Twenty-five-year panorama of corneal immunology: emerging concepts in the immunopathogenesis of microbial keratitis, peripheral ulcerative keratitis, and corneal transplant rejection

Gene therapy in corneal transplantation

Corneal transplantation is the most commonly performed organ transplantation. Immune privilege of the cornea is widely recognized, partly because of the relatively favorable outcome of corneal grafts. The first-time recipient of corneal allografts in an avascular, low-risk setting can expect a 90% success rate without systemic immunosuppressive agents and histocompatibility matching. However, immunologic rejection remains the major cause of graft failure, particularly in patients with a high risk for rejection. Corticosteroids remain the first-line therapy for the prevention and treatment of immune rejection. However, current pharmacological measures are limited in their side-effect profiles, repeated application, lack of targeted response, and short duration of action. Experimental ocular gene therapy may thus present new horizons in immunomodulation. From efficient viral vectors to sustainable alternative splicing, we discuss the progress of gene therapy in promoting graft survival and postulate further avenues for gene-mediated prevention of allogeneic graft rejection.

Amniotic membrane transplantation in surgically induced necrotizing scleritis with peripheral ulcerative keratitis

A case of surgically induced necrotizing scleritis (SINS) after manual small incision cataract surgery that was associated with peripheral ulcerative keratitis (PUK) at a different site. Neither pathology responded to systemic steroids and progressed to become sight threatening, which is unusual. Progression of SINS was aggressive enough to cause a limbal wound gape, similarly PUK extended up to Descemet's membrane and emergency amniotic membrane transplantation (AMT) was required to save the globe. AMT may regress the scleral and corneal melting successfully. It is not common to observe SINS with PUK at a different site that is unresponsive to systemic steroids. AMT, though palliative treatment, was effective at treating this condition successfully.

Interleukin 11 expression in the normal canine eye

OBJECTIVES

The purpose of this study was to characterize the expression of interleukin-11 (IL-11), a cytokine with anti-inflammatory, cytoprotective, and immune-modulating characteristics, in the canine eye.

PROCEDURES

Normal canine eyes were collected from clinically healthy dogs that had been euthanized for reasons unrelated to this study. The distribution of IL-11 expression in the different ocular layers was evaluated by immunofluorescence (eight eyes). Expression levels were quantified (based on fluorescence intensity) using pixel density analysis. Primary cell cultures were derived from all three corneal cell layers. IL-11 mRNA expression was assessed in these cultures using quantitative RT-PCR before and after treatment with TGF-β1, a known inducer of IL-11 expression. IL-11 protein expression was also assessed in the media of these cells by Western blot analysis.

RESULTS

IL-11 protein was detected in the corneal epithelium, keratocytes, and the corneal endothelium of the normal canine eyes examined using immunofluorescence. Baseline IL-11 mRNA expression was noted in the corneal epithelium, fibroblasts, and endothelium using quantitative RT-PCR. Treatment of canine corneal cell lines with TGF-β1 resulted in statistically significant increases in IL-11 expression in the corneal epithelium, endothelial and fibroblast cell lines with strongest induction noted in the fibroblasts and endothelium.

CONCLUSION

This is the first description of IL-11 expression in the canine eye. The protein and mRNA appear to be constitutively present throughout all layers of the cornea and are increased by TGF-β1, a cytokine important in ocular inflammation and disease.

Femtosecond laser lenticule transplantation in rabbit cornea: experimental study

PURPOSE

To evaluate the feasibility of femtosecond laser-induced lenticule transplantation in the rabbit cornea and to observe the relative histologic characteristics of corneal tissue and nerve repair after transplantation.

METHODS

Eight healthy, purebred, New Zealand white rabbits underwent femtosecond laser small-incision lenticule extraction (SMILE) surgery in the right eye. Lenticules were inserted into a femtosecond laser-created corneal stromal pocket in the left eye, which was defined as femtosecond laser corneal lenticule transplantation. Postoperative observation and examination were completed to evaluate the surgery.

RESULTS

In the early postoperative period, inflammation of the cornea was noted, tissue around the lenticule was edematous, and cells were activated. Tissue edema remained at postoperative day 10. By 1 month, edema had resolved, activated cells gradually became quiescent, and nerve fiber regeneration was observed. By 3 months, the lenticule integrated into the recipient cornea, extracellular matrix gradually cleared, and thicker nerve fibers were noted. By 6 months postoperative, morphology and distribution of the corneal stromal fibers were close to normal, and the number of nerve fibers was reduced.

CONCLUSIONS

Femtosecond laser corneal lenticule transplantation in rabbits is feasible, as the lenticule was shown to thrive and integrate with the recipient stroma. Nerve regeneration begins after 1 month.

Corneal Allograft Rejection: Immunopathogenesis to Therapeutics

Corneal transplantation is among the most successful solid organ transplants. However, despite low rejection rates of grafts in the ‘low-risk’ setting, rejection can be as high as 70% when grafted into ‘high-risk’ recipient beds. Under normal homeostatic conditions, the avascular cornea provides a unique environment that facilitates immune and angiogenic privilege. An imbalance in pro-inflammatory, angiogenic and lymphangiogenic mediators leads to a breakdown in corneal immune privilege with a consequent host response against the donor graft. Recent developments in lamellar and endothelial keratoplasties have reduced the rates of graft rejection even more, while providing improved visual outcomes. The corneal layer against which an immune response is initiated, largely determines reversibility of the acute episode. While epithelial and stromal graft rejection may be treated with topical corticosteroids with higher success, acute endothelial rejection mandates a more aggressive approach to therapy due to the lack of regenerative capacity of this layer. However, current immunosuppressive regimens come with the caveat of ocular and systemic side effects, making prolonged aggressive treatment undesirable. With the advent of biologics, efficacious therapies with a superior side effect profile are on the horizon. In our review we discuss the mediators of ocular immune privilege, the roles of cellular and molecular immune players in graft rejection, with a focus on human leukocyte antigen and antigen presenting cells. Furthermore, we discuss the clinical risk factors for graft rejection and compare rates of rejection in lamellar and endothelial keratoplasties to traditional penetrating keratoplasty. Lastly, we present the current and upcoming measures of therapeutic strategies to manage and treat graft rejection, including an overview of biologics and small molecule therapy.

Update on peripheral ulcerative keratitis

Ulcerative inflammation of the cornea occurs in the perilimbal cornea, and is associated with autoimmune collagen vascular and arthritic diseases. Rheumatoid arthritis is the most frequent underlying disease. The tendency for peripheral location is due to the distinct morphologic and immunologic characteristics of the limbal conjunctiva, which provides access for circulating immune complexes to the peripheral cornea via the capillary network. Deposition of immune complexes in the terminal ends of limbal vessels initiates immune-mediated vasculitis, and causes inflammatory cell and protein leakage due to vessel wall damage. Development of peripheral ulcerative keratitis associated with systemic disease may represent worsening of a potentially life-threatening disease. Accompanying scleritis, particularly the necrotizing form, is usually observed in severe cases, which may result in corneal perforation and loss of vision. Although first-line treatment with systemic corticosteroids is indicated for acute phases, immunosuppressive and cytotoxic agents are required for treatment of peripheral ulcerative keratitis associated with multisystem disorders. Recently, infliximab, a chimeric antibody against proinflammatory cytokine tumor necrosis factor-alpha, was reported to be effective in cases refractory to conventional immunomodulatory therapy. The potential side effects of these therapies require close follow-up and regular laboratory surveillance.

Future of an "Asymptomatic" T-cell Epitope-Based Therapeutic Herpes Simplex Vaccine

Considering the limited success of the recent herpes clinical vaccine trial [1], new vaccine strategies are needed. Infections with herpes simplex virus type 1 and type 2 (HSV-1 & HSV-2) in the majority of men and women are usually asymptomatic and results in lifelong viral latency in neurons of sensory ganglia (SG). However, in a minority of men and women HSV spontaneous reactivation can cause recurrent disease (i.e., symptomatic individuals). Our recent findings show that T cells from symptomatic and asymptomatic men and women (i.e. those with and without recurrences, respectively) recognize different herpes epitopes. This finding breaks new ground and opens new doors to assess a new vaccine strategy: mucosal immunization with HSV-1 & HSV-2 epitopes that induce strong in vitro CD4 and CD8 T cell responses from PBMC derived from asymptomatic men and women (designated here as "asymptomatic" protective epitopes") could boost local and systemic "natural" protective immunity, induced by wild-type infection. Here we highlight the rationale and the future of our emerging "asymptomatic" T cell epitope-based mucosal vaccine strategy to decrease recurrent herpetic disease.

Cyclosporine immunomodulation retards regeneration of surgically transected corneal nerves

PURPOSE

To determine whether immunomodulation with cyclosporine (CsA) affects reinnervation after surgical transection of stromal nerves.

METHODS

Thy1-YFP+ neurofluorescent mice underwent lamellar corneal surgery and 3 days later, received artificial tears or CsA eye drops for 6 weeks. Serial in vivo wide-field stereofluorescent microscopy was performed to determine changes in nerve fiber density (NFD). Real-time quantitative PCR was performed to determine the expression of neurotrophins and cytokines (IL6 and TNF-α). Compartmental culture of trigeminal ganglion neurons was performed in Campenot devices to determine whether CsA directly affects neurite outgrowth.

RESULTS

Yellow fluorescent protein (YFP)-positive cells significantly increased at 3 and 7 days after surgery. The number of YFP-positive cells in the cornea was significantly lower in the CsA group than that in the control group. The percentage increase in NFD between 2 to 6 weeks was greater in the control group (80% ± 10%, P = 0.05) than that in the CsA group (39% ± 21%). The CsA group also exhibited lower expression of IL6 and TNF-α (P = 0.01). In compartmental culture experiments, neurite outgrowth toward side compartments containing CsA was significantly less (2.29 ± 0.4 mm, P = 0.01) than that toward side compartments containing vehicle (3.97 ± 0.71 mm).

CONCLUSIONS

Immunomodulation with CsA reduces the expression of cytokines (IL6) in the cornea and retards regenerative sprouting from transected corneal stromal nerve trunks. In addition, CsA has a direct growth inhibitory action on neurites as well.

The eye in rheumatology

Rheumatic conditions affect a wide variety of tissues, including the eye, and can cause significant visual loss. Early diagnosis coupled with appropriate management, using immunosuppression where necessary, can significantly improve the outcome. This article reviews the most common manifestations seen in clinical practice.

Differential effects of low- and high-dose glucocorticoids on the innate immunity of corneal epithelium in vitro

PURPOSE

To evaluate the effect of glucocorticoids on the innate immunity of corneal epithelial cells.

METHODS

Human corneal epithelial cell lines (HCEC) were co-cultured with LPS and hydrocortisone to determine whether hydrocortisone modulates the expression and function of TLR2, 4. The release of IL-6, 8 from cultured HCEC was measured in the presence and absence of specific blocking antibodies to TLR2, 4. The proteins of TLR2, 4 were also compared by Western blot.

RESULTS

Incubation of HCEC with LPS upregulated the expression of TLR2, 4 and increased the release of IL-6, 8. This upregulation was enhanced by low-concentration hydrocortisone, but inhibited by high-concentration hydrocortisone. The concentration of IL-6, 8 was also enhanced by low-concentration hydrocortisone and inhibited by high-concentration hydrocortisone.

CONCLUSIONS

Low-concentration hydrocortisone enhances the expression and function of TLRs in HCEC and provides evidence for a novel function of glucocorticoids in innate immunity.

Outcome of penetrating keratoplasty in corneal ulcer: a single-center experience

Background

Corneal ulcers often lead to scarring and astigmatism, and significant loss of vision is a common consequence.

Objective

To determine the rate of graft rejection, one of the most serious concerns with this procedure, and to evaluate the recovery of visual function in those patients for whom the operation was successful.

Methods

We describe a retrospective study of 33 corneal ulcer patients undergoing penetrating keratoplasty (PK) at the Tabriz Nikookari Eye Hospital.

Results

Mean age of the patients was 44 ± 14 years. Most common risk factors for active keratitis were trauma, dry eye, and malnutrition. Culture-positive results included bacterial keratitis (n = 15) and fungal keratitis (n = 5). Perforation was a significant risk factor for therapeutic failure (P < 0.05). Age or gender had no statistically significant effects on the PK outcome (P > 0.05). Postoperative visual acuity had a significant association with preoperative visual acuity (P < 0.01). Graft rejection rate (27.2%) was similar to that reported in the literature.

Conclusion

Although lamellar keratoplasty has recently been established, there are practical reasons for continuing the use of PK in centers such as ours, with due attention to the requirement for topical immunosuppression to diminish the rate of graft rejection and antimicrobial treatment to prevent postoperative infection.

B7 costimulation molecules encoded by replication-defective, vhs-deficient HSV-1 improve vaccine-induced protection against corneal disease

Herpes simplex virus 1 (HSV-1) causes herpes stromal keratitis (HSK), a sight-threatening disease of the cornea for which no vaccine exists. A replication-defective, HSV-1 prototype vaccine bearing deletions in the genes encoding ICP8 and the virion host shutoff (vhs) protein reduces HSV-1 replication and disease in a mouse model of HSK. Here we demonstrate that combining deletion of ICP8 and vhs with virus-based expression of B7 costimulation molecules created a vaccine strain that enhanced T cell responses to HSV-1 compared with the ICP8⁻vhs⁻ parental strain, and reduced the incidence of keratitis and acute infection of the nervous system after corneal challenge. Post-challenge T cell infiltration of the trigeminal ganglia and antigen-specific recall responses in local lymph nodes correlated with protection. Thus, B7 costimulation molecules expressed from the genome of a replication-defective, ICP8⁻vhs⁻ virus enhance vaccine efficacy by further reducing HSK.

Toward the development of an artificial cornea: improved stability of interpenetrating polymer networks

A novel interpenetrating network (IPN) based on poly(ethylene glycol) (PEG) and poly(acrylic acid) was developed and its use as an artificial cornea was evaluated in vivo. The in vivo results of a first set of corneal inlays based on PEG-diacrylate precursor showed inflammation of the treated eyes and haze in the corneas. The insufficient biocompatibility could be correlated to poor long-term stability of the implant caused by hydrolytic degradation over time. Adapting the hydrogel chemistry by replacing hydrolysable acrylate functionalities with stable acrylamide functionalities was shown to increase the long-term stability of the resulting IPNs under hydrolytic conditions. This new set of hydrogel implants now shows increased biocompatibility in vivo. Rabbits with corneal inlay implants are healthy and have clear cornea and non-inflamed eyes for up to 6 months after implantation.

Peripheral ulcerative keratitis in a patient with systemic-onset juvenile idiopathic arthritis

The recognition of ocular manifestations in juvenile idiopathic arthritis is critical. The authors report an unusual manifestation of corneal involvement in a 10-year-old girl with systemic-onset juvenile idiopathic arthritis who presented with unilateral peripheral ulcerative keratitis during arthritis exacerbation. Corneal inflammation was successfully managed with topical steroids, oral methylprednisolone, and methotrexate.

Cauterization of central cornea induces recruitment of major histocompatibility complex class II+ Langerhans cells from limbal basal epithelium

PURPOSE

The purpose of this study was to investigate the distribution and characterization of Langerhans cells (LCs) in the rat corneal epithelium and to compare the findings with those obtained earlier in the mouse corneal epithelium.

METHODS

Normal and cauterized corneal tissues were excised from Wistar rats, and immunofluorescence staining for major histocompatibility complex (MHC) class II, CD3, CD11c, CD11b, CD45, CD80(B-1), and CD86(B-2) was performed by confocal microscopy. The density of intraepithelial MHC class II+ LCs was quantified.

RESULTS

In the normal corneal epithelium, CD11c+ cells were exclusively distributed in the limbal and peripheral areas. Double staining showed that these cells were CD45 and MHC class II positive and B7 (CD80 or CD86) costimulatory molecules, CD11b, and CD3 negative, exhibiting a dendritic cell phenotype. In cauterized cornea, the expression of MHC class II was significantly enhanced in the limbal basal epithelium. The expression of the activation markers, CD80 and CD86, by MHC class II+ LCs was first present in the limbal basal epithelium as early as 4 hours after corneal inflammation and later throughout the entire corneal epithelium.

CONCLUSIONS

The present study demonstrates for the first time the distribution and characterization of LCs in the rat corneal epithelium, which largely resembles most of those observed in the mouse cornea. In the cauterized cornea, B7+ LCs were first present in the limbal basal epithelium, suggesting that these cells play an important role in corneal inflammatory reaction.

The expression of vascular endothelial growth factor C in transplanted corneas

PURPOSE

To discuss the expression of vascular endothelial growth factor C (VEGF-C) after keratoplasty in rats.

METHODS

The Fischer 344 rat corneas were transplanted into Lewis rat eyes. The expression of VEGF-C in cornea was examined by immunohistochemistry and real-time PCR. The association of corneal lymphangiogenesis, corneal inflammation, and rejection score (RS), with VEGF-C in transplanted corneas was also examined.

RESULTS

Both VEGF-C protein and mRNA upregulated dramatically in rat transplanted corneas. The immunoreactivity was at peak on the 3rd day and the 14th day after keratoplasty, respectively. VEGF-C mRNA was strongly and positively correlated with inflammatory index (IF) (r = 0.93; p < 0.01), lymphatic vessel counting (LVC) (r = 0.40; p < 0.05), and RS (r = 0.50; p < 0.05). The development of VEGF-C mRNA, IF, and RS was almost parallel in the second week after keratoplasty.

CONCLUSIONS

VEGF-C was expressed in rat transplanted corneas. The expression of VEGF-C correlated closely with corneal inflammation, corneal lymphangiogenesis, and allograft rejection.

Role of CCR7 in facilitating direct allosensitization and regulatory T-cell function in high-risk corneal transplantation

PURPOSE

Chemokine receptor 7 (CCR7) is a key homing molecule for immune cell trafficking, including corneal antigen-presenting cell (APC) migration from the inflamed cornea to draining lymph nodes (LNs). Here, the authors investigated the effect of CCR7-facilitated donor APC trafficking on allosensitization, regulatory T-cell (Treg) function, and graft survival in corneal transplantation.

METHODS

CCR7(-/-) or wild-type (WT) allogeneic corneal grafts were transplanted onto the neovascularized high-risk recipient beds. Two weeks later, the frequency of directly alloprimed host T cells was measured by the IFN-gamma ELISPOT assay. Treg function was tested by a coculture suppression assay and an IFN-gamma ELISPOT assay. Kaplan-Meier analysis was performed to evaluate graft survival.

RESULTS

The recipients of CCR7(-/-) grafts had fewer migrated donor APCs and lower frequency of IFN-gamma-producing T cells in the draining LNs. However, there was no statistically significant difference in transplant survival between recipients of CCR7(-/-) and those of WT grafts. Tregs from the CCR7(-/-) graft recipient group showed reduced regulatory potential for the suppression of proliferation of naive T cells and direct alloprimed T cells and expressed lower Foxp3 levels. In vitro studies confirmed that mature CCR7(+) major histocompatibility complex class II(+) CD86(+) graft-derived dendritic cells were critical for Treg function.

CONCLUSIONS

Not only is CCR7-mediated donor-derived APC trafficking to the draining LNs important in the initiation of host T-cell priming, it is crucial for Treg-mediated tolerance.

Local treatment with alpha-melanocyte stimulating hormone reduces corneal allorejection

BACKGROUND

Corneal grafting is by far the most common form of transplantation. Many grafts suffer from immune rejection and current therapies are associated with many side effects, requiring more effective and safe therapies. alpha-Melanocyte stimulating hormone (alpha-MSH) is a neuropeptide that suppresses host inflammatory defense mechanisms. The purpose of this study was to determine the role of local therapy with alpha-MSH on corneal allograft survival, and the mechanisms by which it may influence graft outcome.

METHODS

Orthotopic corneal transplantation was performed, with recipients receiving subconjunctival alpha-MSH or sham injections twice weekly. Grafts were followed up for 70 days, and graft inflammation/opacification was compared between the two groups in a masked fashion. Graft infiltration and ocular gene expression of select inflammatory cytokines was evaluated at different timepoints. Additionally, allospecific delayed-type hypersensitivity was compared among the groups 3 weeks posttransplantation.

RESULTS

Results showed a significant increase in corneal graft survival in alpha-MSH-treated recipients compared with controls. Although 75% of allografts in alpha-MSH-treated hosts survived at 70 days, 43% survived in controls (P=0.04). Graft infiltration studies demonstrated a significant decrease in the number of mononuclear and polymorphonuclear cells in alpha-MSH-treated mice compared with controls at days 7 and 14 after transplantation. Furthermore, allospecific delayed-type hypersensitivity and gene expression of interferon-gamma and interleukin-2 showed a significantly reduced expression in alpha-MSH-treated mice compared with controls.

CONCLUSIONS

This study provides for the first time, in vivo evidence that treatment with local alpha-MSH may significantly reduce allorejection of orthotopic transplants.

Angiogenesis and Lymphangiogenesis—Implications for Corneal Immunity

It is now widely acknowledged that vasculogenesis and immunogenic inflammation are intricately related in many tissues. However, less understood is to what extent blood (heme) angiogenesis (HA) and lymphangiogenesis (LG) are differentially regulated, and in turn contribute potentially to different aspects of adaptive immunity generated to corneal antigens. Herein, we will provide a brief synopsis of relevant work in this field by focusing particularly on the differential regulation of immunity by these two distinct vasculogenic processes in the cornea, illustrating that in spite of significant redundancies in the mechanisms that induce these vascular processes in the cornea, there are also important distinctions in what aspects of immunity are promoted by them.

'Chimeric' grafts assembled from multiple allodisparate donors enjoy enhanced transplant survival

Certain components of a graft that provoke alloimmunity may not be vital for graft function or critical as targets of rejection. Corneal transplantation is an example of this, because graft epithelium plays a role in allosensitization, whereas corneal graft endothelium-which shares the same alloantigens-is the critical target in allorejection. In this study, we found that exploiting this biology by replacing donor epithelium of an allograft with an allodisparate third-party epithelium yields a marked enhancement in transplant survival. Such 'chimeric' allografts consisted of a C3H/He (H-2(k)) corneal epithelium over a C57BL/6 (H-2(b)) epithelial-denuded cornea (or v.v.) and orthotopically placed on BALB/c (H-2(d)) hosts. Conventional corneal allografts (C3H/He or C57BL/6) or isografts (BALB/c) were also transplanted on BALB/c hosts. Alloreactive T-cell frequencies (CD4(+) interferon [IFN]-gamma(+)) primed to the graft endothelium were strongly diminished in chimeric hosts relative to conventionally allografted hosts. This was corroborated by a decreased T-cell infiltration (p = 0.03) and a marked enhancement of allograft survival (p = 0.001). Our results represent the first successful demonstration of chimeric tissue, epithelial-denuded allograft plus third-party allodisparate epithelium, in the promotion of allograft survival. Moreover, chimeric grafting can be readily performed clinically, whereby corneal allograft rejection remains a significant problem particularly in inflamed graft beds.

Depletion of passenger leukocytes from corneal grafts: an effective means of promoting transplant survival?

PURPOSE

To develop and compare effective strategies for depleting graft-derived passenger leukocytes that include antigen-presenting cells from corneal buttons and to assess the effectiveness of this strategy in promoting graft survival using a high-risk (HR) model of corneal transplantation.

METHODS

Corneal buttons harvested from C57BL/6 mice were used in three ex vivo strategies of passenger leukocyte depletion. Two strategies involved storage in medium at different temperatures for prolonged periods. A third strategy used complement-dependent cytotoxicity (CDC) by treating the buttons with anti-CD45 mAb plus complement. Wholemount corneal buttons or cells from enzyme-digested corneas were analyzed using confocal microscopy or flow cytometry, respectively, for the pan-leukocyte surface marker CD45. HR host beds were created and used to evaluate the efficacy of passenger leukocyte depletion on transplant survival.

RESULTS

Passenger leukocyte numbers in the buttons were significantly reduced by all three treatments. CDC was the most efficient strategy for passenger leukocyte depletion with 39% reduction (P < 0.00005) of CD45(+) cells, and negligible damage to the endothelial layer, achievable within 24 hours. However, passenger leukocyte depletion failed to improve HR graft longevity.

CONCLUSIONS

Anti-CD45 antibody plus complement-mediated targeting of donor tissue is the most efficient way to deplete corneal passenger leukocytes and can considerably reduce the time required for cell depletion. However, depletion of graft passenger leukocytes does not have a significant effect on promoting graft survival even in the HR setting.

Gender-dependent HLA-DR-restricted epitopes identified from herpes simplex virus type 1 glycoprotein D

In recent clinical trials, a herpes simplex virus (HSV) recombinant glycoprotein D (gD) vaccine was more efficacious in woman than in men. Here we report six HLA-DR-restricted T-cell gD epitope peptides that bind to multiple HLA-DR (DR1, DR4, DR7, DR13, DR15, and DRB5) molecules that represent a large proportion of the human population. Four of these peptides recalled naturally primed CD4(+) T cells in up to 45% of the 46 HSV-seropositive, asymptomatic individuals studied. For the gD(49-82), gD(77-104), and gD(121-152) peptides, the CD4(+) T-cell responses detected in HSV-seropositive, asymptomatic women were higher and more frequent than the responses detected in men. Immunization of susceptible DRB1*0101 transgenic mice with a mixture of three newly identified, gender-dependent, immunodominant epitope peptides (gD(49-82), gD(77-104), and gD(121-152)) induced a gender- and CD4(+) T-cell-dependent immunity against ocular HSV type 1 challenge. These results revealed a gender-dependent T-cell response to a discrete set of gD epitopes and suggest that while a T-cell epitope-based HSV vaccine that targets a large percentage of the human population may be feasible with a limited number of immunodominant promiscuous HLA-DR-restricted epitopes, gender should be taken into account during evaluations of such vaccines.

Recurrence of peripheral ulcerative keratitis on the corneoscleral button in a young man treated successfully with oral corticosteroids

PURPOSE

To describe recurrent peripheral ulcerative keratitis (PUK) on the corneoscleral graft in a young man treated successfully with oral corticosteroids.

METHODS

Interventional case report.

RESULTS

A 21-year-old Malay man with no previous known medical illnesses presented with a sudden onset of peripheral corneal perforation. It was temporarily sealed with a multilayer amniotic membrane followed by patching with a corneoscleral button. One month later, a recurrence of PUK on the donor button was noted. It was successfully treated with oral corticosteroids.

CONCLUSIONS

PUK without systemic manifestation may recur in the donor corneoscleral graft. Prompt intensive treatment with oral corticosteroids results in a favorable outcome.

Scleritis and peripheral ulcerative keratitis

Scleritis and peripheral ulcerative keratitis (PUK) can present as isolated conditions or as part of a systemic inflammatory or infectious disorder. Both are serious ocular conditions that can result in vision loss and require early diagnosis and treatment. Nearly two thirds of patients with non-infectious scleritis require systemic glucocorticoid therapy and one fourth need a glucocorticoid-sparing agent as well. Essentially all patients with non-infectious PUK require systemic glucocorticoids. A detailed clinical history, thorough physical examination, and thoughtful laboratory evaluations are important in the exclusion of underlying disorders and extraocular involvement.

Canine normal corneal epithelium bears a large population of CD45-positive cells

This investigation sought to identify the presence of immune cells in normal canine corneal epithelium. A whole-mount immunofluorescence study of normal canine epithelium using monoclonal antibodies against CD45, CD11c, CD1c and MHC class II was performed. CD45-positive cells were located in all epithelial layers throughout the cornea, occurring in greater numbers (51.98+/-4.1/mm(2)) at the periphery and decreasing towards the central region (11.8+/-3.1/mm(2)). CD11c-positive cells were also observed, but were fewer in number. The findings show that the normal canine cornea carries a significant number of cells of immune origin; these cells seem to be of an inactive phenotype as they do not express MHC class II. Further studies are needed to determine whether these cells can express co-stimulatory molecules and act as antigen presenting cells if stimulated.

Histopathologic and immunologic aspects of alphacor artificial corneal failure

PURPOSE

To describe the histopathologic and immunologic characteristics of late artificial corneal failure in a small series of patients who underwent AlphaCor implantation and to elucidate the mechanisms involved.

DESIGN

Clinicopathologic case series.

METHODS

Three patients were diagnosed with corneal melting during the late postoperative period and required the removal of the devices. The explanted devices embedded within the corneal tissues were examined by light microscopy, electron microscopy, and immunohistochemical studies.

RESULTS

Light microscopic examination of the specimens disclosed adequate biointegration with no foreign body response. Immunofluorescence studies of the skirt exhibited expression of inflammatory cytokines such as interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNF-alpha), and some interferon gamma (IFN-gamma). The keratocytes stained positively for Thy-1 and smooth muscle actin but negatively for CD34.

CONCLUSIONS

Although these findings confirm the occurrence of biointegration, myofibroblastic differentiation of the ingrowing keratocytes is a prominent feature.

Expression of toll-like receptors in the healthy and herpes simplex virus-infected cornea

PURPOSE

To study the expression of toll-like receptors (TLRs) in healthy corneas and corneas with active or nonactive herpetic stromal keratitis (HSK).

METHODS

Eight corneas with HSK (including 5 active and 3 nonactive cases) and 8 healthy corneas were evaluated for TLR1-10 mRNA by reverse transcription-polymerase chain reaction (RT-PCR) and relative real-time PCR. The proteins of TLR2, 9 in 3 different groups, were also compared by immunofluorescence staining. The data were analyzed with SPSS 11.5.

RESULTS

TLR1-10 mRNA was expressed in both healthy and HSK corneas. In the healthy cornea, the mRNA expression of TLR1, 2, 3, 4, and 6 was higher, whereas the expression of TLR7, 8, and 9 was lower relative to TLR 5 and 10. All the TLRs mRNA expression in the active HSK corneas were upregulated, especially TLR4, 7, 8, and 9, compared with the healthy corneas. However, in nonactive HSK corneas, only TLR7 mRNA expression upregulated, whereas the others downregulated. The immunofluorescence staining showed that the expression of TLR 9 was slightly stronger in the cornea with active HSK than that of nonactive and healthy corneas.

CONCLUSIONS

TLRs are expressed diversely in the healthy cornea and could have an important role in innate corneal immunity. TLR4, 8, and 9 may be implicated in the pathogenesis of active HSV infection in the cornea, whereas TLR7 may play a key role in HSK whether it is active or not.

Corneal antigen presentation: molecular regulation and functional implications

Presentation of corneal antigens for induction of adaptive immune responses is mediated by corneal antigen-presenting cells (APC), including those that infiltrate the cornea in response to inflammatory stimuli and, to a lesser extent, those that reside in the cornea and up-regulate activation markers in response to inflammation. Significant progress has been made in the last decade in dissecting the molecular mechanisms that mediate APC infiltration into the cornea. However, it has recently been determined that exit of APC out of the cornea is critical for induction of T cells that normally reside outside of the cornea in lymphoid reservoirs. Much less is understood about the molecular regulation of APC egress from the cornea, but our laboratory has recently discovered that APC access to afferent lymphatics and draining lymph nodes requires signaling mediated by VEGFR-3. We describe herein the functional implication of APC trafficking and the prospects for novel immunomodulatory strategies based on regulating APC migration.

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.

Inhibition of inflammatory cytokine production in human corneal cells by dexamethasone, but not cyclosporin

PURPOSE

To evaluate the modulatory effects of anti-inflammatory agents, dexamethasone (Dex) and cyclosporin A (CsA), on the production of cytokines and chemokines by human corneal cells in vitro following stimulation by the pro-inflammatory cytokine after interleukin 1beta (IL-1beta).

METHODS

A human corneal epithelial (HCE) cell line and human corneal fibroblasts (HCFs) were stimulated in culture with IL-1beta and treated with Dex or CsA. The gene expression for selected cytokines and chemokines was determined by reverse transcriptase-polymerase chain reaction (RT-PCR). The secretion of cytokines and chemokines was measured by enzyme-linked immunosorbent assay.

RESULTS

IL-1beta enhanced the mRNA and/or protein levels of granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-8, and monocyte chemotactic protein (MCP)-1 in HCE and IL-6, IL-8, MCP-3, and regulated on T-cell activation expressed secreted (RANTES) in HCFs. Treatment with CsA did not inhibit cytokine production in either HCE or HCFs. In contrast, Dex treatment inhibited the IL-1beta-induced production of GM-CSF, IL-6, IL-8, MCP-3, and RANTES, but not MCP-1.

CONCLUSION

These results show that Dex, but not CsA, has direct immunosuppressive effects on the resident corneal cells, HCE and HCFs. This suggests that the clinically observed immunosuppressive effects of topical CsA are mediated primarily through the immune cells.

Lokale Immunsuppressiva nach perforierender Keratoplastik

Topical steroids are routinely used in the postoperative treatment following penetrating keratoplasty. Due to the known side effects such as steroid-response glaucoma, cataract, and surface disorders, a broader armamentarium of topical immunomodulating drugs with comparable efficacy, better tolerance and less side effects is desirable. Cyclosporine A and FK506 eye drops are a promising alternative. A new approach involves subconjunctival drug delivering implants and locally applied antiangiogenic substances, which still have to be tested in clinical studies.

Deletion of the chemokine receptor CCR1 prolongs corneal allograft survival

PURPOSE

Many corneal grafts undergo immune rejection, and current therapies are associated with many side effects. The purpose of this study was to identify critical chemokine pathways involved in generating the alloimmune response to corneal transplants.

METHODS

Orthotopic corneal transplantation was performed in fully mismatched strains. Cytokine and chemokine receptor gene expression was determined by the RNase protection assay. Knockout (KO) strains for chemokine-chemokine receptors that are upregulated after transplantation underwent corneal transplantation. Results derived from KO murine hosts were compared with cyclosporine (Cy) therapy. In addition to graft survival, graft infiltration, allospecific delayed-type hypersensitivity (DTH), and cytokine expression were compared among the recipient groups.

RESULTS

Initial experiments revealed gene upregulation of the chemokine receptors CCR1, -2, and -5 after corneal allorejection. Although CCR1 KO hosts showed a significant increase in graft survival compared with wild-type (WT) hosts, allografts in CCR5, CCR2/CCL3(MIP-1alpha), CXCR3, CXCL10/IP-10, and CCL3/MIP-1alpha KO mice did not show a significant improvement in graft survival. Further, CCR1 KO hosts showed a significantly higher survival rate than with systemic Cy therapy in WT hosts. Moreover, graft infiltration by leukocytes and gene expression of proinflammatory cytokines were reduced in CCR1 KO mice compared with both Cy treated and untreated WT mice, as was the induction of allospecific DTH.

CONCLUSIONS

These studies provide, for the first time, evidence that targeting of specific chemokine pathways can significantly promote survival of corneal transplants, and suggest that select deletion or suppression of CCR1 can be a useful therapeutic target in corneal transplant immunity.

Existence of small slow-cycling Langerhans cells in the limbal basal epithelium that express ABCG2

Despite the obvious importance of limbal stem cells in corneal homeostasis and tumorigenesis, little is known about their specific biological characteristics. The purpose of this study was to characterize limbal slow-cycling cells based on the expression of ABCG2 and major histocompatibility complex (MHC) class II and the cell size. Wistar rats were daily injected with 5-bromo-2-deoxyuridine (BrdU) at a dose of 5 mg/100 g for 2 weeks. After 4-week BrdU-free period, corneal tissues were excised, and immunofluorescence staining for ABCG2, BrdU, and MHC class II was performed by confocal microscopy. In another series, corneal tissues of normal rat were double immunostained for ABCG2, keratin 14, keratin 3, CD11c, and MHC class II. In addition, limbal, peripheral and central corneal epithelial sheets were isolated by Dispase II digestion and dissociated into single cell by trypsin digestion and cytospin preparations were double immunostained for ABCG2 and MHC class II. The cell size and nucleus-to-cytoplasm (N/C) ratio of limbal ABCG2+ cells were analyzed and compared with those of cells from other zones. BrdU label-retaining cells (LRCs) with expression of ABCG2 were found in the limbal epithelial basal layer, but not in other parts of the cornea. Approximately 20% of these cells were MHC class II positive. All MHC class II+ cells in the corneal epithelium were positive for CD11c, a marker for dendritic cells (DCs). Double labeling with ABCG2 and keratin 14 showed that nearly four-fifth of limbal ABCG2+ cells were positive for keratin 14 but negative for keratin 3, exhibiting an undifferentiated epithelial cell lineage. Cytospin sample analysis revealed the presence of a distinct population of smaller ABCG2+ cells with expression of MHC class II with a larger N/C ratio in the limbal epithelium. A new population of small slow-cycling cells with large N/C ratio has been found to express ABCG2 in the limbal epithelial basal layer. Some of these cells normally express MHC class II antigen. These findings may have important implications for our understanding of the characteristics of limbal slow-cycling cells.

Local thermal injury elicits immediate dynamic behavioural responses by corneal Langerhans cells

Langerhans cells (LCs) represent a special subset of immature dendritic cells (DCs) that reside in epithelial tissues at the environmental interfaces. Although dynamic interactions of mature DCs with T cells have been visualized in lymph nodes, the cellular behaviours linked with the surveillance of tissues for pathogenic signals, an important function of immature DCs, remain unknown. To visualize LCs in situ, bone marrow cells from C57BL/6 mice expressing the enhanced green fluorescent protein (EGFP) transgene were transplanted into syngeneic wild-type recipients. Motile activities of EGFP(+) corneal LCs in intact organ cultures were then recorded by time lapse two-photon microscopy. At baseline, corneal LCs exhibited a unique motion, termed dendrite surveillance extension and retraction cycling habitude (dSEARCH), characterized by rhythmic extension and retraction of their dendritic processes through intercellular spaces between epithelial cells. Upon pinpoint injury produced by infrared laser, LCs showed augmented dSEARCH and amoeba-like lateral movement. Interleukin (IL)-1 receptor antagonist completely abrogated both injury-associated changes, suggesting roles for IL-1. In the absence of injury, exogenous IL-1 caused a transient increase in dSEARCH without provoking lateral migration, whereas tumour necrosis factor-alpha induced both changes. Our results demonstrate rapid cytokine-mediated behavioural responses by LCs to local tissue injury, providing new insights into the biology of LCs.

Topical/mucosal delivery of sub-unit vaccines that stimulate the ocular mucosal immune system

Mucosal vaccination is proving to be one of the greatest challenges in modern vaccine development. Although ocular mucosal immunity is highly beneficial for achieving protective immunity, the induction of ocular mucosal immunity against ocular infectious pathogens, particularly herpes simplex virus type 1 (HSV-1), which is the leading cause of infectious corneal blindness, remains difficult. Recent developments in cellular and molecular immunology of the ocular mucosal immune system (OMIS) may help in the design of more effective and optimal immunization strategies against ocular pathogens. In this review, we highlight ocular mucosal immunoprophylactic and immunotherapeutic vaccine strategies that have been evaluated to control the many pathogens that attack the surface of the eye. Next, we describe the current understandings of the OMIS and elucidate the structure and the function of the humoral and cellular immune system that protects the surface of the eye. Results from our recent experiments using topical ocular delivery of peptides-CpG and lipopeptide-based vaccines against HSV-1 infection are presented. The future challenges and issues related to the ocular mucosal delivery of molecularly defined sub-unit vaccines are discussed.

Accessory cell populations in the cornea

According to the "classical" doctrine, resident cells of the cornea include the stratified epithelial cells, quiescent keratocytes, and a single layer of nondividing endothelial cells. However, it has become increasingly evident that other cell types are involved in the homeostasis of the cornea. The presence of various cell types from different lineages has raised concern among researchers as to what we are actually "seeing" in the cornea. Although definitive conclusions cannot yet be drawn, this review attempts to clarify the various accessory cell types reported in the human and murine cornea. The epithelial layer of the limbal area includes melanocytes, as well as antigen-presenting cells that are also present in the peripheral clear cornea. The most debated tissue currently is perhaps the corneal stroma, where resident keratocytes are not as large a population as was previously believed. Bone marrow-derived cells are found in the cornea, and these may not express the typical HLA molecules usually found on the surface of antigen-presenting cells. Nerve fibers extend though the superficial stroma to form a plexus beneath the epithelium. Although the cell body of the neuron itself is not in the cornea, neural glial cells, such as Schwann cells, are present in the stroma. The use of specific molecular markers and high-quality imaging techniques will be required to fully elucidate the various accessory cells of the cornea and their function.

Th-cytotoxic T-lymphocyte chimeric epitopes extended by Nepsilon-palmitoyl lysines induce herpes simplex virus type 1-specific effector CD8+ Tc1 responses and protect against ocular infection

Molecularly defined vaccine formulations capable of inducing antiviral CD8+ T-cell-specific immunity in a manner compatible with human delivery are limited. Few molecules achieve this target without the support of an appropriate immunological adjuvant. In this study, we investigate the potential of totally synthetic palmitoyl-tailed helper-cytotoxic-T-lymphocyte chimeric epitopes (Th-CTL chimeric lipopeptides) to induce herpes simplex virus type 1 (HSV-1)-specific CD8+ T-cell responses. As a model antigen, the HSV-1 glycoprotein B498-505 (gB498-505) CD8+ CTL epitope was synthesized in line with the Pan DR peptide (PADRE), a universal CD4+ Th epitope. The peptide backbone, composed solely of both epitopes, was extended by N-terminal attachment of one (PAM-Th-CTL), two [(PAM)2-Th-CTL], or three [(PAM)3-Th-CTL] palmitoyl lysines and delivered to H2b mice in adjuvant-free saline. Potent HSV-1 gB498-505-specific antiviral CD8+ T-cell effector type 1 responses were induced by each of the palmitoyl-tailed Th-CTL chimeric epitopes, irrespective of the number of lipid moieties. The palmitoyl-tailed Th-CTL chimeric epitopes provoked cell surface expression of major histocompatibility complex and costimulatory molecules and production of interleukin-12 and tumor necrosis factor alpha proinflammatory cytokines by immature dendritic cells. Following ocular HSV-1 challenge, palmitoyl-tailed Th-CTL-immunized mice exhibited a decrease of virus replication in the eye and in the local trigeminal ganglion and reduced herpetic blepharitis and corneal scarring. The rational of the molecularly defined vaccine approach presented in this study may be applied to ocular herpes and other viral infections in humans, providing steps are taken to include appropriate Th and CTL epitopes and lipid groups.