Apoptosis in patients with posterior uveitis

Sympathetic Ophthalmia: Where Do We Currently Stand on Treatment Strategies?

Sympathetic ophthalmia is a rare bilateral diffuse granulomatous panuveitis that usually results from surgical or penetrating trauma to one eye. The symptoms range from impaired near vision to pain, photophobia, and loss of visual acuity. Anterior segment manifestations include bilateral acute uveitis with mutton-fat keratic precipitates and posterior segment findings include vitritis, multifocal neurosensory retinal detachment, choroiditis, optic nerve edema, and Dalen-Fuchs nodules. The diagnosis is clinical. Ancillary investigations include fundus fluorescein angiography, indocyanine green angiography, optical coherence tomography (OCT), ultrasound B scan, and autofluorescence imaging. The management options include corticosteroids (topical and systemic) as the first line along with immunomodulatory therapy started at the presentation of the disease. Recent advances include imaging with OCT-angiography, enhanced depth imaging-OCT (EDI-OCT, choroidal vascular index/CVI), targeting IL-23/IL-17 pathway, and use of biologics for the management of this rare entity. Recent advances in early diagnosis and prompt treatment has led to improved final visual outcomes in both the sympathizing and exciting eye. This review is aimed at giving a comprehensive overview of sympathetic ophthalmia along with a special emphasis on current treatment strategies and recent advances.

Interleukins and cytokine biomarkers in uveitis

Interleukins and cytokines are involved in the pathogenesis of uveitis of heterogeneous origin. Understanding the basics of the ocular immune privilege is a fulcrum to discern their specific role in diverse uveitis to potentially translate as therapeutic targets. This review attempts to cover these elements in uveitis of infectious, noninfectious and masquerade origin. Insights of the molecular targets in novel therapy along with the vision of future research are intriguing.

Fuchs endothelial corneal dystrophy: The vicious cycle of Fuchs pathogenesis

Fuchs endothelial corneal dystrophy (FECD) is the most common primary corneal endothelial dystrophy and the leading indication for corneal transplantation worldwide. FECD is characterized by the progressive decline of corneal endothelial cells (CECs) and the formation of extracellular matrix (ECM) excrescences in Descemet's membrane (DM), called guttae, that lead to corneal edema and loss of vision. FECD typically manifests in the fifth decades of life and has a greater incidence in women. FECD is a complex and heterogeneous genetic disease where interaction between genetic and environmental factors results in cellular apoptosis and aberrant ECM deposition. In this review, we will discuss a complex interplay of genetic, epigenetic, and exogenous factors in inciting oxidative stress, auto(mito)phagy, unfolded protein response, and mitochondrial dysfunction during CEC degeneration. Specifically, we explore the factors that influence cellular fate to undergo apoptosis, senescence, and endothelial-to-mesenchymal transition. These findings will highlight the importance of abnormal CEC-DM interactions in triggering the vicious cycle of FECD pathogenesis. We will also review clinical characteristics, diagnostic tools, and current medical and surgical management options for FECD patients. These new paradigms in FECD pathogenesis present an opportunity to develop novel therapeutics for the treatment of FECD.

Ocular Inflammation and Choroidal Thickness after Pars Plana Vitrectomy in Chronic Recurrent Stage of Vogt-Koyanagi-Harada Disease

Purpose: To evaluate subfoveal choroidal thickness (SCT) changes and ocular inflammation after pars plana vitrectomy (PPV) in Vogt-Koyanagi-Harada (VKH) disease.Methods: We analyzed best-corrected visual acuity (BCVA), ocular inflammation, complications, and SCT in 17 eyes of 14 patients with VKH disease who underwent PPV and had ≥12-month follow-up. Main surgical indications included vitreous opacity, epiretinal membrane, and macular hole.Results: Mean BCVA showed significant improvement at all time-points after PPV. Mean SCT significantly increased up until 3 months after PPV (P = .001), but returned to baseline at 12 months and was lower than baseline at the final visit (P = .025). Mean acute uveitis relapse rate decreased after PPV (P = .008). SCT increase was greater in the nine eyes with postoperative uveitis recurrence than in those without (P = .043).Conclusion: Vision improved after PPV in patients with VKH disease. SCT increase in the early postoperative period was associated with uveitis recurrence during follow-up, suggesting that vitrectomy may induce choroiditis after PPV in VKH.

HMGB1 release triggered by the interaction of live retinal cells and uveitogenic T cells is Fas/FasL activation-dependent

Background

It is not clear how invading autoreactive T cells initiate the pathogenic process inside the diseased organ in T cell-mediated organ-specific autoimmune disease. In experimental autoimmune uveitis (EAU) induced by adoptive transfer of interphotoreceptor retinoid-binding protein (IRBP)-specific T cells in mice, we have previously reported that intraocular inflammation was initiated by infiltrating IRBP-specific T cells that directly interacted with retinal cells and resulted in the active release of high mobility group box 1 (HMGB1), an important member of damage associate molecular patterns (DAMPs). Furthermore, blockade of HMGB1 in our murine model reduced intraocular inflammation via suppression of IRBP-specific T cell functions. These results have demonstrated that HMGB1 is an early and critical mediator of induction of intraocular inflammation. The present study identified the cell surface molecule that triggers HMGB1 secretion.

Methods

Retinal explants from Fas-deficient (Fas^lpr) and wild-type (Wt) C57BL/6 (B6) mice were cultured with activated IRBP 1–20 peptide-specific T cells or with a Fas-activating antibody (Jo2), and then the level of HMGB1 in culture supernatants were detected by ELISA. In addition, released HMGB1 was examined in the eye of Fas^lpr and Wt mice after IRBP-specific T cell transfer. Uveitis was evaluated in the IRBP-specific T cell transferred Fas^lpr mice after recombinant HMGB1 was restored within the eye and in the IRBP-specific T cell transferred Wt mice after they were treated with a Fas antagonist (Met12).

Results

In contrast to retinal explants from Wt mice, those from Fas^lpr mice did not release HMGB1 after exposure to IRBP-specific T cells or to Jo2. The release of HMGB1 by Wt retinal explants was suppressed by Met 12. Moreover, after IRBP-specific T cell injection, Fas^lpr mice did not release HMGB1 in the eye or develop EAU, but intravitreous injection of HMGB1 resulted in intraocular inflammation. Finally, tEAU in Wt mice was attenuated by local treatment with Met 12. Unlike HMGB1, Fas-induced IL-1 and IL-18 were not essential for tEAU induction.

Conclusion

Our results show that interaction of retinal cells with infiltrating uveitogenic T cells leads to rapid release of HMGB1 via the Fas/FasL inflammatory signaling pathway.

Macular atrophy in birdshot retinochoroidopathy: an optical coherence tomography and multifocal electroretinography analysis

PURPOSE

The purpose of this study was to evaluate macular atrophy by frequency-domain optical coherence tomography (OCT) in patients with birdshot retinochoroidopathy and to compare the resulting thickness measures with visual acuity and multifocal electroretinography (mfERG).

METHODS

Measures were obtained from 14 eyes of 7 patients with birdshot retinochoroidopathy and 23 normal eyes. Optical coherence tomography-3 measures of macular thinning were related to visual acuity, mfERG response density, and time since diagnosis. Horizontal midline frequency-domain OCT scans identified which layers of the retina were primarily responsible for macular thinning.

RESULTS

All eyes with a history of birdshot retinochoroidopathy for >10 years had abnormal mfERG response densities. Compared with those without anatomic thinning (n = 8), eyes with anatomic thinning (n = 6) had significantly lower visual acuity (P = 0.0006), foveal response density (P = 0.006), and overall mfERG response density (P = 0.009). Segmentation of retinal layers on frequency-domain OCT scans showed that anatomic thinning was as a result of reduction in the receptor 1 layer (REC+), the thickness of the segment extending from the proximal border of the outer plexiform layer to the Bruch membrane-choroid interface.

CONCLUSION

Macular atrophy, as reflected in OCT evidence of macular thinning and mfERG evidence of macular function, occurs in patients with long-standing birdshot retinochoroidopathy. Measures of retinal layer thicknesses by frequency-domain OCT suggest that the atrophy occurs primarily in the outer retina.

The potential of newer immunomodulating drugs in the treatment of uveitis: a review

Uveitis, or intraocular inflammation, remains an ongoing challenge to ophthalmologists and patients alike. In most patients, uveitis is limited to the anterior ocular structures and is readily managed with topical steroids. The inflammatory process can extend behind the lens to involve the pars plana, the vitreous cavity, the choroid and the retina. These intermediate and posterior uveitides are relatively rare but contribute disproportionately to visual morbidity and present serious diagnostic and therapeutic difficulties. Systemic steroids constitute the first line of treatment for most sight-threatening uveitides. Their long term use is limited by universal and debilitating adverse effects. Second-line, steroid-sparing agents allow a reduction in steroid dosage. Cyclosporin and azathioprine are the main steroid-sparing agents currently in use. However, these compounds are limited by a narrow therapeutic window and significant adverse effects. This paper offers a brief discussion of some of the immune mechanisms involved in the pathogenesis of uveitis and reviews categories of investigational compounds. Inhibitors of T cell function: tacrolimus (previously FK506), licensed for use in liver transplantation, and sirolimus (rapamycin) are macrolide antibiotics. Sirolimus is a functional cytokine antagonist and in vitro studies suggest it could be up to 100 times more potent than cyclosporin. Drug synergy between sirolimus and cyclosporin has been demonstrated, resulting in immunosuppression at lower drug doses and with fewer adverse effects. Nucleotide synthesis inhibitors: mycophenolate mofetil (MMF) and leflunomide. Human lymphocytes are only able to synthesise nucleic acids de novo. Having no alternative or 'salvage' pathway, they are exquisitely sensitive to interference with the de novo nucleotide synthesis enzymatic pathway. MMF is a purine synthesis inhibitor. Compared to other purine inhibitors, early data suggest that MMF is more efficacious and less toxic than azathioprine. Leflunomide is an inhibitor of pyrimidine synthesis. Monoclonal surface receptor antibodies and immunoadhesins: the IL-2 receptor is essential for clonal expansion of activated T cells; this has led to the development of anti-IL-2 receptor antibodies. Daclizumab is a genetically engineered humanised IgG1 monoclonal antibody. In conjunction with cyclosporin, it significantly reduces renal allograft rejection rates and is also showing promise in the treatment of T cell mediated autoimmune disorders. The mechanism of action of monoclonal antibodies to other pro-inflammatory cytokines such as TNFalpha and IL-12 and data from animal and human uveitis trials are also discussed. Finally, new avenues of research in immunopharmaco-modulation are mentioned.

Vitrectomy for Persistent Panuveitis in Behçet's Disease

PURPOSE

To determine whether vitrectomy is safe and effective for the management of vitreoretinal complications in Behçet's patients with persistent panuveitis.

METHODS

Patients who had undergone therapeutic vitrectomy for Behçet's panuveitis were reviewed retrospectively. Those patients who had shown persistent uveitis despite maximum medical therapy were included. Surgical outcomes were measured by an improvement in vision of 0.3 logarithm of minimum angle of resolution, acute relapse rates, and postoperative complications.

RESULTS

Twenty-one patients with a mean postoperative follow-up of 30 months were identified. For almost all patients visual acuity and inflammatory control were significantly improved after vitrectomy. However, patients with optic disc neovascularization (NVD) showed no improvement in their vision or inflammatory control. The postoperative rise of intraocular pressure was frequently associated with intravitreal triamcinolone acetonide injections.

CONCLUSIONS

Our study suggests that vitrectomy may be both safe and effective for the management of vitreoretinal complications in Behçet's patients with persistent uveitis. Patients with NVD, however, may have poor outcomes.

The immediate early 2 protein of human cytomegalovirus (HCMV) mediates the apoptotic control in HCMV retinitis through up-regulation of the cellular FLICE-inhibitory protein expression

Human CMV (HCMV) is a widespread human pathogen that causes blindness by inducing retinitis in AIDS patients. Previously, we showed that viral immediate early 2 (IE2) protein may allow HCMV to evade the immune control by killing the Fas receptor-positive T lymphocytes attracted to the infected retina with increased secretion of Fas ligand (FasL). In this study, we further demonstrate that the secreted FasL also kills uninfected Fas-rich bystander retinal cells and that IE2 simultaneously protects the infected cells from undergoing apoptotic death, in part, by activating the expression of cellular FLIP (c-FLIP), an antiapoptotic molecule that blocks the direct downstream executer caspase 8 of the FasL/Fas pathway. c-FLIP induction requires the N-terminal 98 residues of IE2 and the c-FLIP promoter region spanning nucleotides -978 to -696. In vivo association of IE2 to this region, IE2-specific c-FLIP activation, and decrease of FasL-up-regulated activities of caspases 8 and 3 were all demonstrated in HCMV-infected human retinal cells. Moreover, c-FLIP up-regulation by IE2 appeared to involve PI3K and might also render cells resistant to TRAIL-mediated death. Finally, enhanced c-FLIP signals were immunohistochemically detected in IE-positive cells in the HCMV-infected lesions of the human retina. Taken together, these data demonstrate specific activation of c-FLIP by HCMV IE2 and indicate a novel role for c-FLIP in the pathogenesis of HCMV retinitis.

Inhibition of T cell apoptosis in the aqueous humor of patients with uveitis by IL-6/soluble IL-6 receptor trans-signaling

A fundamental mechanism of immune privilege in the eye is the induction of T lymphocyte apoptosis. Intraocular inflammation in uveitis implies compromise of immune privilege. This study sought to determine whether apoptosis of T cells is actively inhibited in patients with uveitis and by what pathways this may occur. Apoptotic lymphocytes were found to be absent from aqueous humor (AqH) of virtually all patients with recent-onset uveitis. However, T cells removed from the eye were highly susceptible to both spontaneous and Fas ligand-induced apoptosis in vitro. AqH from patients with uveitis had no modulatory effect on Fas ligand-induced apoptosis, but strongly suppressed survival factor deprivation-induced apoptosis. In contrast, noninflammatory AqH from patients undergoing cataract surgery had no modulatory effects on apoptosis at all. These data suggest that triggering of the Fas pathway is diminished in uveitis, and also that homeostatic resolution through survival factor deprivation-induced apoptosis is inhibited by factors present in AqH. The most widely recognized pathways, common gamma-chain cytokines and type I IFNs, did not contribute to AqH-mediated T cell survival. High levels of both IL-6 and soluble IL-6R were found in AqH. IL-6 alone did not induce T cell survival, because IL-6R expression on T cells in AqH was too low to facilitate signaling. However, combinations of IL-6 and soluble IL-6R were highly effective inhibitors of T cell apoptosis, suggesting that the trans-signaling pathway is likely to be a key mediator of T cell apoptosis inhibition mediated by uveitis AqH.

Introduction to apoptosis in ophthalmology

Apoptosis represents a mode of cellular death genetically programmed to maintain homeostasis of tissues. In specific pathologic circumstances, the death program may be activated by various environmental factors such as exposure to toxic substances or bacteria or deprivation of nutrients. From this point of view, apoptosis is considered the final event in several pathologies. In ophthalmology, experimental evidence has confirmed that apoptosis is a type of cellular death involved in various pathologic processes including glaucoma, retinitis pigmentosa, ischemic retinopathy, corneal reparative processes, cataract, and retinoblastoma. The aim of this article is to review the most recent results published in this field and to describe some of the molecular mechanisms responsible for the activation of the apoptotic program in some important ocular disorders. The understanding of such mechanisms could outline new therapeutic strategies for the prevention of cellular death in ophthalmology.

Vitreous surgery in the management of chronic endogenous posterior uveitis

OBJECTIVES

There is evidence that pars plana vitrectomy (PPV) has a beneficial effect on the clinical course of chronic endogenous posterior uveitis (EPU) possibly by physically removing any resident inflammatory cells with the vitreous. We assessed the anatomical and therapeutic effects of PPV performed on patients with chronic EPU for any indication.

PATIENTS AND METHODS

Retrospective review of 41 eyes of 38 consecutive patients with EPU who underwent a PPV for any reason, over a 5-year period. The mean age of the patients was 36.2 years, 46% of the eyes had intermediate uveitis, 32% panuveitis, and 22% posterior uveitis. The visual acuity, disease activity, and the requirement for medications to control it were recorded for 12 months pre- and postoperatively.

RESULTS

Overall, 61% of the eyes gained more than 2 Snellen lines (P<0.001) and the incidence of cystoid macular oedema (CMO) significantly reduced from 44 to 20% (P<0.05). Postoperatively, there was a significant decrease in the recurrence rate of intermediate uveitis, posterior uveitis, and panuveitis (P<0.001). The use of systemic and local depot immunosuppressive agents did not change over the study period, although the use of topical agents increased (P<0.05).

CONCLUSION

PPV appears to have a beneficial effect on the clinical course of EPU in selected cases. This may be mediated by the physical clearance of inflammatory debris, the anti-inflammatory effect of replacing vitreous by aqueous humour, by a reduction of CMO and/or the anatomical correction of sight-threatening retinal pathology.

Birdshot retinochoroiditis: long term follow-up of a chronically progressive disease

PURPOSE

To determine the long-term course of birdshot retinochoroiditis by reviewing patient records from The University of Iowa Hospitals and Clinics.

DESIGN

A descriptive case series.

METHODS

We conducted a retrospective review of 19 patients seen at The University of Iowa for birdshot retinochoroiditis. Inclusion criteria were set before review. Goldmann perimetry isopters were converted to an area measurement in steradians and the I2e and I4e isopters were evaluated at each time point. The visual acuity, electroretinography (ERG), and visual field findings were compared to the clinical appearance of the fundus.

RESULTS

Follow-up ranged from one visit to 220 months. Of the 14 patients who were tested, all were HLA-A29-positive. Seven patients were followed for >or=60 months. Eleven patients were followed for >or=30 months. The initial visual acuity was 20/50 or better in 36 of 38 eyes and 20/60 and 20/80 in the remaining two. Visual acuity was worse than 20/50 in three of 22 eyes followed for more than 30 months. Visual field data demonstrated progressive loss of area for either the I4e or I2e isopters in six of seven patients who were followed for >or=60 months. Multiple ERGs were performed over time on eight of 19 patients; seven of eight patients demonstrated progressive loss of electrophysiologic indices.

CONCLUSION

Retinal function in birdshot retinochoroiditis deteriorated progressively over a period of years despite stable visual acuity. Late in the course of disease, visual acuity may be lost due to chorioretinal atrophy in the posterior pole. Visual acuity alone is not an adequate parameter with which to monitor disease activity and may falsely suggest that a patient is stable or doing well. Intermittent treatment of the inflammatory exacerbations did not prevent progressive visual loss. Other treatment strategies such as prolonged corticosteroid or immunosuppressive treatment should be investigated for patients with birdshot retinochoroiditis.

Immunopathology of the noninfectious posterior and intermediate uveitides

The posterior and intermediate uveitides share an underlying immune etiology; however, they can be clinically and immunopathologically distinguished. Although the initiating stimuli for posterior and intermediate uveities are not known, it is believed that an exogenous agent (such as a bacterium or a virus) or an endogenous molecule may induce disease. In either case, T-helper lymphocytes in conjunction with human leukocyte antigens are likely to be involved. This review examines the epidemiology, histology, immunopathology, and theories of pathogenesis of several posterior and intermediate uveitides, including sympathetic ophthalmia, Vogt-Koyanagi-Harada syndrome, Behçet's disease, sarcoidosis, intermediate uveitis, white dot syndromes, and birdshot retinochoroidopathy.

Fas and Fas ligand expressed on cells of the immune system, not on the target tissue, control induction of experimental autoimmune uveitis

The Fas-Fas ligand (FasL) interaction is important for maintaining lymphocyte homeostasis by signaling for activation-induced cell death. Mice homozygous for the lpr or gld mutations do not express functional Fas or FasL, respectively, and spontaneously develop progressive autoimmune symptoms. Recent studies implicated expression of FasL on immunologically privileged tissues in protection from immune-mediated damage. Conversely, tissue expression of Fas may facilitate damage. We evaluated the susceptibility of lpr and gld mice to induction of experimental autoimmune uveitis (EAU), a T cell-mediated autoimmune disease induced with retinal Ags, which targets the neural retina. gld as well as lpr mice immunized with a retinal Ag developed disease of lower incidence and severity than wild-type controls. Delayed hypersensitivity responses were not significantly different among immunized gld, lpr, or wild-type mice, although in vitro Ag-specific lymphocyte responses of the mutant mice were lower. To evaluate whether the diminished ability of gld and lpr mice to develop EAU was due to a defect at the level of the tissue or the immune system, radiation bone marrow chimeras constructed between wild-type and mutant mice were immunized to induce EAU. Mutant recipients of wild-type bone marrow, but not wild-type recipients of mutant bone marrow, developed normal disease scores. These results indicate that normal expression of Fas and of FasL on cells of the immune system is important for EAU expression. Unexpectedly, neither lack of Fas nor lack of FasL on the ocular tissues affected expression of EAU.

Apoptosis is a prominent feature of acute anterior uveitis in the Fischer 344 rat

AIMS

To examine the hypothesis that apoptosis of infiltrating cells contributes to spontaneous resolution of uveitis in clinically relevant rodent models.

METHODS

Experimental melanin induced uveitis (EMIU) was induced in Fischer 344 rats by immunisation with 250 microg bovine ocular melanin. Endotoxin induced uveitis (EIU) was induced by injection of 200 microg Escherichia coli lipopolysaccharide. Formalin fixed, paraffin embedded ocular cross sections were stained by terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate biotin nick end labelling (TUNEL) to identify apoptotic cells. Indirect immunoperoxidase staining of paraformaldehyde lysine periodate fixed tissue cross sections was used to demonstrate expression of inducible nitric oxide synthase (iNOS).

RESULTS

TUNEL positive mononuclear cells were observed in the anterior uvea during both EMIU and EIU at all selected time points. However, whereas the majority of mononuclear cells appeared apoptotic from the outset of disease, neutrophils were notably TUNEL negative at all time points examined. Many infiltrating neutrophils expressed iNOS.

CONCLUSION

Apoptosis occurs early in the course of rat EMIU and EIU, and may contribute to resolution of these diseases. In general, infiltrating mononuclear cells die rapidly, while neutrophils survive, producing inducible nitric oxide synthase which may contribute to disease pathogenesis.

Apoptosis of CD4+ T cells occurs in experimental autoimmune anterior uveitis (EAAU)

To investigate the spontaneous turning off mechanism of endogenous uveitis, EAAU was induced in Lewis rats. Immunohistochemical and terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) stains revealed that CD4+ T cells were predominant in the uveal tissue of EAAU and that the apoptosis of these cells had occurred and progressed throughout the inflammatory period in EAAU eyes. The immunohistochemistry and in situ hybridization for Fas ligand (FasL) expression showed that the expression of Fas ligand was increased in the EAAU eyes compared with control eyes. These results suggest that the apoptosis of CD4+ T cells may play a key role in the spontaneous turning off mechanism of intra-ocular inflammation and that the induction of apoptosis may be mediated by the Fas-FasL system in EAAU.

Cytokines and apoptotic molecules in experimental melanin-protein induced uveitis (EMIU) and experimental autoimmune uveoretinitis (EAU)

The cytokine profile and occurrence of apoptosis during experimental melanin-protein induced uveitis (EMIU) were investigated and compared with that of experimental autoimmune uveoretinitis (EAU). EMIU or EAU was induced in Lewis rats. Eyes were collected at different time points after immunization. Cytokine mRNA expression was identified in the inflammatory cells in the uvea of EMIU rats; IL-2, IFN-gamma and IL-12 increased at the peak of the inflammation, and then tapered off as inflammation subsided. IL-4 and IL-10 increased at the peak of ocular inflammation, and persisted with inflammation resolved. Fas and FasL were expressed consistently in ocular resident cells of EMIU, but were elevated in EAU. In EAU, Bcl-2 expression showed a sharp peak in inflammatory cells but not in the resident cells. In EMIU, high levels of Bcl-2 were present and persisted in both ocular resident and inflammatory cells. Expression of Bax was relatively stable in both EAU and EMIU. Cellular DNA fragmentation was detected in the retinal glial cells of EAU and some inflammatory cells of EMIU. In EMIU, the dynamics of Th1 cytokines were consistent with the ocular inflammation, whereas persistent expression of Th2 cytokines was consistent with their known regulatory role. The continuous high expression of Bcl-2 and the high ratio of Bcl-2 to Bax in the eyes of EMIU may possibly contribute to prevention of ocular tissue damage, and of inflammatory cells from undergoing apoptosis, thus resulting in chronic recurrent inflammation.

Inhibition of experimental melanin protein-induced uveitis (EMIU) by targeting nitric oxide via phosphatidylcholine-specific phospholipase C

Experimental melanin protein-induced uveitis (EMIU) is an autoimmune uveitis induced by immunization with uveal melanin protein. Fas and FasL enhancement is reported in rats with EMIU. Tricyclodecan-9-yl-xanthogenate (D609), a specific inhibitor of phosphatidylcholine-specific phospholipase C, inhibits inducible nitric oxide synthase (iNOS) induction. In two independent experiments, 35 Lewis rats with EMIU received either D609 or PBS daily. The eyes and draining lymph nodes were collected for histology, analyses of nitrite, peroxide, and superoxide dismutase, Fas and FasL immunochemistry, in situ hybridization for iNOS mRNA and in situ apoptosis detection at the peak of the disease. Both experiments showed significant inhibition of EMIU by D609. Decreases in nitrite and peroxide, increase of superoxide dismutase and lower expressions of iNOS mRNA were found in D609-treated, as compared to PBS-treated eyes. There was mild enhancement of Fas and FasL in the eyes and lymph nodes of D609-injected animals. DNA fragmentation was increased in the lymph nodes of D609-treated rats. We conclude that iNOS activation is responsible for NO production in eyes with EMIU. The suppressive effect of D609 on EMIU may result from scavenging NO and activating apoptosis previously inhibited by NO along with other anti-inflammatory effects.

Fas ligand (CD95 ligand) controls angiogenesis beneath the retina

A principal cause of blindness is subretinal neovascularization associated with age-related macular degeneration. Excised neovascular membranes from patients with age-related macular degeneration demonstrated a pattern of Fas+ new vessels in the center of the vascular complex, surrounded by FasL+ retinal pigment epithelial cells. In a murine model, Fas (CD95)-deficient (Ipr) and FasL-defective (gld) mice had a significantly increased incidence of neovascularization compared with normal mice. Furthermore, in gld mice there is massive subretinal neovascularization with uncontrolled growth of vessels. We found that cultured choroidal endothelial cells were induced to undergo apoptosis by retinal pigment epithelial cells through a Fas-FasL interaction. In addition, antibody against Fas prevented vascular tube formation of choroidal endothelial cells derived from the eye in a three-dimensional in vitro assay. Thus, FasL expressed on retinal pigment epithelial cells may control the growth and development of new subretinal vessels that can damage vision.

Fas-FasL interaction involved in pathogenesis of ocular toxoplasmosis in mice

Ocular toxoplasmosis is a potentially blinding intraocular inflammation. The intent of this study was to investigate the role of Fas-FasL interaction in a murine model of acquired ocular toxoplasmosis induced by intracameral inoculation of Toxoplasma gondii. Intraocular inflammation, Fas and FasL expression on lymphocytes and on ocular tissues, the occurrence of apoptosis, and the frequency of CD8(+) and CD4(+) T cells in the infected eyes were analyzed in C57BL/6 (B6) mice. Susceptibility to parasite-induced intraocular inflammation was observed in Fas-deficient (B6-lpr) and FasL-deficient (B6-gld) mice. Inoculation of 5,000 T. gondii tachyzoites induced significant intraocular inflammation associated with increase of Fas and FasL expression in the inoculated eyes of wild-type B6 mice. Flow cytometry demonstrated a significant increase of Fas and FasL expression on the splenocytes from naive mice incubated in vitro with the parasite and on the splenocytes harvested from the infected mice at day 8 after parasite inoculation. Apoptosis of inflammatory cells and cells in ocular tissues was seen, and a greater frequency of CD8(+) than CD4(+) T cells was observed in the infected eyes. The intensity of intraocular inflammation was greater in B6-lpr and B6-gld mice than in wild-type B6 mice (P < 0.05). The results suggest that Fas-FasL interaction associated with apoptosis is involved in the pathogenesis of acquired ocular toxoplasmosis in mice.