Corneal epithelial proliferation and thickness in a mouse model of dry eye

Although several studies have previously focused on the conjunctival epithelial response to surface dryness, little is known about the effect of a dry environment on corneal epithelium, which is the most clinically significant tissue affected in dry eye. The aim of this study was to quantitatively evaluate the effect of desiccating stress on the number of proliferating corneal epithelial cells and corneal epithelial thickness in mice placed in a controlled-environment chamber (CEC) that induces dry eye. Corneal epithelial cell proliferation and thickness were studied in 8- to 12-week-old female BALB/c mice placed in the CEC (temperature: 22.3+/-0.7 degrees C; relative humidity: 22.5+/-4.5%; airflow: 15 L/min) for 7 days and compared to a control group of mice with no dry eye. Actively proliferating cells were identified by immunofluorescence using a FITC-conjugated antibody against the Ki-67 protein, a cell proliferation marker expressed during active phases of the cell cycle. To detect the spatial distribution of proliferative cells, Ki-67(+) cells were counted in three areas of the epithelium: center, periphery, and limbus. Corneal epithelial thickness was evaluated in the central cornea after staining with hematoxylin-eosin. Results from each experimental group were compared using the Mann-Whitney test. The number of Ki-67(+) cells observed in the corneal epithelium of mice exposed to the CEC was significantly higher in each area (center: 32.1+/-1.1; periphery: 94.2+/-5.3; limbus: 4.0+/-1.5) than in the control group (center: 13.2+/-1.0, p=0.02; periphery: 42.9+/-2.3, p=0.02; limbus: 0.0, p=0.01). In mice subjected to desiccating stress, a significant number of Ki-67(+) positive cells were detected in the basal and suprabasal cell layers (central area 46%; periphery 30.8%: limbus 0%), whereas in the control group the cells were exclusively distributed through the basal cell layer. Ki-67(+) cells were not found in the corneal stroma or endothelium in any group. The corneal epithelium was found to be significantly thicker in dry eye mice (54.94+/-6.09 microm) as compared to the controls (43.9+/-6.23 microm, p<0.0001) by a mean of 25%. These results demonstrate that desiccating stress increases corneal epithelial turnover and thickness, similar to what is observed in other chronic inflammatory states of other epithelialized surfaces. The CEC can facilitate the study of the regulation of epithelial cell function and turnover at the molecular and cellular levels under desiccating stress conditions.

Very late antigen 1 blockade markedly promotes survival of corneal allografts

OBJECTIVE

To investigate the role of very late antigen 1 (VLA-1) (also known as integrin receptor alpha(1)beta(1)) in corneal transplantation inflammation and allograft survival.

METHODS

Cell infiltration and vasculogenesis (both angiogenesis and lymphangiogenesis) associated with allodisparate corneal transplantation were assessed in VLA-1-deficient conditions and controls by immunofluorescent microscopic studies. Corneal allograft survival was also assessed after anti-VLA-1 antibody treatment and in VLA-1 knockout recipient mice.

RESULTS

Anti-VLA-1 antibody treatment leads to a profound reduction in the granulocytic, monocytic, and T-cell infiltration after corneal transplantation. In addition, corneal angiogenesis and lymphangiogenesis were both significantly suppressed in VLA-1 knockout mice. Remarkably, universal graft survival was observed in both anti-VLA-1 antibody treatment and knockout mice.

CONCLUSIONS

Very late antigen 1 blockade markedly reduces inflammation and inflammation-induced tissue responses, including vasculogenic responses, associated with corneal transplantation and promotes allograft survival.

CLINICAL RELEVANCE

These studies offer insights into important integrin-mediated mechanisms of corneal transplant-related inflammation and provide possible new integrin-based immunotherapies for transplant rejection.

Effect of the ocular microenvironment in regulating corneal dendritic cell maturation

OBJECTIVE

To determine whether the ocular anterior segment (aqueous humor and cornea) actively inhibits dendritic cell (DC) maturation.

METHODS

Dendritic cells were injected into syngeneic corneas or conjunctivae, and their surface major histocompatibility complex class II expression in response to the local milieu was assessed using confocal microscopy. Immature DCs were cocultured with corneal supernatant or with aqueous humor to evaluate their regulation of DC phenotypic and functional maturity.

RESULTS

In contrast to conjunctivally injected DCs, DCs injected into the cornea resisted up-regulation in expression of surface major histocompatibility complex class II. Corneal supernatant-treated and aqueous humor-treated DCs retained their immaturity, as reflected by high antigen uptake but low costimulatory molecule (CD80 and CD86) expression and poor T-cell stimulation. Anti-transforming growth factor beta(2) treatment of aqueous humor and of corneal supernatant led to complete and partial blockade of their inhibition of DC maturation, respectively. However, alpha-melanocyte-stimulating hormone and calcitonin gene-related peptide had no demonstrable effect on DC maturation.

CONCLUSION

Cornea and aqueous humor, principally through transforming growth factor beta(2,) promote generation of phenotypically and functionally immature DCs. Clinical Relevance Our results indicate that relative immune quiescence in the cornea and in the anterior segment is actively maintained in part by the inhibitory effect of transforming growth factor beta(2) on resident DCs and by their suppression of T-cell-mediated immune and inflammatory responses.

Exposure to a dry environment induces strain-specific responses in mice

Most current animal models of dry eye have a single causative mechanism and do not take into consideration the influence of environmental conditions on tear secretion and associated ocular surface signs. Since immunity and inflammation have been implicated in dry eye pathogenesis, and different mouse strains are known to have differentially biased immune responses, we conducted the present study to test the hypothesis that strains with specifically polarized T cell responses (T helper-1 [Th1] vs. T helper-2 [Th2]) develop differential signs of dry eye when exposed to a controlled low humidity setting. Eight to 12-week-old BALB/c (Th2 biased) and C57BL/6 (Th1 biased) mice were placed in a controlled environment chamber (CEC) where relative humidity (RH), temperature (T), and air flow (AF) were continuously regulated and monitored. Mice were exposed to specific environmental controlled conditions (RH=15.5+/-3.8%, AF=15 l/min, T=21-23 degrees C) for 3 to 7 days. Aqueous tear production by means of the cotton thread test, corneal fluorescein staining (NEI grading scheme, score 0-15) and goblet cell density in the superior and inferior conjunctivae were measured by a masked observer. No statistically significant differences between the groups were found at baseline. Statistically significant decreases in tear secretion were seen after exposure to the CEC environment. Mean cotton thread wetting was 1.9+/-0.2 (baseline), 1.4+/-0.3 (day 3), and 0.9+/-0.2 mm (day 7) for BALB/c mice, and 1.7+/-0.3 (baseline), 0.9+/-0.3 (day 3), and 0.4+/-0.2 mm (day 7) for C57BL/6 mice. These mice showed reduced tear secretion as compared to BALB/C at each time point tested (P<.005, t-test). Both BALB/c and C57BL/6 mice showed a significant increase in corneal fluorescein staining at both day 3 and day 7 as compared to baseline. With exposure to the CEC goblet cell density significantly decreased in the superior and inferior conjunctivae in BALB/c mice, while it remained unchanged in C57BL/6 mice. This study indicates that exposure of non-pharmacologically modified mice to a low humidity environment in the CEC can lead to significant alterations in tear secretion, goblet cell density, and acquisition of dry eye-related ocular surface signs which are strain-specific.

Dry eye syndromes

Over the past 20 years it has become clear that dry eye syndrome (DES) or keratoconjunctivitis sicca (KCS) is a complex multifactorial disease characterized by an immune and inflammatory process that affects the lacrimal glands and ocular surface. In this paradigm, inflammation is seen as both the cause and consequence of conjunctival and corneal cell damage. In this chapter, we identify the unique characteristics of the lacrimal gland, the role of epithelial cells, regulatory T cells, and cytokines in maintaining ocular surface homeostasis and tear secretion function. We analyze the factors inducing loss of the lacrimal gland homeostasis and its consequences, and in so doing hope to provide a picture of the role of the immune system in the pathophysiology of KCS and useful information to help understand the complexity of DES.

Keratocyte apoptosis and failure of corneal allografts

BACKGROUND

Murine models of high-risk and low-risk corneal transplantation were used to determine the role of keratocyte apoptosis in the failure of orthotopic allogeneic corneal transplants.

MATERIALS AND METHODS

Normal (low-risk, low-rejecting) and inflamed/vascularized (high-risk, high-rejecting) BALB/c recipient beds received fully mismatched C57BL/6 corneal allografts. Apoptosis was detected in the corneal stroma at various time points using an in situ terminal deoxynucleotide tranferase-mediated dUTP nick-end labeling assay, and ex vivo via Western analysis for active caspase-3. Apoptosis was also measured in a (donor-type) C57BL/6 keratocyte cell line after stimulation of Fas or via use of various pro-inflammatory cytokines.

RESULTS

Significantly more apoptotic cells were present in the stroma of rapidly rejecting high-risk corneal allografts compared with low-risk grafts. Apoptotic cells were shown to be nearly uniformly CD45 and hence of a non-hematopoetic lineage. Apoptosis, however, was not present in highly inflamed but ungrafted corneas. Apoptosis was induced in keratocytes in vitro by dual stimulation with agonistic Fas mAb and either interleukin-1beta or tumor necrosis factor-alpha.

CONCLUSION

Apoptosis of resident non-bone marrow-derived fibroblastic cells of the corneal stroma is strongly correlated with the failure of corneal allografts, particularly in the highly inflamed microenvironment of the high-risk allograft.

Novel expression and characterization of lymphatic vessel endothelial hyaluronate receptor 1 (LYVE-1) by conjunctival cells

PURPOSE

Lymphatic vessel endothelial hyaluronic acid receptor (LYVE-1) is a newly discovered lymphatic-specific marker. To date, there is no report of its expression on conjunctival cells. The purpose of this study was to investigate the expression of LYVE-1 in normal conjunctiva, to phenotype LYVE-1+ cells, and to study changes in their expression levels during corneal inflammation.

METHODS

Flat-mounted conjunctivae or cross sections of eyeballs were harvested from BALB/c mice (6-8 weeks of age) for immunofluorescent confocal microscopic studies.

RESULTS

The data demonstrate, for the first time, that in addition to its expression on lymphatic vessels, LYVE-1 was expressed on CD45+, CD11b+, and CD31- conjunctival cells, indicating a bone-marrow-derived monocytic lineage. Surprisingly, the number of cells that expressed LYVE-1 decreased during corneal inflammation, in conjunction with ingrowth of lymphatics into the cornea.

CONCLUSIONS

A new population of monocytic cells has been found to express LYVE-1 in normal conjunctiva. These cells that normally express LYVE-1 may act as a reservoir for lymphangiogenesis and cell recruitment when the immune system is challenged.

Distribution of Conjunctival HLA-DR Expression and the Pathogenesis of Damage in Early Dry Eyes

PURPOSE

To examine the expression of HLA-DR, a marker of inflammation, in the early stages of dry eye disease and to locate the appearance of this marker on specific areas of the bulbar conjunctiva.

METHODS

Dry eye patients were identified and their condition classified as mild (n = 16) or moderate (n = 16) based on Schirmer testing, vital staining, tear break-up time, and symptom questionnaire scores. Brush cytology was used to collect epithelial cells from the nasal, temporal, and superior conjunctivae of patients and age-matched controls. HLA-DR positive cells were detected by immunohistochemical staining and quantified.

RESULTS

Patients with moderate dry eye had the highest rate of conjunctival HLA-DR-positive cells, with significantly higher rates than controls regardless of which region of the conjunctiva was sampled (P < 0.01). The mild dry eye group had similar rates of HLA-DR-positive cells in the superior conjunctival region compared with controls. However, in the nasal and temporal regions, they displayed a significantly higher rate of HLA-DR-positive cells than controls (P < 0.01) and the nasal region showed a significant difference (P < 0.01) when compared with the temporal one. Some of these mild dry eyes had no vital staining.

CONCLUSIONS

The HLA-DR expression pattern in mild and moderate dry eyes appears to reflect disease progression. Overexpression of HLA-DR in mild dry eyes showing no vital staining suggests that inflammation may be a primary cause of ocular surface damage. These data support the use of immunomodulatory drugs in the treatment of dry eye disease.

Radiotherapy-Induced Ocular Surface Disease

Today radiation is routinely used as a therapeutic modality for select tumors of the orbit, adnexa, paranasal sinus, and nasopharynx. Despite significant improvements in mechanisms of delivery and protective shielding, acute and chronic complications of radiation can affect different segments of the eye. In this report, we provide an overview of ocular damage secondary to radiotherapy. We identify the characteristic clinical changes and underlying pathophysiologic mechanisms involving the ocular surface and provide a rational approach to their prevention and treatment.

The Controlled-Environment Chamber: A New Mouse Model of Dry Eye

PURPOSE

To develop a controlled-environment chamber (CEC) for mice and verify the effects of a low-humidity setting on ocular surface signs in normal mice.

METHODS

Eight- to 12-week-old BALB/c mice were used in a controlled-environment chamber (CEC) where relative humidity (RH), temperature (T), and airflow (AF) are regulated and monitored. Mice were placed into the CEC and exposed to specific environmentally controlled conditions (RH = 18.5% +/- 5.1%, AF = 15 L/min, T = 21-23 degrees C) for 3, 7, 14, and 28 days. Control mice were kept in a normal environment (RH = 50%-80%, no AF, T = 21-23 degrees C) for the same duration. Aqueous tear production by means of the cotton thread test, corneal fluorescein staining (score, 0-15), and goblet cell density in the superior and inferior conjunctiva were measured by a masked observer.

RESULTS

No statistically significant differences between the groups were found at baseline. Decreased tear secretion and increased corneal fluorescein staining were significantly present on day 3, 7, 14, and 28 in animals kept in the CEC. Goblet cell density was significantly decreased in the superior conjunctiva on day 7, and on day 3, 7, and 14 in the inferior conjunctiva in the CEC-kept mice compared with control animals.

CONCLUSIONS

This study indicates that exposure of normal mice to a low-humidity environment in a CEC can lead to significant alterations in tear secretion, goblet cell density, and acquisition of dry eye-related ocular surface signs.

Automated Lamellar Keratoplasty for Recurrent Granular Corneal Dystrophy After Phototherapeutic Keratectomy

PURPOSE

To evaluate the safety and efficacy of automated lamellar keratoplasty for the treatment of recurrent granular corneal dystrophy after phototherapeutic keratectomy (PTK).

METHODS

We performed a prospective interventional noncomparative case study of nine eyes (seven patients) with severe recurrent granular corneal dystrophy after PTK. An automated microkeratome was used to cut partial-thickness sections through the anterior surface of the donor and host corneas. The donor disc was placed on the recipient bed with four or eight interrupted sutures. The sutures were removed between 4 and 6 weeks postoperatively. Visual acuity, corneal clarity, corneal thickness, and corneal topography were assessed before and at different time points after surgery.

RESULTS

During a mean follow-up period of 18.9 +/- 4.1 months, all grafts were transparent without visible opacity at the interface, and no serious complications occurred. In all cases, the visual acuity improved: seven eyes had best spectacle-corrected visual acuity of > or = 20/40; two eyes reached 20/25. At last follow-up > 12 months postoperatively, the mean corneal refractive power had significantly increased by 2.34 +/- 0.93 diopters (D) (P<.001), and the corneal astigmatism significantly decreased by 0.91 +/- 0.98 D (P<.05). The mean corneal thickness was 477.4 +/- 26.9 microm preoperatively and 507.8 +/- 23.4 microm at last follow-up (P<.001).

CONCLUSIONS

Our findings suggest that automated lamellar keratoplasty for the treatment of recurrent granular corneal dystrophy is a safe and effective method of improving visual acuity, but recurrence remains a risk.

Effects of a 0.9% sodium chloride ophthalmic solution on the ocular surface of symptomatic contact lens wearers

BACKGROUND

Ocular surface-related discomfort is the main reason for stopping contact lens wear. We carried out a study to evaluate the efficacy of preservative-free artificial tears containing 0.9% sodium chloride on ocular surface signs and symptoms in contact lens wearers experiencing discomfort and its possible influence on the duration of contact lens wear.

METHODS

We studied 49 contact lens wearers experiencing discomfort who had normal results of slit-lamp biomicroscopy, a fluorescein tear film break-up time (BUT) of 10 seconds or more, and wetting greater than 5 mm in 5 minutes on the Schirmer 1 test with and without anesthesia. Twenty-nine subjects (16 men and 13 women with a mean age of 32.5 years [standard deviation (SD) 8.7 years]) received one instillation of the 0.9% sodium chloride solution four times daily in the lower conjunctival fornix for 21 days. Twenty subjects (12 men and 8 women with a mean age of 35.1 [SD 6.2] years) received no drops and served as a control group. The overall comfort and duration of contact lens wear, results of tear film analysis and adverse events were recorded on days 7 and 21. Patients rated their symptoms (while not receiving any medications or hydrating solutions) on a 100-mm visual analogue scale with "Excellent (lenses not felt)" at the left and "Very uncomfortable (lenses cause irritation or discomfort)" at the right. Measurement of corrected visual acuity, slit-lamp examination, determination of the tear film BUT, the Schirmer 1 test with and without anesthesia, and assessment of the colour and surface of the lens were performed at baseline and at day 21. We analysed the data for the more uncomfortable eye or, if the eyes were equally uncomfortable, the right eye.

RESULTS

Significant lessening of ocular discomfort was observed in the treatment group during the study: the mean rating on the visual analogue scale at baseline was 60.2 mm (SD 12.7 mm), compared with 35.8 mm (SD 18.0 mm) at day 21 (p < 0.001, Student's t test). The duration of contact lens wear was significantly longer at day 21 than at baseline (7.0 [SD 2.6] hours vs. 6.4 [SD 2.6] hours, p < 0.05, Student's t test), and the proportion of subjects with conjunctival hyperemia was significantly lower at day 21 (48.3% vs. 82.8%, p < 0.05, chi2 test). No statistically significant changes were observed in tear film BUT, results of the Schirmer 1 test, corneal punctate staining by fluorescein or results of tear film analysis. The treatment was well tolerated by all patients. No significant differences in any of the variables studied were observed in the control group.

INTERPRETATION

Treatment with a preservative-free 0.9% sodium chloride ophthalmic solution reduced ocular surface discomfort and extended the duration of contact lens wear without interfering with the tear film or contact lens materials. Long-term studies are needed to confirm the role of this solution in reducing discomfort experienced by contact lens wearers.

Tear film and ocular surface tests in animal models of dry eye: uses and limitations

Many ocular surface tests have been developed for the clinical diagnosis of keratoconjunctivitis sicca, and several have been used to 'validate' animal models of Sjogren's and non-Sjogren's dry eye. However, many of these tests themselves have not been systematically studied or standardized, and yet their use in animal models of dry eye is common. This review provides a rational approach and systematic review of the tear film and ocular surface tests described in the literature that may be applicable to the current animal models of dry eye, with particular emphasis on their limitations, along with some suggestions regarding their standardization and applications in eye research.

Amniotic membrane transplantation in a case of ligneous conjunctivitis

PURPOSE

To report a case of ligneous conjunctivitis treated with amniotic membrane transplantation.

DESIGN

Interventional case report.

METHODS

A 44-year-old woman presented with woodlike lesions in the upper and lower tarsal conjunctiva, blepharoptosis, and reduced visual acuity in the left eye. After confirmation of the diagnosis of ligneous conjunctivitis, she underwent amniotic membrane transplantation.

RESULTS

At the 2-month, 4-month, and 6-month examinations, the tarsal conjunctiva appeared free from membranes. At 8 months, the patient underwent amniotic membrane transplantation for small recurrences. At the 36-month examination, no membranes were evident, and visual acuity was 20/20.

CONCLUSIONS

In this first report of amniotic membrane transplantation in a case of ligneous conjunctivitis, we found that conjunctival reconstruction shows promising results in this difficult-to-manage disease.