Fibroblasts as local immune modulators in ocular allergic disease

A biomimetic human disease model of bacterial keratitis using a cornea-on-a-chip system

Bacterial keratitis is a common form of inflammation caused by the bacterial invasion of the corneal stroma after trauma. In extreme cases, it can lead to severe visual impairment or even blindness; therefore, timely medical intervention is imperative. Unfortunately, widespread misuse of antibiotics has led to the development of drug resistance. In recent years, organ-on-chips that integrate multiple cell co-cultures have extensive applications in fundamental research and drug screening. In this study, immortalized human corneal epithelial cells and primary human corneal fibroblasts were co-cultured on a porous polydimethylsiloxane membrane to create a cornea-on-a-chip model. The developed multilayer epithelium closely mimicked clinical conditions, demonstrating high structural resemblance and repeatability. By introducing a consistently defective epithelium and bacterial infection using the space-occupying method, we successfully established an in vitro model of bacterial keratitis using S. aureus. We validate this model by evaluating the efficacy of antibiotics, such as levofloxacin, tobramycin, and chloramphenicol, through simultaneously observing the reactions of bacteria and the two cell types to these antibiotics. Our study has revealed the barrier function of epithelium of the model and differentiated efficacy of three drugs in terms of bactericidal activity, reducing cellular apoptosis, and mitigating scar formation. Altogether, the cornea on chip enables the assessment of ocular antibiotics, distinguishing the impact on corneal cells and structural integrity. This study introduced a biomimetic in vitro disease model to evaluate drug efficacy and provided significant insights into the extensive effects of antibiotics on diverse cell populations within the cornea.

Long-Term Clinical Outcome of Tacrolimus Skin Ointment (0.03%) for the Treatment of Vernal Keratoconjunctivitis: A Quasi-Experimental Study

Background Vernal keratoconjunctivitis (VKC) is an allergic conjunctival inflammation with severe ocular complications if left untreated. The current management regimen is plagued with adverse effects, long-term problems, and clinical relapses. Tacrolimus offers an alternative treatment option, and long-term studies are needed to determine its efficacy. Methods A two-year follow-up based study was conducted on moderate to severe VKC patients, who were prescribed tacrolimus skin ointment. The 5-5-5 exacerbation scale was used for the monitoring and grading severity of the disease. Analysis of variance (ANOVA) and intergroup comparisons were conducted on exacerbation scale scores among follow-ups. Results A significant reduction was observed in the total score of severity from baseline (203.17±102.05) to three months' follow-up (69.94±70.54), and it kept reducing for 18 months post therapy. Similar results with statistically significant reduction were observed for all grades of the scale. The relapse rate was 5.71% within a month after therapy cessation, and none of the other patients showed relapse afterward. No significant ocular and systemic complications were observed during the study. Conclusion Tacrolimus is effective in the long-term management of VKC without the complications of conventional steroid-based therapy.

Biologics for allergy: therapeutic potential for ocular allergic diseases and adverse effects on the eye

Biologics applying antibodies against IgE, IL-5, IL-5 receptor α, IL-4 receptor α, and IL-13 have dramatically improved recent treatment outcomes in allergic diseases including asthma, rhinitis, and atopic dermatitis. However, these drugs have not been approved for ocular allergic diseases such as allergic conjunctivitis, vernal keratoconjunctivitis, and atopic keratoconjunctivitis. Although the putative mechanisms suggest that these drugs should have beneficial effects in patients with ocular allergies and some studies have reported such beneficial effects, various adverse ocular symptoms have also been observed in clinical trials and off-label use studies. Since ocular allergic diseases have distinct pathogeneses, each biologic drug must be examined regarding specific effects on each ocular allergy. For example, IgE-mediated type 1 hypersensitivity plays a critical role in allergic conjunctivitis. By contrast, T cells and eosinophilic and non-IgE-mediated type 2 inflammation play important roles in vernal keratoconjunctivitis. Allergists must fully understand the effects of each drug on the eye. This review outlines both potential therapeutic and adverse effects of various biologics on allergic diseases of the eye.

Therapeutic Targets in Allergic Conjunctivitis

Allergic conjunctivitis (AC) is a common condition resulting from exposure to allergens such as pollen, animal dander, or mold. It is typically mediated by allergen-induced crosslinking of immunoglobulin E attached to receptors on primed conjunctival mast cells, which results in mast cell degranulation and histamine release, as well as the release of lipid mediators, cytokines, and chemokines. The clinical result is conjunctival hyperemia, tearing, intense itching, and chemosis. Refractory and chronic cases can result in ocular surface complications that may be vision threatening. Patients who experience even mild forms of this disease report an impact on their quality of life. Current treatment options range from non-pharmacologic therapies to ocular and systemic options. However, to adequately control AC, the use of multiple agents is often required. As such, a precise understanding of the immune mechanisms responsible for this ocular surface inflammation is needed to support ongoing research for potential therapeutic targets such as chemokine receptors, cytokine receptors, non-receptor tyrosine kinases, and integrins. This review utilized several published articles regarding the current therapeutic options to treat AC, as well as the pathological and immune mechanisms relevant to AC. This review will also focus on cellular and molecular targets in AC, with particular emphasis on potential therapeutic agents that can attenuate the pathology and immune mechanisms driven by cells, receptors, and molecules that participate in the immunopathogenesis and immunopathology of AC.

Role of Damage-Associated Molecular Patterns (DAMPs/Alarmins) in Severe Ocular Allergic Diseases

Severe ocular allergic diseases, such as atopic keratoconjunctivitis and vernal keratoconjunctivitis, cause severe allergic inflammation in the conjunctiva and corneal epithelial damage, resulting in visual disturbances. The involvement of damage (danger)-associated molecular patterns (DAMPs/alarmins) in the pathogenesis of these diseases has been recognized. Alarmins released from damaged corneal epithelial cells or eosinophils play a critical role in the induction of corneal lesions, vicious loop of corneal injury, and exacerbation of conjunctival allergic inflammation. Alarmins in the conjunctiva also play an essential role in the development of both allergic inflammation, based on the acquired immune system, and type 2 inflammation by innate immune responses in the ocular surface. Therefore, alarmins may be a potentially important therapeutic target in severe refractory ocular allergic diseases.

Promotion of conjunctival fibroblast-mediated collagen gel contraction by mast cells through up-regulation of matrix metalloproteinase release and activation

Mast cells and conjunctival fibroblasts contribute to conjunctival wound healing and allergic ocular inflammation. The number of mast cells in the conjunctiva is increased in individuals with cicatricial fibrosis-causing ocular surface diseases and after glaucoma filtering surgery, suggesting that these cells may contribute to the scarring observed after such surgery. We studied the potential mechanism of fibroblast-mast cell interaction in the healing of conjunctival wounds using a three-dimensional collagen gel culture system. We found that mast cells derived from the bone marrow of mice embedded in a collagen gel did not induce gel contraction. However, an increase in mast cells was associated with increased collagen gel contraction mediated by mouse conjunctival fibroblasts. The extent of collagen degradation was not affected by the co-culture of mast cells and conjunctival fibroblasts. Gelatin zymography disclosed that mast cells increased the amounts of both the pro form of matrix metalloproteinase (MMP)-9 and the active form of MMP-2 in supernatants of conjunctival fibroblast cultures. Furthermore, the potentiating effect of mast cells on contraction of the collagen gel through conjunctival fibroblasts was attenuated by the addition of a synthetic MMP inhibitor. Thus, current results suggest that mast cells accelerate the conjunctival fibroblast-dependent contraction of collagen gel by increasing the release as well as activation of MMPs. Therefore, the interaction between mast cells and conjunctival fibroblasts may contribute to conjunctival scar formation after glaucoma filtering surgery.

Immunopharmacology in Vernal Keratoconjunctivitis: Current and Future Perspectives

Vernal keratoconjunctivitis (VKC) is a complex and chronic, multifactorial Th2 cell-mediated chronic ocular surface inflammatory condition that typically affects predominantly male children in hot or warm climates. The primary symptom is intense ocular pruritus, often significant enough to affect activities of daily living. Clinical features differ from simple forms of allergic conjunctivitis in that they are more-or-less confined to the superior tarsus and limbus. There is also a risk of corneal involvement, which leads to irreversible vision loss in approximately 6% of patients. Right now, there is no standardized treatment protocol, and many of the currently available options are not effective in severe and recurrent cases. As such, it is imperative to understand this complex allergic immune response in order to identify future therapeutic targets. This review will focus on potential drug targets in VKC, with particular emphasis on immunomodulators and immunobiologic agents.

Nerve Growth Factor (NGF) modulates in vitro induced myofibroblasts by highlighting a differential protein signature

We previously described the profibrogenic effect of NGF on conjunctival Fibroblasts (FBs) and its ability to trigger apoptosis in TGFβ1-induced myofibroblasts (myoFBs). Herein, cell apoptosis/signalling, cytokines' signature in conditioned media and inflammatory as well as angiogenic pathway were investigated. Experimental myoFBs were exposed to NGF (0.1-100 ng/mL), at defined time-point for confocal and biomolecular analysis. Cells were analysed for apoptotic and cell signalling activation in cell extracts and for some inflammatory and proinflammatory/angiogenic factors' activations. NGF triggered cJun overexpression and phospho-p65-NFkB nuclear translocation. A decreased Bcl2:Bax ratio and a significant expression of smad7 were confirmed in early AnnexinV-positive myoFBs. A specific protein signature characterised the conditioned media: a dose dependent decrease occurred for IL8, IL6 while a selective increase was observed for VEGF and cyr61 (protein/mRNA). TIMP1 levels were unaffected. Herein, NGF modulation of smad7, the specific IL8 and IL6 as well as VEGF and cyr61 modulation deserve more attention as opening to alternative approaches to counteract fibrosis.

Corneal fibroblasts: Function and markers

Corneal stromal keratocytes contribute to the maintenance of corneal transparency and shape by synthesizing and degrading extracellular matrix. They are quiescent in the healthy cornea, but they become activated in response to insults from the external environment that breach the corneal epithelium, with such activation being associated with phenotypic transformation into fibroblasts. Corneal fibroblasts (activated keratocytes) act as sentinel cells to sense various external stimuli-including damage-associated molecular patterns derived from injured cells, pathogen-associated molecular patterns of infectious microorganisms, and inflammatory mediators such as cytokines-under pathological conditions such as trauma, infection, and allergy. The expression of various chemokines and adhesion molecules by corneal fibroblasts determines the selective recruitment and activation of inflammatory cells in a manner dependent on the type of insult. In infectious keratitis, the interaction of corneal fibroblasts with various components of microbes and with cytokines derived from infiltrated inflammatory cells results in excessive degradation of stromal collagen and consequent corneal ulceration. Corneal fibroblasts distinguish between type 1 and type 2 inflammation through recognition of corresponding cytokines, with their activation by type 2 cytokines contributing to the pathogenesis of corneal lesions in severe ocular allergic diseases. Pharmacological targeting of corneal fibroblast function is thus a potential novel therapeutic approach to prevention of excessive corneal stromal inflammation, damage, and scarring.

P38 Inhibition Prevents Herpes Simplex Virus Type 1 (HSV-1) Infection in Cultured Corneal Keratocytes

Purpose: To evaluate keratocyte viability and proinflammatory cytokine secretion induced by HSV-1 infection. Methods: Keratocytes were separated from corneal tissues obtained with the SMILE procedure, and an in vitro system was established to study HSV-1 infection in human keratocytes. Cell viability, HSV-1 genomic DNA copy number, and the expression levels of α-SMA, ALDH1A1, phospho-p38, p38, phospho-IRF3, and IRF3 were evaluated. Antibody array and ELISA kits were used to measure the production of proinflammatory cytokines and chemokines. Results: We found that HSV-1 infection reduced cell viability and activated keratocyte transdifferentiation into corneal fibroblast-like cells. Furthermore, p38 inhibition improved cell viability and IFN-β production and played an anti-inflammatory role by reducing the production of proinflammatory cytokines and chemokines. Conclusions: Our study reveals an important role played by keratocytes during innate immune responses and identifies p38 inhibition as a potential therapeutic approach to control ocular HSV-1 infection.

Potential Biomarkers for Allergic Conjunctival Diseases

Allergic conjunctival diseases (ACDs) are a group of ocular allergies that include allergic conjunctivitis, atopic keratoconjunctivitis, vernal keratoconjunctivitis, and giant papillary conjunctivitis. Although a large body of information exists on the pathophysiology of ACDs, this has not yet lead to the development of clear recommendations and guidelines for the diagnosis of ACDs or development of conclusive and objective diagnostic tools. Identification of objectively measurable biomarkers that represent the molecular and cellular mechanisms associated with ACDs will be an important step toward achieving these aims. This is a comprehensive review of biological markers that have the potential to become "biomarker(s)" for ACDs and aid in the classification, diagnosis, and development of new therapeutic strategies for these group of allergic conditions.

Interleukin-13 maintains the stemness of conjunctival epithelial cell cultures prepared from human limbal explants

To use human limbal explants as an alternative source for generating conjunctival epithelium and to determine the effect of interleukin-13 (IL-13) on goblet cell number, mucin expression, and stemness. Human limbal explants prepared from 17 corneoscleral rims were cultured with or without IL-13 (IL-13+ and IL-13-, respectively) and followed up to passage 2 (primary culture [P0]-P2). Cells were characterized by alcian blue/periodic acid-Schiff (AB/PAS) staining (goblet cells); immunofluorescent staining for p63α (progenitor cells), Ki-67 (proliferation), MUC5AC (mucin, goblet cells), and keratin 7 (K7, conjunctival epithelial and goblet cells); and by quantitative real-time polymerase chain reaction for expression of the p63α (TP63), MUC5AC, MUC4 (conjunctival mucins), K3, K12 (corneal epithelial cells), and K7 genes. Clonogenic ability was determined by colony-forming efficiency (CFE) assay. Using limbal explants, we generated epithelium with conjunctival phenotype and high viability in P0, P1, and P2 cultures under IL-13+ and IL-13- conditions, i.e., epithelium with strong K7 positivity, high K7 and MUC4 expression and the presence of goblet cells (AB/PAS and MUC5AC positivity; MUC5AC expression). p63α positivity was similar in IL-13+ and IL-13- cultures and was decreased in P2 cultures; however, there was increased TP63 expression in the presence of IL-13 (especially in the P1 cultures). Similarly, IL-13 increased proliferative activity in P1 cultures and significantly promoted P0 and P1 culture CFE. IL-13 did not increase goblet cell number in the P0-P2 cultures, nor did it influence MUC5AC and MUC4 expression. By harvesting unattached cells on day 1 of P1 we obtained goblet cell rich subpopulation showing AB/PAS, MUC5AC, and K7 positivity, but with no growth potential. In conclusion, limbal explants were successfully used to develop conjunctival epithelium with the presence of putative stem and goblet cells and with the ability to preserve the stemness of P0 and P1 cultures under IL-13 influence.

Immunopathology of Allergic Conjunctivitis

Allergic conjunctivitis is predominantly an immunoglobulin E-mediated hypersensitivity reaction to environmental allergens. Allergic diseases affect >30% of the world’s population, of which 40% report associated ocular manifestations. Cellular and soluble mediators play a major role in the pathophysiology of allergic conjunctivitis. Mast cells, which are major effector cells of allergic conjunctivitis, undergo activation and degranulation to release histamine, tryptase, prostaglandins, leukotrienes, and cytokines. These mediators play important roles in immunopathological mechanisms that generate the clinical manifestations of allergic conjunctivitis. These clinical features include conjunctival hyperaemia, chemosis, tearing, itching, papillae, mucus discharge, and eyelid oedema. Histamine mediates the early phase of the allergic immune response, whereas lipid mediators and cytokines are involved in the late phase of the immunopathology of allergic conjunctivitis. Current management of allergic conjunctivitis includes non-pharmacological approaches such as allergen avoidance and palliative therapy, whereas pharmacological therapeutic modalities may include antihistamine–mast cell stabiliser combination ophthalmic formulations and allergen-specific immunotherapy. Furthermore, as cellular and soluble mediators play a pivotal role in the immunopathogenesis and immunopathology of allergic conjunctivitis, development of immunotherapeutic and pharmacotherapeutic agents specific to these mediators can enhance the therapeutic index and safety profile of anti-allergy treatment.

Corneal Fibroblasts as Sentinel Cells and Local Immune Modulators in Infectious Keratitis

The cornea serves as a barrier to protect the eye against external insults including microbial pathogens and antigens. Bacterial infection of the cornea often results in corneal melting and scarring that can lead to severe visual impairment. Not only live bacteria but also their components such as lipopolysaccharide (LPS) of Gram-negative bacteria contribute to the development of inflammation and subsequent corneal damage in infectious keratitis. We describe the important role played by corneal stromal fibroblasts (activated keratocytes) as sentinel cells, immune modulators, and effector cells in infectious keratitis. Corneal fibroblasts sense bacterial infection through Toll-like receptor (TLR)–mediated detection of a complex of LPS with soluble cluster of differentiation 14 (CD14) and LPS binding protein present in tear fluid. The cells then initiate innate immune responses including the expression of chemokines and adhesion molecules that promote the recruitment of inflammatory cells necessary for elimination of the infecting bacteria. Infiltrated neutrophils are activated by corneal stromal collagen and release mediators that stimulate the production of pro–matrix metalloproteinases by corneal fibroblasts. Elastase produced by Pseudomonas aeruginosa (P. aeruginosa) activates these released metalloproteinases, resulting in the degradation of stromal collagen. The modulation of corneal fibroblast activation and of the interaction of these cells with inflammatory cells and bacteria is thus important to minimize corneal scarring during treatment of infectious keratitis. Pharmacological agents that are able to restrain such activities of corneal fibroblasts without allowing bacterial growth represent a potential novel treatment option for prevention of excessive scarring and tissue destruction in the cornea.

Cytokine expression and barrier disruption in human corneal epithelial cells induced by alarmin released from necrotic cells

PURPOSE

Dying cells release endogenous molecules known as alarmins that signal danger to surrounding tissue. We investigated the effects of necrotic cell-derived alarmins on cytokine expression and barrier function in human corneal epithelial cells.

METHODS

The release of interleukin (IL)-6 and IL-8 from immortalized human corneal epithelial (HCE) cells in culture was measured with enzyme-linked immunosorbent assays. The abundance of IL-6 and 8 mRNAs was quantitated by reverse transcription and real-time polymerase chain reaction analysis. Barrier function of HCE cells was evaluated by measurement of transepithelial electrical resistance (TER). The subcellular localization of the p65 subunit of the transcription factor NF-κB was determined by immunofluorescence analysis, and phosphorylation of the endogenous NF-κB inhibitor IκBα was examined by immunoblot analysis.

RESULTS

A necrotic cell supernatant prepared from HCE cells induced the up-regulation of IL-6 and 8 expression at both mRNA and protein levels as well as reduced TER in intact HCE cells. Among alarmins tested, only IL-1α (not IL-33 or HMGB1) mimicked these effects of the necrotic cell supernatant. Furthermore, IL-1 receptor antagonist (IL-1RA) and neutralizing antibodies to IL-1α (but not those to IL-1β) each attenuated the effects of the necrotic cell supernatant. Exposure of HCE cells to the necrotic cell supernatant also induced the phosphorylation and degradation of IκBα as well as translocation of the p65 subunit of NF-κB to the nucleus.

CONCLUSION

IL-1α released from necrotic corneal epithelial cells may trigger inflammatory responses at the ocular surface, including cytokine production and barrier disruption.

An engineered human conjunctival-like tissue to study ocular surface inflammatory diseases

The aim of this study was to develop a three-dimensional model of the human conjunctiva that can be used to perform physiology and pathophysiology experiments. Fibrin-based matrices (derived from human plasma or plasma cryoprecipitate) were used as scaffolds, and primary cells were obtained from conjunctival tissue. Conjunctival constructs were analyzed by immunofluorescent staining and scanning electron microscopy and cell proliferation was measured with alamarBlue® assay. After characterizing the constructs, four different experimental conditions were analyzed in cryoprecipitate matrices: controls, air-lifted cultures (to increase cell stratification), partially desiccated cultures (to mimic dry eye disease), and IL-13-treated cultures (to mimic allergy). Constructs were stained with hematoxylin/eosin to observe changes in morphology. High molecular weight glycoconjugates were identified by HPA staining. MUC5AC and IL-6 secretion was evaluated by ELISA. The fibrin-based matrices supported conjunctival cell growth. Epithelial cells grew on the surface of the scaffolds and underwent stratification that increased over time. These cells had microvilli, which suggests cell polarization and functionality. Fibroblasts were integrated in the scaffold and showed elongated shape. Compared to controls, air-lifted construct had increased epithelial stratification and upregulated MUC5AC secretion. Increased MUC5AC secretion also occurred in partially desiccated and IL-13-treated cultures. The inflammatory status of cells was evaluated by IL-6 levels which were increased in air-lifted and partially desiccated cultures, but not in IL-13-treated ones. In conclusion, we have developed a new three-dimensional model of human conjunctiva that can be used to study ocular surface inflammatory diseases.

Vernal shield ulcers treated with frequently installed topical cyclosporine 0.05% eyedrops

PURPOSE

To report on the beneficial results of an intense regimen of 0.05% cyclosporine eye drops, eight times a day in patients with therapy resistant vernal shield ulcers.

METHODS

Case cohort of four eyes of three male children with vernal keratoconjunctivitis complicated by shield ulcers, who were treated with frequent cyclosporine 0.05% eye drops and observed for up to 5 years.

RESULTS

Quick resolution of the shield ulcers and complete re-epithelialization within 14-25 days was observed after adding intensive treatment with cyclosporine 0.05% to regular anti-inflammatory, histamine blocking, and surgical therapy. In one patient, additional scraping of the bottom of the ulcer was needed.

CONCLUSIONS

In patients with vernal shield ulcers, frequent installation of low-concentration cyclosporine eye drops seems to have a promising therapeutical value.

Dehydroxymethylepoxyquinomicin, a novel nuclear factor-κB inhibitor, reduces chemokines and adhesion molecule expression induced by IL-1β in human corneal fibroblasts

PURPOSE

Dehydroxymethylepoxyquinomicin (DHMEQ) is derived from the antibiotic, epoxyquinomicin C, and is a novel low molecular weight nuclear factor-κB (NF-κB) inhibitor. We investigated the effects of DHMEQ on the expression of chemokines and the intercellular adhesion molecule (ICAM)-1 induced by proinflammatory cytokines in cultures of the human corneal fibroblasts (HCFs).

METHODS

The cytotoxicity of DHMEQ on cultured HCFs was evaluated by cell proliferation assays. Cultures were exposed to interleukin (IL)-1β, and the production of IL-8 and monocyte chemoattractant protein (MCP)-1 was assessed by enzyme-linked immunosorbent assay. The degree of expression of ICAM-1 was measured by flow cytometry. The translocation of NF-κB p65 into the nucleus of HCFs was assessed by immunocytochemistry.

RESULTS

DHMEQ was not toxic to cultured HCFs at doses up to 10 μg/ml. DHMEQ significantly suppressed the production of both IL-8 and MCP-1 in IL-1β-stimulated HCFs. In addition, DHMEQ down-regulated ICAM-1 expression in IL-1β-stimulated HCFs in a dose-dependent manner. DHMEQ inhibited the IL-1β-induced nuclear accumulation of p65, a component of NF-κB, in HCFs.

CONCLUSIONS

The suppression of inflammatory chemokines IL-8 and MCP-1 and inhibition of the expression of ICAM-1 in cultured HCFs by DHMEQ indicates that DHMEQ may have a therapeutic potential for treating ICAM-1 and chemokine-mediated corneal inflammatory disorders.

Inhibition by rebamipide of cytokine-induced or lipopolysaccharide-induced chemokine synthesis in human corneal fibroblasts

BACKGROUND/AIMS

The dry-eye drug rebamipide has mucin secretagogue activity in and anti-inflammatory effects on corneal epithelial cells. Corneal stromal fibroblasts (transdifferentiated keratocytes) function as immune modulators in the pathogenesis of chronic ocular allergic inflammation and in innate immune responses at the ocular surface. The possible anti-inflammatory effects of rebamipide on human corneal stromal fibroblasts were examined.

METHODS

Serum-deprived cells were incubated for 1 h with rebamipide and then for various times in the additional absence or presence of cytokines or bacterial lipopolysaccharide (LPS). The release of chemokines into culture supernatants was determined with ELISAs. The intracellular abundance of chemokine mRNAs was quantitated by reverse transcription and real-time PCR analysis. Degradation of the nuclear factor κB (NFκB) inhibitor IκBα was detected by immunoblot analysis.

RESULTS

Rebamipide suppressed the release of interleukin (IL)-8 and the upregulation of IL-8 mRNA induced by tumour necrosis factor α (TNF-α) or LPS in corneal fibroblasts. It also inhibited eotaxin-1 (CCL-11) expression at the protein and mRNA levels induced by the combination of TNF-α and IL-4. In addition, rebamipide attenuated the degradation of IκBα induced by TNF-α or LPS.

CONCLUSIONS

Rebamipide inhibited the synthesis of chemokines by corneal fibroblasts in association with suppression of NFκB signalling. Rebamipide may therefore prove effective for the treatment of corneal stromal inflammation associated with allergy or bacterial infection.

Chronic nerve growth factor exposure increases apoptosis in a model of in vitro induced conjunctival myofibroblasts

In the conjunctiva, repeated or prolonged exposure to injury leads to tissue remodeling and fibrosis associated with dryness, lost of corneal transparency and defect of ocular function. At the site of injury, fibroblasts (FB) migrate and differentiate into myofibroblasts (myoFB), contributing to the healing process together with other cell types, cytokines and growth factors. While the physiological deletion of MyoFB is necessary to successfully end the healing process, myoFB prolonged survival characterizes the pathological process of fibrosis. The reason for myoFB persistence is poorly understood. Nerve Growth Factor (NGF), often increased in inflamed stromal conjunctiva, may represent an important molecule both in many inflammatory processes characterized by tissue remodeling and in promoting wound-healing and well-balanced repair in humans. NGF effects are mediated by the specific expression of the NGF neurotrophic tyrosine kinase receptor type 1 (trkA(NGFR)) and/or the pan-neurotrophin glycoprotein receptor (p75(NTR)). Therefore, a conjunctival myoFB model (TGFβ1-induced myoFB) was developed and characterized for cell viability/proliferation as well as αSMA, p75(NTR) and trkA(NGFR) expression. MyoFB were exposed to acute and chronic NGF treatment and examined for their p75(NTR)/trkA(NGFR), αSMA/TGFβ1 expression, and apoptosis. Both NGF treatments significantly increased the expression of p75(NTR), associated with a deregulation of both αSMA/TGFβ1 genes. Acute and chronic NGF exposures induced apoptosis in p75(NTR) expressing myoFB, an effect counteracted by the specific trkA(NGFR) and/or p75(NTR) inhibitors. Focused single p75(NTR) and double trkA(NGFR)/p75(NTR) knocking-down experiments highlighted the role of p75(NTR) in NGF-induced apoptosis. Our current data indicate that NGF is able to trigger in vitro myoFB apoptosis, mainly via p75(NTR). The trkA(NGFR)/p75(NTR) ratio in favor of p75(NTR) characterizes this process. Due to the lack of effective pharmacological agents for balanced tissue repairs, these new findings suggest that NGF might be a suitable therapeutic tool in conditions with impaired tissue healing.

In vitro effect of a corrosive hostile ocular surface on candidate biomaterials for keratoprosthesis skirt

Aim

Keratoprosthesis (KPro) devices are prone to long-term corrosion and microbiological assault. The authors aimed to compare the inflammatory response and material dissolution properties of two candidate KPro skirt materials, hydroxyapatite (HA) and titania (TiO₂) in a simulated in vitro cornea inflammation environment.

Methods

Lipopolysaccharide-stimulated cytokine secretions were evaluated with human corneal fibroblasts on both HA and TiO₂. Material specimens were subjected to electrochemical and long-term incubation test with artificial tear fluid (ATF) of various acidities. Topography and surface roughness of material discs were analysed by scanning electron microscopy and atomic force microscopy.

Results

There were less cytokines secreted from human corneal fibroblasts seeded on TiO₂ substrates as compared with HA. TiO₂ was more resistant to the corrosion effect caused by acidic ATF in contrast to HA. Moreover, the elemental composition of TiO₂ was more stable than HA after long-term incubation with ATF.

Conclusions

TiO₂ is more resistant to inflammatory degradation and has a higher corrosion resistance as compared with HA, and in this regard may be a suitable material to replace HA as an osteo-odonto-keratoprosthesis skirt. This would reduce resorption rates for KPro surgery.

Ocular surface inflammation is regulated by innate immunity

On the ocular surface, as in the intestines and airway, the surface epithelium serves a critical function as the front-line defense of the mucosal innate immune system. Although the detection of microbes is arguably the most important task of the immune system, an exaggerated epithelial host defense reaction to endogenous bacteria may initiate and perpetuate inflammatory mucosal responses. In this review we first describe commensal bacteria found on the ocular surface, which is in contact with the ocular surface epithelium. We also discuss the innate immunity of the ocular surface epithelium and we present the allergic reaction regulated by ocular surface epithelial cells. We address ocular surface inflammation due to disordered innate immunity and we present our hypothesis that the onset of Stevens-Johnson syndrome (SJS) with severe ocular surface complications, a devastating ocular surface inflammatory disease, is strongly associated with abnormality of the innate immune system. In this review we raise the possibility that some ocular surface inflammatory diseases are pathogenetically related with a disordered innate immune response. Focusing on the innate immunity of the ocular surface might help to elucidate the pathogenesis of various ocular surface diseases.

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.

Expression of interleukin-4 receptor α in human corneal epithelial cells

PURPOSE

We previously reported that human conjunctival epithelial cells expressed functioning interleukin-4 receptor α (IL-4Rα). In this study, we investigated whether human corneal epithelial cells also express functioning IL-4Rα.

METHODS

The presence of IL-4Rα mRNA and protein in human corneal epithelium was examined by reverse-transcriptase polymerase chain reaction (RT-PCR) and immunohistology, respectively. The cell surface expression of IL-4Rα and the transcripts upregulated upon IL-4Rα ligand (IL-4 or IL-13) stimulation were examined by flow cytometry and quantitative RT-PCR, respectively, using immortalized human corneal-limbal epithelial (HCLE) cells.

RESULTS

The mRNA and protein of IL-4Rα were detected in human corneal epithelium. Flow cytometry analysis showed the cell surface expression of IL-4Rα protein. Quantitative RT-PCR assay of HCLE cells showed the upregulation of the transcripts tumor necrosis factor alpha-induced protein 6 (TNFAIP6), RAS guanyl-releasing protein 1 (RASGRP1), carbonic anhydrase II (CA2), cytokine-inducible SH2-containing protein (CISH), hyaluronan synthase 3 (HAS3), calpain 14 (CAPN14), endothelin receptor type A (EDNRA), cathepsin C (CTSC), and lecithin retinol acyltransferase (LRAT) as well as human conjunctival epithelial cells.

CONCLUSION

Human corneal epithelial cells expressed functioning IL-4Rα, and stimulation of its ligands, IL-4 and IL-13, could induce the expression of various genes, e.g., antiinflammatory molecule genes such as TNFAIP6 and CISH and cellular differentiation and proliferation-related molecule genes such as RASGRP1, HAS3, EDNRA, and LRAT.

Ocular surface disease: a case of vernal keratoconjunctivitis

Vernal keratoconjunctivitis (VKC) is a recurrent, chronic allergic inflammation of the ocular surface associated with remodeling of the cornea and conjunctiva, with a potential to adversely affect the patient's vision and quality of life. It affects mainly children and young adults. The purpose of this interventional case report is to present a typical case of limbal VKC, which was unresponsive to antiallergic treatment alone. A 5-year-old boy, who was previously unsuccessful with conventional anti-allergic therapy alone, presented with clinicopathological features pathognomonic of limbal VKC. The patient was successfully managed with a combination of palliative, anti-allergic and anti-inflammatory therapy. Prophylaxis with an anti-allergic pharmaceutical agent was initiated for long term use to prevent the release of allergic mediators. This case highlights the importance of prescribing the most appropriate pharmaceutical medication for VKC since conjunctival fibroproliferative lesions are often resistant to anti-allergy therapy. Allergic inflammatory mediators are responsible for the fibroproliferative changes of the conjunctiva and corneal lesions in VKC. Thus, it is crucial to prescribe the most appropriate pharmaceutical medication that will prevent the release of allergic inflammatory mediators, control the allergic inflammatory cascade and prevent ocular surface damage. The fine points of this case are presented with a review of applicable literature.

Case report of restoration of the corneal epithelium in a patient with atopic keratoconjunctivitis resulting in amelioration of ocular allergic inflammation

BACKGROUND

Atopic and vernal keratoconjunctivitis are severe types of ocular allergic disease characterized not only by conjunctival inflammation but also by corneal involvement. In vitro studies have suggested that breakdown of corneal epithelial barrier function and subsequent activation of stromal fibroblasts may amplify ocular allergic inflammation.

CASE SUMMARY

A 27-year-old man with atopic dermatitis developed atopic keratoconjunctivitis including corneal ulcer with plaque deposition in his right eye. Conjunctival inflammation in the right eye was resistant to topical steroid therapy. Surgical removal of corneal plaque and administration of autologous fibronectin eyedrops resulted not only in resurfacing of the corneal epithelium but also in amelioration of conjunctival inflammation.

DISCUSSION

This case suggests that loss of corneal epithelial integrity likely exacerbates conjunctival allergic inflammation and that restoration or maintenance of the barrier function of the corneal epithelium may be one of the important targets for the treatment of severe ocular allergic diseases.

Cytokines and chemokines in immune-based ocular surface inflammation

Altered levels of several cytokines and chemokines have been found in different types of inflammatory ocular surface diseases, such as allergy or dry-eye syndrome. It has also been demonstrated that epithelial cells play a key role in the persistence and even initiation of chronic mucosal inflammation. The recent development of 'multiplex detection' technologies has facilitated the identification of specific patterns of expression of these molecules in some ocular immune-based inflammatory disorders. Analysis of these molecules in tissues, cells (in vivo and in vitro) and tears has revealed that not only inflammatory cells but also epithelial and fibroblast resident cells are sources of these molecules. The purpose of this review is to summarize recent studies in this field.

Prostaglandin E receptor subtype EP3 in conjunctival epithelium regulates late-phase reaction of experimental allergic conjunctivitis

BACKGROUND

We previously demonstrated that the prostaglandin E(2) (PGE(2))-EP3 pathway negatively regulates allergic reactions in a murine allergic asthma model.

OBJECTIVES

We investigated whether the PGE(2)-EP3 pathway also regulates the development of murine experimental allergic conjunctivitis (EAC).

METHODS

The expression of EP3 was examined by means of RT-PCR and immunohistochemistry in wild-type mice, as well as by means of 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside staining in mice deficient in EP3 (Ptger3(-/-) mice) carrying the beta-galactosidase gene at the EP3 gene locus. EAC was induced by immunization of mice with short ragweed pollen (RW), followed by challenge with eye drops of RW, and eosinophil infiltration and eotaxin-1 mRNA expression in the conjunctiva were examined. Mice were also treated with a topical application of an EP3-selective agonist during the elicitation phase. Quantitative RT-PCR was used to detect expression of COXs and prostaglandin E synthases, and ELISA was used to measure PGE(2) production in the eyelid.

RESULTS

EP3 was constitutively expressed in conjunctival epithelium on the ocular surface. Ptger3(-/-) mice demonstrated significantly increased eosinophil infiltration in conjunctiva after RW challenge compared with wild-type mice. Consistently, significantly higher expression of eotaxin-1 mRNA was observed in Ptger3(-/-) mice. Conversely, treatment of wild-type mice with an EP3-selective agonist resulted in a significant decrease in eosinophil infiltration, which was blunted in Ptger3(-/-) mice. Expression of COX-2 and prostaglandin E synthases was upregulated and PGE(2) content was increased in the eyelids after RW challenge.

CONCLUSION

These data suggest that PGE(2) acts on EP3 in conjunctival epithelium and downregulates the progression of EAC.

Immunopathogenesis of ocular allergy: a schematic approach to different clinical entities

PURPOSE OF REVIEW

The immunopathogenesis of ocular allergic disorders is generally related to the specific immunoglobulin E-mediated mast cell activation and the following cascade of inflammatory mediators. Seasonal and perennial allergic conjunctivitis, however, are the only ocular diseases to involve solely type I hypersensitivity. The other main forms, vernal and atopic keratoconjunctivitis, have a more complex immunological basis and a chronic inflammatory component. Involvement of inflammatory cells, particularly eosinophils and T cells, cytokines and proteases can lead to more serious corneal damage with vision-threatening potential.

RECENT FINDINGS

Experimental allergic conjunctival models and clinical research studies have shown that T helper type 2-related mechanisms are definitely involved in the sensitization phase of ocular allergy, however, both T helper type 1 and type 2 cytokines are overexpressed in the active disease, contributing to the development of ocular inflammation.

SUMMARY

A review of the recent literature allows us to better understand the mechanisms involved in the development of ocular allergy and to guide us toward a more schematic approach, which could possibly be useful in forming a new classification, standardizing clinical phases and individuating new treatment targets.

Classification of ocular allergy

PURPOSE OF REVIEW

The purpose of this article is to summarize the clinical presentations associated with the classification of ocular allergy. This article also serves to summarize recent findings of pathophysiological mechanisms associated with ocular allergy and to highlight recently improved diagnostic methods for ocular allergic inflammation.

RECENT FINDINGS

The term allergic conjunctivitis may not sufficiently describe all forms of allergic eye disease, thus a new classification system is desirable, preferably derived from the varied pathophysiological mechanisms operating in the different forms of ocular allergy. Recent published material has further characterized the roles that inflammatory and structural cells have in ocular allergic inflammation. Improved diagnostic methods have also been developed to assess the underlying causes of ocular allergy.

SUMMARY

The underlying immune responses of ocular allergies are complex, indicating the critical need to understand the pathophysiology behind these diseases. Extensive research over the past several years has provided valuable insight into understanding the pathophysiology associated with the different forms of allergic conjunctivitis. Further clarification of the mechanisms associated with different forms of ocular allergy is essential for improved methods of classification, diagnosis, and treatment.