Protective effects of rat splenic lymphocytes and peritoneal exudate cells on herpes simplex virus infection of rat dorsal root ganglia in culture.

An in vitro model system was developed to study the effects that immune cells might have on herpes simplex virus (HSV) infection of rat dorsal root ganglia in culture. Our results demonstrate that rat splenic lymphocytes and peritoneal exudate cells are incapable of replicating HSV even if these cells come from sensitized animals and are stimulated in vitro. Both cell preparations can offer some protection to rat dorsal root ganglia from the effects of HSV infection. The data suggest that an immunologically non-specific (not mediated by sensitized cells) type of protection is important to neurons, while an immunologically specific (mediated by sensitized cells) protection is most beneficial to fibroblasts. This system can be utilized to study the mechanism of latency since the neurons of sensory ganglia are the natural site of latent herpes virus.     

Stress-induced reactivation of latent herpes simplex virus infection in rat lumbar dorsal root ganglia

Clinical reports suggest that stress precipitates recurrent cutaneous Herpes simplex virus (HSV) infection, presumably by reactivating latent infection in sensory ganglia with subsequent centrifugal axonal spread to the skin. As an initial test of this hypothesis, rats with latent HSV, type-1, (HSV-1) infection in lumbar dorsal root ganglia (DRG) were exposed to a well-characterized acute stressor that produced gastric ulcers (U) and elevated plasma corticosterone (CS) concentrations. Stress-induced reactivation of latent HSV infection was suggested by the earlier appearance of cytopathic effect (CPE) in human foreskin fibroblast monolayers co-cultivated with ganglia from stressed rats than from nonstressed ones (4.5 ± 0.2 and 6.4 ± 0.4 [mean ± SEM] days respectively; p<0.001). No CPE was detected in monolayers co-cultivated with ganglia from non-infected rats. These initial results suggest that acute stress reactivates latent HSV-1 ganglionic infection.     

Latent herpes simplex virus infection of mice. Infectious virus in homogenates of latently infected dorsal root ganglia.

C-57 albino weanling mice were latently infected with herpes simplex virus (Mp strain, type 1) by inoculation of 10(4) plaque forming units in the right hind footpad. The virus was demonstrable in explant cultures of the sacral dorsal root ganglia of these mice for as long as 18 months following inoculation. In addition, the virus was detectable when homogenates of these latently infected ganglia were placed on to differentiated organotypic cultures of fetal mouse dorsal root ganglia for as long as 8 months following inoculation of the mice. Virus was not demonstrable in these homogenates when they were placed on the Hela cells. The results suggest that during herpes simplex virus latent infection in mice there is continuous synthesis of infectious virus, probably in a highly localized area, which is detectable if a sensitive indicator substrate, such as these organotypic cultures, is used.     

Neurological complications of herpes simplex virus type 2 infection

Herpes simplex virus type 2 (HSV-2) infection is responsible for significant neurological morbidity, perhaps more than any other virus. Seroprevalence studies suggest that as many as 45 million people in the United States have been infected with HSV-2, and the estimated incidence of new infection is 1 million annually. Substantial numbers of these persons will manifest neurological symptoms that are generally, although not always, mild and self-limited. Despite a 50% genetic homology between HSV-1 and HSV-2, there are significant differences in the clinical manifestations of these 2 viruses. We herein review the neurological complications of HSV-2 infection.     

Comparative effects of herpes simplex virus types 1 and 2 in organotypic cultures of mouse dorsal root ganglion.

Mature organized cultures of mouse dorsal root ganglion (MDRG) were infected with herpes simplex virus, type 1 (HSV 1) and type 2 (HSV 2). Onset of infectious virus production occurred faster and reached higher levels in HSV 2-infected cultures. Neurons, supporting cells and myelin were affected in both types of infection, but morphological changes occurred significantly earlier and more dramatically with the type 2 infection. The pattern of myelin changes was distinctly different in the two types of infection. Within 20 hours post infection nerve cells infected with HSV 2 developed several types of intranuclear inclusions consisting of membranes and filaments; no such neuronal inclusions were seen with HSV 1 infection. HSV 2 infection showed frequent, large, membranous inclusions in supporting cell nuclei whereas, only rare, small inclusions of this type were seen in supporting cells infected with HSV 1. The observations demonstrate that the two virus types produced different virus replication patterns and different morphologic changes in long term cultures of MDRG. There appears to be a differential response of neurons and non-neuronal elements to the virus in this tissue substrate. Viral latency was not induced in this system by direct inoculation of the virus under the conditions described.     

Latent herpes simplex virus type 1 in human geniculate ganglia

Summary Viral infection, especially by reactivation of herpes simplex virus (HSV) has been considered to be a possible explanation for the pathogenesis of idiopathic peripheral facial nerve palsy (Bell's palsy). We investigated whether the geniculate ganglia of man contain latent HSV type 1 (HSV-1), and compared the frequency of HSV-infected ganglia and that of latently infected neurons in human geniculate ganglia and in trigeminal ganglia. From autopsy specimens of eight adults 15 geniculate ganglia and 16 trigeminal ganglia were examined by means of in situ hybridization and immunohistochemical staining. The HSV-1 genome was detected in 11 of the 15 (71%) geniculate ganglia and in 13 of the 16 (81%) trigeminal ganglia. No HSV antigen was noted in any of the ganglia. The incidence of latently infected neurons was 0.9% in the trigeminal ganglia and 5.3% in the geniculate ganglia. The difference in percentages between the two types of ganglia was significant. Our results suggest that reactivation of latent HSV in the geniculate ganglia is a probable cause of some cases of herpetic stomatitis and of idiopathic peripheral facial nerve palsy.Supported by Special Grant-in-Aid for Promotion of Education and Science in Hokkaido University (to K.N.) and Grant-in-Aid for Scientific Research (C) (03670803 to S.F.) provided by the Ministry of Education, Science and Culture     

Purification and culture of adult rat dorsal root ganglia neurons

To study the trophic requirements of adult rat dorsal root ganglia neurons (DRG) in vitro, we developed a purification procedure that yields highly enriched neuronal cultures. Forty to fifty ganglia are dissected from the spinal column of an adult rat. After enzymatic and mechanical dissociation of the ganglia, myelin debris are eliminated by centrifugation on a Percoll gradient. The resulting cell suspension is layered onto a nylon mesh with a pore size of 10 microns. Most of the neurons, the diameter of which ranged from 17 microns to greater than 100 microns, are retained on the upper surface of the sieve; most of the non-neuronal cells with a caliber of less than 10 microns after trypsinization go through it. Recovery of neurons is achieved by reversing the mesh onto a Petri dish containing culture medium. Neurons to non-neurons ratio is 1 to 10 in the initial cell suspension and 1 to 1 after separation. When these purified neurons are seeded at a density of 3,000 neurons/cm2 in 6 mm polyornithine-laminin (PORN-LAM) coated wells, neuronal survival (assessed by the ability to extend neurites), measured after 48 hr of culture, is very low (from 0 to 16%). Addition of nerve growth factor (NGF) does not improve neuronal survival. However, when neurons are cultured in the presence of medium conditioned (CM) by astrocytes or Schwann cells, 60-80% of the seeded, dye-excluding neurons survive. So, purified adult DRG neurons require for their short-term survival and regeneration in culture, a trophic support that is present in conditioned medium from PNS or CNS glia.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Resistance of rat CNS to brain stem infection with herpes simplex virus type 1

Infection of the CNS by herpes simplex type 1 (HSV-1) via the trigeminal route to the brain stem was elucidated in a rat model. In contrast to the earlier described cortical and hippocampal infection after intracranial injection, the CNS showed a profound resistance to HSV-1 infection when the virus was administred by nose inoculation, as judged by histopathology and immunohistochemistry. In contrast, when the distribution of HSV-1 in the brain was investigated after nose inoculation by polymerase chain reaction, viral DNA was detected at all levels from the ganglia to the cortex. When replication of HSV-1 was assayed in primary cell cultures of rat astrocytes derived from brain stem, striatum, hippocampus and cerebral cortex, significantly lower virus yields were obtained in brain stem-derived astrocytes cultures as compared with in cortex-derived astrocytes. This finding was independent of whether HSV-1 strains used originated from brains of patients suffering from herpes simplex encephalitis or from patients with oral cutaneous lesions and lacking neurological symptoms. Also, by immunocytochemistry of cultures after HSV-1 infection, a lower number of plaques were seen in brain stem-derived astrocytes as compared with cortex-derived astrocytes. The observed relative resistance of brain stem-derived astrocytes to replicate HSV-1 might contribute to the ability of the brain stem to withstand infection during reactivation of this virus in the trigeminal neurons.Financial support was received from the Swedish Medical Research Council, the Medical Society of Göteborg, the Swedish Medical Society, and the Faculty of Medicine, University of Göteborg     

Representations of hindlimb digits in rat dorsal root ganglia.

The distribution in dorsal root ganglia of neurones that innervate the distal tips of the hindlimb digits in the rat were mapped after subcutaneous injections of the fluorescent tracers Fast Blue, Diamidino Yellow, and Fluoro-Gold into different digits. Three-dimensional reconstruction was used to describe the intraganglionic distribution of neurones labelled from different digits. Labelled neurones were found mainly in the L3-L5 ganglia. The distribution in ganglia and the number of neurones labelled from each digit varied considerably between cases, but mean numbers of labelled neurones were similar for the different digits. Neurones in L3 tended to innervate medial digits and neurones in L5 tended to innervate lateral digits, but most neurones from any digit were found in L4. Although overlap was considerable, the three-dimensional reconstruction showed tendencies of neurones to be distributed in restricted territories within the dorsal root ganglia. This was especially clear in ganglion L5, where digit IV was found to be represented more rostrally than digit V. The results indicate that primary afferent neurones that innervate the hindlimb digits are represented by a crude rostrocaudal somatotopic organisation both among and within lumbar dorsal root ganglia.     

Herpes simplex virus infection in populations of mouse dorsal root ganglion neurons: effects of inoculation route and virus strain.

To investigate whether herpes simplex virus type-2 (HSV-2) infection of sensory ganglion neurons is restricted to a particular neuronal class, we unilaterally inoculated either the footpad, leg muscle or sciatic nerve of mice with strains of HSV-2 that differ in virulence and examined the soma sizes of lumbar dorsal root ganglion (DRG) neurons containing viral antigen near the peak of acute infection. Each inoculation route appeared relatively selective for a different portion of the neuronal size spectrum. Footpad inoculation primarily infected the smaller population of DRG neurons, by comparison, muscle inoculation tended to spare the smallest neurons while infecting medium and larger cells. Sciatic nerve inoculation infected the entire spectrum of DRG neurons. These results indicate that HSV-2 infection is not restricted to a specific subclass of sensory neurons. With any particular inoculation route, the least virulent strain infected fewer neurons than did those of greater virulence.     

An in vivo model of varicella-zoster virus latent infection of dorsal root ganglia

We describe here the first in vivo model of varicella-zoster virus (VZV) latent infection in the adult rat peripheral nervous system. Infected Mewo cells were injected subcutaneously along the spine of healthy adult rats. No clinical sign of infection was observed even 9 months after inoculation. Humoral immune response to VZV was detected in all infected animals throughout the study (9 months). The presence of viral material in dissociated and cultured dorsal root ganglia (DRG) from inoculated animals was studied by immunoperoxidase and in situ hybridization. When DRGs from infected animals were plated in culture from 1 month and up to 9 months after inoculation, viral nucleic acids and proteins were detected in neurons. Furthermore, trypsinization and subcultivation of infected neurons in culture is needed to reactivate infectious virus at least in some of the neurons. This model provides a useful tool for studying 1) the molecular mechanisms leading to an in vivo latency, 2) the role of the immune system, in particular cellular immunity, on the establishment, maintenance, and reactivation of latency, 3) the neurotropism of mutant viruses, and 4) the effects of antiviral agents.     

Changes in excitability induced by herpes simplex viruses in rat dorsal root ganglion neurons

The physiological properties of rat sensory neurons infected with herpes simplex type 1 viruses and maintained in cell culture were studied using intracellular recording techniques. Two syncytial (cell fusing) and two nonsyncytial strains of virus were examined; individual strains of virus had different effects on neuronal excitability. The nonsyncytial viruses caused a loss of tetrodotoxin-sensitive low-threshold action potentials and blocked hyperpolarization-activated inward rectification, but did not alter the resting membrane potential, depolarization-activated outward rectification, or render the cells leaky. These effects develop progressively over the period 5-15 hr postinfection. One syncytial strain of virus induced spontaneous electrical activity that appeared to be the result of discrete electrical coupling between sensory neuron processes; as a result, action potential discharge is synchronized in coupled neurons. A second syncytial strain of virus rendered neurons inexcitable; however, in these experiments the input resistance fell to low values, possibly as a result of extensive coupling between sensory neurons. Viral replication in sensory neurons was demonstrable with indirect immunofluorescence using an antibody to herpes simplex viruses and correlated with the onset of virally induced changes in excitability. Virally triggered changes in excitability were blocked by the specific herpes virus antimetabolite acyclovir, suggesting that viral adsorption and penetration are by themselves insufficient to evoke changes in excitability. These results suggest that herpes viruses have selective effects on the excitable mechanisms in sensory neurons that are not simply the result of a general loss of membrane conductances or the disruption of transmembrane ion gradients.     

Herpes simplex virus type 1 infection of rat astrocytes in primary culture: effects of dibutyryl cyclic AMP

Monolayer cultures of primary rat astrocytes grown with or without dibutyryl cyclic AMP (dBcAMP) for two weeks or longer were infected with round plaque-forming (Rd) or syncytia-forming (Syn) variants of herpes simplex virus type 1 (HSV-1). Infection with HSV-1 did not stimulate synthesis of glial fibrillary acidic protein (GFAP) or alter the general organization of the intermediate (glial) filaments in astrocyte cultures. However, the dBcAMP-treated astrocytes produced 10- to 100-fold lower titers of cell-free progeny HSV-1 than the untreated astrocyte cultures. Radiolabeled amino acid or glucosamine incorporated into acid precipitable cellular or viral glycoproteins was decreased by 10-25% in dBcAMP-treated astrocytes. Distinctive cell-rounding or syncytial cytopathology was produced by HSV-1 strains infecting untreated astrocytes, but the infected dBcAMP-treated astrocytes displayed only cell-rounding cytopathology. The dBcAMP-related effects on HSV-1 infection were specific to primary astrocyte cultures; they were not observed in HSV-1-infected human fibroblast cultures treated with dBcAMP. Comparison of HSV-1 infection of untreated versus dBcAMP-treated astrocytes suggests that the dBcAMP-induced "reactive" or differentiated state of the astrocyte can affect expression of virus-induced cytopathology and virus-specific polypeptide synthesis. The dBcAMP-treated primary astrocyte culture may afford a non-neoplastic, differentiated in vitro system for studying HSV-neural cell interactions.     

Localization of herpes simplex virus and varicella zoster virus DNA in human ganglia.

Human dorsal root ganglia from 14 randomly autopsied adults and 1 infant (all seropositive for both herpes simplex virus [HSV] and varicella zoster virus [VZV]) were examined for latent HSV-1 and VZV DNA by polymerase chain reaction. Thoracic ganglionic DNA from all subjects and trigeminal ganglionic DNA from 11 adults were analyzed. HSV-1 DNA was detected in trigeminal ganglia from 8 of 11 (73%) adults and in thoracic ganglia from 2 of 14 (14%) adults. VZV DNA was detected in trigeminal ganglia from 10 of 11 (91%) adults and in thoracic ganglia from 12 of 14 (86%) adults. None of the DNA samples were positive with primers specific for HSV-2. These findings indicate the presence of latent HSV-1 and VZV DNA in trigeminal ganglia and latent VZV DNA in thoracic ganglia of most seropositive adults. Furthermore, although HSV-1 latency most commonly develops in trigeminal ganglia, we also show for the first time the presence of HSV-1 latency in thoracic ganglia. Finally, both viruses can become latent in the same trigeminal ganglion.     

Quantitative analysis of herpes simplex virus in cranial nerve ganglia

A susceptible individual exposed to herpes simplex virus (HSV) will develop latent infection in multiple cranial nerve ganglia. There are a few quantitative studies of the viral load within the trigeminal ganglion, but none that investigate other cranial nerve ganglia. In this study, human trigeminal, geniculate, vestibular (Scarpa's) and cochlear (spiral) ganglia were obtained from willed body donors. Real time quantitative polymerase chain reaction (PCR) analysis of the HSV DNA polymerase gene was performed on ipsilateral ganglion sets from the same individual. Viral load, expressed as HSV genomes per 105 cells, was significantly greater in the vestibular ganglion (mean +/- SD, 176705 +/- 255916) than in the geniculate (9948 +/- 22066), cochlear (3527 +/- 9360), or trigeminal (2017 +/- 5578) ganglia. There was not a significant correlation among ganglia from the same individual. The results support the hypothesis that neuronal subpopulations have variable susceptibility to HSV infection.     

Seroprevalence of herpes simplex virus type 2 in multiple sclerosis

BACKGROUND: It has been proposed that multiple sclerosis (MS) might be a sexually transmitted disorder. There is evidence that seropositivity to herpes simplex virus type 2 (HSV-2) correlates well with the number of sexual partners. Accordingly, a raised overall HSV-2 seroprevalence in MS would lend support to this theory. MATERIALS AND METHODS: Serum from 497 UK subjects with clinically definite MS was tested for antibodies to HSV-2 and compared with matched historical controls from within and outside London, blood donors and genito-urinary medicine (GUM) clinics. RESULTS: The unadjusted MS seropositivity rate was 14%. HSV-2 seroprevalence in MS patients aged 35-64 years was significantly higher overall compared with a non-London general population in an unadjusted comparison. HSV-2 seroprevalence in London MS patients compared with London blood donors was significantly greater irrespective of age, but the MS seropositive rate was lower than GUM clinic attenders. In a logistic regression analysis, increased age, female sex and MS diagnosis all independently increased the odds of seropositivity after adjustment for each other. CONCLUSION: It is concluded that there is increased likelihood of HSV-2 exposure in patients with MS and this may indicate a higher than average number of partners.