Role of CD4+ and CD8+ T cells in murine resistance to street rabies virus

A single immunization with core-shell structured lipopolyplex mRNA vaccine against rabies induces potent humoral immunity in mice and dogs

The persistence and clinical consequences of rabies virus (RABV) infection have prompted global efforts to develop a safe and effective vaccines against rabies. mRNA vaccines represent a promising option against emerging and re-emerging infectious diseases, gaining particular interest since the outbreak of COVID-19. Herein, we report the development of a highly efficacious rabies mRNA vaccine composed of sequence-modified mRNA encoding RABV glycoprotein (RABV-G) packaged in core-shell structured lipopolyplex (LPP) nanoparticles, named LPP-mRNA-G. The bilayer structure of LPP improves protection and delivery of RABV-G mRNA and allows gradual release of mRNA molecules as the polymer degrades. The unique core-shell structured nanoparticle of LPP-mRNA-G facilitates vaccine uptake and demonstrates a desirable biodistribution pattern with low liver targeting upon intramuscular immunization. Single administration of low-dose LPP-mRNA-G in mice elicited potent humoral immune response and provided complete protection against intracerebral challenge with lethal RABV. Similarly, single immunization of low-dose LPP-mRNA-G induced high levels of virus-neutralizing antibody titers in dogs. Collectively, our data demonstrate the potential of LPP-mRNA-G as a promising next-generation rabies vaccine used in human and companion animals.

Short-Chain Fatty Acids Alleviate Vancomycin-Caused Humoral Immunity Attenuation in Rabies-Vaccinated Mice by Promoting the Generation of Plasma Cells via Akt-mTOR Pathway

Mounting evidence suggests that gut microbial composition and its metabolites, including short-chain fatty acids (SCFAs), have beneficial effects in regulating host immunogenicity to vaccines. However, it remains unknown whether and how SCFAs improve the immunogenicity of the rabies vaccine. In this study, we investigated the effect of SCFAs on the immune response to rabies vaccine in vancomycin (Vanco)-treated mice and found that oral gavage with butyrate-producing bacteria (C. butyricum) and butyrate supplementation elevated RABV-specific IgM, IgG, and virus-neutralizing antibodies (VNAs) in Vanco-treated mice. Supplementation with butyrate expanded antigen-specific CD4+ T cells and IFN-γ-secreting cells, augmented germinal center (GC) B cell recruitment, promoted plasma cells (PCs) and RABV-specific antibody-secreting cells (ASCs) generation in Vanco-treated mice. Mechanistically, butyrate enhanced mitochondrial function and activated the Akt-mTOR pathway in primary B cells isolated from Vanco-treated mice, ultimately promoting B lymphocyte-induced maturation protein-1 (Blimp-1) expression and CD138+ PCs generation. These results highlight the important role of butyrate in alleviating Vanco-caused humoral immunity attenuation in rabies-vaccinated mice and maintaining host immune homeostasis. IMPORTANCE The gut microbiome plays many crucial roles in the maintenance of immune homeostasis. Alteration of the gut microbiome and metabolites has been shown to impact vaccine efficacy. SCFAs can act as an energy source for B-cells, thereby promoting both mucosal and systemic immunity in the host by inhibiting HDACs and activation of GPR receptors. This study investigates the impact of orally administered butyrate, an SCFA, on the immunogenicity of rabies vaccines in Vanco-treated mice. The results showed that butyrate ameliorated humoral immunity by facilitating the generation of plasma cells via the Akt-mTOR in Vanco-treated mice. These findings unveil the impact of SCFAs on the immune response of the rabies vaccine and confirm the crucial role of butyrate in regulating immunogenicity to rabies vaccines in antibiotic-treated mice. This study provides a fresh insight into the relationship of microbial metabolites and rabies vaccination.

Toll-Like Receptor 4 Regulates Rabies Virus-Induced Humoral Immunity through Recruitment of Conventional Type 2 Dendritic Cells to Lymph Organs

Rabies, caused by rabies virus (RABV), is fatal to both humans and animals around the world. Effective clinical therapy for rabies has not been achieved, and vaccination is the most effective means of preventing and controlling rabies. Although different vaccines, such as live attenuated and inactivated vaccines, can induce different immune responses, different expressions of pattern recognition receptors (PRRs) also cause diverse immune responses. Toll-like receptor 4 (TLR4) is a pivotal PRR that induces cytokine production and bridges innate and adaptive immunity. Importantly, TLR4 recognizes various virus-derived pathogen-associated molecular patterns (PAMPs) and virus-induced damage-associated molecular patterns (DAMPs), usually leading to the activation of immune cells. However, the role of TLR4 in the humoral immune response induced by RABV has not yet been revealed. Based on TLR4-deficient (TLR4^-/-) and wild-type (WT) mouse models, we report that TLR4-dependent recruitment of the conventional type 2 dendritic cells (CD8α^- CD11b⁺ cDC2) into secondary lymph organs (SLOs) is critical for antigen presentation. cDC2-initiated differentiation of follicular helper T (Tfh) cells promotes the proliferation of germinal center (GC) B cells, the formation of GCs, and the production of plasma cells (PCs), all of which contribute to the production of RABV-specific IgG and virus-neutralizing antibodies (VNAs). Collectively, our work demonstrates that TLR4 is necessary for the recruitment of cDC2 and for the induction of RABV-induced humoral immunity, which is regulated by the cDC2-Tfh-GC B axis. IMPORTANCE Vaccination is the most efficient method to prevent rabies. TLR4, a well-known immune sensor, plays a critical role in initiating innate immune response. Here, we found that TLR4-deficient (TLR4^-/-) mice suppressed the induction of humoral immune response after immunization with rabies virus (RABV), including reduced production of VNAs and RABV-specific IgG compared to that occurred in wild-type (WT) mice. As a consequence, TLR4^-/- mice exhibited higher mortality than that of WT mice after challenge with virulent RABV. Importantly, further investigation found that TLR4 signaling promoted the recruitment of cDC2 (CD8α⁺ CD11b^-), a subset of cDCs known to induce CD4⁺ T-cell immunity through their MHC-II presentation machinery. Our results imply that TLR4 is indispensable for an efficient humoral response to rabies vaccine, which provides new insight into the development of novel rabies vaccines.

CD4 T Cells, CD8 T Cells, and Monocytes Coordinate To Prevent Rift Valley Fever Virus Encephalitis

Rift Valley fever virus (RVFV) is an arbovirus that causes disease in livestock and humans in Africa and the Middle East. While human disease is typically mild and self-limiting, some individuals develop severe manifestations, such as hepatitis, hemorrhagic fever, or encephalitis. Encephalitis occurs 2 to 3 weeks after acute illness; therefore, we hypothesized that it was a result of an inadequate adaptive immunity. To test this hypothesis in vivo, we used an attenuated virus (DelNSsRVFV) that does not typically cause disease in mice. We first characterized the normal immune response to infection with DelNSsRVFV in immunocompetent mice and noted expansion of natural killer cells and monocytes, as well as activation of both CD8 and CD4 T cells. Depleting C57BL/6 mice of CD4 T cells prior to DelNSsRVFV infection resulted in encephalitis in 30% of the mice; in encephalitic mice, we noted infiltration of T cells and inflammatory monocytes into the brain. CD4 and CD8 codepletion in C57BL/6 mice, as well as CD4 depletion in CCR2 knockout mice, increased the frequency of encephalitis, demonstrating that these cell types normally contributed to the prevention of disease. Encephalitic mice had similar viral RNA loads in the brain regardless of which cell types were depleted, suggesting that CD4 T cells, CD8 T cells, and inflammatory monocytes did little to control viral replication in the brain. CD4-depleted mice exhibited diminished humoral and T cell memory responses, suggesting that these immune mechanisms contributed to peripheral control of virus, thus preventing infection of the brain.IMPORTANCE RVFV is found in Africa and the Middle East and is transmitted by mosquitos or through contact with infected animals. Infected individuals can develop mild disease or more severe forms, such as hepatitis or encephalitis. In order to understand why some individuals develop encephalitis, we first need to know which immune functions protect those who do not develop this form of disease. In this study, we used a mouse model of RVFV infection to demonstrate that CD4 T cells, CD8 T cells, and monocytes all contribute to prevention of encephalitis. Their likely mechanism of action is preventing RVFV from ever reaching the brain.

Role of nitric oxide in the regulation of immune responses during rabies virus infection in mice

Rabies virus (RABV) stimulates nitric oxide (NO) production, which either triggers T cell differentiation or suppresses T cell function depending on its concentration. Herein, we assessed the potential role of NO in regulation of immune responses during RABV infection in mice model. The experimental animals were divided into four groups and 100LD50 of challenge virus standard (CVS) strain of RABV was inoculated intracerebrally on day 0 and subsequently aminoguanidine (AG; inducible nitric oxide synthase inhibitor) was injected intraperitoneally twice a day, up to 6 days. The samples were collected at 2, 4, 6, 8, 9, 10 and 12 days post infection (DPI). The immune cells including CD4+, CD8+ T lymphocytes and natural killer (NK) cells were estimated from peripheral blood mononuclear cells (PBMCs) and splenocytes. Serum total NO concentration, histopathology, immunohistochemistry, direct fluorescent antibody technique and TUNEL assay was performed. Infection with CVS resulted in significant early increase in CD4+, CD8+ and NK cells in blood and spleen until 2 DPI. From 4 DPI onwards significant reduction was noticed in these parameters which coincided with increased NO on 4 DPI, rising to maximum on 8 DPI, until their death on 10 DPI. Conversely, the CVS-AG treated group showed lower levels of NO and increased number of CD4+, CD8+ and NK cells. Increased number of cells in blood and spleen coincided with increased survival time, delayed development of clinical signs, reduced viral load and less apoptotic cells. NO played important role in regulation of immune responses during RABV infection. The findings of present study confirmed the role of NO and/or iNOS using iNOS inhibitor (aminoguanidine) in immune response during RABV infection, which would further help in understanding the virus immunopathogenesis with adoption of newer antiviral strategies to counter the progression of disease.

Current Status and Development of Vaccines and Other Biologics for Human Rabies Prevention

Rabies is a neglected viral zoonosis with the highest case fatality of any infectious disease. Pasteur's historical accomplishments during the late 19(th) century began the process of human vaccine development, continuing to evolve into the 21(st) century. Over the past 35 years, great improvements occurred in the production of potent tissue culture vaccines and the gradual removal from the market of unsafe nerve tissue products. Timely and appropriate administration of modern biologics virtually assures survivorship, even after severe exposures. Nevertheless, in the developing world, if not provided for free nationally, the cost of a single course of human prophylaxis exceeds the average monthly wage of the common worker. Beyond traditional approaches, recombinant, sub-unit and other novel methods are underway to improve the availability of safe, effective and more affordable rabies biologics.

Ginsenoside Re as an adjuvant to enhance the immune response to the inactivated rabies virus vaccine in mice

The inactivated rabies virus vaccine (RV) is a relatively expensive vaccine, prone to failure in some cases. Ginsenoside Re (Re) is a saponin isolated from Panax ginseng, and has an adjuvant property. Here the adjuvant effect of Re to improve the immune response to the RV is evaluated in mice. ICR mice were immunized with saline, 2.50mg/kg Re, 20μl RV, 100μl RV, or 20μl of RV adjuvanted with Re (1.25, 2.50 or 5.00mg/kg). Different time points after boosting, we measured serum antibodies in blood samples and separated splenocytes to detect lymphocyte proliferation and the production of IL-4, IL-10, IL-12, and IFN-γ in vitro. We also compared immunizations containing 20μl RV and 20μl RV adjuvanted with Re (5.00mg/kg) for the expression of CD4(+) and CD8(+) T-cell subsets at different time points. Results indicated that co-administration of Re significantly enhanced serum antibody titers, increased the CD4(+):CD8(+) ratio, and enhanced both proliferation responses and IL-4, IL-10, IL-12 and IFN-γ secretions. Both Th1 and Th2 immune responses were activated. The supplementation of the Re (5.00mg/kg) to 20μl of RV significantly amplified serum antibody responses and Th1/Th2 responses inducing similar protection as did 100μl of RV. This suggests that Re could be used to reduce the dose, and therefore the cost, of the RV to achieve the same effective protection. Re merits further studies for use with vaccines of mixed Th1/Th2 immune responses.

Survival of rabid rabbits after intrathecal immunization

Rabies is a fatal zoonotic disease for which no effective treatment measures are currently available. Rabies virus (RABV) has anti-apoptotic and anti-inflammatory properties that suppress nerve cell damage and inflammation in the CNS. These features imply that the elimination of RABV from the CNS by appropriate treatment could lead to complete recovery from rabies. Ten rabbits showing neuromuscular symptoms of rabies after subcutaneous (SC) immunization using commercially available vaccine containing inactivated whole RABV particles and subsequent fixed RABV (CVS strain) inoculation into hind limb muscles were allocated into three groups. Three rabbits received no further treatment (the SC group), three rabbits received three additional SC immunizations using the same vaccine, and four rabbits received three intrathecal (IT) immunizations, in which the vaccine was inoculated directly into the cerebrospinal fluid (the SC/IT group). An additional three naïve rabbits were inoculated intramuscularly with RABV and not vaccinated. The rabbits exhibited neuromuscular symptoms of rabies within 4-8 days post-inoculation (dpi) of RABV. All of the rabbits died within 8-12 dpi with the exception of one rabbit in the SC group and all four rabbits in SC/IT group, which recovered and started to respond to external stimuli at 11-18 dpi and survived until the end of the experimental period. RABV was eliminated from the CNS of the surviving rabbits. We report here a possible, although still incomplete, therapy for rabies using IT immunization. Our protocol may rescue the life of rabid patients and prompt the future development of novel therapies against rabies.

Immunogenicity of a reduced-dose whole killed rabies vaccine is significantly enhanced by ISCOMATRIX™ adjuvant, Merck amorphous aluminum hydroxylphosphate sulfate (MAA) or a synthetic TLR9 agonist in rhesus macaques

There is a need for novel rabies vaccines suitable for short course, pre- and post-exposure prophylactic regimens which require reduced doses of antigen to address the current worldwide supply issue. We evaluated in rhesus macaques the immunogenicity of a quarter-dose of a standard rabies vaccine formulated with Merck's amorphous aluminum hydroxylphosphate sulfate adjuvant, the saponin-based ISCOMATRIX™ adjuvant, or a synthetic TLR9 agonist. All adjuvants significantly increased the magnitude and durability of the humoral immune response as measured by rapid fluorescent focus inhibition test (RFFIT). Several three-dose vaccine regimens resulted in adequate neutralizing antibody of ≥ 0.5 IU/ml earlier than the critical day seven post the first dose. Rabies vaccine with ISCOMATRIX™ adjuvant given at days 0 and 3 resulted in neutralizing antibody titers which developed faster and were up to one log10 higher compared to WHO-recommended intramuscular and intradermal regimens and furthermore, passive administration of human rabies immunoglobulin did not interfere with immunogenicity of this reduced dose, short course vaccine regimen. Adjuvantation of whole-killed rabies vaccine for intramuscular injection may therefore be a viable alternative to intradermal application of non-adjuvanted vaccine for both pre- and post-exposure regimens.

Reinvestigating the role of IgM in rabies virus postexposure vaccination

B cells secreting IgG antibodies, but not IgM, are thought to be solely responsible for vaccine-induced protection against rabies virus (RABV) infections in postexposure settings. In this report, we reinvestigated the potential for IgM to mediate protection in a mouse model of RABV vaccination. Immunocompetent mice immunized with an experimental live replication-deficient RABV-based vaccine produced virus neutralizing antibodies (VNAs) within 3 days of vaccination. However, mice unable to produce soluble IgM (sIgM(-/-)) did not produce VNAs until 7 days postimmunization. Furthermore, sIgM(-/-) mice were not protected against RABV infection when challenged 3 days postimmunization, while all wild-type mice survived challenge. Consistent with the lack of protection against pathogenic RABV challenge, approximately 50- to 100-fold higher viral loads of challenge virus were detected in the muscle, spinal cord, and brain of immunized sIgM(-/-) mice compared to control mice. In addition, IgG antibody titers in vaccinated wild-type and sIgM(-/-) mice were similar at all time points postimmunization, suggesting that protection against RABV challenge is due to the direct effects of IgM and not the influence of IgM on the development of effective IgG antibody titers. In all, early vaccine-induced IgM can limit dissemination of pathogenic RABV to the central nervous system and mediate protection against pathogenic RABV challenge. Considering the importance for the rapid induction of VNAs to protect against RABV infections in postexposure prophylaxis settings, these findings may help guide the development of a single-dose human rabies vaccine.

B cell infection and activation by rabies virus-based vaccines

Replication-deficient rabies viruses (RABV) are promising rabies postexposure vaccines due to their prompt and potent stimulation of protective virus neutralizing antibody titers, which are produced in mice by both T-dependent and T-independent mechanisms. To promote such early and robust B cell stimulation, we hypothesized that live RABV-based vaccines directly infect B cells, thereby activating a large pool of antigen-presenting cells (APCs) capable of providing early priming and costimulation to CD4(+) T cells. In this report, we show that live RABV-based vaccine vectors efficiently infect naive primary murine and human B cells ex vivo. Infection of B cells resulted in the significant upregulation of early markers of B cell activation and antigen presentation, including CD69, major histocompatibility complex class II (MHC-II), and CD40 in murine B cells or HLA-DR and CD40 in human B cells compared to mock-infected cells or cells treated with an inactivated RABV-based vaccine. Furthermore, primary B cells infected with a live RABV expressing ovalbumin were able to prime and stimulate naive CD4(+) OT-II T cells to proliferate and to secrete interleukin-2 (IL-2), demonstrating a functional consequence of B cell infection and activation by live RABV-based vaccine vectors. We propose that this direct B cell stimulation by live RABV-based vaccines is a potential mechanism underlying their induction of early protective T cell-dependent B cell responses, and that designing live RABV-based vaccines to infect and activate B cells represents a promising strategy to develop a single-dose postexposure rabies vaccine where the generation of early protective antibody titers is critical.

Differential chemokine responses in the murine brain following lyssavirus infection

The hallmark of lyssavirus infection is lethal encephalomyelitis. Previous studies have reported distinct lyssavirus isolate-related differences in severity of cellular recruitment into the encephalon in a murine model of infection following peripheral inoculation with rabies virus (RABV) and European bat lyssavirus (EBLV)-1 and -2. In order to understand the role of chemokines in this process, comparative studies of the chemokine pattern, distribution and production in response to infection with these lyssaviruses were undertaken. Expression of CCL2, CCL5 and CXCL10 was observed throughout the murine brain with a distinct caudal bias in distribution, similar to both inflammatory changes and virus antigen distribution. CCL2 immunolabelling was localized to neuronal and astroglial populations. CCL5 immunolabelling was only detected in the astroglia, while CXCL10 labelling, although present in the astroglia, was more prominent in neurons. Isolate-dependent differences in the amount of chemokine immunolabelling in specific brain regions and chemokine production by neurons in vitro were observed, with a greater expression of CCL5 in vivo and CXCL10 production in vitro after EBLV infection. Additionally, strong positive associations between chemokine immunolabelling and perivascular cuffing and, to a lesser extent, virus antigen score were also observed. These differences in chemokine expression may explain the variation in severity of encephalitic changes observed in animals infected with different lyssavirus isolates.

Investigating the role for IL-21 in rabies virus vaccine-induced immunity

Over two-thirds of the world's population lives in regions where rabies is endemic, resulting in over 15 million people receiving multi-dose post-exposure prophylaxis (PEP) and over 55,000 deaths per year globally. A major goal in rabies virus (RABV) research is to develop a single-dose PEP that would simplify vaccination protocols, reduce costs associated with RABV prevention, and save lives. Protection against RABV infections requires virus neutralizing antibodies; however, factors influencing the development of protective RABV-specific B cell responses remain to be elucidated. Here we used a mouse model of IL-21 receptor-deficiency (IL-21R-/-) to characterize the role for IL-21 in RABV vaccine-induced immunity. IL-21R-/- mice immunized with a low dose of a live recombinant RABV-based vaccine (rRABV) produced only low levels of primary or secondary anti-RABV antibody response while wild-type mice developed potent anti-RABV antibodies. Furthermore, IL-21R-/- mice immunized with low-dose rRABV were only minimally protected against pathogenic RABV challenge, while all wild-type mice survived challenge, indicating that IL-21R signaling is required for antibody production in response to low-dose RABV-based vaccination. IL-21R-/- mice immunized with a higher dose of vaccine produced suboptimal anti-RABV primary antibody responses, but showed potent secondary antibodies and protection similar to wild-type mice upon challenge with pathogenic RABV, indicating that IL-21 is dispensable for secondary antibody responses to live RABV-based vaccines when a primary response develops. Furthermore, we show that IL-21 is dispensable for the generation of Tfh cells and memory B cells in the draining lymph nodes of immunized mice but is required for the detection of optimal GC B cells or plasma cells in the lymph node or bone marrow, respectively, in a vaccine dose-dependent manner. Collectively, our preliminary data show that IL-21 is critical for the development of optimal vaccine-induced primary but not secondary antibody responses against RABV infections.

A new rabies vaccine based on a recombinant ORF virus (parapoxvirus) expressing the rabies virus glycoprotein

The present study describes the generation of a new Orf virus (ORFV) recombinant, D1701-V-RabG, expressing the rabies virus (RABV) glycoprotein that is correctly presented on the surface of infected cells without the need of replication or production of infectious recombinant virus. One single immunization with recombinant ORFV can stimulate high RABV-specific virus-neutralizing antibody (VNA) titers in mice, cats, and dogs, representing all nonpermissive hosts for the ORFV vector. The protective immune response against severe lethal challenge infection was analyzed in detail in mice using different dosages, numbers, and routes for immunization with the ORFV recombinant. Long-term levels of VNA could be elicited that remained greater than 0.5 IU per ml serum, indicative for the protective status. Single applications of higher doses (10(7) PFU) can be sufficient to confer complete protection against intracranial (i.c.) challenge, whereas booster immunization was needed for protection by the application of lower dosages. Anamnestic immune responses were achieved by each of the seven tested routes of inoculation, including oral application. Finally, in vivo antibody-mediated depletion of CD4-positive and/or CD8-posititve T cell subpopulations during immunization and/or challenge infection attested the importance of CD4 T cells for the induction of protective immunity by D1701-V-RabG. This report demonstrates another example of the potential of the ORFV vector and also indicates the capability of the new recombinant for vaccination of animals.

Protective vaccine-induced CD4(+) T cell-independent B cell responses against rabies infection

A major goal in rabies virus (RV) research is to develop a single-dose postexposure prophylaxis (PEP) that would simplify vaccination protocols, reduce costs associated with rabies prevention in humans, and save lives. Live replication-deficient RV-based vaccines are emerging as promising single-dose vaccines to replace currently licensed inactivated RV-based vaccines. Nonetheless, little is known about how effective B cells develop in response to live RV-based vaccination. Understanding this fundamental property of rabies immunology may help in developing a single-dose RV vaccine. Typically, vaccines induce B cells secreting high-affinity, class-switched antibodies during germinal center (GC) reactions; however, there is a lag time between vaccination and the generation of GC B cells. In this report, we show that RV-specific antibodies are detected in mice immunized with live but not inactivated RV-based vaccines before B cells displaying a GC B cell phenotype (B220(+)GL7(hi)CD95(hi)) are formed, indicating a potential role for T cell-independent and early extrafollicular T cell-dependent antibody responses in the protection against RV infection. Using two mouse models of CD4(+) T cell deficiency, we show that B cells secreting virus-neutralizing antibodies (VNAs) are induced via T cell-independent mechanisms within 4 days postimmunization with a replication-deficient RV-based vaccine. Importantly, mice that are completely devoid of T cells (B6.129P2-Tcrβ(tm1Mom) Tcrδ(tm1Mom)/J) show protection against pathogenic challenge shortly after immunization with a live replication-deficient RV-based vaccine. We show that vaccines that can exploit early pathways of B cell activation and development may hold the key for the development of a single-dose RV vaccine wherein the rapid induction of VNA is critical.

Experimental rabies vaccines for humans

Rabies remains a global public health threat that kills more than 55,000 people per year. Rabies disproportionately affects children and, therefore, is ranked the seventh most important infectious disease due to years lost. Prevention of human rabies is accomplished by controlling rabies in domestic and wild animals, including the use of vaccination programs. The usefulness of human rabies vaccines is hampered by high cost, complicated vaccination regimens and lack of compliance, especially in areas of Africa and Asia where human rabies infections are endemic. A single-dose vaccine would greatly benefit efforts to combat this global health threat. However, a single-dose vaccine based on current inactivated vaccines does not appear feasible and other approaches are needed. Technology has advanced since modern human rabies vaccines were developed over 40 years ago. In addition, our understanding of immunological principles that influence the outcome of vaccination has increased. This article describes the current status of inactivated rabies virus vaccines and recent developments arising from the use of reverse genetics technologies designed to develop replication-deficient or single-cycle live rabies virus-based vectors for use as a single-dose rabies vaccine for humans.

Development in Immunoprophylaxis against Rabies for Animals and Humans

Rabies is a fatal neurological disease and a persistent global problem. It is spread primarily by domestic dogs but other canid, viverrid (skunks and raccoons) and chiropteran species are considered as the most efficient vectors of the disease. Since dogs are the main perpetuator of rabies, special attention has to be given to bring all the dogs including unauthorized stray dogs under immunization umbrella in order to control rabies. Vaccination is the only way to combat the disease before and after exposure or infection as there is no treatment available once the symptoms have appeared. After the first crude nerve tissue vaccine developed by Pasteur in 1885, a number of rabies vaccines for animal and human use have been developed with varying degree of safety and efficacy over the years. Presently, cell culture based inactivated rabies vaccines are largely used in most of the parts of the world. However, these vaccines are too expensive and unaffordable for vaccination of people and animals in developing countries. The comparatively cheaper inactivated nerve tissues vaccines can cause serious side-effects such as autoimmune encephalomyelitis in inoculated animals and production has been discontinued in several countries. Although attenuated live vaccines can efficiently elicit a protective immune response with a smaller amount of virus, they sometimes can cause rabies in the inoculated animals by its residual virulence or pathogenic mutation during viral propagation in the body. New-generation rabies vaccines generated by gene manipulation although in experimental stage may be a suitable alternative to overcome the disadvantages of the live attenuated vaccines. So, awareness must be created in general public about the disease and the cell culture based vaccines available in the market should be recommended for wide scale use to prevent and control this emerging and reemerging infectious disease in foreseeable future.

Comparative pathological study of the murine brain after experimental infection with classical rabies virus and European bat lyssaviruses

European bat lyssaviruses (EBLVs) types 1 (EBLV-1) and 2 (EBLV-2) cause rabies in terrestrial species, but the pathological changes associated with neuroinvasion have yet to be fully elucidated. Swiss OF-1 mice were inoculated peripherally with strain RV61 (classical rabies virus), RV1423 (EBLV-1) or RV1332 (EBLV-2) to compare the nature and extent of histopathological changes produced. Inoculated animals developed varying degrees of non-suppurative encephalitis, and lyssavirus infection was confirmed by the detection of viral antigen. The lesions produced, which included perivascular cuffs and gliosis, were more severe after RV1423 or RV1332 infection than after RV61 infection. Perivascular cuffs were mainly localized to caudal brain regions, irrespective of the infecting strain; after RV1332 infection, however, they were particularly abundant, being composed of large numbers of inflammatory cells. T cells were the predominant lymphocytic component of the inflammatory infiltrate in both the Virchow-Robin space and the brain parenchyma. Viral antigen, which was widespread throughout the brain, was apparently unrelated to the degree of cuffing. The study suggested that there was increased immune activation after inoculation with strain RV1423 or RV1332, particularly the latter, but that this did not affect the final outcome.

Cross-protective and cross-reactive immune responses to recombinant vaccinia viruses expressing full-length lyssavirus glycoprotein genes

Lyssaviruses cause acute, progressive encephalitis in mammals. Current rabies vaccines offer protection against the lyssaviruses, with the notable exceptions of Mokola virus (MOKV), Lagos bat virus (LBV) and West Caucasian bat virus (WCBV). Here we describe the cross-protective and cross-reactive immune responses induced by experimental recombinant vaccinia viruses encoding the glycoprotein genes of rabies virus (RABV), MOKV and WCBV, either singly or in dual combinations. Constructs expressing a single glycoprotein gene protected mice against lethal intracranial challenge with homologous virus. Similarly, recombinants expressing glycoprotein genes from two different lyssaviruses offered mice protection against both homologous viruses. VNAb induced by vaccines that included a MOKV glycoprotein gene cross-neutralized LBV, but not WCBV. We concluded that a single recombinant poxvirus-vectored vaccine including MOKV and RABV glycoprotein genes, should be a major addition to available rabies biologics and should offer broad protection against all of the lyssaviruses, except WCBV.

CD8 T cells require gamma interferon to clear borna disease virus from the brain and prevent immune system-mediated neuronal damage

Borna disease virus (BDV) frequently causes meningoencephalitis and fatal neurological disease in young but not old mice of strain MRL. Disease does not result from the virus-induced destruction of infected neurons. Rather, it is mediated by H-2(k)-restricted antiviral CD8 T cells that recognize a peptide derived from the BDV nucleoprotein N. Persistent BDV infection in mice is not spontaneously cleared. We report here that N-specific vaccination can protect wild-type MRL mice but not mutant MRL mice lacking gamma interferon (IFN-gamma) from persistent infection with BDV. Furthermore, we observed a significant degree of resistance of old MRL mice to persistent BDV infection that depended on the presence of CD8 T cells. We found that virus initially infected hippocampal neurons around 2 weeks after intracerebral infection but was eventually cleared in most wild-type MRL mice. Unexpectedly, young as well as old IFN-gamma-deficient MRL mice were completely susceptible to infection with BDV. Moreover, neurons in the CA1 region of the hippocampus were severely damaged in most diseased IFN-gamma-deficient mice but not in wild-type mice. Furthermore, large numbers of eosinophils were present in the inflamed brains of IFN-gamma-deficient mice but not in those of wild-type mice, presumably because of increased intracerebral synthesis of interleukin-13 and the chemokines CCL1 and CCL11, which can attract eosinophils. These results demonstrate that IFN-gamma plays a central role in host resistance against infection of the central nervous system with BDV and in clearance of BDV from neurons. They further indicate that IFN-gamma may function as a neuroprotective factor that can limit the loss of neurons in the course of antiviral immune responses in the brain.

Enhanced humoral HIV-1-specific immune responses generated from recombinant rhabdoviral-based vaccine vectors co-expressing HIV-1 proteins and IL-2

Recombinant rabies virus (RV) vaccine strain-based vectors expressing HIV-1 antigens have been shown to induce strong and long-lasting cellular but modest humoral responses against the expressed antigens in mice. However, an effective vaccine against HIV-1 may require stronger responses, and the development of such an immune response may depend on the presence of certain cytokines at the time of the inoculation. Here, we describe several new RV-based vaccine vehicles expressing HIV-1 Gag or envelope (Env) and murine IL-2 or IL-4. Cells infected with recombinant RVs expressed high levels of functional IL-2 or IL-4 in culture supernatants in addition to HIV-1 proteins. The recombinant RV expressing IL-4 was highly attenuated in a cytokine-independent manner, indicating that the insertion of two foreign genes into the RV genome is mainly responsible for the attenuation observed. The expression of IL-4 resulted in a decrease in the cellular immune response against HIV-1 Gag and Env when compared with the parental virus not expressing IL-4 and only 2 of 20 mice seroconverted to HIV-1 Env after two inoculations. The IL-2-expressing RV was completely apathogenic after direct intracranial inoculation of mice. In addition, mice immunized with IL-2 maintained strong anti-HIV-1 Gag and Env cellular responses and consistently induced seroconversion against HIV-1 Env after two inoculations. This suggests the potential use of IL-2 in RV-based HIV-1 vaccine strategies, which may require the induction of both arms of the immune response.

Live vaccinia-rabies virus recombinants, but not an inactivated rabies virus cell culture vaccine, protect B-lymphocyte-deficient A/WySnJ mice against rabies: considerations of recombinant defective poxviruses for rabies immunization of immunocompromised individuals

Presently, commercially available cell culture rabies vaccines for humans and animals consist of the five inactivated rabies virus proteins. The vaccines elicit a CD4+ helper T-cell response and a humoral B-cell response against the viral glycoprotein (G) resulting in the production of virus neutralizing antibody. Antibody against the viral nucleoprotein (N) is also present, but the mechanism(s) of its protection is unclear. HIV-infected individuals with low CD4+ T-lymphocyte counts and individuals undergoing treatment with immunosuppressive drugs have an impaired neutralizing antibody response after pre- and post-exposure immunization with rabies cell culture vaccines. Here we show the efficacy of live vaccinia-rabies virus recombinants, but not a cell culture vaccine consisting of inactivated rabies virus, to elicit elevated levels of neutralizing antibody in B-lymphocyte deficient A/WySnJ mice. The cell culture vaccine also failed to protect the mice, whereas a single immunization of a vaccinia recombinant expressing the rabies virus G or co-expressing G and N equally protected the mice up to 18 months after vaccination. The data suggest that recombinant poxviruses expressing the rabies virus G, in particular replication defective poxviruses such as canarypox or MVA vaccinia virus that undergo abortive replication in non-avian cells, or the attenuated vaccinia virus NYVAC, should be evaluated as rabies vaccines in immunocompromised individuals.

Region at amino acids 164 to 303 of the rabies virus glycoprotein plays an important role in pathogenicity for adult mice

The authors have previously reported that the glycoprotein of the pathogenic Nishigahara strain of rabies virus is required to lethality for adult mice. A cluster region of amino acid substitutions exists at the positions 164 to 303 on the glycoprotein between avirulent and virulent strains. In this study, the authors generated a chimeric strain having the region at the positions 164 to 303 of the glycoprotein derived from the pathogenic Nishigahara strain in the genetic background of the avirulent RC-HL strain. The chimeric R(G 164-303) strain restores the lethality for adult mice. This result clearly shows that the region at the position 164 to 303 of glycoprotein plays an important role in the lethality for adult mice. Moreover, the authors observed that the lethality for adult mice correlated well with the viral growth in a brain but not with the pH-dependent fusion activity in vitro.

Immune responses to RNA-virus infections of the CNS

A successful outcome for the host of virus infection of the central nervous system (CNS) requires the elimination of the virus without damage to essential non-renewable cells, such as neurons. As a result, inflammatory responses must be tightly controlled, and many unique mechanisms seem to contribute to this control. In addition to being important causes of human disease, RNA viruses that infect the CNS provide useful models in which to study immune responses in the CNS. Recent work has shown the importance of innate immune responses in the CNS in controlling virus infection. And advances have been made in assessing the relative roles of cytotoxic T cells, antibodies and cytokines in the clearance of viruses from neurons, glial cells and meningeal cells.

Rabies: recent developments

Rabies remains as one of the most feared zoonotic diseases in the world. All warm-blooded animals are susceptible to infection by the virus, but the main vectors of human infection are dogs and cats. The control of rabies largely depends on the prevention of infection of dogs and cats by vaccination in endemic areas and the control of their movement, including measures of quarantine and vaccination, in rabies-free countries. This paper provides an overview on recent developments in rabies, with particular emphasis on the epidemiology, pathogenesis, diagnosis, and control.

Rabies DNA vaccination of non-human primates: post-exposure studies using gene gun methodology that accelerates induction of neutralizing antibody and enhances neutralizing antibody titers

Pre-exposure DNA vaccination protects non-human primates against rabies virus. Post-exposure protection of monkeys against rabies virus by DNA vaccination has not been attempted. Presumably, post-exposure experiments have not been undertaken because neutralizing antibody is usually slow to be induced after DNA vaccination. In this study, we initially attempted to accelerate the induction of neutralizing antibody by varying the route and site of DNA vaccination and booster frequency. Gene gun (GG) vaccinations above axillary and inguinal lymph nodes or in ear pinnae generated higher levels of neutralizing antibody than intradermal (ID) needle vaccinations in the pinnae. Concurrent GG booster vaccinations above axillary and inguinal lymph nodes and in ear pinnae, 3 days after primary vaccination, accelerated detectable neutralizing antibody. GG booster vaccinations also resulted in higher neutralizing antibody levels and increased the durability of this response. Post-exposure vaccination with DNA or the human diploid cell vaccine (HDCV), in combination with an one-time treatment with human rabies immune globulin (HRIG), protected 50 and 75% of the monkeys, respectively, as compared to 75% mortality of the controls. These data will be useful for the refinement, development, and implementation of future pre- and post-exposure rabies DNA vaccination studies.

One-time gene gun or intramuscular rabies DNA vaccination of non-human primates: comparison of neutralizing antibody responses and protection against rabies virus 1 year after vaccination

We have previously shown that Macaca fascicularis (Cynomologus) monkeys receiving a primary and either one or two booster rabies DNA vaccinations are protected against rabies virus. In this study, we determined whether monkeys that had been vaccinated only once via gene gun or intramuscularly (i.m.) with different concentrations of DNA would be protected against rabies virus challenge. Neutralizing antibody responses were assayed for 1 year before the monkeys were challenged. Neutralizing antibody was detected at least 50 days earlier in gene gun vaccinated as compared to i.m. vaccinated animals. Prior to viral challenge, all (6/6, 100%) gene gun vaccinated animals, but only 3/6 (50%) i.m. vaccinated animals seroconverted. In general, antibody titers of the gene gun vaccinated animals were higher than the titers of the i.m. vaccinated animals. There was no correlation between the concentration of DNA used for vaccination, the neutralizing antibody responses elicited and protection against viral challenge. Seven days after viral challenge, a rapid and strong anamnestic antibody response was elicited in 100% of the gene gun vaccinated monkeys and in four i.m. vaccinated monkeys. Neutralizing antibody remained undetectable in two i.m. vaccinated monkeys. Overall, 60% (3/5) of the gene gun vaccinated animals and 87% (5/6) of the i.m. vaccinated monkeys survived viral challenge. This study is the first, to our knowledge, to show long-term protection of non-human primates against a human viral pathogen using a DNA vaccination protocol that did not include a booster immunization.

Post-exposure DNA vaccination protects mice against rabies virus

Post-exposure anti-rabies vaccination for individuals who have not previously been immunized against rabies includes a cell culture-derived vaccine and a one time injection of rabies immune globulin. Recent studies have shown DNA vaccinations to be highly effective in rabies pre-exposure experiments, but post-exposure protection has not been achieved. This failure is likely due to the slow onset of DNA vaccine induced antibody production. In an attempt to accelerate the onset of the antibody response, we manipulated variables, such as the route of vaccination and booster frequency. Anti-rabies virus antibody was detected 5 days after the initial DNA vaccination. Using this vaccination protocol and a single non-protective dose of anti-rabies immune serum, we questioned whether mice injected 6 h previously with rabies virus would be protected if a DNA vaccine was substituted for the cell culture-derived human diploid cell vaccine (HDCV). The DNA vaccine protected 87% of the mice (P = 0.00005, compared with unvaccinated control mice). Some 75% of mice receiving HDCV were protected (P = 0.00097, compared with unvaccinated control mice). Mice receiving only anti-rabies immune serum were not protected (P > 0.05 compared to unvaccinated control mice). Thus, post-exposure therapy, substituting a DNA vaccine for HDCV, did not compromise protection against rabies virus.

Localization of a passively transferred human recombinant monoclonal antibody to herpes simplex virus glycoprotein D to infected nerve fibers and sensory neurons in vivo

A human recombinant monoclonal antibody to herpes simplex virus (HSV) glycoprotein D labeled with the fluorescent dye Cy5 was administered to mice infected in the cornea with HSV type 1 (HSV-1). The distribution of such antibody in the corneas and trigeminal ganglia of the mice was then investigated by confocal microscopy. The antibody was detected on HSV-infected nerve fibers in the cornea--identified by colocalization with HSV antigens and the neuritic markers neurofilament, GAP-43, synapsin-1, and CNPase--and on the perikarya of sensory neurons in the HSV-1-infected neurons in ipsilateral trigeminal ganglia. Antibodies have been shown to be effective against many neurotropic viruses, often in the absence of obvious cell damage. Observations from experimental HSV infections suggest that antibodies could act in part by interfering with virus expression in the ganglia and/or with axonal spread. The present results provide morphological evidence of the localization of antiviral antibodies at anatomical sites relevant to such putative antibody-mediated protective actions and suggest that viral glycoproteins are accessible to antibodies on infected nerve fibers and sensory neurons.

Fine mapping of the friend retrovirus resistance gene, Rfv3, on mouse chromosome 15

Rfv3 is a host resistance gene that operates through an unknown mechanism to control the development of the virus-neutralizing antibody response required for recovery from infection with Friend retrovirus. The Rfv3 gene was previously mapped to an approximately 20-centimorgan (cM) region of chromosome 15. More refined mapping was not possible, due to a lack of microsatellite markers and leakiness in the Rfv3 phenotype, which prevented definitive phenotyping of individual recombinant mice. In the present study, we overcame these difficulties by taking advantage of seven new microsatellite markers in the Rfv3 region and by using progeny tests to accurately determine the Rfv3 phenotype of recombinant mice. Detailed linkage analysis of relevant crossovers narrowed the location of Rfv3 to a 0.83-cM region. Mapping of closely linked genes in an interspecific backcross panel allowed us to exclude two previous candidate genes, Ly6 and Wnt7b. These studies also showed for the first time that the Hsf1 gene maps to the Rfv3-linked cluster of genes including Il2rb, Il3rb, and Pdgfb. This localization of Rfv3 to a region of less than 1 cM now makes it feasible to attempt the cloning of Rfv3 by physical methods.

Requirement for multiple lymphocyte subsets in protection by a live attenuated vaccine against retroviral infection

Infection by live attenuated retroviruses provides excellent protection from challenge with pathogenic viruses in several animal models, but little is known about which immune effectors are necessary for protection. We examined this using adoptive transfer experiments in the Friend virus mouse model. Transfers of immune spleen cells into naive mice conferred complete protection, and transfers of purified lymphocyte subsets demonstrated that this effect required complex immune responses involving CD4+ and CD8+ T cells and also B cells. In addition, passive immunization experiments demonstrated that antibodies alone reduced virus loads but did not prevent infection. These findings may have implications for retroviral vaccine design in general.

DNA immunization protects nonhuman primates against rabies virus

More than 40,000 people die annually from rabies worldwide. Most of these fatalities occur in developing countries, where rabies is endemic, public health resources are inadequate and there is limited access to preventive treatment. Because of the high cost of vaccines derived from cell culture, many countries still use vaccines produced in sheep, goat or suckling mouse brain. The stability and low cost for mass production of DNA vaccines would make them ideal for use in developing countries. To investigate the potential of DNA vaccines for rabies immunization in humans, we vaccinated Macaca fascicularis (Cynomolgus) monkeys with DNA encoding the glycoprotein of the challenge virus standard rabies virus, or with a human diploid cell vaccine (HDCV). The monkeys then were challenged with a non-passaged rabies virus. DNA or HDCV vaccination elicited comparable primary and anamnestic neutralizing antibody responses. All ten vaccinated monkeys (DNA or HDCV) survived a rabies virus challenge, whereas monkeys vaccinated with only the DNA vector developed rabies. Furthermore, serum samples from DNA- or HDCV-vaccinated monkeys neutralized a global spectrum of rabies virus variants in vitro. This study shows that DNA immunization elicits protective immunity in nonhuman primates against lethal challenge with a human viral pathogen of the central nervous system. Our findings indicate that DNA vaccines may have a promising future in human rabies immunization.

Selective downregulation of Th1 response by Linomide reduces autoimmunity but increases susceptibility to viral infection in BALB/c and SJL mice

Susceptibility to autoimmunity has been associated with polarization of Th1/Th2 balance in immune system towards the Th1-type of reactivity. We report here that orally administered quinoline-3-carboxamide (Linomide) selectively downregulates Th1 response in BALB/c and SJL mice, leading to reduction of autoimmunity in the BALB/c and SJL models of experimental allergic encephalomyelitis (EAE). This was shown by prevention of EAE in Th1 responding SJL mice and partial downregulation of EAE in Th2-prone BALB/c mice. In a BALB/c model of EAE, in which infection with Semliki Forest A7 virus (SFV-A7) is used for enhancement of autoimmunity, clinical signs of EAE were reduced while mortality due to viral infection in the CNS was enhanced. Selective downregulation of the Th1 response by Linomide also rendered initially resistant SJL mice susceptible to SFV-A7 CNS infection. This was shown by immunohistochemical detection of extensive deposits of viral antigen in numerous perivascular foci within the CNS and abolished virus antigen-specific lymphocyte reactivity in Linomide-treated SJL mice. In addition, analysis of spleen cell cytokine mRNA production profile revealed decreased number of IFN-gamma producing cells in both SJL and BALB/c mice, reduced number of IL-12p40 producing cells in SJL and increased number of 12p40 producing cells in BALB/c mice along with slightly increased IL-4 production in both strains of mice. These results indicate that oral treatment with Linomide induces selective downregulation of Th1 reactivity causing reduction of autoimmunity and increased susceptibility to SFV-A7 CNS infection. Selective downregulation of Th1 response is a desired effect in the treatment of autoimmune diseases but our results suggest that the benefits have to be balanced against the possible loss in immunoprotection against pathogens.

Polygenic control of antibody production and correlation with vaccine induced resistance to rabies virus in high and low antibody responder mice

The amplification of "high" (H) and "low" (L) multispecific antibody responses achieved respectively by H and L lines of selection GP represents a valuable tool in the genetic study of host-infection interactions. These lines were obtained by bidirectional selective breeding for high (HGP) or low (LGP) antibody production to natural complex antigens. HGP and LGP parental lines and reciprocal F1 hybrids, as well as their F2 segregants and backcrosses were submitted to immunization and challenge with rabies virus CVS strain. Acquired resistance was 1000-fold higher in HGP than LGP mice, with a dominance effect to low antibody production observed in F1 hybrids. An association between high antibody response and acquired resistance (P < 0.001) in F2 segregant mice was noticed. The genetic study was performed in these several populations, with a single dose of 104.5-fold LD50 CVS. We could demonstrate 3 independent loci regulating the anti-rabies antibody production, that are distinct, at least in part, from the 10 genes controlling the antigen selection response (sheep erythrocytes) of selection GP.

Virus-neutralizing antibodies of immunoglobulin G (IgG) but not of IgM or IgA isotypes can cure influenza virus pneumonia in SCID mice

The ability of monoclonal antibodies (MAbs) to passively cure an influenza virus pneumonia in the absence of endogenous T- and B-cell responses was investigated by treating C.B-17 mice, homozygous for the severe combined immunodeficiency (SCID) mutation, with individual monoclonal antiviral antibodies 1 day after pulmonary infection with influenza virus PR8 [A/PR/8/34 (H1N1)]. Less than 10% of untreated SCID mice survived the infection. By contrast, 100% of infected SCID mice that had been treated with a single intraperitoneal inoculation of at least 175 micrograms of a pool of virus-neutralizing (VN+) antihemagglutinin (anti-HA) MAbs survived, even if antibody treatment was delayed up to 7 days after infection. The use of individual MAbs showed that recovery could be achieved by VN+ anti-HA MAbs of the immunoglobulin G1 (IgG1), IgG2a, IgG2b, and IgG3 isotypes but not by VN+ anti-HA MAbs of the IgA and IgM isotypes, even if the latter were used in a chronic treatment protocol to compensate for their shorter half-lives in vivo. Both IgA and IgM, although ineffective therapeutically, protected against infection when given prophylactically, i.e., before exposure to virus. An Fc gamma-specific effector mechanism was not an absolute requirement for antibody-mediated recovery, as F(ab')2 preparations of IgGs could cure the disease, although with lesser efficacy, than intact IgG. An anti-M2 MAb of the IgG1 isotype, which was VN- but bound well to infected cells and inhibited virus growth in vitro, failed to cure. These observations are consistent with the idea that MAbs of the IgG isotype cure the disease by neutralizing all progeny virus until all productively infected host cells have died. VN+ MAbs of the IgA and IgM isotypes may be ineffective therapeutically because they do not have sufficient access to all tissue sites in which virus is produced during influenza virus pneumonia.

Suppression of measles virus expression by noncytolytic antibody in an immortalized macrophage cell line

Immune regulation of measles virus (MV) expression was studied in a persistently infected mouse macrophage cell line. Synthesis of both membrane-associated and internal MV antigens was suppressed when infected macrophages were treated with polyclonal rabbit anti-MV antibody that was specific for MV proteins. Persistently infected macrophages were treated for 3, 5, or 7 days with increasing doses of anti-MV antibody. All MV proteins were down-regulated 2 days after treatment was terminated. One week after treatment was terminated, down-regulation was still evident but to a lesser degree. MV protein synthesis was suppressed whether or not complement components were inactivated by heating all serum supplements and antibodies. However, when complement was active, cell lysis accounted for some of the reduced MV protein synthesis. When lytic destruction of infected cells by antibody and complement was prevented by inactivation of complement, antibody alone reduced the cellular synthesis of viral proteins by noncytolytic mechanisms. The absence of cell death in the absence of complement was confirmed by the lack of 51Cr release from labeled cells, the lack of reduction in cell number, and the lack of a decrease in total protein synthesis when radiolabeled infected cells were treated with antibody. It is noteworthy that low doses of antibody were optimal for suppression in the longer-term experiments and did not cause lysis, even in the presence of active complement. Since infected macrophages disseminate virus in measles infection, noncytolytic regulation of these cells by antibody may supplement viral clearance by cytolytic T cells and other immune mechanisms.

CD4+ T cells are essential in overcoming experimental murine measles encephalitis

Clinical observations and experimental animal models have stressed the importance of the cellular immune response in the recovery from measles virus infection. However, the relative contribution of different T-cell subsets to viral elimination is controversial. The aim of the present study was to define the components of the immune system which contribute to the control of measles virus infection. For this purpose the effect of in vivo depletion of CD4+ and/or CD8+ T lymphocytes in the murine model of experimental acute measles encephalitis was monitored with respect to disease manifestation, survival, neuropathological changes, virus elimination from brain, and antiviral antibody titre. In measles virus-resistant BALB/c mice removal of the CD8+ T-cell subset did not interfere with the clearance of virus from the brain. In contrast, depletion of CD4+ T cells rendered BALB/c mice susceptible to infection. Also, in measles virus-susceptible C3H mice CD4+ T cells played a role in recovery from measles infection, but seemed not to be as effective as CD4+ T cells from resistant BALB/c mice. The data indicate that CD4+ T cells are essential for protection against measles virus-infection of the central nervous system.

Neonatal deletion and selective expansion of mouse T cells by exposure to rabies virus nucleocapsid superantigen

The nucleocapsid (NC) of the rabies virus behaves as an exogenous superantigen (SAg) in humans. In the present report, we analyzed whether it is also a SAg in mice by studying the effect of NC on T cell receptor (TCR) V beta expression in BALB/c mice. Repeated injection of NC in newborn BALB/c mice led to a marked reduction by two- to sixfold of V beta 6 expressing CD4+ T cells in spleen and in peripheral blood. Decrease of V beta 6-expressing CD3+ mature T cells was also observed in thymus. Single NC injection in footpad resulted in a three- to sixfold expansion of V beta 6 CD4+ T cells, but not of CD8+ T cells, in the draining lymph nodes of BALB/c mice. The intensity of the stimulation was dose dependent and was maximal 3 d after the NC injection. The clonal deletion of T cells bearing a particular V beta demonstrates that NC is a SAg in mice. T cells, especially CD4+ T cells, are an essential factor in host resistance to rabies virus and also in the pathophysiology of paralysis; thus, we postulate that a rabies virus component, which stimulates T cells, such as a SAg, may increase virus immunopathogenicity. To evaluate this hypothesis, we compared the course of rabies in adult BALB/c lacking V beta 6, 7, 8.1, and 9 T cells and in normal BALB/c. Immune-related paralysis was decreased in BALB/c missing the NC target V beta T cells. Transfer of V beta 6 but not of V beta 8.1-3 T cells into recipient mice lacking V beta 6, 7, 8.1, and 9 allowed the immune-related paralysis to evolve. Taken together, these results strongly support the hypothesis that T cells expressing rabies SAg-specific V beta 6 T cells, are involved in the genesis of the immunopathology that is characteristic of paralytic rabies.

Theiler's virus is eliminated by a gamma-interferon-independent mechanism in the brain

The intravenous infection of Theiler's virus GD VII strain causes acute encephalomyelitis in infected mice. To determine the cellular mechanism of resistance and interferon (IFN)-gamma-producing cell populations, mononuclear cells isolated from tissues of the brain were analyzed by the flow cytometry method. Antibodies specific for CD3, CD4, CD8, T cell receptor (TCR)-alpha beta, and Asialo GM1 were used to deplete the corresponding cell populations in Theiler's virus-infected mice. CD4+ lymphocytes and CD8+ lymphocytes infiltrated in the brains of infected mice from 5 days postinfection (p.i.). The number of CD3+/TCR-gamma delta+ lymphocytes increased in the brains on Day 6 p.i. The elimination of CD3+ lymphocytes or CD4+ lymphocytes augmented viral replication and suppressed the production of IFN-gamma. The suppression of IFN-gamma production by anti-CD3 monoclonal antibody (mAb) persisted, although the suppression by anti-CD4 mAb was observed only on Day 6 p.i. The depletion of CD8+ lymphocytes as well as TCR-alpha beta+ lymphocytes also augmented the viral replication; however, it did not alter the production of IFN-gamma. Anti-Asialo GM1 antibody had no effect on viral replication and IFN-gamma production. These results indicate that T lymphocytes are important for eliminating Theiler's virus from the brain, CD3+/CD4+/CD8- lymphocytes and CD3+/TCR alpha beta-/CD4-/CD8- lymphocytes would produce IFN-gamma in brain. However, from the result on the experiment of the depletion of TCR-alpha beta+ lymphocytes, the defence mechanisms by T lymphocytes against Theiler's virus would be independent of endogenous IFN-gamma production.

Central neuropathogenesis of vesicular stomatitis virus infection of immunodeficient mice

To determine whether central neuropathogenesis associated with vesicular stomatitis virus (VSV) infection is regulated by T cells, we have examined the effects of intranasal infection of mice lacking T cells. The mice examined were of two kinds: (i) thymus-deficient BALB/c nu/nu nice and (ii) BALB/c mice experimentally depleted of T cells by systemic infusions of a monoclonal antibody to the CD4 or CD8 cell surface molecules. These mice were infected intranasally with a single dose of replication-competent VSV. Brain tissue homogenates were analyzed for the presence of infectious virus. For each population of mice, infection-related mortality was assessed. In histological sections of brain, the distribution of viral antigens (Ags) was examined by immunocytochemistry. We found that recovery of infectious virus from homogenates of tissues obtained from athymic nu/nu animals was more than 10 times greater than that from samples from their euthymic littermates. With a single exception in a BALB/c nu/nu mouse, virus was not isolated from the spleen when it was administered intranasally. In these experimental infections, athymic mice succumbed 1 to 2 days before their euthymic littermates. A dose of virus that resulted in half of the nu/+ survival rate was uniformly lethal to nu/nu mice. In experiments with BALB/c mice depleted of either CD4+ or CD8+ T cells by in vivo antibody treatment, histological analysis revealed an increase in viral Ag distribution in comparison with control (medium-infused) infected mice. Necrosis and inflammation paralleled the extent of viral Ag expression. Viral Ags were detected in discrete areas that usually remain uninfected in immunocompetent mice. These areas include the neocortex and caudate putamen nuclei, the piriform cortex, and the lateral olfactory tract. Neuronal loss and necrosis were consistently found in the olfactory bulb and the horizontal/vertical band of Broca. In some of the T-cell depleted mice, necrosis was also evident in the hippocampus, fimbria, mammillary bodies, and hypothalamic nuclei. In the brain stem, perivascular cuffing was evident, but with little necrosis. Collectively, these data suggest that CD4+ and CD8+ T cells make only a minor contribution to the development of histopathology but rather function together to limit viral replication and transsynaptic or ventricular spread of virus, thus promoting recovery. The primary effectors of histopathology appear to be related more to the cytopathologic nature of the virus infection and non-T-cell-mediated mechanisms.

In vivo role of lymphocyte subpopulations in the control of virus excretion and mucosal antibody responses of cattle infected with rotavirus

T-cell control of primary rotavirus infection and mucosal antibody responses to rotavirus was studied with monoclonal antibodies (MAb) to deplete gnotobiotic calves of CD4+, CD8+, BoWC1+, or both CD4+ and CD8+ lymphocytes prior to infection with rotavirus. Injection of these MAb produced specific reductions in circulating and tissue lymphocyte subpopulations. Following infection, control calves developed fecal immunoglobulin M (IgM) and IgA antibodies and serum IgM and IgG1 antibodies; there was no IgG2 antibody produced. Anti-CD4-treated calves had reduced fecal and serum antibody responses to rotavirus compared with control calves. The IgM response was less affected than the other isotypes. Calves concurrently injected with MAb to CD4 and CD8 had antibody responses similar to those of calves injected with anti-CD4 antibody alone. No effect on serum or fecal antibody levels was seen when MAb to CD8 or BoWC1 were injected alone. Virus excretion was significantly increased in calves depleted of CD8+ cells. Depletion of CD4+ cells or BoWC1+ cells had no effect on virus excretion. Calves depleted of both CD4+ and CD8+ cells excreted amounts of virus similar to those of calves depleted of CD8+ cells alone. Onset and duration of virus excretion were not affected by any of the MAb treatments. We conclude that a CD8+ cell population is involved in limiting primary rotavirus infection, while CD4+ or BoWC1+ (gamma/delta+ TcR) lymphocytes are not. Furthermore, CD4+ lymphocytes (but not CD8+ or BoWC1+ lymphocytes) were shown to be important in the generation of mucosal, as well as systemic, antibody responses.

Rabies virus neuritic paralysis: immunopathogenesis of nonfatal paralytic rabies

Two pathogenetically distinct disease manifestations are distinguished in a murine model of primary rabies virus infection with the Evelyn-Rokitnicky-Abelseth strain, rabies virus neuritic paralysis (RVNP) and fatal encephalopathogenic rabies. RVNP develops with high incidence in immunocompetent mice after intraplantar infection as a flaccid paralysis restricted to the infected limb. The histopathologic correlate of this monoplegia is a degeneration of the myelinated motor neurons of the peripheral nerve involved. While, in this model, fatal encephalopathogenic rabies develops only after depletion of the CD4 subset of T lymphocytes and without contribution of the CD8 subset, RVNP is identified as an immunopathological process in which both the CD4 and CD8 subsets of T lymphocytes are critically implicated.