Neutralizing TNF-alpha activity modulates T-cell phenotype and function in experimental autoimmune uveoretinitis

Cytokines and chemokines in uveitis: is there a correlation with clinical phenotype?

Uveitis is a general term for intraocular inflammation and includes a large number of clinical phenotypes. As a group of disorders, it is responsible for 10% of all registered blind patients under the age of 65 years. Immune-mediated uveitis may be associated with a systemic disease or may be localized to the eye. The pro-inflammatory cytokines interleukin (IL)-1beta, IL-2, IL-6, interferon-gamma and tumor necrosis factor-alpha have all been detected within the ocular fluids or tissues in the inflamed eye together with others, such as IL-4, IL-5, IL-10 and transforming growth factor-beta. The chemokines IL-8, monocyte chemoattractant protein-1, macrophage inflammatory protein (MIP)-1alpha, MIP-1beta and fractalkine are also thought to be involved in the associated inflammatory response. There have been a number of studies in recent years investigating cytokine profiles in different forms of uveitis with a view to determining what cytokines are important in the inflamed eye. This review attempts to present the current state of knowledge from in vitro and in vivo research on the inflammatory cytokines in intraocular inflammatory diseases.

Adalimumab therapy for childhood uveitis

Fourteen children with uveitis (9 JIA associated and 5 idiopathic) were treated with adalimumab for an average of 18.1 months. Inflammation decreased in 21/26 eyes (80.8%), 4 eyes remained stable (15.4%), and 1 worsened (3.8%) (P < .001; 2 tailed paired Wilcoxon rank sum test). No significant adverse events occurred.

Favorable response to high-dose infliximab for refractory childhood uveitis

OBJECTIVE

Uveitis in children most commonly is associated with juvenile idiopathic arthritis. In addition to topical glucocorticoids, treatment may include systemic immunosuppressive agents. Tumor necrosis factor alpha (TNF-alpha) has been implicated in the pathogenesis of uveitis; therefore, TNF-alpha blockade seems to be a reasonable therapeutic option to investigate. We report successful treatment of children with uveitis using infliximab.

STUDY DESIGN

A retrospective study of our complete experience using infliximab for the treatment of childhood uveitis was conducted.

PARTICIPANTS

Seventeen children (14 females, 3 males) with chronic uveitis were administered high-dose infliximab (10-20 mg/kg/dose).

MAIN OUTCOME MEASURES

Our main outcome measure was the ability to eliminate all signs of intraocular inflammation.

RESULTS

All 17 patients demonstrated a dramatic, rapid response, with no observed inflammation in 13 patients after the second infusion, and 4 patients requiring 3 to 7 infusions to achieve disease quiescence. Additional immunosuppressives and topical glucocorticoids were tapered when patients achieved no intraocular inflammation.

CONCLUSIONS

In this series, high-dose infliximab was a rapidly effective, well-tolerated therapeutic agent for the treatment of chronic, medically refractory, noninfectious uveitis.

A selective role for the TNF p55 receptor in autocrine signaling following IFN-gamma stimulation in experimental autoimmune uveoretinitis

IFN-gamma stimulates macrophage activation and NO production, which leads to destruction of the retina in experimental autoimmune uveoretinitis. In this study, we investigate the mechanism of disease resistance in TNF p55 receptor-deficient animals. We show that although T cell priming is relatively unaffected, macrophages lacking the TNF p55 receptor fail to produce NO following IFN-gamma stimulation because of a requirement for autocrine TNF-alpha signaling through the TNF p55 receptor. In contrast to the impaired activation of NO synthesis, MHC class II up-regulation was indistinguishable in wild-type and TNFRp55-/- mice stimulated with IFN-gamma. These defects could be overcome by stimulating macrophages with LPS. Together, these results show that selected aspects of IFN-gamma activation are controlled by autocrine secretion of TNF-alpha, but that this control is lost in the presence of signals generated by pathogen-associated molecular patterns recognizing receptors.

Leukocyte diapedesis in vivo induces transient loss of tight junction protein at the blood-retina barrier

PURPOSE

Although much is now understood about the molecular structure of tight junctions (TJs), little is known about the regulation of their function during neural inflammatory disease processes in vivo. The mechanisms by which leukocytes transmigrate the blood-retina barrier (BRB) without affecting endothelial permeability are controversial.

METHODS

Confocal immunofluorescence microscopy of ex vivo retinal wholemounts was used to study BRB integrity during leukocyte adhesion and migration during experimental autoimmune uveoretinitis (EAU). Western blot analysis was used to measure levels of TJ proteins in EAU retina and RPE and in normal retina or RPE cultured with cytokines or chemokines.

RESULTS

No evidence for discontinuity or other weakness of the endothelial or epithelial barrier at tricellular corners was observed, and maximum disruption of TJ protein expression was focused in retinal venules correlating with sites of leukocyte extravasation. Areas of maximum TJ protein loss in vivo also correlated with redistribution or loss of ensheathing astrocyte processes on venules but not adjacent capillaries or arterioles. Exposure of normal choroidal and retinal explants ex vivo to cytokines and chemokines alone did not downregulate total occludin-1 or claudin-3 TJ protein expression.

CONCLUSIONS

The data presented herein support an active role for leukocytes in TJ disruption and blood-retina barrier (BRB) breakdown during retinal inflammation and further implicate venule microenvironment as a key factor in leukocyte recruitment to retinal tissue in vivo.

Local Administration of an Adeno-associated Viral Vector Expressing IL-10 Reduces Monocyte Infiltration and Subsequent Photoreceptor Damage during Experimental Autoimmune Uveitis

Autoimmune posterior uveitis is a chronic, potentially blinding inflammatory disease of the eye. It is commonly treated with immunosuppressive drugs that have adverse long-term effects. Advances in gene transfer techniques have enabled long-term, stable transduction of retinal cells following subretinal injection with adeno-associated viral (AAV) vectors. Here we report for the first time that subretinal injection of rAAV-2 encoding murine IL-10 into the retina of C57BL/6 mice significantly decreases the median experimental autoimmune uveitis (EAU) disease severity. This protection is shown to be due to a decrease in the number and activation status of infiltrating monocytes during EAU, as determined by costimulatory molecule expression and nitrotyrosine detection. No differences within splenocyte proliferative responses or serum antibody levels were detected, emphasizing the potential of gene therapy strategies in ameliorating autoimmune responses in local microenvironments without unwanted systemic effects.

Anti-TNF-alpha therapy for sight threatening uveitis

AIM

To describe the effect of additional treatment with anti-TNF-alpha therapy in a case series of 13 patients with serious sight threatening uveitis.

METHODS

13 patients with serious sight threatening uveitis were included, of whom six had Behçet's disease, five had idiopathic posterior uveitis, one had sarcoidosis, and one birdshot retinochoroiditis. Onset and course of ocular inflammation, inflammatory signs, and visual acuity were assessed. Patients were treated with 200 mg (approximately 3 mg/kg) infliximab infusion. Repeat infusions were given based on clinical response.

RESULTS

Infliximab treatment resulted in an effective suppression of ocular inflammation in all patients. In patients with non-Behcet's disease uveitis visual acuity in six out of eight improved or was stable. In patients with Behcet's disease visual acuity in five out of six improved or was stable.

CONCLUSION

Anti-TNF-alpha treatment may be of value in the treatment of uveitis, and in patients with Behçet's disease, leading to suppression of ocular inflammation, vasculitis, and improvement of vision in the majority. Based on these results a controlled masked study is warranted.

Ocular inflammation alters swelling and membrane characteristics of rat Müller glial cells

Ocular inflammation is a common cause of retinal edema that may involve swelling of Müller glial cells. In order to investigate whether endotoxin-induced ocular inflammation in rats alters the swelling and membrane characteristics of Müller cells, lipopolysaccharide (LPS; 0.5%) was intravitreally injected. At 3 and 7 days after treatment, hypotonic challenge induced swelling of Müller cell somata that was not observed in non-treated control eyes. Müller cells of LPS-treated eyes displayed a downregulation of inward K(+) currents and upregulation of A-type K(+) currents that was associated with a decreased expression of Kir4.1 protein in retinal slices. The data suggest that ocular inflammation induces alterations of both the swelling characteristics and the K(+) channel expression of Müller cells.

TNF?-Inhibitoren in der Uveitistherapie

Tumor necrosis factor alpha (TNFalpha) is a pleiotropic cytokine that plays a pivotal role in chronic inflammatory diseases. Data from animal experiments indicate that TNFalpha is an important part of the pro-inflammatory processes in non-infectious uveitis. Neutralization of TNFalpha with TNF receptor fusion proteins or monoclonal antibodies, therefore, represents a promising strategy for the treatment of uveitis. In addition, the currently available TNFalpha inhibitors demonstrate a favourable profile of side effects compared to conventional immunosuppressive agents. Previous studies showed the immunological efficacy of TNFalpha inhibitors in the treatment of posterior uveitis. However, the available data on anterior uveitis are inconclusive with respect to the clinical efficacy of these agents.

The role of tumour necrosis factor (TNF-alpha) in experimental autoimmune uveoretinitis (EAU)

The pleiotropic cytokine tumour necrosis factor-alpha (TNF-alpha) is released from cells that include macrophages and T-cells during inflammatory responses, orchestrating the initiation of further leucocytic infiltration via adhesion molecule upregulation, dendritic cell maturation and survival, macrophage activation and driving Th1 T-cells responses within tissues. Exposure to TNF also plays a role in maintaining tissue homeostasis, particularly relating to resident cell responses of both microglia and retinal pigment epithelium. Depending on the balance between duration and dose of TNF exposure, an environment where full expression of inflammatory and autoimmune responses within tissues may occur. In experimental autoimmune uveoretinitis (EAU), increased tissue concentrations of TNF facilitate the on-going T-cell effector responses and macrophage activation. These are responsible for targeted and bystander tissue damage and can be suppressed by anti-TNF therapies, in particular, those directed at the p55 TNF receptor. The ability to suppress disease experimentally has led to the successful translation of anti-TNF therapy for treatment of uveitis in cohort studies and phase I/II trials where, additionally, altered peripheral blood CD4(+) T-cell profiles can be demonstrated following each treatment.

Systemic CD4(+) T cell phenotype and activation status in intermediate uveitis

AIM

To investigate peripheral blood lymphocyte phenotype in patients with intermediate uveitis using CD69, chemokine receptor, and cytokine expression.

METHODS

Peripheral blood lymphocytes of 18 patients with idiopathic intermediate uveitis and 6 patients with presumed sarcoid intermediate uveitis were evaluated for CD4(+) T cell expression of CD69, CCR4, CCR5, CXCR3 and the intracellular cytokines IFNgamma, TNFalpha, and interleukin (IL)-10 by flow cytometry, and for IL-2, IL-4, IL-5, IL-10, IFNgamma, and TNFalpha production following unstimulated and activated culture using cytokine bead array and compared with healthy control subjects.

RESULTS

The expression of CD69 and TNFalpha by peripheral blood CD4(+) lymphocytes of patients with idiopathic intermediate uveitis and presumed sarcoid intermediate uveitis was significantly higher than control subjects (p = 0.002 and p<0.05, respectively). The ratios of the concentrations of IL-2:IL-5 and IFNgamma:IL-5 in supernatants of activated peripheral blood lymphocyte cultures were significantly higher in patients with presumed sarcoid intermediate uveitis than control subjects.

CONCLUSIONS

This study implicates TNFalpha in the pathogenesis of intermediate uveitis, highlighting the potential role of anti-TNF treatments for this disease. Studies of Th1:Th2 cytokine ratios suggested polarisation of the immune response towards Th1 in presumed sarcoid intermediate uveitis despite clinically quiescent systemic disease.

Tumor necrosis factor alpha blockade with infliximab for refractory uveitis and scleritis

OBJECTIVE

To assess the efficacy and safety of the anti-tumor necrosis factor alpha agent infliximab in treatment-resistant uveitis and scleritis.

DESIGN

Retrospective, noncomparative interventional case series.

PARTICIPANTS

Seven patients with noninfectious ocular inflammatory disease that was refractory to alternative immunosuppression. These included one patient with idiopathic retinal vasculitis and panuveitis, one patient with intermediate uveitis, one patient with chronic juvenile anterior uveitis, three patients with scleritis, and one patient with scleritis and peripheral ulcerative keratitis. Four patients had an underlying systemic disease that was in remission in three cases.

INTERVENTION

Infusions of infliximab, 200 mg, were given at 4-week to 8-week intervals, depending on the clinical response.

MAIN OUTCOME MEASURES

Clinical response, including symptoms, visual acuity, degree of scleral vascular engorgement, corneal thinning, anterior chamber activity, and posterior segment inflammation, reduction in concomitant immunosuppression, and adverse effects.

RESULTS

The mean patient age was 47 years (range, 24-78), and four patients were female. The mean number of infliximab infusions was seven (range, 2-19), and the mean follow-up period was 12 months (range, 4-22 months). Six patients experienced a clinical improvement, with five achieving remission and significant reduction in immunosuppression. One patient showed an initial response but developed a delayed hypersensitivity response that precluded further treatment. No other adverse effects occurred.

CONCLUSIONS

Infliximab seems to be an effective and safe treatment for noninfectious uveitis and scleritis and may be indicated as rescue therapy for relapses of ocular inflammation or as maintenance therapy when conventional immunosuppression has failed. Further investigation of infliximab for treatment-resistant scleritis and uveitis is warranted.

Control of myeloid activity during retinal inflammation

Combating myeloid cell-mediated destruction of the retina during inflammation or neurodegeneration is dependent on the integrity of homeostatic mechanisms within the tissue that may suppress T cell activation and their subsequent cytokine responses, modulate infiltrating macrophage activation, and facilitate healthy tissue repair. Success is dependent on response of the resident myeloid-cell populations [microglia (MG)] to activation signals, commonly cytokines, and the control of infiltrating macrophage activation during inflammation, both of which appear highly programmed in normal and inflamed retina. The evidence that tissue CD200 constitutively provides down-regulatory signals to myeloid-derived cells via cognate CD200-CD200 receptor (R) interaction supports inherent tissue control of myeloid cell activation. In the retina, there is extensive neuronal and endothelial expression of CD200. Retinal MG in CD200 knockout mice display normal morphology but unlike the wild-type mice, are present in increased numbers and express nitric oxide synthase 2, a macrophage activation marker, inferring that loss of CD200 or absent CD200R ligation results in "classical" activation of myeloid cells. Thus, when mice lack CD200, they show increased susceptibility to and accelerated onset of tissue-specific autoimmunity.

Constitutive retinal CD200 expression regulates resident microglia and activation state of inflammatory cells during experimental autoimmune uveoretinitis

Recent evidence supports the notion that tissue OX2 (CD200) constitutively provides down-regulatory signals to myeloid-lineage cells via CD200-receptor (CD200R). Thus, mice lacking CD200 (CD200(-/-)) show increased susceptibility to and accelerated onset of tissue-specific autoimmunity. In the retina there is extensive expression of CD200 on neurons and retinal vascular endothelium. We show here that retinal microglia in CD200(-/-) mice display normal morphology, but unlike microglia from wild-type CD200(+/+) mice are present in increased numbers and most significantly, express inducible nitric oxide synthase (NOS2), a macrophage activation marker. Onset and severity of uveitogenic peptide (1-20) of interphotoreceptor retinoid-binding protein-induced experimental autoimmune uveoretinitis is accelerated in CD200(-/-) mice and although tissue destruction appears no greater than seen in CD200(+/+) mice, there is continued increased ganglion and photoreceptor cell apoptosis. Myeloid cell infiltrate was increased in CD200(-/-) mice during experimental autoimmune uveoretinitis, although NOS2 expression was not heightened. The results indicate that the CD200:CD200R axis regulates retinal microglial activation. In CD200(-/-) mice the release of suppression of tonic macrophage activation, supported by increased NOS2 expression in the CD200(-/-) steady state accelerates disease onset but without any demonstration of increased target organ/tissue destruction.

Nitric oxide mediates apoptosis through formation of peroxynitrite and Fas/Fas-ligand interactions in experimental autoimmune uveitis

Conflicting reports have led to the description of nitric oxide as a "double-edged sword" in animal models of autoimmunity. In this study we show that tissue damage within the eye during experimental autoimmune uveoretinitis correlates with peroxynitrite formation in infiltrating monocytes/macrophages within the outer retina together with extensive photoreceptor apoptosis and apoptosis of Fas(+) T cells within the retina. Inducible nitric oxide synthase (NOS2) expression was primarily restricted to infiltrating monocytes/macrophages in the outer retina and photoreceptor rod outer segments (target tissue), but despite showing evidence of lipid peroxidation, myeloid cells remained resistant to apoptosis. The protective effect of the NOS inhibitor N(G)-nitro-L-arginine methyl ester could be attributed to dramatically reduced photoreceptor apoptosis, absence of nitrotyrosine formation, and reduced NOS2 protein expression. However, inhibition of NOS by N(G)-nitro-L-arginine methyl ester was accompanied by a sparing of CD3(+) and CD2(+) T cells despite continued expression of Fas and Fas ligand, thus compromising functional inactivation of T cells in the target tissue. These data suggests that in addition to contributing to tissue damage in the retina through generation of reactive oxygen species, nitric oxide also seems to be required for activation-induced cell death and elimination of T cells in the retina.

Cytokines in immunotherapy of experimental uveitis

A better understanding of the basic mechanisms of uveitis and of the role of cytokines in experimental ocular inflammation autoimmune diseases should allow us to define new approaches for therapy. Modulation of the cytokine network by either blocking cytokine activity or administration of regulatory Th2 cytokines has shown its efficacy in several experimental autoimmune diseases including uveitis. However, cytokines present pleiotropic activities and thus may exert different effects depending on the autoimmune diseases, making interventions on their production complex. Anti-cytokine therapy or a combination of anti-cytokine drugs, antibodies, and cytokine gene therapy to synergize the therapeutical effects of other treatments appear to be of interest. Improvements in drug delivery and in biotechnology will also allow us to elaborate new and safe immunomodulatory strategies.

Tumor necrosis factor receptor p55 and p75 deficiency protects mice from developing experimental autoimmune myasthenia gravis

The precise pathogenic role of proinflammatory cytokines belonging to the tumor necrosis factor (TNF) family has not been investigated yet in antibody-mediated myasthenia gravis (MG) and experimental autoimmune myasthenia gravis (EAMG). In this study we report that TNF receptor p55(-/-) p75(-/-) mice were resistant to the development of clinical EAMG induced by acetylcholine receptor (AChR) immunizations. The resistance was associated with reduced serum levels of IgG, IgG(1), IgG(2a), and IgG(2b) anti-AChR antibody isotypes. However, IgM anti-AChR antibodies were not reduced, suggesting defective anti-AChR IgG class switching in TNF receptor p55(-/-) p75(-/-) mice. We thus demonstrate the genetic evidence for the role of TNF receptor p55 and p75 in EAMG pathogenesis, and their requirement for the generation of anti-AChR IgG antibodies.

Treatment of experimental autoimmune myasthenia gravis with recombinant human tumor necrosis factor receptor Fc protein

Lymphotoxin-alpha (TNF-beta) and TNF receptor p55 gene knockout mice are resistant to the development of antibody and complement mediated experimental autoimmune myasthenia gravis (EAMG), suggesting a possible role of TNF in mediating EAMG. Therefore, we tested the hypothesis that blocking the functional interaction of TNF with their receptors by soluble recombinant human TNFR:Fc would suppress the ongoing clinical EAMG. Recombinant human TNFR:Fc administered daily for 2 weeks to C57BL6 mice with ongoing clinical EAMG significantly improved clinical EAMG when compared with placebo-treated mice. A clinical trial of selected myasthenia gravis patients with recombinant human TNFR:Fc could be attempted.

Corticosteroid-Sparing Effect of Etanercept in Idiopathic Panuveitis Resistant to Immunosuppressive Therapy

Uveitis, an inflammatory eye disease with varying immunopathogenic mechanisms, may be associated with autoimmune disorders, may be secondary to infection, or may be idiopathic. Response to treatment of uveitis is inconsistent. In this report we describe an adult with idiopathic panuveitis who attempted to lower his oral corticosteroid dose from intolerable levels but was unable to do so because of the reappearance of symptoms. His 8-year course was managed with ocular and systemic corticosteroids, methotrexate, and cyclosporine, which allowed only partially successful control of his ocular inflammation. Complete control was not achieved until the addition of etanercept. With this case report we are the first to describe the complete response of idiopathic panuveitis to etanercept. Our success with this patient strongly supports the critical role of tumor necrosis factor in the immunopathogenesis of some cases of idiopathic panuveitis. Furthermore, etanercept offers a relatively nontoxic, safe option in cases of panuveitis that are unresponsive to traditional immunosuppressive therapy.

Differential efficacy of tumor necrosis factor inhibition in the management of inflammatory eye disease and associated rheumatic disease

OBJECTIVE

To evaluate the clinical usefulness of tumor necrosis factor (TNF) inhibitors in patients with inflammatory eye disease that is resistant to conventional immunosuppressive therapies.

METHODS

Sixteen patients (4 males and 12 females aged 7 to 78 years) who received etanercept (n = 14) or infliximab (n = 2) for either inflammatory eye disease or associated joint disease were studied retrospectively to determine the effect of these medications on their ocular inflammation.

RESULTS

Nine cases of uveitis and 7 cases of scleritis were treated. Systemic diagnoses included rheumatoid arthritis (n = 8), juvenile rheumatoid arthritis (n = 3), ankylosing spondylitis (n = 1), and psoriatic spondylarthropathy (n = 1). Three patients had uveitis without associated systemic disease. Although 12 of 12 patients with active articular inflammation (100%) experienced improvement in joint disease, only 6 of 16 with ocular inflammation (38%) experienced improvement in eye disease. Five patients developed inflammatory eye disease for the first time while taking a TNF inhibitor. No patient discontinued treatment because of adverse drug effects.

CONCLUSION

TNF inhibitors are well tolerated immunosuppressive medications that may benefit certain subgroups of patients with inflammatory eye disease, but they appear to be more effective in controlling associated inflammatory arthritis.

Interphotoreceptor retinoid binding protein peptide-induced uveitis in B10.RIII mice: characterization of disease parameters and immunomodulation

Experimental autoimmune uveoretinitis (EAU) can be induced in the B10.RIII mice following immunization with bovine interphotoreceptor retinoid binding protein (IRBP) and human IRBP(161--180)peptide. This study examines the value of the human IRBP(161--180)peptide model in the B10.RIII mice, as a suitable model of EAU in order to examine immunotherapies. Having established a reliable and consistent immunization protocol of 25 micro g peptide and no PTX, the time course of histopathology was performed, which graded both cellular and structural scores individually. Disease was typically of an acute nature, characterized by rapid onset of a massive inflammatory response, resulting in extensive damage to the rod outer segments (ROS) and neuronal layers. Treatment with potent immunosuppressive agents, CD4-specific monoclonal antibodies resulted in the inhibition of disease and a reduction in disease incidence. Treatment with p55-tumor necrosis factor receptor-Ig (p55-TNFR-Ig) fusion protein reduced structural damage to the retina despite a high level of cellular infiltration in the eye, suggesting that target organ damage in an acute model of EAU can be modulated.

Current and future trends in the use of immunosuppressive agents in patients with uveitis

Therapeutic trials for uveitis are seldom performed because of the relative rarity of the disease and its heterogeneity. Promising new approaches to therapy include cytokine or cytokine receptor inhibition; cytokine addition (alpha-interferon or interleukin-10); novel anti-metabolites; combination therapies; intravenous immunoglobulin; intravitreally inserted corticosteroid implants; and oral tolerance. Additional modalities or targets that deserve further testing include T-cell subsets, adhesion molecules, accessory molecules in antigen presentation, novel inflammatory mediators, inducers of apoptosis, photodynamic therapy, and neuroprotective agents.

Local bioactive tumour necrosis factor (TNF) in corneal allotransplantation

The aim of this study was to examine the kinetic profile of bioactive TNF levels in aqueous humour of rabbit eyes undergoing corneal allograft rejection and to investigate the effect of locally blocking TNF activity after corneal transplantation. In a rabbit corneal transplantation, endothelial allograft rejection was identified and correlated with increase in central graft thickness. Samples of aqueous humour obtained on alternate days following transplantation were tested for TNF mRNA and bioactive TNF protein. To investigate the effect of locally blocking TNF activity in allograft recipients, the fusion protein TNFR-Ig was administered by injections into the anterior chamber after transplantation. Pulsatile increases in levels of this cytokine were found in 14 of 15 allograft recipients. Peaks of TNF bioactivity preceded by varying intervals the observed onset of rejection in allograft recipients. TNF levels were not elevated in aqueous humour from corneal autograft recipient controls or in serum of allografted animals. mRNA levels were elevated before onset of and during clinically observed allograft rejection. In three of seven animals receiving TNFR-Ig injections on alternate days from day 8 to day 16 post-transplant, clear prolongation of corneal allograft survival was demonstrated. Bioactive TNF is present in aqueous humour following rabbit corneal allotransplantation. Rather than correlating directly with endothelial rejection onset, pulsatile peak levels of TNF precede and follow the observed onset of endothelial rejection. Blockade of TNF activity prolongs corneal allograft survival in some animals, indicating that this cytokine may be a suitable target in local therapy of corneal allograft rejection.

Free radical mediated photoreceptor damage in uveitis

Uveitis is a major cause of blindness, with the visual loss that occurs being due primarily to retinal tissue damage. The tissue damage is mediated mainly by phagocytic inflammatory cells, such as macrophages, by the release of various proteolytic enzymes, arachidonic acid metabolites, cytokines and free radicals. The latter are found to be potent cytotoxic agents that readily cause tissue damage by peroxidation of lipid cell membranes. Recent studies of experimental uveitis indicate that other potent oxidants are generated in uveitis by macrophages. One of these is ONOO-, which is formed from *NO and O(-)2. The macrophages generate *NO preferentially in the outer retina following iNOS expression. In these phagocytes, outer retinal proteins, especially arrestin, are found to be potent iNOS inducers. Current studies of RPE show that these cells protect the retina from ONOO- mediated damage in uveitis by releasing a novel protein called retinal pigment epithelial protective protein. This protein is found to suppress O(-)2 and *NO generation by the phagocytes, in both in vitro and in vivo uveitis models. The protective protein expression is restricted to RPE, its suppressive effect is a result of the inhibition of the phosphorylation of cytosolic proteins, p47-phox, required for the assembly of NADPH and activation of NFkappaB, which are required for generation of 0(-)2 and expression of iNOS respectively. Either pharmacologically or chemically, up-regulation of RPP generation could help in preventing retinal degeneration in uveitis or other degenerative dis

Activated polyamidoamine dendrimers, a non-viral vector for gene transfer to the corneal endothelium

We investigated the efficiency of activated polyamidoamine dendrimers, a new class of nonviral vectors, to transfect rabbit and human corneas in ex vivo culture. In addition to assessing the expression of a marker gene we have demonstrated that this approach can be used to induce the production of TNF receptor fusion protein (TNFR-Ig), a protein with therapeutic potential. Whole thickness rabbit or human corneas were transfected ex vivo with complexes consisting of dendrimers and plasmids containing lacZ or TNFR-Ig genes. Following optimisation 6-10% of the corneal endothelial cells expressed the marker gene. Expression was restricted to the endothelium and was maximal after transfection with 18:1 (w/w) activated dendrimer:plasmid DNA ratio and culture for 3 days. The supernatant of corneas transfected with TNFR-Ig plasmid contained TNFR-Ig protein which was able to inhibit TNF-mediated cytotoxicity in a bioassay. We have therefore shown that activated dendrimers are an efficient nonviral vector capable of transducing corneal endothelial cells ex vivo. They may have applications in gene-based approaches aimed at prevention of corneal allograft rejection or in treatment of other disorders of corneal endothelium.

Intranasal administration of retinal antigens induces transient T cell activation and apoptosis within drainage lymph nodes but not spleen

Mechanisms of mucosal tolerance induction, including anergy/deletion and active suppression are frequently described as mutually exclusive; dependent upon nature, dose and route of antigen administration. We have previously described induction of low-dose tolerance with administration of retinal autoantigens via the nasorespiratory tract which is antigen-specific, suppresses both cell mediated immunity and ultimately tissue destruction in experimental autoimmune uveoretinitis (EAU) and is mediated by splenic-derived regulatory cells. The present data further shows that splenocytes or fractionated splenic T cells, which secrete IL-4 and IL-10 when stimulated with retinal antigen in vitro, and not regional drainage lymph node cells transfer tolerance to naïve animals. Analysis of apparent mechanistic differences shows that during intranasal antigen administration, the proportion of CD4(+)T cells within drainage lymph nodes increases, concurrent with a burst of IFN-gamma. Following subsequent antigen challenge, T cells downregulate alphabetaTCR expression and undergo apoptosis in regional drainage lymph nodes. An increase in functional Th2 cytokine activity was noted in both Con-A and retinal antigen stimulated lymph node cultures in tolerized animals. T cells from tolerized animals secreted IL-4, whereas IL-10 was secreted predominantly by the non-T cell population present equally in control and tolerized animals. Therefore, spleen derived regulatory cells which suppress Th1 responses and T cell deletion/apoptosis in regional drainage lymph nodes are mechanisms which co-exist in tolerant rats. Th2 cytokine production after immunization appears consequential to tolerance-induced Th1 suppression.

Modulating phenotype and cytokine production of leucocytic retinal infiltrate in experimental autoimmune uveoretinitis following intranasal tolerance induction with retinal antigens

BACKGROUND/AIM

Nasal administration of retinal antigens induces systemic tolerance which results in suppression of experimental autoimmune uveoretinitis (EAU) when subsequently exposed to antigen. The aim was to establish if tolerance induction alters retinal infiltrating leucocyte phenotype and cytokine profile in tolerised animals when there is significantly reduced tissue destruction despite immunisation with retinal antigen.

METHODS

Female Lewis rats were tolerised by intranasal administration with retinal extract (RE) before immunisation with RE to induce EAU. Control animals were administered phosphate buffered saline (PBS) intranasally. Post immunisation, daily clinical responses were recorded and at the height of disease, retinas were removed and either infiltrating leucocytes isolated for flow cytometric phenotype assessment and intracellular cytokine production, or chorioretina processed for immunohistochemistry. Fellow eyes were assessed for cytokine mRNA by semiquantitative RT-PCR.

RESULTS

Flow cytometric analysis showed that before clinical onset of EAU there is no evidence of macrophage infiltration and no significant difference in circulating T cell populations within the retina. By day 14 a reduced retinal infiltrate in tolerised animals was observed and in particular a reduction in numbers of "activated" (with respect to CD4 and MHC class II expression) macrophages. Immunohistochemistry confirmed these findings and additionally minimal rod outer segment destruction was observed histologically. Cytokine analysis revealed that both IL-10 mRNA and intracellular IL-10 production was increased in tolerised eyes 7 days post immunisation. Although by day 14 post immunisation, IL-10 production was equivalent in both groups, a reduced percentage of IFN-gamma + macrophages and IFN-gamma + CD4+ T cells with increased percentage of IL-4+ CD4+ T cells were observed in tolerised animals.

CONCLUSIONS

Leucocytic infiltrate is not only reduced in number but its distinct phenotype compared with controls implies a reduced activation status of infiltrating monocyts to accompany increased IL-10 and reduced IFN-gamma production in tolerised animals. This modulation may in turn contribute towards protection against target organ destruction in EAU.