Early events in HSV keratitis--setting the stage for a blinding disease

Controlling viral immuno-inflammatory lesions by modulating aryl hydrocarbon receptor signaling

Ocular herpes simplex virus infection can cause a blinding CD4⁺ T cell orchestrated immuno-inflammatory lesion in the cornea called Stromal Keratitis (SK). A key to controlling the severity of SK lesions is to suppress the activity of T cells that orchestrate lesions and enhance the representation of regulatory cells that inhibit effector cell function. In this report we show that a single administration of TCDD (2, 3, 7, 8- Tetrachlorodibenzo-p-dioxin), a non-physiological ligand for the AhR receptor, was an effective means of reducing the severity of SK lesions. It acted by causing apoptosis of Foxp3⁻ CD4⁺ T cells but had no effect on Foxp3⁺ CD4⁺ Tregs. TCDD also decreased the proliferation of Foxp3⁻ CD4⁺ T cells. The consequence was an increase in the ratio of Tregs to T effectors which likely accounted for the reduced inflammatory responses. In addition, in vitro studies revealed that TCDD addition to anti-CD3/CD28 stimulated naïve CD4⁺ T cells caused a significant induction of Tregs, but inhibited the differentiation of Th1 and Th17 cells. Since a single TCDD administration given after the disease process had been initiated generated long lasting anti-inflammatory effects, the approach holds promise as a therapeutic means of controlling virus induced inflammatory lesions.

The mechanisms and consequences of ultraviolet-induced immunosuppression in the skin and eye

Ultraviolet radiation (UVR) of the skin results in immune suppression to antigens encountered shortly after the exposure. The pathways leading to the downregulation in immunity are complex, initiated by chromophores located at the surface of the skin and ending with the generation of immunosuppressive mediators and regulatory cells. Ultraviolet-induced immunosuppression can be considered not only as beneficial, such as in preventing chronic inflammatory responses and allergic and automimmune reactions, but it can also be detrimental, such as in the lack of control of skin tumors and infectious diseases. The eye is an immune privileged site through a wide variety of mechanisms that allow selected immune responses without causing inflammation. The role of UVR in altering immune responses in the eye is not clear and is discussed in relation to photokeratitis, herpetic stromal keratitis, and pterygium.

Substance P in the corneal stroma regulates the severity of herpetic stromal keratitis lesions

PURPOSE

To determine whether substance P (SP) in herpes simplex virus-1 (HSV-1) infected cornea regulates the severity of herpetic stromal keratitis (HSK) lesions in a mouse model.

METHODS

C57BL/6 mice were infected ocularly with HSV-1 (RE). The corneas with HSK lesions, on Day 15 postinfection, were grouped on the basis of the corneal opacity as mild (≤2) or severe (>2). The amount of SP was determined in the corneas with mild or severe HSK lesions by enzyme immunosorbent assay (EIA) and confocal microscopy. Subconjunctival inoculation of spantide I, SP receptor antagonist, was carried out during the clinical phase of HSK. ELISA and flow cytometry were used to determine the level of cytokines, chemokines, and influx of immune cell types in the corneal lesions.

RESULTS

The authors determined a significantly higher level of SP in the corneas with severe HSK lesions in comparison with mild lesions. The corneas with a higher level of SP also exhibited higher amounts of proinflammatory cytokines (IL-6, IFN-γ) and chemokines (CCL3, CXCL2) when compared with the corneas with a lower level of SP. SP receptor NK1R expression was determined in CD45- and CD45+ cells in infected cornea. SP present in the corneal stroma of the eyes with severe HSK lesions colocalized with β-III tubulin(+) and IA(b+) cell types. Subconjunctival inoculation of spantide I during the clinical phase of HSK resulted in significant reduction in the corneal opacity and angiogenesis.

CONCLUSIONS

Collectively, these results demonstrate the relative contribution of substance P in regulating the clinical severity of HSK lesions in a mouse model.

Cornea: Window to Ocular Immunology

The ocular surface is continuously exposed to environmental agents such as allergens, pollutants, and microorganisms, which could provoke inflammation. However, an array of anatomical, physiological, and immunological features of the ocular surface conspire to limit corneal inflammation and endow the eye with immune privilege. A remarkable example of ocular immune privilege is the success of corneal allografts, which unlike all other forms of organ transplantation, survive without the use of systemic immunosuppressive drugs or MHC matching. This review describes the anatomical, physiological, and dynamic immunoregulatory processes that contribute to immune privilege.

Herpesvirus entry mediator and nectin-1 mediate herpes simplex virus 1 infection of the murine cornea

Herpes simplex virus 1 (HSV-1) is a ubiquitous human pathogen that enters cells by the receptor-mediated fusion of the viral envelope with a host cell membrane. The envelope glycoprotein gD of HSV must bind to one of its receptors for entry to take place. Recent studies using knockout (KO) mice demonstrated that the gD receptors herpesvirus entry mediator (HVEM) and nectin-1 are the primary entry receptors for HSV-2 in the mouse vagina and brain. Nectin-1 was most crucial for the neuronal spread of HSV-2, particularly in the brain. HVEM was dispensable for infection in these models, but when both HVEM and nectin-1 were absent, infection was completely prevented. We sought to determine the receptor requirements of HSV-1 in an ocular model of infection using knockout mice. Wild-type, HVEM KO, nectin-1 KO, and HVEM/nectin-1 double-KO mice were infected via corneal scarification and monitored for clinical signs of infection and viral replication in various tissues. We report that either HVEM or nectin-1 must be present for HSV-1 infection of the cornea. Additionally, we observed that the infection was attenuated in both HVEM KO and nectin-1 KO mice. This is in contrast to what was reported for studies of HSV-2 in vagina and brain and suggests that receptor requirements for HSV vary depending on the route of inoculation and/or serotype.

Role of IL-17 and Th17 cells in herpes simplex virus-induced corneal immunopathology

HSV-1 infection of the cornea leads to a blinding immunoinflammatory lesion of the eye termed stromal keratitis (SK). Recently, IL-17-producing CD4(+) T cells (Th17 cells) were shown to play a prominent role in many autoimmune conditions, but the role of IL-17 and/or of Th17 cells in virus immunopathology is unclear. In this study, we show that, after HSV infection of the cornea, IL-17 is upregulated in a biphasic manner with an initial peak production around day 2 postinfection and a second wave starting from day 7 postinfection with a steady increase until day 21 postinfection, a time point when clinical lesions are fully evident. Further studies demonstrated that innate cells, particularly γδ T cells, were major producers of IL-17 early after HSV infection. However, during the clinical phase of SK, the predominant source of IL-17 was Th17 cells that infiltrated the cornea only after the entry of Th1 cells. By ex vivo stimulation, the half fraction of IFN-γ-producing CD4(+) T cells (Th1 cells) were HSV specific, whereas very few Th17 cells responded to HSV stimulation. The delayed influx of Th17 cells in the cornea was attributed to the local chemokine and cytokine milieu. Finally, HSV infection of IL-17R knockout mice as well as IL-17 neutralization in wild-type mice showed diminished SK severity. In conclusion, our results show that IL-17 and Th17 cells contribute to the pathogenesis of SK, the most common cause of infectious blindness in the Western world.

Activation of endothelial roundabout receptor 4 reduces the severity of virus-induced keratitis

Antiangiogenic molecules exert a feedback control to restrain pathological angiogenesis, which includes physical binding or inhibition of angiogenic signaling in blood vessel endothelial cells. The latter is the case in which Slit2 ligand-dependent activation of the blood vessel endothelial cell receptor roundabout 4 (Robo4) occurs. In this study, we demonstrate that Robo4 receptors are upregulated following HSV infection of the eye on the majority of the new blood vessel endothelial cells that occur in the corneal stroma. However, expression levels of the ligand for Robo4 receptors, Slit2, was not significantly increased during the disease process, and the knockdown of Slit2 gene expression using lentiviral short hairpin RNAs had no effect on the extent of pathological angiogenesis. In contrast, providing additional Slit2 protein by subconjunctival administration resulted in significantly reduced angiogenesis. The Slit2 binding to Robo4 was shown to block the downstream vascular endothelial growth factor signaling molecules Arf 6 and Rac 1 and reduce the antiapoptotic molecule Bcl-xL in blood vessel endothelial cells. Our results indicate that augmenting the host Robo4/Slit2 system could provide a useful therapeutic approach to control pathological angiogenesis associated with HSV induced stromal keratitis.

An anti-inflammatory role of VEGFR2/Src kinase inhibitor in herpes simplex virus 1-induced immunopathology

Corneal neovascularization represents a key step in the blinding inflammatory stromal keratitis (SK) lesion caused by ocular infection with herpes simplex virus (HSV). In this report, we describe a novel approach for limiting the angiogenesis caused by HSV infection of the mouse eye. We show that topical or systemic administration of the Src kinase inhibitor (TG100572) that inhibits downstream molecules involved in the vascular endothelial growth factor (VEGF) signaling pathway resulted in markedly diminished levels of HSV-induced angiogenesis and significantly reduced the severity of SK lesions. Multiple mechanisms were involved in the inhibitory effects. These included blockade of IL-8/CXCL1 involved in inflammatory cells recruitment that are a source of VEGF, diminished cellular infiltration in the cornea, and reduced proliferation and migration of CD4(+) T cells into the corneas. As multiple angiogenic factors (VEGF and basic fibroblast growth factor [bFGF]) play a role in promoting angiogenesis during SK and since Src kinases are involved in signaling by many of them, the use of Src kinase inhibition represents a promising way of limiting the severity of SK lesions the most common cause of infectious blindness in the Western world.

Ocular neovascularization caused by herpes simplex virus type 1 infection results from breakdown of binding between vascular endothelial growth factor A and its soluble receptor

The normal cornea is transparent, which is essential for normal vision, and although the angiogenic factor vascular endothelial growth factor A (VEGF-A) is present in the cornea, its angiogenic activity is impeded by being bound to a soluble form of the VEGF receptor-1 (sVR-1). This report investigates the effect on the balance between VEGF-A and sVR-1 that occurs after ocular infection with HSV, which causes prominent neovascularization, an essential step in the pathogenesis of the vision-impairing lesion, stromal keratitis. We demonstrate that HSV-1 infection causes increased production of VEGF-A but reduces sVR-1 levels, resulting in an imbalance of VEGF-A and sVR-1 levels in ocular tissues. Moreover, the sVR-1 protein made was degraded by the metalloproteinase (MMP) enzymes MMP-2, -7, and -9 produced by infiltrating inflammatory cells that were principally neutrophils. Inhibition of neutrophils, inhibition of sVR-1 breakdown with the MMP inhibitor marimastat, and the provision of exogenous recombinant sVR-1 protein all resulted in reduced angiogenesis. Our results make the novel observation that ocular neovascularization resulting from HSV infection involves a change in the balance between VEGF-A and its soluble inhibitory receptor. Future therapies aimed to increase the production and activity of sVR-1 protein could benefit the management of stromal keratitis, an important cause of human blindness.

The human microbiome in multiple sclerosis: pathogenic or protective constituents?

The human microbiome is comprised of commensal and pathogenic microorganisms, which exert diverse effects in close proximity to the site of intection as well as in remote tissues through immune-mediated mechanisms. Multiple infectious agents have been implicated in the pathogenesis of multiple sclerosis (MS) with variable findings depending on the agent, techniques, and disease phenotype. Herein, the contributions of individual infectious agents to MS and their effects on the immune and nervous systems are reviewed, focusing on herpes viruses, coronaviruses, retroviruses, and synchronic infections. While infectious agents are often assumed to be pathogenic, their effects might also be beneficial to the host in the long-term, depending on age and the type of immunogen/pathogen exposure, as proposed by the hygiene hypothesis. The human microbiome has potential impact on future diagnostic and therapeutic issues in MS.

Controlling herpes simplex virus-induced ocular inflammatory lesions with the lipid-derived mediator resolvin E1

Stromal keratitis (SK) is a chronic immunopathological lesion of the eye caused by HSV-1 infection and a common cause of blindness in humans. The inflammatory lesions are primarily perpetuated by neutrophils with the active participation of CD4(+) T cells. Therefore, targeting these immune cell types represents a potentially valuable form of therapy to reduce the severity of disease. Resolvin E1 (RvE1), an endogenous lipid mediator, was shown to promote resolution in several inflammatory disease models. In the current report, we determined whether RvE1 administration begun at different times after ocular infection of mice with HSV could influence the severity of SK lesions. Treatment with RvE1 significantly reduced the extent of angiogenesis and SK lesions that occurred. RvE1-treated mice had fewer numbers of inflammatory cells that included Th1 and Th17 cells as well as neutrophils in the cornea. The mechanisms by which RvE1 acts appear to be multiple. These included reducing the influx of neutrophils and pathogenic CD4(+) T cells, increasing production of the anti-inflammatory cytokine IL-10, and inhibitory effects on the production of proinflammatory mediators and molecules, such as IL-6, IFN-γ, IL-17, KC, VEGF-A, MMP-2, and MMP-9, that are involved in corneal neovascularization and SK pathogenesis. These findings are, to our knowledge, the first to show that RvE1 treatment could represent a novel approach to control lesion severity in a virally induced immunopathological disease.

Herpes stromal keratitis: erosion of ocular immune privilege by herpes simplex virus

Herpes stromal keratitis (HSK) is a potentially blinding disease caused by herpes simplex virus corneal infection. Most cases of HSK are due to reactivation of the virus from latency leading to recurrent bouts of corneal inflammation and scarring with progressive loss of vision. Replicating virus is required to initiate HSK, and CD4 T cells of the adaptive immune system appear requisite for stromal inflammation. Corneal neovascularization also contributes significantly to HSK pathogenesis. Combination therapy with topical antivirals and corticosteroids is the current standard of care for human HSK. Future therapies will probably target angiogenesis with anti-VEGF agents to inhibit blood vessel growth into the normally avascular cornea, and target viral reactivation with therapeutic vaccination strategies to inhibit subsequent attacks.

Involvement of p63 in the herpes simplex virus-1-induced demise of corneal cells

Background

The transcription factor p63 plays a pivotal role in the development and maintenance of epithelial tissues, including the ocular surface. In an effort to gain insight into the pathogenesis of keratitis caused by HSV-1, we determined the expression patterns of the p63 and Bax proteins in the Staatens Seruminstitute Rabbit Cornea cell line (SIRC).

Methods

SIRC cells were infected with HSV-1 at various multiplicities and maintained for different periods of time. Virus replication was measured by indirect immunofluorescence assay and Western blot analysis. Cell viability was determined by MTT assay. The apoptotic response of the infected cells was quantified by ELISA detecting the enrichment of nucleosomes in the cytoplasm. Western blot analysis was used to determine the levels of p63 and Bax proteins.

Results

Indirect immunofluorescence assays and Western blot analyses demonstrated the presence of HSV-1 glycoprotein D (gD) in the infected SIRC cell line, and the pattern of gD expression was consistent with efficient viral replication. The results of MTT and ELISA assays showed that HSV-1 elicited a strong cytopathic effect, and apoptosis played an important role in the demise of the infected cells. Mock-infected SIRC cells displayed the constitutive expression of ΔNp63α. The expressions of the Bax-β and TAp63γ isoforms were considerably increased, whereas the level of ΔNp63α was decreased in the HSV-1-infected SIRC cells. Experiments involving the use of acyclovir showed that viral DNA replication was necessary for the accumulation of TAp63γ.

Conclusion

These data suggest that a direct, virus-mediated cytopathic effect may play an important role in the pathogenic mechanism of herpetic keratitis. By disturbing the delicate balance between the pro-survival ΔN and the pro-apoptotic TA isoforms, HSV-1 may cause profound alterations in the viability of the ocular cells and in the tissue homeostasis of the ocular surface.

History and physiology of immune privilege

Immune privilege is the condition in which selected immune responses are suppressed or excluded in certain organs, such as the eye. Immune privilege in the eye was described over 130 years ago, but its significance was not appreciated until the early 1950s. Investigations beginning in the 1970s ushered in a new era and revealed that ocular immune privilege is due to anatomical, physiological, and immunoregulatory processes that prevent the induction and expression of immune-mediated inflammation. It is widely believed that immune privilege is an adaptation for reducing immune-mediated injury to ocular cells that have limited or no capacity for regeneration.

Enhanced antitumor efficacy of vasculostatin (Vstat120) expressing oncolytic HSV-1

Oncolytic viral (OV) therapy is a promising therapeutic modality for brain tumors. Vasculostatin (Vstat120) is the cleaved and secreted extracellular fragment of brain-specific angiogenesis inhibitor 1 (BAI1), a brain-specific receptor. To date, the therapeutic efficacy of Vstat120 delivery into established tumors has not been investigated. Here we tested the therapeutic efficacy of combining Vstat120 gene delivery in conjunction with OV therapy. We constructed RAMBO (Rapid Antiangiogenesis Mediated By Oncolytic virus), which expresses Vstat120 under the control of the herpes simplex virus (HSV) IE4/5 promoter. Secreted Vstat120 was detected as soon as 4 hours postinfection in vitro and was retained for up to 13 days after OV therapy in subcutaneous tumors. RAMBO-produced Vstat120 efficiently inhibited endothelial cell migration and tube formation in vitro (P = 0.0005 and P = 0.0184, respectively) and inhibited angiogenesis (P = 0.007) in vivo. There was a significant suppression of intracranial and subcutaneous glioma growth in mice treated with RAMBO compared to the control virus, HSVQ (P = 0.0021 and P < 0.05, respectively). Statistically significant reduction in tumor vascular volume fraction (VVF) and microvessel density (MVD) was observed in tumors treated with RAMBO. This is the first study to report the antitumor effects of Vstat120 delivery into established tumors and supports the further development of RAMBO as a possible cancer therapy.

Anti-VEGF monoclonal antibody-induced regression of corneal neovascularization and inflammation in a rabbit model of herpetic stromal keratitis

BACKGROUND

To determine the efficacy of bevacizumab (Avastin), an anti-VEGF monoclonal antibody, administrated via subconjunctival injection as a corneal anti-angiogenic treatment.

METHODS

Right corneas of rabbits were infected with herpes simplex virus type 1, KOS strain. On day 13 post-infection (p.i.), animals were treated subconjunctivally (sc) with a single 10-microl dose (25 microg/microl) of bevacizumab (group A) or with the same volume of an isotype monoclonal antibody, as negative control (group B). All animals were observed clinically on days 2, 5, 7, 14, 21, and 28 p.i., and two corneas each day were obtained for histological assessment and viral titration.

RESULTS

Viral replication was observed no longer than 5 days after infection. By day 7 a dense neutrophil invasion of the cornea was detected, which significantly increased while herpetic stromal keratitis progressed in severity. Positive outcomes observed following the treatment with bevacizumab, compared to control, included: (1) Total involution of neovascularization, (2) reduction in disease severity, (3) improved corneal translucency, (4) absence of scarring, (5) preservation of corneal thickness, (6) no neutrophil infiltration of the cornea.

CONCLUSIONS

Subconjunctival administration of bevacizumab induced involution of new vessels, abolished inflammatory response, and resulted in return of corneal function. Furthermore, bevacizumab is a novel approach for the treatment of herpetic stromal keratitis.

Topical ophthalmic cyclosporine: pharmacology and clinical uses

Cyclosporine has been used successfully as a systemic immunomodulator for more than two decades, and numerous studies have investigated its mechanisms of action. In 2003 an ophthalmic formulation, cyclosporine 0.05% ophthalmic emulsion, was approved by the FDA to treat dry eye disease. Topical cyclosporine emulsion has also been investigated for treatment of other ocular surface disorders that may have an immune-based inflammatory component. In these trials, cyclosporine 0.05% ophthalmic emulsion has shown efficacy for management of posterior blepharitis, ocular rosacea, post-LASIK dry eye, contact lens intolerance, atopic keratoconjunctivitis, graft-versus-host disease, and herpetic stromal keratitis. As these disorders are often refractory to other available treatments, ophthalmic cyclosporine is a welcome nontoxic adjunct or replacement to potentially toxic topical or systemic immunosuppressive therapies.

The herpes simplex virus-induced demise of keratinocytes is associated with a dysregulated pattern of p63 expression

p63 plays a pivotal role in the development and maintenance of stratified epithelial tissues. In an effort to gain insight into the pathogenic mechanisms of skin infections caused by HSV-1 and HSV-2, we determined the patterns of p63 expression in primary keratinocytes and in the HaCaT cell line. The levels of DeltaNp63alpha and a 50kDa p73 isoform were decreased, Bax-alpha remained unaffected, while the expressions of the Bax-beta, TAp63gamma and a 44.5kDa p73 isoform were highly increased in both HSV-1-infected HaCaT cells and primary keratinocytes. In contrast, in response to HSV-2 infection the levels of DeltaNp63alpha, a 50kDa p73 isoform and a 44.5kDa p73 protein were decreased, Bax-alpha and TAp63gamma remained unaffected, while the expression of Bax-beta was slightly increased. The knockdown of TAp63 expression enhanced the viability of HSV-1-infected cells. Thus, HSV-1 and HSV-2 modulate the patterns of p63 and Bax expression in a serotype-specific manner. The dysregulated pattern of p63 expression observed in HSV-infected keratinocytes may comprise part of a mechanism by which these viruses perturb the functions of keratinocytes and lead to their demise.

A natural tetranortriterpenoid with immunomodulating properties as a potential anti-HSV agent

Meliacine (MA), an antiviral principle present in partially purified leaf extracts of Melia azedarach L., prevents the development of herpetic stromal keratitis (HSK) in mice by diminishing the viral load in the eye and the severity of lesions caused by a virus-induced immunopathological reaction. The tetranortriterpenoid 1-cinnamoyl-3,11-dihydroxymeliacarpin (CDM), obtained from MA purification, displays anti-herpetic activity and impedes nuclear factor kappaB (NF-kappaB) activation in HSV-1 infected conjunctival cells. To extend our understanding about CDM biological properties, we investigated its anti-HSV-1 activity as well as the effect on NF-kappaB activation and cytokine secretion induced by viral (HSV-1) and no-viral (LPS) stimuli, in corneal cells and macrophages. CDM exerted a potent anti-HSV-1 effect on corneal cells and inhibited NF-kappaB translocation to the nucleus, leading to a decrease in IL-6 production. Besides, CDM seemed to modulate IL-6 and TNF-alpha responses in macrophages, whether they were infected with HSV-1 or stimulated with LPS. However, CDM did not affect NF-kappaB activation in these cells, suggesting that an alternative NF-kappaB cell signaling pathway would be involved in the modulation of cytokine production. We conclude that, in addition to its antiviral effect, CDM would be acting as an immunomodulating compound which would be responsible for the improvement of murine HSK already reported.

HSV immune complex (HSV-IgG: IC) and HSV-DNA elicit the production of angiogenic factor VEGF and MMP-9

Angiogenesis and inflammatory mediators are critical pathogenic factors in herpetic stromal keratitis (HSK). Since disease progresses without infectious virus, HSV-DNA and HSV-IgG complexes (HSV-IC) may contribute to HSK by triggering these factors. Production of VEGF and MMP-9 was studied in vitro using corneal epithelial cells (HCE), fibroblasts (HCRF) and macrophages (THP-1). VEGF was elevated in HCRF and THP-1 following treatment with HSV-DNA and HSV-IC. MMP-9 was elevated in THP-1 but not in corneal cells. When anti-HSV-IgG(Fab')2 complexes stimulated THP-1, MMP-9 was reduced to control levels. Pretreatment of THP-1 with anti-TLR-2 and -3 inhibited MMP-9 production. Thus, HSV-IC may stimulate THP-1 through the Fc receptor and TLRs. Proinflammatory cytokines (IL-1b, IL-6, and TNF-alpha) increased VEGF and MMP-9 in corneal cells and macrophages. These studies indicate that the continued presence of HSV-DNA and HSV-IC contribute to angiogenesis and inflammation in HSK. Thus, cytokines and TLRs may be potential targets for intervention.

Pathogenesis of herpetic stromal keratitis in CCR5- and/or CXCR3-deficient mice

PURPOSE

Herpetic stromal keratitis (HSK) is an immunopathological reaction to herpes simplex virus type 1 (HSV-1) corneal infection. It has been reported that CD4+ cells play the most important role in the pathogenesis of this disease. In this study, we have focused on two chemokine receptors, CCR5 and CXCR3, which are expressed on CD4+ Th1 cells in mice HSK model.

METHODS

CCR5-deficient (CCR5KO), CXCR3-deficient (CXCR3KO), CCR5/CXCR3 double-deficient (DKO), and wild type (WT) mice (C57/BL6 background) were infected intracorneally with HSV-1 (CHR3 strain). The corneas were examined biomicroscopically, and cryosections of the corneas were examined histologically and immunohistochemically. Real-time RT-PCR and RNase protection assay (RPA) were performed, and the virus titers were measured in excised eyes and trigeminal ganglia (TG).

RESULTS

The HSK clinical severity in DKO mice was significantly lower than that in WT mice, and this was reversed by transfer of cells from the spleen of WT mice to DKO mice. Histologically, the numbers of T cells (CD4+ and CD8+ cells) and neutrophils infiltrating the cornea were significantly fewer in CCR5KO, CXCR3KO, and DKO mice. Transcript levels of immune-related cell surface marker in the eye by RPA were reduced in DKO mice. The expression of I-TAC was significantly increased in the cornea of CCR5KO mice, and MIP-1alpha and MIP-1beta were significantly lower in CXCR3KO mice than in WT mice by RT-PCR. There were no significant differences of virus titers in the eye and TG among any groups of mice except the increase in the TG of DKO mice on day 5 PI.

CONCLUSIONS

The suppression of chemotaxis and activation of CD4+ Th1 cells by the lacking of CXCR3 and CCR5 causes a decrease of other infiltrating cells, resulting in a lower severity of HSK. These results suggest that targeting chemokine receptors is a promising way to treat HSK.

Who (what) pays toll for the development of herpetic stromal keratitis (HSK)

In the herpetic stromal keratitis (HSK), HSV DNA fragments and HSV-IgG immune complexes (HSV-IC) are present in most of the corneas long after infective virus has disappeared. These viral components are highly immunogenic and potentiate production of proinflammatory cytokines and chemokines via Toll-like receptors (TLRs) expressed on the corneal cells and macrophages. In addition angiogenic factors, such as vascular endothelium growth factor (VEGF) and the tissue damaging enzyme matrix metalloproteinase 9 (MMP-9) deeply involved in the pathogenesis of HSK, are also induced by corneal cells and macrophages through the recognition of these viral components. These processes elicited by residual viral DNA and HSV-IC are likely one of the sustained driving force in the development of HSK. Hence, strategies developed to alter these pathways should lead to new preventative and therapeutic measures.

Non-mitogenic anti-CD3F(ab')2 monoclonal antibody: a novel approach to control herpetic stromal keratitis

PURPOSE

Treatment with anti-CD3 antibody has been shown to ameliorate and reverse an existing immunopathological condition by inducing tolerance. The purpose of this study is to assess the therapeutic potential of non-Fc receptor (FcR) binding anti-CD3 monoclonal antibody (mAb), CD3F(ab')(2), for the treatment of herpes simplex virus (HSV)-induced stromal keratitis (SK).

METHODS

Balb/c and C57BL/6 mice were ocularly infected with HSV-1 strain RE (HSV-1RE). Infected animals were treated with CD3F(ab')(2). Development of SK starting from day 5 postinfection (p.i.), infiltration of inflammatory cells into the corneas and the generation of the immune response were compared with untreated animals using slit-lamp biomicroscopy, flow cytometry, and ELISA.

RESULTS

In vivo administration of CD3F(ab')(2) resulted in significant reduction in the severity and incidence of SK in the infected animals compared to untreated counterparts. Infiltration of fewer pathogenic CD4(+) T cells into the cornea, along with a lower percentage of cells that could be induced to express IFN-gamma, occurred with anti-CD3F(ab')(2) treatment. Similar observations were noted in the secondary lymphoid tissues. Additionally, an increase in the frequency of CD4(+)Foxp3(+) regulatory T cells was noticed in both cornea and lymphoid tissues of treated animals compared to untreated animals. Treatment with CD3F(ab')(2) also reduced the number of SSIEFARL peptide-specific CD8(+)IFN-gamma(+) T cells in the secondary lymphoid tissues. Furthermore, use of this reagent was moderately effective in limiting lesions in mice with established lesions.

CONCLUSIONS

Taken together, these results show that non-FcR binding anti-CD3 treatment could be useful in limiting SK lesions.

IFN-gamma acts as anti-angiogenic cytokine in the human cornea by regulating the expression of VEGF-A and sVEGF-R1

Inflammatory processes within the cornea are known to be associated with corneal neovascularization (CN). We examined the effects of inflammatory mediators on the expression of angiogenic factors by corneal cells. TNF-alpha and IL-1 induced VEGF-A secretion by corneal fibroblasts (HCRF) and this was inhibited significantly by IFN-gamma. Constitutively secreted VEGF-A by corneal epithelial cells (HCE) was not affected by these cytokines. Moreover, sVEGF-R1(sFlt-1) secretion by HCRF was stimulated significantly by IFN-gamma. JAK-STAT pathway inhibitor reversed the effects of IFN-gamma on VEGF-A and sFlt-1 secretion by HCRF. RT-PCR analysis showed that IFN-gamma influences the expression of VEGF-A and sFlt-1 by affecting their mRNA level. IFN-gamma inhibited TGF-beta induced VEGF-A secretion but not sVEGF-R1 secretion. This is the first report demonstrating the inhibitory and stimulatory effects of IFN-gamma on VEGF-A and sFlt-1 secretion, respectively. Our results suggest that IFN-gamma acts as an anti-angiogenic cytokine in the human cornea.

Anti-herpetic and anti-inflammatory activities of two new synthetic 22,23-dihydroxylated stigmastane derivatives

Stromal keratitis resulting from ocular infection with Herpes simplex virus type 1 (HSV-1) is a common cause of blindness. This report investigates the antiviral and anti-inflammatory properties of two new synthetic stigmastane analogs in the experimental model of HSV-1-induced ocular disease in mice. (22S,23S)-22,23-dihydroxystigmast-4-en-3-one (1) and (22S,23S)-22,23-dihydroxystigmasta-1,4-dien-3-one (2) exhibited anti-HSV-1 activity in vitro and ameliorated the signs of murine herpetic stromal keratitis (HSK), although none of the compounds showed antiviral activity in vivo. We discuss that the improvement of HSK could be due to an immunomodulatory effect of both compounds.

Effect of human apolipoprotein E genotype on the pathogenesis of experimental ocular HSV-1

The isoform-specific role of human apolipoprotein E (apoE) has been assessed in a mouse model of ocular herpes. Female, age-matched transgenic mice knocked-in for the human allele apoE3 or apoE4 and their parent C57Bl/6 mice were inoculated corneally with HSV-1 strain KOS. Ocular HSV-1 pathogenesis was monitored through viral replication and clinical progression of stromal opacity and neovascularization by slit-lamp examination. Establishment of latency was determined by analysis of HSV-1 DNA (copy number) by specific real-time PCR in the cornea, trigeminal ganglia (TG), and brain. Representative groups of transgenic mice were sacrificed for the analysis of gene expression of vascular endothelial growth factor (VEGF) by reverse-transcription PCR, and apoE expression by Western blot analysis. At 6days post-infection (P.I.), the ocular infectious HSV-1 titer was significantly higher (p<0.05) in apoE4 mice compared with apoE3 and C57Bl/6 mice. Corneal neovascularization in apoE4 mice was significantly higher (p<0.05) than apoE3 and C57Bl/6 mice. The onset of corneal opacity in apoE4 mice was accelerated during days 9-11 P.I.; however, no significant difference in severity was seen on P.I. days 15 and beyond. At 28 days P.I., infected mice of all genotypes had no significant differences in copy numbers (range 0-15) of HSV-1 DNA in their corneas, indicating that HSV-1 DNA copy numbers in cornea are independent of apoE isoform regulation. At 28 days P.I., both apoE4 and C57Bl/6 mice had a significantly higher (p=0.001) number of copies of HSV-1 DNA in TG compared with apoE3. ApoE4 mice also had significantly higher (p=0.001) copies of HSV-1 DNA in their TGs compared with C57Bl/6 mice. In brain, both apoE4 and C57Bl/6 mice had significantly higher numbers (p<or=0.03) of copies of HSV-1 DNA compared with apoE3 mice. However, the number of HSV-1 DNA copies in the brain of C57Bl/6 mice was not significantly different than that of apoE4 (p=0.1). Comparative molecular analysis between apoE3 and apoE4 mice on selected days between 7 and 28 P.I., inclusive, revealed that the corneas of apoE4 mice expressed VEGF. None of the corneas in the apoE3 mice expressed VEGF during this time. Western blot analysis showed proteolytic cleavage of the apoE protein in the corneas of the apoE4 mice. Through days 14-28 P.I., a approximately 29 kDa C-terminal truncated apoE fragment was present in the corneas of apoE4 mice, but not in apoE3 mice. ApoE4 is a risk factor for ocular herpes, in part, through increased replication of virus in the eye, an earlier onset in clinical opacity, significantly higher neovascularization, and increased HSV-1 DNA load in TG and brain than that of apoE3. Increased pathogenesis of ocular herpes in apoE4 mice was also mediated, in part through up-regulated expression of VEGF and apoE proteolysis in the cornea. This is the first report linking a human gene, apoE4, as a risk factor for ocular herpes pathogenesis in a transgenic mouse model.

The in vitro immunomodulatory activity of a synthetic brassinosteroid analogue would account for the improvement of herpetic stromal keratitis in mice

Herpes simplex virus type 1 (HSV-1) induces an ocular chronic immunoinflammatory syndrome named herpetic stromal keratitis that can lead to vision impairment and blindness. We have reported that the synthetic brassinosteroid (22S,23S)-3beta-bromo-5alpha,22,23-trihydroxystigmastan-6-one, designated as 2, is a potent antiviral in vitro and reduces the incidence of murine herpetic stromal keratitis, although it does not exert an antiviral effect in vivo. In the present report, we investigated whether brassinosteroid 2 may play a role in the modulation of the response of epithelial and immune cells to HSV-1 infection. Compound 2 blocked HSV-1-induced activation of NF-kappaB by inhibiting its translocation to the nucleus of infected corneal and conjunctival cells in vitro, as well as significantly reduced the secretion of TNF-alpha in infected NHC cells. Conversely, IL-6 production was enhanced by compound 2 after HSV-1 infection in both cell types. The production of these cytokines was considerably reduced in a LPS-stimulated macrophage cell line after treatment with compound 2. In conclusion, brassinosteroid 2 would be playing a modulating effect as an inductor or inhibitor, depending on the cell type involved. The improvement of disease observed in mice could be a balance between both, the immunostimulating and immunosuppressive effects of brassinosteroid 2 in vivo.

Human Eye Infections

The eye contains a variety of cell and tissue types. Conjunctivitis due to respiratory RNA viruses represents by far the most common viral eye disorder. However, any ocular tissue can sustain infection by human viruses, including those viruses with predilection for neural sites. As elsewhere in the body, ocular pathologic changes induced by viruses tend to follow stereotypical patterns. Classical viral mechanisms of infection, including latency, reactivation, and carcinogenesis, can all be demonstrated in the eye. The eye's tissues also demonstrate a wide variety of immune responses, including those of mucosa-associated lymphoid tissue and immune privilege. The ocular complications of AIDS, including viral retinitis and ocular surface squamous carcinoma, remain significant causes of morbidity throughout the world.

IL-17 receptor signaling influences virus-induced corneal inflammation

IL-17 has been associated with selected inflammatory and autoimmune diseases. We characterized the expression of this proinflammatory cytokine following HSV-1 corneal infection and investigated whether IL-17R signaling modulated the host response to the viral pathogen at early time-points postinfection. IL-17 was elevated in the murine cornea 24 h after high-dose virus infection and subsequently persisted at low levels during the first week. Immunofluorescent studies showed that the IL-17R was expressed by cultured mouse corneal fibroblasts. Exposure of corneal cells to IL-17 led to production of IL-6 and MIP-2 in vitro and in vivo, indicating that the IL-17R was functional. Mice lacking IL-17R displayed significantly reduced neutrophil infiltration and corneal opacity. However, this effect was transient, as corneal pathology and neutrophil influx resembled that of wild-type (WT) hosts 4 days postinfection. HSV-1 growth and clearance in IL-17R(-/-) hosts were similar to that of the WT controls. Infection of IFN-gamma gene knockout mice was associated with elevated IL-17 levels and accelerated corneal opacity, suggesting that IFN-gamma negatively regulated IL-17 expression. Collectively, our results establish that IL-17 is rapidly produced in the cornea after HSV-1 infection and is regulated at least in part by IFN-gamma. The absence of IL-17 signaling results in a transient decrease in the expression of proinflammatory mediators, neutrophil migration, and corneal pathology, but control of virus growth in the cornea and trigeminal ganglia is not compromised. Thus, IL-17 actively influences early virus-induced corneal inflammation.

Innate recognition network driving herpes simplex virus-induced corneal immunopathology: role of the toll pathway in early inflammatory events in stromal keratitis

Ocular infection with herpes simplex virus (HSV) sets off an array of events that succeed in clearing virus from the cornea but leaves the tissue with a CD4(+) T-cell-orchestrated chronic inflammatory lesion that impairs vision. We demonstrate that Toll-like receptor (TLR) signaling forms a part of the recognition system that induces the syndrome that eventually culminates in immunopathology. Accordingly, in a comparison of the outcomes of infection in wild-type (WT) mice and those lacking TLR function, it was apparent that the absence of TLR2 and, to a lesser extent, TLR9 resulted in significantly diminished lesions. Similarly, mice lacking the adapter molecule MyD88 were resistant to lesion development, but such animals were also unable to control infection, with most succumbing to lethal encephalitis. The susceptibility of TLR4(-/-) animals was also evaluated. These animals developed lesions, which were more severe, more rapidly than did WT animals. We discuss the possible mechanisms by which early recognition of HSV constituents impacts the subsequent development of immunopathological lesions.

Corneal gene therapy

Gene therapy to the cornea can potentially correct inherited and acquired diseases of the cornea. Factors that facilitate corneal gene delivery are the accessibility and transparency of the cornea, its stability ex vivo and the immune privilege of the eye. Initial corneal gene delivery studies characterized the relationship between intraocular modes of administration and location of reporter gene expression. The challenge of achieving effective topical gene transfer, presumably due to tear flow, blinking and low penetration of the vector through epithlelial tight junctions left no alternative but invasive administration to the anterior chamber and corneal stroma. DNA vaccination, RNA interference and gene transfer of cytokines, growth factors and enzymes modulated the corneal microenvironment. Positive results were obtained in preclinical studies for prevention and treatment of corneal graft rejection, neovascularization, haze and herpetic stromal keratitis. These studies, corneal gene delivery systems and modes of administration, and considerations regarding the choice of animal species used are the focus of this review. Opportunities in the field of corneal gene therapy lie in expanding the array of corneal diseases investigated and in the implementation of recent designs of safer vectors with reduced immunogenicity and longer duration of gene expression.

Expression and function of the OX40/OX40L costimulatory pair during herpes stromal keratitis

Herpes stromal keratitis (HSK) is an immunopathological disease regulated by Th1 CD4 T cells, which require APC and costimulation within the infected cornea to mediate disease. Recent studies suggest the OX40:OX40 ligand (OX40L) interaction enhances effector cell cytokine secretion at inflammatory sites. OX40(+) cells were detected in HSV-1-infected mouse corneas as early as 3 days postinfection (dpi), prior to the onset of HSK, and their frequency increased through 15 dpi, when all mice exhibited severe HSK. OX40L(+) cells were first detected at 7 dpi, coincident with the initiation of HSK. It is interesting that the OX40L(+) cells did not coexpress MHC Class II or the dendritic cell (DC) marker CD11c. Our findings demonstrate rapid infiltration of activated (OX40(+)) CD4(+) T cells into HSV-1-infected corneas and expression of OX40L on MHC Class II-negative cells but surprisingly, not on MHC Class II(+) CD11c(+) DC, which are present in the infected corneas and required for HSK. Moreover, neither local nor systemic treatment of mice with a blocking antibody to OX40L or with a blocking fusion protein altered the course of HSK significantly, possibly as a result of a lack of OX40L expression on functional APC.

Quantitative analysis of herpes simplex virus type 1-specific memory B cells generated by different routes of infection

We compared the herpes simplex virus type 1 (HSV)-specific memory B cell (MBC) populations generated by footpad and intranasal infection in mice. Both routes of infection generated transient antibody-secreting cell responses in the draining lymph nodes and spleen, and sustained circulating IgG. HSV-specific IgG MBCs, analyzed by limiting dilution assay approximately 8 weeks after infection, were distributed in a range of lymph nodes and in the spleen and Peyer's patches. Overall, the route of infection had little effect on the MBC frequency in each anatomical location. Interestingly, after both routes of infection there was a trend towards preferential MBC accumulation in the mediastinal lymph node. Intravaginal challenge of mice primed by footpad or intranasal infection generated similar secondary IgG responses. Our findings indicate that the widespread dispersion of MBCs to lymphoid tissues throughout the body is largely independent of the route of infection, but may be influenced by tissue-specific factors.

Depletion of MCP-1 increases development of herpetic stromal keratitis by innate immune modulation

Chemokines are important chemoattractant inflammatory molecules, but their interdependent network in disease pathogenesis remains unclear. Studies in mouse models have shown that herpetic stromal keratitis (SK) is produced by the consequence of a tissue-destructive immunoinflammatory reaction involving herpes simplex virus type 1 (HSV) infection. Here we found that ocular HSV infection leads to increased expression of monocyte chemoattractant protein-1 (MCP-1), one of the major chemoattractants for immune cells that express CCR2, in the SK cornea. However, MCP-1 is unlikely to be a chemoattractant for infiltrating Gr-1(+), CD11b(+) cells in SK, as these cells are found to be CCR2 negative. Nevertheless, infection of MCP-1(-/-) mice resulted in more severe SK lesion severity compared with WT mice (P<0.01). We demonstrated that the loss of MCP-1 in the SK cornea caused a significant overexpression of macrophage inflammatory protein-2 (MIP-2) (P<0.01) on days 2 and 4 postinfection and increased infiltration of inflammatory cells (Gr-1-high and CD11b(+)) expressing CXCR2, a receptor for MIP-2, into the cornea. Subsequently, increased infiltration of inflammatory cells accelerated by MIP-2 overexpression might result in the high production of inflammatory molecules, including vascular endothelial growth factor (VEGF) and IL-1beta in SK, as well as CpG oligodeoxynucleotide (ODN)-implanted eyes of MCP-1(-/-) mice. These results indicate that MCP-1 in the SK cornea might regulate the expression of other chemokines, as well as the infiltration of inflammatory cells and control development of SK.

Vascular Endothelial Growth Factor Receptor 2-Based DNA Immunization Delays Development of Herpetic Stromal Keratitis by Antiangiogenic Effects

Stromal keratitis (SK) is an immunoinflammatory eye lesion caused by HSV-1 infection. One essential step in the pathogenesis is neovascularization of the normally avascular cornea, a process that involves the vascular endothelial growth factor (VEGF) family of proteins. In this report, we targeted the proliferating vascular endothelial cells expressing VEGFR-2 in the SK cornea by immunization with recombinant Salmonella typhimurium containing a plasmid encoding murine VEGFR-2. This form of DNA immunization resulted in diminished angiogenesis and delayed development of SK caused by HSV-1 infection and also reduced angiogenesis resulting from corneal implantation with rVEGF. CTL responses against endothelial cells expressing VEGFR-2 were evident in the VEGFR-2-immunized group and in vivo CD8+ T cell depletion resulted in the marked reduction of the antiangiogenic immune response. These results indicate a role for CD8+ T cells in the antiangiogenic effects. Our results may also imply that the anti-VEGFR-2 vaccination approach might prove useful to control pathological ocular angiogenesis and its consequences.

Role for 3-O-sulfated heparan sulfate as the receptor for herpes simplex virus type 1 entry into primary human corneal fibroblasts

Herpes simplex virus type 1 (HSV-1) infection of the corneal stroma remains a major cause of blindness. Primary cultures of corneal fibroblasts (CF) were tested and found susceptible to HSV-1 entry, which was confirmed by deconvolution imaging of infected cells. Plaque assay and real-time PCR demonstrated viral replication and hence a productive infection of CF by HSV-1. A role for glycoprotein D (gD) receptors in cultured CF was determined by gD interference assay. Reverse transcription-PCR analysis indicated expression of herpesvirus entry mediator and 3-O-sulfated (3-OS) heparan sulfate (HS)-generating enzyme 3-O sulfotransferase 3 (3-OST-3) but not nectin-1 or nectin-2. Subsequently, HS isolated from these cells was found to contain two distinct disaccharides (IdoUA2S-AnMan3S and IdoUA2S-AnMan3S6S) that are representative of 3-OST-3 activity. The following lines of evidence supported the important role of 3-OS HS as the mediator of HSV-1 entry into CF. (i) Blockage of entry was observed in CF treated with heparinases. The same enzymes had significantly less effect on HeLa cells that use nectin-1 as the entry receptor. (ii) Enzymatic removal of cell surface HS also removed the major gD-binding receptor, as evident from the reduced binding of gD to cells. (iii) Spinoculation assay demonstrated that entry blockage by heparinase treatment included the membrane fusion step. (iv) HSV-1 glycoprotein-induced cell-to-cell fusion was inhibited by either prior treatment of cells with heparinases or by HS preparations enriched in 3-OS HS. Taken together, the data in this report provide novel information on the role of 3-OS HS in mediating infection of CF, a natural target cell type.

Regulatory T cells in virus infections

This review discusses situations when the magnitude and function of immune responses to virus infection are influenced by regulatory T cells (Tregs). The focus is on CD4+ CD25+ forkhead box protein 3+ natural Tregs (nTregs). The immune response may be limited in magnitude and efficacy when animals with normal nTreg function are infected with virus. This limitation can be observed both in vitro and in vivo. In the case of herpes simplex virus (HSV), animals depleted of nTregs prior to infection more effectively control the virus. With some virus infections, Treg responses (either nTregs or interleukin-10-dependent adaptive Tregs) appear to contribute to immune dysfunction, accounting for viral persistence and chronic tissue damage. This may occur with hepatitis C virus and some retrovirus infections that include human immunodeficiency virus (HIV). Under other circumstances, the nTreg response is judged to be beneficial, as it may help limit the severity of tissue damage associated with an immunoinflammatory reaction to virus infection. Such a situation occurs in HSV-induced immunopathological lesions in the eye. With HIV, nTregs may help limit chronic immune activation that may precede collapse of the immune system. This review also discusses how virus infections become recognized by nTreg responses and how such responses might be manipulated to increase immunity or to limit virus-induced immunopathology.

Ocular herpes simplex: changing epidemiology, emerging disease patterns, and the potential of vaccine prevention and therapy

PURPOSE

To review the changing epidemiology of herpes simplex virus infection, emerging patterns of herpetic ocular disease, and the challenges and promise of herpes simplex virus vaccine therapy.

DESIGN

Perspective.

METHODS

Literature review.

RESULTS

An epidemic increase in genital herpes simplex type 2 infection is reflected in a 30% increase in HSV-2 antibodies in the United States since 1976. Approximately one in four people in the United States over age 30 is infected with HSV-2. Primary acquisition of herpes simplex type 1 is becoming progressively delayed in many industrialized countries, in contrast to developing nations where the virus is acquired early in life and is ubiquitous. Changes in sexual behavior among young adults have been associated with a recent increase in genital HSV-1 infection, resulting from oral-genital rather than genital-genital contact. Clinical trials of HSV vaccines using selected herpes simplex virus type 2 proteins mixed in adjuvant have shown limited efficacy in seronegative women, but not in men.

CONCLUSIONS

The recent epidemic of genital herpes simplex type 2 infection is likely to result in an increase in neonatal ocular herpes and in delayed cases of acute retinal necrosis syndrome. The increase in genital HSV-1 may lead to industry production of vaccines that contain components of both HSV-1 and HSV-2 targeted toward limiting genital disease and transmission. As newer herpes simplex vaccines become available, ophthalmologists must be vigilant that a boost in immunity against HSV does not have a paradoxical effect in exacerbating break-through cases that develop immune-mediated herpes simplex stromal keratitis.