Contribution of vascular endothelial growth factor in the neovascularization process during the pathogenesis of herpetic stromal keratitis

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.

Oncolytic HSV-1 infection of tumors induces angiogenesis and upregulates CYR61

Oncolytic viral therapy is under evaluation for toxicity and efficacy in clinical trials relating to several different tumors. We report a significant increase in the angiogenic index of oncolytic virus (OV)-treated glioma-matrigel implants (2.83-fold, P < 0.02). In a rat intracranial glioma model, large tumors from OV-treated animals were significantly more angiogenic than the phosphate-buffered saline (PBS)-treated control tumors (OV: 101 +/- 21.6; PBS: 19.8 +/- 10; P = 0.0037). Transcript profiling of OV-treated tumors revealed dysregulation of several transcripts involved in glioma angiogenesis. OV-mediated induction of CYR61 gene expression (8.94-fold, P = 0.001) correlated significantly with the presence of OV in tumor tissue in vivo (R = 0.7, P < 0.001). Further, induction of CYR61 mRNA and protein were confirmed in multiple human cancer cell lines and primary human tumor-derived cells in vitro, and in tumor lysate and cerebrospinal fluid (CSF) in vivo. Finally, we show that treatment of glioma cells with Cilengitide, known to counter CYR61-induced integrin activation, significantly suppressed the proangiogenic effect of OV treatment of gliomas (P < 0.05).

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 Collapse

Key Words

• hsv-1
• apolipoprotein e
• brain
• cornea
• herpetic stromal keratitis
• trigeminal ganglia
• transgenic mouse model
• vascular endothelial growth factor

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MESH Headings

• Animals
• Apolipoproteins E/genetics
• Apolipoproteins E/metabolism
• Corneal Neovascularization/genetics
• Corneal Neovascularization/metabolism
• Corneal Neovascularization/virology
• Corneal Opacity/genetics
• Corneal Opacity/metabolism
• Corneal Opacity/virology
• DNA, Viral/analysis
• Disease Models, Animal
• Eye Proteins/genetics
• Eye Proteins/metabolism
• Female
• Genetic Predisposition to Disease
• Genotype
• Herpesvirus 1, Human/isolation & purification
• Humans
• Keratitis, Herpetic/genetics
• Keratitis, Herpetic/metabolism
• Keratitis, Herpetic/virology
• Mice
• Mice, Inbred C57BL
• Mice, Transgenic
• Reverse Transcriptase Polymerase Chain Reaction/methods
• Vascular Endothelial Growth Factor A/metabolism
• Viral Load

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Grants

• R01 EY006311 NEI NIH HHS
• R01 EY002672 NEI NIH HHS
• R01 EY06311 NEI NIH HHS
• F32 EY016316 NEI NIH HHS
• F32EY016316 NEI NIH HHS
• P30 EY002377 NEI NIH HHS
• P30EY002377 NEI NIH HHS

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Affiliation(s)

Partha S. Bhattacharjee Department of Ophthalmology, Louisiana State University Health Sciences Center, New Orleans, LA, 70112
Donna M. Neumann Department of Ophthalmology, Louisiana State University Health Sciences Center, New Orleans, LA, 70112
Timothy P. Foster Department of Microbiology, Immunology and Parasitology, Louisiana State University Health Sciences Center, New Orleans, LA, 70112
Sadallah Bouhanik Department of Ophthalmology, Louisiana State University Health Sciences Center, New Orleans, LA, 70112
Christian Clement Department of Ophthalmology, Louisiana State University Health Sciences Center, New Orleans, LA, 70112
Dass Vinay Department of Ophthalmology, Louisiana State University Health Sciences Center, New Orleans, LA, 70112
Hilary W. Thompson Department of Ophthalmology, Louisiana State University Health Sciences Center, New Orleans, LA, 70112 LSU Neuroscience Center, Louisiana State University Health Sciences Center, New Orleans, LA, 70112 Section of Biostatistics, School of Public Health, Louisiana State University Health Sciences Center, New Orleans, LA, 70112
James M. Hill Department of Ophthalmology, Louisiana State University Health Sciences Center, New Orleans, LA, 70112 Department of Microbiology, Immunology and Parasitology, Louisiana State University Health Sciences Center, New Orleans, LA, 70112 Department of Pharmacology, Louisiana State University Health Sciences Center, New Orleans, LA, 70112 LSU Neuroscience Center, Louisiana State University Health Sciences Center, New Orleans, LA, 70112

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Collaborators Collapse

Neutrophils protect the retina of the injected eye from infection after anterior chamber inoculation of HSV-1 in BALB/c mice

PURPOSE

To determine whether infiltrating polymorphonuclear leukocytes PMNs play a role in preventing early direct anterior-to-posterior spread of herpes simplex virus (HSV)-1 and/or in preventing the spread of HSV-1 from the brain back to the retina of the injected eye after anterior chamber (AC) inoculation.

METHODS

BALB/c mice were treated with monoclonal antibody RB6-8C5 (Gr-1) against PMNs or control IgG and inoculated with HSV-1.

RESULTS

In Gr-1-treated mice, PMNs were depleted in the peripheral blood and in the HSV-1-infected eye. More virus (2-3 logs) was recovered from the inoculated eye of Gr-1 antibody-treated mice than from control mice. Immunohistochemistry revealed disseminated virus-infected cells in the junction between the anterior and the posterior segment and also in the posterior segment of the HSV-1-inoculated eye in Gr-1-treated mice. In control IgG-treated mice, virus-infected cells were observed only within the AC. More virus (3 logs) was recovered from the contralateral suprachiasmatic nucleus (SCN), and increased virus staining was observed in the ipsilateral optic nerve of Gr-1-treated mice compared with control mice. In Gr-1-treated mice, the central retina was virus-infected in a patchy fashion beginning on day 7 post infection (pi), and the infection progressed to involve the entire retina.

CONCLUSIONS

Since both direct anterior-to-posterior spread of virus and spread via the optic nerve occurred in PMN-depleted mice, these results suggest that PMNs play an important role both in limiting intraocular spread of virus in the injected eye and in controlling spread of the virus from the brain into the optic nerve and retina of the injected eye.

Activated inflammatory infiltrate in HSV-1-infected corneas without herpes stromal keratitis

PURPOSE

To investigate herpes stromal keratitis (HSK) immunopathology by studying HSV-1-infected corneas that fail to develop HSK.

METHODS

Plaque assay quantified HSV-1 in the tear film of infected mice. FACS analysis enumerated corneal leukocytic infiltrate and characterized infiltrate phenotypically after staining for activation and regulatory T cell (Treg) markers and for markers of antigen-presenting cell (APC) maturation. Treg cells were depleted in vivo using anti-CD25 mAb. Luminex analysis quantified the amount of cytokines and chemokines expressed in corneal tissue homogenate.

RESULTS

Infected corneas without HSK exhibited a pronounced leukocytic infiltrate containing a significantly higher proportion and nearly identical absolute number of activated CD4+ T cells 15 days after infection when compared with those with HSK. Moreover, the frequency and absolute number of regulatory CD4+ T cells (Tregs) was lower in nondiseased corneas, and Treg depletion did not influence HSK incidence. The frequency of mature, immunogenic DCs and the ratio of mature DCs to CD4+ T cells were nearly identical in corneas with and without HSK. The authors observed a reduced population of neutrophils and reduced expression of neutrophil chemoattractants MIP-1beta and keratinocyte chemoattractant and the neutrophil-attracting cytokine IL-6 in corneas without HSK.

CONCLUSIONS

These findings demonstrate that HSV-1-infected corneas can retain clarity in the presence of a substantial secondary leukocytic infiltrate, that activated CD4+ T cells, while necessary, are not sufficient for HSK development, that susceptibility to HSK is not determined by Tregs, and that clinical disease correlates with the accumulation of a critical mass of neutrophils through chemoattraction.

Subconjunctival bevacizumab injection for corneal neovascularization

PURPOSE

To report on the clinical use of subconjunctival bevacizumab in patients with corneal neovascularization.

METHODS

The charts of 10 consecutive patients with corneal neovascularization who received subconjunctival injections of bevacizumab (2.5 mg/0.1 mL) were reviewed. Digital photographs of the cornea were graded by 2 masked observers for density, extent, and centricity of corneal vascularization. Image analysis was used to determine the area of cornea covered by neovascularization as a percentage of the total corneal area.

RESULTS

No significant ocular or systemic adverse events were observed during 3.5 +/- 1.1 months of follow-up. Seven patients showed partial regression of vessels. The extent decreased from 6.0 +/- 1.2 (SD) clock hours before the injection to 4.6 +/- 1.0 clock hours after bevacizumab injection (P = 0.008). Density decreased from 2.7 +/- 0.2 to 1.9 +/- 0.3, respectively. (P = 0.007). No change was noticed in the centricity of corneal vessels. Corneal neovascularization covered, on average, 14.8% +/- 2.5% (SD) of the corneal surface before the injections, compared with 10.5% +/- 2.8% (P = 0.36, t test) after bevacizumab injection. Therefore, bevacizumab decreased corneal neovascularization by 29%.

CONCLUSIONS

Short-term results suggest that subconjunctival bevacizumab is well tolerated and associated with a partial regression of corneal neovascularization.

Enhanced viral immunoinflammatory lesions in mice lacking IL-23 responses

Herpes simplex virus (HSV) infection of the cornea culminates in an immunopathological lesion (stromal keratitis--SK) that impairs vision. This report shows that HSV infection results in IL-23 up-regulation, but if this response fails to occur, as was noted in p19-/- mice, the severity of lesions, their incidence and the level of viral induced angiogenesis were significantly increased compared to wild-type (WT) animals (p<0.05). The higher disease severity in p19-/- mice appeared to be the consequence of an increased IL-12 response that in turn led to the induction of higher numbers of IFN-gamma producing CD4(+)T cells, the principal orchestrators of SK. Our results indicate that the severity of HSV induced immunopathological lesions may be mainly the consequence of IL-12 driven Th1 T cell reactions rather than the action of IL-17 producing cells controlled by IL-23.

Inhibition of corneal neovascularization by subconjunctival bevacizumab in an animal model

PURPOSE

To evaluate the effect of subconjunctival injection of bevacizumab on experimentally induced corneal neovascularization.

DESIGN

Experimental animal study.

METHODS

Twelve New Zealand white rabbits were involved, divided equally into four groups. Only one eye per rabbit was used. Topical instillation of 10 microl 5% NaOH solution was used, under general anesthesia, to induce corneal neovascularization secondary to corneal alkali burn in groups 2, 3, and 4. A single dose of 3.75 mg (25 mg/ml) bevacizumab was injected subconjunctivally. Group 1 (control group 1) was neither cauterized nor treated. Group 2 (control group 2) received a sham injection of balanced salt solution on day 14. Group 3 was treated on day 14 (after corneal neovascularization had been established). Group 4 was treated on day 1. Digital photographs were obtained and analyzed during the entire 28-day procedure. The area of neovascularization and scarring were measured in terms of the percentage of corneal surface affected.

RESULTS

On day 28, the difference of neovascularization between groups 2, 3, and 4 was found to be statistically significant at the .05 level (one-way analysis of variance [ANOVA]): group 4 (4.7%+/-3.1%)<group 3 (13.3%+/-2.3%)<group 2 (41.0%+/-3.6%; P<.05, Mann-Whitney U test). In group 3, the area of neovascularization decreased 14 days after treatment by 42%. Neovascularization was almost completely absent in group 4. The development of scarring was unaffected by bevacizumab (P>.1, one-way ANOVA). No side effects were noted.

CONCLUSIONS

Subconjunctival administration of bevacizumab inhibits corneal neovascularization effectively in the rabbit experimental model, especially if administered early.

Viruses and autoimmunity

Viruses have been suspected as causes and contributors of human autoimmune diseases (AID), although direct evidence for the association is lacking. However, several animal models provide strong evidence that viruses can induce AIDs as well as act to accelerate and exacerbate lesions in situations where self-tolerance is broken. Many models support the hypothesis by acting as molecular mimics that stimulate self-reactive lymphocytes. Mimicry alone is usually inadequate and with human AID, no compelling evidence supports a role for viruses that are acting as molecular mimics. Alternative mechanisms by which viruses participate in autoimmunity are non-specific, involving a mechanistically poorly understood process termed bystander activation or perhaps viral interference with regulatory cell control systems. This review briefly discusses examples where viruses are involved, taking the view point that molecular mimicry is over emphasized as a critical mechanism during AID pathogenesis.

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.

Role of Stat4-mediated signal transduction events in the generation of aggressor CD4+ T cells in herpetic stromal keratitis pathogenesis

Ocular infection with herpes simplex virus (HSV) causes a vision-impairing inflammatory reaction called herpetic stromal keratitis. In murine models, herpetic stromal keratitis lesions appear to be immunopathologic, mediated by CD4(+) T cells of Th1 phenotype. To provide insight about cytokine networks and signaling events involved in the development of aggressor CD4(+) T cells, ocular HSV infection was followed in mice deficient in Stat4 (Stat4(-/-) mice), the signal transducer for the cytokine interleukin-12 (IL-12). After ocular HSV infection of Stat4(-/-) and control BALB/c mice, clinical, histologic, and immunologic analyses were carried out. Further, to evaluate the involvement of Stat4 in the development of this aggressor population, naive CD4(+) T cells from Stat4(-/-) and BALB/c mice were adoptively transferred to C.B-17 SCID mice 1 day after corneal infection. Although Stat4(-/-) mice demonstrated increased susceptibility to lethal encephalitis and facial lesions, interestingly, these mice had less severe stromal keratitis in comparison to control animals. Adoptive transfer of naive CD4(+) T cells from Stat4(-/-) mice failed to produce disease in infected SCID recipients. The data imply a significant role of Stat4-mediated signaling events in the generation of an aggressor CD4(+) T cell population in stromal keratitis pathogenesis.

Therapeutic potential of bevacizumab (Avastin) in herpetic stromal keratitis (HSK)

In the stromal keratitis caused by herpes simplex virus (HSV), the formation of new vessels is the essential step for the pathogenesis of keratitis. Inhibition of angiogenesis diminishes the formation of corneal lesion induced by HSV. Procedures which suppress angiogenesis are proposed as a valuable therapeutic approach to control HSK. The mechanism by which HSV ocular infection results in corneal angiogenesis is not understood. Recent reports identified anti-vascular endothelial growth factor (VEGF) as a molecule that is highly expressed in the HSV infected eye and clearly involved in angiogenesis. The advent of VEGF treatments marks a major advancement in the treatment of angiogenic eye disease. Off-label use of bevacizumab (Avastin), a recombinant humanized monoclonal antibody directed against VEGF, in some neovascular disorders of the eye has been associated with promising short term results. Based on these evidences herein we hypothesize topical application of bevacizumab could inhibit corneal neovascularization and also scarring in HSK. We propose this drug as a novel adjunct to current anti-inflammatory strategies in HSK.

Herpes simplex virus type 1 induction of chemokine production is unrelated to viral load in the cornea but not in the nervous system

Herpes simplex virus type 1 elicits a strong host inflammatory response after corneal infection. The purpose of the current study was to compare the production of chemokines induced by viral infection at sites known to harbor virus after ocular inoculation in order to determine the relationship between viral load and chemokine expression. Using highly resistant IFN-alpha1 transgenic mice whose transgene is under the control of the glial fibrillary acidic protein promoter in comparison with the more sensitive wild-type counterparts, we compared the expression of chemokines versus the amount of infectious virus recovered from the anterior segment of the eye and nervous system. Consistent with our predicted outcome, the level of infectious virus recovered in the iris, trigeminal ganglia, and brainstem of resistant versus sensitive mice correlated with chemokine production; that is, the less virus recovered the less chemokine (CCL2, CCL3, CCL5, CXCL9, and CXCL10) produced. In contrast to the nervous system and iris, there was no correlation between chemokine expression and level of infectious virus recovered in the cornea. We interpret these results as suggesting chemokine expression within the cornea in response to herpes simplex virus type 1 infection is driven by factors other than antigenic stimulation.

Angiogenic Response Caused by Oncolytic Herpes Simplex Virus–Induced Reduced Thrombospondin Expression Can Be Prevented by Specific Viral Mutations or by Administering a Thrombospondin-Derived Peptide

Wild-type (WT) herpes simplex virus (HSV) causes some pathology, such as ocular keratitis, by increasing infected tissue vascularity, possibly reflecting altered angiogenic factor expression in infected cells. Oncolytic HSVs possess specific mutations enabling selective replication in tumor cells. We investigated whether this ability to enhance infected tissue vascularity is retained in oncolytic HSV, which could be an undesirable effect of oncolytic HSVs that may need to be addressed when treating tumors with oncolytic HSVs. s.c. tumors derived from U87 human glioma cells in athymic mice were treated with oncolytic HSVs G207 or G47Delta in the presence or absence of a recombinant protein composed of the three type-1 repeats (3TSR) of thrombospondin-1 (TSP-1). Real-time reverse transcription-PCR and Western blot of infected cultured cells measured angiogenic factor expression. Microvessel density was assessed using immunofluorescence. G207-treated U87 s.c. tumors had elevated microvessel densities compared with saline- and G47Delta-treated tumors, and G207 treatment caused delayed tumor growth resumption. G207-infected U87 and U373 cells exhibited reduced protein, not mRNA, expression of angiogenesis inhibitors TSP-1 and thrombospondin-2 (TSP-2). 3TSR restored the G207-treated tumor microvessel density to the low level of G47Delta-treated tumors and prevented delayed growth resumption. Oncolytic HSV G207 thus retains the ability of WT HSV to increase infected tissue vascularity. In infected tumors, this increased vascularity is mediated by reduced TSP-1 and TSP-2 levels and causes delayed tumor growth resumption. Incorporating viral mutations, such as those seen in G47Delta or administering thrombospondin-derived peptides, counteracts the angiogenic effect of oncolytic HSV and should be considered when designing oncolytic HSV therapies.

Inhibition of experimental corneal neovascularisation by bevacizumab (Avastin)

AIM

To evaluate the effect of topically administered bevacizumab (Avastin) on experimental corneal neovascularisation in rats.

METHODS

Silver nitrate sticks (75% silver nitrate, 25% potassium nitrate) were used to perform chemical cauterisation on the corneas of 16 eyes from 16 male Long Evans rats. For the following 7 days, the 10 eyes in the treatment group were instilled with bevacizumab 4 mg/ml drops twice daily, whereas the 6 eyes in the control group received placebo (normal saline drops twice daily). Digital photographs of the cornea were analysed to determine the area of cornea covered by neovascularisation as a percentage of the total corneal area.

RESULTS

In the bevacizumab-treated eyes, neovascularisation covered, on average, 38.2% (15.5%) (mean (SD)) of the corneal surface compared with 63.5% (5.0%) in the control group (p<0.02, Mann-Whitney U test).

CONCLUSION

Topically administered bevacizumab (Avastin) at a concentration of 4 mg/ml limits corneal neovascularisation following chemical injury in the male Long Evans rat model.

A potential therapeutic strategy for inhibition of corneal neovascularization with new anti-VEGF agents

The factors triggering corneal neovascularization involve various growth factors. The data supporting a causal role for vascular endothelial growth factor (VEGF) in corneal neovascularization are extensive. One possible strategy for treating corneal neovascularization is to inhibit VEGF activity by competitively binding VEGF with a specific neutralizing anti-VEGF antibody. The vireo-retinal service in the recent years enjoyed a high level of success in managing choroidal neovascularization using anti-VEGF strategies. Efficacy and tolerability have been demonstrated for drugs targeting VEGF. We herein hypothesize that topical application of new anti-VEGF agents such as pegaptanib, ranibizumab and bevacizumab are potentially useful for inhibiting corneal neovascularization and restoration of corneal clarity. Further investigations are needed to place these medical treatments alongside corneal neovascularization therapeutics.

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.

Interaction of angiogenic and immune mechanisms in the eye

Although a critical physiologic process, angiogenesis also contributes to the pathology associated with a variety of ocular diseases. Here we describe immune factors that regulate angiogenesis and review recent attempts to exploit these factors in animal models of ocular disease.

Abnormal immune response of CCR5-deficient mice to ocular infection with herpes simplex virus type 1

Ocular herpes simplex virus type 1 (HSV-1) infection elicits a strong inflammatory response that is associated with production of the beta chemokines CCL3 and CCL5, which share a common receptor, CCR5. To gain insight into the role of these molecules in ocular immune responses, the corneas of wild-type (WT) and CCR5-deficient (CCR5-/-) mice were infected with HSV-1 and inflammatory parameters were measured. In the absence of CCR5, the early infiltration of neutrophils into the cornea was diminished. Associated with this aberrant leukocyte recruitment, neutrophils in CCR5-/- mice were restricted to the stroma, whereas in WT mice, these cells trafficked to the stroma and epithelial layers of the infected cornea. Virus titres and cytokine/chemokine levels in the infected tissue of these mice were similar for the first 5 days after infection. However, by day 7 post-infection, the CCR5-/- mice showed a significant elevation in the chemokines CCL2, CCL5, CXCL9 and CXCL10 in the trigeminal ganglion and brainstem, as well as a significant increase in virus burden. The increase in chemokine expression was associated with an increase in the infiltration of CD4 and/or CD8 T cells into the trigeminal ganglion and brainstem of CCR5-/- mice. Surprisingly, even though infected CCR5-/- mice were less efficient at controlling the progression of virus replication, there was no difference in mortality. These results suggest that, although CCR5 plays a role in regulating leukocyte trafficking and control of virus burden, compensatory mechanisms are involved in preventing mortality following HSV-1 infection.

Corneal angiogenic privilege: angiogenic and antiangiogenic factors in corneal avascularity, vasculogenesis, and wound healing (an American Ophthalmological Society thesis)

PURPOSE

To determine the molecular basis of corneal avascularity during wound healing and determine the role of angiogenic and antiangiogenic factors in corneal vasculogenesis.

METHODS

The expression of proangiogenic factors (vascular endothelial growth factor [VEGF]; basic fibroblast growth factor [bFGF]; matrix metalloproteinase-2 [MMP-2]; and membrane-type 1-MMP [MT1-MMP]) and antiangiogenic factors (pigment epithelium-derived factor [PEDF]; angiostatin; restin; and endostatin) was analyzed in avascular corneas and in models of corneal neovascularization (bFGF pellet implantation, intrastromal injection of MT1-MMP cDNA, and surgically induced partial limbal deficiency).

RESULTS

Immunohistochemistry demonstrated the presence of antiangiogenic factors (PEDF, angiostatin, restin, and endostatin) and proangiogenic molecules (VEGF, bFGF, MMP-2, and MT1-MMP) in the cornea after wounding. Proangiogenic MMPs were upregulated in stromal fibroblasts in the vicinity of invading vessels following bFGF pellet implantation. Corneal neovascularization (NV) was also induced by intrastromal injection of MT1-MMP naked cDNA in conjunction with de-epithelialization. Partial limbal deficiency (HLD-) resulted in corneal NV in MMP-7 and MMP-3 knockout mice but not in wild type controls.

CONCLUSIONS

Corneal angiogenic privilege is an active process involving the production of antiangiogenic factors to counterbalance the proangiogenic factors (which are upregulated after wound healing even in the absence of new vessels). Our finding that the potent antiangiogenic factors, angiostatin and endostatin, are colocalized with several MMPs during wound healing suggests that MMPs may be involved in the elaboration of these antiangiogenic molecules by proteolytic processing of substrates within the cornea.

Prostaglandin E2 promotes degranulation-independent release of MCP-1 from mast cells

Mast cells (MCs) are common components of inflammatory infiltrates and a source of proangiogenic factors. Inflammation is often accompanied by vascular changes. However, little is known about modulation of MC-derived proangiogenic factors during inflammation. In this study, we evaluated the effects of the proinflammatory mediator prostaglandin E2 (PGE2) on MC expression and release of proangiogenic factors. We report that PGE2 dose-dependently induces primary MCs to release the proangiogenic chemokine monocyte chemoattractant protein-1 (MCP-1). This release of MCP-1 is complete by 2 h after PGE2 exposure, reaches levels of MCP-1 at least 15-fold higher than background, and is not accompanied by degranulation or increased MCP-1 gene expression. By immunoelectron microscopy, MCP-1 is detected within MCs at a cytoplasmic location distinct from the secretory granules. Dexamethasone and cyclosporine A inhibit PGE2-induced MCP-1 secretion by approximately 60%. Agonists of PGE2 receptor subtypes revealed that the EP1 and EP3 receptors can independently mediate MCP-1 release from MCs. These observations identify PGE2-induced MCP-1 release from MCs as a pathway underlying inflammation-associated angiogenesis and extend current understanding of the activities of PGE2.

Endothelin-1 and ETA/ETB Receptor Protein and mRNA

PURPOSE

Neovascularization of the cornea causes blindness and increases the risk of immune rejections after keratoplasty. The purpose of this study was to investigate involvement of the potent angiogenic growth factor endothelin (ET)-1 and its receptors, ETA and ETB, in corneal neovascularization.

METHODS

ET-1, ETA, and ETB receptor protein expression was evaluated in nonvascularized and vascularized human corneas by immunohistochemistry. Epithelial ET-1 protein expression of both groups was compared using a semiquantitative scoring system. Double immunofluorescence was used to colocalize ETA and ETB receptor with CD31. In situ hybridization and immunoelectron microscopy analyzed ET-1 and its receptors in normal and vascularized corneas.

RESULTS

Nonvascularized corneas displayed ET-1 and ETA/ETB receptor protein and mRNA in epithelial and some corneal endothelial cells. ETA more than ETB receptors were expressed on some keratocytes. In vascularized corneas, ET-1 and ETA/ETB receptor expression was found in the endothelial lining of new blood vessels (as shown by CD31-colocalization). ET-1 protein expression was significantly increased in the epithelium of vascularized corneas (P < 0.001). Immunogold localized ET-1 and its receptors to the nuclear/perinuclear space and to the luminal side of endothelial cells of new blood vessels.

CONCLUSIONS

In corneal neovascularization, ET-1 protein and mRNA expression is upregulated in epithelial cells. Together with ET-1, ETA, and ETB receptor expression on endothelial cells of ingrown new blood vessels, this points to an involvement of ET-1 and its receptors in corneal angiogenesis. As potent ETA and ETB receptors are available, the endothelin system may represent an additional target for corneal antiangiogenic therapy.

Application of plasmid DNA encoding IL-18 diminishes development of herpetic stromal keratitis by antiangiogenic effects

HSV-1 infection of the eye can cause a blinding immunoinflammatory stromal keratitis (SK) lesion. Using the mouse model, we have demonstrated that angiogenesis is an essential step in lesion pathogenesis because its inhibition results in diminished severity. The molecules involved in causing corneal angiogenesis are multiple and include the vascular endothelial growth factor (VEGF) family of proteins. In this report we show that application of plasmid DNA encoding IL-18 to the cornea of mice before HSV-1 ocular infection resulted in reduced angiogenesis and diminished SK immunoinflammatory lesions. The antiangiogenic effects of IL-18 treatment appeared to be mediated by inhibition of VEGF production in the cornea. We also showed that IL-18 controlled VEGF expression in vitro and also decreased CpG oligodeoxynucleotide induced VEGF-dependent neovascularization. In addition the administration of IL-18-binding protein, an IL-18 antagonist, into the inflammatory eye resulted in elevated angiogenesis and increased VEGF expression. Our results indicate that IL-18 is an important endogenous negative regulator of HSV-induced angiogenesis resulting in reduced SK lesion severity. Our results could mean that IL-18 administration may represent a useful approach to manage unwanted angiogenesis.

Involvement of IL-6 in the paracrine production of VEGF in ocular HSV-1 infection

Following ocular HSV-1 infection, neovascularisation of the avascular cornea is a critical event in the pathogenesis of herpetic stromal keratitis. This present study evaluates the role of proinflammatory cytokines such as IL-6 in corneal angiogenesis following virus infection. Both in vivo and in vitro data indicate that IL-6 produced from virus-infected cells can stimulate noninfected resident corneal cells and other inflammatory cells in a paracrine manner to secrete VEGF, a potent angiogenic factor. Antibody neutralisation of IL-6 resulted in a significant decrease in the number of VEGF producing cells in the cornea. Thus, our results further demonstrate the close relationship between proinflammatory cytokines and VEGF-induced corneal neovascularisation.

Expression of basic fibroblast growth factor in rabbit corneal alkali wounds in the presence and absence of granulocytes

PURPOSE

To study the expression of basic fibroblast growth factor (bFGF) in the early phases of corneal wound healing in the presence or absence of granulocytes.

METHODS

A central penetrating corneal alkali wound was inflicted to one eye in each of 14 rabbits under general anaesthesia. Subsequently, seven of the rabbits were given fucoidin i.v. for 36 hours in order to block the selectins on the vascular endothelium, thus preventing blood granulocytes from entering the tissues. Then, corneas were prepared, stained for bFGF and evaluated by light microscopy.

RESULTS

Whereas normal corneal epithelium expressed bFGF weakly, conjunctival epithelium did so strongly, particularly the goblet cells. The corneal endothelium showed medium staining, while keratocytes and vascular endothelial cells did not consistently express bFGF. After 36 hours of wound healing, a marked up-regulation of bFGF expression was observed in the corneal epithelial and endothelial cells, as well as in the keratocytes, that were migrating into the wound. No other changes were noted. None of these features were modulated when granulocyte emigration was prevented by fucoidin administration.

CONCLUSIONS

The difference in bFGF expression between the corneal and conjunctival epithelium suggests a role for this growth factor in the barrier function at the limbus. Moreover, the specific presence of bFGF in cells migrating into the wound indicates the participation of bFGF in corneal wound healing. Expression of bFGF was independent of granulocytes.

[Model of inflammatory angiogenesis in rabbit cornea induced by punctual alkaline cauterization]

PURPOSE

To establish a model of angiogenesis in rabbit cornea induced by punctual alkaline cauterization.

METHODS

Six rabbits were submitted to punctual cauterization in right cornea. It was used a circular piece (3 mm) of filter paper, that was previously soaked in 1 M NaOH and placed 1 mm from the superior limbus for 2 minutes. The animals were evaluated at 3, 6, 9, 12, 15, 18 and 21 days after cauterization. Quantification of angiogenesis was performed according to 4 methods: radial vessel length (V), angiogenic index (I), area of the triangle (T) and area of the circular band sector (S), which provide an approximation of the area of neovascularization.

RESULTS

The analysis of the quantitative data of angiogenesis showed that neovascular response progressed in a biphasic manner: rising between days 0 and 12 (proliferation), stable between days 12 and 21 (maturation). This pattern was observed on the values of the vascular growth mean rate. Between days 0 and 12, it was 16 times greater than that verified between days 12 and 21. It was found a statiscally significant positive linear correlation among the 4 methods of measurement of angiogenesis.

CONCLUSION

The punctual alkaline cauterization of the rabbit cornea induces and sustains corneal neovascularization, so that, it can be used as model of angiogenesis.

Molecular mimicry versus bystander activation: herpetic stromal keratitis

Herpes stromal keratitis (HSK) is a significant inflammatory disease of the cornea as a result of herpes simplex virus (HSV) infection often progressing to vision loss if left untreated. However, even with immunosuppressive compounds and anti-viral drug treatment, HSV continues to be the leading cause of infectious corneal blindness in the industrialized world. The inflammatory nature of the disease is the root of the pathogenic process characterized by irreversible corneal scarring, neovascularization of the avascular cornea, and infiltration of activated leukocytes. Experimental evidence using mice suggest HSK is the result of either molecular mimicry or a bystander activation phenomenon. This review will revisit the basis of HSK focusing on issues that pertain to the autoimmune component versus collateral damage as a result of non-specific activation as a means to explain the pathologic manifestations of the disease.

A novel flow cytometry based assay for quantification of corneal angiogenesis in the mouse model of herpetic stromal keratitis

In this study a novel flow cytometry based quantitative assay for measuring corneal angiogenesis is demonstrated. Corneas of Balb/c mice were lightly scarified and infected with 5 x 10(5), 5 x 10(4) and 5 x 10(3) pfu Herpes simplex virus 1 (HSV-1) RE virus. Development of corneal angiogenesis was studied on day 15 post infection by direct visualisation of infected cornea with a slit-lamp biomicroscope. Endothelial cells constituting the newly developed blood vessels in cornea were stained with murine anti CD31 antibody on frozen corneal sections and corneal whole mounts at day 15 post infection. Total number of endothelial cells was quantified at day 15 post infection by flow cytometry. Mice infected with different doses of HSV-1 RE developed severe to mild corneal angiogenesis at day 15 post infection. Endothelial cells constituting the newly formed blood vessels expressed CD31 at day 15 post infection. Flow cytometry revealed that, the number of CD31 positive cells isolated from diseased corneas increased with the increase in Neovascularisation index. The flow cytometry analysis used in this present study is a useful, accurate and cost effective method for quantifying corneal angiogenesis.

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

The last decade has seen herpes simplex virus (HSV)-induced stromal keratitis (SK) research shift from being a topic only of interest to vision researchers to one that fascinates the general field of inflammatory disease. Studies on experimental mouse lesions have uncovered several fundamental processes that explain lesion development. In this model, the chronic immuno-inflammatory lesions are mainly orchestrated by CD4+ T cells, but multiple early events occur that set the stage for the subsequent pathology. These include virus replication, the production of key cytokines and chemokines, neovascularization of the avascular cornea and the influx of certain inflammatory cell types. Many of these early events are subject to modulation, providing an approach to controlling this important cause of human blindness. We also comment on events ongoing during chronic SK, debating whether or not these represent virus-induced or autoimmune lesions.

Upregulation of functionally active vascular endothelial growth factor by human cytomegalovirus

Human cytomegalovirus (HCMV) infection is known to modulate host gene expression and has been linked to the pathogenesis of vasculopathies; however, relevant pathomechanisms are still unclear. It was shown that HCMV infection leads to upregulation of vascular endothelial growth factor (VEGF) expression in human foreskin fibroblasts and coronary artery smooth muscle cells (SMC). Activation of VEGF transcription by HCMV infection was confirmed by transient-expression experiments, which revealed that a short promoter fragment, pLuc135 (-85 to +50), is sufficient for activation. Site-directed mutagenesis of Sp1-recognition sites within this fragment abolished the upregulation of transcription. Functional VEGF protein is released into the culture supernatant of infected SMC. Incubation of endothelial cells with supernatants from HCMV-infected SMC cultures induced upregulation of VEGF receptor-2 expression on endothelial cells, as well as a significant upregulation of DNA synthesis, implicating cell proliferation. The mean incline of DNA synthesis at 48 and 72 h post-infection was 148 and 197 %, respectively. Addition of neutralizing antibodies against VEGF completely abolished this effect. Supernatants from SMC cultures incubated with UV-inactivated virus induced a comparable effect. This virus-induced paracrine effect may represent a molecular mechanism for HCMV-induced pathogenesis, such as inflammatory vasculopathies, by inducing a proatherogenic phenotype in SMC.

Inhibition of ocular angiogenesis by siRNA targeting vascular endothelial growth factor pathway genes: therapeutic strategy for herpetic stromal keratitis

Ocular neovascularization often results in vision impairment. Frequently vascular endothelial cell growth factors (VEGFs) are mainly responsible for the pathological neovascularization as in the case in neovascularization induced by CpG oligodeoxynucleotides and herpes simplex virus infection in this report. siRNAs targeting either VEGFA, VEGFR1, VEGFR2, or a mix of the three were shown to significantly inhibit neovascularization induced by CpG when given locally or systemically. The efficacy of systemic administration was facilitated by the use of a polymer delivery vehicle. Additional experiments showed a significant inhibitory effect of the siRNAs mix when given either locally or systemically in vehicle against herpes simplex virus-induced angiogenesis as well as against lesions of stromal keratitis. These results indicate that the use of VEGF pathway-specific siRNAs represents a useful therapy against neovascularization-related eye diseases.

[The latest in herpes simplex keratitis therapy]

Herpetic keratitis is characterized by spontaneous recurrences and a risk of vision loss, the latter being more serious when relapses are frequent and severe. Two clinical forms are commonly distinguished: epithelial keratitis, usually quickly resolved with topical antivirals, and stromal keratitis, which has a slower progression, even when both steroids and antivirals are used. Great strides have been made during the last 20 Years in the therapy of herpes keratitis, which is now considered and treated as a chronic disease. Randomized controlled studies definitively showed the decrease in spontaneous herpetic ocular events in patients treated with long-term oral acyclovir. The effectiveness of preventive treatment has also been shown during high-risk periods, especially ocular surgery, in patients with a history of herpes keratitis. However, the optimal duration and dosage of antiviral prevention have yet to be defined. We can also hope that in the future novel antiviral strategies such as vaccination will reduce the place of herpes keratitis as an indication for corneal graft.

Heat Treatment Enhances Healing Process of Experimental Pseudomonas Corneal Ulcer

We investigated the effects of hyperthermia on the healing process of experimental Pseudomonas corneal ulceration (PCU). Hartley guinea pigs were used to develop animal models of PCU. As a heat source, disposable chemical pocket warmers were applied. The healing process of PCU was compared between the heat-treated corneas and the control corneas. The severity of infection and the degree of angiogenesis were classified by a clinical scoring system. The animals were euthanized 14 days after infection and the corneas were submitted for histopathological examination. The expression of vascular endothelial growth factor (VEGF) was examined immunohistochemically. Comparative reverse transcription polymerase chain reaction was performed to measure the expression level of VEGF in the cornea. Hyperthermia significantly promoted corneal epithelization and neovascularization in the PCU model. Heat treatment significantly decreased the number of viable Pseudomonas organisms present in PCU. On immunohistochemistry, the heated cornea demonstrated more intense staining for VEGF. Comparative reverse transcription polymerase chain reaction showed upregulation of the expression level of VEGF mRNA in the heat-treated cornea. Hyperthermia accelerated the healing process of PCU with increased corneal neovascularization. Angiogenesis may play an important role in the PCU healing process, which is enhanced by the heat treatment.

Vascular endothelial growth factor: basic science and clinical progress

Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen in vitro and an angiogenic inducer in a variety of in vivo models. Hypoxia has been shown to be a major inducer of VEGF gene transcription. The tyrosine kinases Flt-1 (VEGFR-1) and Flk-1/KDR (VEGFR-2) are high-affinity VEGF receptors. The role of VEGF in developmental angiogenesis is emphasized by the finding that loss of a single VEGF allele results in defective vascularization and early embryonic lethality. VEGF is critical also for reproductive and bone angiogenesis. Substantial evidence also implicates VEGF as a mediator of pathological angiogenesis. In situ hybridization studies demonstrate expression of VEGF mRNA in the majority of human tumors. Anti-VEGF monoclonal antibodies and other VEGF inhibitors block the growth of several tumor cell lines in nude mice. Clinical trials with various VEGF inhibitors in a variety of malignancies are ongoing. Very recently, an anti-VEGF monoclonal antibody (bevacizumab; Avastin) has been approved by the Food and Drug Administration as a first-line treatment for metastatic colorectal cancer in combination with chemotherapy. Furthermore, VEGF is implicated in intraocular neovascularization associated with diabetic retinopathy and age-related macular degeneration.

Counteracting corneal immunoinflammatory lesion with interleukin-1 receptor antagonist protein

Herpetic stromal keratitis (HSK) is a T cell-orchestrated, immunoinflammatory lesion that results from corneal Herpes simplex virus infection. Previous reports indicate an essential role for proinflammatory cytokine interleukin (IL)-1 in HSK pathogenesis. The present study evaluates the efficacy of IL-1 receptor antagonist (IL-1 ra) protein in the management of HSK. Mice receiving IL-1 ra had diminished disease severity. The administration of IL-1 ra was shown to reduce the influx into the cornea of cells of the innate and adaptive immune response. In addition, the treatment diminished corneal vascular endothelial growth factor levels, resulting in reduced angiogenic response. Our results show the importance of targeting early proinflammatory molecules such as IL-1 to counteract HSK and advocate IL-1 ra as an effective agent to achieve this.

Mice Transgenic for IL-1 Receptor Antagonist Protein Are Resistant to Herpetic Stromal Keratitis: Possible Role for IL-1 in Herpetic Stromal Keratitis Pathogenesis

Ocular infection with HSV may result in the blinding immunoinflammatory lesion stromal keratitis (SK). This represents a CD4+ T cell-mediated immunopathologic lesion in both humans and a mouse model. Early events in the pathogenesis that set the stage for SK are poorly understood. The present study evaluates the role of IL-1 using a transgenic mouse that overexpresses the IL-1 receptor antagonist (IL-1ra) protein. Such transgenic mice were markedly resistant to SK compared with IL-1ra(-/-) and C57BL/6 control animals. The resistance was shown to be the consequence of reduced expression of molecules such as IL-6, macrophage-inflammatory protein-2, and vascular endothelial growth factor, normally up-regulated directly or indirectly by IL-1. A critical event impaired in IL-1ra transgenic mice was vascular endothelial growth factor production with a consequent marked reduction in angiogenesis, an essential step in SK pathogenesis. Targeting IL-1 could prove to be a worthwhile therapeutic approach to control SK, an important cause of human blindness.

Pathogenesis of pterygia: role of cytokines, growth factors, and matrix metalloproteinases

Pterygium is a common ocular surface disease apparently only observed in humans. Chronic UV exposure is a widely accepted aetiological factor in the pathogenesis of this disease and this concept is supported by epidemiological data, ray tracing models and histopathological changes that share common features with UV damaged skin. The mechanism(s) of pterygium formation is incompletely understood. Recent data have provided evidence implicating a genetic component, anti-apoptotic mechanisms, cytokines, growth factors, extracellular matrix remodelling (through the actions of matrix metalloproteinases), immunological mechanisms and viral infections in the pathogenesis of this disease. In this review, the current knowledge on pterygium pathogenesis is summarised, highlighting recent developments. In addition, we provide novel data further demonstrating the complexity of this intriguing disease.

The good, the bad and the ugly--APCs of the eye

Dendritic-cell (DC) populations throughout the body have a wide range of features in common, which are associated with their primary function in antigen presentation. The unique immune milieu of the anterior segment of the eye is characterized by a selective DC-dependent inability to develop delayed hypersensitivity responses following antigen invasion into the eye. Recent research papers provide evidence that different maturation stages of DC subsets are detectable at different corneal sites. Thus, the corneal DC, as well as the DC and the macrophages in the iris and ciliary body, have the potential of determining the outcome of immunity or tolerance within this organ.

CXCR2−/−Mice Show Enhanced Susceptibility to Herpetic Stromal Keratitis: A Role for IL-6-Induced Neovascularization

Ocular infection with HSV results in a blinding immunoinflammatory lesion known as herpetic stromal keratitis (HSK). Early preclinical events include inflammatory cell, mainly neutrophils, infiltration of the stroma, and neovascularization. To further evaluate the role of neutrophils in pathogenesis, HSV infection was compared in BALB/c and mice of the same background, but lacking CXCR2, the receptor for chemokines involved in neutrophil recruitment. Our results show clear differences in the outcome of ocular HSV infection in CXCR2-/- compared with control BALB/c mice. Thus, CXCR2-/- animals had minimal PMN influx during the first 7 days postinfection, and this correlated with a longer duration of virus infection in the eye compared with BALB/c mice. The CXCR2-/- mice were also more susceptible to HSV-induced lesions and developed HSK upon exposure to a dose of HSV that was minimally pathogenic to BALB/c mice. The basis for the greater HSK lesion susceptibility of CXCR2-/- mice was associated with an elevated IL-6 response, which appeared in turn to induce the angiogenic factor, vascular endothelial growth factor. Our results serve to further demonstrate the critical role of angiogenesis in the pathogenesis of ocular lesions.

Herpes simplex virus type 1 DNA is immunostimulatory in vitro and in vivo

Recently, prokaryotic DNAs containing unmethylated CpG motifs have been shown to be intrinsically immunostimulatory both in vitro and in vivo, tending to promote Th1-like responses. In contrast, CpG dinucleotides in mammalian DNAs are extensively methylated on cytosines and hence immunologically inert. Since the herpes simplex virus (HSV) genome is unmethylated and G+C rich, we predicted that CpG motifs would be highly prevalent in the HSV genome; hence, we examined the immunostimulatory potential of purified HSV DNA in vitro and in vivo. Mouse splenocyte cultures treated with HSV DNA or HSV-derived oligodeoxyribonucleotides (ODNs) showed strong proliferative responses and production of inflammatory cytokines (gamma interferon [IFN-gamma], tumor necrosis factor [TNF], and interleukin-6 [IL-6]) in vitro, whereas splenocytes treated with mammalian CV-1 DNA or non-CpG ODN did not. After immunization with ovalbumin (OVA), only splenocytes from mice immunized with HSV DNA or HSV-ODN as the adjuvants proliferated strongly and produced typical Th1 responses, including CD8(+) cytotoxic T-lymphocyte responses, upon restimulation with OVA. Furthermore, HSV-ODN synergized with IFN-gamma to induce nitric oxide (NO), IL-6, and TNF production from macrophages. These results demonstrate that HSV DNA and HSV-ODN are immunostimulatory, driving potent Th1 responses both in vitro and in vivo. Considering that HSV DNA has been found to persist in nonneuronal cells, these results fuel speculation that HSV DNA might play a role in pathogenesis, in particular, in diseases like herpes stromal keratitis (HSK) that involve chronic inflammatory responses in the absence of virus or viral antigens.

Effect of anti-CXCL10 monoclonal antibody on herpes simplex virus type 1 keratitis and retinal infection

The inflammatory response to acute ocular herpes simplex virus type 1 (HSV-1) infection in mice involves the innate and adaptive immune response, with an associated increase in the secretion of chemokines, including CXCL10 (interferon-inducible protein 10 kDa [IP-10]). Neutralizing antibodies to mouse CXCL10 were used to determine the role of CXCL10 during the acute phase of HSV-1 ocular infection. Treatment of HSV-1-infected mice with antibody to CXCL10 significantly reduced CXCL10 levels in the eye and trigeminal ganglion and reduced mononuclear cell infiltration into the corneal stroma. These results coincided with reduced ICAM-1 and CXCR3 transcript expression, macrophage inflammatory protein-1alpha and CXCL10 levels, and corneal pathology but increased viral titers in the stroma and trigeminal ganglion. Progression of the virus from the corneal stroma to the retina during acute infection was significantly hindered in anti-CXCL10-treated mice. In addition, colocalization of viral antigen with infiltrating leukocytes in the iris and retina during acute infection suggests that one means by which HSV-1 traffics to the retina involves inflammatory cells (primarily CD11b(+) cells). Collectively, the results suggest that CXCL10 expression in the eye initially orchestrates the inflammatory response to acute HSV-1 infection, which facilitates the spread of the virus to other restricted sites within the eye.

Genotyping of herpes simplex virus type 1 strains isolated from ocular materials of patients with herpetic keratitis

Herpes simplex virus type 1 (HSV-1) is the etiological agent of herpetic keratitis. The epithelial form ("epithelial keratitis") is attributed mainly to destruction of the epithelium through active viral replication within the epithelium. The stromal form ("stromal keratitis") is associated with immune reactions within the stroma and is the common cause of human blindness. In the present study, 29 HSV-1 strains isolated from human ocular materials of herpetic keratitis were classified into 14 genotypes on the basis of DNA polymorphisms. Twenty-one of 29 (72%) strains from eyes examined in the present study were of genotypes that were shown previously to be present in strains from non-ocular lesions (including genital herpes). Five of nine (56%) strains from eyes related to stromal keratitis were of the F1 genotype, while four of twenty (20%) strains from eyes not related to stromal keratitis were of the F1 genotype. Thus, the proportion of F1 genotype was assumed to be larger in the group of strains related to stromal keratitis than in that not so related, suggesting an association of the F1 genotype with stromal keratitis. A connection of F1 genotype with recurrence was proposed previously; hence, F1 genotype seems to be associated to both stromal keratitis and the recurrence, thereby supporting the relationship between stromal keratitis and recurrence.

Local treatment of viral disease using photodynamic therapy

Although reports of the photodynamic inactivation of viruses appeared in 1928, long before chemotherapeutic antiviral drugs, the first clinical trial in humans-the topical treatment of herpes genitalis-did not take place until the early 1970s. Trials were discontinued due to the transformation of healthy cells and concomitant incidence of Bowen's disease in some patients, probably due to the migration of infective sections of photodamaged viral nucleic acid. With the modern development of photodynamic therapy as a cancer treatment and the use of photosensitisers in the photodecontamination of blood products, a great deal of experience has been gained, both in the minimisation of side effects in humans and in the targeting and eradication of viruses. This suggests that the photodynamic approach to a range of virus-associated infections, lesions and cancer might now be revisited with greater success.

Role of matrix metalloproteinase-9 in angiogenesis caused by ocular infection with herpes simplex virus

In this report, we demonstrate that herpes simplex virus (HSV) infection of the cornea results in the upregulation of the matrix-degrading metalloproteinase enzyme MMP-9. This enzyme was shown to contribute to the neovascularization process that occurs in the corneal stroma in response to HSV infection. The likely source of MMP-9, at least initially after infection, was neutrophils that were signaled to invade the cornea soon after infection. Corneal infiltrating neutrophils were shown to express MMP-9, and preventing the neutrophil response with specific mAb diminished MMP-9 expression as well as the extent of angiogenesis. Further supporting a role for MMP-9 in HSV-induced corneal angiogenesis was the observation that inhibition of MMP-9 with the specific inhibitor TIMP-1 resulted in reduced angiogenesis. In addition, angiogenesis was diminished in ocularly infected MMP-9 knockout mice. Our results demonstrate that MMP-9 is involved in angiogenesis caused by HSV. Since angiogenesis appears to represent a vital step in the pathogenesis of herpetic stromal keratitis, these results indicate that targeting MMP-9 for inhibition should prove useful for the therapy of herpetic stromal keratitis.

Macrophage inflammatory protein-2 and vascular endothelial growth factor regulate corneal neovascularization induced by infection with Pseudomonas aeruginosa in mice

Pseudomonas aeruginosa ocular infection causes extensive corneal neovascularization. The purpose of the present study was to investigate the role of the angiogenic factors macrophage inflammatory protein-2 (MIP-2) and vascular endothelial growth factor (VEGF) in the regulation of corneal neovascularization during P. aeruginosa ocular infection. After administering anti-MIP-2 antibody or control antibody, mouse corneas were challenged with P. aeruginosa. The expression of MIP-2 and VEGF was detected using an ELISA from ocular homogenates. Corneal neovascularization was examined by histology. The cellular sources of MIP-2 and VEGF were identified by immunohistochemistry. In addition, protein expression of MIP-2 and VEGF in isolated corneas was measured to determine the ability of the cornea to produce these two mediators. Results showed that the expression of MIP-2 and VEGF was significantly (P < 0.05) elevated after bacterial infection, and high levels of these two mediators paralleled the extensive corneal neovascularization seen at later stages of the infection. Anti-MIP-2 antibody treatment resulted in a significant (P < 0.05) reduction in VEGF expression and in corneal neovascularization. Both corneal resident cells and infiltrating neutrophils had the ability to produce MIP-2 and VEGF after stimulation. The present study demonstrates that both MIP-2 and VEGF are important mediators in the regulation of corneal neovascularization caused by P. aeruginosa infection, and that MIP-2 regulates the production of VEGF.

DNA containing CpG motifs induces angiogenesis

New blood vessel formation in the cornea is an essential step in the pathogenesis of a blinding immunoinflammatory reaction caused by ocular infection with herpes simplex virus (HSV). By using a murine corneal micropocket assay, we found that HSV DNA (which contains a significant excess of potentially bioactive "CpG" motifs when compared with mammalian DNA) induces angiogenesis. Moreover, synthetic oligodeoxynucleotides containing CpG motifs attract inflammatory cells and stimulate the release of vascular endothelial growth factor (VEGF), which in turn triggers new blood vessel formation. In vitro, CpG DNA induces the J774A.1 murine macrophage cell line to produce VEGF. In vivo CpG-induced angiogenesis was blocked by the administration of anti-mVEGF Ab or the inclusion of "neutralizing" oligodeoxynucleotides that specifically oppose the stimulatory activity of CpG DNA. These findings establish that DNA containing bioactive CpG motifs induces angiogenesis, and suggest that CpG motifs in HSV DNA may contribute to the blinding lesions of stromal keratitis.