Membranes of herpes simplex virus type-1-infected human corneal epithelial cells are not permeabilized to macromolecules and therefore do not release IL-1alpha

Who pays the toll for solving the enigma of corneal herpes?

In herpetic stromal keratitis (HSK), herpes simplex virus type-1 DNA fragments and herpes simplex virus-immunoglobulin G immune complexes are present in corneas long after the infective virus has disappeared. These viral components are highly immunogenic and potentiate the production of proinflammatory cytokines and chemokines via Toll-like receptors expressed on corneal cells and macrophages. In addition, angiogenic factors, such as the vascular endothelium growth factor and the tissue-damaging enzyme, matrix metalloproteinase 9, are induced by corneal cells and macrophages through the recognition of these viral components in the pathogenesis of HSK. Upon neovascularization, robust infiltration of leukocytes via leaky new vessels is elicited. Activated polymorphonuclear leukocytes (PMNs) secrete hydrogen peroxide and myeloperoxidase, which inhibit viral growth. PMNs also produce tumor necrosis factor, monokine-induced by interferon-γ (CXCL9), and nitric oxide. These factors provide a local environment that can induce the differentiation of peripheral CD4* T cells to induce Th1-predominant immunopathology. Thus, strategies developed to alter these pathways should lead to new preventative and therapeutic measures for the treatment of 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.

Human corneal epithelial cells synthesize ELR(-)alpha-chemokines in response to proinflammatory mediators

The purpose of this study was to characterize the synthesis of alpha-chemokines IP-10, MIG, and I-TAC by human corneal epithelial cells (HCE) following exposure to proinflammatory mediators. Supernatants were collected from HCE cultures stimulated with individual or combinations of TNF-alpha, IL-1alpha, and IFN-gamma, and assayed for alpha-chemokines by ELISA. RT-PCR was used to detect IFN-gamma receptor mRNA. Activation of STAT 1 was determined by Western blotting. Stimulation of HCE with either IL-1alpha or TNF-alpha increased IP-10 protein synthesis up to 6-fold, whereas insignificant levels of MIG and I-TAC were induced. The epithelial cells were found to express IFN-gamma receptors constitutively. Exposure to the ligand resulted in STAT 1 phosphorylation and production of nanogram amounts of IP-10, I-TAC, and MIG. When HCE were stimulated with combinations of TNF-alpha and IFN-gamma, or IL-1alpha and IFN-gamma, the levels of IP-10 and I-TAC secreted were > 150-fold higher than that produced following exposure to a single cytokine. In contrast, MIG protein synthesis was not enhanced upon stimulation with cytokine combinations. The abundant production of ELR(-)alpha -chemokines following appropriate stimulation suggests that HCE may play an important role in the recruitment of effector cells such as activated T-lymphocytes to inflamed corneal tissue. The data also indicate that the synthesis of IP-10, I-TAC, and MIG are differentially regulated in HCE.

Differential Responses of Murine Vaginal and Uterine Epithelial Cells Prior to and Following Herpes Simplex Virus Type 2 (HSV-2) Infection

PROBLEM

This study was undertaken to evaluate the susceptibility of upper and lower reproductive tract epithelial cells (ECs) to herpes simplex virus type 2 (HSV-2) infection and examine their cytokine secretion patterns prior to and following infection.

METHOD OF STUDY

Primary EC cultures, grown from murine vaginal and uterine tissue, were inoculated with HSV-2. Viral shedding was measured in apical and basolateral compartments. Multi-analyte bead-based immunoassays run on Luminex, were used to analyse cytokine profiles.

RESULTS

Both vaginal and uterine ECs became productively infected with HSV-2, ex-vivo. Uterine ECs displayed varying degrees of infection, dependent on transepithelial resistance of the monolayers. Co-culturing stromal cells did not significantly change levels of viral shedding from ECs. Uterine ECs and epithelial-stromal co-cultures constitutively secreted interleukin (IL)-1alpha, IL-6, mouse homologue of human IL-8 (KC) and monocyte chemotactic protein-1 (MCP-1), while vaginal epithelial-stromal co-cultures secreted granulocyte-macrophage colony stimulating factor (GM-CSF) and KC. Following exposure to HSV-2, IL-6 and MCP-1 levels decreased in uterine EC cultures.

CONCLUSIONS

This data shows that ECs from the upper and lower reproductive tract have different cytokine secretion profiles and respond differentially to infection. HSV-2 may be able to suppress epithelial cytokine secretion as a strategy to evade host immune system.

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.

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.

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.

Interleukin-1alpha released from epithelial cells after adenovirus type 37 infection activates intercellular adhesion molecule 1 expression on human vascular endothelial cells

A key event in virus-induced inflammation (leukocyte extravasation through the endothelium) is the local activation of endothelial cells, as indicated by the expression of adhesion molecules such as intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), and E-selectin. In order to identify triggers of inflammation in adenovirus infection, we inoculated respiratory and ocular epithelial cells with adenovirus type 37 (Ad37), a human pathogen associated with keratoconjunctivitis as well as urogenital and respiratory infections. Fluids from virus-infected epithelial cells activated ICAM-1 (and to a lesser extent, VCAM-1) expression on cultured human umbilical vein endothelial cells. Blocking studies with anticytokine antibodies implicated interleukin-1alpha (IL-1alpha) as the epithelial cell-derived factor which activated endothelial cell ICAM-1 expression. The results thus identify epithelial cell-derived IL-1alpha as a potentially important activator of endothelial cells in Ad37-induced inflammation.

Calcitonin gene-related peptide induces IL-8 synthesis in human corneal epithelial cells

Calcitonin gene-related peptide (CGRP), a neuropeptide with proinflammatory activities, is released from termini of corneal sensory neurons in response to pain stimuli. Because neutrophil infiltration of the clear corneal surface is a hallmark of corneal inflammation in the human eye, we determined whether CGRP can bind to human corneal epithelial cells (HCEC) and induce expression of the neutrophil chemotactic protein IL-8. It was found that HCEC specifically bound CGRP in a saturable manner with a Kd of 2.0 x 10-9 M. Exposure of HCEC to CGRP induced a significant increase in intracellular cAMP levels and enhanced IL-8 synthesis nearly 4-fold. The capacity of CGRP to stimulate cAMP and IL-8 synthesis was abrogated in the presence of the CGRP receptor antagonist CGRP8-37. CGRP stimulation had no effect on the half-life of IL-8 mRNA while increasing IL-8 pre-mRNA synthesis >2-fold. In contrast to IL-8, CGRP did not induce monocyte chemotactic protein-1 or RANTES synthesis, nor did the neuropeptide enhance detectable increases in steady state levels of mRNA specific for these two beta-chemokines. The results suggest that HCEC possess CGRP receptors capable of initiating a signal transduction cascade that differentially activates expression of the IL-8 gene but not the genes for monocyte chemotactic protein-1 or RANTES. The capacity of CGRP to stimulate IL-8 synthesis in HCEC suggests that sensory neurons are involved in induction of acute inflammation at the eye surface.

Nuclear targeting of plasmid DNA in human corneal cells

PURPOSE

To characterize the mechanisms of plasmid DNA nuclear localization in primary cultures of human corneal epithelial cells and keratocytes.

METHODS

Purified, supercoiled plasmid DNA was microinjected into the cytoplasm of human corneal epithelial cells and keratocytes that had been established from donor corneas two to three passages previously, and localized 8 hours later by in situ hybridization. To confirm the sequence-specificity of nuclear import observed in microinjected cells, liposome-mediated transient transfection experiments also were performed on human corneal epithelial cell and keratocyte cultures.

RESULTS

Primary cultures of human corneal epithelial cells and keratocytes have the capacity to transport plasmid DNA from the cytoplasm to the nucleus in the absence of cell division. This transport activity is sequence-dependent requiring portions of the simian virus 40 (SV40) early promoter and enhancer. The majority of this nuclear transport activity resides within the enhancer domain of the SV40 DNA, a region rich in transcription factor binding sites. This DNA nuclear import sequence also manifested itself in liposome-mediated transfection experiments, causing a greater than 2-fold increase in reporter gene expression in human corneal cells in a beta-galactosidase-expressing vector and up to a 1000-fold increase in a luciferase-expressing vector when compared to similar expression plasmids lacking the sequence.

CONCLUSION

These results demonstrate that primary, non-transformed human corneal epithelial cells and keratocytes display sequence-specific nuclear import of plasmid DNA in the absence of mitosis. The small sequence that mediates nuclear localization of plasmids is active both in microinjected and cationic liposome transfected cells, and leads to increased gene expression. Thus, inclusion of this DNA sequence into non-viral vectors should improve the efficiency of ocular gene transfer in vivo.