Presence of virus neutralizing antibodies in cerebral spinal fluid correlates with non-lethal rabies in dogs

Characterisation of a Live-Attenuated Rabies Virus Expressing a Secreted scFv for the Treatment of Rabies

Rabies virus (RABV) causes possibly the oldest disease and is responsible for an estimated >59,000 human fatalities/year. Post exposure prophylaxis (PEP), the administration of vaccine and rabies immunoglobulin, is a highly effective tool which is frequently unavailable in RABV endemic areas. Furthermore, due to the constraints of the blood-brain barrier, current PEP regimes are ineffective after the onset of clinical symptoms which invariably result in death. To circumvent this barrier, a live-attenuated recombinant RABV expressing a highly RABV-neutralising scFv antibody (62-71-3) linked to the fluorescent marker mCherry was designed. Once rescued, the resulting construct (named RABV-62scFv) was grown to high titres, its growth and cellular dissemination kinetics characterised, and the functionality of the recombinant 62-71-3 scFv assessed. Encouraging scFv production and subsequent virus neutralisation results demonstrate the potential for development of a therapeutic live-attenuated virus-based post-infection treatment (PIT) for RABV infection.

Risks related to a possible reduction of the waiting period for dogs after rabies antibody titration to 30 days compared with 90 days of the current EU legislative regime

EFSA received a mandate from the European Commission to assess the risks related to a possible reduction of the waiting period after rabies antibody titration test to 30 days compared with 90 days of the current EU legislation, for dogs moving from certain non-EU countries to the EU. This Scientific Report assessed the probability of introduction of rabies into the EU through commercial and non-commercial movements of vaccinated dogs with a positive titration test (≥ 0.5 IU/mL) if the waiting period decreases from 90 to 30 days. Assuming that all the legal requirements are complied with, the risk of transmission of rabies through the movement of a vaccinated dog is related to the risk of introducing an animal incubating rabies that was infected before the day of vaccination or shortly after vaccination but before the development of immunity (21 days post-vaccination). Using published data on the incubation period for experimental and field cases in dogs and considering the rabies incidence data in certain countries, the aggregated probability for the annual introduction of rabies through dogs was assessed. Considering the uncertainty related to the duration of the incubation period, the number of imported dogs, and the disease incidence in some countries it was concluded with a 95% certainty that the maximum number of rabies-infected imported dogs complying with the regulations in a 20-year period could increase from 5 to 20 when decreasing the waiting period from 90 to 30 days. Nevertheless, the potential impact of even a small increase in probability means the risk is increased for a region like the EU where rabies has long been a focus for eradication, to protect human and animal health.

Innate Immune Signaling and Role of Glial Cells in Herpes Simplex Virus- and Rabies Virus-Induced Encephalitis

The environment of the central nervous system (CNS) represents a double-edged sword in the context of viral infections. On the one hand, the infectious route for viral pathogens is restricted via neuroprotective barriers; on the other hand, viruses benefit from the immunologically quiescent neural environment after CNS entry. Both the herpes simplex virus (HSV) and the rabies virus (RABV) bypass the neuroprotective blood-brain barrier (BBB) and successfully enter the CNS parenchyma via nerve endings. Despite the differences in the molecular nature of both viruses, each virus uses retrograde transport along peripheral nerves to reach the human CNS. Once inside the CNS parenchyma, HSV infection results in severe acute inflammation, necrosis, and hemorrhaging, while RABV preserves the intact neuronal network by inhibiting apoptosis and limiting inflammation. During RABV neuroinvasion, surveilling glial cells fail to generate a sufficient type I interferon (IFN) response, enabling RABV to replicate undetected, ultimately leading to its fatal outcome. To date, we do not fully understand the molecular mechanisms underlying the activation or suppression of the host inflammatory responses of surveilling glial cells, which present important pathways shaping viral pathogenesis and clinical outcome in viral encephalitis. Here, we compare the innate immune responses of glial cells in RABV- and HSV-infected CNS, highlighting different viral strategies of neuroprotection or Neuroinflamm. in the context of viral encephalitis.

Modelling the influence of naturally acquired immunity from subclinical infection on outbreak dynamics and persistence of rabies in domestic dogs

A number of mathematical models have been developed for canine rabies to explore dynamics and inform control strategies. A common assumption of these models is that naturally acquired immunity plays no role in rabies dynamics. However, empirical studies have detected rabies-specific antibodies in healthy, unvaccinated domestic dogs, potentially due to immunizing, non-lethal exposure. We developed a stochastic model for canine rabies, parameterised for Laikipia County, Kenya, to explore the implications of different scenarios for naturally acquired immunity to rabies in domestic dogs. Simulating these scenarios using a non-spatial model indicated that low levels of immunity can act to limit rabies incidence and prevent depletion of the domestic dog population, increasing the probability of disease persistence. However, incorporating spatial structure and human response to high rabies incidence allowed the virus to persist in the absence of immunity. While low levels of immunity therefore had limited influence under a more realistic approximation of rabies dynamics, high rates of exposure leading to immunizing non-lethal exposure were required to produce population-level seroprevalences comparable with those reported in empirical studies. False positives and/or spatial variation may contribute to high empirical seroprevalences. However, if high seroprevalences are related to high exposure rates, these findings support the need for high vaccination coverage to effectively control this disease.

Modelling the factors affecting the probability for local rabies elimination by strategic control

Dog rabies has been recognized from ancient times and remains widespread across the developing world with an estimated 59,000 people dying annually from the disease. In 2011 a tri-partite alliance consisting of the OIE, the WHO and the FAO committed to globally eliminating dog-mediated human rabies by 2030. Regardless of global support, the responsibility remains with local program managers to implement successful elimination programs. It is well known that vaccination programs have a high probability of successful elimination if they achieve a population-coverage of 70%. It is often quoted that reducing population turnover (typically through sterilizations) raises the probability for local elimination by maintaining herd immunity for longer. Besides this, other factors that affect rabies elimination are rarely mentioned. This paper investigates the probability for local elimination as it relates to immunity, fecundity, dog population size, infectivity (bite rates), in-migration of immune-naïve dogs, and the initial incidence. To achieve this, an individual-based, stochastic, transmission model was manipulated to create a dataset covering combinations of factors that may affect elimination. The results thereof were analysed using a logistic regression model with elimination as the dependent variable. Our results suggest that smaller dog populations, lower infectivity and lower incidence (such as when epidemics start with single introductions) strongly increased the probability for elimination at wide ranges of vaccination levels. Lower fecundity and lower in-migration had weak effects. We discuss the importance of these findings in terms of their impact and their practical application in the design of dog-mediated rabies control programs.

Most guidelines for rabies control call for at least 70% vaccination coverage of dogs. This level of immunity has a very high probability for the local elimination of rabies, but it is often not an achievable ideal due to resource constraints. Campaign managers can be strategic on how they allocate their resources. Lower infectivity rates are present in areas with more restricted dog movements and have higher probabilities for elimination at lower vaccination rates. Smaller sub-populations have higher probabilities for elimination at the same vaccination coverage levels compared to larger sub-populations. Vaccinating immune corridors can divide meta-populations into smaller sub-populations that are likely to result in elimination either due to their small size or due to the local low infectivity. Areas already free of rabies require lower vaccination levels to maintain freedom compared to endemic areas. Where donors do not specifically require sterilization campaigns, funds meant for rabies control should not be diverted to sterilizations.

Brain tissue-resident immune memory cells are required for long-term protection against CNS infection with rabies virus

Immune memory cells residing in previously infected, nonlymphoid tissues play a role in immune surveillance. In the event that circulating antibodies fail to prevent virus spread to the tissues in a secondary infection, these memory cells provide an essential defense against tissue reinfection. CNS tissues are isolated from circulating immune cells and antibodies by the blood-brain barrier, making the presence of tissue-resident immune memory cells particularly needed to combat recurrent infection by neurotropic viruses. Wild-type and laboratory-engineered rabies viruses are neurotropic, differ in pathogenicity, and have varying effects on BBB functions. These viruses have proven invaluable tools in demonstrating the importance of tissue-resident immune memory cells in the reinfection of CNS tissues. Only Type 1 immune memory is effective at therapeutically clearing a secondary infection with wild-type rabies viruses from the CNS and does so despite the maintenance of blood-brain barrier integrity.

Experimental Lagos bat virus infection in straw-colored fruit bats: A suitable model for bat rabies in a natural reservoir species

Rabies is a fatal neurologic disease caused by lyssavirus infection. Bats are important natural reservoir hosts of various lyssaviruses that can be transmitted to people. The epidemiology and pathogenesis of rabies in bats are poorly understood, making it difficult to prevent zoonotic transmission. To further our understanding of lyssavirus pathogenesis in a natural bat host, an experimental model using straw-colored fruit bats (Eidolon helvum) and Lagos bat virus, an endemic lyssavirus in this species, was developed. To determine the lowest viral dose resulting in 100% productive infection, bats in five groups (four bats per group) were inoculated intramuscularly with one of five doses, ranging from 100.1 to 104.1 median tissue culture infectious dose (TCID50). More bats died due to the development of rabies after the middle dose (102.1 TCID50, 4/4 bats) than after lower (101.1, 2/4; 101.1, 2/4) or higher (103.1, 2/4; 104.1, 2/4) doses of virus. In the two highest dose groups, 4/8 bats developed rabies. Of those bats that remained healthy 3/4 bats seroconverted, suggesting that high antigen loads can trigger a strong immune response that abrogates a productive infection. In contrast, in the two lowest dose groups, 3/8 bats developed rabies, 1/8 remained healthy and seroconverted and 4/8 bats remained healthy and did not seroconvert, suggesting these doses are too low to reliably induce infection. The main lesion in all clinically affected bats was meningoencephalitis associated with lyssavirus-positive neurons. Lyssavirus antigen was detected in tongue epithelium (5/11 infected bats) rather than in salivary gland epithelium (0/11), suggesting viral excretion via the tongue. Thus, intramuscular inoculation of 102.1 TCID50 of Lagos bat virus into straw-colored fruit bats is a suitable model for lyssavirus associated bat rabies in a natural reservoir host, and can help with the investigation of lyssavirus infection dynamics in bats.

A combination of two human monoclonal antibodies cures symptomatic rabies

Rabies is a neglected disease caused by a neurotropic Lyssavirus, transmitted to humans predominantly by the bite of infected dogs. Rabies is preventable with vaccines or proper post-exposure prophylaxis (PEP), but it still causes about 60,000 deaths every year. No cure exists after the onset of clinical signs, and the case-fatality rate approaches 100% even with advanced supportive care. Here, we report that a combination of two potent neutralizing human monoclonal antibodies directed against the viral envelope glycoprotein cures symptomatic rabid mice. Treatment efficacy requires the concomitant administration of antibodies in the periphery and in the central nervous system through intracerebroventricular infusion. After such treatment, recovered mice presented good clinical condition, viral loads were undetectable, and the brain inflammatory profile was almost normal. Our findings provide the unprecedented proof of concept of an antibody-based therapeutic approach for symptomatic rabies.

Acute RNA Viral Encephalomyelitis and the Role of Antibodies in the Central Nervous System

Acute RNA viral encephalomyelitis is a serious complication of numerous virus infections. Antibodies in the cerebral spinal fluid (CSF) are correlated to better outcomes, and there is substantive evidence of antibody secreting cells (ASCs) entering the central nervous system (CNS) and contributing to resolution of infection. Here, we review the RNA viruses known to cause acute viral encephalomyelitis with mechanisms of control that require antibody or ASCs. We compile the cytokines, chemokines, and surface receptors associated with ASC recruitment to the CNS after infection and compare known antibody-mediated mechanisms as well as potential noncytolytic mechanisms for virus control. These non-canonical functions of antibodies may be employed in the CNS to protect precious non-renewable neurons. Understanding the immune-specialized zone of the CNS is essential for the development of effective treatments for acute encephalomyelitis caused by RNA viruses.

Rabies viruses of different virulence regulates inflammatory responses both in vivo and in vitro via MAPK and NF-κB pathway

Immune responses and central nervous system dysfunction are two main factors to be considered during rabies virus (RABV) infection. However, the mechanisms by which RABV strains of different virulence regulate with chemokine expression and the signaling pathways responsible for the immune responses in the terminal stage of infection both in vivo and in vitro have not been fully elucidated. In this study, we found low expression levels of proinflammatory chemokines in the mouse brain upon infection with street RABV strains (CXZ17 and HN10) at the late stage of infection. We also examined the difference in inflammatory response upon infection with RABV strains of different virulence in a mouse model. We found that the expression of proinflammatory chemokines increased to a varying degree upon infection with street RABV (CXZ17 and HN10) or laboratory-fixed RABV (CVS-11, aG, and CTN); CXCL10, CCL5, and CCL2 were the most significantly upregulated chemokines in brain tissue and microglial BV-2 cells in response to infection with RABV strains of different virulence. Our data also demonstrate significant activation of the MAPK and NF-κB pathways in mouse brain tissue at the late stage of RABV infection. We also found (i) low phosphorylation signals of MAPK and NF-κB p65 in neuronal cells upon infection with CXZ17 and HN10 in the mouse brain and (ii) strong phosphorylation signals in cerebrovascular endothelial cells and neuronal cells upon CTN or aG infection. Moreover, we quantified the nuclear localization status of MAPK signals and NF-κB p65 upon infection with CVS-11, aG, and CTN in BV-2 cells in vitro. We also found (i) that the activation of the p38, ERK1/2, and NF-κB p65 pathway, which stimulates CXCL10, CCL5, and CCL2 expression upon infection with RABV strains of different virulence (aG, CTN, and CVS-11), is triggered after virus entry into BV-2 cells and (ii) that the expression of CXCL10, CCL5, and CCL2 is required for the activation of NF-κB, p38, and ERK1/2, but not JNK. Overall, our study provides insight into the regulation of inflammatory responses mediated by MAPK and NF-κB in the mouse brain and in microglial cells upon RABV infection of different virulence.

Rabies virus-neutralising antibodies in healthy, unvaccinated individuals: What do they mean for rabies epidemiology?

Rabies has been a widely feared disease for thousands of years, with records of rabid dogs as early as ancient Egyptian and Mesopotamian texts. The reputation of rabies as being inevitably fatal, together with its ability to affect all mammalian species, contributes to the fear surrounding this disease. However, the widely held view that exposure to the rabies virus is always fatal has been repeatedly challenged. Although survival following clinical infection in humans has only been recorded on a handful of occasions, a number of studies have reported detection of rabies-specific antibodies in the sera of humans, domestic animals, and wildlife that are apparently healthy and unvaccinated. These 'seropositive' individuals provide possible evidence of exposure to the rabies virus that has not led to fatal disease. However, the variability in methods of detecting these antibodies and the difficulties of interpreting serology tests have contributed to an unclear picture of their importance. In this review, we consider the evidence for rabies-specific antibodies in healthy, unvaccinated individuals as indicators of nonlethal rabies exposure and the potential implications of this for rabies epidemiology. Our findings indicate that whilst there is substantial evidence that nonlethal rabies exposure does occur, serology studies that do not use appropriate controls and cutoffs are unlikely to provide an accurate estimate of the true prevalence of nonlethal rabies exposure.

Combination therapy of rabies-infected mice with inhibitors of pro-inflammatory host response, antiviral compounds and human rabies immunoglobulin

Recent studies demonstrated that inhibitors of pro-inflammatory molecular cascades triggered by rabies infection in the central nervous system (CNS) can enhance survival in mouse model and that certain antiviral compounds interfere with rabies virus replication in vitro. In this study different combinations of therapeutics were tested to evaluate their effect on survival in rabies-infected mice, as well as on viral load in the CNS. C57Bl/6 mice were infected with Silver-haired bat rabies virus (SHBRV)-18 at virus dose approaching LD₅₀ and LD₁₀₀. In one experimental group daily treatments were initiated 4 h before-, in other groups 48 or 96 h after challenge. In the first experiment therapeutic combination contained inhibitors of tumour necrosis factor-α (infliximab), caspase-1 (Ac-YVAD-cmk), and a multikinase inhibitor (sorafenib). In the treated groups there was a notable but not significant increase of survival compared to the virus infected, non-treated mice. The addition of human rabies immunoglobulins (HRIG) to the combination in the second experiment almost completely prevented mortality in the pre-exposure treatment group along with a significant reduction of viral titres in the CNS. Post-exposure treatments also greatly improved survival rates. As part of the combination with immunomodulatory compounds, HRIG had a higher impact on survival than alone. In the third experiment the combination was further supplemented with type-I interferons, ribavirin and favipiravir (T-705). As a blood-brain barrier opener, mannitol was also administered. This treatment was unable to prevent lethal consequences of SHBRV-18 infection; furthermore, it caused toxicity in treated mice, presumably due to interaction among the components. In all experiments, viral loads in the CNS were similar in mice that succumbed to rabies regardless of treatment. According to the findings, inhibitors of detrimental host response to rabies combined with antibodies can be considered among the possible therapeutic and post-exposure options in human rabies cases.

Recombinant rabies virus expressing interleukin-6 enhances the immune response in mouse brain

Rabies, which is caused by the rabies virus (RABV), is an ancient zoonosis that has a high mortality rate. Previous studies have indicated that recombinant RABV expressing canine interleukin-6 (rHEP-CaIL6), induced more virus-neutralizing antibodies than parental RABV in mice following intramuscular immunization. To investigate the immune response induced in the CNS by rHEP-CaIL6 after intranasal or intracranial administration in mice, the permeability of the blood-brain barrier (BBB), the infiltration of CD3 T cells, and innate immune response-related effector molecules in the CNS were examined. It was observed that infection of rHEP-CaIL6 led to enhanced BBB permeability following intranasal infection. More CD3 T cells infiltrated into the central nervous system (CNS) in mice infected with rHEP-CaIL6 than in those infected with the HEP-Flury strain. Furthermore, rHEP-CaIL6 induced an increased expression of innate immune response-related effector molecules, compared with the parental HEP-Flury strain, within the CNS. Taken together, these findings suggest that rHEP-CaIL6 induced stronger immune responses in mice brains, which is more beneficial for virus clearance. These results may also partly illustrate the role of IL6 in RABV infection.

Another Look at the "Dismal Science" and Jenner's Experiment

The follow-up to Jenner's experiment, routine vaccination, has reduced more disease and saved more vertebrate lives than any other iatrogenic procedure by orders of magnitude. The unassailability of that potentially provocative cliché has been ciphered in human medicine, even if it is more difficult in our profession. Most public relations headaches concerning vaccines are a failure to communicate, often resulting in overly great expectations. Even in the throes of a tight appointment schedule remembering and synopsizing (for clients), some details of the dismal science can make practice great again.

Immunological aspects of rabies: a literature review

Rabies is a lethal disease caused by the neurotropic virus rabies virus (RABV), and it remains an important public health problem globally. It is known that the host immune response is important for control of viral infection and promoting viral clearance. In this context, it is well documented that, in addition to RABV neutralizing antibody, interferons and cell-mediated immunity also have an important role in preventing the establishment of disease. On the other hand, RABV suppresses host immunity through different mechanisms, for example, direct inhibition of host gene expression, sequestration of pathogen-associated molecular patterns, or modification of cytokine signalling pathways, which hinder the protective host immune responses to RABV infection. Here, we review the immunological aspects of rabies, highlighting innate and adaptive immunity, as well as the host evasion immune mechanisms used by the virus. Finally, we briefly discuss how this knowledge can direct new research and be harnessed for future therapeutic strategies.

Comparison of immune responses to attenuated rabies virus and street virus in mouse brain

Rabies is a lethal neurological disease caused by the neurotropic rabies virus (RABV). To investigate the innate immune response in the brain during rabies infection, key gene transcripts indicative of innate immunity in a mouse model system were measured using real-time RT-PCR. Mice were infected via the intracerebral or intramuscular route with either attenuated rabies virus (SRV9) or pathogenic rabies virus (BD06). Infection with SRV9 resulted in the early detection of viral replication and the rapid induction of innate immune response gene expression in the brain. BD06 infection elicited innate immune response gene expression during only the late stage of infection. We measured Na-fluorescein uptake to assess blood-brain barrier (BBB) permeability, which was enhanced during the early stage of SRV9 infection and significantly enhanced during the late stage of BD06 infection. Furthermore, early SRV9 replication increased the maturation and differentiation of dendritic cells (DCs) and B cells in the inguinal lymph nodes and initiated the generation of virus-neutralizing antibodies (VNAs), which cooperate with the innate immune response to eliminate virus from the CNS. However, BD06 infection did not stimulate VNA production; thus, the virus was able to evade the host immune response and cause encephalitis. The rabies virus phosphoprotein has been reported to counteract IFN activation. In an in vitro study of the relationship between IFN antagonism and RABV pathogenicity, we demonstrated that SRV9 more strongly antagonized IFN activity than did BD06. Therefore, there is no positive relationship between the IFN antagonist activity of the virus and its pathogenicity.

Interplay between rabies virus and the mammalian immune system

Rabies is a disease caused following infection of the brain by the rabies virus (RABV). The principle mechanism of transmission is through a bite wound. The virus infects peripheral nerves and moves to the central nervous system (CNS). There appears to be little involvement of other organ systems and little detectable immune stimulation prior to infection of the CNS. This failure of the mammalian immune system to respond to rabies virus infection leads, in the overwhelming majority of cases, to death of the host. To some extent, this failure is likely due to the exclusive replication of RABV in neurons and the limited ability to generate, sufficiently rapidly, an anti-viral antibody response in situ. This is reflected in the ability of post-exposure vaccination, when given early after infection, to prevent disease. The lack of immune stimulation during RABV infection preceding neural invasion is the Achilles heel of the immune response. Whilst many viruses infect the brain, causing encephalitis and neuronal deficit, none are as consistently fatal to the host as RABV. This is in part due to prior replication of many viruses in peripheral, non-neural tissue by other viruses that allows timely activation of the immune response before the host is overwhelmed. Our current understanding of the correlates of protection for rabies suggests that it is the action of neutralising antibodies that prevent infection and control spread of RABV. Furthermore, it tells us that the induction of immunity can protect and understanding how and why this happens is critical to controlling infection. However, the paradigm of antibody development suggests that antigen presentation overwhelmingly occurs in lymphoid tissue (germinal and non-germinal centres) and these are external to the CNS. In addition, the blood-brain-barrier may provide a block to the delivery of immune effectors (antibodies/plasma B-cells) entering where they are needed. Alternatively, there may be insufficient antigen exposure after natural infection to mount an effective response or the virus actively suppresses immune function. To improve our ability to treat this fatal infection it is imperative to understand how immunity to RABV develops and functions so that parameters of protection are better defined.

Differential Host Immune Responses after Infection with Wild-Type or Lab-Attenuated Rabies Viruses in Dogs

METHODOLOGY/PRINCIPAL FINDINGS

The experimental infection of dogs with TriGAS induced high levels of VNA in the serum, whereas wt RABV infection did not. Dogs infected with TriGAS developed antibodies against the virus including its glycoprotein, whereas dogs infected with DRV-NG11 only developed rabies antibodies that are presumably specific for the nucleoprotein, (N) and not the glycoprotein (G). We show that infection with TriGAS induces early activation of B cells in the draining lymph nodes and persistent activation of DCs and B cells in the blood. On the other hand, infection with DRV-NG11 fails to induce the activation of DCs and B cells and further reduces CD4 T cell production. Further, we show that intrathecal (IT) immunization of TriGAS not only induced high levels of VNA in the serum but also in the CSF while intramuscular (IM) immunization of TriGAS induced VNA only in the serum. In addition, high levels of total protein and WBC were detected in the CSF of IT immunized dogs, indicating the transient enhancement of blood-brain barrier (BBB) permeability, which is relevant to the passage of immune effectors from periphery into the CNS.

CONCLUSIONS/SIGNIFICANCE

IM infection of dogs with TriGAS induced the production of serum VNA whereas, IT immunization of TriGAS in dogs induces high levels of VNA in the periphery as well as in the CSF and transiently enhances BBB permeability. In contrast, infection with wt DRV-NG11 resulted in the production of RABV-reactive antibodies but VNA and antibodies specific for G were absent. As a consequence, all of the dogs infected with wt DRV-NG11 succumbed to rabies. Thus the failure to activate protective immunity is one of the important features of RABV pathogenesis in dogs.

Novel Approaches to the Prevention and Treatment of Rabies

Rabies is a highly lethal disease caused by the neurotropic rabies virus (RABV), and it remains an important public health problem globally. Effective vaccines have been developed for pre- and post-exposure prophylaxis (PEP). PEP is only effective if it is initiated promptly after recognizing exposure. Once neurological symptoms develop, however, it is widely accepted that there is no effective treatment available. Recent studies indicate that the presence of RABV-specific immunity (i.e. Virus neutralizing antibodies, VNA) and the transient enhancement of the BBB permeability are absolutely required for effective virus clearance from the CNS. In principle, it has been shown in mice using various live-attenuated RABVs or recombinant RABVs expressing three copies of the G or expressing chemokine/cytokines, which can induce high levels of VNA in the serum and also capable of transiently enhancing the BBB permeability that it is possible to clear the virus from CNS. Also, it has been demonstrated that, intravenous administration of VNA together with MCP-1 (shown to transiently open up BBB) can clear RABV from the CNS in both immunocompetent and immunocompromised mice, as late as 5 days after lethal challenge. Novel therapeutic approaches aimed at allowing the peripheral VNA to cross the BBB by administration of the VNA in combination with biological or chemical agents that can transiently open up the BBB would be useful to establish an effective therapy for rabies in humans. In this review, we focus on the some of the approaches that can be used to meet the challenges in the field of rabies treatment.

The inability of wild-type rabies virus to activate dendritic cells is dependent on the glycoprotein and correlates with its low level of the de novo-synthesized leader RNA

Dendritic cells (DCs) are the most efficient antigen-presenting cells, playing a key role in the adaptive immune responses to viral infections. Our studies demonstrate that wild-type (wt) rabies virus (RABV) does not activate DCs. Adoptive transfer of DCs primed with wt RABV did not activate DCs, stimulate virus neutralizing antibodies (VNA), or protect recipients against challenge. However, adoptive transfer of DCs primed with laboratory-attenuated RABV resulted in DC activation, production of VNA, and protection against challenge. In vitro studies with recombinant RABV (laboratory-attenuated RABV expressing the glycoprotein or the phosphoprotein from wt RABV) demonstrate that DC activation is dependent on the glycoprotein and involves the IPS-1 pathway. Furthermore, binding to and entry into DCs by wt RABV is severely blocked, and the copy number of de novo-synthesized leader RNA was two logs lower in DCs infected with the wt than in DCs treated with laboratory-attenuated RABV. However, transient transfection of DCs with synthesized leader RNA from either wt or attenuated RABV is capable of activating DCs in a dose-dependent manner. Thus, the inability of wt RABV to activate DCs correlates with its low level of the de novo-synthesized leader RNA.

IMPORTANCE

Rabies remains a public health threat, with more than 55,000 fatalities each year around the world. Since DCs play a key role in the adaptive immune responses to viral infections, we investigated the ability of rabies virus (RABV) to activate DCs. It was found that the adoptive transfer of DCs primed with wt RABV did not activate DCs, stimulate VNA, or protect mice against lethal challenge. However, laboratory-attenuated RABV mediates the activation of DCs via the IPS-1 pathway and is glycoprotein dependent. We further show that wt RABV evades DC-mediated immune activation by inefficient binding/entry into DCs and as a result of a reduced level of de novo-synthesized leader RNA. These findings may have important implications in the development of efficient rabies vaccines.

Met-CCL5 represents an immunotherapy strategy to ameliorate rabies virus infection

Background

Infection of rabies virus (RABV) causes central nervous system (CNS) dysfunction and results in high mortality in human and animals. However, it is still unclear whether and how CNS inflammation and immune response contribute to RABV infection.

Methods

Suckling mice were intracerebrally infected with attenuated RABV aG and CTN strains, followed by examination of chemokine or cytokine production, inflammatory cell infiltration and neuron apoptosis in the brain. Furthermore, the suckling mice and adult mice that were intracerebrally infected with aG and the adult mice that were intramuscularly infected with street RABV HN10 were treated with CCL5 antagonist (Met-CCL5) daily beginning on day 2 postinfection. The survival rates and inflammation responses in the CNS of these mice were analyzed.

Results

Excessive CCL5 in the CNS was associated with CNS dysfunction, inflammation, and macrophage or lymphocyte infiltration after attenuated or street RABV infection. Administration of exogenous CCL5 induced excessive infiltration of immune cells into the CNS and enhanced inflammatory chemokine and cytokine production. Met-CCL5 treatment significantly prolonged survival time of the suckling mice inoculated with aG and adult mice infected with aG and HN10.

Conclusions

These results suggest that CCL5 in the CNS is a key regulator involved in inducing rabies encephalomyelitis. Furthermore, treatment with the CCL5 antagonist Met-CCL5 prolongs survival time of the mice infected with attenuated or street RABVs, which might represent a novel therapeutic strategy to ameliorate RABV infection.