Identifying HSV infected neurons after ocular inoculation

A procedure to deliver herpes simplex virus to the murine trigeminal ganglion

Although initial herpes simplex virus (HSV) infections of the cornea are relatively easily treated, recurrent infections following reactivation of latent virus in the sensory ganglion cells are more difficult to treat. Untreated infections may result in severe consequences, including corneal scarring, glaucoma, and encephalitis. To develop such treatments, an experimental in vivo model was needed in which HSV can be applied directly to trigeminal ganglion cells. We have previously developed such a model to examine the mechanisms of HSV spread from trigeminal neurons to corneal epithelial cells. The current paper describes in detail the technical steps required for implementation of that model. Immunocytochemistry and electron microscopy have been used to validate the efficacy of the described procedures. This technique will be useful for future in vivo studies of neurotrophic viral infections of trigeminal ganglion cells.

Retrograde axonal transport of herpes simplex virus: evidence for a single mechanism and a role for tegument

Herpes simplex virus type I (HSV) typically enters peripheral nerve terminals and then travels back along the nerve to reach the neuronal cell body, where it replicates or enters latency. To monitor axoplasmic transport of HSV, we used the giant axon of the squid, Loligo pealei, a well known system for the study of axoplasmic transport. To deliver HSV into the axoplasm, viral particles stripped of their envelopes by detergent were injected into the giant axon, thereby bypassing the infective process. Labeling the viral tegument protein, VP16, with green fluorescent protein allowed viral particles moving inside the axon to be imaged by confocal microscopy. Viral particles moved 2.2 +/- 0.26 micrometer/sec in the retrograde direction, a rate comparable to that of the transport of endogenous organelles and of virus in mammalian neurons in culture. Electron microscopy confirmed that 96% of motile (stripped) viral particles had lost their envelope but retained tegument, and Western blot analysis revealed that these particles had retained protein from capsid but not envelope. We conclude that (i) HSV recruits the squid retrograde transport machinery; (ii) viral tegument and capsid but not envelope are sufficient for this recruitment; and (iii) the giant axon of the squid provides a unique system to dissect the viral components required for transport and to identify the cellular transport mechanisms they recruit.

Evidence for antigenic cross-reactivity between herpesvirus and the acetylcholine receptor

Herpes simplex virus (HSV) is neurotropic and can pass from neuron to neuron at nerve terminals. During the long evolutionary relationship between HSV and vertebrates, this virus may have evolved surface ligands that mimic nerve cell receptors. The present study was undertaken to determine if herpes simplex virus type 1 (HSV-1) has an antigenic relationship with the acetylcholine receptor (AChR). Mice immunized with HSV-1 antigens or an AChR-expressing cell line were tested for antibodies directed against the AChR. By flow cytometry and ELISA, mouse anti-HSV-1 sera were found to contain antibodies that would bind to an epitope on the plasma membrane of AChR-expressing cells. Mice immunized with the AChR-expressing cells were tested for their resistance to HSV-1 infection. Statistically significantly more of the animals immunized with AChR-expressing cells resisted infection and fatal encephalitis, compared to control animals immunized with a cell line not expressing the AChR. Sera from AChR-immunized mice were tested for anti-HSV antibody by ELISA and were found to contain antibodies cross-reactive with HSV-1 antigens. These sera also neutralized virus in a plaque inhibition assay. The results indicate that there are one or more antigenic epitopes shared by herpesvirus and the AChR. Studies are in progress to define the pathogenetic significance of this molecular mimicry.

The spread of herpes simplex virus type 1 from trigeminal neurons to the murine cornea: an immunoelectron microscopy study

An animal model has been developed to clarify the mechanism for spread of herpes simplex virus (HSV) from neuron to epithelial cells in herpetic epithelial keratitis. HSV was introduced into the murine trigeminal ganglion via stereotaxic guided injection. After 2 to 5 days, the animals were euthanized. Ganglia and corneas were prepared for light and electron microscopic immunocytochemistry with antisera to HSV. At 2 days, labeled axons were identified in the stromal layer. At 3 days, we could detect immunoreactive profiles of trigeminal ganglion cell axons that contained many vesicular structures. By 3 and 4 days, the infection had spread to all layers of epithelium, and the center of a region of infected epithelium appeared thinned. At 5 day, fewer basal cells appeared infected, although infection persisted in superficial cells where it had expanded laterally. Mature HSV was found in the extracellular space surrounding wing and squamous cells. Viral antigen was expressed in small pits along the apical surfaces of wing and squamous cells but not at the basal surface of these cells or on basal cells. This polarized expression of viral antigen resulted in the spread of HSV to superficial cells and limited lateral spread to neighboring basal cells. The pathogenesis of HSV infection in these mice may serve as a model of the human recurrent epithelial disease in the progression of focal sites of infection and transfer from basal to superficial cells.

Herpes simplex virus as a transneuronal tracer

Determining the connections of neural systems is critical for determining how they function. In this review, we focus on the use of HSV-1 and HSV-2 as transneuronal tracers. Using HSV to examine neural circuits is technically simple. HSV is injected into the area of interest, and after several days, the animals are perfused and processed for immunohistochemistry with antibodies to HSV proteins. Variables which influence HSV infection include species of host, age of host, titre of virus, strain of virus and phenotype of infected cell. The choice of strain of HSV is critically important. Several strains of HSV-1 and HSV-2 have been utilized for purposes of transneuronal tract-tracing. HSV has been used successfully to study neuronal circuitry in a variety of different neuroanatomical systems including the somatosensory, olfactory, visual, motor, autonomic and limbic systems.

Distribution of tumor necrosis factor receptor messenger RNA in normal and herpes simplex virus infected trigeminal ganglia in the mouse

PURPOSE

to investigate the distribution of p55 and p75 tumor necrosis factor (TNF) receptor mRNA in normal murine trigeminal ganglia, and in murine trigeminal ganglia acutely infected with McKrae strain herpes simplex virus (HSV).

METHODS

in situ hybridization with antisense 35S-labeled riboprobes for mRNA encoding both the p55 and p75 TNF receptor (TNFR) subtypes was used in normal and HSV-infected murine trigeminal ganglia. Sense riboprobes were used as controls.

RESULTS

in situ hybridization with both p55 and p75 riboprobes produced a strong autoradiographic signal over many, but not all, trigeminal sensory neurons. Signal for mRNA encoding both TNFR subtypes was also present over the arachnoid layers surrounding trigeminal ganglia. Acute ocular HSV infection was accompanied by an intense leukocytic infiltrate into the ophthalmic portion of the trigeminal ganglia, and, in this setting, increased p55 and p75 mRNA signal was closely related to the location and number of infiltrating white blood cells. The distribution and number of trigeminal sensory neurons expressing mRNA for the two TNFR subtypes did not appear to change following infection. Signal over control sections hybridized with sense p55 and p75 TNFR cRNA probes was comparable to background.

CONCLUSIONS

the observed distribution of p55 and p75 TNFR mRNA over trigeminal sensory neurons and over the arachnoid layers surrounding trigeminal ganglia supports suggestions that TNF has a direct effect on neurons, either as a neuromodulator or neurotrophic factor, and that TNF may play a central role in blood-brain barrier regulation. Increased signal for TNFR mRNA in acutely infected trigeminal ganglia appears to reflect infiltration by receptor-bearing white blood cells.

Comparative efficacy of expression of genes delivered to mouse sensory neurons with herpes virus vectors

To achieve gene delivery to sensory neurons of the trigeminal ganglion, thymidine kinase-negative (TK-) herpes simplex viruses (HSV) containing the reporter gene lacZ (the gene for E. coli beta-galactosidase) downstream of viral (in vectors RH116 and tkLTRZ1) or mammalian (in vector NSE-lacZ-tk) promoters were inoculated onto mouse cornea and snout. Trigeminal ganglia were removed 4, 14, 30, and 60 days after inoculation with vectors and histochemically processed with 5-bromo-4-chloro-3 indolyl-beta-galactoside (X-Gal). With vector tkLTRZ1, large numbers of labeled neurons were observed in rostromedial and central trigeminal ganglion at 4 days after inoculation. A gradual decline in the number of labeled neurons was observed with this vector at subsequent time points. With vectors RH116 and NSE-lacZ-tk, smaller numbers of labeled neurons were seen at 4 days following inoculation than were observed with vector tkLTRZ1. No labeled neurons could be observed at 14 days after inoculation with vectors RH116 and NSE-lacZ-tk. Immunocytochemistry for E. coli beta-galactosidase and in situ hybridization to HSV latency-associated transcripts revealed labeled neurons in regions of the trigeminal ganglion similar to that observed with X-Gal staining. A comparable distribution of labeled neurons in trigeminal ganglion was also observed after application of the retrograde tracer Fluoro-Gold to mouse cornea and snout. These data provide evidence that retrogradely transported tk- herpes virus vectors can be used to deliver a functional gene to sensory neurons in vivo in an anatomically predictable fashion.

The retrograde tracer Fluoro-Gold interferes with the infectivity of herpes simplex virus

Fluoro-Gold has been used previously to identify those trigeminal ganglion cells that innervate the central cornea. To examine the effects of Fluoro-Gold treatment on infection and spread of HSV in vivo, we measured the number of plaque forming units recovered from trigeminal ganglia 3 or 5 days after corneal scratch and inoculation with Fluoro-Gold and HSV. Treatment with Fluoro-Gold reduced the amount of virus recovered after retrograde transport 63% at 3 days and 28% at 5 days after inoculation. When we examined trigeminal ganglion sections from animals treated with HSV and Fluoro-Gold, we found the number of neurons double labeled with antibodies that recognize HSV and Fluoro-Gold was only 13% of all Fluoro-Gold labeled neurons. This was significantly fewer cells that we had anticipated, on the basis of double labeling experiments with wheat germ agglutinin combined with Fluoro-Gold. The effects of varying doses of the retrograde tracer, Fluoro-Gold on Herpes simplex virus (type 1) (HSV) infectivity were also assayed in vitro using a standard viral plaque assay. At 1 x 10(-3) mg/ml Fluoro-Gold there was no effect on the number of plaque forming units. At 5 x 10(-1) mg/ml the number of plaques was reduced about 67%. We conclude that Fluoro-Gold interferes with productive HSV infection in vivo and in vitro after retrograde transport of HSV by neurons.

Bilateral electroretinographic changes induced by unilateral intra-visual cortex inoculation of herpes simplex virus type 1 in BALB/c mice

Intra-visual cortex inoculation of 10(2) plaque-forming units of herpes simplex virus type 1 (KOS-63) induced physiologic and morphologic retinal changes in 62.3% (33/53) of infected animals; of these, 91% were bilateral. In contrast, inoculation of the same viral titers into the frontal lobe induced retinal alterations in only 13.3% (2/15). Initially, there was a decrease of the b-wave amplitude and retinal sensitivity and necrotic changes of the ganglion cells and nuclei in the inner nuclear layer. Immunoperoxidase staining for virus-specific antigens showed positive staining of the same cell type. Over time, there was a progressive decrease in the electroretinogram until it was extinguished and the retina was replaced by gliotic tissue. Parallel viral recovery studies demonstrated detectable infectious virus in one of eight eyes on day 2 after inoculation and in three of eight eyes on day 4. Thereafter, there was an increase in the percentage of eyes with infectious virus and a concomitant increase in viral titers. Immunoperoxidase staining of brain sections obtained on days 6 through 8 demonstrated virus-specific antigens on cells in the lateral geniculate nuclei and the suprachiasmatic nuclei bilaterally.

Biology and molecular aspects of herpes simplex and varicella-zoster virus infections

The herpes simplex and varicella-zoster viruses are members of the subfamily alpha herpesviruses with specific properties of the virion and with the capacity to establish latent infections in humans. The genome of each of these viruses has been determined with an estimate of the number of genes and proteins encoded. The biology and molecular events of the herpes simplex virus productive and latent infection have been detailed with the use of both in vitro and in vivo model systems. The neuron is the site of latency in the ganglia with a limited transcription of genes expressed during the latent period. The specific molecular regulation of latency and reactivation are not well established. There are co-cultivation, electron microscopy, and biochemical studies that support the concept of corneal latency, although this has not been proven conclusively. Details about the varicella-zoster virus biology and molecular events are not as well advanced since animal models have been lacking. The biology of the productive infection (varicella) is different from herpes simplex virus infection since the portal of entry is the respiratory system. Data support the concept of the maintenance of latency within satellite cells in the ganglia rather than within neurons. There are multiple genes expressed during this latency. These features may explain the different clinical presentations and course of reactivation (zoster) compared with herpes simplex virus reactivation.

Anterograde transport of HSV-1 and HSV-2 in the visual system

The anterograde spread of herpesvirus in the visual system subsequent to retinitis has been observed clinically. We compared the ability of two well-studied Herpes simplex virus (HSV) strains to be transported in the anterograde direction in the hamster visual system: strain McIntyre, representing HSV-1, and strain 186, representing HSV-2. Intravitreal injection of HSV-2 labeled more retinorecipient neurons than did HSV-1, suggesting important type differences in the ability of HSV to infect retinorecipient neurons after intravitreal injection. The most likely explanation for our results is that HSV-2 is more efficiently adsorbed than HSV-1 in the retinal ganglion cells. Our results also suggest that HSV may be useful as an anterograde transneuronal tracer for neuroanatomical studies of the visual system.

Two alpha-herpesvirus strains are transported differentially in the rodent visual system

Uptake and transneuronal passage of wild-type and attenuated strains of a swine alpha-herpesvirus (pseudorabies [PRV]) were examined in rat visual projections. Both strains of virus infected subpopulations of retinal ganglion cells and passed transneuronally to infect retino-recipient neurons in the forebrain. However, the location of infected forebrain neurons varied with the strain of virus. Intravitreal injection of wild-type virus produced two temporally separated waves of infection that eventually reached all known retino-recipient regions of the central neuraxis. By contrast, the attenuated strain of PRV selectively infected a functionally distinct subset of retinal ganglion cells with restricted central projections. The data indicate that projection-specific groups of ganglion cells are differentially susceptible to the two strains of virus and suggest that this sensitivity may be receptor mediated.

Ultrastructural immunocytochemical localization of herpes simplex virus (type 1) in trigeminal ganglion neurons

Four days after corneal inoculation of mice with herpes simplex (type 1) virus (HSV), infected trigeminal ganglion cells with and without calcitonin gene-related peptide (CGRP) antigenicity were examined by electron microscopy in sections treated with colloidal gold labeled antibodies. Cells that contain CGRP were identified by the dense gold labeling of small vesicles about 100 nm in diameter. Adjacent thin sections were stained using an indirect colloidal gold immunocytochemical technique to reveal HSV-1 antigens. In CGRP-positive neurons, HSV antigens were located over both nuclear and cytoplasmic compartments. HSV label was found over cytoplasmic vesicles that were significantly larger than those labeled with anti-CGRP antisera; the HSV-containing vesicles ranged in profile diameter from less than 170 to greater than 400 nm. There was no overlap in the distribution of the two labels. Thus, for this time period, the organelles involved in transport of the endogenous neuropeptide and HSV appear to remain discrete. Furthermore, there was no significant difference in the distribution of HSV in CGRP-reactive and CGRP-negative trigeminal ganglion cells. Thus, there is no indication of a preferential distribution or limited replication of HSV in CGRP-positive neurons.

Selective spread of herpes simplex virus in the central nervous system after ocular inoculation

The spread of herpes simplex virus (HSV) was studied in the mouse central nervous system (CNS) after ocular inoculation. Sites of active viral replication in the CNS were identified by autoradiographic localization of neuronal uptake of tritiated thymidine. Labeled neurons were first noted in the CNS at 4 days postinoculation in the Edinger-Westphal nucleus, ipsilateral spinal trigeminal nucleus, pars caudalis, pars interpolaris, and ipsilateral dorsal horn of the rostral cervical spinal cord. By 5 days postinoculation, additional sites of labeling included the seventh nerve nucleus, nucleus locus coeruleus, and the nuclei raphe magnus and raphe pallidus. None of these sites are contiguous to nuclei infected at 4 days, but all are synaptically related to these nuclei. By 7 days postinoculation, no new foci of labeled cells were noted in the brain stem, but labeled neurons were noted in the amygdala, hippocampus, and somatosensory cortex. Neurons in both the amygdala and hippocampus receive axonal projections from the locus coeruleus. On the basis of these findings, we conclude that the spread of HSV in the CNS after intracameral inoculation is not diffuse but is restricted to a small number of noncontiguous foci in the brain stem and cortex which become infected in a sequential fashion. Since these regions are synaptically related, the principal route of the spread of HSV in the CNS after ocular infection appears to be along axons, presumably via axonal transport rather than by local spread.