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

AMPK protects endothelial cells against HSV-1 replication via inhibition of mTORC1 and ACC1

Herpes simplex virus type 1 (HSV-1) is a widespread contagious pathogen, mostly causing mild symptoms on the mucosal entry side. However, systemic distribution, in particular upon reactivation of the virus in immunocompromised patients, may trigger an innate immune response and induce damage of organs. In these conditions, HSV-1 may infect vascular endothelial cells, but little is known about the regulation of HSV-1 replication and possible defense mechanisms in these cells. The current study addresses the question of whether the host cell protein AMP-activated protein kinase (AMPK), an important metabolic sensor, can control HSV-1 replication in endothelial cells. We show that downregulation of the catalytic subunits AMPKα1 and/or AMPKα2 increased HSV-1 replication as monitored by TCID50 titrations, while a potent AMPK agonist, MK-8722, strongly inhibited it. MK-8722 induced a persistent phosphorylation of the AMPK downstream targets acetyl-CoA carboxylase (ACC) and the rapamycin-sensitive adaptor protein of mTOR (Raptor) and, related to this, impairment of ACC1-mediated lipid synthesis and the mechanistic target of the rapamycin complex-1 (mTORC1) pathway. Since blockade of mTOR by Torin-2 as well as downregulation of ACC1 by siRNA also decreased HSV-1 replication, MK-8722 is likely to exert its anti-viral effect via mTORC1 and ACC1 inhibition. Importantly, MK-8722 was able to reduce virus replication even when added after HSV-1. Together, our data highlight the importance of endothelial cells as host cells for HSV-1 replication upon systemic infection and identify AMPK, a metabolic host cell protein, as a potential target for antiviral strategies against HSV-1 infection and its severe consequences. IMPORTANCE Herpes simplex virus type 1 (HSV-1) is a common pathogen that causes blisters or cold sores in humans. It remains latent in infected individuals and can be reactivated multiple times. In adverse conditions, for instance, in immunocompromised patients, HSV-1 can lead to serious complications such as encephalitis, meningitis, or blindness. In these situations, infection of endothelial cells lining the surface of blood vessels may contribute to the manifestation of disease. Here, we describe the role of AMP-activated protein kinase (AMPK), a potent regulator of cellular energy metabolism, in HSV-1 replication in endothelial cells. While downregulation of AMPK potentiates HSV-1 replication, pharmacological AMPK activation inhibits it by limiting the availability of required host cell macromolecules such as proteins or fatty acids. These data highlight the role of metabolic host cell proteins as antiviral targets and reveal activation of endothelial AMPK as a potential strategy to protect from severe consequences of HSV-1 infection.

METTL3-mediated m6A RNA modification promotes corneal neovascularization by upregulating the canonical Wnt pathway during HSV-1 infection

BACKGROUND

Corneal neovascularization (CNV) is a symptom of herpes simplex keratitis (HSK), which can result in blindness. The corneal angiogenesis brought on by herpes simplex virus type 1 (HSV-1) is strongly affected by vascular endothelial growth factor A (VEGFA). The N⁶-methyladenosine (m⁶A) modification catalyzed by methyltransferase-like 3 (METTL3) is a crucial epigenetic regulatory process for angiogenic properties. However, the roles of METTL3 and m⁶A in HSK-induced CNV remain unknown. Here, we investigated these roles in vitro and in vivo.

METHODS

A PCR array in HSV-1-infected human umbilical vein endothelial cells (HUVECs) was used to screen for METTL3 among the epitranscriptomic genes. Tube formation and scratch assays were conducted to investigate cell migration capacity. The global mRNA m⁶A abundance was evaluated using a dot blot assay. Gene expression was assessed by RT-qPCR, western blotting, and fluorescence immunostaining. In addition, bioinformatic analysis was conducted to identify the downstream molecules of METTL3 in HUVECs. METTL3 knockdown and STM2457 treatment clarified the specific underlying molecular mechanisms affecting HSV-1-induced angiogenesis in vitro. An acute HSK mouse model was established to examine the effects of METTL3 knockdown or inhibition using STM2457 on pathological angiogenic development in vivo.

RESULTS

METTL3 was highly upregulated in HSV-1-infected HUVECs and led to increased m⁶A levels. METTL3 knockdown or inhibition by STM2457 further reduced m⁶A levels and VEGFA expression and impaired migration and tube formation capacity in HUVECs after HSV-1 infection. Mechanistically, METTL3 regulated LRP6 expression through post-transcriptional mRNA modification in an m⁶A-dependent manner, increasing its stability, upregulating VEGFA expression, and promoting angiogenesis in HSV-1-infected HUVECs. Furthermore, METTL3 knockdown or inhibition by STM2457 reduced CNV in vivo.

CONCLUSION

Our findings revealed that METTL3 promotes pathological angiogenesis through canonical Wnt and VEGF signaling in vitro and in vivo, providing potential pharmacological targets for preventing the progression of CNV in HSK.

Detection of herpes simplex virus type 1 in failed descemet stripping automated endothelial keratoplasty grafts

PURPOSE

To determine the prevalence of herpes simplex virus type 1 (HSV-1) DNA in failed Descemet membrane stripping automated endothelial keratoplasty (DSAEK) grafts.

METHODS

A retrospective interventional case series of patients with DSAEK graft failure treated at the New York Eye and Ear Infirmary between January 2009 and July 2012 was performed. Repeat DSAEK, penetrating keratoplasty, or keratoprosthesis procedure was subsequently performed on eyes with failed grafts. All failed grafts were examined immunohistochemically and with qualitative real-time polymerase chain reaction for HSV-1 DNA. In HSV-1-positive cases, corneoscleral donor rims from the original DSAEK procedures were also examined immunohistochemically and with polymerase chain reaction.

RESULTS

Fifty-one failed DSAEK grafts from 50 eyes of 49 patients were identified. Indications for DSAEK were pseudophakic bullous keratopathy (28/51, 55%), Fuchs corneal endothelial dystrophy (12/51, 23%), failed penetrating keratoplasty (7/51, 14%), corneal decompensation from glaucoma (2/51, 4%), herpetic endotheliitis (1/51, 2%), and failed DSAEK (1/51, 2%). Forty-three grafts (83%) were primary DSAEK graft failure. HSV-1 DNA was isolated from 2 of 51 failed DSAEK grafts (4.0%). The corresponding corneoscleral donor rims did not demonstrate the presence of HSV-1.

CONCLUSIONS

Based on our results, HSV-1 infection plays a minor role in DSAEK graft failure. The data suggest that recipient reactivation, rather than donor transmission, plays a role in HSV infection.

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.

HSV-1 infection of human corneal epithelial cells: receptor-mediated entry and trends of re-infection

PURPOSE

The human cornea is a primary target for herpes simplex virus-1 (HSV-1) infection. The goals of the study were to determine the cellular modalities of HSV-1 entry into human corneal epithelial (HCE) cells. Specific features of the study included identifying major entry receptors, assessing pH dependency, and determining trends of re-infection.

METHODS

A recombinant HSV-1 virus expressing beta-galactosidase was used to ascertain HSV-1 entry into HCE cells. Viral replication within cells was confirmed using a time point plaque assay. Lysosomotropic agents were used to test for pH dependency of entry. Flow cytometry and immunocytochemistry were used to determine expression of three cellular receptors--nectin-1, herpesvirus entry mediator (HVEM), and paired immunoglobulin-like 2 receptor alpha (PILR-a). The necessity of these receptors for viral entry was tested using antibody-blocking. Finally, trends of re-infection were investigated using viral entry assay and flow cytometry post-primary infection.

RESULTS

Cultured HCE cells showed high susceptibility to HSV-1 entry and replication. Entry was demonstrated to be pH dependent as blocking vesicular acidification decreased entry. Entry receptors expressed on the cell membrane include nectin-1, HVEM, and PILR-α. Receptor-specific antibodies blocked entry receptors, reduced viral entry and indicated nectin-1 as the primary receptor used for entry. Cells re-infected with HSV-1 showed a decrease in entry, which was correlated to decreased levels of nectin-1 as demonstrated by flow cytometry.

CONCLUSIONS

HSV-1 is capable of developing an infection in HCE cells using a pH dependent entry process that involves primarily nectin-1 but also the HVEM and PILR-α receptors. Re-infected cells show decreased levels of entry, correlated with a decreased level of nectin-1 receptor expression.

HSV-1 infection suppresses TGF-beta1 and SMAD3 expression in human corneal epithelial cells

PURPOSE

The present study was undertaken to investigate whether transforming growth factor-beta (TGF-beta) isoforms (TGF-beta1, TGF-beta2, and TGF-beta3) and SMADs (SMAD2 and SMAD3) are involved in herpes simplex virus type 1 (HSV-1) corneal infection.

METHODS

Human corneal epithelial cells (HCE) were infected with HSV-1 at a multiplicity of infection of 5. Cell morphological changes were observed under phase-contrast microscopy. Levels of mRNA for TGF-beta isoforms 1, 2, and 3 as well as for SMAD2 and SMAD3 were measured by reverse transcription polymerase chain reaction (RT-PCR) at 0 h, 4 h, 8 h, 12 h, and 24 h after infection. Protein expression of TGF-beta1, TGF-beta2, SMAD3, and phospho-SMAD3 were analyzed by indirect immunofluorescence at 0 h, 12 h, and 24 h post-infection (p.i.) in HCE cells. Protein expression of TGF-beta1 was also evaluated by ELISA.

RESULTS

Following HSV-1 infection, a cytopathic effect in HCE cells was observed at 8 h p.i. and became significant at 24 h p.i. Compared with normal cells, the mRNA levels of TGF-beta1 in HSV-1 infected HCE cells decreased significantly at 8 h, 12 h, and 24 h p.i. (p<0.01), and the expression of SMAD3 was also dramatically decreased 12 h and 24 h p.i. (p<0.01). No noticeable changes were found as a result of infection with respect to levels of TGF-beta2, TGF-beta3, and SMAD2 in HCE cells. Protein expression of TGF-beta1, SMAD3, and phospho-SMAD3 decreased in infected cells at 12 h and 24 h p.i. compared with normal cells, but TGF-beta2 had no change.

CONCLUSIONS

TGF-beta1 and SMAD3 may be involved in the pathology of corneal diseases associated with HSV-1 infection.

Major Endothelial Loss From Corneas in Organ Culture

PURPOSE

The aim of this study was to show that major losses can still occur on corneas judged suitable for grafting at the first count. In addition, we studied the frequency of these losses on 1992 corneas over a period of 4 years to evaluate the risk incurred.

METHODS

We evaluated the incidence of these major losses and the associated risk factors. An Ishigawa diagram was created with the Cornea Bank team and the ophthalmologists involved in organ retrieval. Endothelial losses caused by bacterial or fungicidal contamination were excluded from the study. For the 29 corneas that suffered major losses, we analyzed the donor files for donor age, clinical file, geographical origins of the corneas, the person who did the retrieval, the length of time the cornea was stored, the data resulting from examining the endothelium at the bank by optical microscope, and the method used for sterilizing the material used. Specific analyses in cases of major loss of endothelial content: anatomopathologic examination of the corneas and search for the herpes simplex virus (HSV; type 1 or 2) by polymerase chain reaction (PCR). We carried out a statistical analysis using a chi(2) test on the 1992 corneas studied to see if the presence of diabetes (type 1 or 2) in the donor led to reduction levels different from those of corneas originating from nondiabetic donors.

RESULTS

The incidence was evaluated at between 0.4% and 3% of corneas sampled, and the associated risk factor was between 0.8% and 6% of grafted corneas. The occurrence of major losses was independent of donor age and was independent of the person who did the retrieval. The occurrence of major losses was independent of geographical origin. We tested our media for endotoxin before use and found levels from 0.22 to 3.9 UI/mL. We verified the absence of a chronological relationship between the batches of media used in the bank and the number of major losses observed, showing that the pyrogenicity limit was independent of cytotoxicity limits. Data analysis showed no difference in reduction levels between diabetic and nondiabetic donors (P < 0.05). Results on the detection of HSV-1 by PCR on the storage media were all negative, and these results agree with the anatomopathologic examinations that showed no signs of viral infection.

CONCLUSION

Total endothelial losses amounted to 1.4%/yr. Without the double endothelial counts, we would have had 29 primary graft rejections over that period. During storage, this loss has not been linked to a specific cause, but risk factors such as traumatic death, herpes infections, and badly controlled endotoxin levels should be considered when taking preventative actions. For the moment, a second endothelial count before grafting should be carried out, because all these problem grafts conformed to grafting criteria after the first count. The possibility of carrying out this second count is one of the recognized advantages of storage in organ culture.

HSV-1 antigens and DNA in the corneal explant buttons of patients with non-herpetic or clinically atypical herpetic stromal keratitis

BACKGROUND

Little is known about the role of HSV-1 in keratitis not primarily attributed to herpetic origin. This study therefore aimed to prospectively evaluate the corneal explant buttons of patients with non-herpetic or clinically atypical herpetic stromal keratitis (experimental group: non-HSK) for the presence of HSV-1 antigens and DNA, and to compare the findings with those from individuals with typical herpetic stromal keratitis (positive control group: HSK) or non-inflammatory degenerative keratopathy (negative control group).

METHODS

Corneal buttons derived from 51 patients with HSK, from 72 with non-HSK and from 30 with degenerative keratopathy were prospectively collected and subjected to immunohistochemical analysis for HSV-1 antigens and to HSV-1 DNA amplification.

RESULTS

In corneal buttons derived from patients with non-HSK, viral antigens were detected immunohistochemically in 8/72 cases and DNA amplified in 16/72. Corresponding values for the HSK group were 16/51 and 11/51. Taking viral antigen and DNA findings together, HSV-1 was detected in 18/72 (25%) patients with non-HSK and in 19/51 (37%) with HSK (p=0.2), but in only 2/30 (6%) individuals with non-inflammatory degenerative keratopathy.

CONCLUSION

Since the detection frequencies for HSV-1 antigens and DNA were comparable in the HSK and non-HSK groups, Herpes may play an underestimated and as yet undefined role in non-herpetic and clinically atypical herpetic stromal keratitis, either as a primary trigger of the disease or as a secondary contributor to it. In this category of individuals, early anti-herpetic therapy should be considered if patients do not respond in the expected manner to treatment for non-herpetic stromal keratitis.

Primary graft failure : a clinicopathologic and molecular analysis

OBJECTIVE

Primary graft failure (PGF) corneal tissues were analyzed for herpes simplex virus (HSV) and varicella-zoster virus (VZV).

DESIGN

Retrospective, noncomparative case series.

MATERIALS

Formalin-fixed, paraffin-embedded tissue of 21 donor corneas and 14 recipient corneas of PGF cases, as well as 10 control corneas.

METHODS

Clinical, histologic, immunohistochemical, polymerase chain reaction (PCR), and, in selected cases, transmission electron microscopic characteristics were studied.

MAIN OUTCOME MEASURES

Evidence of HSV or VZV in donor tissues.

RESULTS

Median patient age was 65 years, and median donor age was 48 years. Donor cornea parameters, including endothelial cell counts, death-to-preservation time, and time in storage, were generally within accepted standards. Stromal edema was found in all 21 donor corneas with PGF. Eighteen donor corneas demonstrated severely reduced or absent endothelium and mild to moderate lymphocytic infiltration without necrosis. Three donor corneas (14%) had necrotizing stromal keratitis (NSK) with keratic precipitates. Positive immunohistochemical staining of keratocytes for HSV was present in two of two donor corneas with NSK and was negative in 18 other donor corneas. Polymerase chain reaction analysis revealed the DNA of HSV type 1 (HSV1) in all donor corneas with NSK and in four donor corneas without NSK (33%). Recipient corneal tissue was negative for HSV1 DNA in three patients with NSK and positive in two of the four other PCR-positive patients. Transmission electron microscopy analysis showed viral particles in two donor corneas with NSK. Polymerase chain reaction analysis revealed no evidence of HSV type 2 or VZV in any cornea. All control corneas were negative for viral DNA. Sixteen corneas remained clear and two had failed after regraft for PGF, with a median follow-up of 3.6 years.

CONCLUSIONS

Herpes simplex virus type 1 DNA was present in 33% of patients of PGF. Herpetic stromal keratitis was found in some failed corneas; the lack of HSV in the paired recipient suggests importation within the donor cornea. The overall prognosis for regrafting after PGF is good.

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.

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)

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.

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.

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.

Pathogenesis of corneal oedema associated with herpetic eye disease

Corneal oedema and stromal disease, induced in rabbits by intrastromal injection of herpes simplex virus, type 1, strain RE (HSV-1, RE), reached a peak of 12-15 days after infection. Corneal oedema as measured by ultrasonic pachymetry, and stromal disease as measured by a subjective scoring system, were closely related for 30 days after infection. Morphometric analysis of wide field specular micrographs showed that no immediate endothelial cell damage occurred in either control or HSV-1 infected corneas. Alizarin red S staining of corneas taken during the period of most severe oedema indicated no significant endothelial cell loss; however, visual inspection indicated numerous staining abnormalities. Scanning and transmission electron microscopy provided evidence of an intact endothelial layer possessing integrated infiltrating cells. Virus antigen could not be detected on endothelial cells by immunoperoxidase staining at any time during development of corneal oedema. The results indicate that corneal oedema associated with HSV-1 induced disease can occur in the absence of detectable virus replication and cytolysis of corneal endothelial cells.

Detection of herpes viral genomes in normal and diseased corneal epithelium

Herpetic ocular disease is one of the major causes of corneal blindness. Clinical diagnosis of corneal disease is based principally on corneal appearance. However, abnormal morphology of the corneal epithelium (CE) is not an indicator for the presence of a herpes virus. Further, it has not been established if herpes viruses are present in normal corneal epithelial tissue. In these studies, the polymerase chain reaction was used to evaluate normal and diseased corneal epithelium for the presence of herpes simplex virus type 1 (HSV-1), Epstein-Barr virus (EBV) and cytomegalovirus (CMV) genomic sequences. Thirty-two normal corneal epithelium specimens obtained from cadavers shortly after death were analyzed for HSV-1, EBV and CMV genomic sequences. Three of the 32 normal CE specimens were positive for amplified EBV DNA, 1 was positive for HSV-1 DNA, and none was positive for CMV DNA. We also tested eight herpetic dendritic lesions of which 3 were HSV-1 culture and PCR positive. The remaining five dendritic lesions were HSV-1 culture and PCR negative. Since these lesions were not evaluated for other herpesviruses, the etiology of these dendritic lesions is unknown. Six corneal epithelium samples from HIV-infected donors were negative for EBV, CMV and HSV-1 amplified sequences. Positive EBV, CMV and HSV-1 serology on all normal donors and on donors with clinically apparent disease did not correlate with positive PCR results. The results of these studies suggest that EBV and HSV-1 DNA can be amplified from a small percentage of apparently normal corneal epithelium.

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 1 infection upregulates stress protein expression in cultured retinal neurons

The production of a 57K stress protein (StrP) after herpes simplex virus type 1 (HSV-1) infection was examined in cultured neonatal rat retinal cells. StrP expression in individual cells was identified using a monoclonal antibody, TI56. Indirect immunofluorescence of uninfected retinal cultures showed that approximately 40% of cells expressed neurofilament (NF+) and 5% expressed a low level of StrP. Following HSV infection the proportion of NF+ cells decreased while the proportion of StrP positive cells became greater and the intensity of staining increased. The number of cells labelled with a polyclonal anti-HSV antibody increased with time after infection. Retinal neurons in culture can be infected with HSV, after which StrP expression is significantly upregulated.

A simplified technique for the short-term tissue culture of rabbit corneal cells

A technique for the short-term culture of pure populations of rabbit corneal endothelial and epithelial cells has been developed. Rabbit corneas were placed on concave agarose surfaces, treated briefly with a solution of trypsin and ethylenediamine tetracetic acid, and transferred, either epithelial cell surface or endothelial cell surface down, to microscope slide culture chambers. Within 6 to 12 h the epithelial cells or endothelial cells attached to the slide chamber surface and the cornea was removed, leaving behind a pure population of cells which spread out and grew to fill the surface of the slide chamber. This technique provides a simple and economic means for the reproducible initiation of primary cultures of rabbit corneal epithelial and endothelial cells for us in a variety of experiments.

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.

Growth and characterization of rabbit corneal cells in vitro

Primary organ cultures of rabbit corneal epithelium, stroma, and endothelium were established by microdissection. Secondary cultures of epithelial cells, keratocytes, and endothelial cells were established by serial passage. The doubling time for epithelial cells and keratocytes was 18 h, and endothelial cells doubled their number in 5 days. Ultrastructural studies demonstrated characteristic morphological, nuclear, and cytoplasmic features of corneal epithelial cells, keratocytes, and endothelial cells and confirmed the identity of the cell lines. The purity of the three distinct cell types was ascertained by indirect immunofluorescence techniques, using antibodies against keratin, which identified epithelial cells, and fibronectin, which identified keratocytes and endothelial cells. The indirect immunofluorescence technique represents a simple method to screen an aliquot of a cell suspension and determine the purity of corneal cells grown in vitro.