Corneal Tissue From Dry Eye Donors Leads to Enhanced Graft Rejection

Role of Inhibiting Inflammation of LC3-Associated Phagocytosis in Dry Eye Disease

PURPOSE

To confirm the expression and investigate the role of LC3-associated phagocytosis (LAP) in dry eye disease (DED).

METHODS

The DED model of mice was established by scopolamine subcutaneous injection in a low-humidity environment chamber. Tear secretion test and corneal fluorescein sodium staining were used to evaluate the severity of DED. Expression levels of Rubicon, microtubule-associated protein light chain 3-II (LC3-II), Beclin-1 and autophagy-related gene-7 (Atg-7) in corneas of mice with DED were tested by western blot. Cell Counting Kit-8 (CCK-8) assay was used to detect the effects of different concentrations of hypertonic solutions on the proliferation activity of human corneal epithelial cells (HCECs). The expression levels of Dectin-1, IL-6 and IL-1β in HCECs after stimulation with different concentrations of hypertonic solutions were tested. The expressions of Rubicon, LC3-II, Beclin-1 and ATG-7 in HCECs were detected by reverse transcription polymerase chain reaction (RT-PCR). After being pretreated with 10 μM si-Rubicon, the severity of the disease was documented by corneal fluorescein sodium staining. And the expression levels of IL-6 and IL-1β were also tested by RT-PCR.

RESULTS

Compared with the normal control group, the corneal fluorescein sodium staining scores and tear secretion were significantly reduced. Rubicon, LC3-II, Beclin-1 and ATG-7 were significantly elevated. CCK-8 showed that the 400 and 450 mOsM hypertonic solutions did not affect the proliferation activity of HCECs. The expression of Dectin-1, IL-1β and IL-6 were elevated after stimulation with 450 mOsM solution. LC3-II, Rubicon, ATG-7 and Beclin-1 increased after stimulation with 450 mOsM hyperosmolar solution in HCECs. Corneal fluorescein staining showed that si-Rubicon increased the severity of DED in mice. Moreover, the mRNA expressions of inflammatory factors IL-1β and IL-6 in the cornea of mice were significantly increased.

CONCLUSION

DED increased the expression of proteins associated with LAP. LAP could play an anti-inflammatory effect in DED.

Biological effects of stored platelet-rich plasma eye-drops in corneal wound healing

BACKGROUND/AIMS

This study aimed to assess the efficacy and sterility of stored platelet-rich plasma (PRP) eye-drops for corneal epithelial wound healing compared with those of autologous serum (AS) eye-drops.

METHODS

At our single institution, PRP and AS eye-drops were prepared using peripheral blood obtained from six healthy volunteers and stored at 4°C. Platelet and leucocyte counts and transforming growth factor (TGF)-β1, epidermal growth factor (EGF), and fibronectin levels were assessed during storage for up to 4 weeks. Sterility was assessed by culturing 4-week poststorage samples. PRP, AS, and phosphate-buffered saline (PBS) eye-drop efficacies were compared using corneal epithelial wound healing assays in vitro and in vivo and monitoring wound areas under a microscope every 3 hours.

RESULTS

Higher platelet and lower leucocyte counts were seen in PRP than in whole blood on the day of preparation. After storage, TGF-β1, EGF, and fibronectin levels were significantly higher in PRP than in AS eye-drops. In vitro and in vivo, PRP eye-drops used on the day of preparation significantly promoted corneal epithelial wound healing compared with PBS. Moreover, PRP eye-drops stored for 4 weeks significantly promoted corneal wound healing compared with PBS and AS eye-drops.

CONCLUSION

PRP eye-drops stored at 4°C for 4 weeks promoted corneal epithelial wound healing with higher levels of growth factors than those observed in AS eye-drops, while maintaining sterility, suggesting that this preparation satisfies the unmet medical needs in the treatment of refractory keratoconjunctival epithelial disorders.

Local T cell infiltrates are predominantly associated with corneal allograft rejection

BACKGROUND

Corneal transplantations (CTXs) are a vision-saving procedure. Routinely, while CTXs' survival rates remain high, the risk of graft failure increases significantly for repeated CTXs. The reason is an alloimmunization following previous CTXs and development of memory T (Tm) and B (Bm) cells.

METHODS

We characterized populations of cells present in explanted human corneas from patients receiving the first CTX and marked as a primary CTX (PCTX) or the second or more CTXs and marked as a repeated CTX (RCTX). Cells extracted from resected corneas and from peripheral blood mononuclear cells (PBMCs) were analyzed by the flow cytometry method using multiple surface and intracellular markers.

RESULTS

Overall, the number of cells was similar in PCTX and RCTX patients. Extracted infiltrates from PCTXs and RCTXs contained similar numbers of T cell subsets, namely CD4+, CD8+, CD4+ Tm, CD8+ Tm, CD4+Foxp3+ T regulatory (Tregs), CD8+ Treg cells, while very few B cells (all p = NS). However, when compared to peripheral blood, PCTX and RCTX corneas contained significantly higher percentages of effector memory CD4+ and CD8+ T cells (both p < 0,05). In comparison to PCTX, RCTX group had the highest levels of Foxp3 in T CD4+ Tregs (p = 0,04) but decreased percentage of Helios-positive CD4+ Tregs.

CONCLUSION

PCTXs and especially RCTXs are rejected mainly by local T cells. The accumulation of effector CD4+ and CD8+ T cells, as well as CD4+ and CD8+ Tm cells is associated with the final rejection. Furthermore, local CD4+ and CD8+ Tregs expressing Foxp3 and Helios are probably insufficient to impose the acceptance of CTX.

Interferon-γ elicits the ocular surface pathology mimicking dry eye through direct modulation of resident corneal cells

Despite accumulating evidence indicating a key role of interferon-γ (IFN-γ)-producing immune cells in ocular infection and immunity, little is known about the direct effects of IFN-γ on resident corneal cells or on the ocular surface. Here, we report that IFN-γ impacts corneal stromal fibroblasts and epithelial cells to promote inflammation, opacification, and barrier disruption on the ocular surface, leading to dry eye. Our results demonstrated that IFN-γ dose-dependently induced cytotoxicity, pro-inflammatory cytokine/chemokine production, and expression of major histocompatibility complex class II and CD40 in cultures of corneal stromal fibroblasts and epithelial cells while increasing myofibroblast differentiation of corneal stromal fibroblasts. In mice, subconjunctival IFN-γ administration caused corneal epithelial defects and stromal opacity in dose- and time-dependent manners while promoting neutrophil infiltration and inflammatory cytokine expression in the cornea. Moreover, IFN-γ reduced aqueous tear secretion and the number of conjunctival goblet cells responsible for mucinous tear production. Together, our findings suggest that IFN-γ induces the ocular surface changes characteristic of dry eye disease at least in part through its direct effects on resident corneal cells.

Prevalence and Characteristics of Dry Eye Disease After Cataract Surgery: A Systematic Review and Meta-Analysis

Dry eye disease (DED) after cataract surgery is associated with various risk factors, while causing a wide range of heterogeneous symptoms including decreased quality of vision. This systematic review and meta-analysis aimed to determine the prevalence and characteristics of DED after cataract surgery. We searched PubMed and EMBASE and included studies on patients with DED after cataract surgery, between January 2011 and June 2020. Study-specific estimates (DED prevalence rates after cataract surgery in patients without preexisting DED) were combined using one-group meta-analysis in a random-effects model. We included 36 studies published between 2013 and 2020. We included nine of these in the meta-analysis of DED prevalence after cataract surgery. Overall 37.4% (95% CI 22.6-52.3; 206/775) of patients without preexisting DED developed DED after cataract surgery. The risk factors for DED after cataract surgery included age, female sex, systemic diseases, systemic medications, psychiatric conditions, preexisting DED, meibomian gland dysfunction, preservatives in eye drops, surgery techniques, and lifestyle. DED severity peak occurred 1 day postoperatively and persisted for at least 1-12 months following cataract surgery; therefore, consistent follow-up for DED is warranted for at least 1 month after cataract surgery. Topical administration of preservative-free diquafosol tetrasodium solution and preoperative meibomian gland treatment were effective in preventing and treating DED following cataract surgery. As more than one-third of patients develop DED after cataract surgery, careful DED management and treatment is needed after cataract surgery to improve satisfaction and vision quality.

Anti-CD80/86 antibodies inhibit inflammatory reaction and improve graft survival in a high-risk murine corneal transplantation rejection model

We investigated the effects of anti-CD80/86 antibodies in a murine high-risk corneal transplantation rejection model. A mixed lymphocyte reaction (MLR) assay was conducted with anti-CD80/86 antibodies. Inflammatory cytokine levels in the culture supernatant were measured using an enzyme-linked immunosorbent assay. Interferon (IFN)-γ-producing CD4⁺ T cell frequencies in the MLR were assessed using flow cytometry. In vivo, high-risk corneal allograft survival and IFN-γ-producing CD4⁺ T cell frequencies in corneal grafts were assessed with intraperitoneal injection of anti-CD80/86 antibodies compared to phosphate-buffered saline (PBS). RNA-sequencing was performed on corneal grafts 2 weeks post-transplantation. Anti-CD80/86 antibodies significantly decreased T-cell proliferation, IFN-γ⁺-producing CD4⁺ T cell frequencies, and IFN-γ, interleukin (IL)-1β, IL-2, IL-10, and tumor necrosis factor-α production in the MLR compared to PBS injection. Intraperitoneal injection of anti-CD80/86 antibodies significantly prolonged corneal graft survival and decreased IFN-γ⁺-producing CD4⁺ T cell frequencies compared to PBS injection. Gene set enrichment analysis showed that the gene sets mainly enriched in the control group were related to allograft rejection and inflammatory response compared to PBS injection. Anti-CD80/86 antibodies significantly prolonged corneal graft survival by inhibiting T-cell proliferation and inflammatory response.

Application of Animal Models in Interpreting Dry Eye Disease

Different pathophysiologic mechanisms are involved in the initiation, development, and outcome of dry eye disease (DED). Animal models have proven valuable and efficient in establishing ocular surface microenvironments that mimic humans, thus enabling better understanding of the pathogenesis. Several dry eye animal models, including lacrimal secretion insufficiency, evaporation, neuronal dysfunction, and environmental stress models, are related to different etiological factors. Other models may be categorized as having a multifactorial DED. In addition, there are variations in the methodological classification, including surgical lacrimal gland removal, drug-induced models, irradiation impairment, autoimmune antibody-induced models, and transgenic animals. The aforementioned models may manifest varying degrees of severity or specific pathophysiological mechanisms that contribute to the complexity of DED. This review aimed to summarize various dry eye animal models and evaluate their respective characteristics to improve our understanding of the underlying mechanism and identify therapeutic prospects for clinical purposes.

Blockage of P2X7R suppresses Th1/Th17-mediated immune responses and corneal allograft rejection via inhibiting NLRP3 inflammasome activation

P2X7R is a vital modifier of various inflammatory and immune-related diseases. However, the immunomodulatory effects of P2X7R on corneal allograft rejection remains unknown. Here we showed that P2X7R expression was significantly upregulated in corneal grafts of allogeneic transplant mice. Pharmacological blockage of P2X7R remarkably prolonged graft survival time, and reduced inflammatory cell infiltration in corneal grafts, in particular Th1/Th17 cells. Meanwhile, the frequencies of Th1/Th17 cells in draining lymph nodes were significantly decreased in P2X7R blocked allogeneic mice. Further results showed that the effect of P2X7R on promoting Th1/Th17 mediated immune responses in corneal allograft rejection relied heavily on its activation on the NLRP3/caspase-1/IL-1β axis, while P2X7R blockage could mitigate such activation. Nevertheless, the addition of IL-1β in vivo abrogated the protective effect of P2X7R blockage on promoting corneal graft survival. These findings demonstrate that blockage of P2X7R can substantially alleviate corneal allograft rejection and promote grafts survival, highlighting it as a promising target for preventing or treating corneal allograft rejection.

Role of Immune Cell Diversity and Heterogeneity in Corneal Graft Survival: A Systematic Review and Meta-Analysis

Corneal transplantation is one of the most successful forms of solid organ transplantation; however, immune rejection is still a major cause of corneal graft failure. Both innate and adaptive immunity play a significant role in allograft tolerance. Therefore, immune cells, cytokines, and signal-transduction pathways are critical therapeutic targets. In this analysis, we aimed to review the current literature on various immunotherapeutic approaches for corneal-allograft rejection using the PubMed, EMBASE, Web of Science, Cochrane, and China National Knowledge Infrastructure. Retrievable data for meta-analysis were screened and assessed. The review, which evaluated multiple immunotherapeutic approaches to prevent corneal allograft rejection, showed extensive involvement of innate and adaptive immunity components. Understanding the contribution of this immune diversity to the ocular surface is critical for ensuring corneal allograft survival.

Ex Vivo-Induced Bone Marrow-Derived Myeloid Suppressor Cells Prevent Corneal Allograft Rejection in Mice

Purpose

To investigate the effects of ex vivo-induced bone marrow myeloid-derived suppressor cells (BM-MDSCs) on allogeneic immune responses in corneal transplantation.

Methods

Bone marrow cells from C57BL/6J (B6) mice were cultured with IL-6 and GM-CSF for four days. The ex vivo induction of the BM-MDSCs was assessed using flow cytometry, inducible nitric oxide synthase (iNOS) mRNA expression using reverse transcription-quantitative polymerase chain reaction, and nitric oxide (NO) production in allogeneic stimulation. T-cell proliferation and regulatory T-cell (Treg) expansion were investigated on allogeneic stimulation in the presence of ex vivo-induced BM-MDSCs. IFN-γ, IL-2, IL-10, and TGF-β1 protein levels were measured using enzyme-linked immunosorbent assays. After subconjunctival injection of ex vivo-induced BM-MDSCs, the migration of the BM-MDSCs into corneal grafts, allogeneic corneal graft survival, neovascularization, and lymphangiogenesis were assessed using flow cytometry, slit-lamp microscopy, and immunohistochemistry.

Results

The combination of GM-CSF and IL-6 significantly induced BM-MDSCs with increased iNos mRNA expression. The ex vivo-induced BM-MDSCs promoted NO release in allogeneic stimulation in vitro. The ex vivo-induced BM-MDSCs inhibited T-cell proliferation and promoted Treg expansion. Decreased IFN-γ and increased IL-2, IL-10, and TGF-β1 production was observed in coculture of ex vivo-induced BM-MDSCs. Injected ex vivo-induced BM-MDSCs were confirmed to migrate into the grafts. The injected BM-MDSCs also prolonged corneal graft survival and prevented angiogenesis and lymphangiogenesis.

Conclusions

The ex vivo-induced BM-MDSCs have suppressive effects on allogeneic immune responses and prolong corneal allograft survival via the iNOS pathway, indicating that they may be a potential therapeutic tool for corneal transplantation.

Topical administration of the kappa opioid receptor agonist nalfurafine suppresses corneal neovascularization and inflammation

Corneal neovascularization (CNV) causes higher-order aberrations, corneal edema, ocular inflammation, and corneal transplant rejection, thereby decreasing visual acuity. In this study, we investigated the effects of topical administration of the kappa opioid receptor agonist nalfurafine (TRK-820) on CNV. To induce CNV, intrastromal corneal sutures were placed on the corneal stroma of BALB/c mice for 2 weeks. Nalfurafine (0.1 µg/2 μL/eye) was topically administered to the cornea once or twice daily after CNV induction. The CNV score, immune cell infiltration, and mRNA levels of angiogenic and pro-inflammatory factors in neovascularized corneas were evaluated using slit-lamp microscopy, immunohistochemistry, flow cytometry, and polymerase chain reaction. The mRNA expression of the kappa opioid receptor gene Oprk1 was significantly upregulated following CNV induction. Topical administration of nalfurafine twice daily significantly suppressed CNV and lymphangiogenesis, as well as reduced the mRNA levels of angiogenic and pro-inflammatory factors in the neovascularized corneas. Moreover, nalfurafine administration twice daily reduced the numbers of infiltrating leukocytes, neutrophils, macrophages, and interferon-γ-producing CD4⁺ T cells in the neovascularized corneas. In this study, we demonstrated that topical administration of nalfurafine suppressed local CNV in a mouse model along with the activation of KOR, suggesting that nalfurafine may prevent and control CNV in humans.

Novel immunotherapeutic effects of topically administered ripasudil (K-115) on corneal allograft survival

Corneal allograft survival is mediated by the variety of immunological reactions and wound healing process. Our aim was to explore the effects of topical administration of ripasudil, a selective Rho-associated coiled-coil protein kinase inhibitor, on corneal allograft survival. Ripasudil was administered to mice thrice a day after allogeneic corneal transplantation. Corneal graft survival, opacity, neovascularization, re-epithelization, immune cell infiltration, and mRNA levels of angiogenic and pro-inflammatory factors in the grafted cornea and draining lymph nodes (dLNs) were evaluated with slit-lamp microscopy, immunohistochemistry, flow cytometry, and polymerase chain reaction. Graft survival was significantly prolonged with lower graft opacity and neovascularization scores in 0.4% and 2.0% ripasudil-treated groups, and mRNA levels of angiogenic and pro-inflammatory factors in ripasudil-treated grafted corneas were reduced. Moreover, 0.4% and 2.0% ripasudil reduced CD45⁺-infiltrated leukocyte frequency, Cd11b and Cd11c mRNA levels, and the frequencies of mature dendritic cells, IFNγ-, and IL-17- producing CD4⁺T cells in the dLNs of recipients. Re-epithelization rate of the grafted cornea was significantly higher in the 0.4% and 2.0% ripasudil groups than in the control. Topically applied ripasudil prolonged graft survival by downregulating neovascularization and inflammation factors, while promoting corneal re-epithelization, suggesting that ripasudil may be useful for suppressing immunological rejection in corneal transplantation.

Using Medical Big Data to Develop Personalized Medicine for Dry Eye Disease

Dry eye disease (DED) is a chronic, multifactorial ocular surface disorder with multiple etiologies that results in tear film instability. Globally, the prevalence of DED is expected to increase with an aging society and daily use of digital devices. Unfortunately, the medical field is currently unprepared to meet the medical needs of patients with DED. Noninvasive, reliable, and readily reproducible biomarkers have not yet been identified, and the current mainstay treatment for DED relies on symptom alleviation using eye drops with no effective preventative therapies available. Medical big data analyses, mining information from multiomics studies and mobile health applications, may offer a solution for managing chronic conditions such as DED. Omics-based data on individual physiologic status may be leveraged to prevent high-risk diseases, accurately diagnose illness, and improve patient prognosis. Mobile health applications enable the portable collection of real-world medical data and biosignals through personal devices. Together, these data lay a robust foundation for personalized treatments for various ocular surface diseases and other pathologies that currently lack the components of precision medicine. To fully implement personalized and precision medicine, traditional aggregate medical data should not be applied directly to individuals without adjustments for personal etiology, phenotype, presentation, and symptoms.

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."

Variable Responses to Corneal Grafts: Insights from Immunology and Systems Biology

Corneal grafts interact with their hosts via complex immunobiological processes that sometimes lead to graft failure. Prediction of graft failure is often a tedious task due to the genetic and nongenetic heterogeneity of patients. As in other areas of medicine, a reliable prediction method would impact therapeutic decision-making in corneal transplantation. Valuable insights into the clinically observed heterogeneity of host responses to corneal grafts have emerged from multidisciplinary approaches, including genomics analyses, mechanical studies, immunobiology, and theoretical modeling. Here, we review the emerging concepts, tools, and new biomarkers that may allow for the prediction of graft survival.

Dry Eye Disease: Emerging Approaches to Disease Analysis and Therapy

Dry eye disease (DED) is among the most common ocular disorders affecting tens of millions of individuals worldwide; however, the condition remains incompletely understood and treated. Valuable insights have emerged from multidisciplinary approaches, including immunometabolic analyses, microbiome analyses, and bioengineering. Furthermore, we have seen new developments in clinical assessment approaches and treatment strategies in the recent past. Here, we review the emerging frontiers in the pathobiology and clinical management of DED.

The purinergic receptor antagonist oxidized adenosine triphosphate suppresses immune-mediated corneal allograft rejection

Adenosine triphosphate (ATP) is released into the extracellular environment during transplantation, and acts via purinergic receptors to amplify the alloimmune response. Here, using a well-established murine model of allogeneic corneal transplantation, we investigated the immunomodulatory mechanisms of the purinergic receptor antagonist oxidized ATP (oATP). Corneal transplantation was performed using C57BL/6 donors and BALB/c hosts. oATP or sterile saline was administered via intraperitoneal injection for 2 weeks postoperatively. Frequencies of CD45⁺ leukocytes, CD11b⁺MHCII⁺ antigen presenting cells (APCs), CD4⁺IFN-γ⁺ effector Th1 cells and CD4⁺Foxp3⁺ regulatory T cells (Tregs) were evaluated by flow cytometry. Slit-lamp microscopy was performed weekly for 8 weeks to evaluate graft opacity and determine transplant rejection. Treatment with oATP was shown to significantly reduce graft infiltration of CD45⁺ leukocytes, decrease APC maturation and suppress effector Th1 cell generation relative to saline-treated control. No difference in Treg frequencies or Foxp3 expression was observed between the oATP-treated and control groups. Finally, oATP treatment was shown to reduce graft opacity and increase graft survival. This report demonstrates that oATP limits the alloimmune response by regulating APC maturation and suppressing the generation of alloreactive Th1 immunity.

Regulatory T cell modulation of cytokine and cellular networks in corneal graft rejection

PURPOSE OF REVIEW

Corneal allografts placed in vascularized or inflamed host beds are at increased risk of graft rejection due to the preponderance of activated immune cells in the host bed. Regulatory T cells (Tregs) are master regulators of the adaptive immune response and play a key role in the induction of immune tolerance. The aim of this review is to discuss mechanisms through which Tregs mediate tolerance in corneal transplantation and the novel therapeutic approaches that target Tregs to promote transplant survival.

RECENT FINDINGS

The inflammatory environment of high-risk allografts not only promotes activation of effector T cells and their infiltration to graft site, but also impairs Treg immunomodulatory function. Recent studies have shown that expansion of Tregs and enhancing their modulatory function significantly improve graft survival.

SUMMARY

As our understanding of the cellular and molecular pathways in corneal transplantation has deepened, novel therapeutic strategies have been developed to improve allograft survival. In this review, we discuss therapeutic approaches that focus on Tregs to promote corneal allograft survival.

Method for selective quantification of immune and inflammatory cells in the cornea using flow cytometry

The cornea serves as a protective surface against the environment (i.e., allergens, pollutants, desiccation and microorganisms) and promotes vision, made possible by corneal transparency. This protocol describes corneal preparation for flow cytometry to assess cells localized in the cornea. Our model details the process, from determining how many corneas are needed in the experiment to corneal excision to digestion and staining of the cornea cells. The simplicity of the model allows for systematic analysis of different corneal mechanisms of immunity, inflammation, angiogenesis and wound healing. In corneal transplantation, residential immune and inflammatory cells are key to the mechanisms that underlie angiogenesis, opacity, and graft rejection. In addition, this model can also elucidate cellular mechanisms mediating corneal graft outcomes and wound healing. Lastly, this model can be used to analyze the efficacy of new medications such as instillation and subconjunctival injections and assess the potential of therapeutic molecules to enhance graft survival and wound healing in vivo.

Pathological conversion of regulatory T cells is associated with loss of allotolerance

CD4+CD25+Foxp3+ Regulatory T cells (Tregs) play a critical role in immune tolerance. The plasticity and functional adaptability of Tregs in an inflammatory microenvironment has been demonstrated in autoimmunity. Here, using a double transgenic mouse model that permits Foxp3 lineage tracing, we investigated the phenotypic plasticity of Foxp3+ Tregs in a well-characterized murine model of corneal transplantation. In order to subvert the normal immune privilege of the cornea and foster an inflammatory milieu, host mice were exposed to desiccating stress prior to transplantation. Treg frequencies and function were decreased following desiccating stress, and this corresponded to decreased graft survival. A fraction of Tregs converted to IL-17+ or IFNγ+ 'exFoxp3' T cells that were phenotypically indistinguishable from effector Th17 or Th1 cells, respectively. We investigated how Foxp3 expression is modulated in different Treg subsets, demonstrating that neuropilin-1- peripherally-derived Tregs are particularly susceptible to conversion to IL-17+/IFNγ+ exFoxp3 cells in response to cues from their microenvironment. Finally, we show that IL-6 and IL-23 are implicated in the conversion of Tregs to exFoxp3 cells. This report demonstrates that the pathological conversion of Tregs contributes to the loss of corneal immune privilege.