Isolation of herpes simplex virus from the cornea in chronic stromal keratitis

Wessely corneal ring phenomenon: An unsolved pathophysiological dilemma

The cornea is a densely innervated, avascular tissue showing exceptional inflammatory and immune responses. The cornea is a site of lymphangiogenic and angiogenic privilege devoid of blood and lymphatic vessels that limits the entry of inflammatory cells from the adjacent and highly immunoreactive conjunctiva. Immunological and anatomical differences between the central and peripheral cornea are also necessary to sustain passive immune privilege. The lower density of antigen-presenting cells in the central cornea and the 5:1 peripheral-to-central corneal ratio of C1 are 2 main features conferring passive immune privilege. C1 activates the complement system by antigen-antibody complexes more effectively in the peripheral cornea and, thus, protects the central corneas' transparency from immune-driven and inflammatory reactions. Wessely rings, also known as corneal immune rings, are non-infectious ring-shaped stromal infiltrates usually formed in the peripheral cornea. They result from a hypersensitivity reaction to foreign antigens, including those of microorganism origin. Thus, they are thought to be composed of inflammatory cells and antigen-antibody complexes. Corneal immune rings have been associated with various infectious and non-infectious causes, including foreign bodies, contact lens wear, refractive procedures, and drugs. We describe the anatomical and immunologic basis underlying Wessely ring formation, its causes, clinical presentation, and management.

An intact complement system dampens cornea inflammation during acute primary HSV-1 infection

Corneal transparency is an essential characteristic necessary for normal vision. In response to microbial infection, the integrity of the cornea can become compromised as a result of the inflammatory response and the ensuing tissue pathology including neovascularization (NV) and collagen lamellae destruction. We have previously found complement activation contributes to cornea pathology-specifically, denervation in response to HSV-1 infection. Therefore, we investigated whether the complement system also played a role in HSV-1-mediated neovascularization. Using wild type (WT) and complement component 3 deficient (C3 KO) mice infected with HSV-1, we found corneal NV was accelerated associated with an increase in inflammatory monocytes (CD11b⁺CCR2⁺CD115^+/-Ly6G^-Ly6C^high), macrophages (CD11b⁺CCR2⁺CD115⁺Ly6G^-Ly6C^high) and a subpopulation of granulocytes/neutrophils (CD11b⁺CCR2^-CD115⁺Ly6G⁺Ly6C^low). There were also increases in select pro-inflammatory and pro-angiogenic factors including IL-1α, matrix metalloproteinases (MMP)-2, MMP-3, MMP-8, CXCL1, CCL2, and VEGF-A that coincided with increased inflammation, neovascularization, and corneal opacity in the C3 KO mice. The difference in inflammation between WT and C3 KO mice was not driven by changes in virus titer. However, viral antigen clearance was hindered in C3 KO mouse corneas suggesting the complement system has a dynamic regulatory role within the cornea once an inflammatory cascade is initiated by HSV-1.

Gene therapy in the anterior eye segment

This review provides comprehensive information about the advances in gene therapy in the anterior segment of the eye including cornea, conjunctiva, lacrimal gland, and trabecular meshwork. We discuss gene delivery systems including viral and non-viral vectors as well as gene editing techniques, mainly CRISPR-Cas9, and epigenetic treatments including antisense and siRNA therapeutics. We also provide a detailed analysis of various anterior segment diseases where gene therapy has been tested with corresponding outcomes. Disease conditions include corneal and conjunctival fibrosis and scarring, corneal epithelial wound healing, corneal graft survival, corneal neovascularization, genetic corneal dystrophies, herpetic keratitis, glaucoma, dry eye disease, and other ocular surface diseases. Although most of the analyzed results on the use and validity of gene therapy at the ocular surface have been obtained in vitro or using animal models, we also discuss the available human studies. Gene therapy approaches are currently considered very promising as emerging future treatments of various diseases, and this field is rapidly expanding.

20 years since the Herpetic Eye Disease Study: Lessons, developments and applications to clinical practice

Herpes Simplex Virus (HSV) is the most common virus that causes eye disease. Although around 60% of the world's population are seropositive for HSV antigens, fortunately, it is estimated that only 1% of seropositive individuals develop eye disease. The most common ocular manifestation of HSV is keratitis, while uveitis and retinal necrosis occur in a small number of cases. HSV keratitis is a debilitating disease, for several reasons: pain , photophobia, and vision loss in acute disease, latency of the virus which leads to infection reactivation from various triggers, scarring, and neovascularisation, leading to permanent vision loss with poor visual rehabilitation prospects. The Herpetic Eye Disease Study (HEDS) was a landmark series of randomised controlled trials in the 1990s that set the benchmark for evidence-based treatment guidelines for anterior eye herpetic disease. Since this time, there has been a change in the distribution of seroprevalence of herpes in the community, a simplified diagnostic classification, advances in treatment options, an emergence of new and a better understanding of risk factors, and discoveries in science that show promise for vaccine and novel future treatments. However, many of the principles of the HEDS study remain rightly entrenched in clinical practice. In this article, the HEDS study is revisited 20 years on through the lens of published literature, to determine current best practise and look towards the future.

HSV1 latent transcription and non-coding RNA: A critical retrospective

Virologists have invested great effort into understanding how the herpes simplex viruses and their relatives are maintained dormant over the lifespan of their host while maintaining the poise to remobilize on sporadic occasions. Piece by piece, our field has defined the tissues in play (the sensory ganglia), the transcriptional units (the latency-associated transcripts), and the responsive genomic region (the long repeats of the viral genomes). With time, the observed complexity of these features has compounded, and the totality of viral factors regulating latency are less obvious. In this review, we compose a comprehensive picture of the viral genetic elements suspected to be relevant to herpes simplex virus 1 (HSV1) latent transcription by conducting a critical analysis of about three decades of research. We describe these studies, which largely involved mutational analysis of the notable latency-associated transcripts (LATs), and more recently a series of viral miRNAs. We also intend to draw attention to the many other less characterized non-coding RNAs, and perhaps coding RNAs, that may be important for consideration when trying to disentangle the multitude of phenotypes of the many genetic modifications introduced into recombinant HSV1 strains.

Real-time polymerase chain reaction for the diagnosis of necrotizing herpes stromal keratitis

AIM

To design, optimize and validate a rapid, internally controlled real-time polymerase chain reaction (RT-PCR) test for herpes simplex virus (HSV) in the diagnosis of necrotizing herpes stromal keratitis.

METHODS

Tears alone or together with corneal epithelium scrapings from 30 patients (30 eyes) suspected of necrotizing herpes stromal keratitis were tested for HSV DNA by RT-PCR. The samples were collected during the first visit and then on the subsequent 7, 14, 28, 42, and 56d. The symptoms of the patients were scored before treatment to determine the correlation between HSV concentration in the corneal epithelium scrapings and clinical scores.

RESULTS

The positive rate (46.4%) in the corneal epithelium group before the therapy was significantly higher than that (13.3%) in the tears group (P=0.006). There were 13 positive HSV patients before the therapy, the concentration of HSV DNA in corneal epithelium scrapings group was significantly higher than that in the tears group (paired t-test, P=0.0397). Multilevel mixed-effects model analysis showed that the difference between the corneal epithelium scrapings group and the tears group was statistically significant (P=0.0049). The Spearman rank correlation analysis indicated a positive correlation between the HSV concentration in the corneal epithelium scrapings and clinical scores before the treatment (r=0.844, P<0.0001).

CONCLUSION

RT-PCR appears to be a powerful molecular tool for the diagnosis of necrotizing herpes stromal keratitis.

Novel biotinylated lipid prodrugs of acyclovir for the treatment of herpetic keratitis (HK): transporter recognition, tissue stability and antiviral activity

PURPOSE

Biotinylated lipid prodrugs of acyclovir (ACV) were designed to target the sodium dependent multivitamin transporter (SMVT) on the cornea to facilitate enhanced cellular absorption of ACV.

METHODS

All the prodrugs were screened for in vitro cellular uptake, interaction with SMVT, docking analysis, cytotoxicity, enzymatic stability and antiviral activity.

RESULTS

Uptake of biotinylated lipid prodrugs of ACV (B-R-ACV and B-12HS-ACV) was significantly higher than biotinylated prodrug (B-ACV), lipid prodrugs (R-ACV and 12HS-ACV) and ACV in corneal cells. Transepithelial transport across rabbit corneas indicated the recognition of the prodrugs by SMVT. Average Vina scores obtained from docking studies further confirmed that biotinylated lipid prodrugs possess enhanced affinity towards SMVT. All the prodrugs studied did not cause any cytotoxicity and were found to be safe and non-toxic. B-R-ACV and B-12HS-ACV were found to be relatively more stable in ocular tissue homogenates and exhibited excellent antiviral activity.

CONCLUSIONS

Biotinylated lipid prodrugs demonstrated synergistic improvement in cellular uptake due to recognition of the prodrugs by SMVT on the cornea and lipid mediated transcellular diffusion. These biotinylated lipid prodrugs appear to be promising drug candidates for the treatment of herpetic keratitis (HK) and may lower ACV resistance in patients with poor clinical response.

Targeting herpetic keratitis by gene therapy

Ocular gene therapy is rapidly becoming a reality. By November 2012, approximately 28 clinical trials were approved to assess novel gene therapy agents. Viral infections such as herpetic keratitis caused by herpes simplex virus 1 (HSV-1) can cause serious complications that may lead to blindness. Recurrence of the disease is likely and cornea transplantation, therefore, might not be the ideal therapeutic solution. This paper will focus on the current situation of ocular gene therapy research against herpetic keratitis, including the use of viral and nonviral vectors, routes of delivery of therapeutic genes, new techniques, and key research strategies. Whereas the correction of inherited diseases was the initial goal of the field of gene therapy, here we discuss transgene expression, gene replacement, silencing, or clipping. Gene therapy of herpetic keratitis previously reported in the literature is screened emphasizing candidate gene therapy targets. Commonly adopted strategies are discussed to assess the relative advantages of the protective therapy using antiviral drugs and the common gene therapy against long-term HSV-1 ocular infections signs, inflammation and neovascularization. Successful gene therapy can provide innovative physiological and pharmaceutical solutions against herpetic keratitis.

Ocular herpes simplex virus type 1: is the cornea a reservoir for viral latency or a fast pit stop?

PURPOSE

To present a review supporting and refuting evidence from mouse, rabbit, nonhuman primate, and human studies of herpes simplex virus type 1 (HSV-1) concerning corneal latency.

METHODS

More than 50 research articles on HSV-1 published in peer-reviewed journals were examined.

RESULTS

Infectious HSV-1 has been found in mouse denervated tissues and in tissues with negative cultures from the corresponding ganglion. However, the different mouse strains have shown varied responses to different strains of HSV, making it difficult to relate such findings to humans. Rabbit studies provide excellent evidence for HSV-1 corneal latency including data on HSV-1 migration from the cornea into the corneoscleral rim and on the distribution of HSV-1 DNA in the cornea. However, the available methods for the detection of infectious HSV-1 may not be sensitive enough to detect low-level infection. Infectious HSV-1 has been successfully isolated from the tears of nonhuman primates in the absence of detectable corneal lesions. The recurrence of corneal ulcers in nonhuman primates before the appearance of infectious HSV-1 in tears suggests that the origin of the HSV-1 is the cornea, rather than the trigeminal ganglion. Human studies presented evidence of both ganglion and corneal latency.

CONCLUSIONS

Understanding HSV-1 disease progression and the possibility of corneal latency could lead to more effective treatments for herpetic keratitis. However, it is unlikely that operational latency in the cornea will be definitively proven unless a new method with higher sensitivity for the detection of infectious virus is developed.

Corneal latency and transmission of herpes simplex virus-1

The transmission of herpes simplex virus (HSV)-1 by corneal transplantation has rarely been reported. It is believed that these cases have resulted either from reactivated virus traveling from the trigeminal ganglion to the cornea or from latent HSV-1 in the donor cornea itself. Studies of long-term viral presence in corneal tissue have sought to determine whether there is evidence of true non-neuronal latency, although there are problems in its definition. Recent studies provide new insights into neuronal latency, while similar HSV-1 gene regulation in the cornea may implicate corneal latency in pathophysiology and as a potential risk for transplant recipients. This issue has led to concerns over eye banking, which currently screens for other infectious agents but not HSV-1. Here we review the literature regarding corneal latency and the transmission of HSV-1.

Extraneuronal herpetic latency: animal and human corneal studies

HSV DNA has been previously detected by both in situ and dot blot hybridization in neuronal tissues latently infected with herpes simplex virus (HSV), but not in extraneuronal tissues. The present study, using dot blot hybridization with a cloned full-length HSV DNA probe and subtractive hybridization assays for detecting HSV RNA, reveals both the presence and activity of the HSV genome in 100% of HSV latently infected rabbit corneas tested. Studies on human herpetic corneas taken at keratoplasty using slot blot hybridization with a cloned full-length HSV DNA probe demonstrated positive binding (hybridization) to the probe in 50% of samples tested but no binding to normal human control DNA. These studies confirm earlier, less sensitive virus recovery assays and implicate the cornea as an extraneuronal site of HSV latency and reactivation.

Corneal Toxicity of Cell-Penetrating Peptides That InhibitHerpes simplexVirus Entry

Cell-penetrating peptides (CPPs) inhibit Herpes simplex virus entry at low micromolar concentrations and may be useful either as prophylactic or therapeutic agents for herpetic keratitis. The aim of this study was to assess the in vitro and in vivo toxicity of three CPPs-EB, TAT-C, and HOM (penetratin)-for the cornea. Incubation of primary (HK320) or immortalized (THK320) human keratocytes with the EB peptide (up to 100 microM), bHOMd (up to 200 microM), or TAT-C (up to 400 microM) resulted in no evidence of toxicity using a formazan dye-reduction assay. Similar results were obtained with a human trabecular meshwork cell line (TM-1), primary human foreskin fibroblasts (DP-9), Vero, and HeLa cells with EB and TATC. The bHOMd peptide showed some toxicity in Vero and HeLa cells, with CC50 values of 70 and 93 microM, respectively. The EB peptide did not inhibit macromolecular synthesis in Vero cells at concentrations below 150 microM, although cell proliferation was blocked at concentrations of EB above 50 microM. In vivo toxicity was assessed by applying peptides in Dulbecco's modified Eagle's medium to the cornea 4 times daily for 7 d. At concentrations 1000 times the IC50 values, the EB and bHOM peptides showed no toxicity, whereas TAT-C caused some mild eyelid swelling. Some slight epithelial cell sloughing was seen with the bKLA peptide in vivo. These results suggest that these CPPs-and EB in particular-have a favorable toxicity profile, and that further development is warranted.

Pathogenesis and management of herpes simplex virus keratitis

Herpes simplex keratitis (HSK) remains a common cause of unilateral corneal disease. Despite intense research over three decades, the mainstay of therapy continues to be topical and, more recently, systemic acyclovir plus topical corticosteroid in some cases. There is increasing recognition that HSK after keratoplasty can occur not only as a result of recurrence in patients with HSK, but also in patients with other primary diagnoses as a result of activation of HSV in the host, or by transmission of virus in the donor tissue.

The outcome of corneal grafting in patients with stromal keratitis of herpetic and non-herpetic origin

AIM

To evaluate the outcome of corneal grafting in patients with stromal keratitis of herpetic (HSK) and non-herpetic origin, using predefined diagnostic criteria and standardised postoperative therapeutic strategies.

METHODS

384 adult immunocompetent recipients of a corneal graft for herpetic (n = 186) or non-herpetic (n = 198) keratitis were followed up prospectively for up to 5 years.

RESULTS

The herpetic group displayed significantly more corneal vascularisation (p = 0.013), more epithelial defects (p = 0.049), lower corneal sensitivity (p <0.001), more graft rejection episodes (p = 0.002), and required larger grafts (p<0.001). However, the postoperative course of visual acuity, endothelial cell numerical density, and rate of graft failures were similar in both groups. After 5 years, cumulative probability of graft survival in HSK patients (40.85%) was similar to that observed in individuals with non-herpetic keratitis (50.15%; log rank = 0.874; relative risk: 1.04).

CONCLUSION

Despite a markedly higher preoperative risk profile in herpetic eyes, the functional outcomes of grafts in individuals with keratitis of herpetic or non-herpetic origin were similar. Probably the most important contribution is a consequent close follow up and a therapeutic strategy including systemic prophylaxis of viral recurrence and of graft rejection by well adopted local steroid therapy.

Advances in diagnosis and management of herpetic uveitis

Herpetic eye disease is common and is frequently associated with intraocular inflammation or uveitis. Despite recent advances in measuring anti-herpes virus antibodies and viral DNA in ocular fluids, diagnosis remains largely clinical. The two more common syndromes include anterior uveitis, often associated with keratitis, and the acute retinal necrosis (ARN) syndrome. Treatment is complex and requires careful monitoring to provide the appropriate balance of antiviral medication and corticosteroids. Long-term prophylaxis with oral antiviral agents may be required in selected patients to help prevent the vision-compromising complications associated with recurrences.

Human herpesviruses in the cornea

AIMS

To determine the sensitivity and specificity of culture, immunohistochemistry (IHC), the polymerase chain reaction (PCR), and in situ hybridisation (ISH) for detecting herpes simplex virus (HSV-1) in the cornea of patients undergoing penetrating keratoplasty. To compare the incidence of HSV-1 in the cornea with that of varicella zoster virus (VZV), cytomegalovirus (CMV), and Epstein-Barr virus (EBV).

METHODS

The corneas of 110 patients, 52 with a documented history of herpes keratitis (HSK) and 58 with non-herpetic corneal disease, were investigated using IHC, PCR, ISH, and culture.

RESULTS

HSV-1 DNA and antigen were detected in 82% and 74% respectively, of corneas of patients with HSK and in 22% and 15% of corneas of patients with no history of HSK. The sensitivity of PCR and IHC was 82% and 74% with a specificity of 78% and 85%, respectively. HSV-1 DNA and antigen were found more frequently and in increased amounts in corneas of patients with a short interval between their last attack of HSK and surgery. There was a good correlation between PCR and IHC in 71%. HSV-1 was isolated by culture in 2%. Latency associated transcripts were not detected using ISH. Evidence of VZV DNA or antigen was found significantly more frequently in the corneas of patients with a history of HSK (p<0.001). No evidence of EBV or CMV was found in any cornea.

CONCLUSIONS

PCR and IHC are both sensitive for the detection of HSV-1 in the cornea. A combination of PCR and IHC increases the specificity for the diagnosis of HSK to 97%. HSV-1 appears to be slowly removed from the cornea. VZV and HSV-1 may co-infect the cornea.

The impact of the herpetic eye disease studies on the management of herpes simplex virus ocular infections

Herpes simplex virus (HSV) is a leading cause of chronic infectious ocular disease in the United States. The morbidity from recurrent herpetic episodes is high, and the resultant corneal scarring may require penetrating keratoplasty for visual rehabilitation. Effective treatments for acute episodes of HSV have been verified by early Herpetic Eye Disease Study (HEDS) trials. The recent HEDS trial on the efficacy of oral acyclovir as prophylaxis against recurrent stromal keratitis represents the first report of a treatment likely to reduce long-term scarring from herpetic disease. This article reviews all the HEDS trials and the implications of their findings for the management of patients with ocular HSV.

Molecular aspects of herpes simplex virus I latency, reactivation, and recurrence

The application of molecular biology in the study of the pathogenesis of herpes simplex virus type 1 (HSV-1) has led to significant advances in our understanding of mechanisms that regulate virus behavior in sensory neurons and epithelial tissue. Such study has provided insight into the relationship of host and viral factors that regulate latency, reactivation, and recurrent disease. This review attempts to distill decades of information involving human, animal, and cell culture studies of HSV-1 with the goal of correlating molecular events with the clinical and laboratory behavior of the virus during latency, reactivation, and recurrent disease. The purpose of such an attempt is to acquaint the clinician/scientist with the current thinking in the field, and to provide key references upon which current opinions rest.

Low rate shedding of HSV-1 DNA, but not of infectious virus from human donor corneae into culture media

Fluid samples derived from 451 organ cultured corneae were tested for the presence of HSV-1 DNA after electroseparation and amplification for fragments of the glycoprotein D- and thymidine kinase-encoding genes. Of the culture media, 134 were processed immediately after withdrawal (Group 1); 100 were stored at ambient temperature for 6 to 60 weeks (Group 2); 90 were stored at -8 degrees C for 4 to 9 weeks (Group 3); and 127 were stored at -20 degrees C for 2 to 30 weeks (Group 4). The degradation of human DNA (marker gene, betaglobin) under these different storage conditions and of human and HSV-1 DNA as a sequential function of time at ambient temperature was gauged by the loss of a detectable signal for the respective component. Endothelial cell density within each of the corneal discs was determined before and after organ culture. In 7/451 culture fluid samples, HSV-1 DNA corresponding to either the glycoprotein D- or thymidine kinase-encoding genes was detected. In culture fluid samples derived from Group 2 at ambient temperature, for 6 to 60 weeks) and 3 (at -8 degrees C, for 4 to 9 weeks), complete degradation precluded the detection of human DNA, and hence probably also of HSV-1 DNA; only at -20 degrees C did DNA remain stable for protracted periods of time. Even so, HSV-1 DNA was detected in only 2% of those media in which no degradation was to be expected; additionally, there existed no correlation between its presence in culture fluid samples and the loss of endothelial cells or cytopathic changes. DNA can be extracted successfully and concentrated twenty-fold from high-volume samples by electroseparation. When shed into culture fluid, it is remarkably prone to a time and temperature dependent degradation, which may lead to false negative results. It is concluded that there is no infectious virus to be expected in the specimens; the occurrence of HSV-1 DNA in donor corneae would not appear to be an important factor influencing their biological quality during the period of organ culture.

Slow viral replication of HSV-1 is responsible for early recurrence of herpetic keratitis after corneal grafting

BACKGROUND

The presence of herpetic DNA has been shown in diseased and healthy corneal tissue. A clinical correlation with the activity of the disease has not yet been demonstrated. This study was done to evaluate the use of DNA amplification for HSV-1 from different sites for the clinical prognosis after corneal grafting.

PATIENTS AND METHODS

Eighteen patients with herpetic keratitis, 8 patients with other forms of keratitis, and 15 patients with corneal disease unrelated to herpes undergoing penetrating keratoplasty were investigated. From these, aqueous humor was obtained at the time of surgery. The excised cornea was divided into three parts for paraffin embedding, 24 h tissue culture and preparation of minced tissue. All samples were processed for HSV-1 glycoprotein D PCR followed by Southern blot and DNA hybridization.

RESULTS

In the herpes group, target DNA was detected in 4/18 aqueous humor samples, 7/16 minced tissue preparations, 6/18 explant culture fluid samples and 4/15 paraffin sections. In the control groups of other keratitis and non-herpetic eye disease, respectively, target DNA was found in 0/5 and 2/12 aqueous humor samples, 1/6 and 0/12 minced tissue preparations, 0/8 and 0/15 explant culture fluid samples and in 1/6 and 1/14 paraffin sections. Five of six patients in whom herpes DNA was detected in the short-term tissue culture experienced an episode of herpes reactivation, within 4 months after transplantation, whereas only one of the remaining patients in all three groups did so (p = 0.0005).

CONCLUSION

A slow viral replication may be responsible for early recurrence of herpetic keratitis after corneal grafting. Detection of herpetic DNA in short-term tissue cultures from explant tissues may help to define the patients at risk.

Detection of herpes simplex virus DNA in donor cornea culture medium by polymerase chain reaction

AIMS/BACKGROUND

Herpes simplex virus (HSV) may establish latent infection in the cornea and therefore be transmissible by corneal transplantation. Monitoring of donor cornea culture medium was evaluated for HSV infection.

METHODS

HSV was sought using virus isolation in cell culture, and its DNA was amplified to detectable levels using the polymerase chain reaction (PCR).

RESULTS

Virus isolation in cell culture was negative on neat, cell pellet, and cell free supernatant prepared from the spent culture media of 80 corneas. Three cell pellets (3.8%) were positive for HSV DNA. The PCR positive culture negative results might have reflected latent rather than active HSV infection of the cornea. Post transplant follow up of the three recipients of corneas with HSV PCR positive organ culture media revealed no evidence of HSV induced eye disease or primary graft failure.

CONCLUSION

Screening of corneal culture medium for HSV by virus culture or for HSV DNA by PCR could not be recommended.

Herpes simplex virus DNA in normal corneas: persistence without viral shedding from ganglia

Herpes simplex virus type 1 (HSV-1) DNA has been shown to persist in the cornea not only after inoculation of experimental animals but also in surgical samples from patients with herpes keratitis. The further observation of corneal HSV-1 DNA in subjects without known HSV eye disease prompted the present study of the presence and distribution of HSV-1 in eye bank corneas. Prior to DNA extraction, the corneas were trephined, separating the central and peripheral cornea. With polymerase chain reaction (PCR) for HSV-1 thymidine kinase (TK) and glycoprotein D (gD) gene sequences, we found HSV-1 in 10 of 24 eye bank corneas, from the 4 mm wide corneal rim in 8 eyes and from the 8 mm diameter central cornea in 2 eyes. In 9 subjects, both eyes were assayed, and HSV-1 was detected in 6 subjects. In only one subject was HSV-1 detected in both eyes and in only one subject was HSV-1 detected in the central and peripheral cornea of the same eye. The biological role of HSV-1 DNA corneal sequences is unknown. To investigate this, a rabbit animal model was established by transplantation of corneas containing viral DNA sequences in HSV-1 naive recipients. Followed for 5 months, there was no evidence of sheeding of HSV-1 in the tear film or seroconversion of the recipient rabbits. At the end of this time, HSV-1 DNA was detected in the corneal graft at a similar intensity to the PCR signal from the donor rims.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-traumatic acquisition of herpes simplex virus infection through the eye

Primary ocular herpes is usually seen as a follicular conjunctivitis and blepharitis, with or without involvement of the cornea. It is unknown, however, to what extent asymptomatic and/or subclinical primary disease occurs, and whether primary ocular herpes follows direct droplet spread to the eye. Previous models of murine ocular herpes have used trauma (scarification) to introduce virus into the cornea, producing disease which results in significant corneal scarring. To mimic a likely route of infection in humans, a droplet containing virus was placed on the mouse eye and clinical disease recorded. At least 1 month after inoculation, serum was assayed for neutralising antibodies and the cornea, iris, and trigeminal ganglion were investigated for evidence of herpes simplex virus type 1, by cocultivation and the polymerase chain reaction. Some animals showed a severe ulcerative blepharitis with little to no involvement of the cornea, while disease was undetectable in others. The development of disease depended on the dose and strain of virus and age of the animal, with older mice appearing more resistant. Virus was isolated from the trigeminal ganglion of younger animals inoculated with higher doses of virus, after 21 days in culture, suggesting that latency had been established. Neutralising antibodies were present in most mice irrespective of the presence of recognisable clinical disease. Using primers for the thymidine kinase and glycoprotein C regions of the viral genome, herpes simplex virus type 1 DNA was found in the cornea, iris, and trigeminal ganglion of most animals and showed a good correlation with the presence of neutralising antibodies. It would thus appear that herpes simplex virus type 1 is able to accede into the cornea, iris, and trigeminal ganglion following nontraumatic application of virus onto the mouse eye. This model mimics primary ocular disease in humans and may be useful for studies on recurrent disease and the spread of ocular herpes.

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.

Evaluation of 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-ethyluracil in a rabbit model of herpetic keratitis

The nucleoside analog 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5- ethyluracil (FEAU) was tested in a rabbit model of acute herpetic keratitis and its effectiveness compared with that of acyclovir (ACV). FEAU or ACV was applied topically 3 times daily, beginning 3 days post-HSV-1 inoculation and continued for a period of 7 days. FEAU at a concentration of 1% (w/v) or 3% ACV resulted in significant lessening of the severity of corneal lesions, conjunctivitis, iritis, and corneal clouding at 24 to 48 h after beginning chemotherapy. No toxic reaction was observed in any rabbit eyes treated with either FEAU or ACV. The duration of virus shedding into tear film and colonization of the trigeminal ganglia, however, were not reduced by either FEAU or ACV treatment begun 3 days post-inoculation. Fifty percent effective dose (ED50) of FEAU determinations performed on isolates from tear film and on the virus inoculum in secondary rabbit kidney cultures yielded a range of 4.6-7 microM, with two in vitro resistant isolates having ED50S of greater than or equal to 1500 microM of FEAU. Fifty percent cell growth inhibition for FEAU was 3000 microM at 72 h.

Latency-associated transcripts in corneas and ganglia of HSV-1 infected rabbits

Herpes simplex virus (HSV) establishes latent infection in the sensory neuron and possibly in non-neuronal tissue, particularly the cornea. During latency only one region of the HSV genome is transcribed, producing RNAs known as latency associated transcripts (LAT). The gene for LAT overlaps with the HSV gene for the protein ICPO in the downstream regions of both genes. Latency can occur in the absence of LAT. This study reports the detection of ICPO/LAT and thymidine kinase (TK) gene fragments by the polymerase chain reaction in DNA extracted from the corneas and trigeminal ganglia of latently infected rabbits. Both genes were detected in four of four trigeminal ganglia tested and in three of five corneas tested. More importantly, this study reports the first detection of LAT in RNA extracted from 9% of corneas from latently infected rabbits (n = 22) by the polymerase chain reaction. LAT was detected in RNA from 100% of the corresponding trigeminal ganglia (n = 22). Although LAT is not essential for latency, it remains the only known molecular marker for latent HSV infections. Detection of LAT in these rabbit corneas suggests that HSV latency may occur in this non-neuronal tissue and that reactivation from non-neuronal tissue may occur at a low frequency in animals in which HSV latency has been established.

Herpes simplex virus: molecular biology and the possibility of corneal latency

Herpes simplex virus (HSV) is known to be latent in ganglionic neurons. Over the past eight years, a series of reports have described the isolation of HSV after organ culture of human corneas that had been removed in the course of penetrating keratoplasty. None of the corneas showed any clinical signs of active herpetic disease immediately before keratoplasty. Studies in rabbits and mice confirmed that HSV can be recovered from corneas by organ culture long after primary infection has subsided. Recently, sophisticated techniques of molecular biology, such as specific DNA or RNA probes, have been used to detect HSV nucleic acids in the cornea. The crux of the matter is whether the virus recovered from or detected in the cornea is 1) truly latent in cell populations that are nonneuronal; 2) resident in the cornea, replicating at a slow rate; or 3) newly arrived in the cornea following ganglionic reactivation. The evidence suggests that a guarded case can be made for limited HSV latency within corneal cells. HSV corneal latency would allow for reactivation, replication, and the immune response to occur in the absence of ganglionic HSV reactivation. Such a localized phenomenon has not, however, been demonstrated to occur clinically.

Evidence for herpes simplex viral latency in the human cornea

Patients undergoing penetrating keratoplasty for prior herpes simplex keratitis (group A) and corneal disease unrelated to herpes simplex (group B) were investigated to assess whether the cornea is a site for herpes simplex viral latency. All patients were seropositive for herpes simplex viral antibody. Virus was isolated from the tear film postoperatively in one patient and on cocultivation from the cornea of another patient. Herpes simplex viral DNA, however, was detected in the corneas of all patients from group A and half of those from group B by means of the polymerase chain reaction and primers to three well separated regions of the viral genome. Three donor corneas had no evidence of herpes simplex viral DNA. Using RNA polymerase chain reaction, we found evidence of a latency associated transcript and also that of a glycoprotein C coding transcript in two corneas, indicating viral replication. Nine corneas had evidence of a latency associated transcript but no glycoprotein C transcript, which suggests that herpes simplex virus may be maintained in a latent state in the corneas of patients with prior herpes simplex keratitis and in some patients with corneal disease unrelated to the herpes simplex virus.

Detection of herpes simplex virus DNA sequences in corneal transplant recipients by polymerase chain reaction assays

Polymerase chain reaction (PCR) assays were used to amplify herpes simplex virus type 1 (HSV-1) thymidine kinase (TK) sequences in DNA extracted from formalin-fixed, paraffin embedded corneas of patients undergoing corneal transplantation. PCR reamplification with an internal (nested) set of primers was required for detection in 10 of the 12 positive corneas indicating very low abundance of viral sequences. Three of the positive corneal samples were from failed corneal grafts. Overall, TK sequences were detected in 8 of 11 corneas from subjects with a past history of herpes keratitis and in 4 of 11 corneas from subjects with no past history of herpetic eye disease.

HSV antigens and HSV DNA in avascular and vascularized lesions of human herpes simplex keratitis

Fifty-one corneal buttons obtained by penetrating keratoplasty from patients with a preoperative clinical diagnosis of nonulcerative herpetic keratitis and/or disciform stromal scarring (44) as well as ulcerative necrotizing stromal keratitis (7) were processed for herpes simplex virus (HSV) antigens using an immunoperoxidase technique and for HSV DNA by the polymerase chain reaction (PCR). HSV antigens were detected significantly more often (p less than 0.025) in specimens with avascular nonulcerative keratitis than in those with vascularization. In contrast to HSV antigens, HSV DNA was identified at equal proportions in avascular and vascularized lesions. Both HSV antigens and HSV DNA were detected in all specimens from patients with ulcerative necrotizing stromal keratitis. The implications of these findings with regard to possible mechanisms underlying herpetic keratitis in man are discussed.

Antiviral drug sensitivity in ocular herpes simplex virus infection

Thirty-nine herpes simplex virus (HSV) isolates were assayed for their sensitivity to 10 different antiviral agents. Of these 39 HSV isolates 10 were cultured from recipient buttons obtained at penetrating keratoplasty in patients with inactive stromal scarring due to recurrent herpetic keratitis, 25 were cultured from patients with conjunctival and ulcerative ocular infections, and the remaining four were laboratory strains with known drug sensitivity patterns, thus providing controls for the experiment. All but one of the 35 clinical isolates of HSV were type 1 and all were sensitive to the 10 antiviral agents. A single type 2 isolate from a young man with recurrent conjunctivitis proved to be resistant to a number of the antiviral agents. Since many of the clinical isolates had been exposed to multiple and protracted antiviral drug treatment, it is suggested that antiviral drug resistance in type 1 HSV ocular infection is not a significant problem.

Herpes simplex stromal and endothelial keratitis. Granulomatous cell reactions at the level of Descemet's membrane, the stroma, and Bowman's layer

Fifty-three (25%) of 215 keratectomy specimens of patients with herpes simplex stromal keratitis displayed granulomatous reactions at the level of Descemet's membrane (50/53), midstroma (13/53), and Bowman's layer (5/53). Using an immunoperoxidase technique, herpes simplex virus (HSV) antigens were detected in keratocytes, endothelial cells, and foci of epithelioid histiocytes and multinucleated giant cells around Descemet's membrane. Both granulomatous reactions and HSV antigens were identified significantly more often in specimens with ulcerative necrotizing stromal keratitis than in those from patients with stromal scarring or nonulcerative nonnecrotizing keratitis (P less than 0.00001 and P less than 0.005, respectively). Herpes simplex virus antigens also were present in endothelial cells adjacent to foci of granulomatous reactions around Descemet's membrane in association with disciform stromal scarring. To our knowledge, this is the first demonstration of HSV antigens in human corneal endothelial cells and in the granulomatous reactions at the level of Descemet's membrane.

Herpes simplex virus ocular infections: current concepts of acute, latent and reactivated disease

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Reactivation of latent herpes simplex virus-1 (HSV) from mouse footpad cells demonstrated by in situ hybridization

HSV-1 specific RNA sequences became detectable by in situ hybridization 5-6 days after culture of footpads (FP) explanted from latently infected mice. HSV-specific RNA first appeared in basal cells of hair follicles and cells of the hair root sheath, in epithelial cells of sebaceous glands and in cells within the epidermis. When first detected graining was light and usually present over individual cells, subsequently graining became heavy and present over large groups of cells. HSV reactivation from latency could be demonstrated in individual cells and therefore identified those cells in which the virus has been latent. The heavy graining over clumps of cells characteristic of a lytic infection was seen at later times after explantation; we infer that the infection had spread progressively from the initial foci of reactivation from latency.

MHC class I and class II antigen expression in normal human corneas and in corneas from cases of herpetic keratitis

The expression of HLA class I and class II antigens in corneas from normal donors and patients with quiescent herpetic keratitis was investigated using specific monoclonal antibodies. Keratocytes from diseased corneas showed aberrant expression of HLA class I and class II (DR, DP and DQ) antigens. The expression of HLA antigens in these corneas was not associated with immune cell infiltrates or viral antigens.

Detection of HSV nucleic acid sequences in the cornea during acute and latent ocular disease

This study evaluated the continued presence of herpes simplex virus (HSV) nucleic acid sequences after resolution of acute herpetic stromal keratitis in the rabbit ocular model. Forty-four rabbits were inoculated bilaterally with 10(5) plaque-forming units of RE strain HSV-1 by intrastromal injection. All eyes were cultured for the presence of HSV during acute disease and immediately before the animals were killed. Full-thickness corneal buttons were then removed and processed for in situ hybridization with a 3H-labelled HSV DNA probe representing the full-length HSV genome. HSV nucleic acid sequences were detected autoradiographically at all time intervals examined. HSV nucleic acid sequences were localized in the epithelium and the anterior stromal keratocytes during acute disease and in all corneal layers during latent infection. Retention of HSV nucleic acid sequences, either HSV DNA or HSV RNA, or both, in corneal tissues (epithelium, stroma, and endothelium) may be a contributing factor in the development of HSV-induced stromal keratitis.

Severe herpetic keratitis. I: Prevalence of visual impairment in a clinic population

We report a prevalence study of the best visual acuity in the affected eye of 100 selected patients with herpetic keratitis seen during a two-year period. Sixty-two patients retained an acuity of 6/9 or better without requiring penetrating keratoplasty (PK). The prevalence of reduced visual acuity severe enough to warrant PK was 33%. Patients requiring PK for whom full clinical records were available suffered a mean of 6.8 episodes of keratitis. In this group of patients the vision of 18 fell from 6/6 to 6/60 over a mean period of 8.5 years. Once visual acuity was permanently reduced to 6/12, 78% of patients proceeded to lose vision to 6/60. Unilateral visual impairment occurs in at least a third of patients with severe herpetic keratitis. Once vision falls permanently to 6/12, the long-term prognosis for vision appears to be poor.

Does herpes simplex virus establish latency in the eye of the mouse?

Clinically scarred and neovascularised corneas observed after zosteriform spread of herpes simplex virus (HSV) to the eye of the mouse were found to contain chronic inflammatory cells with a loose retrocorneal membrane. Goblet cells were found in the corneal epithelium. The trigeminal ganglia of such animals were latently infected with HSV. Whereas HSV was not isolated from eye-washings of diseased eyes, it was isolated from some anterior segments after culture in vitro for up to 13 days. When anterior segments were halved sagittally, HSV could not be isolated from the halves assayed immediately, whereas it was isolated from some of the other halves after organ culture. The possibility of ocular latency is discussed.

Rational acyclovir therapy in herpetic eye disease

Acyclovir has been widely used against the various manifestations of eye disease due to herpes simplex since it first became generally available in the UK nearly five years ago. This paper discusses the rational indications for its use, through considerations of its pharmacology and pharmacokinetics, and through results of the many clinical trials that have been carried out to investigate its effects since its clinical efficacy was first demonstrated in 1979.

Herpes simplex virus isolation in chronic stromal keratitis: human and laboratory studies

The corneal discs of 41 patients with scarring reminiscent of herpetic infection were organ cultured for HSV isolation. Of the 41 patients, 34 had a definite history of herpetic keratitis, from 10 of whom (29.4%) HSV was isolated. There were no clinical features which distinguished between these groups; there was however an indication that those from whom HSV was not isolated had been previously treated with substantial amounts of topical acycloguanosine. In three patients of 12 patients when the disc was separated into 7 parts using a punch technique, virus was isolated exclusively from those portions demonstrating clinical scarring. Electron microscopy (EM) demonstrated HSV particles in stromal cells in the cultured corneas of seven patients. In two of the patients no virus was detected prior to culture with EM. In one patient HSV antigen was not found using peroxidase-antiperoxidase (PAP) staining prior to subsequently positive organ culture. Studies were made to determine how HSV accedes to the corneal stroma using a murine model in which keratitis occurs by zosteriform spread of HSV following inoculation of the snout. Preliminary evidence using PAP staining indicates that the virus reaches the stroma at the same time as the epithelium, via the sensory nerves. Evidence of HSV persistence in anterior segments was obtained in the same model, in contrast to which no virus could be isolated following direct inoculation into the cornea. It is speculated that for virus to set up a longterm association with the stromal keratocyte, it must be introduced via the sensory nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Histopathology of herpes simplex virus keratouveitis

Twenty-four eyes removed for complications of HSV keratitis were studied histopathologically. There were 20 men and 4 women with an average age of 61 years. Severe keratitis was seen in 14, moderate in 7, and mild in 3 eyes. Common features associated with severe keratitis were: acute perforation, granulomatous keratitis with giant cells in the stroma and Descemet's region, stromal inflammatory cells, angle-closure, severe iridocyclitis with diffuse or focal infiltration of lymphocytes and plasma cells, low-grade vitritis, choroiditis, and/or retinal periphlebitis. Specimens with moderate to mild keratitis had a similar distribution of inflammation but a lower incidence of granulomatous keratitis.

Peripheral adrenergic stimulation and indomethacin in experimental ocular shedding of HSV

The application of 6-hydroxydopamine to the cornea by iontophoresis, followed by topical epinephrine, effectively induces herpes simplex virus (HSV) shedding from the external eye of latently infected rabbits. In this study the beta adrenergic blocker, Timolol, reduced virus shedding when applied immediately before the epinephrine, but continued administration resulted in increased viral shedding. While indomethacin, a prostaglandin synthesis inhibitor decreased HSV replication in cell culture, it failed to decrease virus shedding when applied topically to the eye in adrenergically stimulated animals. Timolol may act then by its effect on the peripheral cells of the eye rather than by stimulation of virus production in ganglionic neurons. These same animals were subsequently tested for latent infection of the trigeminal and superior cervical ganglia and corneas 14 months after primary infection. Only 2 of 14 animals had virus in the trigeminal ganglia, a finding which suggests that latent virus may be depleted by repeated reactivations. Virus was recovered from corneas of five rabbits by co-cultivation so it is possible that corneal latency occurs in this rabbit model as it does in humans.

Herpes simplex virus type 1 persistence and latency in cultured rabbit corneal epithelial cells, keratocytes, and endothelial cells

Cell cultures of rabbit corneal epithelium, keratocytes, and endothelium were used to determine the lytic cycle of herpes simplex virus type 1. Viral growth was fastest in epithelial cells. A novel HSV-1 in-vitro latency system was established in the three distinct cell types. Cell cultures were inoculated at low multiplicities of infection with HSV-1. Temperature manipulation alone was used to induce and reactivate latent HSV-1 infections. The presence of cellular stress proteins was demonstrated at supraoptimal temperatures. All cell types were capable of maintaining latent viral infections under these conditions. Viral persistence was present in 20% of epithelial cell cultures at supraoptimal temperatures, but not in keratocyte cultures or endothelial cell cultures.

Herpes simplex virus type 2 establishes latency in the mouse footpad and in the sensory ganglia

Three mouse strains as well as wt and 7 ts mutants of herpes simplex virus (HSV) type 2 (strain HG52) have been used to investigate latency. The mice were inoculated in the right rear footpad. Virus reactivation following explanation and culture of the dorsal root ganglia and the footpad was scored. The results show that: HSV-2 can be maintained in the mouse footpad in a state indistinguishable from latency; virus gene functions necessary for latency can be identified by the use of ts mutants; and mouse strains differ in their ability to support latent infection. An infectious center assay was used to quantitate virus reactivation from dissociated dorsal root ganglia. HSV-1 strain 17 wt spread after inoculation at doses of greater than or equal to 5.0 X 10(5) plaque-forming units (pfu), producing latency also in contralateral ganglia but with lower efficiency.