Effects of all-trans retinoic acid nanoparticles on corneal epithelial wound healing.

BACKGROUND: We have developed inorganically-coated all-trans retinoic acid (atRA) nanoparticles, nano-sized egg-like particles of atRA (NANOEGG®-atRA). The purpose of this study was to determine the effects of NANOEGG®-atRA on corneal wound healing in vivo and in vitro. METHODS: A rabbit corneal epithelial wound healing model was exposed to different concentrations of NANOEGG®-atRA. Wound healing was serially quantified as the ratio of fluorescein-stained area at the selected times to that at baseline. After wound closure, the barrier function of the cornea was determined using low concentrations of tropicamide. At the completion of the experiments, the corneal epithelium was histologically examined. For the in vitro studies, linear scratch wounds were made on cultured SV40-immortalized human corneal epithelial cells (HCE-T). Then, the cells were exposed to different concentrations of NANOEGG®-atRA, and wound healing was determined by the degree of closure of the scratch wound. In addition, the effects of NANOEGG®-atRA on the proliferation of HCE-T cells were determined by WST-8 assays. RESULTS: Exposure to NANOEGG®-atRA decreased the injured area 24 hrs after the ablation. The maximum effect of NANOEGG®-atRA was observed at a concentration of 33 mM. Histologically, no abnormal or differentiated corneal epithelial cells were observed in the histological sections treated with NANOEGG®-atRA. The tropicamide-induced pupillary dilation was significantly slowed in the eyes treated with NANOEGG®-atRA. NANOEGG®-atRA at concentrations of 3.3 and 33 nM induced earlier wound closure in vitro, but did not induce proliferation of HCE-T cells. CONCLUSION: NANOEGG®-atRA promotes wound healing and should be considered for the treatment of wounds of the corneal epithelium.

Stromal architecture and immune tolerance in additive corneal xenografts in rodents.

PURPOSE: To examine immune tolerance and corneal ultrastructure following additive corneal xenografts in rodents. METHODS: We carried out surgical implantation of excised BALB/c mouse corneal tissue, either freshly isolated (n=6) or after storage at--20 degrees C for 1 week (n=7), into the corneas of Wistar rats at approximately mid-stromal depth. Corneal opacity and neovascularization were evaluated postoperatively, and stromal ultrastructure was observed by transmission electron microscopy. RESULTS: Corneal opacification and neovascularization in the weeks after surgery were less prevalent in grafts of frozen-then-thawed tissue than in grafts of fresh tissue. In a well tolerated frozen-then-thawed xenograft, the matrix architecture was normal throughout most of the recipient and donor tissue, but pronounced fibrillar disorganization was evident adjacent to Descemet's membrane. CONCLUSION: We attribute the improved tolerance of frozen-then-thawed xenografts over fresh xenografts to a reduced cellular immune response.

Phlyctenular keratitis associated with meibomitis in young patients.

PURPOSE: To describe the unique clinical features of phlyctenular keratitis, including the association with meibomitis, in young patients. DESIGN: Observational case series. METHODS: The study population consisted of 23 Japanese patients aged under 35 years with phlyctenular keratitis. We examined their clinical history, signs and symptoms, human leukocyte antigen (HLA), bacterial cultures of meibum, and the efficacy of antibiotics. The minimal diagnostic criteria included corneal nodules consisting of cellular infiltrates and superficial neovascularization. RESULTS: Of the 23 patients, 20 (87%) were women, and 13 (56.5%) had a history of chalazia. In all cases, the lesions and the severity of corneal nodules and neovascularization corresponded well with the location and the severity of meibomitis. The frequency of HLA-A26 and HLA-B35 was significantly increased in our patients (P = .003 and .016, respectively). Propionibacterium acnes in bacterial cultures of pure meibum in 12 of the 20 patients (60%) was statistically more highly positive than those in four of the 17 age-matched normal control subjects (23.5%; P = .028). CONCLUSION: The characteristics of phlyctenular keratitis in our cases include significantly higher prevalence in female patients, severity variation of ocular surface manifestation corresponding to meibomitis, specific HLA association, and possible P. acnes involvement.

Allogeneic corneal tolerance in rodents with long-term graft survival.

BACKGROUND: Healthy C57BL/6 orthotopic corneal allografts in place for more than 8 weeks in BALB/c mice (acceptor8w+) can survive indefinitely due to active suppression of the donor-specific delayed-type hypersensitivity (DTH) response. This suggests a state of tolerance in the acceptor mice, however, the mechanism(s) underlying this acceptance remains to be demonstrated. We investigated the relationship between tolerance-induction and the DTH response using murine re-grafting models to explore the possibility of promoting allogeneic corneal regraft acceptance in high-risk graft beds. METHODS: Acceptor8w+ BALB/c mice received C57BL/6- or C3H corneal regrafts onto the same eye. Re-grafting models were prepared by inducing corneal neovascularization in the graft beds of naive BALB/c mice 2 weeks before corneal allografting. These mice were intravenously (iv) injected with purified splenic T cells or T-cell-depleted splenocytes from acceptor8w+ mice at the time they received re-grafts of C57BL/6 corneas. We also iv injected acceptor8w+ splenocytes into mice bearing healthy primary corneal allografts for 4 weeks (acceptor4w) and assessed their DTH response to C57BL/6 alloantigen(s). In those experiments, acceptor4w mice received a C57BL/6 corneal regraft onto the same eye. RESULTS: In all acceptor8w+ mice there was indefinite survival of C57BL/6-, but not of C3H regrafts. The iv injection of T cells, but not of T-cell-depleted populations, from acceptor8w+ splenocytes promoted allograft survival. Acceptor4w mice iv injected with acceptor8w+ splenocytes manifested a reduced C57BL/6-specific DTH response and the survival rate of C57BL/6 regrafts was increased from 0% to 87.5%. CONCLUSION: As donor-specific T cells from acceptor8w+ mice induced prolonged regraft survival, we posit that the active suppression of DTH responses by T cells may have contributed to indefinite allogeneic regraft survival via the induction of corneal allograft tolerance.

Corneal endothelial transplantation: results of a clinical series using deep lamellar endothelial keratoplasty (DLEK).

PURPOSE: We present the results of our clinical series replacing posterior stroma and endothelium only by deep lamellar endothelial keratoplasty (DLEK) in patients with corneal endothelial diseases. METHODS: Through a 9.0-mm superior scleral incision, a deep stromal pocket was created across the cornea. A 7.5-mm posterior lamellar disc of recipient tissue was excised and replaced by same-size donor posterior disc without suture fixation. Three cases were followed for 12 months after DLEK. Best spectacle-corrected visual acuity (BSCVA), endothelial cell density, and corneal thickness were examined. RESULTS: At 12 months after surgery, all transplants were clear and in position. In the 3 cases, BSCVA at 12 months was 20/200 (hand motion before operation), 20/50 (6/200 before operation), and 20/60 (20/250 before operation), respectively. In one patient, postoperative endothelial cell density was 533 cells/mm(2) with a very thin donor disc. In the other two patients, postoperative endothelial cell density was >2000 cells/mm(2). Corneal thickness (+/-SD) averaged 0.51 +/- 0.06 mm. CONCLUSIONS: DLEK in the setting of corneal endothelial diseases is an effective surgical procedure without corneal surface incisions and sutures.

Effects of dexamethasone and cyclosporin A on human beta-defensin in corneal epithelial cells.

Human beta-defensins (hBDs), which are mainly expressed in epithelial tissues, may contribute to infection-protective mechanisms in the ocular surface. We examined hBD1 and hBD2 expression in the ocular surface by RT-PCR and immunohistochemistry and studied the effects of immunosuppressive agents on their expression in human corneal epithelial cells in vitro. mRNA expression of hBD1 and hBD2 was confirmed in corneal epithelial cells. While the hBD1 peptide was immunohistochemically detected in corneal, limbal, and conjunctival epithelium, the level of expression was stronger in limbal- and conjunctival- than in corneal epithelium. Very weak expression of the hBD2 peptide was detected only in corneal epithelium. After 48-h culture of human corneal epithelial cells in the presence of 10(-5) M dexamethasone or 1 mg l(-1) cyclosporin A, total RNA was extracted and hBD1 and hBD2 mRNA expressions compared using semi-quantitative RT-PCR and introduced amplified fragment length polymorphism (iAFLP) assay. The two methods yielded almost identical results. hBD1 mRNA expression was not changed by dexamethasone but was down-regulated by cyclosporin A. hBD2 mRNA expression was up-regulated by dexamethasone and down-regulated by cyclosporin A. Our findings suggest that hBD1 and hBD2 are regulated by different mechanisms and that hBD1 may contribute to infection-protective mechanisms in the relatively immunosuppressed status induced by dexamethasone.

[A retrospective analysis of infection after corneal transplantation].

PURPOSE: We studied retrospectively the background of postoperative infection after corneal transplantation. METHODS: We reviewed the records of 753 eyes that had undergone corneal transplantation at Kyoto Prefectural University of Medicine or the Baptist Eye Clinic over a period of 6 years from April 1994 to March 2000. Patients who developed microbial keratitis after corneal transplantation were evaluated for the incidence of infection, age, the interval between transplantation and infection, microbiological etiology, the use of topical steroids, therapy, and complications. RESULTS: Follow-up after keratoplasty averaged 43.2+/-25.6 months (mean+/-standard deviation). Among 753 eyes examined, microbial keratitis developed in 27 eyes (3.6%), 14 eyes had bacterial, and 13 had fungal infections. The ages at presentation were 51.4+/-21.5 years for bacterial infections, and 66.5+/-11.1 for fungal infections. The time intervals between transplantation and the onset of infection averaged 7.8+/-7.9 months for bacterial infections, and 24.2+/-17.2 for fungal infections. Infections in 7 (50.0%) of the bacterial eyes were caused by methicillin-resistant Staphylococcus aureus (MRSA) or epidermidis (MRSE), and 9 (69.2%) of the fungal infections by yeast type fungus (8 were Candida species). At onset of keratitis, 3 (21.4%) of the bacterial eyes and 6 (46.2%) of the fungal eyes were treated with fluorometholone, and 11 (78.6%) of the bacterial eyes and 7 (53.8%) of the fungal eyes were treated with betamethazone or dexamethasone. The treatment duration until the focus of disappeared was 32.8+/-19.7 days for bacterial eyes, and 74.8+/-56.3 for fungal eyes. Major complications associated with infection included corneal perforation in 2 eyes of both the bacterial (14.3%) and fungal (15.4%) eyes, graft rejection in 4 (28.6%) bacterial eyes and 1 (7.7%) fungal eye, there was no recurrence of infection in the bacterial eyes but there were 3 (23.1%) cases of recurrence in the fungal eyes. CONCLUSIONS: Infection after corneal transplantation is opportunistic. Fungal infections occurred later than bacterial infections. Also in fungal infections, the mean age at presentation was higher and the recurrence of infection was more frequent.

Amniotic membrane as a carrier for cultivated human corneal endothelial cell transplantation.

PURPOSE: It would be advantageous if cultivated human corneal endothelial cells (cHCECs) could be transplanted for the treatment of diseases caused by corneal endothelial disorders. To achieve this, a matrix that can serve as a carrier for cHCECs is needed. The present study was conducted to examine the feasibility of using amniotic membrane (AM) as a carrier for this application. METHODS: HCECs obtained from peripheral corneal tissue were cultivated, passaged, and transplanted onto denuded AM. The cell density and morphology of the resultant cHCECs on AM were examined by light, scanning electron, and transmission electron microscopy. To determine whether these cHCEC sheets on AM carrier were functional in vivo, the cHCEC sheets on AM were transplanted onto rabbit corneas whose Descemet's membrane and endothelial cells had been completely removed. After transplantation, the corneal appearance was examined by slit lamp biomicroscopy, and corneal thickness was measured daily by pachymetry. At 7 days after surgery, the grafts were examined by light, scanning electron, and transmission electron microscopy. RESULTS: The density of the cHCECs on AM was greater than 3000 cells/mm(2). Morphologically, the cHCEC sheets consisted of a fairly continuous layer of flat squamous polygonal endothelial cells that appeared uniform in size with tightly opposed cell junctions in vitro and in vivo after transplantation. The corneas that received transplanted cHCEC sheets had little edema and retained their thinness and transparency. CONCLUSIONS: The cell density and morphology of cHCECs on AM were similar to those of normal corneas, and cHCECs on AM were functional in vivo. These results indicate that AM maintains HCEC morphology and function and could serve as a carrier for cHCEC transplantation.

Promotion of corneal allograft survival by the induction of oxidative macrophages.

PURPOSE: A Th1-type immune response was detected in allotransplanted, rejected corneas. Because the intracellular thiol redox status of antigen-presenting cells (APCs) reportedly regulates the Th1/Th2 balance through distinctive cytokine production by APCs, this study was conducted to investigate the effect of the intracellular thiol redox status of macrophages (Mps) on corneal allograft survival. METHODS: N,N'-diacetyl-L-cystine dimethylester (NACOMe)(2) was injected intraperitoneally into BALB/c (H-2(d)) mice to induce Mps with a low intracellular glutathione content (icGSH). Corneal grafts from C57BL/10 (H-2(b)), B10.D2 (H-2(d)), and DBA/2 (H-2(d)) donor mice were placed on neovascularized BALB/c graft beds for assessment. B10.D2-grafted recipients were evaluated for donor-specific delayed-type hypersensitivity (DTH), and the cytokines produced by their lymphocytes were examined (IFN-gamma, IL-4, and IL-10). In other experiments, naïve BALB/c mice, injected intravenously with Mps of low icGSH content, received B10.D2 corneal grafts. RESULTS: In (NACOMe)(2)-treated mice, 13 of 20 B10.D2 grafts and 6 of 10 DBA/2 grafts survived indefinitely. No grafts survived in the control mice (P < 0.0001). (NACOMe)(2) treatment did not enhance C57BL/10 graft survival. At 2 weeks after B10.D2 grafting, control mice exhibited DTH, but (NACOMe)(2)-treated mice did not (P < 0.01). Lymphocytes from (NACOMe)(2)-treated mice did not respond to donor splenocytes. Those of control mice showed Th1-type cytokine secretion. The intravenous transfer of peritoneal Mps from (NACOMe)(2)-treated mice prolonged corneal allograft survival (P < 0.003). CONCLUSIONS: The observed enhanced graft acceptance may be due to the suppression of alloantigen-induced Th1 polarization through the induction of Mps with reduced icGSH levels.

Th2-biased immune system promotion of allogeneic corneal epithelial cell survival after orthotopic limbal transplantation.

PURPOSE: The Th2-biased immune system can promote penetrating keratoplasty survival in mice. A series of experiments were performed to determine whether this system could prolong corneal limbal transplant (LT) survival. METHODS: BALB/c (H-2d) mice were immunized with 50 microg of keyhole limpet hemocyanin (KLH) in incomplete Freud's adjuvant. Four weeks later, the corneal epithelium, including the limbal area, was removed, and the mice received LT from B10.D2 (H-2d), C57BL/10 (H-2b), or enhanced green fluorescence protein (EGFP) transgenic (H-2b) donor mice. Immediately thereafter, recipient mice were immunized with 50 micro g of KLH or Hanks' balanced salt solution (HBSS; control) in complete Freund's adjuvant. The allograft fates were assessed clinically. Lymphocytes of recipients were examined for donor-specific proliferation and for donor-specific cytokine production in vitro. RESULT: The regenerated epithelia of all C57BL/10 (n=14) and B10.D2 (n=18) grafts were rejected swiftly in control mice, whereas 66.6% of C57BL/10 grafts (8/12, P<0.001) and 62.8% of B10.D2 grafts (22/35, P<0.001) in the KLH immune group remained significantly clear for 8 weeks. Moreover, EGFP donor epithelial cells were detected from the healthy corneas of KLH-immunized mice. As for the in vitro assay, at 1 week after B10.D2 grafting, lymphocytes from KLH-immunized groups showed neither proliferation nor increased cytokine secretion. CONCLUSIONS: The Th2-biased immune system can support LT prolongation irrespective of donor disparity and can suppress corneal neovascularization. This prolongation is not due to induction of donor-specific regulatory cells, but is presumably at least associated with the suppression of allosensitization.

[Herpes simplex keratitis after ophthalmic surgery].

PURPOSE: We report 6 cases of herpes simplex keratitis after ophthalmic surgery, in eyes without clinical history of herpes simplex keratitis. CASES: These cases comprised 6 patients examined at our hospital between April 1992 and November 2001. Past operations were keratoplasty in 5 eyes and cataract surgery in 1 eye. Clinical findings and predisposing factors were evaluated retrospectively. The period between herpetic epithelial keratitis onset and ophthalmic surgery ranged from 1.5 to 79 months. Predisposing factors included corticosteroid therapy and operative wound. The herpetic epithelial lesions were dendritic ulcers in 2 eyes, geographic ulcer in 1 eye, and atypical epithelial lesions in 3 eyes; in all cases, herpes simplex virus (HSV)-DNA was detected by polymerase chain reaction (PCR) in tear fluid. All herpetic epithelial lesions healed with oral and topical acyclovir. CONCLUSIONS: When corticosteroids are used following ophthalmic surgery, physicians should be alert to the possibility of herpetic epithelial keratitis, even in patients with no clinical history of herpes simplex keratitis. PCR detection in tear fluid is helpful in diagnosing this disease.

Successful regrafting of cultivated corneal epithelium using amniotic membrane as a carrier in severe ocular surface disease.

PURPOSE: Our group performed cultivated allogeneic corneal epithelial transplantation in 13 eyes from 11 patients with severe ocular surface disorders. After the clinical application of this new surgical treatment, some patients experienced epithelial and subepithelial opacities. We applied our procedure again in these patients to achieve successful ocular surface reconstruction. METHODS: The corneal limbal epithelial cells from donor corneas were cultivated for 4 weeks on denuded amniotic membrane (AM) carrier, with 3T3 fibroblast coculture and airlifting. The study subjects consisted of 3 patients. At 3 and 12 months after the first operation, the failed epithelial graft with AM was replaced with new allogeneic corneal epithelium cultivated on AM. RESULTS: At 48 hours after transplantation, the corneal surfaces of the 3 eyes were clear and smooth; the entire corneal surfaces were evenly covered with the transplanted cultivated corneal epithelium, which did not stain with fluorescein. The ocular surface epithelia of these patients are all stable without epithelial defects. CONCLUSIONS: We have shown that, in cases where the initially transplanted cultivated epithelium becomes opaque, it is possible to repeat the transplantation process with new cultivated epithelium on AM.

The successful culture and autologous transplantation of rabbit oral mucosal epithelial cells on amniotic membrane.

PURPOSE: To determine the feasibility of using human amniotic membrane (AM) as a substrate for culturing oral epithelial cells and to investigate the possibility of using autologous cultivated oral epithelial cells in ocular surface reconstruction. METHODS: An ocular surface injury was created in one eye of each of eight adult albino rabbits by a lamellar keratectomy, and a conjunctival excision was performed, including and extending 5 mm outside the limbus. Oral mucosal biopsy specimens were obtained from these eight adult albino rabbits and cultivated for 3 weeks on a denuded AM carrier. The cultivated epithelium was examined by electron microscopy (EM) and immunohistochemically labeled for several keratins. At 3 to 4 weeks after the ocular surface injury, the conjunctivalized corneal surfaces of the eight rabbits were surgically reconstructed by transplanting the autologous cultivated oral epithelial cells on the AM carrier. RESULTS: The cultivated oral epithelial sheet had four to five layers of stratified, well-differentiated cells. EM revealed that the epithelial cells were very similar in appearance to those of normal corneal epithelium, had numerous desmosomal junctions, and were attached to a basement membrane with hemidesmosomes. Immunohistochemistry confirmed the presence of the keratin pair 4 and 13 and keratin-3 in the cultivated oral epithelial cells. Corneas that were grafted with the cultivated oral epithelial cells on an AM carrier were clear and were all epithelialized 10 days after surgery. CONCLUSIONS: Cultures of oral epithelial cells can be generated to confluence on AM expanded ex vivo from biopsy-derived oral mucosal tissue. Autologous transplantation was performed with these cultivated oral epithelial cells onto the ocular surfaces of keratectomized rabbit eyes. Autologous transplantation of cultivated oral epithelium is a feasible method for ocular surface reconstruction. The long-term outcome of such transplantation is not yet clear, and its feasibility in clinical use should be evaluated further.

Methicillin-resistant Staphylococcus aureus and methicillin-resistant Staphylococcus epidermidis infections in the cornea.

PURPOSE: To describe the incidence and clinical management of corneal infections with methicillin-resistant Staphylococcus aureus (MRSA) or methicillin-resistant Staphylococcus epidermidis (MRSE). METHODS: The incidence of methicillin-resistant Staphylococcus (MRS) at the Department of Ophthalmology, Kyoto Prefectural University of Medicine, was reviewed during the 5-year period from January 1996 to December 2000. Clinical aspects of MRS colonization or infection in the eye were investigated. RESULTS: Methicillin-resistant S. aureus or MRSE was detected from 30 eyes with ocular diseases; post-keratoplasty (11 eyes), ocular surface disorders without operation (9 eyes), and others (10 eyes). Among the 30 eyes, 12 manifested keratitis. Eight cases (8 eyes) occurred after keratoplasty, including four postoperative cases in patients with Stevens-Johnson syndrome, and two bilateral cases (4 eyes) in patients with acute-phase Stevens-Johnson syndrome. The degree of MRS keratitis was classified into 4 groups: asymptomatic carrier or conjunctivitis, intraepithelial infiltrations, superficial keratitis, and severe keratitis leading to corneal perforation. All cases of keratitis were treated successfully with topical ofloxacin (OFLX), vancomycin (VCM), or arbekacin (ABK). CONCLUSION: Factors associated with ocular MRS colonization were long-term use of antibiotics and/or steroids, and hospitalization. Patients who had undergone keratoplasty or who had Stevens-Johnson syndrome were at increased risk of MRS keratitis. Superficial stromal infiltrations, minimal melting, and minimal stromal scarring are characteristic of MRS keratitis. Therapy for MRS keratitis is summarized. Ofloxacin, VCM, and ABK are effective in the treatment of MRS keratitis. Vancomycin eye ointment is effective as the final choice in serious cases.

Ocular surface inflammation induced by Propionibacterium acnes.

PURPOSE: In the eye, is commonly isolated in the lid, conjunctiva, and meibomian gland secretion. Well known as a causative bacterium of granulomatous endophthalmitis and a potent inflammatory stimulus, reportedly induces a delayed-type hypersensitivity (DTH) response and forms granulomas in the liver and lung in animal models. In this study, we examined whether can induce a DTH response in the cornea. METHODS: Six- to 8-week-old female Lewis rats were immunized with heat-killed suspension of and assessed as to DTH response via ear challenge at 2 weeks after immunization. At 3 weeks after immunization, suspension was injected in the rat corneal stroma, which was then observed biomicroscopically at 6, 24, and 48 hours after injection. Phenol-killed suspension was also used for the comparison. Histological examination was also performed on the corneal tissues, using hematoxylin and eosin staining as well as immunohistochemical staining against CD4 and CD8 T cells. RESULTS: Rats immunized with suspension showed significantly higher ear swelling values at both the 24- and 48-hour measurements than did the naïve controls (p < 0.005). Massive cellular infiltration with stromal edema was observed biomicroscopically at 48 hours after injection of suspension in the corneal stroma. Histological study showed that the cell infiltration pattern was similar to that of DTH in the skin, i.e., neutrophils infiltrated at 6 hours, followed by mononuclear cells that, including macrophages and lymphocytes, increased and mixed with neutrophils, accompanied by stromal edema at 48 hours. Immunohistochemical study revealed that CD4 T-cell infiltration in the corneal stroma appeared to predominate over CD8 T-cell infiltration. CONCLUSIONS: These results indicate that can induce a DTH response in the cornea and may be a causative bacterium of ocular surface inflammation.

Non-cleavable mutant Fas ligand transfection of donor cornea abrogates ocular immune privilege.

The expression of Fas ligand (FasL) in donor corneal tissue has been thought to contribute to the prolonged survival of orthotopic corneal allografts. However, in solid organ transplantation, FasL gene-transfected tissues have been reported to lead to graft destruction through neutrophil recruitment. We wished to examine whether transfection of mutant FasL cDNA, which produces only membrane-binding forms of FasL because of its cleavage site, prolonged corneal allograft survival in mice. Donor corneal tissues were transduced with two adenovirus vectors containing human mutant FasL cDNA (AxCALNmFasL) and Cre recombinase (AxCANCre). Donor corneal tissues were then transplanted orthotopically onto recipient mice, and graft clarity was examined by slit lamp microscopy. We found that donor corneal grafts transfected with mutant FasL were intensely opaque for 1-2 weeks after grafting, when grafts without transfection remained clear. Histological examination revealed polymorphonuclear cell infiltration in the transfected grafted tissue. Moreover, mutant FasL transduced to donor tissues was found to exert its effects by binding to host, rather than donor Fas molecules, since corneal grafts with mutant FasL survived as long as those without transfection only when host animals, but not donor animals, lacked Fas molecules. Our results indicate that membrane-binding FasL over expression in donor cornea does not prolong corneal allograft survival; indeed, it causes rapid graft destruction.

Role of Fas ligand in ocular tissue.

The expression of Fas ligand (FasL) in the eye is an important factor in the maintenance of immune privilege. Although FasL expression in donor corneas contributes to prolonged survival of orthotopic corneal allografts in solid organ transplantation, FasL gene-transfected tissues reportedly lead to graft destruction through neutrophil recruitment. Differences in the effects of FasL have been attributed to different roles of soluble FasL (sFasL) and membrane FasL (mFasL). This is based on the presumption that the signals through sFasL and mFasL differ, with one causing apoptosis and the other activating inflammation. It was recently reported that inflammation caused by FasL was inhibited at an immune-privileged site, and therefore the effects of FasL may depend on differences in the anatomic sites where FasL-expressing cells are located. In this article, we discuss the role of sFasL and mFasL in ocular immune privilege.