Corneal graft rejection occurs despite Fas ligand expression and apoptosis of infiltrating cells

A Novel Rat Model of Dry Eye Induced by Aerosol Exposure of Particulate Matter

Purpose

The purpose of this study was to introduce a novel dry eye rat model induced by aerosol exposure of particulate matter (PM).

Methods

A total of 30 female Sprague Dawley (SD) rats divided into 3 groups: the control group, the low-level exposed group, and the high-level exposed group. The rats in the experience groups were directly exposed to PM samples in the exposure chamber over 14 days. The clinical observation, including tear volume, corneal fluorescein staining, breakup time (BUT), inflammation index, corneal irregularity score, and corneal confocal microscopy. Eyeballs were collected on day 14 for hematoxylin and eosin (H&E) staining and PAS staining. TUNEL assay, CD45, and Ki67 immunostaining was performed and corneal ultrastructural changes were detected by electron microscopy. IL-1β, TNF-α, IFN-γ, and NF-κB Western blot analysis were used to observe the possible pathogenesis.

Results

In the PM-treated groups, the number of layers in the corneal epithelium and corneal nerve fiber length were significantly decreased compared with that of the control group. The number of corneal epithelial microvilli and chondriosome/desmosomes were drastically reduced in PM-treated groups. Confocal microscopy and CD45 immunohistochemistry showed inflammatory cell infiltration in the PM-treated groups. PM caused apoptosis of corneal and conjunctival epithelial cells while leading to abnormal epithelial cell proliferation, meanwhile, conjunctival goblet cells in the PM-treated group were also significantly reduced. PM significantly increased the levels of IL-1β, TNF-α, IFN-γ, and p-NF-κB-p65 in the cornea.

Conclusions

Aerosol exposure of PM can reduce the stability of tear film and cause the change of ocular surface, which is similar to the performance of human dry eye, suggesting a novel animal model of dry eye.

Dry eye induced by exposure to cigarette smoke pollution: An in vivo and in vitro study

Exposure to cigarette smoke (CS) pollution has previously associated with dry eye symptoms but without detailed experimental data and elucidation of the mechanism. We aimed to evaluate the effects of CS on the ocular surfaces of mice and the extraction of DMSO lipid-soluble cigarette smoke particles (DCSP) on cultured human corneal epithelial cells (HCECs), and explore to elucidate the probable mechanism. C57BL mice were exposed to CS challenging. In vivo clinical evaluations, including corneal fluorescein staining, tear film break-up time, and confocal microscopic observations, were performed before exposure and post-exposure. At the end of the in vivo study, changes in corneal and conjunctival histology, corneal ultrastructure, and conjunctival goblet cell intensity were examined, expression of TUNLE and Ki67 in tissue were also detected. In vitro, cell confluence and caspase3/7 were assessed in DCSP treated HCECs. Production of TNF-α, IL-1β and IL-6, activation of NF-κB and Ki67 were evaluated by means of ELISA and Western blot respectively in HCECs cultured with 0.6 μL/mL DCSP. We found that longer-term CS exposure induced dry eye symptoms in mice. Additionally, corneal and conjunctival epithelial damage occurred, the corneal ultrastructure changed, and the density of goblet cells decreased. Apoptosis and Ki67 increased in both the conjunctiva and the cornea of CS-exposed animals. Furthermore, although DCSP inhibited the proliferation of HCECs, expression of Ki67 increased and apoptosis was only induced significantly by 2.0 μL/mL DCSP. The release of IL-1β and IL-6, activation of NF-κB were prompted by DCSP. The results indicated that CS is toxic to the ocular surface of mice and HCECs. Longer-term CS exposure in mice stimulates ocular surface changes that resemble those observed with dry eye. The mechanism may relate to inflammation and activation of NF-κB. In this study, we established a novel animal model to study dry eye, with the experimental data and elucidation of mechanism facilitating further research.

Air pollutant particulate matter 2.5 induces dry eye syndrome in mice

In this study, we explored the effects of particulate matter 2.5 (PM_2.5) eye drops on the ocular surface structure and tear function in mice and established a novel animal model for dry eye research. We found that, following treatment with PM_2.5, the tear volume and, the tear film break-up time showed statistical differences at each time point (P < 0.05). The FL score of the PM_2.5-treated group was higher than that of others (P < 0.05). The average number of corneal epithelial layer cells in groups A and B was significantly lower than that in group C (P < 0.05). Scanning electron microscopy and transmission electron microscopy revealed that the number of corneal epithelial microvilli and corneal desmosomes was drastically reduced in group C. PM_2.5 induced apoptosis in the corneal superficial and basal epithelium and led to abnormal differentiation and proliferation of the ocular surface with higher expression levels of Ki67 and a reduced number of goblet cells in the conjunctival fornix in group C. PM_2.5 significantly increased the levels of TNF-α, NF-κB p65 (phospho S536), and NF-κB in the cornea. Thus, the topical administration of PM_2.5 in mice induces ocular surface changes that are similar to those of dry eye in humans, representing a novel model of dry eye.

A murine model of dry eye induced by topical administration of erlotinib eye drops

In the present study, the effects of erlotinib on mouse tear function and corneal epithelial tissue structure were investigated. Throughout the 3 weeks of treatment, no notable differences were observed in the body, eye or lacrimal gland weights of the control and experimental mice. However, in the experimental group, the tear volume and break‑up times of tear film were significantly lower following treatment with erlotinib compared with the control group. Corneal fluorescein staining in the experimental group revealed patchy staining, and the Lissamine green staining and inflammatory index were significantly higher in the experimental group at 3 weeks than in the control group. In the experimental group, the number of corneal epithelium layers increased significantly following treatment with erlotinib for 3 weeks and a significant increase in the number of vacuoles was observed compared with the control group. Treatment with erlotinib significantly increased the corneal epithelial cell apoptosis, and led to a significantly increased number of epithelial cell layers and increased keratin 10 expression. It also significantly reduced the number of conjunctival goblet cells. Transmission electron microscopy and scanning electron microscopy revealed that the corneal epithelial surface was irregular and there was a substantial reduction and partial loss of the microvilli in the experimental group. Mice treated with erlotinib also exhibited an increased protein expression of tumor necrosis factor‑α and decreased protein expression of phosphorylated‑epidermal growth factor receptor in the corneal epithelial cells. The topical application of erlotinib eye drops was revealed to induce dry eyes in mice. This is a novel method of developing a model of dry eyes in mice.

A mouse dry eye model induced by topical administration of the air pollutant particulate matter 10

AIM

To introduce a novel dry eye mouse model induced by topical administration of the air pollutant particulate matter 10 (PM₁₀).

METHOD

A total of 60 male BALB/c mice were used in this study and divided into two groups: group A (PBS eye drops, n=30) and group B (PM₁₀ eye drop group, n=30). Each treatment was dosed four times a day, every time 50ul with the concentration of 5mg/ml PM10, for 14 consecutive days in the right eye. The clinical manifestations of dry eye were measured before therapy and 4, 7 and 14days post-treatment respectively, which included the tear volume, tear break-up (BUT) time, corneal fluorescein staining, rose bengal staining, Lissamine Green staining and inflammatory index. Eye samples were collected on D14 and examined by histologic light microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM), corneal cytokeration 10 (K10) immunnostaining, and tumor necrosis factor-α (TNF-α), NF-κB-p65 and NF-κB Western Blot analysis.

RESULTS

At 0d, 7d and 14d, there were no statistical changes in tear volume, BUT after treatment (P>0.05) with PBS in group A. In group B, all items showed statistical differences at each time point (P<0.05). At 14d after therapy, the fluorescein staining score of group B was higher than group A (P<0.05). The score of rose bengal staining and Lissamine Green staining in group B was also higher than that in group A (P<0.05). The number of mean layers of corneal epithelial cells in the group A was significantly lower than that in the group B (P<0.05). TEM and SEM revealed that the number of corneal epithelial microvilli were drastically reduced in group B. The number of corneal chondriosome/desmosomes was also reduced in group B by TEM. PM₁₀ induced apoptosis in the superficial and basal corneal epithelium, and leaded to abnormal differentiation and proliferation of the ocular surface with higher expression levels of K10 and reduced number of goblet cells in the conjunctival fornix in group B. PM₁₀ significantly increased the levels of TNF-α, NF-κB-p65 and NF-κB in the cornea.

CONCLUSION

PM₁₀ can damage the tear film function and cause the destruction of the structural organization of ocular surface in mice. Topical administration of PM₁₀ in mice induces ocular surface changes that are similar to those of dry eye in humans, representing a novel model of DES.

Gene Therapy for Modulation of T-Cell-Mediated Immune Response Provoked by Corneal Transplantation

Corneal transplantation (keratoplasty) is the most common type of tissue replacement in the world. The increased rate of graft rejection after keratoplasty is a central problem for repeated transplantations and in inflamed host corneas. It has been shown that apoptosis of grafted epithelium has a role in corneal allograft rejection. This study focused on the T-cell response triggered in BALB/c mice after allogeneic corneal transplantation with and without anti-apoptotic p35-transduced epithelium. To restrict p35 expression to the epithelial cells, modified allogeneic composite grafts were created. As a result, it was found that the proportion of alloreactive CD4⁺ T cells in postoperatively removed cervical lymph nodes was reduced in the p35-transduced group compared to the allogeneic control group. Diminished priming of the CD4⁺ T cells was supported by significantly decreased proliferation and lower interferon gamma secretion when compared to allogeneic engraftments. The reduced priming of CD4⁺ lymphocytes is the first confirmation of the functionality of p35 in the epithelium of corneal grafts to alter the development of the recipient's immune response. Thus, modification of allosensibilization seems to be a promising tool for reducing graft-mediated immune response following corneal 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.

The immunobiology of corneal transplantation

Corneal allotransplantation is highly successful in the short term, but much less successful in the longer term. Many corneal grafts in recipients with corneal neovascularization or the sequelae of ocular inflammation undergo irreversible rejection, despite topical immunosuppression with glucocorticosteroids. Sensitization to cornea-derived alloantigen proceeds by both direct and indirect routes, but the anatomic location of sensitization remains unclear. Multiple and redundant mechanisms operate in the effector phase of corneal graft rejection, which is largely cell-mediated rather than antibody-mediated. Human leukocyte antigen matching may improve outcomes in high-risk patients but systemic immunosuppression is frequently ineffective and is seldom used.

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.