Impairment of ocular surface epithelium barrier function in patients with atopic dermatitis

Ocular surface disease in moderate-to-severe atopic dermatitis patients and the effect of biological therapy

Atopic dermatitis (AD) is a chronic inflammatory skin disease for which new targeted therapies are currently available. Due to the increased rates of ocular surface disease (OSD) reported during treatment with these new targeted treatments, more insight into the occurrence and pathomechanism of OSD in moderate-to-severe AD patients is needed. Therefore, this review's first part highlights that most patients with moderate-to-severe AD already have characteristics of OSD before starting targeted treatment. Remarkably, not all AD patients with OSD report ocular symptoms. OSD in AD is associated with less conjunctival goblet cells (GC) compared to healthy controls. In addition, OSD severity in AD patients is associated with high AD activity, the presence of eyelid and/or facial eczema, and high levels of AD-related severity biomarkers in tear fluid. The second part of this review highlights that pre-existing ocular pathology (e.g. in combination with the use of ophthalmic medication or eyelid eczema) may be associated with the development of dupilumab-associated ocular surface disease (DAOSD). During dupilumab treatment, DAOSD (which can be new-onset OSD or worsening of pre-existing OSD) is observed in approximately one-third of the dupilumab-treated AD patients. Anti-inflammatory ophthalmic treatment improves DAOSD, and dose reduction of dupilumab may also be an effective treatment option. The pathomechanism of DAOSD is still not fully elucidated. In a prospective study low, but stable conjunctival GC numbers were observed in moderate-to-severe AD patients, before and during dupilumab treatment. However, the Mucin 5 AC (MUC5AC) expression of GCs decreased during dupilumab treatment, suggesting an impairment of the GC function by dupilumab treatment. In addition, higher dupilumab tear fluid levels were found in dupilumab-treated AD patients with moderate-to-severe OSD compared to patients with no or mild OSD, whereas the dupilumab serum levels are similar. Clinicians should be aware of the frequent occurrence of OSD in moderate-to-severe AD patients, and a low-threshold referral to an ophthalmologist is recommended.

High dupilumab levels in tear fluid of atopic dermatitis patients with moderate-to-severe ocular surface disease

BACKGROUND

The patho-mechanism of ocular surface disease (OSD) in dupilumab-treated atopic dermatitis (AD) patients remains unclear. The aim of this study is to measure dupilumab levels in tear fluid and serum, and relate these findings to the severity of OSD during dupilumab treatment in AD patients.

METHODS

This prospective study included dupilumab-treated moderate-to-severe AD patients who were seen by a dermatologist and an ophthalmologist before the start of dupilumab (baseline), and after 4 and 28 weeks of dupilumab treatment. Dupilumab levels in tear fluid and serum were measured by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Additionally, a pilot study was conducted to measure dupilumab on conjunctival epithelial cells using flow cytometry and LC-MS/MS.

RESULTS

At baseline, 89.6% (n = 43/48) of the patients had OSD, with 50.0% having moderate-to-severe OSD. After 28 weeks of dupilumab treatment, the median dupilumab tear fluid levels were 0.55 mg/L (IQR 0.35-1.31) and 0.29 mg/L (IQR 0.16-0.60) in patients with moderate-to-severe OSD and patients with no or mild OSD, respectively (p = 0.02). Dupilumab levels could be detected on conjunctival epithelial cells of 5 AD patients treated with dupilumab for 4 weeks.

CONCLUSION

Patients with moderate-to-severe OSD had higher dupilumab tear fluid levels compared to patients with no or mild OSD, indicating that dupilumab reaches the ocular surface. Dupilumab was also detected in conjunctival cell suspensions and was found to directly bind CD45-conjunctival epithelial cells. This suggests that AD-induced changes of the conjunctival epithelium may play a role in the development of OSD as well as increased local drug availability.

Epithelial barrier dysfunction in ocular allergy

The epithelial barrier is the first line of defense that forms a protective barrier against pathogens, pollutants, and allergens. Epithelial barrier dysfunction has been recently implicated in the development of allergic diseases such as asthma, atopic dermatitis, food allergy, and rhinitis. However, there is limited knowledge on epithelial barrier dysfunction in ocular allergy (OA). Since the ocular surface is directly exposed to the environment, it is important to understand the role of ocular epithelia and their dysfunction in OA. Impaired epithelial barrier enhances allergen uptake, which lead to activation of immune responses and development of chronic inflammation as seen in allergies. Abnormal expression of tight junction proteins that helps to maintain epithelial integrity has been reported in OA but sufficient data not available in chronic atopic (AKC) and vernal keratoconjunctivitis (VKC), the pathophysiology of which is not just complex, but also the current treatments are not completely effective. This review provides an overview of studies, which indicates the role of barrier dysfunction in OA, and highlights how ocular barrier dysfunction possibly contributes to the disease pathogenesis. The review also explores the potential of ocular epithelial barrier repair strategies as preventive and therapeutic approach.

Detrimental impact of fine dust on zebrafish: Investigating a protective agent against ocular-damage using in vitro and in vivo models

Pollution caused by fine dust is becoming a global problem in the aquatic environment. Many studies have investigated the hazards that fine dust may pose to terrestrial organisms; however, information on the effects on aquatic environments remain limited. In this study, the physicochemical characteristics of the fine dust associated with the captured powder or liquid state were compared using scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). Raw fine dust (RFD), in the captured powder state, was suspended in water (SFD), and the elemental composition, morphology, and size distribution of both were analyzed. Zebrafish were used as a model to study the effects of SFD-exposure on aquatic organisms. A fatal malformation was observed in the integuments of zebrafish exposed to SFD, specifically in the exterior and interior eye tissues. Furthermore, the exposure of SFD to Tg (flk; EGFP) zebrafish remarkably increased ocular vessel diameter expansion along with blood flow velocity. Regarding vessel diameter expansion, EA.hy926 cells exposed to SFD were adversely affected, with a significant increase in cell migration and capillary-like structure formation, which are angiogenic markers. The SFD-induced angiogenesis in vitro and in vivo was dramatically restored to normal via α/β-adenosine isolated from the anti-angiogenic brown algae Ishige okamurae extract. Taken together, the current study presents solid evidence of the altered physicochemical characteristics of SFD compared to RFD, and the detrimental impact of SFD in an aquatic in vivo zebrafish model. In addition, the protective effect of α/β-adenosine, a marine natural product, on SFD-induced angiogenesis suggests that it can be used as an agent to reduce the adverse effects of SFD on aquatic animals.

Conjunctivitis in adult patients with moderate-to-severe atopic dermatitis: results from five tralokinumab clinical trials

BACKGROUND

Tralokinumab, a fully human immunoglobulin G4 monoclonal antibody that specifically binds to the interleukin-13 cytokine with high affinity, effectively reduces moderate-to-severe atopic dermatitis when given every 2 weeks. The incidence of conjunctivitis is elevated compared to placebo, but severity and etiology have not been examined.

OBJECTIVE

To analyze conjunctivitis data recorded in five randomized, placebo-controlled trials of tralokinumab in adult patients with moderate-to-severe atopic dermatitis.

METHODS

Overall, 2285 adults with atopic dermatitis were studied up to 16 weeks. Cochran-Mantel-Haenszel weights were applied to calculate adjusted adverse-event incidences.

RESULTS

Incidence of conjunctivitis was higher (7.5%) with tralokinumab compared to placebo (3.2%). Most events were mild or moderate in severity and 78.6% and 73.9% of events resolved during the trial in the tralokinumab and placebo groups, respectively. Two (1.4%) events led to permanent discontinuation of tralokinumab. An increased incidence of conjunctivitis, regardless of treatment group, was associated with more severe baseline atopic dermatitis, and history of allergic conjunctivitis/atopic keratoconjunctivitis, as well as the number of atopic comorbidities. Limitation This analysis reports events up to Week 16 only, with limited confirmation of conjunctivitis and its etiology by an ophthalmologist and insufficient reporting of ophthalmic treatments.

CONCLUSIONS

Treatment with tralokinumab was associated with increased incidence of conjunctivitis compared to placebo, but these cases were mostly mild and transient.

Keratoconus, allergy, itch, eye‐rubbing and hand‐dominance

BACKGROUND

One hypothesis for the pathogenesis of keratoconus includes teenage allergy, ocular itch and associated eye-rubbing.

METHODS

This study examined the prevalence of these factors for teenage and adult patients. The results for a sample of 53 subjects with bilateral keratoconus were compared with those for a control sample of non-keratoconus subjects, who also routinely wore RGP contact lenses. The strongest dominant hand and the eye with more advanced keratoconus were also determined, to examine for a relationship between them.

RESULTS

The keratoconic sample reported significantly higher levels of allergy, itch and rubbing as teenagers and as adults. However, all distributions were bimodal, consistent with the hypothesis that allergy, itch and rubbing are relevant in the pathogenesis of keratoconus only when the highest levels of these factors are present. For example, a significant relationship between the stronger dominant hand and the more advanced eye was evident only in subjects who reported the most severe rubbing.

CONCLUSIONS

This finding adds weight to the circumstantial evidence that rubbing contributes to the pathogenesis of keratoconus. Low levels of teenage rubbing by some keratoconic subjects suggest a non-rubbing pathogenesis and that emphasis on rubbing management is not warranted in these cases. However, high levels of adult rubbing reported by many keratoconic subjects indicate that the standard advice to avoid vigorous and prolonged rubbing is often not effective, even when repeated. There appears to be an indication for the need to improve the management of eye-rubbing for some patients with keratoconus or at risk of developing this disease.

Effects of ambient particulate matter on a reconstructed human corneal epithelium model

We evaluated the effects of ambient particulate matter (PM) on the corneal epithelium using a reconstructed human corneal epithelium (HCE) model. We collected two PM size fractions [aerodynamic diameter smaller than 2.4 µm: PM_0.3–2.4 and larger than 2.4 µm: PM_>2.4] and exposed these tissues to PM concentrations of 1, 10, and 100 µg/mL for 24 h. After exposure, cell viability and interleukin (IL) IL-6 and IL-8 levels were determined, and haematoxylin and eosin and immunofluorescence staining of the zonula occludens-1 (ZO-1) were performed on tissue sections. In addition, the effects of a certified reference material of urban aerosols (UA; 100 µg/mL) were also examined as a reference. The viability of cells exposed to 100 μg/mL UA and PM_>2.4 decreased to 76.2% ± 7.4 and 75.4% ± 16.1, respectively, whereas PM_0.3–2.4 exposure had a limited effect on cell viability. These particles did not increase IL-6 and IL-8 levels significantly even though cell viability was decreased in 100 μg/mL UA and PM_>2.4. ZO-1 expression was reduced in a dose-dependent manner in all groups. Reconstructed HCE could be used as an in vitro model to study the effects of environmental PM exposure on ocular surface cell viability and inflammation.

The spectrum of allergic ocular diseases

OBJECTIVE

The purpose of this article is to review the pathophysiologic mechanisms, differential diagnosis, evaluation, and treatment of the various manifestations of ocular allergy, with an especial focus on immunoglobulin E (IgE)-mediated disease.

DATA SOURCES

A PubMed search was performed to include articles, using the search terms ocular allergy and allergic conjunctivitis.

STUDY SELECTIONS

Recent and relevant human studies in the English language pertaining to our topic of study were selected. Animal studies pertaining to pathophysiology of ocular allergy were also reviewed. We focused on clinical trials, practice guidelines, reviews, and systematic reviews. In addition, case reports were reviewed if they described rare clinical presentations, disease mechanisms, or novel therapies.

RESULTS

Ocular allergy encompasses both IgE- and non-IgE-mediated disease, and the clinical severity may range from mild to sight-threatening inflammation. A comprehensive treatment regimen including education, lifestyle measures, topical therapies, and even systemic interventions may be necessary for the effective management of ocular allergies, tailored according to symptom severity.

CONCLUSION

Ocular allergy is frequently encountered by allergists and eye-care specialists, and despite progressively increasing incidence, it often remains underdiagnosed and, hence, untreated.

Why Chain Length of Hyaluronan in Eye Drops Matters

The chain length of hyaluronan (HA) determines its physical as well as its physiological properties. Results of clinical research on HA eye drops are not comparable without this parameter. In this article methods for the assessment of the average molecular weight of HA in eye drops and a terminology for molecular weight ranges are proposed. The classification of HA eye drops according to their zero shear viscosity and viscosity at 1000 s-1 shear rate is presented. Based on the gradient of mucin MUC5AC concentration within the mucoaqueous layer of the tear film a hypothesis on the consequences of this gradient on the rheological properties of the tear film is provided. The mucoadhesive properties of HA and their dependence on chain length are explained. The ability of HA to bind to receptors on the ocular epithelial cells, and in particular the potential consequences of the interaction between HA and the receptor HARE, responsible for HA endocytosis by corneal epithelial cells is discussed. The physiological function of HA in the framework of ocular surface homeostasis and wound healing are outlined, and the influence of the chain length of HA on the clinical performance of HA eye drops is illustrated. The use of very high molecular weight HA (hylan A) eye drops as drug vehicle for the next generation of ophthalmic drugs with minimized side effects is proposed and its advantages elucidated. Consequences of the diagnosis and treatment of ocular surface disease are discussed.

Conjunctivitis in patients with atopic dermatitis treated with dupilumab

Atopic dermatitis (AD) is a common, chronic, inflammatory skin disorder with high physical and emotional burden. Robust evidence suggests that interleukin (IL)-4 and IL-13 are key cytokines in the immunopathogenesis of AD. New emerging agents include dupilumab, a fully human monoclonal antibody directed against the IL-4 receptor a subunit that blocks both IL-4 and IL-13 signaling and has shown significant efficacy in patients with moderate-to-severe AD. Dupilumab is approved for the treatment of moderate-to-severe AD, moderate-to-severe eosinophilic or oral corticosteroid-dependent asthma, and chronic rhinosinusitis with nasal polyps. Data from phase phase 2 and 3 studies have revealed that dupilumab generally has a low rate of adverse events, although an increased incidence of mild-to-moderate conjunctivitis has been reported for dupilumab compared with placebo.

The present paper reviews the data of dupilumab-associated conjunctivitis and risk factors in adults with moderate-to-severe AD and other atopic diseases in dupilumab clinical trials and addresses the characteristics and treatment options available for this clinically highly relevant condition. Additionally, it presents data from ten studies in the real-life setting with dupilumab. Dupilumab-associated conjunctivitis incidence is higher in AD, although most cases are mild-to-moderate and have good response to topical treatment, with no need to suspend dupilumab therapy.

Conjunctivitis in dupilumab clinical trials

BACKGROUND

Dupilumab blocks the shared receptor component for interleukin (IL)-4 and IL-13. It is approved in the U.S.A. for patients aged ≥ 12 years with moderate-to-severe atopic dermatitis (AD) uncontrolled by topical prescription medicines or who cannot use topical medicines, for patients in Japan whose AD is uncontrolled with existing therapies, for patients with moderate-to-severe AD in Europe who are candidates for systemic therapy and for patients aged ≥ 12 years for maintenance treatment of moderate-to-severe asthma uncontrolled with their current medicines. AD trials have reported increased incidence of conjunctivitis for dupilumab vs. placebo.

OBJECTIVES

To characterize further the occurrence and risk factors of conjunctivitis in dupilumab clinical trials.

METHODS

We evaluated randomized placebo-controlled trials of dupilumab in AD (n = 2629), asthma (n = 2876), chronic rhinosinusitis with nasal polyps (CRSwNP) (n = 60) and eosinophilic oesophagitis (EoE) (n = 47).

RESULTS

In most AD trials, dupilumab-treated patients had higher conjunctivitis incidence than placebo controls. Higher baseline AD severity and previous history of conjunctivitis were associated with increased conjunctivitis incidence. Conjunctivitis was mostly mild to moderate. Most cases recovered or resolved during the treatment period; two patients permanently discontinued dupilumab due to conjunctivitis or keratitis. Common treatments included ophthalmic corticosteroids, antibiotics, and antihistamines or mast cell stabilizers. Most cases were diagnosed by the investigators. In asthma and CRSwNP trials, the incidence of conjunctivitis was lower for both dupilumab and placebo than in AD trials; dupilumab did not increase the incidence compared with placebo. In the EoE trial, no patients had conjunctivitis.

CONCLUSIONS

Conjunctivitis was more frequent with dupilumab treatment in most AD trials. In dupilumab trials in other type 2 diseases, incidence of conjunctivitis was overall very low, and was similar for dupilumab and placebo. In AD, the incidence of conjunctivitis was associated with AD severity and prior history of conjunctivitis. The aetiology and treatment of conjunctivitis in dupilumab-treated patients require further study. What's already known about this topic? Ocular disorders, including allergic conjunctivitis, are common in patients with atopic dermatitis (AD). In most dupilumab AD trials, dupilumab-treated patients had higher conjunctivitis incidence than those receiving placebo. Most cases were mild to moderate and recovered or were recovering during study treatment; study treatment discontinuation due to conjunctivitis was rare. Conjunctivitis incidence was very low and similar for dupilumab and placebo in clinical trials in asthma, chronic rhinosinusitis with nasal polyps and eosinophilic oesophagitis. What does this study add? This analysis confirms and extends the results of the individual clinical trials. Baseline disease-related factors, including AD severity, prior conjunctivitis history and certain biomarkers (thymus and activation-regulated chemokine, IgE, eosinophils), were associated with increased incidence of conjunctivitis. Patients who responded well to dupilumab had reduced incidence of conjunctivitis. Further study is needed to elucidate the aetiology and treatment of conjunctivitis in dupilumab-treated patients with AD.

Corneal permeability changes in dry eye disease: an observational study

Background

Diagnostic tests for dry eye disease (DED), including ocular surface disease index (OSDI), tear breakup time (TBUT), corneal fluorescein staining, and lissamine staining, have great deal of variability. We investigated whether fluorophotometry correlated with previously established DED diagnostic tests and whether it could serve as a novel objective metric to evaluate DED.

Methods

Dry eye patients who have had established signs or symptoms for at least 6 months were included in this observational study. Normal subjects with no symptoms of dry eyes served as controls. Each eye had a baseline fluorescein scan prior to any fluorescein dye. Fluorescein dye was then placed into both eyes, rinsed with saline solution, and scanned at 5, 10, 15, and 30 min. Patients were administered the following diagnostic tests to correlate with fluorophotometry: OSDI, TBUT, fluorescein, and lissamine. Standard protocols were used. P < 0.05 was considered significant.

Results

Fifty eyes from 25 patients (DED = 22 eyes, 11 patients; Normal = 28 eyes, 14 patients) were included. Baseline scans of the dry eye and control groups did not show any statistical difference (p = 0.84). Fluorescein concentration of DED and normal patients showed statistical significance at all time intervals (p < 10⁻⁵, 0.001, 0.002, 0.049 for 5, 10, 15, & 30 min respectively). Fluorophotometry values converged towards baseline as time elapsed, but both groups were still statistically different at 30 min (p < 0.01). We used four fluorophotometry scoring methods and correlated them with OSDI, TBUT, fluorescein, and lissamine along with adjusted and aggregate scores. The four scoring schemes did not show any significant correlations with the other tests, except for correlations seen with lissamine and 10 (p = 0.045, 0.034) and 15 min (p = 0.013, 0.012), and with aggregate scores and 15 min (p = 0.042, 0.017).

Conclusions

Fluorophotometry generally did not correlate with any other DED tests, even though it showed capability of differentiating between DED and normal eyes up to 30 min after fluorescein dye instillation. There may be an aspect of DED that is missed in the current regimen of DED tests and only captured with fluorophotometry. Adding fluorophotometry may be useful in screening, diagnosing, and monitoring patients with DED.

Epigenetic mechanisms might help explain environmental contributions to the pathogenesis of keratoconus

The etiology of keratoconus (KC) seems to involve genetic and/or environmental factors such as rubbing and/or contact lens trauma and/or exposure to ultraviolet radiation. An examination of the possibility that epigenetic mechanisms could contribute to the tissue changes in KC has been considered in this review. The tissue changes in KC result in thinning and/or other forms of mechanical weakening of the cornea, which cause it to become more susceptible to the distending forces of intraocular pressure with associated development of a cone. Rather than being caused by a single gene mutation, a complex or multifactorial disease such as KC involves multiple genes plus lifestyle and environmental factors. The epigenome of a cell is highly dynamic, being governed by a complex interplay of genetic and environmental factors. The full range of epigenetic marks is currently unknown but is potentially enormous. Although further elucidation of the genetic determinants of KC is important, there is now increasing interest in exploring how non-genetic variants, such as epigenetic factors, could influence complex disease etiology. Studies of epigenetic processes in KC may help explain the relationship between the genome and the environment and provide new clues for modifying these processes with the possibility of preventing the development of KC or stabilizing its progress. Epigenetic linking may be relevant to other complex ocular diseases that involve environmental factors including those that involve exposure to ultraviolet radiation.

The ocular surface epithelial barrier and other mechanisms of mucosal protection: from allergy to infectious diseases

PURPOSE OF REVIEW

Studies completed in the last decade provide new insights into the role of the epithelial glycocalyx in maintaining ocular surface barrier function. This review summarizes these findings, their relevance to allergic and infectious disease, and highlights the potential benefits of exploiting the modulation of barrier integrity for therapeutic gain.

RECENT FINDINGS

The molecular components sealing the space between adjacent ocular surface epithelial cells, such as tight junctions, have been extensively characterized, and their contribution to the paracellular barrier established. A second layer of protection - the transcellular barrier - is provided by transmembrane mucins and their O-glycans on the glycocalyx. Cell surface glycans bind carbohydrate-binding proteins to promote formation of complexes that are no longer thought to be a static structure, but, instead, a dynamic system that responds to extrinsic signals and modulates pathogenic responses. Although functioning as a protective mechanism to maintain homeostasis, the glycocalyx also restricts drug targeting of epithelial cells.

SUMMARY

The traditional model of intercellular junctions protecting the ocular surface epithelia has recently been expanded to include an additional glycan shield that lines apical membranes on the ocular surface. A better understanding of this apical barrier may lead to better management of ocular surface disease.

Synergistic induction of eotaxin and VCAM-1 expression in human corneal fibroblasts by staphylococcal peptidoglycan and either IL-4 or IL-13

BACKGROUND

Common features of allergic or atopic ocular and skin diseases are the participation of Th2 lymphocytes and eosinophils and colonization by Staphylococcus aureus. To examine the role of interaction between Th2 cells and bacterial infection in tissue eosinophilia, we determined the effects of Th2 cytokines and peptidoglycan derived from the cell wall of S. aureus on corneal fibroblasts.

METHODS

Chemokine concentrations and the cell surface expression of adhesion molecules were determined by ELISAs, and chemokine and adhesion molecule mRNAs were quantitated by real-time PCR analysis. Signaling by the transcription factor NF-κB was evaluated by immunoblot and immunofluorescence analyses as well as by assay of DNA binding activity.

RESULTS

Among Th2 cytokines tested, only interleukin (IL)-4 and IL-13 induced a low level of eotaxin release by corneal fibroblasts, as did peptidoglycan. However, the combination of peptidoglycan and either IL-4 or IL-13 induced a marked synergistic increase both in eotaxin release (without affecting that of IL-8) and in the abundance of eotaxin mRNA. The combination of peptidoglycan and IL-4 or IL-13 also synergistically increased the surface expression of VCAM-1, but not that of ICAM-1. Peptidoglycan activated NF-κB in corneal fibroblasts, and inhibitors of NF-κB attenuated eotaxin release induced by peptidoglycan alone or in combination with IL-4 or IL-13.

CONCLUSIONS

Interaction of innate and adaptive immunity, as manifested by synergistic stimulation of eotaxin and VCAM-1 expression in corneal fibroblasts by peptidoglycan and Th2 cytokines, may play an important role in tissue eosinophilia associated with ocular allergy.

Atopic dermatitis and keratoconjunctivitis

Atopic dermatitis, a chronic disease seen by allergist-immunologists, has both dermatologic and ocular manifestations. The ocular component is often disproportionately higher than the dermatologic disease. Even if skin abnormalities seem well controlled, these patients require ophthalmic evaluation. Atopic keratoconjunctivitis in atopic dermatitis patients is characterized by acute exacerbations and requires maintenance therapy for long-term control. Future studies will continue to emphasize the use of steroid-sparing, immunomodulating agents that have the potential to provide long-lasting anti-inflammatory control with a more favorable side-effect profile.

Mast Cell Chymase Decreases the Barrier Function and Inhibits the Migration of Corneal Epithelial Cells

PURPOSE

We investigated the in vitro effects of human mast cell chymase on corneal epithelial cells.

METHODS

Human corneal epithelial cells were incubated with human chymase at activity levels that were likely to exist in the tears of patients with vernal keratoconjunctivitis.

RESULTS

Incubation of chymase resulted in a decrease of barrier function of corneal epithelium. Occludin protein was cleaved by chymase. In the wound assay, incubation with chymase resulted in an inhibition of cell migration.

CONCLUSION

Human chymase causes the proteolysis of occludin and fibronectin, resulting in a decrease of barrier function and inhibition of the migration of corneal epithelial cells.

Role of structural cells of the cornea and conjunctiva in the pathogenesis of vernal keratoconjunctivitis

Vernal keratoconjunctivitis (VKC) is a severe type of allergic conjunctival disease characterized by the presence both of various corneal epithelial and stromal lesions as well as of conjunctival proliferative changes such as giant papillae of the upper tarsal conjunctiva and limbal lesions. These clinical findings as well as various pathophysiological characteristics of VKC are distinct from those of other types of ocular allergy and allergic diseases of other organs. The outer eye possesses specific allergological characteristics, one of which is communication between the cornea and conjunctiva through a thin layer of tear fluid. Fibroblasts of the cornea and the conjunctiva are activated by proinflammatory and T helper 2 (Th2) cell-derived cytokines. Corneal fibroblasts enhance ocular allergic reactions as a result of their activation-induced expression both of chemokines such as eotaxin and TARC as well as of adhesion molecules such as ICAM-1 and VCAM-1, all of which together promote the activation and infiltration of eosinophils and Th2 lymphocytes. In contrast, corneal epithelial cells suppress such reactions by physically separating corneal fibroblasts from bioactive substances in tear fluid. Exaggerated proliferation of and deposition of extracellular matrix by conjunctival fibroblasts likely exacerbate conjunctival inflammation. Restoration of an intact corneal epithelium and inhibition of the activities of corneal and conjunctival fibroblasts may provide a basis for the development of new treatments for severe ocular allergic diseases such as VKC.

Synergistic effect of TNF-alpha and either IL-4 or IL-13 on VCAM-1 expression by cultured human corneal fibroblasts

PURPOSE

To examine the role of corneal fibroblasts in the pathogenesis of vernal keratoconjunctivitis, we investigated the effects of tumor necrosis factor (TNF)-alpha, interleukin (IL)-4, and IL-13 on the expression of vascular cell adhesion molecule (VCAM)-1 by cultured human corneal fibroblasts.

METHODS

Cultured human corneal fibroblasts were incubated with various combinations and concentrations of TNF-alpha, IL-4, and IL-13. The cell surface expression of VCAM-1 was subsequently evaluated by whole-cell enzyme-linked immunosorbent assay and immunocytochemistry, and the abundance of VCAM-1 mRNA in cell lysates was determined by quantitative reverse transcription and polymerase chain reaction analysis.

RESULTS

Corneal fibroblasts incubated in the absence of cytokines exhibited minimal expression of VCAM-1. Whereas incubation of the cells with TNF-alpha, IL-4, or IL-13 alone, or with the combination of IL-4 and IL-13, induced only a small increase in VCAM-1 expression, exposure of the cells to TNF-alpha in combination with either IL-4 or IL-13 resulted in a marked synergistic increase in expression of this adhesion molecule that was both time and dose dependent. The abundance of VCAM-1 mRNA in corneal fibroblasts was also increased in a synergistic manner by incubation of the cells with TNF-alpha together with either IL-4 or IL-13.

CONCLUSION

Stimulation of human corneal fibroblasts with the combination of TNF-alpha and either IL-4 or IL-13 resulted in synergistic increases in both the abundance of VCAM-1 mRNA and the cell surface expression of VCAM-1 protein. This cytokine-induced increase in VCAM-1 expression by corneal fibroblasts may contribute to eosinophil infiltration in corneal lesions associated with vernal keratoconjunctivitis.

Characteristics of the human ocular surface epithelium

An appreciation of the biological characteristics of the human ocular surface epithelium affords us a great insight into the physiology of the human ocular surface in health and disease. Here, we review five important aspects of the human ocular surface epithelium. First, we recognize the discovery of corneal epithelial stem cells, and note how the palisades of Vogt have been suggested as a clinical marker of their presence. Second, we introduce the concept of the gene expression profile of the ocular surface epithelium as arrived at using a new strategy for the systematic analysis of active genes. We also provide a summary of several genes abundantly or uniquely expressed in the human corneal epithelium, namely clusterin, keratin 3, keratin 12, aldehyde dehydrogenase 3 (ALDH3), troponin-I fast-twitch isoform, ssig-h3, cathepsin L2 (cathepsin V), uroplakin Ib, and Ca(2+)-activated chloride channel. Genes related to limbal and conjunctival epithelia are also described. Third, we touch upon the genetic abnormalities thought to be involved with epithelial dysfunction in Meesmann's dystrophy, gelatinous drop-like corneal dystrophy, and the ssig-h3-mutated corneal dystrophies. Fourth, we provide an update regarding the current state of knowledge of the role of cytokines, growth factors and apoptosis in relation to ocular surface homeostasis and tissue reconstruction; the main factors being epidermal growth factor (EGF), keratinocyte growth factor (KGF), hepatocyte growth factor (HGF), transforming growth factor-ss (TGF-ss), and some inflammatory cytokines. Fifth, corneal epithelial barrier function and dysfunction as measured by fluorophotometry is remarked upon, with an explanation of the FL-500 fluorophotometer and its ability to detect corneal epithelial dysfunction at a subclinical level. The research described in this review has undoubtedly generated a complete understanding of corneal epithelial pathophysiology-an understanding that, directly or indirectly, has helped advance the development of new therapeutic modalities for ocular surface reconstruction.

Allergic and immunologic disorders of the eye. Part II: ocular allergy

Allergy affects more than 15% of the world population, and some studies have shown that up 30% of the US population has some form of allergy. Most of these patients have various target organs for their allergies, and most have ocular involvement. The ocular component may be the most prominent and sometimes disabling feature of their allergy. Some are affected for only a few weeks to months, whereas others have symptoms that last throughout the year. The seasonal forms may present to clinical allergists, whereas the more chronic forms may present to ophthalmologists. Thus, in the second of this 2-part review series (Part I: Ocular Immunology appeared in the November issue of the Journal), an overview is provided of the spectrum of ocular allergy that ranges from acute seasonal allergic conjunctivitis to chronic variants of atopic keratoconjunctivitis. With a better understanding of the immunologic mechanisms, we now can develop better treatment approaches and design further research in intervention of allergic eye diseases.