Inhibition of herpes simplex virus reactivation by dipyridamole.

Herpes simplex virus (HSV) reactivation from latency was investigated. Reactivation of thymidine kinase-negative HSV, which is defective for reactivation, was greatly enhanced by thymidine (TdR). The reactivation-enhancing effect of TdR was blocked by dipyridamole (DPM), a known nucleoside transport inhibitor. DPM also inhibited wild-type HSV reactivation, suggesting potential antiviral use.

Herpes zoster infection and postherpetic neuralgia.

Varicella-zoster virus (VZV), the cause of chicken pox, establishes latent infection in sensory ganglia. Reactivation results in zoster (shingles), sometimes complicated by encephalitis (myelitis). Postherpetic neuralgia (PHN) is the major morbidity of zoster. PHN typically increases in frequency with age. The VZV vaccine, which was developed for children, may be effective in enhancing VZV immune reactivity and decreasing zoster in adults. Early antiviral treatment may be effective in decreasing PHN onset. Several other medications may be useful in treating established PHN. A recent report discussed intrathecal steroid use.

Leukotropic herpesviruses in multiple sclerosis.

Detection frequency of human herpesvirus 6 (HHV-6) and Epstein Barr virus (EBV) DNA in multiple sclerosis (MS) patients and controls was investigated. DNA of peripheral blood mononuclear leukocytes (PBL) was isolated and amplified by polymerase chain reaction techniques. EBV DNA was detected in all patients and controls. HHV-6 DNA was detected in 7% of MS patients and in 14% of controls. Results are compared with other investigations of HHV-6 DNA in PBL, serum, CSF and brain of patients with MS. Results of the present study and other investigations do not show an association between HHV-6 in PBL and MS. Multiple Sclerosis (2000) 6, 66 - 68

Herpes simplex virus latency after direct ganglion virus inoculation.

Herpes simplex virus (HSV) latent infection of ganglion neurons follows axoplasmic transport of HSV, probably in the form of nucleocapsid from peripheral sites of infection (e.g. footpad). This raises the possibility that latency is dependent on this particular means of presenting HSV to ganglion neurons. To investigate this, we directly infected ganglia of mice with HSV and evaluated latency. Initially, ganglia were surgically exposed in intact mice, infected with HSV and after 4 weeks evaluated for HSV latency-associated transcript (LAT) expression. LAT expression suggested latency. To more fully evaluate latency after direct ganglion inoculation, a transplant model was developed. In this model, ganglia were removed from mice, inoculated with HSV, transplanted into syngeneic recipients and evaluated for latency after several weeks. Latency was evident in transplanted ganglia by (1) the presence of LAT in neurons; (2) the lack of HSV ICP4 RNA or viral antigen, and (3) the isolation of HSV from explants of transplants but not from direct homogenates. The transplant model was then used to evaluate the effect of inhibition of HSV replication on latency. Antivirals which inhibited HSV replication markedly decreased the number of LAT-positive neurons in transplants, suggesting a role for HSV replication mechanisms and latency. It is thought that direct ganglion inoculation and ganglion transplant methods will permit unique investigations of mechanisms of latency.

Trigeminal neuralgia: mechanisms of treatment.

BACKGROUND: Mechanisms of the surgical treatment of trigeminal neuralgia are considered. RESULTS: Trigeminal neuralgia is effectively treated by microvascular decompression (MVD) and other surgical procedures. These procedures often cause reactivation of herpes simplex virus (HSV), which is latent in trigeminal ganglion neurons. CONCLUSION: MVD and other surgical procedures alter ganglion neuron transcription, as indicated by HSV reactivation. Controlled injury of the trigeminal root-ganglion probably occurs with the disparate surgical procedures, and this is likely the means of their effectiveness.

Inhibition of herpes simplex virus reactivation by dipyridamole in a mouse model.

Herpes simplex virus (HSV) thymidine kinase (TK) has been demonstrated to be important for reactivation from latency. Specifically, HSV latency-associated transcripts (LAT) are expressed during latent infection established by TK-negative (TK-) HSV mutants, but reactivation is minimal. TK- HSV, however, readily reactivated in the presence of exogenous thymidine (TdR) in explant medium [Tenser et al. (1996): Journal of Virology 70:1271-1276]. In the present report this was further studied by evaluating the effect of dipyridamole (DPM) on HSV reactivation. DPM is known to interfere with nucleoside transport. Inhibition of TdR-enhanced reactivation of TK- HSV and inhibition of reactivation of wild-type TK+ HSV were evaluated in an experimental mouse model of latency. Without DPM, TK- HSV reactivation was increased from 0% to 88% with TdR in explant medium, demonstrating TdR-enhanced reactivation of TK- HSV (as seen previously), TdR-enhanced reactivation of TK- HSV was decreased when DPM (25 or 50 microM) was also present, to 30%-60% and to 0%, respectively. Secondly, DPM also decreased reactivation of wild-type TK+ HSV. The reactivation frequency of latently infected dorsal root ganglia was 90% in standard medium (no added TdR), and this was decreased by DPM to 9% and 0%, respectively. Reactivation of trigeminal ganglia in standard medium was 100%, and this decreased to 59% and 23%, respectively. The possibility of a direct toxic effect of DPM on ganglion neurons to explain the results was unlikely. DPM had a modest antiviral effect on HSV replication in cell culture, and its efficacy in blocking reactivation may be related to this activity, probably by inhibition of nucleoside transport.

Reactivation of thymidine kinase-defective herpes simplex virus is enhanced by nucleoside.

Herpes simplex virus (HSV) mutants defective for thymidine kinase expression (TK-) have been reported to establish latent infection of sensory ganglia of mice, in that HSV latency-associated transcript is expressed, but to be defective for reactivation. In the present study, the mechanism of defective reactivation by TK- HSV was investigated. Latent infection established by each of three reactivation-defective HSV type 1 mutants was studied. Reactivation in explant culture was markedly enhanced by the addition of thymidine (dTdR) to the explant culture medium. Without added dTdR, reactivation occurred in 0 of 32 ganglia, while when dTdR (200 microM) was present, reactivation occurred in 32 of 37 ganglia (86%). Reactivation was minimal or did not occur after treatment with other nucleosides; specificity for dTdR would suggest the importance of dTdR nucleotide levels rather than more general nucleotide pool imbalance. Enhanced reactivation by dTdR was dose dependent and was blocked by acyclovir. While some degree of inhibition of TK- HSV by acyclovir may be expected, the complete block of dTdR-enhanced reactivation was unexpected. This result may suggest that HSV is particularly vulnerable during initial reactivation events. The mechanism of dTdR-enhanced reactivation of TK- HSV was further evaluated during in vivo infection by TK- HSV. For mice infected with TK- HSV, virus was undetectable in ganglia 3 days later. However, for mice infected with TK- HSV and treated with dTdR, virus was readily detected (2.8 x 10(3) PFU per ganglion). This result suggested that in vivo treatment with dTdR enhanced replication of TK- HSV in ganglion neurons. In turn, this suggests that in latently infected ganglia, dTdR-enhanced reactivation of TK- HSV occurred as a result of viral replication in neurons following initial reactivation events.

The role of herpes simplex thymidine kinase expression in neurovirulence and latency in newborn vs. adult mice.

Infection by standard thymidine kinase-positive (TK+) and TK- mutant herpes simplex virus (HSV) was performed in order to evaluate the role of HSV TK expression in neurovirulence and in HSV latency. In newborn mice, mortality and trigeminal ganglion (TG) HSV titer correlated (both were high) for TK+ and TK- HSV. In adult mice after TK- HSV infection they also correlated (both were low). After TK+ infection of adult mice, correlation was not present; mortality was low while HSV titer was moderately high. During the period of HSV latent infection (> 28 days after HSV infection), the number of neurons expressing HSV latency-associated transcript (LAT) was much greater for TK- HSV newborn-inoculated mice (average of 943/ganglion) than adult-inoculated mice (average of 138/ganglion). In addition, total amount of TG LAT was greater in the former than the latter. Reactivation from latency was restricted, however, for both groups. This result supported the important role of HSV TK expression in HSV reactivation, even when the number of LAT-positive neurons was greatly increased. The following conclusions were drawn from the study of TK- HSV in newborn mice: (i) HSV TK expression was of limited importance for neurovirulence and in vivo HSV TG infection (but was of importance in adult mice); (ii) increased in vivo HSV TG infection correlated with increased number of LAT-positive neurons, so that HSV replication and establishment of latency were not completely separable; and (iii) even with greatly increased numbers of latently infected neurons, HSV TK expression was important for reactivation from latency. Results in newborn mice suggested that the role of HSV TK expression in reactivation from latency and in neurovirulence were separable. To further investigate HSV replication in newborn and adult mice, ganglia were infected with HSV in vitro and either maintained in vitro or transplanted beneath the renal capsule of adult recipients. In both of these studies, HSV titers in ganglia were much higher in newborn than adult ganglia. This suggested that in addition to the well-know role of the immune system in HSV neurovirulence in newborn mice, it is likely that HSV replication per se in neural tissue is greater in newborn than adult mice. This may be related to the high level of HSV neurovirulence in newborn mice.

Secondary herpes simplex virus latent infection in transplanted ganglia.

Sensory ganglia latently infected with herpes simplex virus (HSV) were transplanted beneath the renal capsule of syngeneic recipients, and the latent infection remaining was investigated. HSV latency-associated transcript (LAT) expression and reactivation of HSV after explant of transplanted dorsal root ganglia were monitored as markers of latency. Two to four weeks after transplantation, both indicated evidence of HSV latency in transplants. At those times, infectious virus was not detected in direct ganglion homogenates. In addition, viral antigen and infected cell polypeptide 4 RNA were not detected. Taken together, the results suggested that HSV latent infection rather than persistent infection was present in transplants. From these results, two explanations seemed possible: latency was maintained in transplanted neurons, or alternatively, latency developed after transplantation, in neurons not previously latently infected. The latter was considered putative secondary latency and was investigated in three ways. First, evidence of reactivation which might serve as a source for secondary latency was evaluated. Reactivation of HSV in transplants was evident from HSV antigen expression (52% of transplants) and the presence of cell-free virus (38% of transplants) 3 to 5 days after transplantation. Second, putative secondary latency was investigated in recipients immunized with HSV prior to receiving latently infected ganglia. Reactivation was not detected 3 to 5 days after transplantation in immunized recipients, and LAT expression was rare in these recipients after 3 to 4 weeks. Lastly, the possibility of secondary latency was investigated by comparing results obtained with standard HSV and with reactivation-defective thymidine kinase-negative (TK-) HSV. Defective reactivation of TK- HSV was demonstrated by immunohistochemistry and by the inability to isolate infectious virus. Donor dorsal root ganglia latently infected with TK+ HSV showed many LAT-positive neurons 2 or more weeks after transplantation (average, 26 per transplant). However, LAT expression was undetectable or minimal > 2 weeks after transplantation in donor ganglia latently infected with TK- HSV (average, 0.2 per transplant). Impaired reactivation of TK- HSV-infected donor ganglia after transplantation, therefore, was correlated with subsequent limited LAT expression. From these results, the occurrence of secondary latency was concluded for ganglia latently infected with TK+ HSV and transplanted beneath the kidney capsule. In vivo reactivation in this transplant model may provide a more useful means to investigate HSV reactivation than in usual in vitro explant models and may complement other in vivo reactivation models. The occurrence of secondary latency was unique. The inhibition of secondary latency by the immune system may provide an avenue to evaluate immunological control of HSV latency.

Neuronal control of herpes simplex virus latency.

Herpes simplex virus (HSV) is a common neurotropic virus, and latent infection of sensory ganglion neurons readily occurs in humans and in experimentally infected animals. During HSV latency, infectious virus and viral antigen are not detected, and HSV transcription is limited to specific RNA termed latency-associated transcript (LAT). In the present study, the effect of altered nervous system function on HSV latent infection was investigated in dorsal root ganglia (drg) of experimentally infected mice. Latent infection of lumbar drg was established by footpad inoculation of HSV. During latency, sciatic neurectomy was performed in order to modify the in vivo function of latently infected neurons, and HSV LAT and HSV DNA in drg were investigated. Neurectomy has been used in many neurobiological studies to alter neuronal RNA and protein expression. After neurectomy there was a marked decrease in the number of LAT-positive neurons and in the amount of ganglion LAT. This was determined by in situ and RNA (Northern) blot hybridization. The neurectomy-related decrease of HSV LAT was apparent 9-10 days after neurectomy and was more marked after 21 days. The decrease was noted both in drg latently infected with standard thymidine kinase-positive (TK+) HSV and in ganglia infected with mutant TK- HSV. Since TK- HSV is largely reactivation defective, it is concluded that the neurectomy-induced decrease of LAT was probably not the result of in vivo HSV reactivation. It is acknowledged, however, that abortive reactivation by TK- HSV may occur, and decrease of latency may have resulted from neuronal or other host mechanisms subsequent to this. In order to investigate residual HSV latency, in addition to viral transcription, HSV DNA in drg was evaluated by polymerase chain reaction techniques. Decrease of HSV DNA was noted after neurectomy in drg latently infected with either TK+ or TK- HSV. It is suggested that the decrease in LAT expression detected was due to the change in neuronal transcription which is part of the neurectomy-induced axon reaction. Decreased HSV LAT may have led to decreased HSV DNA and latency. The decrease in the molecular markers of HSV latency following neurectomy emphasized the importance of neuronal control mechanisms in the pathogenesis of HSV latent infection.

Immunoglobulin G immunosuppression of multiple sclerosis. Suppression of all three major lymphocyte subsets.

Six patients with relapsing chronic progressive multiple sclerosis were treated on 2 consecutive days with large amounts of IgG to induce immunosuppression. Peripheral blood lymphocyte subsets were monitored for 5 weeks after IgG treatment to determine immunosuppression. Decreased numbers of B, T, and natural killer lymphocytes were detected after treatment. Lymphocyte numbers were at a nadir 1 week after treatment, but an immunosuppressive effect continued to be present after 5 weeks. Although clinical efficacy was not evident in this brief open trial, the decrease of peripheral lymphocyte numbers and the apparent safety of the procedure warrant further study.

Reversible decrease of fluoride resistant acid phosphatase-positive neurons after herpes simplex virus infection.

Herpes simplex virus (HSV) frequently infects human sensory ganglion neurons, and similar infections have been reported in experimental animals. Reported here is an investigation of in vivo neuronal function after HSV infection. It was observed that the proportion of fluoride resistant acid phosphatase (FRAP)-positive trigeminal ganglion neurons was decreased for several months after experimental infection of mice, and it is suggested that other neuronal functions may also be altered by HSV.

Expression of herpes simplex virus type 2 latency-associated transcript in neurons and nonneurons.

The presence of herpes simplex virus type 2 (HSV-2) transcription during in vivo latent infection was investigated by in situ hybridization. Latent infection of mouse dorsal root ganglion was investigated with the BamHI p fragment of HSV-2, which resulted in evidence of ganglion hybridization, and other fragments representing approximately 40% of the genome, which did not result in hybridization. Strand specificity of hybridization was investigated in studies with synthetic oligonucleotides, which supported the conclusion that a latency-associated transcript(s) had been detected. Hybridization was detected with oligonucleotides complementary to the infected-cell polypeptide 0 (ICP0) template strand but not with oligonucleotides synthesized from the ICP0 template strand. Although most hybridization occurred over neurons, in some instances hybridization appeared to occur over nonneuronal ganglion cells, and this was more evident when tissue sections were examined by phase contrast microscopy. Although these results supported the usual neuronal site of HSV-2 latency, latency in nonneuronal cells may be important in considering the pathobiology of HSV-2 infections.

Role of herpes simplex virus thymidine kinase expression in viral pathogenesis and latency.

Herpes simplex virus (HSV) thymidine kinase (TK) expression and the HSV TK gene have been evaluated in studies of gene control, as well as in animal and human studies of viral pathogenesis, including HSV latency. In investigations of the biological role of HSV TK, enzyme expression was noted to be important for HSV infection of nonreplicating cells in culture; and, in experimental animal studies, HSV TK was shown to be important for in vivo latent infection of sensory ganglion neurons. Latency in these studies was determined by the ability of HSV to reactivate from sensory ganglion explants. In recent studies, investigators sought to determine whether the role HSV TK expression plays in latency is primarily in the establishment and maintenance of latency or in the reactivation process. Following infection of experimental animals with HSV TK-deficient mutants, the presence of HSV in ganglia was detected in complementation, rescue, and molecular biological studies. Results suggest that HSV TK expression may be important for HSV reactivation from latency. This was supported by in situ hybridization investigations. In the latter studies, HSV latency associated transcript (LAT) was present in ganglion neurons, although reactivation of HSV from such ganglia was defective. LAT-expressing, reactivation-defective infections established by TK mutants of HSV are considered examples of incomplete latency. From the present review, it appears that HSV TK expression, particularly TK expression of HSV-1, is important for the reactivation of latent HSV infection of sensory ganglion neurons, probably because of limited neuronal TK expression and absent replication capacity of these cells.

Prostaglandin production in chronic progressive multiple sclerosis.

Peripheral blood monocytes have been implicated in the immune reactions that accompany demyelination in patients with multiple sclerosis (MS). We measured prostaglandin E2 (PGE2) and thromboxane B2 (TxB2) release from peripheral monocytes exposed in vitro to complement. Our studies suggest that there is a significantly higher production of PGE2 in monocytes from patients with chronic progressive MS than in those with exacerbation or remitting MS and healthy controls. No significant differences in TxB2 release were noted between the three groups.

Latency-associated transcript but not reactivatable virus is present in sensory ganglion neurons after inoculation of thymidine kinase-negative mutants of herpes simplex virus type 1.

The presence of herpes simplex virus (HSV) latency-associated transcript (LAT) was investigated in sensory ganglion neurons of mice after inoculation with thymidine kinase (TK) mutants of HSV. Ganglion serial sections were examined in order to quantitate numbers of LAT-positive neurons. After inoculation with TK-positive HSV, virus was isolated during latency from explants of most ganglia, and LAT was detected by in situ hybridization in 96% of ganglia. After inoculation with HSV TK mutants, virus was isolated from 0% of ganglia, but LAT was detected in 95 to 100% of ganglia. After inoculation of TK mutants of HSV, therefore, although latent infection as indicated by the isolation of virus from ganglion explants was not detected, the presence of LAT was common. These results suggest that the lack of reactivatable virus after inoculation of HSV TK mutants may be related to a role for HSV TK expression in the reactivation process.