Modulation of ocular surface desiccation in a murine model by histatin-5 application.

PURPOSE: To determine the efficacy of Histatin-5 (Hst5) peptide treatment in ameliorating dry eye disease (DED) phenotype in an in-vivo mouse model of scopolamine and desiccating stress (SDS) dry eye. METHODS: SDS was induced in female C57BL/6 mice by subcutaneous injections of scopolamine hydrobromide and exposure to low relative humidity and forced air draft for five days. Mouse eyes were topically treated with synthetic Hst5 peptide or balanced salt solution (BSS) twice a day for four days. Control mice were not exposed to SDS induction and did not receive any treatments. Oregon green dextran (OGD) staining was used to evaluate corneal permeability. Histologically, staining with periodic acid schiff (PAS), immunohistochemistry (IHC) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), were used to quantify the number of goblet cells (GC), CD45+ immune cells and apoptotic cells respectively in formalin fixed paraffin embedded (FFPE) mouse whole eye sections. RESULTS: Compared to treatment with BSS, Hst5 treatment significantly lowered corneal epithelial permeability, prevented conjunctival epithelial GC loss, decreased conjunctival CD45+ immune cell infiltration and reduced conjunctival epithelial cell apoptosis. CONCLUSIONS: Hst5 peptide topical treatment significantly improves the clinical parameters observed in SDS experimental model of DED. This is the first report of the efficacy of Hst5 treatment of dry eye phenotype, and potential novel treatment for DED in the clinic. Hst5 represents a new class of efficacious therapeutic agents, demonstrating pro-epithelial and anti-inflammatory activities at the ocular surface.

Once-Daily Cyclosporine-A-MiDROPS for Treatment of Dry Eye Disease.

PURPOSE: To determine if a Microemulsion Drug Ocular Penetration System (MiDROPS) formulation of cyclosporine A (CsA) delivers more drug and is more efficacious for treatment of dry eye disease (DED) than the current clinical formulation. METHODS: Tissue distribution of CsA was quantified by liquid chromatography with tandem mass spectrometry (LC-MS/MS). To assess tolerability, CsA-MiDROPS (0.1%) was applied to the eyes of rabbits twice per day for 14 days and assessed using ophthalmoscopic examinations. Mice were exposed to desiccating stress for 10 days and received daily topical instillation of the vehicle or test agent. Cornea staining was done to quantify corneal permeability. Histologic quantification of goblet cell (GC) density and CD4+ T-cell infiltration in the conjunctiva was performed. RESULTS: Ophthalmic distribution studies indicate significantly increased drug concentration with CsA-MiDROPS compared with Restasis. CsA-MiDROPS is well tolerated with little toxicity in a 2-week tolerability study. In the DED model, both 0.05% and 0.1% CsA-MiDROPS conferred a significant effect and were more effective than Restasis for treating experimental DED when dosed twice per day. As compared with Restasis dosed twice per day, 0.1% CsA-MiDROPS dosed once per day demonstrated superiority. CONCLUSIONS: CsA-MiDROPS showed superior drug delivery and efficacy compared with other clinical formulations. As this product is simple to produce and needs to be only applied once daily, the clinical development of CsA-MiDROPS will help to reduce societal and patient burdens by lowering drug costs and accelerating/improving the activity of CsA. TRANSLATIONAL RELEVANCE: MiDROPS has broad application concerning the ophthalmic development of lipophilic small molecule therapeutics.

Identification for Differential Localization of Putative Corneal Epithelial Stem Cells in Mouse and Human.

Human Corneal epithelial stem cells (CESCs) have been identified to reside in limbus for more than 2 decades. However, the precise location of CESCs in other mammalian remains elusive. This study was to identify differential localization of putative CESCs in mice. Through a series of murine corneal cross-sections from different directions, we identified that anatomically and morphologically the murine limbus is composed of the thinnest epithelium and the thinnest stroma without any palisades of Vogt-like niche structure. The cells expressing five of stem/progenitor cell markers are localized in basal layer of entire murine corneal epithelium. BrdU label-retaining cells, a key characteristic of epithelial stem cells, are detected in both limbal and central cornea of mouse eye. Functionally, corneal epithelium can be regenerated in cultures from central and limbal explants of murine cornea. Such a distribution of mouse CESCs is different from human cornea, where limbal stem cell concept has been well established and accepted. We are aware that some new evidence supports limbal stem cell concept in mouse recently. However, it is important to know that central cornea may provide an alternative source of stem cells when one utilizes mice as animal model for corneal research.

Meibomian Gland Dysfunction in Type 2 Diabetic Patients.

PURPOSE: To investigate meibomian gland and tear film function in patients with type 2 diabetes. METHODS: This prospective study compared changes in meibomian gland and tear film function in type 2 diabetic patients with nondiabetic patients. Meibomian gland function was evaluated by measuring lipid layer thickness (LLT), grading of meibomian gland loss, lid margin abnormalities, and expression of meibum. Tear film function was assessed by measuring tear breakup time (TBUT), the Schirmer I test, noninvasive breakup time (NIBUT), tear meniscus height (TMH), and corneal fluorescein staining. RESULTS: Meibography scores were significantly higher in the diabetic group compared with the nondiabetic group (p = 0.004). The number of expressible glands was significantly lower in the diabetic group in temporal, central, and nasal third of the lower eyelid (nasal: p = 0.002; central: p = 0.040; and temporal: p = 0.039). The lid margin abnormality score was significantly higher in the diabetic group than in the nondiabetic group (p = 0.04). There was no statistically significant difference in the tear film function parameters between the two groups. CONCLUSIONS: Meibomian gland dysfunction (MGD) in type 2 diabetic patients is more severe compared with nondiabetic patients. Overall, most of the diabetic patients manifest as having asymptomatic MGD.

Goblet Cells Contribute to Ocular Surface Immune Tolerance-Implications for Dry Eye Disease.

Conjunctival goblet cell (GC) loss in dry eye is associated with ocular surface inflammation. This study investigated if conjunctival GCs contribute to ocular surface immune tolerance. Antigens applied to the ocular surface, imaged by confocal microscopy, passed into the conjunctival stroma through goblet cell associated passages (GAPs) in wild type C57BL/6 (WT), while ovalbumin (OVA) was retained in the epithelium of SAM pointed domain containing ETS transcription factor (Spdef) knockout mice (Spdef-/-) that lack GCs and are a novel model of dry eye. Stimulated GC degranulation increased antigen binding to GC mucins. Induction of tolerance to topically applied OVA measured by cutaneous delayed type hypersensitivity (DTH) was observed in WT, but not Spdef-/-. OTII CD4⁺ T cells primed by dendritic cells (DCs) from the conjunctival draining lymph nodes of Spdef-/- had greater IFN-γ production and lower Foxp3 positivity than those primed by WT DCs. These findings indicate that conjunctival GCs contribute to ocular surface immune tolerance by modulating antigen distribution and antigen specific immune response. GC loss may contribute to the abrogation of ocular surface immune tolerance that is observed in dry eye.

Long-term outcomes of ciliary sulcus versus capsular bag fixation of intraocular lenses in children: An ultrasound biomicroscopy study.

PURPOSE: To evaluate the long-term outcomes of ciliary sulcus versus capsular bag fixation of intraocular lenses (IOLs) in children after pediatric cataract surgery. METHODS: IOL was implanted in the ciliary sulcus in 21 eyes of 14 children, and in the capsular bag in 19 eyes of 12 children for the treatment of pediatric cataract in an institutional setting. Ultrasound biomicroscopy (UBM) was performed. Main outcome measures included IOL decentration, IOL tilt, anterior chamber depth (ACD), angle-opening distance at 500 µm (AOD500), trabecular-iris angle (TIA), best-corrected visual acuity (BCVA), intraocular pressure (IOP), and incidence of postoperative complications. RESULTS: The mean follow-up period was 6.81 ± 1.82 years. Comparing to the capsular bag fixation group, the ciliary sulcus fixation group had higher vertical IOL decentration, horizontal IOL tilt, and vertical IOL tilt (p = 0.02, 0.01,0.01, respectively), higher incidence of iris-IOL contact and peripheral anterior synechia (p = 0.001, 0.03, respectively), smaller ACD, AOD500, and TIA (p = 0.02, 0.03, 0.04, respectively), higher mean IOP (17.10 ±6.06 mmHg vs.14.15± 4.74 mmHg, p = 0.01), and higher incidence of secondary glaucoma (28.57% vs. 10.53%, p = 0.007).There was no significant difference between the two groups with regard to the BCVA, refractive errors, incidence of myopic shift, nystagmus, strabismus, and visual axis opacity. CONCLUSIONS: Ciliary sulcus fixation of IOLs in pediatric eyes may increase IOL malposition and crowding of the anterior segment, and may associate with a higher risk of secondary glaucoma compared to capsular bag fixation of IOLs.

Interferon-γ-Induced Unfolded Protein Response in Conjunctival Goblet Cells as a Cause of Mucin Deficiency in Sjögren Syndrome.

Goblet cells (GCs) are specialized secretory cells that produce mucins and a variety of other proteins. Significant conjunctival GC loss occurs in both experimental dry eye models and patients with keratoconjunctivitis sicca due to the induction of interferon (IFN)-γ. With the use of a primary murine culture model, we found that GCs are highly sensitive to IFN-γ with significantly reduced proliferation and altered structure with low concentrations. GC cultures treated with IFN-γ have increased gene expression of Muc2 and Muc5AC but do not express these mucin glycoproteins. We hypothesized that IFN-γ induces endoplasmic reticulum stress and the unfolded protein response (UPR) in GCs. Cultures treated with IFN-γ increased expression of UPR-associated genes and proteins. Increased GRP78 and sXBP1 expression was found in experimental dry eye and Sjögren syndrome models and was GC specific. Increased GRP78 was also found in the conjunctiva of patients with Sjögren syndrome at the gene and protein levels. Treatment with dexamethasone inhibited expression of UPR-associated genes and increased mucin production. These results indicate that induction of UPR by IFN-γ is an important cause of GC-associated mucin deficiency observed in aqueous-deficient dry eye. Therapies to block the effects of IFN-γ on the metabolically active endoplasmic reticulum in these cells might enhance synthesis and secretion of the protective GC mucins on the ocular surface.

X-Linked Retinoschisis: Phenotypic Variability in a Chinese Family.

X-linked juvenile retinoschisis (XLRS), a leading cause of juvenile macular degeneration, is characterized by a spoke-wheel pattern in the macular region of the retina and splitting of the neurosensory retina. Our study is to describe the clinical characteristics of a four generations of this family (a total of 18 members)with X-linked retinoschisis (XLRS) and detected a novel mutations of c.3G > A (p.M1?) in the initiation codon of the RS1 gene. by direct sequencing.Identification of this mutation in this family provides evidence about potential genetic or environmental factors on its phenotypic variance, as patients presented with different phenotypes regardless of having the same mutation. Importantly, OCT has proven vital for XLRS diagnosis in children.

Blueberry Component Pterostilbene Protects Corneal Epithelial Cells from Inflammation via Anti-oxidative Pathway.

Blueberries have been recognized to possess protective properties from inflammation and various diseases, but not for eye and ocular disorders. This study explores potential benefits of pterostilbene (PS), a natural component of blueberries, in preventing ocular surface inflammation using an in vitro culture model of human corneal epithelial cells (HCECs) exposed to hyperosmotic medium at 450 mOsM. Gene expression was detected by RT-qPCR, and protein production or activity was determined by ELISA, zymography, Western blotting and immunofluorescent staining. Reactive oxygen species (ROS) production was measured using DCFDA kit. The addition of PS significantly reduced the expression of pro-inflammatory mediators, TNF-α, IL-1 ß, IL-6, MMP-2 and MMP-9 in HCECs exposed to hyperosmotic medium. Pre-treatment with PS (5 to 20 µM) suppressed ROS overproduction in a dose-dependent manner. Additionally, PS significantly decreased the levels of oxidative damage biomarkers, malondialdehyde (MDA), 4-hydroxynonenal (4-HNE), aconitase-2 and 8-hydroxydeoxyguanosine (8-OHdG). Importantly, PS was found to rebalance homeostasis between oxygenases and anti-oxidative enzymes by decreasing cyclooxygenase 2 (COX2) expression and restoring the activity of antioxidant enzymes, superoxide dismutase 1 (SOD1) and peroxiredoxin-4 (PRDX4) during hyperosmotic stress. Our findings demonstrate that PS protects human cornea from hyperosmolarity-induced inflammation and oxidative stress, suggesting protective effects of PS on dry eye.

IL-13 Stimulates Proliferation and Expression of Mucin and Immunomodulatory Genes in Cultured Conjunctival Goblet Cells.

PURPOSE: To investigate the effects of IL-13 on goblet cell proliferation, differentiation, and expression of mucin and immunomodulatory genes. METHODS: Explants were excised from the conjunctiva of young C57BL/6 mice. Cultures received 200 µL per week of either Keratinocyte media (KSFM) or KSFM supplemented with 10 ng/mL IL-13 and were incubated for 3 (D3), 7 (D7), or 14 (D14) days. Subsequently, cell proliferation was assessed or cultures were immunostained, collected for dot blot, or for reverse transcription (RT) and quantitative real-time PCR (qPCR) or for RT-PCR gene array. RESULTS: The cultured conjunctival epithelium expressed goblet cell associated keratin 7 and mucins MUC5AC and MUC2 and when stimulated with IL-13 showed increased proliferation at D3 and D7 (P < 0.05) compared with control. MUC5AC expression was increased in the IL-13-treated group at D3 and D14 (P < 0.05). IL-13-treated cultures showed increased chemokine ligand 26 (CCL26), chloride channel calcium activated channel 3 (CLCA3), fas ligand (FasL), and Relm-ß at D7. All conjunctival cultures expressed MUC2, and its expression was decreased at D3 (P < 0.05) and increased at D14 (P < 0.05) with IL-13 treatment. CONCLUSIONS: This study demonstrated that conjunctival goblet cells are IL-13 responsive cells that produce factors known to maintain epithelial barrier, stimulate mucin production, and modulate immune response in nonocular mucosa when treated with IL-13. The functional significance of IL-13-stimulated factors remains to be determined.

Dexamethasone nanowafer as an effective therapy for dry eye disease.

Dry eye disease is a major public health problem that affects millions of people worldwide. It is presently treated with artificial tear and anti-inflammatory eye drops that are generally administered several times a day and may have limited therapeutic efficacy. To improve convenience and efficacy, a dexamethasone (Dex) loaded nanowafer (Dex-NW) has been developed that can release the drug on the ocular surface for a longer duration of time than drops, during which it slowly dissolves. The Dex-NW was fabricated using carboxymethyl cellulose polymer and contains arrays of 500 nm square drug reservoirs filled with Dex. The in vivo efficacy of the Dex-NW was evaluated using an experimental mouse dry eye model. These studies demonstrated that once a day Dex-NW treatment on alternate days during a five-day treatment period was able to restore a healthy ocular surface and corneal barrier function with comparable efficacy to twice a day topically applied dexamethasone eye drop treatment. The Dex-NW was also very effective in down regulating expression of inflammatory cytokines (TNF-α, and IFN-γ), chemokines (CXCL-10 and CCL-5), and MMP-3, that are stimulated by dry eye. Despite less frequent dosing, the Dex-NW has comparable therapeutic efficacy to topically applied Dex eye drops in experimental mouse dry eye model, and these results provide a strong rationale for translation to human clinical trials for dry eye.

A Novel Innate Response of Human Corneal Epithelium to Heat-killed Candida albicans by Producing Peptidoglycan Recognition Proteins.

Fungal infections of the cornea can be sight-threatening and have a worse prognosis than other types of microbial corneal infections. Peptidoglycan recognition proteins (PGLYRP), which are expressed on the ocular surface, play an important role in the immune response against bacterial corneal infections by activating toll-like receptors (TLRs) or increasing phagocytosis. However, the role of PGLYRPs in innate immune response to fungal pathogens has not been investigated. In this study, we observed a significant induction of three PGLYRPs 2-4 in primary human corneal epithelial cells (HCECs) exposed to live or heat-killed Candida albicans (HKCA). The C-type lectin receptor dectin-1 plays a critical role in controlling Candida albicans infections by promoting phagocytic activity and cytokine production in macrophages and dendritic cells. Here, we demonstrate that dectin-1 is expressed by normal human corneal tissue and primary HCECs. HKCA exposure increased expression of dectin-1 on HCECs at mRNA and protein levels. Interestingly, dectin-1 neutralizing antibody, IκB-α inhibitor BAY11-7082, and NF-κB activation inhibitor quinazoline blocked NF-κB p65 nuclear translocation, as well as the induction of the PGLYRPs by HKCA in HCECs. Furthermore, rhPGLYRP-2 was found to suppress colony-forming units of Candida albicans in vitro. In conclusion, these findings demonstrate that dectin-1 is expressed by human corneal epithelial cells, and dectin-1/NF-κB signaling pathway plays an important role in regulating Candida albicans/HKCA-induced PGLYRP secretion by HCECs.

Macrophage Phenotype in the Ocular Surface of Experimental Murine Dry Eye Disease.

To evaluate the phenotype of macrophages in the cornea and conjunctiva of C57BL/6 mice with induced experimental dry eye. C57BL/6 mice exposed to desiccating stress (DS) were evaluated at 1, 5, and 10 days and C57BL/6 mice maintained in non-stressed environment were used as controls. Whole eyes and adnexa were excised for histology or used for gene expression analysis. Location and phenotype of macrophages infiltrating the cornea and conjunctiva was evaluated by immunofluorescence analysis. Quantitative polymerase chain reaction evaluated macrophage markers and T cell-related and inflammatory cytokine expression in cornea and conjunctiva. Immunofluorescence staining demonstrated that macrophages reside in the conjunctiva of control and dry eye mice and their number did not change with DS. Real-time RT-PCR demonstrated that the level of M1 macrophage marker, iNOS, increased prominently in the conjunctiva at DS 10 days. In contrast, there was a non-significant decrease of the M2 marker Arg1 with DS. The levels of inflammatory cytokine, IL-12a mRNA transcript in the conjunctiva increased significantly at DS1 and decreased at DS5, while levels of IL-18 were significantly increased at DS 10. Macrophages reside in the ocular surface tissues of C57BL/6 mice. Although the number of macrophages in the conjunctiva does not change, evidence of inflammatory M1 activation after desiccating stress was observed. Better understanding of phagocyte diversity and activation in dry eye disease provide a basis for the development of phagocyte-targeted therapeutic strategies.

Desiccating stress-induced chemokine expression in the epithelium is dependent on upregulation of NKG2D/RAE-1 and release of IFN-γ in experimental dry eye.

The Th1-associated chemokines CXCL9, CXCL10, and CXCL11 coordinate migration of CXCR3(+) Th1 cells. The objective of this study was to evaluate the role of the innate immune system in stimulating chemokine expression in an experimental model of dry eye and bridge the gap between innate and adaptive immunity. Desiccating stress (DS) induced very early (6 h) expression and production of Th1-associated chemokines in cornea and conjunctiva of C57BL/6 and RAG1 knockout (KO) mice, demonstrating that chemokine expression does not require innate T cells. We then demonstrated that activating the innate immune system prior to adoptive transfer of T cells to RAG1KO mice increased disease severity. Interestingly, lack of induction of chemokines CXCL9, CXCL10, and CXCL11 in IFN-γKO mice provided evidence that their expression requires IFN-γ for induction. Treatment of RAG1KO mice with anti-NK1.1 prevented the increase of CXCL9, CXCL10, and CXCL11 in response to DS, compared with isotype controls. Additionally, DS increased the expression of NKG2D in the conjunctiva. The expression of the NKG2D ligand, retinoic acid early inducible gene 1, also increased at the ocular surface at both the protein and gene levels. Neutralization of NKG2D at the ocular surface decreased the expression of CXCL9, CXCL10, CXCL11, and IFN-γ. In summary, upregulation of CXCL9, CXCL10, and CXCL11 expression in experimental dry eye is T cell-independent, requiring IFN-γ-producing NKG2D(+) NK cells that are activated in response to DS-induced stress signals. This study provides insight into the events that trigger the initial immune response in dry eye pathology.

Managing Sjögren's Syndrome and non-Sjögren Syndrome dry eye with anti-inflammatory therapy.

Dry eye from Sjögren's syndrome is a multifactorial disease that results in dysfunction of the lacrimal functional unit. Studies have shown changes in tear composition, including inflammatory cytokines, chemokines, and metalloproteinase. T-lymphocytes have been shown to increase in the conjunctiva and lacrimal glands in patient and animal models. This inflammation is in part responsible for the pathogenesis of the disease, which results in symptoms of eye irritation, ocular surface epithelial disease, and loss of corneal barrier function. There are a number of anti-inflammatory approaches for treating this disease. The current study reviews details of immune response and anti-inflammatory therapies used to control this disease.

Chemokine receptors CCR6 and CXCR3 are necessary for CD4(+) T cell mediated ocular surface disease in experimental dry eye disease.

CD4(+) T cells are essential to pathogenesis of ocular surface disease in dry eye. Two subtypes of CD4(+) T cells, Th1 and Th17 cells, function concurrently in dry eye to mediate disease. This occurs in spite of the cross-regulation of IFN-γ and IL-17A, the prototypical cytokines Th1 and Th17 cells, respectively. Essential to an effective immune response are chemokines that direct and summon lymphocytes to specific tissues. T cell trafficking has been extensively studied in other models, but this is the first study to examine the role of chemokine receptors in ocular immune responses. Here, we demonstrate that the chemokine receptors, CCR6 and CXCR3, which are expressed on Th17 and Th1 cells, respectively, are required for the pathogenesis of dry eye disease, as CCR6KO and CXCR3KO mice do not develop disease under desiccating stress. CD4(+) T cells from CCR6KO and CXCR3KO mice exposed to desiccating stress (DS) do not migrate to the ocular surface, but remain in the superficial cervical lymph nodes. In agreement with this, CD4(+) T cells from CCR6 and CXCR3 deficient donors exposed to DS, when adoptively transferred to T cell deficient recipients manifest minimal signs of dry eye disease, including significantly less T cell infiltration, goblet cell loss, and expression of inflammatory cytokine and matrix metalloproteinase expression compared to wild-type donors. These findings highlight the important interaction of chemokine receptors on T cells and chemokine ligand expression on epithelial cells of the cornea and conjunctiva in dry eye pathogenesis and reveal potential new therapeutic targets for dry eye disease.

IFN-γ-independent intraocular tumor rejection is mediated by a macrophage-dependent process that leaves the eye intact.

Intraocular tumors reside in an immune-privileged site, yet in certain circumstances, they can undergo immune rejection. Ocular tumor rejection can follow one of two pathways. One pathway is CD4(+) T cell-dependent and culminates in ischemic necrosis of the tumor and phthisis (atrophy) of the eye. A second pathway is also CD4(+) T cell-dependent but does not inflict collateral injury to ocular tissues, and the eye is preserved. We isolated two clones of a murine tumor, Ad5E1 that undergo profoundly different forms of immune rejection in the eye. Clone 2.1 tumors undergo an ischemic necrotizing form of rejection that requires IFN-γ, T cells, and ocular macrophages and culminates in destruction of the eye. By contrast, the second clone of Ad5E1, clone 4, undergoes rejection that also requires T cells and ocular macrophages, but leaves the eye in pristine condition (nonphthisical rejection). Here, we demonstrate that nonphthisical tumor rejection of clone 4 tumors is IFN-γ-independent but requires an ocular macrophage population that contains M1 and M2 macrophages. Clone 4 tumor-bearing eyes displayed ten- and 15-fold increases in M2- and M1-associated markers Arg1 and NO2, respectively. This is in sharp contrast to previous results with clone 2.1 tumor rejection, in which M2 markers were undetectable, and the eye was destroyed. These results suggest that the presence of M2 macrophages tempers the immune rejection of intraocular tumors and promotes immune effectors that inflict minimal injury to innocent bystander cells and thereby preserve the integrity and function of the eye.

IL-17-dependent, IFN-gamma-independent tumor rejection is mediated by cytotoxic T lymphocytes and occurs at extraocular sites, but is excluded from the eye.

Although intraocular tumors reside in an immune-privileged site where immune responses are suppressed, some tumors are rejected. An example of this is the rejection of intraocular adenovirus-induced (adenovirus type 5 early region 1 [Ad5E1]) tumors in C57BL/6 mice. We previously identified an Ad5E1 tumor clone in which the rejection is IFN-γ dependent and culminates in the destruction of both the tumor and the eye. Although Ad5E1 tumors are not rejected when transplanted into the eyes of IFN-γ KO mice, they are rejected after s.c. transplantation. Thus, outside of the eye Ad5E1 tumors elicit a form of tumor immunity that is IFN-γ independent. In this article, we demonstrate that IFN-γ-independent s.c. rejection requires both CD4(+) and CD8(+) T cells. Furthermore, s.c. tumor rejection requires IL-17, which is produced by IFN-γ-deficient CD4(+) T cells in response to tumor Ags (TAs). Splenocytes from CD4-depleted IFN-γ KO mice produce significantly less IL-17 compared with splenocytes from isotype-treated IFN-γ KO animals in response to TAs. Furthermore, depletion of IL-17 decreases CTL activity against Ad5E1 tumor cells. In this model we propose that, in the absence of IFN-γ, CD4(+) T cells produce IL-17 in response to TAs, which increases CTL activity that mediates tumor rejection; however, this does not occur in the eye. IL-6 production within the eye is severely reduced, which is consistent with the failure to induce Th17 cells within the intraocular tumors. In contrast, the s.c. environment is replete with IL-6 and supports the induction of Th17 cells. Therefore, IFN-γ-independent tumor rejection is excluded from the eye and may represent a newly recognized form of ocular immune privilege.

Abrogating TNF-α expression prevents bystander destruction of normal tissues during iNOS-mediated elimination of intraocular tumors.

Although intraocular tumors reside in an immune privileged site, some tumors are rejected nonetheless. For example, intraocular adenovirus-induced (Ad5E1; adenovirus type 5 early region 1) tumors are rejected in syngeneic C57BL/6 mice by one of two pathways. One pathway leads to extensive necrosis of innocent bystander cells and culminates in destruction of the eye, a condition called phthisis. The second pathway is characterized by piecemeal tumor cell death that rids the eye of the tumor while preserving the architecture and function of the eye. To study the mechanisms of phthisical tumor rejection, we isolated a cell clone-designated clone 2.1 that consistently undergoes rejection in a phthisical manner. CD4(+) T cells and macrophages were required for phthisical rejection of intraocular clone 2.1 tumors and M1 macrophages were involved in mediating tumor rejection. In vitro and in vivo inhibition of iNOS (inducible nitric oxide synthase) abolished macrophage-mediated killing of tumor cells and rejection of intraocular tumors. A role for M1 macrophages was further supported by investigations showing that intraocular tumors grew progressively in IFN-γ KO (knockout) mice. Studies in mice deficient in TNF-α, TNF receptor-1, or TNF receptor-2 revealed that although TNF-α was not needed for tumor rejection, it was required for the development of necrotizing inflammation and phthisis of tumor-bearing eyes. Together, our findings suggest new strategies to successfully eliminate ocular tumors while preserving the integrity of the eye.