Risk factors for human corneal graft failure within the Australian corneal graft registry.

BACKGROUND: Our aims were to examine graft survival and visual outcome after full-thickness corneal transplantation. METHODS: Records of 18,686 penetrating corneal grafts, 14,622 with archival follow-up from 1 to 22 years, were examined within a national database. Kaplan-Meier survival analysis indicated variables of interest for Cox proportional hazards regression analysis. A model clustered by patient to control intereye or intergraft dependence was constructed to identify variables best predicting penetrating corneal graft failure. Visual acuity in the grafted eye was measured by Snellen acuity. RESULTS: Probability of corneal graft survival was 0.87, 0.73, 0.60, and 0.46 at 1, 5, 10, and 15 years, respectively. Reasons for graft failure included irreversible rejection (34%), corneal endothelial cell failure including cases of glaucoma (24%), and infection (14%). Variables predicting graft failure in multivariate analysis included transplant center, location and volume of surgeon's case-load, graft era, indication for graft, number of previous ipsilateral grafts, lens status, corneal neovascularization at transplantation, a history of ocular inflammation or raised intraocular pressure, graft diameter, and postoperative events including graft neovascularization and rejection. Best-corrected Snellen acuity of 6/12 or better was achieved by 45%, and of less than 6/60 by 26%, of grafted eyes at last follow-up. CONCLUSIONS: The short-term survival of penetrating corneal transplants is excellent, but the eventual attrition rate appears inexorable and many factors that influence graft survival significantly are not amenable to change. Most penetrating grafts are performed for visual improvement, and excellent acuity will be achieved by approximately half of all grafts.

Regeneration of corneal cells and nerves in an implanted collagen corneal substitute.

PURPOSE: Our objective was to evaluate promotion of tissue regeneration by extracellular matrix (ECM) mimics, by using corneal implantation as a model system. METHODS: Carbodiimide cross-linked porcine type I collagen was molded into appropriate corneal dimensions to serve as substitutes for natural corneal ECM. These were implanted into corneas of mini-pigs after removal of the host tissue, and tracked over 12 months, by clinical examination, slit-lamp biomicroscopy, in vivo confocal microscopy, topography, and esthesiometry. Histopathology and tensile strength testing were performed at the end of 12 months. Other samples were biotin labeled and implanted into mice to evaluate matrix remodeling. RESULTS: The implants promoted regeneration of corneal cells, nerves, and the tear film while retaining optical clarity. Mechanical testing data were consistent with stable, seamless host-graft integration in regenerated corneas, which were as robust as the untreated fellow corneas. Biotin conjugation is an effective method for tracking the implant within the host tissue. CONCLUSIONS: We show that a simple ECM mimetic can promote regeneration of corneal cells and nerves. Gradual turnover of matrix material as part of the natural remodeling process allowed for stable integration with host tissue and restoration of mechanical properties of the organ. The simplicity in fabrication and shown functionality shows potential for ECM substitutes in future clinical applications.

Expression of the chemokine antagonist vMIP II using a non-viral vector can prolong corneal allograft survival.

BACKGROUND: The expression of chemokines is central to the recruitment of inflammatory cells for graft rejection, and modulation of chemokine action is of potential in preventing graft rejection. We have examined chemokine expression in a murine model of corneal allograft rejection, and also determined the effect of expressing a broad acting chemokine antagonist, viral macrophage inflammatory protein II (vMIP II), on graft survival. METHOD: The expression of chemokines in a murine model of corneal transplantation was determined by real time RT-PCR and, in the case of regulated on activation normal T-cell expressed and secreted, by ELISA. The plasmid encoding the virally derived chemokine antagonist, vMIP II, was introduced into the corneal endothelial cells using a non-viral vector consisting of liposomes and transferrin. The expression and activity of vMIP II was determined by ELISA and functional assays, and the effect on graft survival noted. RESULTS: After allotransplantation, there was up-regulation of all 11 chemokines examined. After gene delivery, there was expression of active vMIP II for more than 14 days and considerable prolongation of graft survival. This was associated with a decrease in leukocyte infiltration of the stroma of the cells. CONCLUSION: As expected there was considerable up-regulation of chemokines during allograft rejection. The expression of vMIP II showed considerable prolongation of graft survival. This is the first time we have observed prolongation of graft survival after a non-viral (as opposed to viral) means of gene delivery and indicates the potential of interfering with chemokine action to prevent corneal graft failure.

Endothelial keratoplasty: improvement of vision after healthy donor tissue exchange.

OBJECTIVE: To report 3 cases of graft exchange by using a microkeratome-prepared donor tissue in place of a manually prepared donor tissue for inadequate postoperative visual acuity after deep lamellar endothelial keratoplasty and to discuss possible etiologies. METHODS: Prospective, observational case series. The patients were 3 consecutive patients who underwent endothelial graft replacement for unsatisfactory vision after initial deep lamellar endothelial keratoplasty. This is a review of clinical findings in 3 cases of endothelial keratoplasty that underwent graft exchange for unacceptable vision after deep lamellar endothelial keratoplasty. RESULTS: Two patients benefited from graft exchange by using a microkeratome-prepared donor in place of a manually prepared donor with improvement in best spectacle-corrected visual acuity and 1 did not because of recipient bed irregularities. Vision improved in this patient with penetrating keratoplasty. CONCLUSIONS: Endothelial keratoplasty results in rapid visual recovery and excellent vision. However, fewer eyes achieve 20/20 vision than with full-thickness penetrating keratoplasty. This report shows that some patients with suboptimal vision after endothelial keratoplasty felt to be caused by interface optical problems may benefit from either graft exchange or penetrating keratoplasty.

WZS-pig is a potential donor alternative in corneal xenotransplantation.

PURPOSE: To explore the characteristics of rejection of Wuzhishan (WZS) pig-to-rhesus monkey corneal transplants and to evaluate WZS pig corneas as potential donor material for a clinical setting. METHODS: Wuzhishan pigs were used as donors and rhesus monkeys as recipients for corneal xenotransplantation. Eighteen rhesus monkeys were divided into three groups. Groups 1 and 2 underwent penetrating corneal xenotransplantation, while group 3 underwent lamellar corneal xenotransplantation. Only group 2 received subconjunctival injections with betamethasone for 3 months. All xenografts were evaluated by slit-lamp microscopy. Two recipients in each group were killed for corneal histopathological staining at 30 days after surgery. The concentrations of cytokines in the aqueous humor were detected by cytometric bead array. RESULTS: Rejection of the xenografts occurred at approximately 15 days after surgery in group 1. Rejection was delayed for more than 4 months by conjunctival injection with betamethasone (group 2). Use of lamellar corneal xenografts (group 3) maintained corneal transparency for more than 3 months. Histopathological examination in group 1 showed that the xenografts were infiltrated with inflammatory cells. The corneal endothelia were destroyed and exudative membranes were formed in the anterior chamber. However, in the betamethasone-treated group, the corneal xenografts showed only minimal edema and almost no inflammatory cell infiltrate. The corneal endothelia were intact and there was no exudative membrane formation. The concentration of interleukin (IL)4, IL5 and IL10 showed an increased shift 3 weeks after surgery in group 1 and 2, but no change of cytokine's concentration was found in group 3. CONCLUSION: Rejection of pig-rhesus xenografts occurred early in penetrating corneal transplantation, but not in lamellar corneal transplantation. The endothelium of the xenograft might be a primary target of immune attack. Corticosteroid treatment inhibited rejection of the corneal xenografts.

Gal alpha(1-3)Gal expression of the cornea in vitro, in vivo and in xenotransplantation.

BACKGROUND: To investigate alpha Gal (Gal alpha1-3Gal beta 1-4GlcNAc-R) expression of the porcine cornea in vitro, in vivo and after xenotransplantation. METHODS: Using the GS-IB4 lectin (Griffonia simplifolia I isolectin B4), the expression of alpha Gal was evaluated in the normal porcine cornea and in cultured corneal stromal and endothelial cells of the second passages. The distribution of alpha Gal epitopes was also evaluated in corneal grafts at 4, 7 and 10 days after pig-to-rat orthotopic corneal transplantation. RESULTS: The expression of alpha Gal was mostly confined to the anterior stromal keratocytes of the normal porcine cornea. However, reactivity for GS-IB4 was markedly increased during cell culture passage (P)-by 18.0% (P1) and 39.0% (P2) in cultivated keratocytes, and by 62.1% (P1) and 87.1% (P2) in cultured endothelial cells. The expression of alpha Gal epitopes was gradually enhanced in all corneal layers of the graft after transplantation. CONCLUSION: Alpha Gal expression in the cornea was gradually induced during in vitro culture and after xenotransplantation, suggesting a role of putative Gal-related acute humoral rejection in porcine corneal xenotransplantation.

Nitrosative stress and corneal transplant endothelial cell death during acute graft rejection.

BACKGROUND: Nitrosative stress takes place in endothelial cells (EC) during corneal acute graft rejection. The purpose of this study was to evaluate the potential role of peroxynitrite on corneal EC death. METHODS: The effect of peroxynitrite was evaluated in vivo. Fifty, 250, and 500 microM in 1.5 microL of the natural or denatured peroxynitrite in 50 microM NaOH, 50 microM NaOH alone, or balanced salt solution were injected into the anterior chamber of rat eyes (n=3/group). Corneal toxic signs after injection were assessed by slit-lamp, in vivo confocal imaging, pachymetry, and EC count. The effect of peroxynitrite was also evaluated on nitrotyrosine and leucocyte elastase inhibitor/LDNase II immunohistochemistry. Human corneas were incubated with peroxynitrite and the effect on EC viability was evaluated. A specific inducible nitric oxide synthase inhibitor (iNOS) was administered systemically in rats undergoing allogeneic corneal graft rejection and the effect on EC was evaluated by EC count. RESULTS: Rat eyes receiving as little as 50 microM peroxynitrite showed a specific dose-dependent toxicity on EC. We observed an intense nitrotyrosine staining of human and rat EC exposed to peroxynitrite associated with leucocyte elastase inhibitor nuclear translocation, a noncaspase dependent apoptosis reaction. Specific inhibition of iNOS generation prevented EC death and enhanced EC survival of the grafted corneas. However, inhibition of iNOS did not have a significant influence on the incidence of graft rejection. CONCLUSION: Nitrosative stress during acute corneal graft rejection in rat eyes induces a noncaspase dependent apoptotic death in EC. Inhibition of nitric oxide production during the corneal graft rejection has protective effects on the corneal EC survival.

Influence of final corneal thickness in visual acuity after deep lamellar endothelial keratoplasty.

PURPOSE: To determine if the final corneal thickness after deep lamellar endothelial keratoplasty (DLEK) is correlated in any way with visual performance. METHODS: One hundred fifty-five consecutive eyes without macular disease underwent DLEK surgery and had pachymetry recorded at 6 months postoperatively. The eyes were grouped according to visual acuity, and pachymetry was correlated between groups: group 1 (20/20, 20/25, or 20/30), n = 38; group 2 (20/40 or 20/50), n = 79; group 3 (20/60, 20/70, or 20/80), n = 30; group 4 (20/100 or worse), n = 8. RESULTS: The mean pachymetry, SD, and range of pachymetry for each group are as follows: group 1, 0.571 +/- 0.080 mm (range, 0.408-0.784 mm); group 2, 0.598 +/- 0.080 mm (range, 0.437-0.816 mm); group 3, 0.605 +/- 0.099 mm (range, 0.454-0.945 mm); group 4, 0.607 +/- 0.120 mm (range, 0.410-0.781 mm). There was no significant correlation between vision and corneal thickness (P = 0.312). There was no statistical difference in pachymetry among all 4 groups (P = 0.323). The influence of pachymetry in visual acuity is not relevant (r = 0.03). CONCLUSIONS: The variance in corneal thickness in DLEK does not seem to influence visual results.

Importance of nutrition to corneal grafts when used as a carrier of the Boston Keratoprosthesis.

PURPOSE: Necrosis, melt, and perforation have historically been frequent around a Keratoprosthesis (KPro), even resulting in extrusion or endophthalmitis. Autoimmune diseases such as Stevens-Johnson Syndrome (SJS) and Ocular Cicatricial Pemphigoid (OCP) have been notorious in this respect. The purpose of this study was to compare the frequency of tissue melt after implantation of two designs of the Boston KPro, one allowing much better access of nutrition from the aqueous humor to the carrier graft. METHODS: We retrospectively reviewed charts of 157 eyes implanted since 1990 with a poly (methylmethacrylate) Boston KPro, including 79 eyes implanted with the model having 8 small (1.3-mm diameter) holes in the back plate, and 78 eyes implanted with the older solid back plate. We compared the frequency of tissue melts between the two KPro designs, for all implants as well as for subgroups based on preoperative diagnosis. RESULTS: In total, 48/157 eyes (31%) developed some degree of tissue melt around the stem, including 8/79 eyes (10%) in the back plate with holes group and 40/78 eyes (51%) in the solid back plate group (P < 0.0001). Among the melts in the back plate with holes group, 4/8 (50%) suffered from an underlying autoimmune disease such as SJS or OCP. CONCLUSIONS: The Boston KPro design with a back plate containing holes protects the overlying corneal tissue from necrosis and melts. This improved situation is likely due to increased aqueous access and better nutrition to the corneal graft cells. In addition, this study confirms earlier work regarding the particular corneal fragility of patients with autoimmune diseases.

In situ versus whole-globe harvesting of corneal tissue from remote donor sites: effects on initial tissue quality.

PURPOSE: There are 2 methods of corneal tissue procurement currently in widespread use: in situ extraction of the corneal button directly to preservation media and whole-globe enucleation of eyes with removal of the button to preservation media at a later time. This study evaluates the effects of these 2 procurement procedures on the initial quality of donor corneal tissue. METHODS: Slit-lamp examination results and endothelial cell counts were compared for a total of 468 donor corneas harvested at 2 remote locations: one where in situ procurement was practiced and the other that used whole-globe enucleation procedures. RESULTS: In both univariate and multivariate analysis, in situ corneas were found to have a lower incidence of moderate or severe haze and folds in Descemet membrane. No differences in mean endothelial cell counts were noted between the 2 populations of donated tissue. CONCLUSIONS: In situ procurement of corneal tissue results in higher initial corneal tissue quality than whole-globe procedures.

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.

Surface wave elastometry of the cornea in porcine and human donor eyes.

PURPOSE: To introduce a nondestructive technique for characterization of corneal stiffness, determine measurement precision, and investigate comparative stiffness values along central, radial, and circumferential vectors in porcine corneas. The effects of epithelial debridement, relaxing incisions, and crosslink-mediated stiffening on surface wave velocity are also studied. METHODS: A handheld prototype system was used to measure ultrasound surface wave propagation time between two fixed-distance transducers along a ten-position map. Repeatability was assessed with replicate measurements in 6 porcine corneas. In 12 porcine globes with controlled intraocular pressure (IOP), serial measurements were performed before and after epithelial removal, then after 250- and 750-microm-deep relaxing incisions. In human globes with constant intravitreal pressure, central wave velocity and transcorneal IOP measurements were compared before and after collagen cross-linking. RESULTS: Measurement repeatability across all regions was between 2.2% and 8.1%. Epithelial removal resulted in increases in measured stiffness in 67% of eyes, but statistical power was insufficient to detect a systematic change. Wave velocity across a central incision decreased significantly after 250-microm keratotomy (P < .001), but did not undergo a significant further decrease with deeper keratotomy. Meridional stiffness changes consistent with coupling effects were detected after keratotomy. Surface wave velocity and transcorneal IOP measurements increased markedly after collagen cross-linking despite maintenance of a constant IOP. CONCLUSIONS: Handheld corneal elastometry provides a repeatable measure of regional stiffness changes after relaxing incisions and collagen cross-linking in in vitro experiments. Surface wave elastometry allows focal assessment of corneal biomechanical properties that are relevant in refractive surgery, ectatic disease, and glaucoma.

Comparison of topical interleukin-1 vs tumor necrosis factor-alpha blockade with corticosteroid therapy on murine corneal inflammation, neovascularization, and transplant survival (an American Ophthalmological Society thesis).

PURPOSE: Interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) play critical roles in mediating corneal inflammation. In this study, topical blockade of IL-1 and TNF-alpha, alone or in combination, was compared to conventional corticosteroid anti-inflammatory therapy in suppressing infiltration of the cornea by antigen-presenting Langerhans cells (LCs) and in promoting corneal transplant survival in a mouse model of keratoplasty. METHODS: Study drugs included topical 2% IL-1 receptor antagonist (IL-1Ra), 1.5% soluble TNF-alpha receptor (sTNFR), and 1% prednisolone phosphate (Pred), all formulated in hyaluronic acid vehicle. Fifty eyes of BALB/c mice were used for LC studies where the numbers of LCs were determined 1 week after electrocautery to the corneal surface or transplantation of C57BL/6 corneas. Additionally, 65 BALB/c mice received corneal allografts and were randomized to receive one of the following for 8 weeks: (1) IL-1Ra, (2) sTNFR, (3) Pred, (4) combined IL-1Ra and Pred, or (5) vehicle alone. RESULTS: Mean suppression of LC infiltration after electrocautery or transplantation was 67% and 71%, respectively, for IL-1Ra, 40% and 62% for sTNFR, 70% and 72% for sTNFR+IL-1Ra, and 77% and 78% for Pred alone. Rejection rates were 15% for IL-1Ra (P = .01), 38% for sTNFR (P = .1), 17% for Pred (P = .02), and 7% for combined IL-1Ra+Pred (P = .002) as compared to 69% for the vehicle-treated group. IL-1Ra and Pred, but not sTNFR, significantly inhibited post-transplantation neovascularization. CONCLUSIONS: Topical IL-1Ra and prednisolone are comparable in their capacity to promote graft survival. sTNFR therapy, though effective, has much lower efficacy as compared to IL-1Ra or Pred. Combination IL-1Ra and steroid therapy offers only minimal added efficacy over either agent used alone.

Biomechanical model of corneal transplantation.

PURPOSE: Refractive consequences of corneal transplants are analyzed using corneal biomechanical models assuming homogeneous and inhomogeneous stiffness distributions across the cornea. Additionally, refractive effects of grafts combined with volume removal procedures are also evaluated to develop methods to reduce postoperative refractive management of patients. METHODS: Refinements of a two-dimensional finite element model are applied to simulate the biomechanical and refractive effects of different corneal transplant procedures: anterior lamellar keratoplasty, posterior lamellar keratoplasty, and penetrating keratoplasty. The models are based on a nonlinearly elastic, isotropic formulation. Predictions are compared with published clinical data. RESULTS: The model simulating the penetrating keratoplasty procedure predicts more change in the postoperative corneal curvature than models simulating anterior lamellar keratoplasty or posterior lamellar keratoplasty procedures. When a lenticle-shaped tissue with a central thickness of 50 microns and a diameter of 4 mm is removed from the anterior corneal surface along with the anterior lamellar keratoplasty or posterior lamellar keratoplasty, the models predict a refractive correction of -8.6 and -8.9 diopters, respectively. CONCLUSIONS: Simulations indicate that a posterior lamellar keratoplasty procedure is preferable for obtaining a better corneal curvature profile, eliminating the need for specific secondary treatments.

The impact of corneal allograft rejection on the long-term outcome of corneal transplantation.

PURPOSE: To examine the influence of corneal allograft rejection on the survival of penetrating corneal transplantation, to review the status of conventional therapies to improve graft survival, and to consider prospects for alternative approaches to reduce the impact of rejection. DESIGN: Perspective, including prospective, observational cohort study. METHODS: An examination of the literature on human corneal graft rejection and data from the Australian Corneal Graft Registry, reviewed in the context of clinical experience. RESULTS: Corneal graft outcome is not improving with era. The sequelae of inflammation, whether occurring before corneal transplantation or subsequently, exert a profound influence by predisposing the graft to rejection. Of the developments that have been instrumental in reducing rejection in vascularized organ transplantation, living-related donation is not an option for corneal transplantation. However, HLA matching may be beneficial and requires reassessment. The evidence base to support the use of systemic immunosuppressive agents in corneal transplantation is thin, and topical glucocorticosteroids remain the drugs of choice to prevent or reverse rejection episodes. Experimental approaches to local allospecific immunosuppression, including the use of antibody-based reagents and gene therapy, are being developed but may be difficult to translate from the laboratory bench to the clinic. CONCLUSIONS: Corneal allograft rejection remains a major cause of graft failure. High-level evidence to vindicate the use of a particular approach or treatment to prevent or treat corneal graft rejection is lacking. In the absence of extensive data from randomized, controlled clinical trials, corneal graft registers and extrapolation from experimental models provide some clinically useful information.

Cornea graft endothelial cells undergo apoptosis by way of an alternate (caspase-independent) pathway.

PURPOSE: To look for apoptosis pathways involved in corneal endothelial cell death during acute graft rejection and to evaluate the potential role of nitric oxide in this process. MATERIALS AND METHODS: Corneal buttons from Brown-Norway rats were transplanted into Lewis rat corneas. At different time intervals after transplantation, apoptosis was assessed by diamino-2-phenylindol staining and annexin-V binding on flat-mount corneas, and by terminal transferase dUTP nick end labeling (TUNEL), caspase-3 dependent and leukocyte elastase inhibitor (LEI)/LDNase II caspase-independent pathways on sections. Inducible nitric oxide synthase (NOS-II) expression and the presence of nitrotyrosine were assayed by immunohistochemistry. RESULTS: Graft endothelial cells demonstrated nuclear fragmentation and LEI nuclear translocation, annexin-V binding, and membranes bleb formation. Apoptosis associated with caspase-3 activity or TUNEL-positive reaction was not observed at any time either in the graft or in the recipient corneal endothelial cells. During 14 days posttransplantation, the recipient corneal endothelial cells remained unaltered and their number unchanged in all studied corneas. NOS-II was expressed in infiltrating cells present within the graft. This expression was closely associated with the presence of nitrotyrosine in endothelial and infiltrating cells. CONCLUSION: During the time course of corneal graft rejection, graft endothelial cells undergo apoptosis. Apoptosis is caspase 3 independent and TUNEL negative and is, probably, carried out by an alternative pathway driven by an LEI/L-Dnase II. Peroxynitrite formation may be an additional mechanism for cell toxicity and programmed cell death of the graft endothelial cells during the rejection process in this model.

Influence of donor storage time on corneal allograft survival.

PURPOSE: To investigate the influence of graft storage time on corneal allograft survival in high-risk and low-risk patients. DESIGN: Comparative retrospective nonrandomized clinical trial. PARTICIPANTS: Overall, 193 patients with 210 corneal allografts were classified as high risk or low risk for corneal allograft rejection on the basis of recipient corneal neovascularization and number of ipsilateral transplants. METHODS: Data from 3 groups were evaluated. The first group received fresh (no storage in culture medium) corneas, the second received corneas of donor storage time less than 7 days in minimum essential medium (MEM) at 37 degrees C, and the final group received corneas stored in MEM longer than 7 days. Recipients were analyzed for development of immune rejection according to storage time of the corneal tissue. Corneal allograft survival rate was determined with Kaplan-Meier survival analysis. The log-rank test was used to determine statistical significance. MAIN OUTCOME MEASURES: Risk of reversible and irreversible allograft rejection in corneas stored at various intervals in high-corneal and low-corneal transplant patients. RESULTS: High-risk corneal allograft recipients had a significantly prolonged allograft survival when the tissue was stored for 7 days or greater, compared with recipients receiving fresh tissues. Patients at low risk of corneal allograft rejection also showed a tendency for prolonged survival, although not statistically significant (P = 0.06). CONCLUSIONS: Storage of corneal tissue may reduce the frequency of allograft rejection, especially in high-risk patients.

Lymph node removal enhances corneal graft survival in mice at high risk of rejection.

BACKGROUND: As shown previously, the submandibular (SM) lymph node (LN) is required for priming the immune response during corneal graft rejection. In this study, we wished to determine whether corneal grafts at "high-risk" of rejection were also protected after selective SM LN removal and if so to investigate whether this improved corneal graft survival was due to induction of specific regulatory/suppressor cells or was due to immunological "ignorance". METHODS: Two sets of experiments were performed. (1) Adoptive transfer of possible regulatory splenocytes from mice with long-term accepted corneal graft after SM LN removal. (2) SM LN removal and corneal grafts in "high-risk" hosts, which had been (A) subjected to corneal trauma with vascularization or (B) allosensitized by previous corneal graft or (C) allosensitized by previous skin graft. RESULTS: Adoptive transfer of splenocytes from tolerant mice after SM LN removal did not enhance corneal graft survival in naive recipients (p > 0.05). SM LN removal in mice with corneal vascularization enhanced corneal allograft survival compared to grafted controls with/without vascularization (p < 0.0001). The removal of the SM LN in mice, who had already been allosensitized by a previous corneal graft, did not statistically prolong corneal graft survival (p > 0.05). SM LN removal procedure did not delay rejection of corneal grafts in mice allosensitized by a previous skin transplant with the same strain combination (p > 0.05). CONCLUSION: The results suggest that removal of the SM LN in "high-risk" mice prevents rejection by mechanisms involving immune "ignorance", since prior allosensitization prevents graft acceptance after LN removal. In allosensitized recipients the stronger the allosensitization (skin- vs. corneal graft-presensitization) the greater the possibility of priming for rejection at alternative draining LN sites.

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.