The Topical Ocular Delivery of Rapamycin to Posterior Eye Tissues and the Suppression of Retinal Inflammatory Disease

Treatment of posterior eye diseases with intravitreal injections of drugs, while effective, is invasive and associated with side effects such as retinal detachment and endophthalmitis. In this work, we have formulated a model compound, rapamycin (RAP), in nanoparticle-based eye drops and evaluated the delivery of RAP to the posterior eye tissues in a healthy rabbit. We have also studied the formulation in experimental autoimmune uveitis (EAU) mouse model with retinal inflammation. Aqueous RAP eye drops were prepared using N-palmitoyl-N-monomethyl-N,N-dimethyl-N,N,N-trimethyl-6-O-glycolchitosan (Molecular Envelope Technology - MET) containing 0.23 ± 0.001% w/v RAP with viscosity, osmolarity, and pH within the ocular comfort range, and the formulation (MET-RAP) was stable in terms of drug content at both refrigeration and room temperature for one month. The MET-RAP eye drops delivered RAP to the choroid-retina with a Cmax of 145 ± 49 ng/g (tmax = 1 hour). The topical application of the MET-RAP eye drops to the EAU mouse model resulted in significant disease suppression compared to controls, with activity similar to dexamethasone eye drops. The MET-RAP eye drops also resulted in a reduction of RORγt and an increase in both Foxp3 expression and IL-10 secretion, indicating a mechanism involving the inhibition of Th17 cells and the up-regulation of T-reg cells. The MET-RAP formulation delivers RAP to the posterior eye segments, and the formulation is active in EAU.

Adhesion Molecule Targeted Therapy for Non-Infectious Uveitis

Non-infectious uveitis (NIU) is an inflammatory eye disease initiated via CD4+ T-cell activation and transmigration, resulting in focal retinal tissue damage and visual acuity disturbance. Cell adhesion molecules (CAMs) are activated during the inflammatory process to facilitate the leukocyte recruitment cascade. Our review focused on CAM-targeted therapies in experimental autoimmune uveitis (EAU) and NIU. We concluded that CAM-based therapies have demonstrated benefits for controlling EAU severity with decreases in immune cell migration, especially via ICAM-1/LFA-1 and VCAM-1/VLA-4 (integrin) pathways. P-selectin and E-selectin are more involved specifically in uveitis related to vasculitis. These therapies have potential clinical applications for the development of a more personalized and specific treatment. Localized therapies are the future direction to avoid serious systemic side effects.

CD4+ T-Cell Plasticity in Non-Infectious Retinal Inflammatory Disease

Non-infectious uveitis (NIU) is a potentially sight-threatening disease. Effector CD4⁺ T cells, especially interferon-γ-(IFNγ) producing Th1 cells and interleukin-17-(IL-17) producing Th17 cells, are the major immunopathogenic cells, as demonstrated by adoptive transfer of disease in a model of experimental autoimmune uveitis (EAU). CD4⁺FoxP3⁺CD25⁺ regulatory T cells (Tregs) were known to suppress function of effector CD4⁺ T cells and contribute to resolution of disease. It has been recently reported that some CD4⁺ T-cell subsets demonstrate shared phenotypes with another CD4⁺ T-cell subset, offering the potential for dual function. For example, Th17/Th1 (co-expressing IFNγ and IL-17) cells and Th17/Treg (co-expressing IL-17 and FoxP3) cells have been identified in NIU and EAU. In this review, we have investigated the evidence as to whether these ‘plastic CD4⁺ T cells’ are functionally active in uveitis. We conclude that Th17/Th1 cells are generated locally, are resistant to the immunosuppressive effects of steroids, and contribute to early development of EAU. Th17/Treg cells produce IL-17, not IL-10, and act similar to Th17 cells. These cells were considered pathogenic in uveitis. Future studies are needed to better clarify their function, and in the future, these cell subsets may in need to be taken into consideration for designing treatment strategies for disease.

Immune-Mediated Retinal Vasculitis in Posterior Uveitis and Experimental Models: The Leukotriene (LT)B4-VEGF Axis

Retinal vascular diseases have distinct, complex and multifactorial pathogeneses yet share several key pathophysiological aspects including inflammation, vascular permeability and neovascularisation. In non-infectious posterior uveitis (NIU), retinal vasculitis involves vessel leakage leading to retinal enlargement, exudation, and macular oedema. Neovascularisation is not a common feature in NIU, however, detection of the major angiogenic factor—vascular endothelial growth factor A (VEGF-A)—in intraocular fluids in animal models of uveitis may be an indication for a role for this cytokine in a highly inflammatory condition. Suppression of VEGF-A by directly targeting the leukotriene B4 (LTB4) receptor (BLT1) pathway indicates a connection between leukotrienes (LTs), which have prominent roles in initiating and propagating inflammatory responses, and VEGF-A in retinal inflammatory diseases. Further research is needed to understand how LTs interact with intraocular cytokines in retinal inflammatory diseases to guide the development of novel therapeutic approaches targeting both inflammatory mediator pathways.

Functionally distinct IFN-γ+ IL-17A+ Th cells in experimental autoimmune uveitis: T-cell heterogeneity, migration, and steroid response

Immunopathogenic roles for both Th1 (CD4⁺ IFN-γ⁺ ) and Th17 (CD4⁺ IL-17A⁺ ) cells have been demonstrated in experimental autoimmune uveitis (EAU). However, the role for Th17/Th1 (CD4⁺ T cells co-expressing IFN-γ and IL-17A) cells in EAU is not yet understood. Using interphotoreceptor retinoid-binding protein peptide-induced EAU in mice, we found increased levels of Th17/Th1 cells in EAU retinae (mean 9.6 ± 4.2%) and draining LNs (mean 8.4 ± 3.9%; p = 0.01) relative to controls. Topical dexamethasone treatment effectively reduced EAU severity and decreased retinal Th1 cells (p = 0.01), but had no impact on retinal Th17/Th1 or Th17 cells compared to saline controls. Using in vitro migration assays with mouse CNS endothelium, we demonstrated that Th17/Th1 cells were significantly increased within the migrated population relative to controls (mean 15.6 ± 9.5% vs. 1.9 ± 1.5%; p = 0.01). Chemokine receptor profiles of Th17/Th1 cells (CXCR3 and CCR6) did not change throughout the transendothelial migration process and were unaffected by dexamethasone treatment. These findings support a role for Th17/Th1 cells in EAU and their resistance to steroid inhibition suggests the importance of targeting both Th17 and Th17/Th1 cells for improving therapy.

Clinical Remission of Sight-Threatening Non-Infectious Uveitis Is Characterized by an Upregulation of Peripheral T-Regulatory Cell Polarized Towards T-bet and TIGIT

Background

Non-infectious uveitis can cause chronic relapsing and remitting ocular inflammation, which may require high dose systemic immunosuppression to prevent severe sight loss. It has been classically described as an autoimmune disease, mediated by pro-inflammatory Th1 and Th17 T-cell subsets. Studies suggest that natural immunosuppressive CD4⁺CD25⁺FoxP3⁺ T-regulatory cells (Tregs) are involved in resolution of inflammation and may be involved in the maintenance of clinical remission.

Objective

To investigate whether there is a peripheral blood immunoregulatory phenotype associated with clinical remission of sight-threatening non-infectious uveitis by comparing peripheral blood levels of Treg, Th1, and Th17, and associated DNA methylation and cytokine levels in patients with active uveitic disease, control subjects and patients (with previously active disease) in clinical remission induced by immunosuppressive drugs.

Methods

Isolated peripheral blood mononuclear cells (PBMC) from peripheral blood samples from prospectively recruited subjects were analyzed by flow cytometry for CD3, CD4, FoxP3, TIGIT, T-bet, and related orphan receptor γt. Epigenetic DNA methylation levels of FOXP3 Treg-specific demethylated region (TSDR), FOXP3 promoter, TBX21, RORC2, and TIGIT loci were determined in cryopreserved PBMC using a next-generation sequencing approach. Related cytokines were measured in blood sera. Functional suppressive capacity of Treg was assessed using T-cell proliferation assays.

Results

Fifty patients with uveitis (intermediate, posterior, and panuveitis) and 10 control subjects were recruited. The frequency of CD4⁺CD25⁺FoxP3⁺ Treg, TIGIT⁺ Treg, and T-bet⁺ Treg and the ratio of Treg to Th1 were significantly higher in remission patients compared with patients with active uveitic disease; and TIGIT⁺ Tregs were a significant predictor of clinical remission. Treg from patients in clinical remission demonstrated a high level of in vitro suppressive function compared with Treg from control subjects and from patients with untreated active disease. PBMC from patients in clinical remission had significantly lower methylation levels at the FOXP3 TSDR, FOXP3 promoter, and TIGIT loci and higher levels at RORC loci than those with active disease. Clinical remission was also associated with significantly higher serum levels of transforming growth factor β and IL-10, which positively correlated with Treg levels, and lower serum levels of IFNγ, IL-17A, and IL-22 compared with patients with active disease.

Conclusion

Clinical remission of sight-threatening non-infectious uveitis has an immunoregulatory phenotype characterized by upregulation of peripheral Treg, polarized toward T-bet and TIGIT. These findings may assist with individualized therapy of uveitis, by informing whether drug therapy has induced phenotypically stable Treg associated with long-term clinical remission.

Pharmacological Inhibition of Bromodomain Proteins Suppresses Retinal Inflammatory Disease and Downregulates Retinal Th17 Cells

Experimental autoimmune uveitis (EAU), in which CD4⁺ Th1 and/or Th17 cells are immunopathogenic, mimics various clinical features of noninfectious uveitis in humans. The impact of bromodomain extraterminal (BET) inhibitors on Th17 cell function was studied in a mouse model of EAU in vivo and in mouse and human Th17 cells in vitro. Two BET inhibitors (GSK151 and JQ1) were able to ameliorate the progression of inflammation in EAU and in mouse CD4⁺ T cells in vitro, downregulating levels of Th17 cells. Additionally, the uveitogenic capacity of Th17 cells to transfer EAU was abrogated by BET inhibitors in an adoptive transfer model. In human CD4⁺ T cells, a 5-d exposure to BET inhibitors was accompanied by a significant downregulation of Th17-associated genes IL-17A, IL-22, and retinoic acid-related orphan receptor γt. However, in vitro, the inhibitors had no effect on already polarized Th17 cells. The key finding is that, in response to BET inhibitors, Th17-enriched cultures developed a regulatory phenotype, upregulated FOXP3 expression and IL-10 secretion, and lost pathogenicity in vivo. We conclude that BET targeting of Th17 cells is a potential therapeutic opportunity for a wide range of inflammatory and autoimmune diseases, including uveitis.

Classical dendritic cells mediate fibrosis directly via the retinoic acid pathway in severe eye allergy

Fibrosis is a shared end-stage pathway to lung, liver, and heart failure. In the ocular mucosa (conjunctiva), fibrosis leads to blindness in trachoma, pemphigoid, and allergy. The indirect fibrogenic role of DCs via T cell activation and inflammatory cell recruitment is well documented. However, here we demonstrate that DCs can directly induce fibrosis. In the mouse model of allergic eye disease (AED), classical CD11b⁺ DCs in the ocular mucosa showed increased activity of aldehyde dehydrogenase (ALDH), the enzyme required for retinoic acid synthesis. In vitro, CD11b⁺ DC-derived ALDH was associated with 9-cis-retinoic acid ligation to retinoid x receptor (RXR), which induced conjunctival fibroblast activation. In vivo, stimulating RXR led to rapid onset of ocular mucosal fibrosis, whereas inhibiting ALDH activity in DCs or selectively depleting DCs markedly reduced fibrosis. Collectively, these data reveal a profibrotic ALDH-dependent pathway by DCs and uncover a role for DC retinoid metabolism.

Aldehyde dehydrogenase inhibition blocks mucosal fibrosis in human and mouse ocular scarring

Mucous membrane pemphigoid (MMP) is a systemic mucosal scarring disease, commonly causing blindness, for which there is no antifibrotic therapy. Aldehyde dehydrogenase family 1 (ALDH1) is upregulated in both ocular MMP (OMMP) conjunctiva and cultured fibroblasts. Application of the ALDH metabolite, retinoic acid (RA), to normal human conjunctival fibroblasts in vitro induced a diseased phenotype. Conversely, application of ALDH inhibitors, including disulfiram, to OMMP fibroblasts in vitro restored their functionality to that of normal controls. ALDH1 is also upregulated in the mucosa of the mouse model of scarring allergic eye disease (AED), used here as a surrogate for OMMP, in which topical application of disulfiram decreased fibrosis in vivo. These data suggest that progressive scarring in OMMP results from ALDH/RA fibroblast autoregulation, that the ALDH1 subfamily has a central role in immune-mediated ocular mucosal scarring, and that ALDH inhibition with disulfiram is a potential and readily translatable antifibrotic therapy.

T-bet Activates Th1 Genes through Mediator and the Super Elongation Complex

The transcription factor T-bet directs Th1 cell differentiation, but the molecular mechanisms that underlie this lineage-specific gene regulation are not completely understood. Here, we show that T-bet acts through enhancers to allow the recruitment of Mediator and P-TEFb in the form of the super elongation complex (SEC). Th1 genes are occupied by H3K4me3 and RNA polymerase II in Th2 cells, while T-bet-mediated recruitment of P-TEFb in Th1 cells activates transcriptional elongation. P-TEFb is recruited to both genes and enhancers, where it activates enhancer RNA transcription. P-TEFb inhibition and Mediator and SEC knockdown selectively block activation of T-bet target genes, and P-TEFb inhibition abrogates Th1-associated experimental autoimmune uveitis. T-bet activity is independent of changes in NF-κB RelA and Brd4 binding, with T-bet- and NF-κB-mediated pathways instead converging to allow P-TEFb recruitment. These data provide insight into the mechanism through which lineage-specifying factors promote differentiation of alternative T cell fates.

Effect of high-dose simvastatin on brain atrophy and disability in secondary progressive multiple sclerosis (MS-STAT): a randomised, placebo-controlled, phase 2 trial

BACKGROUND

Secondary progressive multiple sclerosis, for which no satisfactory treatment presently exists, accounts for most of the disability in patients with multiple sclerosis. Simvastatin, which is widely used for treatment of vascular disease, with its excellent safety profile, has immunomodulatory and neuroprotective properties that could make it an appealing candidate drug for patients with secondary progressive multiple sclerosis.

METHODS

We undertook a double-blind, controlled trial between Jan 28, 2008, and Nov 4, 2011, at three neuroscience centres in the UK. Patients aged 18-65 years with secondary progressive multiple sclerosis were randomly assigned (1:1), by a centralised web-based service with a block size of eight, to receive either 80 mg of simvastatin or placebo. Patients, treating physicians, and outcome assessors were masked to treatment allocation. The primary outcome was the annualised rate of whole-brain atrophy measured from serial volumetric MRI. Analyses were by intention to treat and per protocol. This trial is registered with ClinicalTrials.gov, number NCT00647348.

FINDINGS

140 participants were randomly assigned to receive either simvastatin (n=70) or placebo (n=70). The mean annualised atrophy rate was significantly lower in patients in the simvastatin group (0·288% per year [SD 0·521]) than in those in the placebo group (0·584% per year [0·498]). The adjusted difference in atrophy rate between groups was -0·254% per year (95% CI -0·422 to -0·087; p=0·003); a 43% reduction in annualised rate. Simvastatin was well tolerated, with no differences between the placebo and simvastatin groups in proportions of participants who had serious adverse events (14 [20%] vs nine [13%]).

INTERPRETATION

High-dose simvastatin reduced the annualised rate of whole-brain atrophy compared with placebo, and was well tolerated and safe. These results support the advancement of this treatment to phase 3 testing.

FUNDING

The Moulton Foundation [charity number 1109891], Berkeley Foundation [268369], the Multiple Sclerosis Trials Collaboration [1113598], the Rosetrees Trust [298582] and a personal contribution from A Pidgley, UK National Institute of Health Research (NIHR) University College London Hospitals/UCL Biomedical Research Centres funding scheme.

SIRT1 activation protects against autoimmune T cell-driven retinal disease in mice via inhibition of IL-2/Stat5 signaling

Sirtuins are a mammalian family of NAD(+)-dependent histone deacetylases that regulate cell function and survival as well as regulating cell responses under inflammatory conditions. SIRT1 activator treatment in vitro using mouse pLN cells, normal human and ocular Behçet's disease donor PBMC resulted in suppressed T cell proliferation and pro-inflammatory cytokine production. Our data suggest a novel mechanism by which SIRT1 activators contribute to suppression of T cell proliferation by both down regulating STAT5A/B expression and suppression of pSTAT5A/B signaling in response to IL-2. Experimental autoimmune uveoretinitis (EAU) in B10.RIII mice is an antigen-specific cell-mediated model of human intra-ocular inflammatory disease. Infiltrating CD4(+) T cells in the retina secrete both IFN-γ and IL-17 and are accompanied by inflammatory granulocytes and macrophages which together result in retinal destruction. Oral SIRT1 activator treatment administered to EAU mice suppressed disease with an accompanying reduction in retinal leukocytic infiltrate, suppressed antigen-specific T cell responses and marked suppression of innate and adaptive pro-inflammatory cytokine production in the eye including IL-6, IL-17A and IFN-γ. In vivo SIRT1 activator treatment also suppressed production of IL-17A, IL-17F, IL-6, TGFβ and IL-22 by pLN cells. Oral SIRT1 activator treatment administered to mice during the efferent phase (days7-14) of EAU was effective at suppressing disease. These observations demonstrate that SIRT1 activation is anti-inflammatory in nature and future targeted activation of SIRT1 shows promise as a potential treatment for non-infectious intra-ocular disorders such as uveitis associated with Behçets disease.

Autoantibodies contribute to the immunopathogenesis of experimental dry eye disease

PURPOSE

The purpose of this study was to determine if autoantibodies play a role in the immunopathogenesis of experimental dry eye disease.

METHODS

Dry eye was induced by exposing female C57BL/6 wild-type mice or hen egg lysozyme B-cell receptor transgenic mice to desiccating stress (subcutaneous scopolamine [0.5 mg/0.2 mL] 3 times a day, humidity < 40%, and sustained airflow) for 3 weeks, allowing sufficient time for a humoral immune response. Serum or purified IgG isolated from dry-eye mice or untreated controls was passively transferred to nude recipient mice, which were evaluated for ocular surface inflammation 3 days after transfer. To determine if complement activation contributed to serum-induced dry eye disease, cobra venom factor was used to deplete complement activity.

RESULTS

Autoantibodies against kallikrein 13 were identified in serum from dry-eye mice, but were undetectable in untreated controls. Autoantibody-containing serum or purified IgG from dry-eye mice was sufficient to mediate complement-dependent ocular surface inflammation. Serum or purified IgG caused marked inflammatory burden and tissue damage within the ocular surface tissues, including elevated Gr1+ neutrophil infiltration and proinflammatory cytokines/chemokines associated with goblet cell loss. Moreover, complement C3b deposition was found within the ocular surface tissues of mice receiving dry-eye serum, but not in recipients of control serum. Functionally, complement depletion attenuated the ability to transfer dry-eye-specific serum or IgG-mediated disease.

CONCLUSIONS

These data demonstrate for the first time a complement-dependent pathogenic role of dry-eye-specific autoantibodies, and suggest autoantibody deposition within the ocular surface tissues contributes to the predominantly T-cell-mediated immunopathogenesis of dry eye disease.

Conjunctival interleukin-13 expression in mucous membrane pemphigoid and functional effects of interleukin-13 on conjunctival fibroblasts in vitro

Interleukin-13 (IL-13) is the dominant effector cytokine of fibrosis in pulmonary and liver disease. Excessive conjunctival fibrosis in the immunobullous disease ocular mucous membrane pemphigoid (MMP) causes blindness; the pathogenesis of scarring in this disease is incompletely understood. To determine whether IL-13 is involved in conjunctival fibrosis in MMP, we studied the expression of IL-13 in ocular MMP patients before and after systemic immunosuppression and examined the effects of IL-13 on normal human conjunctival fibroblasts. We found high stromal cell expression of IL-13 in active ocular MMP by immunohistochemistry; 80% of these cells were CD3-positive T cells. Following immunosuppression, in clinically uninflamed, treated, ocular MMP patients, the number of IL-13 positive cells was significantly reduced, but this was still fourfold greater than in normal conjunctiva. IL-13 stimulated collagen lattice contraction and migration, and decreased production of mmp-3 and mmp-10 by human conjunctival fibroblasts. The addition of T cell culture supernatant to IL-13 synergistically augmented fibroblast migration. IL-13 also up-regulated surface expression of HLA-DR, CD80, CD40, and CD154 by conjunctival fibroblasts, suggesting a potential mechanism for fibroblast-T cell cross talk, via which fibroblasts may actively engage in perpetuating chronic inflammation and continued fibrosis. Together, these findings suggest that IL-13 is involved in conjunctival fibrosis in MMP, and that IL-13 has both profibrotic and pro-inflammatory effects on human conjunctival fibroblasts.

Ocular anti-allergic compounds selectively inhibit human mast cell cytokines in vitro and conjunctival cell infiltration in vivo

BACKGROUND

Conjunctival mast cells (MCs) are important effector cells in seasonal allergic conjunctivitis, via histamine and cytokine secretion. Several new anti-allergic eye drops stabilize MCs and block histamine receptors, but their anti-inflammatory effects are unclear.

OBJECTIVE

Anti-allergic drugs were compared for their anti-inflammatory effects in an in vitro model of human MC activation and in an experimental murine model of allergic conjunctivitis.

METHODS

Human cord blood stem cell-derived (CBMC) and conjunctival biopsy-derived MCs were stimulated via FcepsilonRI, degranulation and histamine release were assayed at 1 h and cytokine secretion at 24 h using multiplex arrays. Mice sensitized to short ragweed pollen were given anti-allergics topically before allergen challenge, and conjunctival immuno-staining was performed at 24 h.

RESULTS

After a 1 h stimulation, 80% of the CBMC had degranulated and secreted histamine (27.9+/-4.7 ng/10(6) cells; P<0.05). Pre-treatment by all drugs significantly reduced histamine and TNF-alpha, whereas IL-5, IL-8, IL-10 and TNF-beta profiles were differentially decreased. For conjunctival biopsy-derived cultures (n=11), FcepsilonR1 stimulation increased histamine, TNF-alpha, TNF-beta, IL-5 and IL-8 levels and the production of IL-5, IL-6 (P<0.05), histamine and IL-8 (P<0.01) was inhibited by epinastine. In vivo, epinastine and olopatadine pre-treatment significantly reduced the clinical scores and eosinophil numbers (n=6; P<0.05) while epinastine also reduced neutrophils (P<0.02).

CONCLUSION

Differential effects on MC cytokine inhibition were observed, with epinastine inhibiting MC secretion of IL-5, IL-8, IL-10 and conjunctival neutrophil infiltration. The anti-allergic drugs have anti-histamine and mast-cell stabilizing properties but might differ in clinical improvement depending on the individual and the cytokines involved.

Pathways of corneal and ocular surface inflammation: a perspective from the cullen symposium

The goal of this symposium was to coalesce information presented by 22 investigators in the field of corneal and ocular surface inflammation into common pathways of inflammation. The perspective elucidated in this article defines the components of the normal ocular surface immune architecture and describes the consensus reached on the mechanisms/pathways involved in 1) acute inflammation; 2) late-stage (chronic) response; and 3) allergic disease. Seven diagrams didactically illustrate mechanisms. This paper is the introductory article in a supplement containing 18 articles by the symposium participants.

Cytokine profiles in conjunctival allergy and inflammation

Identifying the cells and cytokines present at the ocular surface in different clinical subgroups of patients with conjunctival allergy and inflammation has led to an improved understanding of the immune-mediated mechanisms that occur. Together with the recent advances in immunotherapeutic interventions for various immune-mediated diseases, it is hoped that some of these will be applicable for the treatment of conjunctival inflammatory diseases in the near future.

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.

Multiple cytokines in human tear specimens in seasonal and chronic allergic eye disease and in conjunctival fibroblast cultures

BACKGROUND

Several cytokines are involved in the recruitment and activation of inflammatory cells in ocular allergic diseases. The purpose of the study was to assay multiple cytokines and chemokines in tears, to compare subgroups of allergic conjunctivitis (AC) with controls, and in culture supernatants to determine whether conjunctival fibroblasts produce some of these cytokines.

METHODS

Fifty to one hundred microlitre tears were obtained from patients with active seasonal allergic conjunctivitis (SAC; n=12), vernal keratoconjunctivitis (VKC; n=18), atopic keratoconjunctivitis (AKC; n=6) and non-atopic controls (n=14). Primary conjunctival fibroblasts grown in vitro were stimulated with IL-4, IL-13 or TNF-alpha for 24 h. Cell-free tear and culture supernatants were assayed for IL-1beta, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12, IL-13, IFN-gamma, TNF-alpha, eotaxin, MCP-1 and RANTES using multiplex bead analysis. Induction of chemokine gene expression was determined by PCR.

RESULTS

IL-1beta, IL-2, IL-5, IL-6, IL-12, IL-13, MCP-1 were increased in all tears groups compared with controls, with highly significant correlations between many of these molecules. In addition IL-4, IFN-gamma, and IL-10 were elevated in SAC and VKC, while eotaxin and TNF-alpha were only increased in VKC. IL-6, IL-8, MCP-1, RANTES and eotaxin were detected from fibroblasts cultures, and were all up-regulated by TNF-alpha. By PCR, fibroblasts expressed MCP-1 transcripts constitutively, whereas IP-10 and Mig were up-regulated by TNF-alpha.

CONCLUSIONS

Differential cytokine levels support tears as a useful indicator of immune mechanisms occurring during AC. The striking similarities in chemokine profiles between tears and fibroblasts suggest these cells as likely sources of chemokines in tears.

Th1- and Th2-type cytokines in chronic ocular allergy

BACKGROUND

Previous reports have suggested that Th2-type cytokines are important in the pathogenesis of ocular allergic diseases. The purpose of this study is to measure levels and mRNA expression of Th1- and Th2-type cytokines in patients with active vernal keratoconjunctivitis (VKC) and atopic keratoconjunctivitis (AKC).

METHODS

Tear samples and tear-isolated cells were obtained from 9 healthy participants (CT--controls), 28 VKC, and 6 AKC patients. IL-4, IL-13, and interferon gamma (IFNgamma) tear levels were determined by ELISA, and IL-4 and IFNgamma tear cell mRNA expression by RT-PCR. Effects of these cytokines on IL-6 and IL-8 secretion, and on ICAM-1 expression by conjunctival fibroblasts, were evaluated by ELISA and flow cytometry respectively.

RESULTS

Interleukin-4 tear levels were increased in VKC and AKC compared with CT, but only IFNgamma significantly correlated with corneal involvement. An IL-4/13-dominant profile was found in 50% of VKC and in 17% of AKC patients, while a IFNgamma-dominant profile was found in 18% of VKC and in 17% of AKC patients. IL-4 and IFNgamma transcripts were detected in tear cells from 11 out of 12 VKC patients. IFNgamma upregulated expression of ICAM-1 on conjunctival fibroblasts and the secretion of IL-6 and IL-8.

CONCLUSIONS

Although both IL-4 and IFNgamma are detected in tears, only IFNgamma levels correlated with disease severity and upregulated ICAM-1 on conjunctival fibroblasts, suggesting the role of IFNgamma in the inflammatory phase of chronic allergic eye diseases.

Multiplex Cytokine Detection versus ELISA for Aqueous Humor: IL-5, IL-10, and IFNγ Profiles in Uveitis

PURPOSE

The purpose of this study was to determine levels of IL-2, -4, -5, -10, TNF-alpha, and IFN-gamma in aqueous humor (AH) from patients with active panuveitis, anterior uveitis (AU), and noninflammatory controls by using a flow cytometric mutiplex array (CBA) and to compare with results from ELISA.

METHODS

Pooled normal AH was spiked with six cytokines at decreasing concentrations for evaluating the CBA. AH was also obtained from 10 controls (cataract patients) and 36 patients with active uveitis. Cell-free supernatants were added to a cocktail of capture beads and detector antibodies or to antibody-coated wells for CBA and ELISA determination, respectively.

RESULTS

CBA demonstrated greater sensitivity for detecting IL-4, IL-10, and TNF-alpha than with ELISA. Increased IFN-gamma was detected in both AU and panuveitis groups compared with controls (P < 0.01). IL-10 was higher in the panuveitis group on steroids (P < 0.01). IL-5 was detected in the control (P < 0.01) and AU groups (P < 0.05) but was undetectable in the panuveitis group (n = 10). Correlations between IFN-gamma and IL-10 were found in all uveitis groups (P < 0.01) but not in controls, whereas TNF-alpha correlations with IL-4/IFN-gamma were obtained in controls but not in the uveitis groups (P < 0.01).

CONCLUSIONS

It was possible to measure cytokines titrated into normal AH specimens by CBA, and a greater number of cytokines were detected with increased sensitivity than with ELISA. Elevated IFN-gamma in active uveitis and decreased IL-5 in posterior uveitis suggest Th1 polarity is more marked, with greater uveal tract involvement. The increased IL-10 in the steroid treated group suggests glucocorticoid-induced IL-10 upregulation.

Basic science and pathophysiology of ocular allergy

Ocular allergy includes several clinical subtypes ranging from the mild seasonal allergic conjunctivitis to the potentially sight-threatening atopic keratoconjunctivitis. Current therapies, particularly for the severe forms of disease, need to be more localized and with fewer side effects. For this to be achieved, it requires a better understanding of the basic mechanisms involved. In this chapter, recent findings are discussed that suggest that it is important to take an integrated approach, including both immune and structural elements of the eye. This provides potential new strategies for therapy, addressing the influence of structural cells in disease. These might influence the immune processes that take place and, as the structural cells are precisely localized, topical application is likely to be effective.

The immunomodulatory role of human conjunctival epithelial cells

PURPOSE

To characterize phenotypically the primary epithelial cells obtained from normal bulbar conjunctival biopsy specimens and a human conjunctival epithelial cell line (Wong-Kilbourne derivative of Chang conjunctiva; ChWK) with regard to their immunostimulatory function.

METHODS

The effects on expression of HLA-DR and costimulatory molecules (CD80, CD86, ICAM-1, and CD40) on normal conjunctival epithelial cells and ChWK treated with various cytokines (IFN-gamma, TNF-alpha, IL-4, and IL-13) were determined using flow cytometry and confocal microscopy.

RESULTS

Epithelial cells were successfully grown from conjunctival explants and cultures passaged three times, while retaining their cell surface markers. At least 97% of primary epithelial cells (n = 10) and more than 96% of ChWK cells (n = 10) were cytokeratin positive by flow cytometry and immunocytochemistry and demonstrated epithelial cell morphology. Both primary conjunctival epithelial cells and ChWK had a low basal expression of HLA-DR and ICAM-1, and both were upregulated by IFN-gamma. For ChWK cells, CD80 and CD86 were constitutively expressed at low levels. CD80 was significantly upregulated after IFN-gamma treatment (P = 0.043), whereas IL-4 induced a significant upregulation of CD86 (P = 0.039). Treatment with IL-13 and TNF-alpha did not induce significant effects.

CONCLUSIONS

The ability of conjunctival epithelial cells to express costimulatory molecules suggests a proinflammatory role for conjunctival epithelial cells.

Antigen-specific T-cell downregulation by human dendritic cells following blockade of NF-kappaB

Dendritic cells (DCs) are important for presenting antigen to T cells, especially naïve T cells. It has recently been shown that blocking the transcription factor, nuclear factor kappa B (NF-kappaB) in human DCs inhibited the mixed leukocyte reaction. The aim of this study was to investigate the effect of blocking NF-kappaB in DCs during presentation of antigen to memory T cells in vitro. Peripheral blood monocytes were differentiated into immature DCs with interleukin-4 (IL-4) and granulocyte-macrophage colony-stimulating factor, and pulsed with an immunogenic tetanus toxoid peptide. Upon maturation, the antigen-pulsed DCs were highly effective in presenting antigen to autologous T cells. However, stimulation with antigen-pulsed DCs overexpressing IotakappaBetaalpha, the endogenous inhibitor of NF-kappaB, led to a significant reduction in T-cell proliferation, and decreased production of interferon-gamma, IL-4 and IL-10, whereas transforming growth factor-beta production was low throughout. There was a significant increase in apoptosis of antigen-specific T cells, even in the presence of IL-2, which was not found in resting T cells. Similar findings were observed using a proteasome inhibitor to block NF-kappaB. The effective downregulation of antigen-specific T-cell responses following blockade of NF-kappaB in DCs could be a useful approach for immunomodulating inflammatory T-cell responses.

Tear and mucus eotaxin-1 and eotaxin-2 in allergic keratoconjunctivitis

OBJECTIVE

Eotaxin-1 and eotaxin-2 are potent eosinophil chemotactic and activating peptides that may be implicated in the pathogenesis of the chronic allergic eye diseases vernal keratoconjunctivitis (VKC) and atopic keratoconjunctivitis (AKC). The purpose of this study was to measure these chemokines in tear and mucus samples of active-disease patients and in vitro cultured conjunctival epithelial cells and fibroblasts.

DESIGN

Comparative, observational case series and in vitro study.

PARTICIPANTS

Sixteen patients with clinically active and untreated VKC or AKC, six age-matched control patients, and five nonactive seasonal allergic conjunctivitis patients.

METHODS

Tears were collected from the active VKC and AKC patients, and from the normal patients. Mucus was collected from six of these VKC patients. Tears were also collected from an additional five allergic patients after obtaining a positive reaction to conjunctival allergen challenge. Conjunctival epithelial cell and conjunctival fibroblast cultures were exposed to interleukin (IL)-4, IL-13, and tumor necrosis factor-alpha (TNF-alpha), or to combinations of these cytokines.

MAIN OUTCOME MEASURES

Levels of eotaxin-1 and eotaxin-2 in tears, mucus, and culture medium.

RESULTS

High levels of eotaxin-1 and eotaxin-2 were found in mucus of VKC patients, whereas only eotaxin-2 was found to have increased significantly in tears of VKC and AKC patients compared with those of normal patients. Mucus contained higher levels of chemokines than did tears. Both tear eotaxin-1 and eotaxin-2 were correlated significantly with the percent of eosinophils in tear fluid. Eotaxin-1 also was correlated significantly with the sum clinical score and corneal involvement in VKC patients. Conjunctival epithelial cells in culture did not produce eotaxin-1 or eotaxin-2, either at baseline or after cytokine exposure. Conjunctival fibroblasts produced eotaxin-1 only after exposure to IL-4, TNF-alpha, and the combination of IL-4 plus TNF-alpha or IL-13 plus TNF-alpha.

CONCLUSIONS

Eotaxin-1 and eotaxin-2 are implicated in eosinophil recruitment and in the pathogenesis of VKC and AKC. Cytokine-stimulated conjunctival fibroblasts may be one source of eotaxin-1 in severely allergic tissues.

Cytokine production and mRNA expression by conjunctival T-cell lines in chronic allergic eye disease

BACKGROUND

Activated CD4+ T cells, mast cells and eosinophils are the main cytokine-producing cell-types infiltrating the conjunctiva during chronic allergic eye diseases. Interactions between these cells are thought to play an important immunopathogenic role in these disorders (giant papillary conjunctivitis; vernal keratoconjunctivitis; atopic keratoconjunctivitis).

OBJECTIVE

The objective was to compare the cytokine profiles of conjunctival T-cell lines from patients with different forms of chronic allergic eye disease.

METHODS

T cells were isolated from conjunctival biopsies and non-specifically expanded into lines. The lines were immunophenotyped by flow cytometry. Cytokine production was quantified by immunoassays and more sensitive molecular techniques were used to investigate cytokine mRNA expression to identify the presence of interleukin (IL) -2, IL-4 and interferon (IFN) -gamma transcripts.

RESULTS

Following four to six rounds of stimulation, the conjunctival T-cell populations were CD3+ (> 93%), with variable levels of CD4 and CD8 expression. All were HLA-DR+ (> 80%) with some HLA-DQ expression. Conjunctival T-cell lines from atopic keratoconjunctivitis produced selective increases in IFN-gamma, IL-10 and IL-13 (P<0.01), those from vernal keratoconjunctivitis produced increased IL-5 (P<0.01) whereas T-cell lines from giant papillary conjunctivitis produced only low levels of cytokines. IL-4 was only detected at the mRNA level and was expressed in four out of five T-cell lines in the vernal keratoconjunctivitis group. In contrast there was moderate to strong expression of IFN-gamma in five out of six T-cell lines in atopic keratoconjunctivitis.

CONCLUSION

Different patterns of T-cell cytokine profiles were observed for each disease, with low-level, non-polarized cytokine production in giant papillary conjunctivitis, a TH2-like profile in vernal keratoconjunctivitis and a shift towards a TH1-like profile in atopic keratoconjunctivitis.

Increased CD4+ expression and decreased IL-10 in the anterior chamber in idiopathic uveitis

PURPOSE

To compare cell types and cytokines in aqueous humor from patients with uveitis either occurring in association with a systemic disease or apparently isolated and not associated with a systemic disease.

METHODS

Cells were collected by centrifugation of fresh aqueous humor from uveitis and controls, and immunofluorescence techniques were performed with markers for T cells, B cells, and monocytes. Cytokines were measured in the aqueous supernatants, and serum samples were assayed for soluble interleukin-2 receptors.

RESULTS

When aqueous samples from idiopathic uveitis were compared with those from uveitis associated with a systemic disease, there were increases in CD3+, CD4+ (p = 0.001), and activated CD4+ T cells (p = 0.02) and a decrease in B cells (p = 0.0013). This was not reflected in the peripheral blood where there were no differences in the cell types or in soluble interleukin-2 receptor levels. No cells were obtainable from control aqueous. Interleukins-10 and -12, interferon-gamma, and transforming growth factor-beta2 were detected in aqueous supernatants. Interleukin-10 was reduced (p = 0.024) in uveitis in comparison with controls.

CONCLUSIONS

The results suggest a selective recruitment of CD4+ T cells within aqueous humor but only in idiopathic uveitis. In both disease groups there was a decrease in the immunoregulatory cytokine interleukin-10, which might enable an immune response to occur in an otherwise highly immunosuppressive microenvironment. Increases in activated CD4+ T cells combined with depressed interleukin-10 levels could partially explain why, for example, in acute anterior uveitis, the inflammatory disease is often more severe.

Characterization of phenotype and cytokine profiles of T cell lines derived from vitreous humour in ocular inflammation in man

Intermediate uveitis (IU) and Fuchs' heterochromic cyclitis (FHC) are two chronic ocular inflammatory disorders. They differ considerably in ocular morbidity, which is higher in IU. T cell lines were derived from the vitreous humour (VH) and peripheral blood (PB) of 10 patients with IU and four patients with FHC. There was a predominance of CD8+ in all the lines. However, there was a significantly higher percentage of CD4+ T cells in the T cell lines derived from VH of IU (32.0 +/- 8.6%) compared with FHC patients (19. 2 +/- 8.9%) (P = 0.04). The VH-derived T cell lines (VDTC) produced significantly higher levels of IL-2, interferon-gamma (IFN-gamma) and IL-10, but not IL-4, compared with PB-derived T cell lines (PBDTC) in both entities. There was significantly higher IL-2 production by VDTC from IU when compared with FHC patients (1810 +/- 220 pg/ml versus 518 +/- 94 pg/ml; P = 0.009), which could account for the more aggressive clinical features of this condition. In contrast IL-10 production was significantly higher by the VDTC from FHC compared with IU patients. The high IL-10 production by T cells infiltrating VH of FHC patients could down-regulate the inflammatory responses, thereby contributing to the benign clinical course seen in these patients. The accumulation of T cells with differing cytokine profiles in the VH suggests an important role for these cytokines in the pathogenesis of these chronic uveitides.

The immunomodulatory effect of topical cyclosporin A in atopic keratoconjunctivitis

PURPOSE

To perform a detailed examination of the immunomodulatory effects of topical cyclosporin A (CsA) in conjunctival tissue from patients with atopic keratoconjunctivitis (AKC).

METHODS

Patients with active AKC were randomly allocated into two groups of four patients. For 3 months one group received 2% CsA drops, and the other group received placebo drops. Superior tarsal conjunctival biopsy specimens were harvested before and after treatment and examined by one- and two-color immunohistochemistry to compare leukocyte counts, HLA-DR+ and IL-2R+ cell counts, HLA-DR positivity of conjunctival epithelial cells, and counts of T cells expressing the cytokines interleukin (IL)-2, IL-3, IL-4, IL-5, and interferon (IFN)-gamma.

RESULTS

Posttreatment values were significantly less than pretreatment values for the total number of leukocytes and in the numbers of CD3+ T cells, CD4+ cells, CD8+ cells, CD20+ B cells, neutrophils, and macrophages, and there was a decrease in the CD4-CD8 ratio (P = 0.03) in the CsA group. There was a reduction from before CsA treatment to after CsA-treatment in the numbers of HLA-DR+ and IL-2R+ cells (P = 0.03), but the reduction in the epithelial cell HLA-DR expression did not reach significance. The number of T cells staining for IL-3 and IL-5 was reduced, although not to statistical significance, but there was a significant reduction in the number of T cells expressing IL-2 and IFN-gamma (P = 0.03) after CsA treatment compared with initial values. There were no statistically significant differences between pretreatment and posttreatment values in the placebo group. There was a clinical improvement in the CsA group and a clinical worsening in the placebo group.

CONCLUSIONS

The in vitro effects of CsA translate into a reduction in T cells, a normalization of the CD4-CD8 ratio, a decrease in T-cell activation, and a reduction in T-cell cytokine expression, especially IL-2 and IFN-gamma. The decrease in HLA-DR expression may be mediated by the change in IFN-gamma. There were fewer B cells but not fewer plasma cells after CsA and no change in IL-4 expression, suggesting minimal effects on type I hypersensitivity responses. There was no significant reduction in mast cell or eosinophil numbers, but direct effects of topical CsA on their function may play a role in the therapy of ocular allergic disease. These results show that the beneficial effects of topical CsA in AKC are accompanied by important changes in conjunctival immune cell profiles.

The role of conjunctival epithelial cells in chronic ocular allergic disease

Recent evidence suggests that mucosal epithelial cells are capable of actively participating in immune reactions via expression of surface antigens, such as adhesion molecules, and synthesis of cytokines. This appears to be important in the pathophysiology of non-ocular allergic disorders. The objectives of the experiments were to compare the expression of HLA-DR, ICAM-I and pro-allergic cytokines in conjunctival epithelial cells in the different chronic ocular allergic disorders with each other and with normal subjects. Conjunctiva from normal patients (n=10) and patients with vernal keratoconjunctivitis (VKC, n=10), atopic keratoconjunctivitis (AKC, n=10) and contact lens-associated giant papillary conjunctivitis (GPC, n=10) were examined by immunohistochemistry. Epithelial cell staining for surface antigens and cytokines was graded by one masked observer using a four point scale based on the percentage of epithelial cells staining positive. There was no expression of ICAM-1 or HLA-DR in the normal conjunctival epithelial cells, but both antigens were induced on conjunctival epithelial cells in the allergic tissue, and there was greater expression in AKC and VKC compared with GPC. Cytokines IL-6, IL-8, RANTES and TNF-alphaall localised to normal conjunctival epithelial cells. RANTES was upregulated in all the allergic disorders and IL-8 was upregulated in GPC. IL-3 and GM-CSF were not expressed in normal conjunctival epithelial cells. GM-CSF was expressed in all disorders and there was greater expression in AKC compared with GPC and VKC. IL-3 was expressed only in AKC and VKC epithelial cells. These results suggest that conjunctival epithelial cells play an important pro-inflammatory role in chronic ocular allergic diseases; ICAM-1 may allow epithelial cells to recruit, retain and locally concentrate leukocytes; the presence of HLA-DR raises the question of conjunctival epithelial cell antigen presentation. The epithelial cytokines which are upregulated are known to promote eosinophilic inflammation and are typical of allergic inflammation. The differences in cytokine patterns may be exploitable for future therapy.

A randomized, placebo-controlled trial of topical cyclosporin A in steroid-dependent atopic keratoconjunctivitis

OBJECTIVE

This study aimed to investigate the therapeutic effect of topical cyclosporin A (CsA) 2% in maize oil as a steroid-sparing agent in steroid-dependent atopic keratoconjunctivitis.

DESIGN

Prospective, randomized, double-masked, placebo-controlled trial.

PARTICIPANTS

Twenty-one patients with steroid-dependent atopic keratoconjunctivitis were studied.

INTERVENTION

Patients used either topical CsA or vehicle four times daily for 3 months in addition to their usual therapy, and the clinical response was used to taper or stop topical steroids when possible.

MAIN OUTCOME MEASURES

Steroid drop usage per week, ability to cease steroid use, scores for symptoms and clinical signs, drop side effects, and overall subjective rating of trial drop by patients and clinician were measured.

RESULTS

Cyclosporin A had a greater steroid-sparing effect than did placebo. Nine of 12 CsA patients ceased steroids compared to 1 of 9 placebo patients (P = 0.01), the final steroid use was lower in the CsA group (2.6 +/- 1.4 vs. 27.7 +/- 17.7, P = 0.005), and the mean reduction in steroid use was greater for CsA (85.5 +/- 14.7 vs. 13.9 +/- 16.0, P = 0.005). Clinical signs and symptom scores were reduced to a greater level for CsA. Serious side effects were lid skin maceration in one patient using CsA and an allergic reaction in one placebo patient. Marked blurring of vision after drop instillation was common in both groups, but intense stinging was more common in CsA patients (9/12 vs. 1/9, P = 0.01), limiting frequency of drop use. The clinician rated the trial drops as good or excellent more frequently for CsA (11/12 vs. 0/9, P < 0.0001).

CONCLUSIONS

Topical CsA is an effective and safe steroid-sparing agent in atopic keratoconjunctivitis and, despite difficulties in patient tolerance, also improves symptoms and signs.

T-cell cytokines in chronic allergic eye disease

BACKGROUND

The pathophysiology of chronic allergic eye disease cannot be explained by type I hypersensitivity alone, and T cell-mediated inflammation has been strongly implicated as a possible additional mechanism. Previous studies suggested that T(H2)-like T cells play an important role in one form of chronic allergic eye disease.

OBJECTIVES

This study examined the cytokine profile of T cells in different clinical groups of subjects with chronic allergic eye disease (i.e., vernal keratoconjunctivitis [VKC], atopic keratoconjunctivitis [AKC], and giant papillary conjunctivitis [GPC]) and normal control subjects.

METHODS

In situ hybridization was used to identify cytokine messenger RNA (mRNA), and two-color immunohistochemical analysis was used to demonstrate cytokine immunoreactivity localizing to T cells in the conjunctiva.

RESULTS

Allergic tissue expressed increased levels of mRNA for IL-3, IL-4, and IL-5 when compared with normal tissue. There was significantly greater IL-2 mRNA expression in subjects with AKC than in those with VKC (p = 0.004) and those with GPC (p = 0.02). Immunoreactivity for T-cell IL-5 was present more frequently in subjects with VKC (p = 0.004), GPC (p = 0.02), and AKC (p = 0.04) than in normal control subjects. However, T-cell IFN-gamma protein expression was greater in subjects with AKC than in subjects with VKC (p = 0.01), GPC (p = 0.01), and control subjects (p = 0.005).

CONCLUSIONS

These results show a T(H2)-like T-cell cytokine array in subjects with VKC and GPC but a shift in cytokine profile toward a T(H1)-like pattern, potentially because of differences in chronicity of the disorders, in subjects with AKC. These important functional T-cell variations in chronic allergic eye conditions are likely to be important in understanding differences in clinical characteristics and therapeutic responses.

Identification and characterization of cells infiltrating the graft and aqueous humour in rat corneal allograft rejection

In a rat model of corneal transplantation, Fischer 344 (RT1(lv1)) rats received orthotopic corneal isografts or Wistar-Furth (RT1(u)) donor allografts. Rejection was observed in 25 of 26 allograft recipients, at a median time of 18 days, with all isografts surviving > 100 days. Flow cytometric analysis of aqueous humour identified cellular infiltration of the aqueous at the time of allograft rejection, in contrast to the acellular aqueous found in isografts at corresponding times following transplantation. A higher proportion of CD8+ than CD4+ cells was found at days 1-3 following rejection, whereas there was a higher proportion of CD4+ cells at days 5-8. No changes in peripheral blood T cell subsets were found at the time of rejection. Immunohistochemical analysis of cells infiltrating recipient iris and grafted cornea undertaken at days 1-2, 4 and 7-10 following onset of rejection, demonstrated inflammatory cells in the graft epithelium, stroma and aggregated on the endothelium. Large numbers of macrophages, T cells (CD4+ > CD8+ at all time points), natural killer (NK) cells and neutrophils were detected in graft tissue at days 1-2 and 4, diminishing after that time. Most infiltrating cells expressed MHC class II antigen, and a smaller number expressed IL-2R. Expression of the co-stimulatory marker B7 was identified in a few cells at day 4 in the region of the graft-host wound. The immune response in graft rejection was characterized at day 4 also by expression of intercellular adhesion molecule-1 (ICAM-1) on endothelial cells of iris and corneal vessels, demonstration of interferon-gamma on mononuclear cells in the peripheral (recipient) cornea, and tumour necrosis factor-alpha on aggregated mononuclear cells on the graft, but not recipient, endothelium. Only sparse cellular infiltrates were found in isograft controls, with inflammation located at the graft-host wound. These findings suggest that inflammatory cells reach a corneal allograft by two routes--from vessels in the peripheral recipient cornea, and from vessels in the recipient iris via the aqueous humour. Different aqueous and intragraft T cell subset proportions were seen early in rejection, although a preponderance of CD4+ cells was found in both aqueous and graft at later times.