptor for treatment and prevention of HIV infection. Although several CCR5 antagonists have been evaluated in clinical trials, only maraviroc has been approved for clinical use in the treatment of HIV-infected patients. The efficacy, safety and resistance profile of CCR5 antagonists with a focus on maraviroc are reviewed here along with their usage in special and emerging clinical situations. Despite being approved for use since 2007, the optimal use of maraviroc has yet to be well-defined in HIV and potentially in other diseases. Maraviroc and other CCR5 antagonists have the potential for use in a variety of other clinical situations such as the prevention of HIV transmission, intensification of HIV treatment and prevention of rejection in organ transplantation. The use of CCR5 antagonists may be potentiated by other agents such as rapamycin which downregulate CCR5 receptors thus decreasing CCR5 density. There may even be a role for their use in combination with other entry inhibitors. However, clinical use of CCR5 antagonists may have negative consequences in diseases such as West Nile and Tick-borne encephalitis virus infections. In summary, CCR5 antagonists have great therapeutic potential in the treatment and prevention of HIV as well as future use in novel situations such as organ transplantation. Their optimal use either alone or in combination with other agents will be defined by further investigation.

Chemokine receptor Ccr2 is critical for monocyte accumulation and survival in West Nile virus encephalitis

West Nile virus (WNV) is a re-emerging pathogen responsible for outbreaks of fatal meningoencephalitis in humans. Previous studies have suggested a protective role for monocytes in a mouse model of WNV infection, but the molecular mechanisms have remained unclear. In this study, we show that genetic deficiency in Ccr2, a chemokine receptor on Ly6c(hi) inflammatory monocytes and other leukocyte subtypes, markedly increases mortality due to WNV encephalitis in C57BL/6 mice; this was associated with a large and selective reduction of Ly6c(hi) monocyte accumulation in the brain. WNV infection in Ccr2(+/+) mice induced a strong and highly selective monocytosis in peripheral blood that was absent in Ccr2(-/-) mice, which in contrast showed sustained monocytopenia. When a 1:1 mixture of Ccr2(+/+) and Ccr2(-/-) donor monocytes was transferred by vein into WNV-infected Ccr2(-/-) recipient mice, monocyte accumulation in the CNS was not skewed toward either component of the mixture, indicating that Ccr2 is not required for trafficking of monocytes from blood to brain. We conclude that Ccr2 mediates highly selective peripheral blood monocytosis during WNV infection of mice and that this is critical for accumulation of monocytes in the brain.

The innate immune adaptor molecule MyD88 restricts West Nile virus replication and spread in neurons of the central nervous system

Type I interferons (IFN-α/β) control viral infection by triggering the expression of genes that restrict transcription, translation, replication, and assembly. Many viruses induce IFN responses after recognition by cytoplasmic or endosomal RNA sensors (RIG-I-like RNA helicases [RLR] and Toll-like receptors [TLR]), which signal through the cognate adaptor signaling molecules IPS-1, TRIF, and MyD88. Recent studies have demonstrated that IPS-1-dependent induction of IFN-α/β downstream of RLR recognition restricts West Nile virus (WNV) infection in many cell types, whereas TRIF-dependent TLR3 signaling limits WNV replication in neurons. Here, we examined the contribution of MyD88 signaling to the control of WNV by evaluating IFN induction and virus replication in genetically deficient cells and mice. MyD88(-/-) mice showed increased lethality after WNV infection and elevated viral burden primarily in the brain, even though little effect on the systemic type I IFN response was observed. Intracranial inoculation studies corroborated these findings, as WNV spread more rapidly in the central nervous system of MyD88(-/-) mice, and this phenotype preceded the recruitment of inflammatory leukocytes. In vitro, increased WNV replication was observed in MyD88(-/-) macrophages and subsets of neurons but not in myeloid dendritic cells. MyD88 had an independent effect on recruitment of monocyte-derived macrophages and T cells into the brain that was associated with blunted induction of the chemokines that attract leukocytes. Our experiments suggest that MyD88 restricts WNV by inhibiting replication in subsets of cells and modulating expression of chemokines that regulate immune cell migration into the central nervous system.

Confidence intervals that match Fisher's exact or Blaker's exact tests

When analyzing a 2 x 2 table, the two-sided Fisher's exact test and the usual exact confidence interval (CI) for the odds ratio may give conflicting inferences; for example, the test rejects but the associated CI contains an odds ratio of 1. The problem is that the usual exact CI is the inversion of the test that rejects if either of the one-sided Fisher's exact tests rejects at half the nominal significance level. Further, the confidence set that is the inversion of the usual two-sided Fisher's exact test may not be an interval, so following Blaker (2000, Confidence curves and improved exact confidence intervals for discrete distributions. Canadian Journal of Statistics 28, 783-798), we define the "matching" interval as the smallest interval that contains the confidence set. We explore these 2 versions of Fisher's exact test as well as an exact test suggested by Blaker (2000) and provide the R package exact2x2 which automatically assigns the appropriate matching interval to each of the 3 exact tests.