Cytokine mRNA expression during experimental corneal allograft rejection

Blockade of costimulatory CD27/CD70 pathway promotes corneal allograft survival

PURPOSE

To determine whether the CD27/CD70 pathway plays a significant role in corneal allograft rejection by investigating the effect of blocking the CD27/CD70 pathway by anti-CD70 antibody on corneal allograft survival.

METHODS

Orthotopic penetrating keratoplasty was performed using C57BL/6 donor grafts and BALB/c recipients. Expression of CD27 and CD70 on rejected cornea was examined by immunohistochemistry. Corneal transplant recipients received intraperitoneal injection of anti-CD70 antibody (FR70) or control rat IgG. Alloreactivity was measured by mixed lymphoid reaction (MLR) in recipients administered control rat IgG and those administered anti-CD70 antibody. Corneal expression of IFN-γ and IL-12 was also examined in both groups. Graft opacity was assessed over an 8-week period and graft survival was evaluated using Kaplan-Meier survival curves. Proportion of CD4⁺CD44⁺ memory T cells in lymph nodes was measured by flow cytometry.

RESULTS

CD4⁺CD27⁺ cells and CD11c⁺CD70⁺ cells were present in rejected cornea. Anti-CD70 antibody administration suppressed alloreactivity in corneal allograft recipients, and inhibited IFN-γ expression in recipient cornea (p < 0.05). Anti-CD70 antibody suppressed opacity score of recipient cornea and prolonged corneal allograft survival (p < 0.05). Proportion of CD4⁺CD44⁺ memory T cells in recipient lymph nodes was reduced by anti-CD70 antibody treatment.

CONCLUSION

The CD27/CD70 pathway plays a significant role in corneal allograft rejection by initiating alloreactive Th1 cells and preserving memory T cells. Anti-CD70 antibody administration prolongs corneal allograft survival indicating the potential therapeutic effect of CD27/CD70 pathway blockade on corneal allograft rejection.

Immune reactions after modern lamellar (DALK, DSAEK, DMEK) versus conventional penetrating corneal transplantation

In the past decade, novel lamellar keratoplasty techniques such as Deep Anterior Lamellar Keratoplasty (DALK) for anterior keratoplasty and Descemet stripping automated endothelial keratoplasty (DSAEK)/Descemet membrane endothelial keratoplasty (DMEK) for posterior keratoplasty have been developed. DALK eliminates the possibility of endothelial allograft rejection, which is the main reason for graft failure after penetrating keratoplasty (PK). Compared to PK, the risk of endothelial graft rejection is significantly reduced after DSAEK/DMEK. Thus, with modern lamellar techniques, the clinical problem of endothelial graft rejection seems to be nearly solved in the low-risk situation. However, even with lamellar grafts there are epithelial, subepithelial and stromal immune reactions in DALK and endothelial immune reactions in DSAEK/DMEK, and not all keratoplasties can be performed in a lamellar fashion. Therefore, endothelial graft rejection in PK is still highly relevant, especially in the "high-risk" setting, where the cornea's (lymph)angiogenic and immune privilege is lost due to severe inflammation and pathological neovascularization. For these eyes, currently available treatment options are still unsatisfactory. In this review, we will describe currently used keratoplasty techniques, namely PK, DALK, DSAEK, and DMEK. We will summarize their indications, provide surgical descriptions, and comment on their complications and outcomes. Furthermore, we will give an overview on corneal transplant immunology. A specific focus will be placed on endothelial graft rejection and we will report on its incidence, clinical presentation, and current/future treatment and prevention options. Finally, we will speculate how the field of keratoplasty and prevention of corneal allograft rejection will develop in the future.

Effects of an intravitreal injection of interleukin-35-expressing plasmid on pro-inflammatory and anti-inflammatory cytokines

In order to explore the potential effects of interleukin (IL)-35 on IL-10, transforming growth factor-β (TGF-β), interferon-γ (INF)-γ, IL-12 and IL-17, a pcDNA3.1‑IL-35 plasmid was injected into the vitreous cavity of BALB/c mice. Enzyme-linked immunosorbent assay, western blot analysis and quantitative PCR analysis were performed to confirm the successful expression of IL-35. Slit-lamp biomicroscopy, hematoxylin and eosin staining and immunofluorescence were employed to detect the status of eyes, and western blot analysis was performed to examine the expression of corneal graft rejection-related cytokines. There were no abnormalities in the eyes pre-mydriasis or post-mydriasis and no injuries to the cornea or retina following the injection of IL-35-expressing plasmid. An immunofluorescence assay detected the positive expression of IL-35 in corneal epithelial cells from IL-35‑injected mice and negative staining in the control group. Further study revealed that IL-35 enhanced the expression of IL-10 and TGF-β which reached their highest levels at 1 and 2 weeks after injection, respectively (p<0.01). Moreover, the expression of INF-γ and IL-12 was decreased significantly at 2 weeks after the injection of IL-35-expressing plasmid (p<0.05), and the expression of IL-17 was suppressed notably at 4 weeks after the injection (p<0.05). The intravitreal injection of IL-35-expressing plasmid in mice downregulates the expression of pro-inflammatory cytokines and upregulates the expression of anti-inflammatory cytokines. Thus, IL-35 may further be assessed as a potential target for the treatment of corneal graft rejection.

Targeted complement inhibition and microvasculature in transplants: a therapeutic perspective

Active complement mediators play a key role in graft-versus-host diseases, but little attention has been given to the angiogenic balance and complement modulation during allograft acceptance. The complement cascade releases the powerful proinflammatory mediators C3a and C5a anaphylatoxins, C3b, C5b opsonins and terminal membrane attack complex into tissues, which are deleterious if unchecked. Blocking complement mediators has been considered to be a promising approach in the modern drug discovery plan, and a significant number of therapeutic alternatives have been developed to dampen complement activation and protect host cells. Numerous immune cells, especially macrophages, develop both anaphylatoxin and opsonin receptors on their cell surface and their binding affects the macrophage phenotype and their angiogenic properties. This review discusses the mechanism that complement contributes to angiogenic injury, and the development of future therapeutic targets by antagonizing activated complement mediators to preserve microvasculature in rejecting the transplanted organ.

Topical application of soluble CD83 induces IDO-mediated immune modulation, increases Foxp3+ T cells, and prolongs allogeneic corneal graft survival

Modulation of immune responses is one of the main research aims in transplant immunology. In this study, we investigate the local immunomodulatory properties of soluble CD83 (sCD83) at the graft-host interface using the high-risk corneal transplantation model. In this model, which mimics the inflammatory status and the preexisting vascularization of high-risk patients undergoing corneal transplantation, allogeneic donor corneas are transplanted onto sCD83-treated recipient animals. This model allows the direct and precise application of the immune modulator at the transplantation side. Interestingly, sCD83 was able to prolong graft survival after systemic application as well as after topical application, which is therapeutically more relevant. The therapeutic effect was accompanied by an increase in the frequency of regulatory T cells and was mediated by the immune-regulatory enzyme IDO and TGF-β. In vitro, sCD83 induced long-term IDO expression in both conventional and plasmacytoid dendritic cells via autocrine or paracrine production of TGF-β, a cytokine previously shown to be an essential mediator of IDO-dependent, long-term tolerance. These findings open new treatment avenues for local immune modulation after organ and tissue transplantation.

Concise review: immunological properties of ocular surface and importance of limbal stem cells for transplantation

Cornea transplantation has been considered to be different from other solid organ transplantation because of the assumed immune-privileged state of the anterior chamber of the eye. Three major lines of thought regarding the molecular mechanisms of immune privilege in the eye are as follows: (a) anatomical, cellular, and molecular barriers in the eye; (b) anterior chamber-associated immune deviation; and (c) immunosuppressive microenvironment in the eye. However, cornea transplants suffer allograft rejection when breached by vascularization. In recent developments, cellular corneal transplantation from cultivated limbal epithelial cells has shown impressive advances as a future therapy. The limbal stem cell niche contains stem cells that promote proliferation and migration and have immunosuppressive mechanisms to protect them from immunological reactions. Limbal stem cells are also noted to display an enhanced expression of genes for the antiapoptotic proteins, a property that is imperative for the survival of transplanted tissues. Further investigation of the molecular mechanisms regulating the immune regulation of limbal stem cells is relevant in the clinical setting to promote the survival of whole corneal and limbal stem cell transplantation.

Gamma-irradiation reduces the allogenicity of donor corneas

PURPOSE

To evaluate the utility and allogenicity of gamma-irradiated corneal allografts.

METHODS

Corneal buttons were harvested from C57BL/6 mice and decellularized with gamma irradiation. Cell viability was assessed using TUNEL and viability/cytotoxicity assays. Orthotopic penetrating keratoplasty was performed using irradiated or nonirradiated (freshly excised) C57BL/6 donor grafts and BALB/c or C57BL/6 recipients. Graft opacity was assessed over an 8-week period and graft survival was evaluated using Kaplan-Meier survival curves. Mixed-lymphocyte reactions and delayed-type hypersensitivity assays were performed to evaluate T-cell alloreactivity. Real-time PCR was used to investigate the corneal expression of potentially pathogenic T-helper 1, 2, and 17 cell-associated cytokines.

RESULTS

Corneal cells were devitalized by gamma irradiation as evidenced by widespread cellular apoptosis and plasma membrane disruption. Nonirradiated allograft and isograft rates of survival were superior to irradiated allograft and isograft rates of survival (P < 0.001). Mixed lymphocyte reactions demonstrated that T-cells from irradiated allograft recipients did not exhibit a secondary alloimmune response (P < 0.001). Delayed-type hypersensitivity assays demonstrated that irradiated allografts did not elicit an alloreactive delayed-type hypersensitivity response in graft recipients (P ≤ 0.01). The corneal expression of T-helper 1, 2, and 17 cell-associated cytokines was significantly lower in failed irradiated allografts than rejected nonirradiated allografts (P ≤ 0.001).

CONCLUSIONS

Gamma-irradiated corneas failed to remain optically clear following murine penetrating keratoplasty; however, gamma irradiation reduced the allogenicity of these corneas, potentially supporting their use in procedures such as anterior lamellar keratoplasty or keratoprosthesis implantation.

An experimental study on in situ transfection of the interleukin-1 receptor antagonist (IL-1ra) gene into the rat cornea

OBJECTIVE

To investigate the efficiency of the transfection of PEGFP-IL-1ra plasmid via cation polymer mediation (poly-ethylenimine, PEI) by injection into the corneal stroma.

METHODS

Plasmid PEGFP-hIL-1ra recombinants were constructed and transferred into corneal endothelial cells via cation polymer mediation. Plasmid PEGFP-hIL-1ra recombinants and/or PEI-in-vivo were injected into the corneal stroma of Wistar rats. Corneas were harvested at different time points (days 3, 6, 14 and 21) after injection. The expression of IL-1ra after transfection was studied by fluorescence microscopy, transmission electron microscopy, real time polymerase chain reaction (RT-PCR) and immunohistochemistry.

RESULTS

Plasmid PEGFP-hIL-1ra recombinants were constructed successfully. After injection of pEGFP-hIL-1ra plasmid into the cornea, IL-1ra mRNA expression was detected in the corneal stroma and reached a peak on day 6. IL-1ra-GFP granules could be observed in every layer of the cornea in the PEGFP-hIL-1ra recombinant group by transmission electron microscopy, but not in the negative control (PEI-in-vivo) group. P63 immunocytochemical staining in the corneal epithelium was positive in both groups. There was no impairment in the ultrastructure of cells in both groups.

CONCLUSIONS

By direct injection of PEGFP-hIL-1ra into the corneal stroma and mediation by the cation polymer, the IL-1ra gene could be transferred and expressed in corneal tissue efficiently. This may be a novel technique for gene transfection to the cornea in situ.

Therapeutic effect of intravitreal injection of triamcinolone in the treatment of endothelial graft rejection: a pilot study

PURPOSE

To investigate the efficacy of intravitreal triamcinolone acetonide (IVTA) injection in the treatment of endothelial graft rejection and the expression of T-helper type 1 (Th-1) chemokines in the aqueous humor.

METHODS

Eleven patients (11 eyes) with acute endothelial graft rejection underwent IVTA (4 mg/0.1 mL) injection in addition to conventional treatment, including systemic and topical steroids and cyclosporine A (group A); 13 patients (13 eyes) received conventional treatment only (group B). Clinical characteristics were analyzed. In group A, Th-1 chemokines (CXCL-9, -10, and -11) in aqueous humor were measured by enzyme-linked immunosorbent assay and CXCR3(+) cells were counted by flow cytometry before treatment and at the period of improvement.

RESULTS

There were no significant differences in visual acuity, intraocular pressure, and recurrence rate between the 2 groups. The mean time to improvement was 9.1 ± 3.9 days in group A and 15.4 ± 5.5 days in group B (P = 0.04). The concentrations of CXCL-9, -10, and -11 were 562.7 ± 109.4, 30293.1 ± 12537.1, and 228.3 ± 80.8 pg/mL before treatment and 6.7 ± 6.8 (P < 0.01), 207.5 ± 209.8 (P < 0.01), and 18.9 ± 19.5 (P < 0.01) pg/mL after treatment, respectively. The CXCL-10 level correlated with the time to improvement of graft rejection (P = 0.02). Flow cytometry demonstrated a significantly decreased number of CXCR3(+) and CXCR3(+)CD4(+) cells in the aqueous humor after treatment.

CONCLUSION

IVTA injection was effective in reducing the time to improvement of endothelial graft rejection. Increased expression of CXCL-9, -10, and -11, and their receptors in the aqueous humor of patients with endothelial graft rejection decreased after treatment.

Xenotransplantation--the future of corneal transplantation?

Although corneal transplantation (Tx) is readily available in the United States and certain other regions of the developed world, the need for human donor corneas worldwide far exceeds supply. There is currently renewed interest in the possibility of using corneas from other species, especially pigs, for Tx into humans (xeno-Tx). The biomechanical properties of human and pig corneas are similar. Studies in animal models of corneal xeno-Tx have documented both humoral and cellular immune responses that play roles in xenograft rejection. The results obtained from the Tx of corneas from wild-type (ie, genetically unmodified) pigs into nonhuman primates have been surprisingly good and encouraging. Recent progress in the genetic manipulation of pigs has led to the prospect that the remaining immunological barriers will be overcome. There is every reason for optimism that corneal xeno-Tx will become a clinical reality within the next few years.

Barrier dysfunction of the corneal endothelium in response to TNF-alpha: role of p38 MAP kinase

PURPOSE

TNF-alpha is elevated in the cornea and aqueous humor during allograft rejection and anterior uveitis. The authors investigated the involvement of p38 MAP kinase in the TNF-alpha-induced loss of barrier integrity in monolayers of cultured bovine corneal endothelial cells.

METHODS

Transendothelial electrical resistance (TER), a measure of barrier integrity, was determined by electrical cell-substrate impedance sensing. Barrier integrity was further assessed in terms of permeability to FITC dextran. Reorganization of the apical junctional complex (AJC) in response to TNF-alpha was visualized by immunofluorescence. The expression of TNF-alpha receptors was confirmed by RT-PCR. Activation of p38 MAP kinase in response to TNF-alpha was determined by Western blot analysis.

RESULTS

Exposure to TNF-alpha induced a continuous decline in TER that persisted for more than 20 hours. It also led to a significant increase in permeability to FITC dextran. At the AJC, the cytokine caused disassembly of microtubules, disruption of perijunctional actomyosin ring (PAMR), and dislocation of ZO-1 and cadherins. Western blot analysis showed that TNF-alpha also led to the activation of p38 MAP kinase. All these responses to the cytokine were opposed by treatment with SB-203580, a selective p38 MAP kinase inhibitor. TNFR1, but not TNFR2, was expressed in untreated cells with no change in the expression pattern on treatment with the cytokine.

CONCLUSIONS

TNF-alpha breaks down the barrier integrity of corneal endothelium, concomitant with the disruption of PAMR, remodeling of AJC, and disassembly of microtubules. These effects are mediated by transient activation of p38 MAP kinase. Thus, the TNF-alpha-induced barrier dysfunction in the corneal endothelium can be suppressed by inhibitors of p38 MAP kinase and agents downstream of the kinase that affect the cytoskeleton.

Increased Rac2 mRNA expression in peripheral blood during human corneal graft rejection

PURPOSE

Allograft rejection is the main cause of graft failure in human corneal transplantation, for which underlying pathomechanism is not yet clear. We compared gene expression in the peripheral blood of patients who after undergoing corneal transplantation experienced graft rejection with those patients who accepted grafts.

METHODS

Sixty-six patients who underwent corneal transplantation were studied including 18 patients who suffered subsequent graft rejection. cDNA array technology was used to survey and quantify transcript expression. A semiquantitative reverse transcriptase-PCR (RT-PCR) was used to confirm the gene expression pattern measured by a cDNA array of selected genes.

RESULTS

Among 265 genes present on the array, eight genes were found to be differentially expressed. Four genes (Rac 2, RhoA, paxillin, and CD18) were further analysed by semiquantitative RT-PCR, and significant differences in mRNA expression levels in the rejection group were confirmed.

CONCLUSIONS

Our study demonstrated that the expression of Rac2 mRNA was upregulated in the peripheral blood of patients experiencing corneal transplantation rejection compared to those patients who had no rejection episodes. In addition, three genes, RhoA, paxillin, and CD18, showed decreased expression in rejecting patients. cDNA array technology provides a potentially useful approach to identify novel genes that might participate in pathogenic pathways during corneal graft rejection.

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.

Immune mechanisms of corneal allograft rejection

Penetrating keratoplasty has been successfully performed on humans for over 100 years and remains the most common form of solid tissue transplantation. Although corneal allografts enjoy a remarkable degree of immune privilege, immune rejection remains the leading cause of keratoplasty failure. The immunologic basis for corneal allograft rejection was established in animal studies over 50 years ago, yet large gaps remain in our knowledge regarding the cellular and molecular mechanisms of corneal allograft rejection. The enormous redundancy in the mammalian immune system creates a condition that favors the development of multiple independent immune mechanisms that can produce corneal allograft rejection. Although there are few absolute principles, it is certain that the immune rejection of corneal allografts is (1) T cell-dependent, (1) heavily dependent upon CD4(+) T cells, (3) not restricted to either Th1 or Th2 T cell populations, and (4) dependent upon an intact repertoire of resident antigen presenting cells.

Effects of interleukin-12p40 gene transfer on rat corneal allograft survival

PURPOSE

Despite the immunologically privileged nature of the cornea, graft rejection remains the major cause of human corneal allograft failure. Gene therapy is an interesting approach to introduce immunoregulatory molecules into the graft or the recipient to prevent rejection. In this study we investigated the immmunomodulatory effects of adenovirus-mediated gene transfer of a Th1 antagonist, interleukin-12p40 (IL-12p40), in vitro and on allogeneic graft survival in a rat experimental keratoplasty model.

METHODS

Donor corneas were transduced with an E1/E3 deleted adenoviral (Ad) vector encoding the IL-12p40 gene (AdIL-12p40) and assayed for the expression of the therapeutic gene. Cell culture supernatants containing IL-12p40 protein were generated by transducing human corneal endothelial cells with AdIL-12p40 and analysed for their capacity to inhibit production of IFN-gamma by naive T cells. The effect of both local (ex vivo Ad-mediated gene transfer) and systemic (i.p.-injection) over-expression of IL-12p40 was investigated by analysing the survival of corneal allografts transplanted from Wistar-Furth rats to fully MHC-class I/II incompatible Lewis rats. Moreover, the intra-graft mRNA-expression profile of cytokines and T cell markers was investigated at different time points after gene transfer.

RESULTS

Adenovirus-mediated gene transfer in cultured corneas led to significant IL-12p40 protein expression as determined by specific ELISA. Moreover we could show that IL-12p40 protein containing supernatants significantly inhibited the production of IFN-gamma by alloreactive naive T cells. Interestingly, neither ex vivo genetic modification of cultured corneas before transplantation nor systemic AdIL-12p40 treatment of recipients receiving allogeneic corneas did improve corneal allograft survival. Real-time RT-PCR analysis of ex vivo modified cornea allografts on day 7 after transplantation showed significantly higher IL-4 mRNA-expression levels in the AdIL-12p40 group compared to the control group. Other significant differences in mRNA-expression levels of intra-graft CD3, CD25, IFN-gamma, TNF-alpha, and IL-10 could not be detected, neither on day 7 nor on the day of rejection.

CONCLUSIONS

Despite the capacity of IL-12p40 protein to inhibit the production of IFN-gamma of naive T cells in vitro and some Th1/Th2 shift in vivo, no prolongation of allogeneic graft survival of both AdIL-12p40 modified rat corneas and systemically treated rats could be obtained after transplantation. The possible binding of Ad-mediated IL-12p40 with ubiquitously expressed IL-12p35 in vivo might therefore limit the application of IL-12p40 for the prevention of transplant rejection.

Effects of local and systemic viral interleukin-10 gene transfer on corneal allograft survival

In this study, we explored the immunomodulatory effects of viral interleukin (IL) IL-10 after ex vivo and in vivo gene transfer in experimental corneal transplantation. Wistar-Furth rats were used as donors and major histocompatibility complex class I/II-disparate Lewis rats served as recipients. For ex vivo gene therapy donor corneas were either transfected with liposome/vIL-10 plasmid DNA mixtures or transduced with a vIL-10 expressing adenovirus vector (AdvIL-10). For in vivo studies, recipients were treated with AdvIL-10 intraperitoneally 1 day before transplantation. Graft survival was analysed using the Kaplan-Meier survival method. To monitor the efficacy of the therapy messenger RNA (mRNA) cytokine expression profiles in grafts and draining lymph nodes were analysed by quantitative real-time reverse transcription-polymerase chain reaction. Moreover, anti-adenovirus immunity was also investigated. Neither ex vivo liposome-mediated vIL-10 gene transfer nor ex vivo AdvIL-10 gene transfer led to prolonged corneal allograft survival. In contrast, corneal allograft survival was significantly prolonged in animals receiving systemic AdvIL-10 gene transfer. Moreover, only systemic vIL-10 gene therapy modulated the cytokine mRNA expression profile in draining lymph nodes. Interestingly, systemic AdvIL-10 gene transfer could not inhibit the generation of anti-adenovirus antibodies. Our data indicate systemic expression of the vIL-10 gene is required to modulate the cytokine expression profile in the draining lymph nodes, which might be a pre-requisite for the success of cytokine gene therapy.

Differences in leukocyte phenotype and interferon-γ expression in stroma and endothelium during corneal graft rejection

Critical to the success of human corneal transplants is prevention of corneal endothelial rejection, yet little is known about the endothelial infiltrate. To examine the endothelium, a method for removal and processing this layer as a flat sheet was used and the infiltrate was compared with stroma and epithelium. LEW or PVG strain rat corneas were transplanted to PVG strain recipients. Clinical changes after transplantation were monitored by slit lamp and animals sacrificed at a range of time points during rejection. Clinically defined rejection, accompanied by an epithelial rejection line and endothelial cell infiltration, occurred between days 10 and 15. There was some infiltration of leukocytes in the stroma of isografts at these time points, but significantly more in allografts (p<0.003 for all subsets). There was no infiltration of isograft endothelium at any time and no infiltration of allograft endothelium on day 10. On day 15, there were similar numbers of all major subsets except B cells in the stroma, while on the endothelium macrophages, MHC class II(+) cells and CD8(+) cells predominated (p<0.001 CD4(+) vs CD8(+) cells). T cells and NK cells predominated in the epithelial rejection line. While TNF-alpha and IFN-gamma-producing cells were numerous in stroma and epithelium, no IFN-gamma-producing cells were found on endothelium. Distinct differences in infiltrative profile within layers of the cornea suggest that the mechanisms of rejection may also differ. The restricted endothelial cell profile and lack of IFN-gamma suggests that the anti-endothelial response may be modulated by the anterior chamber environment.

Corneal rat-to-mouse xenotransplantation and the effects of anti-CD4 or anti-CD8 treatment on cytokine and nitric oxide production

Corneal xenotransplantation may be an alternative approach to overcome shortage of allografts for clinical transplantation. Orthotopic corneal rat-to-mouse xenotransplantation and syngeneic transplantation was performed and the effects of anti-CD4 and anti-CD8 treatments on corneal xenograft survival and production of cytokines, interleukin (IL)-2, IL-4, IL-10, gamma-interferon (IFN-gamma) and nitric oxide (NO) were evaluated. RT-PCR was used to determine the expression of genes for cytokines and inducible nitric oxide synthase (iNOS) in the grafts. The presence of iNOS protein in grafts was detected by immunofluorescent staining. We found that corneal xenotransplantation was associated with a strong upregulation of genes for both Th1 and Th2 cytokines and with NO production in the graft. Treatment of xenograft recipients with mAb anti-CD4, but not anti-CD8, resulted in a profound inhibition of IL-2, IL-4 and IL-10 production, and in a significant prolongation of corneal xenograft survival. The results show that upregulation of Th2 cytokines after corneal xenotransplantation does not correlate with xenograft rejection. Rather, corneal graft rejection is associated with the expression of genes for IFN-gamma and iNOS and with NO production.

Cutting edge: atopy promotes Th2 responses to alloantigens and increases the incidence and tempo of corneal allograft rejection

A large body of evidence suggests that corneal allograft rejection is mediated by a type 1 Th cell response and that deviation toward type 2 immunity favors graft survival. However, clinical observations indicate that patients with severe ocular allergies have increased risk of corneal allograft rejection. We used a mouse model of atopic conjunctivitis to evaluate the effects of Th2 immune deviation on corneal allograft survival and possible mechanisms of graft rejection. Our results reveal the following novel findings: 1) atopic conjunctivitis promotes systemic Th2 immune responses to corneal graft donor alloantigens; 2) corneal allografts in atopic host eyes have an increased incidence and swifter tempo of rejection; 3) increased rejection is associated with alterations in systemic T cell-mediated responses to donor alloantigens; and 4) corneal allograft rejection in atopic hosts does not require the direct involvement of infiltrating eosinophils.

Effects of a selective glucocorticoid receptor agonist on experimental keratoplasty

BACKGROUND

New insights into the molecular mechanisms of corticosteroid-mediated actions have revealed new substances, such as selective glucocorticoid receptor agonists (SEGRA), for the treatment of inflammatory diseases. We set out to evaluate the effect of a SEGRA compound following topical application on the course of experimental orthotopic corneal grafts.

METHODS

A total of 42 female Lewis rats received 3.5-mm MHC I/II-incompatible corneal grafts from DA donors. Recipients were randomly assigned to receive either no therapy, 0.25% cyclodextrin-encapsulated SEGRA compound in a new microemulsion formulation or carrier system only. All treatments started on the day of surgery and were given five times daily for 35 days. Grafts were graded every day and a rejection score was generated based on cornea clarity and edema. In addition, intragraft mRNA expression of CD3, IFN-gamma, TNF-alpha, IL-10 and IL-4 was analyzed using real-time RT-PCR analysis at day 7 after transplantation before rejection occurred in additional control animals.

RESULTS

Topical application of a SEGRA compound was highly effective in prolonging the mean survival time of corneal grafts (42.2+/-4.0 days) compared with untreated controls (11.7+/-1.2 days, p=0.00003) or animals that received the vehicle only (15.0+/-1.5 days, p=0.114). In addition, real-time RT-PCR analysis of SEGRA-treated grafts revealed lower mRNA expression of intragraft cytokines; the difference was significant for IL-4 (p<0.05).

CONCLUSIONS

Our results indicate that topical application of a SEGRA compound significantly prolongs corneal graft survival in an experimental keratoplasty model. It further suggests that SEGRA can be a potentially useful drug to suppress the immune response.

Gene therapy approaches to prolonging corneal allograft survival

Irreversible immunological rejection is the major cause of human corneal allograft failure and occurs despite the use of topical glucocorticoid immunosuppression. Systemic pharmacological interventions have not found widespread favour in corneal transplantation because of associated morbidities and inadequate demonstration of efficacy. Gene therapy offers tantalising prospects for improving corneal allograft survival, especially in those recipients at high risk of graft rejection. Donor corneas can be gene-modified ex vivo, while in storage prior to implantation, and the relative isolation of the transplanted cornea from the circulation decreases the risk of potential systemic complications. A wide variety of vectors have been found suitable for gene transfer to the cornea. The mechanisms involved in corneal graft rejection have been placed on a relatively secure footing over the past decade and in consequence a number of transgenes with promise for modulating rejection have been identified. However, relatively few studies have thus far demonstrated significant prolongation of corneal allograft survival after gene transfer to the donor cornea. In these instances, the therapeutic protein almost certainly acted at a proximal level in the afferent immune response, within the ocular environs.

Corneal transplantation: the forgotten graft

The most commonly performed transplant is that of the cornea, with 2292 corneal grafts performed in the UK in 2002-03, compared with 1775 renal transplants [1]. In the USA approximately 40 000 transplants are performed every year [2]. However this preponderance is not reflected in the amount of attention given to this transplanted tissue by the scientific community: for example up till now there have been no papers published in the American Journal of Transplantation that have cornea as a key or title word (as determined by a Medline search in December 2003). There are several reasons for this. The first is that corneal grafting is the province of ophthalmologists, who (with notable exceptions) are isolated from the transplant community. The second is that there is a widespread belief that, because of the existence of immune privilege, corneal grafts are not rejected and so there is no need for further research. As we will discuss later, this is incorrect. In this article we will seek to show that study of corneal transplantation is important in its own right, and also that it has lessons for those interested in other forms of allograft.

Anti-angiogenic role of angiostatin during corneal wound healing

The purpose of this study is to determine whether angiostatin is involved in maintaining corneal avascularity after wounding. We generated polyclonal rabbit anti-mouse angiostatin antibodies directed against each of the five kringle domains, (K1-5) and anti-mouse plasmin B chain antibodies. Mouse corneas were immunostained with anti-K1 angiostatin antibody after excimer laser keratectomy. Corneal epithelial cell lysate was harvested and angiostatin was isolated using lysine sepharose. Purified plasminogen was incubated with lysate of mouse corneal epithelial cells from wild type mice in the presence or absence of MMP inhibitors. Angiostatin activity was determined using calf pulmonary artery endothelial (CPAE) cell proliferation assay with and without angiostatin immunoprecipitation; and corneal neovascularization was assayed by intrastromal injection of anti-plasminogen, anti-K1-3 or anti-B chain antibodies after corneal wounding. Using the anti-mouse angiostatin antibodies that we generated, we confirmed that angiostatin-like molecules were expressed in the corneal epithelium and in cultured corneal epithelial cells. Western blotting after incubation of scraped corneal epithelial cell lysate with purified plasminogen showed reduction of the plasminogen bands at 6, 12, and 24 hr, respectively. Complete cleavage of plasminogen occurred by 48 hr. Functional assays in which corneal epithelial cell extracts were incubated with CPAE cells resulted in inhibition of vascular endothelial cell proliferation. Depletion experiments using anti-angiostatin (K1) antibodies resulted in a 25 +/- 1.2% increase in vascular endothelial cell proliferation as compared to 12 +/- 1.8% using the protein A control (p < 0.05). Corneal neovascularization was observed after excimer laser keratectomy when anti-angiostatin antibodies were injected into the cornea (65 +/- 13%) which was significantly higher than when plasmin B chain antibodies were injected (10 +/- 2.6%; p < 0.05). Plasminogen and angiostatin are produced in the cornea. They may play a role in preventing vascularization and may contribute to the maintenance of corneal avascularity after excimer laser keratectomy.

Preliminary findings in corneal allograft rejection in patients with keratoconus

PURPOSE

Classically, corneal allograft rejection is thought to be a T(H)1-mediated phenomenon. However, T(H)2-mediated allograft rejection has been reported in other transplanted organ systems, including the heart and kidney. We previously reported a form of T(H)2-mediated corneal allograft rejection in a murine model with a T(H)2 immune bias. In this study we sought to determine if there was any evidence for this form of corneal allograft rejection in humans.

DESIGN

Experimental study with an interventional case series.

METHODS

The clinical records of all keratoconus patients undergoing penetrating keratoplasty at the University of Texas, Southwestern Medical Center from 1994 to 1999 were reviewed. Careful attention was paid to a clinical history of atopy. Atopic patients were selected, because these patients have been shown to have a "T(H)2 immune bias." The corneal graft rejection rate in these patients and the number of repeat corneal transplants performed was determined. The experimental group consisted of patients with a clinical history of atopy and keratoconus who had at least one repeat penetrating keratoplasty for an immunologically rejected corneal transplant. Any patient with evidence of primary allograft failure was excluded from this study. Tissue specimens from these patients were embedded in paraffin, serially sectioned, stained with Giemsa stains, and examined histologically. The control group consisted of patients without a clinical history of allergy (and therefore no T(H)2 immune bias) who underwent corneal transplantation for Fuch corneal endothelial dystrophy, or aphakic/pseudophakic bullous keratopathy. Failed grafts from these control patients were also paraffin embedded, serially sectioned, stained, and examined histologically. The human experimental and control corneal specimens were compared with data obtained in a murine model of T(H)2-mediated corneal allograft rejection. Briefly, full-thickness penetrating C57BL/6ByJ corneal allografts were transplanted onto Balb/cByJ and Balb/c-IFN-gamma(tm1Ts) (Balb/c-IFN-gamma knockout) mice. Additionally, full-thickness Balb/cByJ corneal allografts were transplanted onto C57BL/6ByJ and C57BL/6ByJ-IFN-gamma(tm1Ts) mice. Corneal allograft rejection rates and mean rejection times were calculated and compared between wild-type and interferon gamma (IFN-gamma) knockout hosts. The rejected allografts were examined histologically by the same methods used in the human tissue.

RESULTS

There were 84 penetrating keratoplasties performed from 1994 to 1999 for keratoconus. Seven of these 84 patients rejected their corneal grafts. Of the 7 patients who rejected their corneal allografts, 4 had repeat penetrating keratoplasty. Of these 4 repeat corneal allografts, 3 showed eosinophilia when compared with rejected grafts in control patients. Atopic keratoconus patients had a mixed inflammatory cellular infiltrate in the rejected corneal tissue specimen with a significantly greater density of eosinophils (P =.001) compared with patients who did not have a pre-existing T(H)2 bias. The inflammatory infiltrate in these patients without a T(H)2 immune bias was mononuclear. In the murine model, corneal allograft rejection did occur in the absence of IFN-gamma, a critical T(H)1 cytokine in both fully allogeneic donor-host combinations. Histologically, rejection in these ("T(H)2 mice") was characterized by a predominant eosinophilic infiltrate in the rejected graft bed when compared with wild-type animals ("T(H)1 mice") that had a predominantly mononuclear infiltrate in the rejected corneal graft bed.

CONCLUSIONS

Preliminary findings show that corneal allograft rejection in patients with a pre-existing T(H)2 phenotype is similar to what is seen in the murine model of T(H)2-mediated corneal allograft rejection. Based on this small sample, it appears that eosinophils may play a role in corneal allograft rejection in this group of patients. However, further study is necessary to determine the importance of these cells in allograft rejection.

Recent developments in the pharmacological treatment and prevention of corneal graft rejection

At present, given the high initial success rate of corneal transplantation (although late survival is poor), immunosuppression is often reserved for 'high-risk' patients. Despite immune privilege, corneal graft rejection remains the leading cause of corneal allograft failure. Interpreting the limited and also restricted design of most trials, immunosuppressive therapy has not enjoyed the success seen in solid organ grafts. This review discusses the limited data available whilst proposing newer therapies that have developed as a result of our increased understanding of the immunobiology of corneal graft rejection.

The role of cytokines in corneal immunopathology

Cytokines play an important role in the pathogenesis of various corneal diseases and during corneal graft rejection. Furthermore, cytokines may also play a role in the maintenance of the integrity of the normal cornea. This review focuses on the effects of several cytokines in corneal immunopathology, including the type of the corneal immune response, angiogenesis, chemotaxis, apoptosis, wound healing, corneal disease, and transplantation. It may provide clues for the future treatment of corneal disease and corneal transplantation rejection.

Are cytokine patterns in aqueous humour useful in distinguishing corneal graft rejection from opacification due to herpetic stromal keratitis?

PURPOSE

Intra-ocular cytokine profiles were determined to study the immunological mechanisms of corneal graft opacification due to rejection and/or herpetic stromal keratitis (HSK).

METHODS

Sera and aqueous humour (AH) were sampled shortly after the onset of corneal graft opacification, group I (n=18). In eyes with clear grafts, samples were taken 5 months after transplantation, group II (n=59). Samples of non-inflamed eyes, prior to cataract surgery, were used to determine baseline cytokine levels, group III (n=49). Total protein (TP) levels were measured with Bradford reagent and interleukin (IL)-6, IL-10, IL-4 and interferon (IFN)-gamma with ELISAs.

RESULTS

All patients who's corneal grafts showed clinical evidence of graft opacification due to rejection and/or HSK were sampled. In the AH-samples of group I, increased levels of TP were found in 60% (9/15), IL-6 in 79% (11/14), IL-10 in 39% (7/18) and IL-4 in none (0/12). IFN-gamma was detected in 19% (3/16), in the case of HSK only. In contrast, samples obtained from patients with clear grafts in group II showed increased levels of TP in 36% (20/55), IL-6 in 14% (8/57) and IL-10, IL-4 or IFN-gamma in none (n=58).

CONCLUSIONS

During corneal graft rejection and/or HSV-infection, increased levels of TP and IL-6 in AH confirmed anterior chamber inflammation with breakdown of the blood-aqueous barrier. Based on the data presented, cytokine patterns in the AH do not appear to distinguish corneal opacification due to graft rejection from that due to herpes keratitis.

Cytokine and chemokine expression kinetics after corneal transplantation

BACKGROUND

Allogeneic rejection is the most common cause of corneal graft failure. The aim of this work was to establish the kinetics of cytokine and chemokine mRNA expression before and after onset of corneal graft rejection.

METHODS

Intracorneal cytokine and chemokine mRNA levels were investigated in the Brown Norway-->Lewis inbred rat model in which rejection onset is observed at 8/9 days after grafting in all animals. Nongrafted corneas and syngeneic (Lewis-->Lewis) corneal transplants were used as controls. Donor and recipient cornea was examined by quantitative competitive reverse transcription-polymerase chain reaction (RT-PCR) for hypoxyanthine phosphoribosyltransferase (HPRT), CD3, CD25, interleukin (IL)-1beta, IL-1RA, IL2, IL-6, IL-10, interferon-gamma (IFN-gamma), tumor necrosis factor (TNF), transforming growth factor (TGF)-beta1, and macrophage inflammatory protein (MIP)-II and by nonquantitative RT-PCR for IL4, IL-5, IL-12 p40, IL-13, TGF-beta2, monocyte chemotactic protein-1 (MCP-1), MIP-1alpha, MIP-1beta, and RANTES (for regulated upon activation normal T cell expressed and secreted).

RESULTS

A biphasic expression of cytokine and chemokine mRNA was found after transplantation. During the early phase (days 3-9), there was an elevation of the majority of the cytokines examined, including IL-1beta, IL-6, IL-10, IL-12 p40, and MIP-II. There was no difference in cytokine expression patterns between allogeneic or syngeneic recipients at this time. In syngeneic recipients, cytokine levels reduced to pretransplant levels by day 13, whereas levels of all cytokines rose after observed rejection onset in the allografts, including TGF-beta1, TGF-beta2, and IL-1RA. The T cell-derived cytokines IL-4, IL-13, and IFN-gamma were detected only during the rejection phase in allogeneic recipients.

CONCLUSIONS

There is an early cytokine and chemokine response to the transplantation process, evident in syngeneic and allogeneic grafts, that probably drives angiogenesis, leukocyte recruitment, and affects leukocyte functions. After an immune response has been generated, allogeneic rejection results in the expression of Th1 cytokines (IL-2, IL-12 p40, IFN-gamma), Th2 cytokines (IL-4, IL-6, IL-10, and IL-13), and antiinflammatory/Th3 cytokines (TGF-beta1/2 and IL-1RA).

Local bioactive tumour necrosis factor (TNF) in corneal allotransplantation

The aim of this study was to examine the kinetic profile of bioactive TNF levels in aqueous humour of rabbit eyes undergoing corneal allograft rejection and to investigate the effect of locally blocking TNF activity after corneal transplantation. In a rabbit corneal transplantation, endothelial allograft rejection was identified and correlated with increase in central graft thickness. Samples of aqueous humour obtained on alternate days following transplantation were tested for TNF mRNA and bioactive TNF protein. To investigate the effect of locally blocking TNF activity in allograft recipients, the fusion protein TNFR-Ig was administered by injections into the anterior chamber after transplantation. Pulsatile increases in levels of this cytokine were found in 14 of 15 allograft recipients. Peaks of TNF bioactivity preceded by varying intervals the observed onset of rejection in allograft recipients. TNF levels were not elevated in aqueous humour from corneal autograft recipient controls or in serum of allografted animals. mRNA levels were elevated before onset of and during clinically observed allograft rejection. In three of seven animals receiving TNFR-Ig injections on alternate days from day 8 to day 16 post-transplant, clear prolongation of corneal allograft survival was demonstrated. Bioactive TNF is present in aqueous humour following rabbit corneal allotransplantation. Rather than correlating directly with endothelial rejection onset, pulsatile peak levels of TNF precede and follow the observed onset of endothelial rejection. Blockade of TNF activity prolongs corneal allograft survival in some animals, indicating that this cytokine may be a suitable target in local therapy of corneal allograft rejection.

Characterization of cytokine profiles in corneal allograft with anti-adhesion therapy

BACKGROUND

The cytokine profiles of specific immunosuppression after anti-adhesion molecule therapy are unknown in a mouse corneal transplantation model.

METHODS

Orthotopic mouse corneal transplantation was performed using BALB/c (H-2d) mice as recipients and C3H/He (H-2k) mice as donors. Anti-mouse very late antigen-4 and anti-mouse lymphocyte function-associated antigen-1 monoclonal antibodies (each at a dose of 0.25/mg/day) were administered i.p. until day 7. A second corneal transplantation was performed 5 weeks after the first grafting. Delayed hypersensitivity was tested after the second grafting. Corneal cytokine expression was examined immunohistochemically. The cytokine gene transcription level was assessed in the corneas and splenocytes.

RESULTS

All allografts with anti-adhesion molecule therapy survived for 5 weeks. Two weeks after the second grafts in the fellow eye (7 weeks after the first grafts), 50% of the mice with successful grafts bilaterally had low delayed hypersensitivity responses. Low helper T 1 (interferon-gamma and interleukin-2) cytokine gene and protein expression in corneas was observed in monoclonal antibody-treated mice 3 weeks after the first grafting. The mice with successful second grafts showed low corneal T helper 1 cytokine gene and protein expression. High interleukin-4 gene transcription levels in corneas and splenocytes was obtained in both groups in which the grafts were accepted and rejected after the second grafts.

CONCLUSIONS

The cytokine profile to differentiate alloantigen-specific acceptance with anti-adhesion therapy to lymphocyte function-associated antigen-1 and very late antigen-4 molecules from rejection after the second grafting is local and systemic low T helper 1 cytokine in corneal transplantation. High interleukin-4 cytokine expression in corneas and splenocytes is not associated with achievement of tolerance induction.

Role of tumor necrosis factor receptors TNFR-I (P55) and TNFR-II (P75) in corneal transplantation

BACKGROUND

To determine the role of tumor necrosis factor-alpha (TNF-alpha) receptor (TNFR) function in corneal allograft immunology.

METHODS

Animals with gene-targeted deficiency in TNFR-I (p55-/-), TNFR-II (p75-/-), or combined TNFR-I/TNFR-II deficiency (p55-/-p75-/-) and their wild-type controls were used as recipients of fully-mismatched (BALB/c; n=88) or multiple minor alloantigen-mismatched (BALB.b; n=62) orthotopic corneal transplants to determine the effect of selective deficiency in one or both TNF-alpha receptors on corneal allograft survival. Grafted recipients were followed biomicroscopically for signs of rejection, and survival data were analyzed by the Kaplan-Meier method.

RESULTS

There was no discernible difference in survival of fully-mismatched BALB/c corneal grafts in p55-/- (n=12; P=0.76) or in double-knockout p55-/-p75-/- (n=13; P=0.41) as compared with wild-type C57BL/6.129 hosts. However, the survival of BALB/c allografts was lower in p75-/- (n=10; median survival 20 days) as compared with control C57BL/6 (n=30; median survival 30 days) hosts (P=0.02). In contrast, there was no discernible effect in survival of minor alloantigen-disparate BALB.b corneal grafts in p75-/- (n=13; P=0.95) or in combined p55-/-p75-/-(n=10; P=0.17) hosts as compared with C57BL/6 (n=9) and C57BL/6.129 (n=10) wild-type controls, respectively. However, there was a profound enhancement in the survival of BALB.b allografts in p55-/- recipients (n= 10; median survival 35 days) as compared to wild-type C57BL/6.129 (n=10; median survival 25 days) controls (P<0.01).

CONCLUSIONS

Our data suggest that the two TNF-alpha receptors largely play discrete roles in mediating rejection of murine corneal allografts. TNFR-I (p55) function seems to be integral to the rejection of minor-disparate grafts, and its selective suppression leads to enhancement of allograft survival. In contrast, TNFR-II (p75) function appears to be associated with enhanced survival of major histocompatibility complex-disparate allografts. The combined deletion of TNFR functionality in p55-/-p75-/- confers no net advantage or disadvantage to major histocompatibility complex or minor alloantigen-disparate grafts.

Early expression of proinflammatory cytokines interleukin-1 and tumor necrosis factor-alpha after corneal transplantation

This study's aim was to determine the early postoperative expression of proinflammatory cytokines interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) by corneal grafts. BALB/c (n = 90) and C57BL/6 (n = 90) murine recipients were grafted with donor corneas from either syngeneic or allogeneic mice. At 7 and 14 days after surgery, corneal grafts were excised and the recipient rims separated from the donor tissue. Corneal segments were cultured and assayed for cytokines by enzyme-linked immunosorbent assay (ELISA). There was profound upregulation in expression of both IL-1alpha and TNF-alpha after corneal transplantation. Among both low-rejecting BALB/c and high-rejecting C57BL/6 hosts, levels of IL-1alpha were significantly (p < 0.01) more marked in allogeneic as compared to syngeneic grafts. TNF-alpha overexpression was similarly more marked in allogeneic as compared to syngeneic grafts in both BALB/c and C57BL/6 hosts, although the difference was generally more marked among high-rejecting C57BL/6 recipients. In the case of both IL-1alpha and TNF-alpha, the principal source of cytokine expression in the transplanted tissue was the recipient rim. There is significant overexpression of both IL-1alpha and TNF-alpha during the first 2 weeks after transplantation in both syngeneic and allogeneic orthotopic corneal grafts. However, whereas in syngeneic grafts cytokine expression generally decreases after the first postoperative week, significantly elevated cytokine levels are sustained in allogeneic grafts, implicating IL-1 and TNF-alpha as mediators of the alloimmune response in corneal transplantation.

A new model of orthotopic penetrating corneal transplantation in the sheep: graft survival, phenotypes of graft-infiltrating cells and local cytokine production

BACKGROUND

Orthotopic penetrating keratoplasty in the sheep was developed as an outbred preclinical model to allow correlation of the cellular infiltrate during graft rejection with local production of cytokine mRNA.

METHODS

Penetrating corneal autografts and allografts were performed in Merino sheep. Graft outcome was followed at the slit-lamp. Corneal infiltrates were examined by immunoperoxidase staining on postmortem specimens. Cytokine mRNA was detected by polymerase chain reaction.

RESULTS

Corneal autografts survived indefinitely. Allografts became vascularized and underwent rejection at a median of 20 days postgraft. Both endothelial and epithelial rejection lines were observed. Immunohistochemical staining of rejecting grafts showed up-regulation of major histocompatibility complex class I molecules on corneal graft epithelium, damaged or absent graft endothelium and a marked, predominantly mononuclear cell infiltrate. CD4-positive T cells were observed in the graft within 2 days of the onset of rejection, followed several days later by CD8-positive T cells. Messenger RNA transcripts for interleukin (IL)-2, tumour necrosis factor (TNF)-alpha and IL-10 (but not for interferon (IFN)-gamma or IL-4) were found in autografted corneas. Proportionately, more allografts than autografts contained transcripts for IL-2 and TNF-alpha, and IFN-gamma was detected in three of four allografts.

CONCLUSIONS

Corneal graft rejection in the sheep is macroscopically and histologically similar to human corneal graft rejection. Allografts become infiltrated by both CD4- and CD8-positive T cells and local production of pro-inflammatory cytokines occurs during graft rejection.

Cytokine profiles of aqueous humor and graft in orthotopic mouse corneal transplantation

BACKGROUND

Cytokine profile is a key in understanding the mechanisms of allograft rejection. Cytokine expression in the aqueous humor and the correlation between the aqueous humor cells and corneal infiltrating cells are not fully understood in corneal transplantation.

METHODS

Orthotopic mouse corneal transplantation was performed using BALB/c (H2d) mice as recipients, and C3H/He (H2k) and BALB/c mice as donors for allografts and isografts, respectively. Immunocytochemistry was performed on aqueous humor cells. Corneal graft was studied immunohistochemically. Cytokine gene expressions of the cells infiltrating the aqueous humor and corneal grafts were determined by the semiquantitative reverse transcription and polymerase chain reaction method.

RESULTS

Interferon-gamma, interleukin (IL)-2, IL-4, and IL-10 were detected in the cells infiltrating the aqueous humor and corneal grafts at both the protein and gene expression levels. T helper 1 (Th1) cytokine expressions at the protein level, however, were consistently predominant in the rejected allografts compared to those of Th2 cytokines. The cytokine and surface marker profiles of the cells in the aqueous humor corresponded well to those of the cells infiltrating the corneal grafts. Cytokine protein and mRNA expression levels in the aqueous humor decreased rapidly.

CONCLUSIONS

Allorejection in corneal transplantation is Th1 cytokine-predominant. Infiltrating cells do not express Th2 cytokine so much in allograft rejection, as compared with Th1 cytokine. The cell infiltration patterns of the aqueous humor were well correlated with those of the cornea.

An improved method for examining the corneal endothelium during graft rejection in the rat

An improved method of removing rat corneal endothelial sheets for study of endothelial pathology is described. The method was validated by examining morphological changes and changes in expression of major histocompatibility complex (MHC) and intercellular adhesion molecule (ICAM)-1 on endothelium undergoing immunological rejection. PVG strain rats received LEW strain corneal transplants or corneal isografts. Just prior to and during graft rejection, animals were killed, together with a group of untreated animals. The corneal stroma was injected with dispase or PBS, the cornea was carefully removed, fixed in acetone and the endothelium was gently peeled off and flattened on to a glass slide. Morphological changes, together with MHC class I, class II and ICAM-1 expression were visualised by immuno-histochemical staining and quantified by image analysis. Near complete endothelial sheets were obtained by this method. Because of the thin cell layer, there was minimal background staining, permitting rejection-associated changes to be clearly seen. MHC class I expression on normal endothelium was low and not significantly increased on endothelial cells of allografts at the time of rejection compared with controls (P = 0.1). MHC class II and ICAM-1 were induced de novo, expression being significantly higher on allografts than on isografts (P = 0.004 for MHC class II and P = 0.01 for ICAM-1). MHC class I and II and ICAM-1 were expressed on many infiltrating cells. Thus, this preparation method permits clear identification of the distribution and morphology of infiltrating cells and other mediators of the immune response in the entire donor endothelium. It confirms that MHC class I expression is low during rejection, while MHC class II and ICAM-I are induced de novo and strongly expressed.

Early cytokine and chemokine gene expression during Pseudomonas aeruginosa corneal infection in mice

Using a multiprobe RNase protection assay, we examined cytokine and chemokine mRNAs that were expressed after corneal infection with Pseudomonas aeruginosa in mice. Cytokines that were upregulated included interleukin-1alpha (IL-1alpha) and -1beta, IL-1 receptor antagonist, IL-6, IL-11, granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, macrophage colony-stimulating factor, stem cell factor, lymphotoxin beta, transforming growth factor beta1, and tumor necrosis factor alpha. Chemokine transcripts that were upregulated included Eotaxin; gamma-interferon-inducible protein 10; monocyte chemoattractant protein 1; macrophage inflammatory proteins 1alpha, 1beta, and 2; and RANTES. Peak expression of these cytokines and chemokines was observed between 1 and 3 days after infection. These responses returned to or approached baseline preinfection levels by 7 days after ocular challenge. Identification of the various cytokines and chemokines upregulated during corneal infection provides important information relevant to unraveling the pathogenesis induced by this bacterium and provides hope that specific molecules can be targeted for therapy.