Corneal Transplantation In Mice Research Articles

Mouse Corneal Transplantation.

Corneal transplantation is the most common form of organ transplantation worldwide. Transplant survival depends on various factors, many of which are not fully understood. Due to the existence of many genetically defined strains, mouse models of corneal transplantation are most commonly used. Here, we describe a method for a mouse corneal transplantation.

HSV-1 and Zika Virus but Not SARS-CoV-2 Replicate in the Human Cornea and Are Restricted by Corneal Type III Interferon

Here, we report our studies of immune-mediated regulation of Zika virus (ZIKV), herpes simplex virus 1 (HSV-1), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in the human cornea. We find that ZIKV can be transmitted via corneal transplantation in mice. However, in human corneal explants, we report that ZIKV does not replicate efficiently and that SARS-CoV-2 does not replicate at all. Additionally, we demonstrate that type III interferon (IFN-λ) and its receptor (IFNλR1) are expressed in the corneal epithelium. Treatment of human corneal explants with IFN-λ, and treatment of mice with IFN-λ eye drops, upregulates antiviral interferon-stimulated genes. In human corneal explants, blockade of IFNλR1 enhances replication of ZIKV and HSV-1 but not SARS-CoV-2. In addition to an antiviral role for IFNλR1 in the cornea, our results suggest that the human cornea does not support SARS-CoV-2 infection despite expression of ACE2, a SARS-CoV-2 receptor, in the human corneal epithelium.

Different Innate Immune Responses in BALB/c and C57BL/6 Strains following Corneal Transplantation

Purpose: To investigate immunological differences and the role of CD38+/F4/80 + M1 macrophages in C57BL/6J- and BALB/c-recipient mouse corneal transplantation models. Methods: Allogeneic transplantation was performed crosswise in BALB/c mice and C57BL/6J mice; syngeneic transplantation was performed in both strains. Anterior chamber depth (ACD) was measured before and central corneal thickness (CCT) was measured both before and after transplantation. In vivo graft rejection was monitored using anterior eye segment optical coherence tomography (ASOCT) evaluating the CCT and grading of corneal oedema using a well-established clinical score (CS). Histology of corneal grafts was performed 18 or 21 days after surgery. Immunohistochemistry with anti-F4/80 antibody and anti-CD38 antibody was used for detecting M1 macrophages within the grafts. Results: High CS and CCT values after allogeneic transplantation persisted in both BALB/c (n = 18) and C57BL/6J recipients (n = 20). After syngeneic transplantation, CS and CCT values increased in both models in the early phase after surgery due to the surgical trauma. Surprisingly, in the syngeneic C57BL/6J model, high CCT values persisted. Furthermore, anterior synechiae developed in C57BL/6 recipients after both syngeneic and allogeneic transplantation, whereas BALB/c recipients showed almost no synechiae – even though C57/BL6J animals tended to have a deeper anterior chamber (281 ± 11 pixels [mean ± SD]) compared with BALB/c animals of the same age (270 ± 9 pixels [mean ± SD]). Immunohistochemistry revealed numerous CD38+/F4/80 + M1 macrophages in grafts of C57BL/6J recipients following both syngeneic and allogeneic transplantation. However, in BALB/c-recipient mice only sparse M1 macrophages were detectable (CD38 + M1 macrophages relative to all F4/80 + cells: 75 vs. 17% [after allogeneic transplantation] and 66 vs. 17% [after syngeneic transplantation]; p < 0.05). Conclusions: Allogeneic corneal transplants are rejected in BALB/c as well as C57BL/6J mice, but tissue alterations with anterior synechiae are more pronounced in C57BL/6J recipients. Following syngeneic transplantation, C57BL/6J-recipient animals show a persistent graft swelling with increased numbers of CD38+/F4/80 + M1 macrophages in grafted tissue, in contrast to the common model using BALB/c-recipient mice. Our data strongly suggest that strain-dependent differences convey different innate immune responses in BALB/c and C57BL/6J strains. Accordingly, in murine keratoplasty experiments, the mouse line of both donor and recipient animals must be carefully considered. C57BL/6J-recipient mice might be particularly suited to study corneal graft rejection in a clinical setting considered “high risk.”

The Effects of Anti-LAP Monoclonal Antibody Down-regulation of CD4+LAP+ T Cells on Allogeneic Corneal Transplantation in Mice

CD4+latency-associated peptide (LAP)+ T cells are a newly discovered T cell subset with suppressive function on immune responses. In this study, we investigate the role of CD4+LAP+ T cells on mice corneal allograft survival by down-regulating their expression using anti-LAP mAb. We show that a blockage of LAP leads to a decrease in the percentage of T cells expressing CD4+Foxp3+, CD4+GARP+, CD4+LAP+ and CD4+IL-10+ in the lymph nodes and spleens of mice undergoing orthotopic penetrating transplantation of corneal allograft, without affecting corneal graft survival. In addition, higher percentages of CD4+IFN-γ+ and CD4+IL-17A+ T cells in the lymph nodes and spleens, as well as TNF, IFN-γ, IL-17A and IL-6 levels in the aqueous humor, significantly increase in mice with rejected corneal grafts. The expression of TGF-β1 decreases in corneal grafts during corneal rejection period. It is therefore possible that anti-LAP mAb can down-regulate the regulatory T cell subsets with its immunosuppressive effects. The rejection of corneal grafts seems to mainly be associated with the up-regulation of Th1 and Th17 cell subsets in peripheral lymph nodes.

Topical application of sphingosine 1-phosphate receptor 1 prolongs corneal graft survival in mice.

The present study aimed to investigate the effects of topical application of sphingosine 1‑phosphate receptor 1 (S1P1) on allogeneic corneal transplantation in mice. A total of 45 BALB/c mice received corneal grafts from C57BL/6 donors. The recipients were randomly divided into three groups and treated with eye drops containing 0.5% S1P1, 1% cyclosporine A or saline as a negative control. The serum levels of interleukin (IL)‑2, IL‑10, tumor growth factor (TGF)‑β1 and interferon (IFN)‑γ were measured by ELISA. The numbers of CD4+ T cell and T‑regulatory (Treg) cell phenotypes were measured by flow cytometry. The cytokine mRNA expression was analyzed by quantitative polymerase chain reaction. The results demonstrated that corneal graft survival was prolonged in the S1P1 group [mean survival time (MST), 24.11±1.58 days], and 1% cyclosporine A (MST, 25.0±1.91 days) compared with the controls (MST, 13.44±0.48 days; P<0.01). S1P1 and cyclosporine A decreased CD4+ T‑cell levels (P<0.05) in the peripheral blood compared with those of the controls. However, an increase of CD4+ T cells in the spleen was noted in the S1P1 group (P<0.05) and Treg cells were also increased in the cervical lymph nodes in the S1P1 group (P<0.01). TGF‑β1 mRNA transcription in the corneal grafts increased following treatment with S1P1 (P<0.05) and TGF‑β1 in the serum following treatment with S1P1 also increased (P<0.01). In conclusion, S1P1 had a significant effect in corneal allograft rejection inhibition.

Analysis of Macrophage Phenotype in Rejected Corneal Allografts

We investigated the phenotype of macrophages infiltrating rejected corneal allografts. We performed allogeneic or syngeneic corneal transplantation in mice, and humanely killed animals at day 28 during allograft rejection when 60% of corneal allografts were rejected. We divided allografts into two groups: grafts with rejection as rejectors and grafts without rejection as nonrejectors, and analyzed for macrophage infiltration and their phenotype using immunohistochemistry. In addition, we investigated the time course of proinflammatory cytokines and chemokines by analyzing corneal grafts at days 7, 28, and 42 using real-time RT-PCR. Also, we assayed human corneal allografts with chronic graft failure. We found that a large number of CD11b(+), F4/80(+), or inducible nitrous oxide synthase cells (iNOS(+)) infiltrated corneal allografts during rejection in mice, while the cells were found rarely in syngeneic or allogeneic grafts that were not rejected. There were rare CD11c(+) cells in rejectors and nonrejectors. Many mannose receptor cells (MRC(+)) were present in nonrejectors, but not in rejectors. The levels of Th1 cytokines, IFN-γ, and IL-2 were highly increased in rejectors at day 28, indicating immune rejection. Also, the levels of IL-12a, IL-1β, TNF-α, CCL3, and iNOS that are produced by activated macrophages were markedly increased in rejectors at day 28, compared to syngeneic grafts or nonrejectors. Similarly, human corneal allografts with chronic graft failure had higher levels of IL-12a, IL-1β, CCL3, and iNOS than controls. Increased numbers of macrophages in rejected corneal allografts implicate that these cells might contribute to the immunopathogenesis of corneal graft rejection.

Systemic application of sphingosine 1‐phosphate receptor 1 immunomodulator inhibits corneal allograft rejection in mice

This study aims to investigate the effects of systemic application of sphingosine 1-phosphate receptor 1(S1P1) on allogeneic corneal transplantation in mice. A total of 112 BALB/c mice received corneal grafts from C57BL/6 donors. Recipients were randomly divided into seven groups and treated with intraperitoneal injections of S1P1 (5 mg/kg/days), cyclosporine A (5 mg/kg/days), dexamethasone (1 mg/kg/days) and rapamycin (2 mg/kg/days). S1P1was combined with rapamycin or cyclosporine A, and saline served as negative control. Serum levels of IL-2, IL-10, TGF-β1 and IFN-γ were measured by Elisa. The numbers of CD4+ T and regulatory (Treg) cell phenotype were measured by flow cytometry. Cytokine mRNA expression was analysed by real-time quantitative PCR. CD4+ T cells and cytokines were histologically identified by immunofluorescence staining. Corneal graft survival was prolonged by intraperitoneal injections in S1P1 alone (mean survival time MST, 35.3 ± 5.6 days), S1P1 combined with rapamycin (MST, 38.7 ± 6.5 days) or S1P1 and cyclosporine A (MST, 32.7 ± 4.8 days) compared with the controls (MST, 14.6 ± 0.2 days; n = 5, p < 0.01). S1P1 alone increased CD4+ T (p < 0.01) and Treg cells (p < 0.01; n = 5) in the cervical and mesenteric lymph nodes compared with the controls and S1P1 + rapamycin (p < 0.05; n = 5). TGF-β1 and IL-10 mRNA transcriptions in corneal grafts following S1P1+ rapamycin increased (both p < 0.01; n = 3), and TGF-β1 and IL-10 in the serum level following S1P1 alone increased (both p < 0.01; n = 3). These results paralleled the findings obtained from immunofluorescence. S1P1 has significant effect in corneal allograft rejection inhibition. The combined treatment of S1P1 and rapamycin results in synergistic effect.

The Semaphorin 3A Inhibitor SM-345431 Accelerates Peripheral Nerve Regeneration and Sensitivity in a Murine Corneal Transplantation Model

BackgroundPeripheral nerve damage of the cornea is a complication following surgery or infection which may lead to decreased visual function. We examined the efficacy of the semaphorin 3A inhibitor, SM-345431, in promoting regeneration of peripheral nerves in a mouse corneal transplantation model.Methodology/Principal FindingsP0-Cre/Floxed-EGFP mice which express EGFP in peripheral nerves cells were used as recipients of corneal transplantation with syngeneic wild-type mouse cornea donors. SM-345431 was administered subconjunctivally every 2 days while control mice received vehicle only. Mice were followed for 3 weeks and the length of regenerating nerves was measured by EGFP fluorescence and immunohistochemistry against βIII tubulin. Cornea sensitivity was also measured by the Cochet-Bonnet esthesiometer. CD31 staining was used to determine corneal neovascularization as a possible side effect of SM-345431. Regeneration of βIII tubulin positive peripheral nerves was significantly higher in SM-345431 treated mice compared to control. Furthermore, corneal sensitivity significantly improved in the SM-345431 group by 3 weeks after transplantation. Neovascularization was limited to the peripheral cornea with no difference between SM-345431 group and control.Conclusions/SignificanceSubconjunctival injections of SM-345431 promoted a robust network of regenerating nerves as well as functional recovery of corneal sensation in a mouse keratoplasty model, suggesting a novel therapeutic strategy for treating neurotrophic corneal disease.

Further study on molecular biological effects of CD4 D1 inhibitor J2 on allografts following corneal transplantation in mice

Our previous experiments have revealed that a non-peptide organic ligand of CD4 D1-J2 as a potential inhibitor of CD4 D1 can inhibit corneal allograft injection and prolong the corneal allograft survival. The present study aimed to further investigate molecular biological effects of J2 treatment on allografts following corneal transplantation in mice. Allogeneic orthotopic penetrating keratoplasty was performed using C57BL/6 mice as donors and BALB/c mice as recipients. Allograft recipient mice were randomly divided into J2-treated group, CsA-treated group (positive control) and DMSO treatment group (negative control). After treatment for consecutive 12 days, T cell phenotype analysis, CD4, CD8 immunohistochemical staining, T-cell proliferation and mRNA expression analysis of cytokines were performed. The subsequent molecular biological assays revealed that the immunosuppressive activity of J2 was associated with its inhibitory effects on the CD4+ T cells and cells-mediated responses. J2 is as effective as CsA in prevention of allograft rejection following corneal transplantation. Key words: CD4+ T cells, immunosuppressive agent, CD4 D1 inhibitor, CsA, corneal transplantation.

Cross Presentation of Antigen on MHC Class II via the Draining Lymph Node after Corneal Transplantation in Mice

We investigated Ag trafficking from the cornea and T effector cell activation in secondary lymphoid tissue after corneal transplantation. In preliminary experiments, the central cornea was shown to contain a population of CD45(+), CD11b(+), CD11c- cells, with a few MHC class II(+) cells, and F4/80(+) cells. However, MHC class II(+) passenger leukocytes in donor cornea after allografting did not traffic to the draining lymph node. Instead, Ag (plasmid) delivered to the eye via the donor cornea during allograft was detected in host CD11c(+) and F4/80(+) APC in the draining lymph nodes and spleen. The earliest detection of APC-associated Ag was at 6 h in the draining lymph node and 24 h in the spleen. After 48 h Ag was not detected in the draining lymph node but was still present in the spleen. Ag applied to the donor corneal epithelium before allografting induced Ag-specific T cell activation and expansion in the draining lymph node with a peak response at 4-6 days, indicating that cross-presentation of Ag had occurred. We conclude therefore, that Ag is transported from the donor cornea within host APC and that this event occurs within hours after grafting. Ag is cross-presented to host CD4(+) T cells on MHC class II and leads to the activation of Ag-specific effector T cells and clonal expansion in the draining lymph node.

CTLA4-FasL protein for the prevention of immune rejection in mouse corneal transplantation

To investigate the therapeutic effect of double-functioned CTLA4-FasL protein for the prevention of immune rejection in murine corneal allografts. It was a experimental study. C57BL/6 mice (n = 45) were as donors and BALB/c mice (n = 90) as recipients. BALB/c mice accepted penetrating keratoplasty were randomly divided into 3 groups including no therapy (A), CsA DDS implanted in anterior chamber (B), 10 microg/mL CTLA4-FasL (C). Survival time of corneal allografts was observed and routine assays were performed including immunohistochemistry, reverse-transcription polymerase chain reaction (RT-PCR), TdT-mediated dUTP nick end labeling (TUNEL). Survival time of corneal transplants was (14.3 +/- 1.3) days, (58.0 +/- 2.8) days, (106.3 +/- 17.5) days respectively. There was significant difference between groups in statistics analysis (P = 0.000). Inflammatory cells, predominant for CD4 + T cells, showed an increasing tendency for rejected corneal allografts in A group, peaked on postoperative 7 d and then decreased in C group compared with invisible in B group. CD80 or CD86 was detected on postoperative 3 d or 7 d respectively in excised cornea and iris of both A and B group, while either showed weakening expression in C group. On postoperative 14 d, IL-10, TNF-alpha, IFN-gamma mRNA were only detected in rejected cornea allograft of A group other than clear allografts of B or C group. Compared with no apoptosis in the other groups, abundant apoptosis cells were visible in cornea and iris of C group on postoperative 7 d. CTLA4-FasL is able to prolong survival time of corneal allografts by dual action mechanism to exert immunosuppressive effects, both blockade of CD28-CD80/86 pathway and induction of apoptosis of T cell.

Effects of a small non-peptidic CD4 inhibitor J2 in prevention of mouse corneal allograft rejection

To investigate the effects of small non-peptidic CD4 inhibitor J2 on the prevention of allograft rejection in mouse corneal transplantation. Twenty-three C57BL/6 mice (donor) and 76 BALB/c mice (recipients) were used to establish corneal allograft model, and were divided into 4 groups randomly. Group A, autograft control; Group B, allograft control (placebo was given in both control groups); Group C and Group D, allograft groups, were treated with orally ciclosporin A and J2, respectively. Drugs were delivered for 12 days beginning on the day of transplantation. Graft survival was assessed by Kaplan-Meier analysis. On day 21 after transplantation, flow cytometry analysis of peripheral blood mononuclear cells and histological examination of graft were performed. No graft rejection was observed in Group A. The average transplant survival time of Group B was (17.8 +/- 2.1) d. In Group D, the transplant survival time showed a statistically prolongation to (40.6 +/- 8.3) d (P = 0.00) as compared with Group B, but the survival time was less than that of Group A (P = 0.04). There was no statistically significant difference between Group D and Group C (38.1 +/- 9.9) d (P = 0.99). The results of flow cytometry analysis showed that CD4(+) cells and CD8(+) cells in peripheral blood mononuclear cells did not increase in Group D. Fewer inflammatory cells were found in the corneal allograft in Group D. J2 could inhibit rejection and prolong corneal allograft survival time in mouse.

Low-dose anesthesia for corneal transplantation in mice.

Despite technical difficulties caused by the small dimensions, scientific and economic considerations stimulated activities in the murine keratoplasty model. Delicate surgery requires stable anesthesia with rapid postoperative waking. For corneal transplantation, all animals were intraperitoneally injected with 0.08 ml of a 1:8 mixture of 2% xylazine and 2.5% esketamine hydrochloride. Thus they all received 0.18 mg of xylazine and 1.8 mg of ketamine. In other words, 4.5 mg/kg BW of xylazine and 45 mg/kg BW of ketamine were injected in a mouse weighing 25 g. The inhalation anesthetic isoflurane was used for short interventions like removing lid sutures or in the case of an animal awaking before the end of the operation. A small but effective set of apparatus comprising a glass bottle, a test tube and several interconnected syringes was developed to create a closed system and visualize the amount of isoflurane used in the animal. Air bubbles showed the amount of isoflurane escaping from the opened respiratory mask. The dose reduction of systemic anesthesia requires additional inhalation anesthesia with isoflurane in nearly all cases. The equipment developed is easy to handle and allows systemic anesthesia with a very low dose. This murine anesthesia model may be expected to help other surgeons performing corneal transplantations in mice.

Role of resident corneal leukocytes and draining cervical lymph nodes in corneal allograft rejection.

We review recently published experimental evidence on corneal transplant immunology involving cornea and draining cervical lymph nodes (CLNs) in the mouse. In the cornea, major histocompatibility complex (MHC) class II- dendritic cells (DCs) are present in the corneal epithelium. These DCs can express MHC class II antigen in vivo and in vitro. In the corneal stroma, there are many leukocytes of monocyte or macrophage lineage. Normal cornea has been reported to contain a significant number of bone marrow-derived resident cells, which may be able to act as antigen-presenting cells. Allograft rejection does not occur if draining CLNs are removed before corneal transplantation, indicative of an essential role of CLNs in promoting corneal allorejection. Moreover, donor cornea-derived DCs were detected in host draining CLNs in a mouse corneal transplantation model. These findings provide direct evidence that MHC class II- bone marrow-derived antigen-presenting leukocytes exist in the part of cornea used for transplantation and that direct allorecognition of antigen is, at least in part, relevant to the occurrence of corneal allograft rejection in which draining CLNs play a central role.

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

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

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

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. 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. 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. 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.

Th2-type cytokine response after orthotopic corneal transplantation in mice

Th2-type cytokine response after orthotopic corneal transplantation in mice

Th2-type cytokine response after orthotopic corneal transplantation in mice

Th2-type cytokine response after orthotopic corneal transplantation in mice

Minor H, rather than MHC, alloantigens offer the greater barrier to successful orthotopic corneal transplantation in mice

Irrespective of HLA matching, a far higher proportion of human corneal allografts placed orthotopically in avascular corneal graft beds are accepted indefinitely, compared to other types of solid tissue allografts. However, many more corneal grafts are rejected if they are transplanted onto neovascularized recipient eyes. Using a murine model of orthtopic corneal transplantation in which grafts were placed in normal eyes, we have reported previously that grafts bearing minor H antigens alone are more likely to be rejected (approximately 50%) than are grafted displaying only MHC alloantigens (<20%). Moreover, recipients of MHC plus minor H incompatible corneal grafts developed delayed hypersensitivity (DH) directed solely at minor H antigens. These studies have now been extended to include corneal grafts placed in neovascularized recipient eyes. Neovascularization was induced by placing sutures in the central cornea of one eye of BALB/c mice. Two weeks later corneas from C57BL/10 donors were grafted into these eyes. Rejection reactions were first apparent within 7 days and all grafts were destroyed by 14 days. Donor-specific DH responses were examined by injecting irradiated donor antigen-bearing spleen cells into the ear pinna. To distinguish DH directed at MHC versus minor antigens, some graft recipients were ear-challenged with BALB.B cells (donor MHC only), while other received B10.D2 cells (donor minor H only). Intense ear-swelling responses were evoked by B10.D2 cells, but not by BALB.B cells. These findings indicate that, for orthotopic corneal allografts, minor H antigen offer a more formidable barrier to graft acceptance than do MHC-encoded antigens. We speculate that this unexpected outcome may reflect a reduced level of MHC expression on corneal tissue. Moreover since the cornea lacks bone marrow derived dendritic cells, allorecognition by recipient T cells must occur via the indirect pathway, and in this situation minor H antigens may compete with MHC antigens for processing and presentation by recipient antigen-presenting cells.

Orthotopic corneal transplantation in mice--evidence that the immunogenetic rules of rejection do not apply.

The fate of orthotopic corneal transplants has been studied in inbred strains of mice. Using a surgical technique that achieves > 95% success of syngeneic cornea grafts, it was determined that a high proportion of orthotopic cornea allografts were accepted indefinitely, irrespective of the degree of immunogenetic disparity between graft donor and recipient. Grafts that succumbed to irreversible rejection developed extensive corneal edema and intrastromal neovascularization as harbingers of corneal opacity and endothelial cell failure. The highest rate of rejection occurred among grafts that confronted their hosts with multiple minor histocompatibility antigens, with or without major histocompatibility antigens. Much lower rates of rejection (< 35%) were observed when the donors of the grafts differed from recipients at class I and/or class II major histocompatibility loci. Corneal grafts that confronted their hosts with class II MHC alloantigens alone experienced early, acute inflammation, and eventually developed stomal neovascularization, but only a small minority of these grafts were eventually destroyed. Allogeneic corneas that were transplanted orthotopically into eyes of presensitized mice were uniformly subjected to an acute rejection process that produced opacity within three weeks; however, in a minority of instances, the inflammation and opacity subside, and after eight weeks the grafts displayed a clear, nonvascularized appearance. The high rate of success of even grossly histoincompatible orthotopic corneal allografts in mice resembles the extraordinary success of unmatched allogeneic corneas transplanted into human eyes. The results are discussed in terms of the possible mechanisms that permit orthotopic corneal allografts to enjoy significantly better survival than orthotopic grafts of other types of solid tissues.