M. leprae components induce nerve damage by complement activation: identification of lipoarabinomannan as the dominant complement activator

Peripheral nerve damage is the hallmark of leprosy pathology but its etiology is unclear. We previously identified the membrane attack complex (MAC) of the complement system as a key determinant of post-traumatic nerve damage and demonstrated that its inhibition is neuroprotective. Here, we determined the contribution of the MAC to nerve damage caused by Mycobacterium leprae and its components in mouse. Furthermore, we studied the association between MAC and the key M. leprae component lipoarabinomannan (LAM) in nerve biopsies of leprosy patients. Intraneural injections of M. leprae sonicate induced MAC deposition and pathological changes in the mouse nerve, whereas MAC inhibition preserved myelin and axons. Complement activation occurred mainly via the lectin pathway and the principal activator was LAM. In leprosy nerves, the extent of LAM and MAC immunoreactivity was robust and significantly higher in multibacillary compared to paucibacillary donors (p = 0.01 and p = 0.001, respectively), with a highly significant association between LAM and MAC in the diseased samples (r = 0.9601, p = 0.0001). Further, MAC co-localized with LAM on axons, pointing to a role for this M. leprae antigen in complement activation and nerve damage in leprosy. Our findings demonstrate that MAC contributes to nerve damage in a model of M. leprae-induced nerve injury and its inhibition is neuroprotective. In addition, our data identified LAM as the key pathogen associated molecule that activates complement and causes nerve damage. Taken together our data imply an important role of complement in nerve damage in leprosy and may inform the development of novel therapeutics for patients.

The demyelination neurophysiological criteria can be misleading in Campylobacter jejuni-related Guillain-Barré syndrome

OBJECTIVE

The exclusive association of Campylobacter jejuni infection with the axonal variant of Guillain-Barré syndrome (GBS) is debatable. The current study aims to elucidate the GBS subtypes of patients with an antecedent C. jejuni infection.

METHODS

Nerve conduction study results of 73 patients with GBS were reviewed. Patients were defined as having a recent C. jejuni infection when there was a positive stool culture or serological evidence of C. jejuni in the presence of preceding diarrhea.

RESULTS

A total of 23 patients had evidence of a recent C. jejuni infection. At the early stage, patients were classified as AMAN (n=9; 39%), AIDP (n=3; 13%) or equivocal (n=9) using existing electrophysiological criteria. Prolonged distal latencies and conduction slowing that were seen in 11 patients rapidly normalized within 3 weeks in seven, whereas four had minor abnormalities throughout the course. Subsequently, all patients showed either acute motor axonal neuropathy pattern or reversible conduction failure.

CONCLUSION

Serial neurophysiology suggests that C. jejuni infections are exclusive to axonal GBS.

SIGNIFICANCE

Our findings suggest that AMAN can demonstrate the full complement of demyelinating features at the early stages of disease.

Axonal transport of Listeria monocytogenes and nerve-cell-induced bacterial killing

Listeria monocytogenes (L. monocytogenes) can cause fatal brainstem encephalitis in both sheep and humans. Here we review evidence that the bacteria can be incorporated into axons following a primary cycle of replication in macrophages/dendritic cells after subcutaneous injection in projection areas of peripheral neurons. The molecular mechanisms for the rocketing of L. monocytogenes in the cytosol by asymmetric cometic tails and the utility of this phenomenon for bacterial migration intraaxonally both in retro- and in anterograde directions to reach the central nervous system are described. The role of the immune response in the control of L. monocytogenes spread through peripheral neurons is highlighted, and a mechanism by which bacteria may be killed inside infected neurons through a nitric oxide-dependent pathway is pointed out.

Contact-dependent demyelination by Mycobacterium leprae in the absence of immune cells

Demyelination results in severe disability in many neurodegenerative diseases and nervous system infections, and it is typically mediated by inflammatory responses. Mycobacterium leprae, the causative organism of leprosy, induced rapid demyelination by a contact-dependent mechanism in the absence of immune cells in an in vitro nerve tissue culture model and in Rag1-knockout (Rag1-/-) mice, which lack mature B and T lymphocytes. Myelinated Schwann cells were resistant to M. leprae invasion but undergo demyelination upon bacterial attachment, whereas nonmyelinated Schwann cells harbor intracellular M. leprae in large numbers. During M. leprae-induced demyelination, Schwann cells proliferate significantly both in vitro and in vivo and generate a more nonmyelinated phenotype, thereby securing the intracellular niche for M. leprae.

Evidence for intraaxonal spread of Listeria monocytogenes from the periphery to the central nervous system

Rhombencephalitis due to Listeria monocytogenes is characterized by progressive cranial nerve palsies and subacute inflammation in the brain stem. In this paper, we report observations made on mice infected with L. monocytogenes. Unilateral inoculation of bacteria into facial muscle, or peripheral parts of a cranial nerve, induced clinical and histological signs of mainly ipsilateral rhombencephalitis. Similarly, unilateral inoculation of bacteria into lower leg muscle or peripheral parts of sciatic nerve was followed by lumbar myelitis. In these animals, intraaxonal bacteria were seen in the sciatic nerve and its corresponding nerve roots ipsilateral to the bacterial application site. Development of myelitis was prevented by transsection of the sciatic nerve proximally to the hindleg inoculation site. Altogether, our results support the hypothesis that Listeria rhombencephalitis is caused by intraaxonal bacterial spread from peripheral sites to the central nervous system.

Role of the cell wall phenolic glycolipid-1 in the peripheral nerve predilection of Mycobacterium leprae

The cell wall of pathogenic mycobacteria is abundant with complex glycolipids whose roles in disease pathogenesis are mostly unknown. Here, we provide evidence for the involvement of the specific trisaccharide unit of the phenolic glycolipid-1 (PGL-1) of Mycobacterium leprae in determining the bacterial predilection to the peripheral nerve. PGL-1 binds specifically to the native laminin-2 in the basal lamina of Schwann cell-axon units. This binding is mediated by the alpha(2LG1, alpha2LG4, and alpha2LG5 modules present in the naturally cleaved fragments of the peripheral nerve laminin alpha2 chain, and is inhibited by the synthetic terminal trisaccharide of PGL-1. PGL-1 is involved in the M. leprae invasion of Schwann cells through the basal lamina in a laminin-2-dependent pathway. The results indicate a novel role of a bacterial glycolipid in determining the nerve predilection of a human pathogen.

Rat dorsal root ganglia neurons as a model for Listeria monocytogenes infections in culture

Neurotropism of Listeria monocytogenes was studied in rat dorsal root ganglia (DRG) and hippocampal neurons in culture. Using a system in which the DRG neurons can grow relatively free from other cells, it was observed that such DRG neurons, in contrast to hippocampal neurons, can be effectively infected by L. monocytogenes. The bacteria aligned along DRG axons, but not along hippocampal neurites. A mutant deficient in internalin, a protein required for entry into E-cadherin-expressing cells, did not interact with DRG neurons. Axonal migration of bacteria was studied in the DRG neurons grown in a double-chamber system, where either the neurites or the nerve cell bodies were exposed to the bacteria. The data suggest that L. monocytogenes can infect both axons and DRG nerve cell bodies, and that the bacteria can migrate in a retrograde as well as anterograde direction. These results support the notion that L. monocytogenes can spread via primary sensory neurons to the central nervous system. Infection of DRG primary sensory neurons, as employed in the present study, provides a model for analysis of bacterial and neuronal factors of importance for neurovirulence of L. monocytogenes.

Campylobacter species and Guillain-Barré syndrome

Since the eradication of polio in most parts of the world, Guillain-Barré syndrome (GBS) has become the most common cause of acute flaccid paralysis. GBS is an autoimmune disorder of the peripheral nervous system characterized by weakness, usually symmetrical, evolving over a period of several days or more. Since laboratories began to isolate Campylobacter species from stool specimens some 20 years ago, there have been many reports of GBS following Campylobacter infection. Only during the past few years has strong evidence supporting this association developed. Campylobacter infection is now known as the single most identifiable antecedent infection associated with the development of GBS. Campylobacter is thought to cause this autoimmune disease through a mechanism called molecular mimicry, whereby Campylobacter contains ganglioside-like epitopes in the lipopolysaccharide moiety that elicit autoantibodies reacting with peripheral nerve targets. Campylobacter is associated with several pathologic forms of GBS, including the demyelinating (acute inflammatory demyelinating polyneuropathy) and axonal (acute motor axonal neuropathy) forms. Different strains of Campylobacter as well as host factors likely play an important role in determining who develops GBS as well as the nerve targets for the host immune attack of peripheral nerves. The purpose of this review is to summarize our current knowledge about the clinical, epidemiological, pathogenetic, and laboratory aspects of campylobacter-associated GBS.

Axonal transport of herpes simplex virions to epidermal cells: evidence for a specialized mode of virus transport and assembly

To examine the transmission of herpes simplex virus (HSV) from axon to epidermal cell, an in vitro model was constructed consisting of human fetal dorsal root ganglia cultured in the central chamber of a dual-chamber tissue culture system separated from autologous skin explants in an exterior chamber by concentric steel cylinders adhering to the substratum through silicon grease and agarose. Axons grew through the agarose viral diffusion barrier and terminated on epidermal cells in the exterior chamber. After inoculation of HSV onto dorsal root ganglia, anterograde axonal transport of glycoprotein and nucleocapsid antigen was observed by confocal microscopy to appear in exterior chamber axons within 12 h and in epidermal cells within 16 h, moving at 2-3 mm/h. Although both enveloped and unenveloped nucleocapsids were observed in the neuronal soma by transmission electron microscopy, only nucleocapsids were observed in the axons, closely associated with microtubules. Nodule formation at the surface of HSV-infected axons, becoming more dense at the axon terminus on epidermal cells, and patches of axolemmal HSV glycoprotein D expression were observed by scanning (immuno)electron microscopy, probably representing virus emerging from the axolemma. These findings strongly suggest a specialized mode of viral transport, assembly, and egress in sensory neurons: microtubule-associated intermediate-fast anterograde axonal transport of unenveloped nucleocapsids with separate transport of glycoproteins to the distal regions of the axon and assembly prior to virus emergence at the axon terminus.

Rabies and borna disease. A comparative pathogenetic study of two neurovirulent agents

BACKGROUND

Rabies and Borna disease viruses have been regarded as classical neurotropic agents. Many pathogenetic similarities are shared by these two negative strand RNA viruses. In view of recently gained data on the virology and pathology of these two diseases, and up-to-date comparative pathogenetic study seems to be justified.

EXPERIMENTAL DESIGN

This study is based on a survey of experimental and natural infections of laboratory animals and natural hosts. The morphologic damage to the nervous system has been evaluated by light and electron microscopy, with special emphasis on immunocytochemical methods.

RESULTS

This comparative study disclosed that both viruses are transported inside axons, pass synapses and propagate along neuronal networks. At the sites of synaptic transfer, full virus particles can never be detected in the early phase of rabies virus infection; in Borna disease virus (BDV) infection, virus particles cannot be found in any phase of disease progression. Thus, a major difference exists between the two agents insofar as rabies virus is morphologically well characterized, whereas BDV has never been visualized in tissue sections. Furthermore, rabies virus infects only neurons, whereas BDV also infects glial cells. The host range and the scale of infection of extraneural tissues by both agents is extremely similar.

CONCLUSIONS

These observations allow us to postulate that the synaptic transfer of both viruses likely ensures in the form of bare nucleocapsids (ribonucleoprotein-transcriptase complexes). While in the later phases of replication complete rabies virions are regularly assembled, BDV propagates within the central nervous system in an incomplete form, so that it remains morphologically imperceptible. Thus, BDV may appear in a complete, enveloped form only when exiting the host organism. The dissemination patterns of the two agents may be influenced by specific affinities to neurotransmitter receptor sites. It remains unresolved, why BDV readily infects non-neuronal central nervous system cells, while rabies virus remains restricted to neuronal elements.

Demonstration of Treponema pallidum in axons of cutaneous nerves in experimental chancres of rabbits

After cutaneous inoculation of viable Treponema pallidum subsp pallidum into the skin of chancre-immune or previously uninfected rabbits, organisms move from perivascular connective tissue to localize extracellularly in hair follicles, erector pili muscles, and cutaneous nerves. Large numbers of intact organisms can be seen within the perineurium using electron microscopy, and after extensive sampling a few organisms can be detected within the axon cytoplasm. These findings support the concept that T. pallidum may be able to pass along the nerve fibers to the central nervous system.

Axonal and transsynaptic (transneuronal) spread of Herpesvirus simiae (B virus) in experimentally infected mice

In order to study the pathogenesis of B virus infection of the nervous system, newborn and young mice were inoculated by four different routes: 1. Intramuscular (i.m.) in the forelimb; 2. I.m. in the hindlimb; 3. Subcutaneous (s.c.) in the abdominal wall; 4. Intraperitoneal (i.p.). Spread of virus was followed by immunohistochemical demonstration of viral antigen in tissue sections of the peripheral and central nervous system. Three distinct patterns emerged: 1. After i.m. limb inoculations, virus progressed along the ipsilateral dorsal column, the bilateral spinothalamic and bilateral spinoreticular systems and along central autonomic pathways. 2. After s.c. inoculation, the dorsal column was spared, otherwise the spread was similar to that following i.m. inoculations. 3. After i.p. inoculation, virus spread in the spinal cord bilaterally, mainly along spinothalamic and central autonomic pathways. The peripheral motoneurons were conspicuously spared, even in the i.m. inoculation mode. In the brain stem, B virus antigen appeared bilaterally, at multiple sites. In the cerebrum, virus infected cells appeared first in the thalamus, hypothalamus and the motor cortex. The mode of spread from spinal levels was mainly orthograde along the ascending systems (dorsal columns, spinothalamic, spinoreticular tracts), but also retrograde along descending systems (pyramidal tract, central autonomic pathways). Oligosynaptic systems transmitted virus more quickly than the polysynaptic ones. In the involvement of various neuronal systems in virus spread, a certain selectivity, sparing the peripheral motoneuron and the cerebellar systems, could be assessed.

Axonal-transsynaptic spread as the basic pathogenetic mechanism in B virus infection of the nervous system

An experimental study on the pathogenesis of B virus infection in the mouse has documented that the agent spreads in an axonal-transsynaptic manner in the nervous system. The characteristics of the spread of B virus are similar to those of other members of the herpes virus group.

Rabies virus infection and transport in human sensory dorsal root ganglia neurons

Cultured human sensory neurons are directly susceptible to CVS rabies virus infection and produce virus yields of 10(5) p.f.u./ml; infection can persist for more than 20 days without any sign of c.p.e. The use of a compartmentalized two-chamber culture system, with access to either the cell soma or neuritic extensions, permitted the study of viral retrograde transport, which occurs at between 50 and 100 mm/day. Neurons of human origin were more susceptible to virus infection than rat neurons and the axonal transport of rabies virus was more efficient. Electron microscopy allowed virus transport and infection of human dorsal root ganglia neurons to be observed.

Transneuronal transport of herpes simplex virus from the cervical vagus to brain neurons with axonal inputs to central vagal sensory nuclei in the rat

The recent introduction of live viruses as intra-axonal tracing agents has raised questions concerning which central neurons are transneuronally labelled after application of the virus to peripheral organs or peripheral nerves. Since the central connections of the vagus nerve have been well described using conventional neuronal tracing agents, we chose to inject Herpes Simplex Virus Type 1 into the cervical vagus of the rat. After survival times of up to 3 days the rat brains were processed immunohistochemically using a polyclonal antiserum against herpes simplex virus. Two days after injection of the virus we observed viral antigen in the area postrema and in the nucleus tractus solitarius and the dorsal motor nucleus of the vagus (dorsal vagal complex), principally ipsilaterally. At this survival time the viral antigen in the dorsal vagal complex was largely confined to glial cells. After 3 days the viral antigen was localized both in glia and in nerve cells within the dorsal vagal complex and in brain regions previously demonstrated, using conventional tracing procedures, to contain neurons with axonal projections to the dorsal vagal complex. This was true for medullary, pontine, midbrain and hypothalamic regions and for telencephalic regions including the amygdala, the bed nucleus of the stria terminalis, and the insular and medial frontal cortices. Many of the nerve cells containing viral antigen were displayed in a Golgi-like manner, with excellent visualization of the dendritic tree. Axonal processes, in contrast, were not visualized. We used co-localization studies to confirm previous findings concerning monoamine neurotransmitter-related antigens present in medullary and pontine neurons projecting to the dorsal vagal complex. After 3 days there were many Herpes Simplex Virus Type 1-containing glial cells along the intra-medullary course of the vagal rootlets. However, no viral antigen was found in brain regions containing neurons whose axons pass through the region of glial cell-labelled rootlets. Glial cells containing viral antigen were particularly numerous in brain regions known to receive an input from neurons in the area postrema and the dorsal vagal complex. Taken together with our observation concerning the early appearance of viral antigen within glial cells in the dorsal vagal complex, this suggests that when the virus reaches the axon terminal portion it is transferred to nearby glial cells and possibly enters central neurons by way of these structures.

Polarized sorting of viral glycoproteins to the axon and dendrites of hippocampal neurons in culture

Cultured hippocampal neurons were infected with a temperature-sensitive mutant of vesicular stomatitis virus (VSV) and a wild-type strain of the avian influenza fowl plague virus (FPV). The intracellular distribution of viral glycoproteins was monitored by immunofluorescence microscopy. In mature, fully polarized neurons the VSV glycoprotein (a basolateral protein in epithelial MDCK cells) moved from the Golgi complex to the dendritic domain, whereas the hemagglutinin protein of FPV (an apically sorted protein in MDCK cells) was targeted preferentially, but not exclusively, to the axon. The VSV glycoprotein appeared in clusters on the dendritic surface, while the hemagglutinin was distributed uniformly along the axonal membrane. Based on the finding that the same viral glycoproteins are sorted in a polarized fashion in both neuronal and epithelial cells, we propose that the molecular mechanisms of surface protein sorting share common features in the two cell types.

Light- and electron-microscopic study of M. leprae-infected armadillo nerves

Lesions in peripheral nerves of armadillos experimentally infected with Mycobacterium leprae were studied by light- and electron-microscopy. Bacilli could be found clearly inside axons of unmyelinated nerve fibers. Heavily bacillated Schwann cells were seen embracing unmyelinated axons with interrupted cytoplasmic membranes. This indicated the initiation of rupture of those cells which were responsible for the liberation of bacilli into the axons. The nerve lesions were divided into three grades according to their severity: grade I showed lesions focalized in the perineurium; grade II lesions were scattered inside nerve tissue; and in grade III lesions the nerve tissues were diffusely affected. No regressive changes, such as fibrosis or scar formation, were seen in the nerve lesions. Bacillated macrophages were not as foamy as those of human lesions, indicating that these bacillated cells were younger or more easily disrupted with a higher turnover than the cells in human lesions. This would promote the spread of lesions in armadillos, and would explain the less foamy appearance of the cells. We found bacilli inside lymphatics surrounding the nerves, substantiating the opinion that lesions spread to peripheral nerves not only by a hematogenous route but also by the lymphatics.

Immunomodulation of experimental murine herpes simplex keratitis: I. UV-HSV protection

A/J mice were immunized subcutaneously with ultraviolet light (UV) inactivated herpes simplex virus type-1, MP strain (HSV-MP). Control A/J mice were immunized subcutaneously either with media (unimmunized controls) or with live HSV-MP (immunized controls). Immunized and control mice were challenged ocularly with either MP or mP strain HSV-1 after corneal scarification and were followed for 3 weeks post corneal challenge. The mice were observed during this time period for signs of herpes simplex keratitis (HSK), lid lesions and encephalitis. At the time of sacrifice, the ipsilateral trigeminal ganglia were removed and assayed for latent HSV-1 using cocultivation on Vero cell monolayers. The results of these studies demonstrated that immunization with UV inactivated HSV (UV-HSV) gave the same protection against keratitis and encephalitis as immunization with live virus. Furthermore, the cocultivation assays indicated that immunization with either live HSV-1 or UV inactivated HSV-1 protected against the establishment of latency.

Corneal nerves contain intra-axonal HSV-1 after virus reactivation by epinephrine iontophoresis

Experimental ocular models of herpes simplex virus type 1 (HSV-1) reactivation have been used to monitor viral shedding in the tear film and the appearance of corneal epithelial lesions, but the temporal correlation between reactivation and the presence of viral particles in the corneal nerves has not been made. Two New Zealand white rabbits were inoculated with 20 microliters of HSV-1 McKrae strain (5.0 x 10(6) PFU/ml) in each eye. Beginning on postinfection day 82, ocular iontophoresis (0.8 mAmps for 8 min) of 0.01% epinephrine was done once a day for 3 consecutive days to induce reactivation. Ten limbal nerves from four corneas processed for transmission electron microscopy contained 883 unmyelinated and 40 myelinated axons. Seven nerves were positive for virus. Viral particles were found only in unmyelinated axons, and in low frequency (24/883). Virus was not found in Schwann cells, perineurium, or adjacent stroma nor were virus particles seen exiting axons. No enveloped virions were found. Axons from six nerves of four control corneas from rabbits with latent, but not reactivated, HSV-1 did not contain virus particles. Induction by corneal iontophoresis of epinephrine suggests that HSV-1 is translocated from the ganglion to the cornea through axonal transport mechanisms. For the first time, evidence of anterograde, intra-axonal transport of HSV-1 particles in response to epinephrine reactivation is demonstrated.

Axonal transport of rabies virus in the central nervous system of the rat

Stereotaxic inoculation of rabies virus into specific nuclei in the central nervous system has been used for the investigation of the central neural transport mechanisms of viral information. The infection was monitored by specific fluorescence and peroxidase studies and the titration of viral infectivity in dissected brain areas. Twenty-four hours after inoculation into the striatum, cortex, or substantia nigra, infected neurons were detected only in cells from areas and nuclei which were related to the site of inoculation. The distribution of infected neurons showed that retrograde axoplasmic flow plays a determining role in the transport of rabies virus 24 hours after delivery of virus to specific target nuclei. Local destruction of neurons by kainic acid at the site of viral inoculation did not prevent the uptake and subsequent retrograde axonal transport of virus. There was an overall correlation between the major neural connections of the inoculated areas (e.g. the striatum) and the infected areas 24 hours later (e.g. the substantia nigra).

Binding, uptake and retrograde axonal transport of herpes virus suis in sympathetic neurons

Newborn rat dissociated sympathetic neurons were grown in a chamber culture system, where a Teflon ring sealed with silicon grease separated the axonal plexus from the corresponding nerve cell bodies. The binding of 35S-labeled herpes virus suis (HVS) to the neurites was partially inhibited by an excess of unlabeled HVS as well as by concanavalin A, indicating the presence of specific binding sites for the virus. Specific binding was a prerequisite for the subsequent uptake and retrograde transport of HVS to the nerve cell bodies. Predominantly free nucleocapsids were detected by electron microscopy in the axons at the time of retrograde transport, both in culture and in vivo, suggesting the possibility that nucleocapsids without lipid membrane and not contained in cellular membrane compartments can be transported by retrograde axonal transport.

Neuritic transport of herpes simplex virus in rat sensory neurons in vitro. Effects of substances interacting with microtubular function and axonal flow [nocodazole, taxol and erythro-9-3-(2-hydroxynonyl)adenine]

Herpes simplex virus type 1 and a fluorescein-labelled lectin (wheat germ agglutinin) were selectively transported to nerve cell bodies located in the inner compartment of a two-chamber tissue culture system after the application of virus or lectin to the neuritic processes in the outer culture compartment. Taxol, which stabilizes and alters intracellular arrangements of microtubules, and nocodazole, which disrupts microtubules, both inhibited this retrograde axonal transport of viral particles and lectin. The transport was also inhibited by erythro-9-3-(2-hydroxynonyl)adenine (EHNA), which blocks ATPases. However, EHNA was also an effective inhibitor of infection with the virus in non-neuronal cells (GMK AH-1). The nature of the action(s) of EHNA on neuritic transport of the virus is therefore less clear.

Intra-axonal virus in demyelinative lesions of experimental herpes simplex type 2 infection

Three-week-old mice which had been infected intracerebrally with herpes simplex virus type 2 (HSV-2) were examined electron-microscopically for the presence of intra-axonal virus in or near optic nerve and spinal cord demyelinative lesions. Acute lesions and their margins frequently contained a very small proportion of abnormal axons, and in a few of these mature virus particles, nucleocapsids, or other incomplete forms were found. A similar range of particle morphology was present in the cytoplasm of infected and degenerating glia. Axons containing similar particles were not identified in fibers in normal white matter surrounding demyelinative lesions. It is proposed that neuronal infection and axonal transport of virus may lead to foci of oligodendroglial infection, destruction and central nervous system (CNS) demyelination near to or remote from the cell bodies of infected neurons. In some instances, the topography of lesions could reflect a tract association. Anatomical features of nervous tissue could favor amplification of demyelination from a relatively minimal neuronal infection, with little evidence of tract degeneration. This hypothesis is consistent with the great predominance of demyelination relative to gray matter disease seen experimentally in non-fatal CNS infections with HSV-2. It would also explain the marked tendency for demyelinative lesions in at least certain CNS locations to be greatly elongated in the long axis of fiber tracts. This mechanism could be of importance in other animal models of virus-induced demyelination, and perhaps also in multiple sclerosis.

Uptake and transport of herpes simplex virus in neurites of rat dorsal root ganglia cells in culture

Attachment and neuritic transport of herpes simplex virus (HSV) type 1 (McIntyre) were studied in a cell culture system with dissociated cells of rat dorsal root ganglia. The two-chamber cell culture system containing a diffusion barrier penetrated by neurites of cultured sensory neurons permitted infection of neurites extending outside the diffusion barrier without exposure of the neuronal cell soma. HSV adsorbed to neuritic extensions and reached the neuronal soma within 1.5 h post-inoculation. Neuritic uptake and transport of HSV were inhibited in the presence of cytochalasin B. Internalization of virus in neurites was preceded by attachment of virus to the neurite plasma membrane. Neurites transported viral nucleocapsids (NC) through the diffusion barrier of the cultures. Destruction of the neuritic extensions before or shortly after peripheral virus inoculation blocked spread of infection to the cell soma. No infection was established when neuritic extensions were exposed to viral NC and NC were then not observed inside the neurite plasma membrane. Virus produced in neurons, when HSV was inoculated into the inner culture chamber containing the neuronal cell bodies, was transported as enveloped virus in cytoplasmic vesicles from the neuronal cell body towards the periphery. Schwann cells were infected by viropexis. Shortly after infection virions were observed in vacuoles of the cytoplasm.

The continuing problem of herpes simplex virus persistence

While the main interest in the pathogenesis of herpes simplex virus (HSV) in the sixties had been focussed on acute infections, in the seventies latent infection has become the main foal of investigation. Despite of overwhelming literature, the HSV persistence has remained a continuing problem from the practical as well as theoretical points of view. Nevertheless, the following conclusions can be made: 1) HSV spreads along nerves inside as well as outside axons; 2) it resides in a non-productive form for lifelong in the sensory or vegetative ganglia; and 3) it is intermittently activated when causing peripheral virus shedding or recurrent disease. The persistence of HSV DNA in neurons may be associated with a limited transcription and translation, but the ganglia in a great majority of subjects are uninfectious during the latency period.

Mode of entry of a neurotropic arbovirus into the central nervous system. Reinvestigation of an old controversy

The mechanism by which neurotropic arboviruses gain access to the central nervous system remains uncertain, although it is generally assumed that viremic infection results in growth across or passive diffusion through brain capillaries. In contrast to the natural reservoir hosts of these arboviruses, clinical hosts (e.g., horses, humans) have viremias of very brief duration and low magnitude. We investigated the question of neuroinvasion in 5- to 6-week-old Syrian hamsters infected with St. Louis encephalitis virus (strain TBH-28). This model shares with the human disease low or undetectable viremia and many clinical and pathoanatomical features. The mortality rate after intraperitoneal inoculation of a moderate viral dose was 88%. No viremia was detectable by a sensitive assay in 31% of the animals. In the remaining hamsters, the mean peak viremia was 1.0 log10 plaque-forming units/0.05 ml and the mean duration 1 to 2 days. There was no correlation between viremia and outcome of infection, length of incubation period, or brain virus titer. Tissue infectivity studies showed a rise in titer in the olfactory neuroepithelium on day 4 postinoculation, then in the olfactory bulbs (day 5 postinoculation), and finally in the remainder of the brain (day 6 postinoculation). Specific immunofluorescence was demonstrated in the bipolar neurons of the olfactory epithelium, their dendrites, and in axon bundles of the olfactory nerves in the submucosa. By electron microscopy, virus particles and associated tubular structures were demonstrated within dendrites, perikarya, and axons of olfactory neurons, and to a lesser extent in macrophages and Bowman's gland cells in the lamina propria. In cells of Bowman's glands large numbers of virions were sequestered within secretory granules. Virus was recovered from nasal washings on day 4 postinoculation. Similar findings were obtained in weanling mice inoculated intraperitoneally with another (mouse-virulent) St. Louis encephalitis viral strain (77V-12908). These data taken together indicate that the olfactory pathway is the principal route of viral entry into the central nervous system. After peripheral inoculation a low-level viremia results in infection of highly susceptible cells in the olfactory neuroepithelium, allowing centripetal axonal transport of virus to the olfactory bulb, whence spread is unimpeded throughout the neuropil of the central nervous system. Infection of Bowman's gland cells in the olfactory mucosa and shedding of virus in nasal mucus may be an adaptation for nonarthropod-borne transmission, a feature of many flaviviruses.

Uncoupled relationship between demyelination and primary infection of myelinating cells in Theiler's virus encephalomyelitis

Theiler's virus infection in mice produces a chronic demyelinating disease which appears to be based on an immune pathogenesis rather than on direct viral destruction of myelin-supporting cells. The purpose of the present study is to ascertain whether viral antigen is present in the cytoplasm of such cells in areas of demyelination. Because of the difficulty of identifying oligodendrocytes in tissues rich in infiltrating mononuclear cells and fixed for immunohistochemistry, I turned to a recently described form of Theiler's virus encephalomyelitis which follows inoculation with the attenuated ww strain and is characterized by extensive spinal cord remyelination by invading Schwann cells and by recurrent demyelination of Schwann cell-remyelinated axons. The unlabeled antibody peroxidase-antiperoxidase technique was employed to study whether such spinal cord Schwann cells were primarily infected by virus at the time when recurrent demyelination was occurring. Whereas other types of cells, including neurons, astrocytes, and macrophages, contained abundant viral antigen, no positive immune reaction was observed in Schwann cells. These results correlate with our previous studies which had suggested that demyelination in this viral model is not dependent on primary viral attack on myelinating cells but is probably dependent on the host immune response.

Spiroplasma-like inclusions in Creutzfeldt-Jakob disease

Spiral membranous inclusions were discovered on electron microscopic study of brain biopsy tissues from a 46-year-old man with Creutzfeldt-Jakob disease (CJD). These replicate coiled membranous configurations measured 850 to 1,000 nm in length and 75 to 137.5 nm in width and were located within axoplasm, primarily in presynaptic terminals. These inclusions closely resemble Spiroplasma, a plant pathogen, and the finding of these structures in CJD suggests the concurrence of Spiroplasma infection with a human chronic degenerative brain disease.

Ultrastructure of peripheral nerves of mice inoculated with rabies virus

Fourty adult female albino mice were inoculated in the right hind leg with rabies viruses of the street type. The mice were sacrificed with an interval of 24 hours each, starting in the next day after inoculation. From the 10th day ownwards the animals started presenting signs of paralysis, first on the leg where the viruses were inoculated anbnormalities were found in peripheral nerves compatible with axonal degeneration with secondary demyelination but the rabies viruses were not found in the axoplasm, myelin sheet, Schwann cell cytoplasm, endoneural or in the epineural structures.

Evidence for an intraaxonal transport of fixed and street rabies virus

Colchicine was used to inhibit axonal transport and to demonstrate that rabies virus spread from the peripheral inoculation site to the CNS by the retrograde axoplasmic flow. Colchicine was applied by the mean of elastomer implants around the sciatic nerve of young rats in order to obtain higher local concentrations of the drug. This procedure avoided the systemic effects of colchicine encountered with the usual treatment. To confirm the efficiency of the axoplasmic flow inhibition by colchicine, 125I-tetanus toxin was used as a marker. Uptake of colchicine by the sciatic nerve was monitored by the use of 3H-labelled colchicine. Interruption of the retrograde axoplasmic flow resulted in prevention of fixed and street rabies virus propagation. Moreover, the centrifugal spread of rabies could be inhibited using this experimental procedure.

The pathogenesis and pathway into the central nervous system after intraocular infection of herpes simplex virus type I in rabbits

Herpes simplex virus (HSV) type I was injected into the right eye of 18-day-old New Zealand albino rabbits and the animals were killed on the fourth and eighth days after inoculation. Longitudinal section of the optic nerves and chiasma showed that both myelinated axons and neuroglial cells crossed at the chiasma. Semi-serial (1 micrometer) and ultrathin sections showed the presence of HSV in both astrocytes and oligodendrocytes, although no particles were seen in the myelinated axons; the infected cells were confined to the medial side of the right optic nerve. HSV travels centropetally along the optic pathway and slowly spreads laterally by cell-to-cell infection. The virus does not appear to kill the astrocytes and oligodendrocytes, and also does not directly damage the myelin sheath.

Mouse hepatitis virus-induced recurrent demyelination. A preliminary report

Four-week-old BALB/c mice inoculated intracerebrally with the JHM strain of mouse hepatitis virus developed an acute demyelinating disease followed by apparent recovery with remyelination. When surviving mice were examined 16 months later, small areas of active demyelination were still present. This is the first reported example, to our knowledge, of an experimental viral infection in which acute demyelination with recovery is followed by persisting or recurring demyelination.

The pathogenesis of pseudorabies in mice: virus replication at the inoculation site and axonal uptake

Three-week-old mice were inoculated in the right ear pinna with pseuforabies virus. Ears were surgically removed at various times after inoculation and changes from the normal pathogenesis were observed. Virus replication in the ear tissue and cervical dorsal root ganglia was also monitored. Followed inoculation with a small dose of virus, local multiplication of the virus was necessary before the infection spread to the nerves. With larger infecting doses there was probably direct uptake of virus from the inoculum into the nerve endings. After these larger doses virus was first detected in the dorsal root ganglia 17 h agter infection, suggesting a retrograde axonal flow rate of at lease 1-7 mm/h.

Experimental latent herpesvirus infection in rabbits, mice and hamsters: ultrastructure of the virus activation in explanted gasseric ganglia

The frequency of latent infection as established in trigeminal ganglia of rabbits, mice and hamsters with human herpesvirus type 1 (HVH) was compared using two different virus strains. Explantation proved to be effective in reisolation of HVH from ganglion tissue, which did not yield infectious virus at time of its removal. After healing of acute keratitis, the latent infection in homolateral gasseric ganglia of rabbits was detected at a relatively high frequency (60-80 per cent) up to 120 days post infection (p.i.) in case of both virus strains. The activation rate was a little lower in hamsters. After inoculation of suckling and young mice with a sublethal dose of HVH by oral and nasal routes, approximately 40-100 per cent of the animals had virus in their gasseric ganglia during the acute period; 30-60 days later only 10-25 per cent had virus in the latent form. Immunofluorescent and electron microscopic examination of the explanted ganglion tissue showed the presence of HVH in neurons, neuronal satellites and Schwann cells. The nuclei of noneural cells contained numerous crystalline arrays. The possibility that pseudounipolar neurons of the regional sensoric ganglion are not the exclusive site of HVH latency is discussed.

Pathogenesis of herpetic neuritis and ganglionitis in mice: evidence for intra-axonal transport of infection

The pathogenesis of acute herpetic infection in the nervous system has been studied following rear footpad inoculation of mice. Viral assays performed on appropriate tissues at various time intervals indicated that the infection progressed sequentially from peripheral to the central nervous system, with infectious virus reaching the sacrosciatic spinal ganglia in 20 to 24 hr. The infection also progressed to ganglia in mice given high levels of anti-viral antibody. Immunofluorescent techniques demonstrated that both neurons and supporting cells produced virus-specific antigens. By electron microscopy, neurons were found to produce morphologically complete virions, but supporting cells replicated principally nucleocapsids. These results are discussed in the context of possible mechanisms by which herpes simplex virus might travel in nerve trunks. They are considered to offer strong support for centripetal transport in axons.