Pathophysiology of rabies virus infection of the nervous system

Differential pathogenesis of intracerebral and intramuscular inoculation of street rabies virus and CVS-11 strains in a mouse model

Objective(s):

The mechanisms of rabies evasion and immunological interactions with the host defense have not been completely elucidated. Here, we evaluated the dynamic changes in the number of astrocytes, microglial and neuronal cells in the brain following intramuscular (IM) and intracerebral (IC) inoculations of street rabies virus (SRV).

Materials and Methods:

The SRV isolated from a jackal and CVS-11 were used to establish infection in NMRI-female mice. The number of astrocytes (by expression of GFAP), microglial (by Iba1), and neuronal cells (by MAP-2) in the brain following IM and IC inoculations of SRV were evaluated by immunohistochemistry and H & E staining 7 to 30 days post-infection.

Results:

Increased numbers of astrocytes and microglial cells in dead mice infected by SRV via both IC and IM routes were recorded. The number of neuronal cells in surviving mice was decreased only in IC-infected mice, while in the dead group, this number was decreased by both routes.

The risk of death in SRV-infected mice was approximately 3 times higher than in the CVS-11 group. In IC-inoculated mice, viral dilution was the only influential factor in mortality, while the type of strain demonstrated a significant impact on the mortality rate in IM inoculations.

Conclusion:

Our results suggested that microglial cells and their inflammatory cytokines may not contribute to the neuroprotection and recovery in surviving mice following intracerebral inoculation of SRV. An unexpected decrease in MAP2 expression via intramuscular inoculation indicates the imbalance in the integrity and stability of neuronal cytoskeleton which aggravates rabies infection.

Lentiviral Expression of Rabies Virus Glycoprotein in the Rat Hippocampus Strengthens Synaptic Plasticity

Rabies virus (RABV) is a neurotropic virus exclusively infecting neurons in the central nervous system. RABV encodes five proteins. Among them, the viral glycoprotein (RVG) plays a key role in viral entry into neurons and rabies pathogenesis. It was shown that the nature of the C-terminus of the RABV G protein, which possesses a PDZ-binding motif (PBM), modulates the virulence of the RABV strain. The neuronal protein partners recruited by this PBM may alter host cell function. This study was conducted to investigate the effect of RVG on synaptic function in the hippocampal dentate gyrus (DG) of rat. Two μl (10⁸ T.U./ml) of the lentiviral vector containing RVG gene was injected into the DG of rat hippocampus. After 2 weeks, the rat's brain was cross-sectioned and RVG-expressing cells were detected by fluorescent microscopy. Hippocampal synaptic activity of the infected rats was then examined by recording the local field potentials from DG after stimulation of the perforant pathway. Short-term synaptic plasticity was also assessed by double pulse stimulation. Expression of RVG in DG increased long-term potentiation population spikes (LTP-PS), whereas no facilitation of LTP-PS was found in neurons expressing δRVG (deleted PBM). Furthermore, RVG and δRVG strengthened paired-pulse facilitation. Heterosynaptic long-term depression (LTD) in the DG was significantly blocked in RVG-expressing group compared to the control group. This blockade was dependent to PBM motif as rats expressing δRVG in the DG-expressed LTD comparable to the RVG group. Our data demonstrate that RVG expression facilitates both short- and long-term synaptic plasticity in the DG indicating that it may involve both pre- and postsynaptic mechanisms to alter synaptic function. Further studies are needed to elucidate the underlying mechanisms.

Neuroanatomical evidence of the transport of the rabies virus through the propriospinal tract in the spinal cord of mice

Introduction: Information about the neuroanatomical details of the ascendant transport of the rabies virus through the spinal cord is scarce. Objective: To identify the neuroanatomical route of dissemination of the rabies virus at each of the levels of the spinal cord of mice after being inoculated intramuscularly. Materials and methods: Mice were inoculated with the rabies virus in the hamstrings. After 24 hours post-inoculation, every eight hours, five animals were sacrificed by perfusion with paraformaldehyde. Then, the spinal cord was removed, and transverse cuts were made at the lumbosacral, thoracic, and cervical levels. These were processed by immunohistochemistry for the detection of viral antigens. Results: The first antigens of rabies were observed as aggregated particles in the lumbar spinal cord at 24 hours post-inoculation, within the ventral horn in the same side of the inoculated limb. At 32 hours post inoculation the first motoneurons immunoreactive to the virus became visible. At 40 hours postinoculation the first immunoreactive neurons were revealed in the thoracic level, located on lamina 8 and at 48 hours post-inoculation in the cervical cord, also on lamina 8. At 56 hours post-inoculation the virus had spread throughout the spinal cord, but the animals still did not show signs of the disease. Conclusion: In the mouse model we used, the rabies virus entered the spinal cord through the motoneurons and probably used the descending propriospinal pathway for its retrograde axonal transport to the encephalus.

Overexpression of MAP2 and NF-H Associated with Dendritic Pathology in the Spinal Cord of Mice Infected with Rabies Virus

Rabies is a viral infection that targets the nervous system, specifically neurons. The clinical manifestations of the disease are dramatic and their outcome fatal; paradoxically, conventional histopathological descriptions reveal only subtle changes in the affected nervous tissue. Some researchers have considered that the pathophysiology of rabies is based more on biochemical changes than on structural alterations, as is the case with some psychiatric diseases. However, we believe that it has been necessary to resort to other methods that allow us to analyze the effect of the infection on neurons. The Golgi technique is the gold standard for studying the morphology of all the components of a neuron and the cytoskeletal proteins are the structural support of dendrites and axons. We have previously shown, in the mouse cerebral cortex and now with this work in spinal cord, that rabies virus generates remarkable alterations in the morphological pattern of the neurons and that this effect is associated with the increase in the expression of two cytoskeletal proteins (MAP2 and NF-H). It is necessary to deepen the investigation of the pathogenesis of rabies in order to find therapeutic alternatives to a disease to which the World Health Organization classifies as a neglected disease.

Perspectives in Diagnosis and Treatment of Rabies Viral Encephalitis: Insights from Pathogenesis

Rabies viral encephalitis, though one of the oldest recognized infectious disease of humans, remains an incurable, fatal encephalomyelitis, despite advances in understanding of its pathobiology. Advances in science have led us on the trail of the virus in the host, but the sanctuaries in which the virus remains hidden for its survival are unknown. Insights into host-pathogen interactions have facilitated evolving immunologic therapeutic strategies, though we are far from a cure. Most of the present-day knowledge has evolved from in vitro studies using fixed (attenuated) laboratory strains that may not be applicable in the clinical setting. Much remains to be unraveled about this elusive virus. This review attempts to re-examine the current advances in understanding of the pathobiology of the rabies virus that modulate the diagnosis, treatment, and prevention of this fatal disease.

Synaptic Plasticity and Neurological Disorders in Neurotropic Viral Infections

Based on the type of cells or tissues they tend to harbor or attack, many of the viruses are characterized. But, in case of neurotropic viruses, it is not possible to classify them based on their tropism because many of them are not primarily neurotropic. While rabies and poliovirus are considered as strictly neurotropic, other neurotropic viruses involve nervous tissue only secondarily. Since the AIDS pandemic, the interest in neurotropic viral infections has become essential for all clinical neurologists. Although these neurotropic viruses are able to be harbored in or infect the nervous system, not all the neurotropic viruses have been reported to cause disrupted synaptic plasticity and impaired cognitive functions. In this review, we have discussed the neurotropic viruses, which play a major role in altered synaptic plasticity and neurological disorders.

Street rabies virus causes dendritic injury and F-actin depolymerization in the hippocampus

Rabies is an acute viral infection of the central nervous system and is typically fatal in humans and animals; however, its pathogenesis remains poorly understood. In this study, the morphological changes of dendrites and dendritic spines in the CA1 region of the hippocampus were investigated in mice that were infected intracerebrally with an MRV strain of the street rabies virus. Haematoxylin and eosin and fluorescence staining analysis of brain sections from the infected mice showed very few morphological changes in the neuronal bodies and neuronal processes. However, we found a significant decrease in the number of dendritic spines. Primary neuronal cultures derived from the hippocampus of mice (embryonic day 16.5) that were infected with the virus also showed an obvious decrease in the number of dendritic spines. Furthermore, the decrease in the number of dendritic spines was related to the depolymerization of actin filaments (F-actin). We propose that the observed structural changes can partially explain the severe clinical disease that was found in experimental models of street rabies virus infections.

Viruses and the brain: from inflammation to dementia

Many viruses cause encephalitis, but understanding the mechanisms by which viral infection leads to encephalopathy or dementia remain elusive. In many cases, inflammation generated by the host's attempt to combat the infection is itself implicated as a primary factor in causing neuronal dysfunction or degeneration. In this review, we outline the current state of knowledge regarding the pathophysiology of CNS (central nervous system) injury in viral infection. We focus our review on the neuropathogenesis of HIV type 1 (HIV-1)-associated dementia, because, within this class of infection, it is the best studied. We will also discuss the key similarities and differences in the pathological mechanisms of other important viral encephalitides. Understanding these mechanisms should ultimately enable development of immunomodulatory therapies for treating these infections, as well as other neuro-inflammatory conditions.

Difference in neuropathogenetic mechanisms in human furious and paralytic rabies

Whereas paralysis is the hallmark for paralytic rabies, the precise pathological basis of paralysis is not known. It is unclear whether weakness results from involvement of anterior horn cells or of motor nerve fibers. There is also no conclusive data on the cause of the neuropathic pain which occurs at the bitten region, although it has been presumed to be related to sensory ganglionopathy. In this study, six laboratory-proven rabies patients (three paralytic and three furious) were assessed clinically and electrophysiologically. Our data suggests that peripheral nerve dysfunction, most likely demyelination, contributes to the weakness in paralytic rabies. In furious rabies, progressive focal denervation, starting at the bitten segment, was evident even in the absence of demonstrable weakness and the electrophysiologic study suggested anterior horn cell dysfunction. In two paralytic and one furious rabies patients who had severe paresthesias as a prodrome, electrophysiologic studies suggested dorsal root ganglionopathy. Postmortem studies in two paralytic and one furious rabies patients, who had local neuropathic pain, showed severe dorsal root ganglionitis. Intense inflammation of the spinal nerve roots was observed more in paralytic rabies patients. Inflammation was mainly noted in the spinal cord segment corresponding to the bite in all cases; however, central chromatolysis of the anterior horn cells could be demonstrated only in furious rabies patient. We conclude that differential sites of neural involvement and possibly different neuropathogenetic mechanisms may explain the clinical diversity in human rabies.

Cervical spinal cord delivery of a rabies G protein pseudotyped lentiviral vector in the SOD-1 transgenic mouse. Invited submission from the Joint Section Meeting on Disorders of the Spine and Peripheral Nerves, March 2004

OBJECT

Lentiviral vectors may constitute a vehicle for long-term therapeutic gene expression in the spinal cord. In amyotrophic lateral sclerosis, spinal cord sclerosis and altered axonal transport pose barriers to therapeutic gene distribution. In the present study the authors characterize gene expression distribution and the behavioral impact of the rabies G (RabG) protein pseudotyped lentiviral vector EIAV.LacZ through cervical spinal cord injection in control and Cu/Zn superoxide dismutase-1 (SOD-1) transgenic mice.

METHODS

Seven-week-old SOD-1 transgenic mice and their wild-type littermates underwent exposure of the cervicomedullary junction and microinjection of RabG.EIAV.LacZ or vehicle. The Basso-Beattie-Bresnahan locomotor score, grip strength meter, and Rotarod assays were used to assess the effects of disease progression, spinal cord microinjection, and lentiviral gene expression. Spinal cords were removed when the mice were in the terminal stage of the disease. The distribution of LacZ gene expression was histologically evaluated and quantified. Direct cervical spinal cord microinjection of RabG.EIAV.LacZ results in extensive central nervous system uptake in SOD-1 transgenic mice; these findings were statistically similar to those in wild-type mice (p > 0.05). Gene expression lasts for the duration of the animal's survival (132 days). The SOD-1 mutation does not prevent retrograde axonal transport of the vector. Three behavioral assays were used to demonstrate that long-term gene expression does not alter sensorimotor function. In comparison with normative data, vector injection and transgene expression do not accelerate disease progression.

CONCLUSIONS

Direct spinal cord injection of RabG.EIAV vectors represents a feasible method for delivering therapeutic genes to upper cervical spinal cord and brainstem motor neurons. Distribution is not affected by the SOD-1 mutation or disease phenotype.

Rabies and other lyssavirus diseases

The full scale of the global burden of human rabies is unknown, owing to inadequate surveillance of this fatal disease. However, the terror of hydrophobia, a cardinal symptom of rabies encephalitis, is suffered by tens of thousands of people each year. The recent discovery of enzootic European bat lyssavirus infection in the UK is indicative of our expanding awareness of the Lyssavirus genus. The main mammalian vector species vary geographically, so the health problems created by the lyssaviruses and their management differ throughout the world. The methods by which these neurotropic viruses hijack neurophysiological mechanisms while evading immune surveillance is beginning to be unravelled by, for example, studies of molecular motor transport systems. Meanwhile, enormous challenges remain in the control of animal rabies and the provision of accessible, appropriate human prophylaxis worldwide.

Differences in the activation of the GFAP gene promoter by prion and viral infections

The expression of glial fibrillary acidic protein (GFAP), a component of astroglial intermediate filaments, is regulated under developmental and pathological conditions. After surgical injury or viral infections, an increase in this protein reflects reactive gliosis in the brain. We analyzed the activation of the GFAP gene in transgenic mice using a prion and two different viruses (rabies and Theiler viruses). Inoculation of the transgenic mice with the C506M3 mouse prion strain resulted in activation of the GFAP-lacZ transgene. Expression of the GFAP transgene increased concomitantly with the expression of GFAP in astrocytes from the infected mice. In contrast, infection with rabies or Theiler's virus had no effect on the expression of the GFAP transgene, showing that the glial reactions to these infectious agents involved different mechanisms. These findings indicate that the activation of the endogenous GFAP gene as a consequence of viral infection could involve different regulatory pathways than activation as a result of prion infection. The first 2 kb upstream from the start codon of the GFAP gene seems to provide enough activation domains to produce efficient activation of the reporter gene in prion-infected mice.

Human rabies: a disease of complex neuropathogenetic mechanisms and diagnostic challenges

Rabies is inevitably fatal and presents a horrifying clinical picture. Human rabies can manifest in either encephalitic (furious) or paralytic (dumb) forms. The brainstem is preferentially involved in both clinical forms, though there are no clinical signs of brainstem dysfunction. Differences in tropism at the inoculation site or the CNS, in the route of spread, or in the triggering of immune cascades in the brainstem may account for clinical variation. Rabies still poses diagnostic problems, particularly the paralytic form, which closely resembles Guillain-Barré syndrome, or when a patient is comatose and cardinal signs may be lacking. Molecular methods allow reliable detection of rabies-virus RNA in biological fluids or tissue before death. Deviations from the recommendations on prophylaxis of the World Health Organization lead to unnecessary loss of life. To date, attempts to treat human rabies have been unsuccessful.

Early rabies antibody response to intramuscular booster in previously intradermally immunized travelers using human diploid cell rabies vaccine

BACKGROUND

Postexposure treatment (PET) of travelers who may have had a potential rabies exposure is simpler, safer, and cheaper if the traveler is preimmunized. Preimmunization can be done with human diploid cell rabies vaccine (HDCV) administered intramuscularly or intradermally. Some authorities, however, are now advocating that travelers vaccinated by the intradermal (ID) route should be treated as if they are not immunized. A particular concern raised is that travelers who have received pre-exposure rabies vaccination intradermally, may have a delayed response to postexposure boosters. This study is designed to elucidate whether a single intramuscular (IM) HDCV booster will provoke an early (day 5) immune response in individuals given pre-exposure ID HDCV.

METHODS

Twenty-nine travelers who had received a course of three 0.1 mL ID HDCV between 12 and 24 months previously were given a single 1.0 mL IM booster of HDCV. Rabies antibody levels were compared 5 days later to those before the booster.

RESULTS

Twenty-five of the 29 subjects (86%) showed an adequate rise in virus neutralizing antibody (VNA) titer 5 days after booster. Nine of the 29 subjects (31%) had inadequate antibody levels prior to the simulated postexposure booster. Five days after the postexposure booster, 27 of 29 (93%) had adequate antibody levels. The other 2 travelers were subsequently shown to have adequate VNA levels when tested 4 and 6 weeks later, respectively.

CONCLUSION

For travelers who were given pre-exposure ID HDCV vaccination within the last 2 years and received one IM postexposure booster dose of HDCV, most mounted an adequate early immune response. This data does not support a change in current recommendations for rabies PET in this group. Further research to ascertain the duration of protection of pre-exposure ID rabies immunization is required.

Rabies as a transneuronal tracer of circuits in the central nervous system

The ability of selected neurotropic viruses to move transneuronally in the central nervous system makes them particularly well suited for use as tracers in experimental neuroanatomy. Recently, techniques have been developed for using rabies virus as a transneuronal tracer. Several features of rabies infection make the virus particularly useful for this purpose. We examined transneuronal transport of rabies in the central nervous system of primates after intracortical and intramuscular injections. Rabies was transported in a time-dependent manner to infect synaptically-connected chains of neurons. Transport occurred exclusively in the retrograde direction. At the survival times we used, rabies infection was restricted to neurons and did not cause cell lysis. There are several methodological and safety issues that must be considered when designing studies that use rabies as a transneuronal tracer. When appropriate protocols and laboratory practices have been established, transneuronal transport of rabies can be a safe and efficient tool for revealing the organization of multi-synaptic circuits in the central nervous system.

Modification of membrane currents in mouse neuroblastoma cells following infection with rabies virus

1. The effect on membrane currents of infection of mouse neuroblastoma NA cells with rabies virus was studied by using the whole-cell patch clamp technique. 2. Three types of membrane currents, namely voltage-dependent Na+ current (I(Na)), delayed rectifier K+ current (I(K-DR)) and inward rectifier K+ current (I(K-IR)) were elicited in uninfected cells. 3. In cells 3 days after infection with the virus, no detectable change was observed in morphology and membrane capacitance, but I(Na) and I(K-IR) were significantly decreased in amplitude without any appreciable difference in the time course of current activation and inactivation. The voltage-dependence of I(Na) activation was significantly shifted in the positive direction along the voltage axis with a decreased slope. I(K-DR) remained almost unaltered after the viral infection. 4. The resting membrane potential, measured with a physiological K+ gradient across the cell membrane, was decreased (depolarized) after the viral infection. The depolarization was associated with the decreased amplitude of I(K-IR). 5. These results suggest that infection of mouse neuroblastoma NA cells with rabies virus causes reduction of functional expression of ion channels responsible for I(Na) and I(K-IR), and provide evidence for possible involvement of the change in membrane properties in the pathogenesis of rabies disease.

Rabies virus infection of cultured adult mouse dorsal root ganglion neurons

An in vitro model of adult dorsal root ganglion neurons infection by rabies virus is described, Viral marked neurotropism is observed, and the percentage and the degree of infection of the neurons is higher than in non neuronal cells, even if neurons are the minority of the cells in the culture. The neuritic tree is also heavily infected by the virus.

Induction of immunoreactive interleukin-1 beta and tumor necrosis factor-alpha in the brains of rabies virus infected rats

Interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF alpha) are important cytokines in the development of brain inflammation during pathological process. During rabies virus infection, the level of these proinflammatory cytokines are enhanced in the brain. In the present study we determined the cellular localization of these two cytokines by immunocytochemistry in brains of rats infected with rabies virus, at different time-intervals of the disease (day 1, 3, 4, 5 and at final stage day 6 post-infection (p.i.)). Cellular identification of IL-1 beta (irIL-1 beta) and TNF alpha (irTNF alpha) immunopositive cells was studied using a polyclonal antibody against these cytokines and against glial fibrillary acidic protein (GFAP) to detect astrocytes and GSA-I-B4 isolectin to detect microglial cells and/or infiltrating macrophages. In brains of control and early infected rats, irIL-1 beta was only detected in fibers located in the hypothalamus, supraoptic and tractus optic nuclei and infundibular nucleus. From day 4 onwards until day 6 p.i., enhanced irIL-1 beta was found and identified either in activated ameboid and/or infiltrated macrophages (amygdala, thalamus, internal capsula, subtantia nigra, septal nuclei and around blood vessels), or in activated ramified cells (hypothalamus and periventricular nucleus, piriformis and cingulate cortex, hippocampus). IrTNF alpha was observed in the brains of rats at a final stage of disease (day 5 and 6 p.i.): in the hypothalamus, the amygdala, the internal capsula, the thalamus, the septal nuclei, the hippocampus, the habenular nuclei and around the blood vessels. Ir-TNF alpha was detected in round cells identified as ameboid microglia and/or infiltrated macrophages. A marked activation of microglial and astroglial cells was observed mainly in the hypothalamus, the thalamus and hippocampus and around the blood vessels, at day 4 p.i. and later, revealing a high central inflammatory reaction in brains of rabies virus infected rats. These results showed that IL-1 beta and TNF alpha are produced in the brain both by local microglial cells and infiltrating macrophages during rabies infection. Thus, these cytokines may play an important role in coordinating the dramatic inflammatory response associated with the rabies-encephalopathy as well as in the neural modification and alteration of brain functions.

Ionizing radiation modulates the spread of an apathogenic rabies virus in mouse brain

Ionizing radiation has been shown to affect a broad range of viral diseases including neurotropic infections through an immunosuppression mechanism. In the present study we have investigated the effect of ionizing radiation on the characteristics of neurotropic infection by rabies virus, which has the unusual feature of infecting almost exclusively neurons. In order to analyze better the effect produced, the study concerned the spread of an apathogenic rabies virus variant in mouse brain. Irradiation was shown to increase both the intensity and duration of the infection in a reversible and dose-dependent manner and was effective in whole-body irradiation and in head-protected body irradiation, whereas cephalic irradiation had no effect. These results underline the role played by the immune system in the regulation of neurotropic virus infections in the brain and show that phenomena such as viral clearance and time-course of a neurotropic viral infection may be significantly modified by ionizing radiation, even for viruses whose infection involves only neurons.

Alteration of muscarinic acetylcholine receptors in rabies viral-infected dog brains

Functions of the muscarinic acetylcholine receptor (mAChR) were studied in rabid dog brains using [3H]quinuclidinyl benzilate (QNB) as a radioligand. Of various brain regions, hippocampus and brainstem were the areas mostly affected in terms of impaired specific binding to [3H]QNB, as compared to other regions, as well as to those of controls. Saturation studies of the hippocampus revealed significantly elevated dissociation equilibrium constant (K(d)) values in both furious (n = 5) (9.80 + or - 2.77 nM) and dumb (n = 6) (6.01 + or - 1.08 nM) types of rabies as compared to 11 controls (2.15 + or - 0.31 nM), whereas the maximum number of receptor sites (B (max)) values were comparable among all subgroups of normal (1.38 + or - 0.10 pmol/mg protein), dumb (1.43 + or - 0.17 pmol/mg protein) and furious (1.28 + or - 0.12 pmol/mg protein) rabies types. Hippocampal K(d) values were comparable between high (fluorescent antibody test-FAT and polymerase chain reaction-PCR positive; n = 4) (7.47 + or - 3.27 nM), and low (FAT-negative and PCR-positive; n = 4) virus amount (8.34 + or - 3.93 nM) but these were significantly higher than controls (n = 4) (1.58 + or - 0.17 nM). Our data suggest a functional derangement of mAChR at specific sites of hippocampus and brainstem which is not dependent on the amount of virus.

Alteration of interleukin-1 alpha production and interleukin-1 alpha binding sites in mouse brain during rabies infection

We have evaluated the effect of rabies virus infection on interleukin-1 alpha (IL-1 alpha) production and its receptors in mouse brain. Study of virus dissemination in the central nervous system (CNS) showed a massive infection of main brain structures from day 4 post infection (p.i.) up to the agony stage on day 6 p.i. At the same time, IL-1 alpha concentrations increased in cortical and hippocampal homogenates, whereas no change was detected in serum. In non-infected mice, IL-1 alpha binding sites were observed in the dentate gyrus, the cortex, the choroid plexus, the meninges and the anterior pituitary. During rabies virus infection, a striking decrease in IL-1 alpha binding sites was observed on day 4 p.i. with a complete disappearance on day 6 p.i., except in the pituitary gland where they remained at control level. In conclusion, concomitantly with the early rabid pathological signs, brain IL-1 alpha production and IL-1 alpha binding sites are specifically and significantly altered by brain viral proliferation. These results indicate that IL-1 alpha could be involved in the brain response to viral infection as a mediator and could participate in the genesis of the rabies pathogeny.

Appearance of inducible nitric oxide synthase in the rat central nervous system after rabies virus infection and during experimental allergic encephalomyelitis but not after peripheral administration of endotoxin

The cellular localization of inducible (iNOS) and constitutive (cNOS) nitric oxide synthase was studied in rats by immunocytochemical techniques involving specific iNOS and cNOS directed antibodies and by NADPH-diaphorase histochemistry. Paraformaldehyde-fixed vibratome sections of brains and cryostat sections of peripheral lymph nodes were studied of rats treated with endotoxin (2.5 micrograms/kg or 2.5 mg/kg i.v.), rats infected with rabies virus, and rats exposed to experimental allergic encephalomyelitis (EAE). Endotoxin-treated animals showed no appearance of immunoreactive iNOS (ir-iNOS) cells in the brain with the exception of a few microglial cells near the median eminence and some meningeal macrophages. In the same animals however, iNOS-immunoreactive cells were found in peripheral lymph nodes. Neurons that stain positive for cNOS and for NADPH-diaphorase could be observed in brains of control as well as of endotoxin-treated animals with a similar distribution and staining intensity. In contrast, animals that had been infected with rabies virus or subjected to EAE, showed the appearance of ir-iNOS-positive cells in several brain areas. These cells are located near blood vessels and lesion sites. The majority of these cells are GSA-I-B4 isolectin-positive and therefore are likely to represent macrophages. Our data suggest that increased production of nitric oxide may play a role in the altered brain functions in rabies-infected and EAE rats. On the contrary, increased nitric oxide production is probably not involved in the non-specific symptoms of sickness induced by endotoxin.

Characterization of protein involvement in rabies virus binding to BHK-21 cells

Prior studies established the specificity of rabies virus receptors on BHK-21 cells based on the saturability of the receptors and on competitive binding. In the present study, we used protease-treated cells to identify the involvement of protein in the specific binding of rabies virus to these cells. In addition, biochemical characterization of n-octylglucoside solubilized BHK-21 plasma membranes demonstrated the involvement of a protease sensitive, heat insensitive, integral membrane protein or protein complex in rabies virus binding to these cells. The membrane component that binds rabies virus is associated with a high molecular weight fraction of the n-octylglucoside-plasma membrane extract isolated by gel filtration. This high molecular weight fraction (approximately 450 KDa) is enriched with a cell surface integral membrane component that comigrates with denatured bovine serum fibronectin (220 KDa). This cellular component did not bind polyclonal antisera to fibronectin in Western blot (native or denatured) or immunoprecipitation experiments. Direct and specific virus binding to high molecular weight plasma membrane protein(s) separated on Western blots further confirmed the role of a protein receptor in rabies virus binding to these cells.

Mumps virus alters aggregation of acetylcholine receptors in cultured rat skeletal muscle cells

Cultured myoblasts, but not myotubes, from rat skeletal muscles were infected with the RW strain of mumps virus. Such myoblasts then fused to form myotubes containing viral antigen. The infected myotubes showed a significant decrease in the number of dorsal, linear acetylcholine receptor (AChR) aggregates as determined by FITC-conjugated alfa-bungarotoxin. Infected myotubes co-cultivated with spinal cord cells showed no increase in the number of dorsal, linear AChR aggregates, compared to normal, uninfected myotubes. In addition, an increased proliferation of the myoblasts, which remained uninfected in the infected cultures, was noted. This may indicate a release of a growth stimulating factor from the virus containing cells. This study shows that mumps virus infection can lead to an altered receptor organization in a morphologically preserved cell.