CD25+, interleukin-10-producing CD4+ T cells are required for suppressor cell production and immune privilege in the anterior chamber of the eye

Conditional deletion of CD25 in the corneal epithelium reveals sex differences in barrier disruption

PURPOSE

IL-2 promotes activation, clonal expansion, and deletion of T cells. IL-2 signals through its heterotrimeric receptor (IL-2R) consisting of the CD25, CD122 and CD132 chains. CD25 knockout (KO) mice develop Sjögren Syndrome-like disease. This study investigates whether corneal CD25/IL-2 signaling is critical for ocular health.

METHODS

Eyes from C57BL/6 mice were collected and prepared for immunostaining or in-situ hybridization. Bulk RNA sequencing was performed on the corneal epithelium from wild-type and CD25KO mice. We generated a conditional corneal-specific deletion of CD25 in the corneal epithelium (CD25Δ/ΔCEpi). Corneal barrier function was evaluated based on the uptake of a fluorescent dye. Mice were subjected to unilateral corneal debridement, followed by epithelial closure over time.

RESULTS

In C57BL/6 mice, CD25 mRNA was expressed in ocular tissues. Protein expression of CD25, CD122, and CD132 was confirmed in the corneal epithelium. Delayed corneal re-epithelization was seen in female but not male CD25KO mice. There were 771 differentially expressed genes in the corneal epithelium of CD25KO compared to wild-type mice. While barrier function is disrupted in CD25Δ/ΔCEpi mice, re-epithelialization rates are not delayed.

CONCLUSIONS

All three chains of the IL-2R are expressed in the corneal epithelium. Our results indicate for the first time, deleting CD25 systemically in all tissues in the mouse and deleting CD25 locally in just the corneal epithelium compromises corneal epithelial barrier function, leading to dry eye disease in female mice. Future studies are needed to delineate the pathways used by IL-2 signaling to influence cornea homeostasis.

The Host-Pathogen Interplay: A Tale of Two Stories within the Cornea and Posterior Segment

Ocular infectious diseases are an important cause of potentially preventable vision loss and blindness. In the following manuscript, we will review ocular immunology and the pathogenesis of herpesviruses and Pseudomonas aeruginosa infections of the cornea and posterior segment. We will highlight areas of future research and what is currently known to promote bench-to-bedside discoveries to improve clinical outcomes of these debilitating ocular diseases.

Developmental characteristics of the cytokine profile in aqueous humor and its relationship with the inflammatory response in children

Background

Although influencing the severity of postoperative intraocular inflammation of congenital cataract, the developmental characteristics of cytokine profile in the aqueous humor during childhood had not been described. And its relationship with the inflammatory response after intraocular surgery remained unsolved.

Methods

Preoperative aqueous humor samples were collected from 65 eyes of congenital cataract patients (CC group) and 13 eyes of age-related cataract patients (ARC group) from January 2015 to May 2017. The concentrations of 22 cytokines were measured. Differences in concentrations between the CC and ARC groups were described. Correlation analysis, least absolute shrinkage and selection operator (LASSO) and multivariate linear regression were then used to investigate the dynamic changes in the cytokine profile with age and their relationships with the postoperative inflammatory response.

Results

The concentrations of granulocyte colony stimulating factor (G-CSF), interferon (IFN)-α2, interleukin (IL)-1α and IL-7 were higher in the CC group than in the ARC group, while the concentrations of epidermal growth factor (EGF), granulocyte-macrophage colony stimulating factor (GM-CSF), IL-10, IL-12p70, IL-2, IL-3, IL-4, IL-5, IL-6, IL-8, and tumor necrosis factor (TNF)-α were more abundant in the ARC group (P<0.05). Within the CC group, the concentrations of EGF and IL-3 were positively correlated with age, while negative correlations were observed for monocyte chemotactic protein-1 (MCP-1) and IL-8 (P<0.05). Further multivariate analysis revealed that age was an independent associated factor of MCP-1 (β=−0.337, P<0.001). IL-3 (β=−0.490, P=0.006) and EGF (β=−0.415, P=0.044) were significantly correlated with the postoperative inflammatory response [evaluation of posterior capsule opacification (EPCO)] at 3 and 12 months after surgery, respectively.

Conclusions

This study demonstrated the dynamic change in the cytokine profile of the aqueous humor in children and its relationship with the postoperative inflammatory response. These findings can serve as the foundation for further investigation into the mechanisms that underlie the early development of intraocular immunology.

VISTA Is Crucial for Corneal Allograft Survival and Maintenance of Immune Privilege

Purpose

V-domain immunoglobulin suppressor of T cell activation (VISTA) is a novel immune checkpoint receptor and ligand for regulating T cell proliferation and cytokine production. The purpose of the present study was to determine the role of VISTA in the immune privilege of corneal allografts.

Methods

Expression of VISTA mRNA in mouse eyes was assessed with reverse-transcription PCR. Corneas of C57BL/6 mice were orthotopically transplanted into the eyes of BALB/c wild-type recipients treated with anti-VISTA mAb, and graft survival was assessed. A separate set of BALB/c mice treated with anti-VISTA mAb or rat IgG received injection of C57BL/6 splenocytes into the anterior chamber, and induction of allospecific anterior chamber-associated immune deviation (ACAID) was assessed. CD4+ and CD8+ T cells in the spleen were assessed with flow cytometry.

Results

VISTA mRNA was constitutively expressed in the cornea, and the expression of VISTA was localized to CD11b+ cells on the corneal stroma. Survival of allografts treated with anti-VISTA mAb was less than that of the control. ACAID was induced less efficiently in BALB/c mice treated with VISTA mAb. The proportions of CD8+ T cells and CD8+ CD103+ T cells (CD8+ T regulatory cells) in the spleen of BALB/c mice treated with anti-VISTA mAb were significantly lower than those of the control.

Conclusions

VISTA may play an essential role in the acceptance of corneal allografts via involvement with allospecific ACAID, which suppresses T cell infiltration into the cornea.

Immune privilege in corneal transplantation

Corneal transplantation is the most successful solid organ transplantation performed in humans. The extraordinary success of orthotopic corneal allografts, in both humans and experimental animals, is related to the phenomenon of "immune privilege". Inflammation is self-regulated to preserve ocular functions because the eye has immune privilege. At present, three major mechanisms are considered to provide immune privilege in corneal transplantation: 1) anatomical, cellular, and molecular barriers in the cornea; 2) tolerance related to anterior chamber-associated immune deviation and regulatory T cells; and 3) an immunosuppressive intraocular microenvironment. This review describes the mechanisms of immune privilege that have been elucidated from animal models of ocular inflammation, especially those involving corneal transplantation, and its relevance for the clinic. An update on molecular, cellular, and neural interactions in local and systemic immune regulation is provided. Therapeutic strategies for restoring immune privilege are also discussed.

Cellular and Molecular Mechanisms of Anterior Chamber-Associated Immune Deviation (ACAID): What We Have Learned from Knockout Mice

Anterior chamber-associated immune deviation (ACAID) is a well-known phenomenon that can occur after an antigen is introduced without any danger signal into the anterior chamber of a murine eye. It is reported to lead to an antigen-specific immune deviation throughout the body. Despite the relatively little evidence of this phenomenon in humans, it has been suggested as a potential prophylactic strategy in allograft rejections and in several autoimmune diseases. Cellular and molecular mechanisms of ACAID have been explored in different murine models mainly as proofs of concept, first by direct analyses of immune components in normal immunocompetent settings and by cell transfer experiments. Later, use of knockout (KO) mice has helped considerably to decipher ACAID mechanisms. However, several factors raise questions about the reliability and validity of studies using KO murine models. This mini-review summarizes results obtained with KO mice and discusses their advantages, their potential weaknesses, and their potential methods for further progress.

Wound-Healing Studies in Cornea and Skin: Parallels, Differences and Opportunities

The cornea and the skin are both organs that provide the outer barrier of the body. Both tissues have developed intrinsic mechanisms that protect the organism from a wide range of external threats, but at the same time also enable rapid restoration of tissue integrity and organ-specific function. The easy accessibility makes the skin an attractive model system to study tissue damage and repair. Findings from skin research have contributed to unravelling novel fundamental principles in regenerative biology and the repair of other epithelial-mesenchymal tissues, such as the cornea. Following barrier disruption, the influx of inflammatory cells, myofibroblast differentiation, extracellular matrix synthesis and scar formation present parallel repair mechanisms in cornea and skin wound healing. Yet, capillary sprouting, while pivotal in proper skin wound healing, is a process that is rather associated with pathological repair of the cornea. Understanding the parallels and differences of the cellular and molecular networks that coordinate the wound healing response in skin and cornea are likely of mutual importance for both organs with regard to the development of regenerative therapies and understanding of the disease pathologies that affect epithelial-mesenchymal interactions. Here, we review the principal events in corneal wound healing and the mechanisms to restore corneal transparency and barrier function. We also refer to skin repair mechanisms and their potential implications for regenerative processes in the cornea.

Involvement of B cells in non-infectious uveitis

Non-infectious uveitis-or intraocular inflammatory disease-causes substantial visual morbidity and reduced quality of life amongst affected individuals. To date, research of pathogenic mechanisms has largely been focused on processes involving T lymphocyte and/or myeloid leukocyte populations. Involvement of B lymphocytes has received relatively little attention. In contrast, B-cell pathobiology is a major field within general immunological research, and large clinical trials have showed that treatments targeting B cells are highly effective for multiple systemic inflammatory diseases. B cells, including the terminally differentiated plasma cell that produces antibody, are found in the human eye in different forms of non-infectious uveitis; in some cases, these cells outnumber other leukocyte subsets. Recent case reports and small case series suggest that B-cell blockade may be therapeutic for patients with non-infectious uveitis. As well as secretion of antibody, B cells may promote intraocular inflammation by presentation of antigen to T cells, production of multiple inflammatory cytokines and support of T-cell survival. B cells may also perform various immunomodulatory activities within the eye. This translational review summarizes the evidence for B-cell involvement in non-infectious uveitis, and considers the potential contributions of B cells to the development and control of the disease. Manipulations of B cells and/or their products are promising new approaches to the treatment of non-infectious uveitis.

γδ T Cell-Dependent Regulatory T Cells Prevent the Development of Autoimmune Keratitis

To prevent potentially damaging inflammatory responses, the eye actively promotes local immune tolerance via a variety of mechanisms. Owing to trauma, infection, or other ongoing autoimmunity, these mechanisms sometimes fail, and an autoimmune disorder may develop in the eye. In mice of the C57BL/10 (B10) background, autoimmune keratitis often develops spontaneously, particularly in the females. Its incidence is greatly elevated in the absence of γδ T cells, such that ∼80% of female B10.TCRδ(-/-) mice develop keratitis by 18 wk of age. In this article, we show that CD8(+) αβ T cells are the drivers of this disease, because adoptive transfer of CD8(+), but not CD4(+), T cells to keratitis-resistant B10.TCRβ/δ(-/-) hosts induced a high incidence of keratitis. This finding was unexpected because in other autoimmune diseases, more often CD4(+) αβ T cells, or both CD4(+) and CD8(+) αβ T cells, mediate the disease. Compared with wild-type B10 mice, B10.TCRδ(-/-) mice also show increased percentages of peripheral memory phenotype CD8(+) αβ T cells, along with an elevated frequency of CD8(+) αβ T cells biased to produce inflammatory cytokines. In addition, B10.TCRδ-/- mice have fewer peripheral CD4(+) CD25(+) Foxp3(+) αβ regulatory T cells (Tregs), which express lower levels of receptors needed for Treg development and function. Together, these observations suggest that in B10 background mice, γδ T cells are required to generate adequate numbers of CD4(+) CD25(+) Foxp3(+) Tregs, and that in B10.TCRδ(-/-) mice a Treg deficiency allows dysregulated effector or memory CD8(+) αβ T cells to infiltrate the cornea and provoke an autoimmune attack.

Beneficial effect of annexin A1 in a model of experimental allergic conjunctivitis

Annexin A1 (ANXA1), a 37 kDa glucocorticoid-regulated protein, is a potent anti-inflammatory mediator effective in terminating acute inflammatory response, and its role in allergic settings has been poorly studied. The aim of this investigation was to evaluate the mechanism of action of ANXA1 in intraocular inflammation using a classical model of ovalbumin (OVA)-induced allergic conjunctivitis (AC). OVA-immunised Balb/c mice, wild-type (WT) and ANXA1-deficient (AnxA1(-/-)), were challenged with eye drops containing OVA on days 14-16 with a subset of WT animals pretreated intraperitoneally with the peptide Ac2-26 (N-terminal region of ANXA1) or dexamethasone (DEX). After 24 h of the last ocular challenge, WT mice treated with Ac2-26 and DEX had significantly reduced clinical signs of conjunctivitis (chemosis, conjunctival hyperaemia, lid oedema and tearing), plasma IgE levels, leukocyte (eosinophil and neutrophil) influx and mast cell degranulation in the conjunctiva compared to WT controls. These anti-inflammatory effects of DEX were associated with high endogenous levels of ANXA1 in the ocular tissues as detected by immunohistochemistry. Additionally, Ac2-26 administration was effective to reduce IL-2, IL-4, IL-10, IL-13, eotaxin and RANTES in the eye and lymph nodes compared to untreated WT animals. The lack of ANXA1 produced an exacerbated allergic response as detected by the density of the inflammatory cell influx to the conjunctiva and the cytokine/chemokine release. These different effects observed for Ac2-26 were correlated with diminished level of activated ERK at 24 h in the ocular tissues compared to untreated OVA group. Our findings demonstrate the protective effect of ANXA1 during the inflammatory allergic response suggesting this protein as a potential target for new ocular inflammation therapies.

Toxoplasma gondii oral infection induces intestinal inflammation and retinochoroiditis in mice genetically selected for immune oral tolerance resistance

Toxoplasmosis is a worldwide disease with most of the infections originating through the oral route and generates various pathological manifestations, ranging from meningoencephalitis to retinochoroiditis and inflammatory bowel disease. Animal models for these pathologies are scarce and have limitations. We evaluated the outcome of Toxoplasma gondii oral infection with 50 or 100 cysts of the ME-49 strain in two lines of mice with extreme phenotypes of susceptibility (TS) or resistance (TR) to immune oral tolerance. Therefore, the aim of this study was to evaluate the behaviour of TS and TR mice, orally infected by T. gondii, and determine its value as a model for inflammatory diseases study. Mortality during the acute stage of the infection for TR was 50% for both dosages, while 10 and 40% of the TS died after infection with these respective dosages. In the chronic stage, the remaining TS succumbed while TR survived for 90 days. The TS displayed higher parasite load with lower intestinal inflammation and cellular proliferation, notwithstanding myocarditis, pneumonitis and meningoencephalitis. TR presented massive necrosis of villi and crypt, comparable to inflammatory bowel disease, with infiltration of lymphoid cells in the lamina propria of the intestines. Also, TR mice infected with 100 cysts presented intense cellular infiltrate within the photoreceptor layer of the eyes, changes in disposition and morphology of the retina cell layers and retinochoroiditis. During the infection, high levels of IL-6 were detected in the serum of TS mice and TR mice presented high amounts of IFN-γ and TNF-α. Both mice lineages developed different disease outcomes, but it is emphasized that TR and TS mice presented acute and chronic stages of the infection, demonstrating that the two lineages offer an attractive model for studying toxoplasmosis.

In vitro-induced cell-mediated immune deviation to encephalitogenic antigens

The injection of antigens into the Anterior Chamber (AC) of the eye induces Anterior Chamber Associated Immune Deviation (ACAID), which is a potent form of immune deviation that is largely attributed to the effect of TGFβ2 in the aqueous humor on ocular antigen-presenting cells (APCs). ACAID antigen presentation via APCs and B cells leads to the generation of antigen-specific T regulatory cells. The encephalitogenic antigens Myelin oligodendrocyte glycoprotein (MOG) and Myelin basic protein (MBP) have an obvious clinical relevance. We hypothesized that the intravenous injection of in vitro-generated ACAID APCs or in vitro-generated ACAID B cells specific to the encephalitogenic antigens MOG35-55/MBP induces specific peripheral tolerance in recipient BALB/c mice. We examined the suppression of MOG35-55-specific/MBP-specific inflammatory responses using delayed-type hypersensitivity (DTH) assays and Local Adoptive Transfer (LAT) assays. Results indicated that MOG35-55-specific/MBP-specific tolerance was generated after the intravenous injections of MOG35-55-specific/MBP-specific ACAID APCs, MOG35-55-specific/MBP-specific ACAID B cells, and MOG35-55-specific/MBP-specific ACAID T regulatory cells. The specific immune deviation was in vitro-induced, cell-mediated, and specific to the encephalitogenic antigens MOG35-55/MBP. This in vitro-mediated approach for the generation of MOG35-55/MBP-specific tolerance opens up avenues for the application of ACAID as a tool for the therapy of Multiple Sclerosis, Schizophrenia, and other diseases.

Eye-mediated induction of specific immune tolerance to encephalitogenic antigens

AIMS

Administration of antigens into the anterior chamber (AC) of the eye induces a form of antigen-specific immune tolerance termed anterior chamber-associated immune deviation (ACAID). This immune tolerance effectively impairs host delayed-type hypersensitivity (DTH) responses. We hypothesized that ACAID could be generated in BALB/c mice following AC inoculation of the encephalitogenic antigens myelin oligodendrocyte glycoprotein (MOG) and myelin basic protein (MBP).

METHODS

We used DTH assays and local adoptive transfer (LAT) assays to test whether MOG/MBP-induced ACAID following their administration into the AC, whether they elicited this immune tolerance via CD8(+) T cells, and whether their AC coadministration (MOG/MBP) induced specific immune tolerance to one or both antigens.

RESULTS

We showed that MOG/MBP-induced AC-mediated specific immune tolerance, as evident from impaired DTH responses. This antigen-driven DTH suppression was solely mediated via splenic CD8(+) T cells as confirmed by LAT assays. Finally, a single AC injection with both antigens was sufficient to induce specific immune tolerance to these antigens, as evident from DTH and LAT assays.

CONCLUSION

ACAID T-cell regulation could be used as a therapeutic tool in the treatment of complicated autoimmune diseases that involve multiple antigens such as multiple sclerosis.

Levocetirizine inhibits migration of immune cells to lymph nodes and induces treg cells in a murine type I allergic conjunctivitis model

Background & Purpose:

Levocetirizine is a histamine H(1) receptor antagonist. Here, we utilised DO11.10TCR transgenic mice to establish an antigen-specific T cell-dependent allergic conjunctivitis (AC) model to determine the effect of the topical application of an ophthalmic formulation of Levoceritizine as a treatment for AC.

Experimental Approach:

DO11.10 mice (n=6/each) were exposed to ovalbumin (OVA, 50 µg) and treated with a Levocetirizine ophthalmic formulation (0.001–0.02% v/w) or placebo (vehicle) for 24–72 h. Serum, aqueous/vitreous humour and conjunctiva were obtained. Immunoglobulin (Ig)-E, interleukin (IL)-10 and lipoxin (LX)A₄ were determined by ELISA. Levels of tumour necrosis factor (TNF)-α, transforming growth factor (TGF)-β, interferon (IFN)-γ and 18rS expression were measured by RT-PCR. Proportions of total and activated antigen-presenting cells (APC), recruited T lymphocytes (CD4+), activated T lymphocytes (CD25+) and T regulatory cells (Treg) were measured by flow cytometry.

Key Results:

OVA exposure induced AC in the animal model indicated by increased expression of LXA₄, TNF-α and TGF-β. Levocetirizine treatment (0.01–0.02% v/w) reduced LXA₄ in the eye humours. This treatment approach increased systemic IL-10 secretion and reduced TNF-α and TGF-β expression in conjunctiva without changing IFN-γ expression. Levocetirizine reduced APC levels in draining lymph nodes but increased the proportion of total lymphocytes recruited and their differentiation to Treg cells.

Conclusions & Implications:

Levocetirizine effectively reduces the activation and migration of APC to local draining lymph nodes and induces differentiation of Treg cells as one possible mechanism of its anti-inflammatory action.

Roles of IL-10 in ocular inflammations: a review

INTRODUCTION

This review represents the current in vitro, in vivo, animal and human investigations on the roles of IL-10 in ocular inflammatory conditions.

MATERIALS AND METHODS

The data sources were literature reviews, including Pub Med, Medline, and ISI databases (since 1989 to mid-2012). Search items were, IL-10, chemokines, cytokines, alone or in combination with, serum, aqueous, vitreous eye, ocular, ocular tissues, ophthalmic, and review.

RESULTS

Ocular effects of IL-10 depend on the sources of the secretion and sites of the action. IL-10 plays important anti-inflammatory and especially anti-angiogenic activities in ocular tissues such as the conjunctiva, cornea, retina, choroid, and orbit.

CONCLUSION

IL-10 plays major anti-inflammatory and anti-angiogenic roles in most of the ocular inflammations. Also, IL-10 plays a role in development of anterior chamber-associated immune deviation (ACAID). Any manipulation of IL-10 for treatment purposes should be considered very cautiously due to its potential hazards to the immune system.

Type II collagen induces peripheral tolerance in BALB/c mice via the generation of CD8+ T regulatory cells

Antigens introduced into the anterior chamber (AC) of the eye induce a potent form of antigen-specific peripheral immune tolerance termed AC-associated immune deviation (ACAID), which prevents inflammatory immune responses and is characterized by impaired delayed-type hypersensitivity (DTH) responses. Type-II collagen (CII) is a fibrillar protein expressed exclusively in cartilage tissues. Although of its clinical relevance to Rheumatoid arthritis, aging, and osteoarthritis, there have been no studies to date to test if CII has the ability to induce ACAID. We hypothesized that ACAID could be generated via AC injection of CII in BALB/c mice. Using a DTH assay, the hypothesis was supported and led to another hypothesis that CII is capable of inducing specific immune tolerance via CD8(+) T regulatory cells (Tregs). Thus, we performed functional local adoptive transfer (LAT) assays to examine the regulatory roles of spleen cells, T cells, and CD8(+) T cells in the specific immune regulation induced by CII injection into the AC. Results indicated that CII induced ACAID when injected into the AC. Spleen cells of mice injected with CII in the AC significantly suppressed DTH responses. The T cell compartment of the spleen was capable of expressing this suppression. CD8(+) Tregs could solely express this CII-driven suppression and even exerted more noticeable suppression than spleen cells or splenic T cells. This study suggests a crucial role for CD8(+) Tregs in mediating CII-driven ACAID-mediated immune tolerance. This could have therapeutic implications in Rheumatoid arthritis, aging, osteoarthritis, and other diseases in which CII is involved.

Role of IFN-γ in the establishment of anterior chamber-associated immune deviation (ACAID)-induced CD8+ T regulatory cells

Introduction of alloantigens into the AC induces a form of immune tolerance known as ACAID, which induces antigen-specific CD8+ Tregs, contributing to ocular immune privilege by down-regulating immune responses. Recent evidence suggests IFN-γ is needed for the suppressive function of CD8+ ACAID Tregs. This study tested the hypothesis that IFN-γ is needed for alloantigen-specific ACAID CD8+ Tregs to execute their suppressive function but is not required for the establishment of ACAID CD8+ Tregs. To address this hypothesis, ACAID was induced by injecting BALB/c spleen cells into the AC of WT C57BL/6 mice, IFN-γ(-/-) C57BL/6 mice, or anti-IFN-γ-treated WT C57BL/6 mice. LAT assays using C57BL/6 APCs as stimulators, CD4+ T cells from C57BL/6 mice previously immunized toward BALB/c alloantigens as effector cells, and IFN-γ-competent, IFN-γ(-/-), or IFN-γR(-/-) CD8+ Tregs were used to evaluate the suppressive function of CD8+ ACAID Tregs in response to IFN-γ. IFN-γ(-/-) mice or mice treated with anti-IFN-γ antibody prior to AC injection of alloantigen failed to develop ACAID. The suppressive function of IFN-γ(-/-) ACAID CD8+ Tregs was restored through the administration of exogenous IFN-γ. This suppressive responsiveness toward IFN-γ was CD8+ Treg-intrinsic, as CD8+ Tregs from IFN-γR(-/-) mice, which were primed in the AC with alloantigens, were not able to suppress alloantigen-specific DTH responses. These results indicate that IFN-γ is not needed for the induction of CD8+ ACAID Tregs but is required for ACAID Tregs to exert the suppression of allospecific DTH responses.

Future therapeutics for the induction of peripheral immune tolerance in autoimmune disease and organ transplantation

Rodent models of transplantation and autoimmune disease have demonstrated that it is possible to induce lifelong and specific immunological tolerance to both self and graft antigens in the absence of any continued immunosuppression. If this situation could be achieved clinically, it would avoid many of the longer-term complications of immunosuppression, such as the increased risk of infection, cancer and other side effects, such as nephrotoxicity. In this review, we shall consider the interplay between regulatory T cells, dendritic cells and the tissue itself, and the resulting local protective mechanisms that are coordinated to maintain the tolerant state and an acquired local immune privilege. The current status of attempts to apply tolerogenic approaches to the clinical treatment of autoimmune diseases and to induce either tolerance to organ grafts or sufficient immune regulation so that conventional immunosuppression can be minimized will also be considered.

Two different regulatory T cell populations that promote corneal allograft survival

PURPOSE

To compare and contrast the T regulatory cells (Tregs) induced by anterior chamber (AC) injection of antigen with those induced by orthotopic corneal allografts.

METHODS

Anterior chamber-associated immune deviation (ACAID) Tregs were induced by injecting C57BL/6 spleen cells into the AC of BALB/c mice. Delayed-type hypersensitivity responses to C57BL/6 alloantigens were evaluated by a conventional ear swelling assay. Corneal allograft Tregs were induced by applying orthotopic C57BL/6 corneal allografts onto BALB/c hosts. The effects of anti-CD25, anti-CD8, anti-interferon-γ (IFN-γ), anti-IL-17A, or cyclophosphamide treatments on corneal allograft survival and ACAID were evaluated.

RESULTS

Administration of either anti-CD25 or anti-IFN-γ antibodies prevented the expression of ACAID and abolished the immune privilege of corneal allografts. By contrast, in vivo treatment with anti-CD8 antibody abrogated ACAID but had no effect on corneal allograft survival. Further discordance between ACAID and corneal allograft survival emerged in experiments in which the induction of allergic conjunctivitis or the administration of anti-IL-17A abolished the immune privilege of corneal allografts but had no effect on the induction or expression of ACAID.

CONCLUSIONS

Although orthotopic corneal allografts are strategically located for the induction of ACAID by the sloughing of corneal cells into the AC, the results reported here indicate that the Tregs induced by orthotopic corneal allografts are remarkably different from the Tregs that are induced by AC injection of alloantigen. Although both of these Treg populations promote corneal allograft survival, they display distinctly different phenotypes.

Desiccating stress promotion of Th17 differentiation by ocular surface tissues through a dendritic cell-mediated pathway

PURPOSE

To explore the phenomenon that corneal and conjunctival tissues subjected to desiccating stress (DS) promote Th17 differentiation by stimulating the production of Th17-inducing cytokines through a dendritic cell (DC)-mediated pathway.

METHODS

Experimental dry eye was created by subjecting C57BL/6 mice to desiccating environmental stress. Corneal and conjunctival explants from dry eye or control mice were cocultured with DCs for 24 hours before CD4(+) T cells were added for an additional 4 to 7 days. Expression of Th17-associated genes in the cornea, conjunctiva, DCs, and CD4(+) T cells was evaluated by real-time PCR. Cytokine concentrations in coculture supernatants were measured by immunobead assay. IL-17-producing T cells were identified by ELISPOT bioassay.

RESULTS

Higher levels of IL-17A, TGF-beta1, TGF-beta2, IL-6, IL-23, and IL-1beta mRNA transcripts and TGF-beta1, IL-6, and IL-1beta protein were observed in corneal epithelium and conjunctiva from dry eye mice. DCs cocultured with epithelial explants from dry eye mice for 2 days produced higher levels of TGF-beta1, IL-6, IL-23, and IL-1beta mRNA transcripts and of TGF-beta1, IL-6, and IL-1beta protein. CD4(+) T cells cocultured with DCs and epithelial explants from dry eye mice expressed increased levels of IL-17A, IL-17F, IL-22, CCL-20, and retinoic acid receptor-related orphan receptor-gammat mRNA transcripts and increased IL-17A protein and number of IL-17-producing T cells (Th17 cells).

CONCLUSIONS

These findings demonstrate that DS creates an environment on the ocular surface that stimulates the production of Th17-inducing cytokines by corneal and conjunctival epithelia that promote Th17 differentiation through a dendritic cell-mediated pathway.

Expression of Tim-3 Is Transiently Increased before Development of Anterior Chamber-Associated Immune Deviation

PURPOSE

To assess the expression of T-cell immunoglobulin- and mucin-domain-containing molecule 3 (Tim-3) in the spleens of BALB/c mice undergoing anterior chamber-associated immune deviation (ACAID).

METHODS

ACAID was generated after intracameral (i.c.) injection of ovalbumin (OVA) into BALB/c mice and evaluated by assessing the delayed-type hypersensitivity (DTH) response following a subsequent subcutaneous (s.c.) injection of OVA emulsified in complete Freund's adjuvant (CFA) on Days 0, 3, 7, 14, 21 and 28. Tim-3 mRNA levels were detected using real-time RT-PCR, and the frequency of CD4+Tim-3+ T cells in splenocytes as well as the coexpression of Tim-3 with CD25 on CD4+ T cells were assessed by flow cytometry.

RESULTS

A significantly suppressed DTH response was observed on Days 7, 14, 21, and 28, but not on Days 0 and 3 during the development of ACAID. The levels of Tim-3 mRNA and the frequency of CD4+CD25+Tim-3+ T cells in the splenocytes reached a peak on Day 3, declined on Day 7, and returned to basal levels thereafter.

CONCLUSIONS

A transient upregulation of Tim-3 expression was observed in the early stage of ACAID, suggesting its possible involvement in the development of ACAID.

Immunoregulation on the ocular surface: 2nd Cullen Symposium

A one-day symposium with 20 invited participants was held to review current knowledge regarding immunoregulation in the ocular surface and cornea. The program consisted of 11 lectures on various aspects of ocular and systemic immunoregulation, followed by a group discussion to formulate regulatory pathways. The ocular surface and its secondary lymphoid tissues contain numerous components of the innate and adaptive immune systems, which modulate the immune response to suppress or prevent excessive damaging immune reactions. These include factors that regulate induction of the immune response (afferent loop), as well as effector cells and soluble factors (efferent loop). The ocular surface is an immunologically active mucosal site that contains numerous mechanisms to regulate the immune response to prevent tissue destruction and vision loss.

Immune regulation and the eye

The eye is an immune privileged site that is styled to maintain the visual pathway while at the same time provide defense against invading organisms. The eye does this by selecting immune responses that function in the absence of inflammation. Immune regulation by the eye takes the form of several active processes including a local immunosuppressive environment, the contribution of soluble factors, Fas-FasL-induced apoptosis and unique suppressive mechanisms used by pigment epithelial cells in the eye. These processes are so effective that antigens encountered in the eye result in specific systemic tolerization; a phenomenon akin to gut-induced oral tolerance. This review discusses the cellular and molecular basis of tolerance induction by the eye and notes the parallels to gut-induced peripheral tolerance.

T cell sensitivity to TGF-beta is required for the effector function but not the generation of splenic CD8+ regulatory T cells induced via the injection of antigen into the anterior chamber

The introduction of antigen into the anterior chamber (AC) of the eye induces the production of antigen-specific splenic CD8⁺ regulatory T cells (AC-SPL cells) that suppress a delayed-type hypersensitivity (DTH) reaction in immunized mice. Because the generation of these regulatory T cells is also induced by exposure to transforming growth factor (TGF)-β and antigen or F4/80⁺ cells exposed to TGF-β and antigen in vitro, we investigated (i) whether these cells are produced in dominant negative receptor for transforming growth factor β receptor type II (dnTGFβRII) or Cbl-b^−/− mice whose T cells are resistant to TGF-β, (ii) whether DTH is suppressed by wild type (WT) CD8⁺ AC-SPL cells in Cbl-b^−/− and dnTGFβRII mice and (iii) the effect of antibodies to TGF-β on the suppression of DTH by CD8⁺ AC-SPL cells. DnTGFβRII immunized and Cbl-b^−/− mice produced splenic CD8⁺ regulatory cells after the intracameral injection of antigen and immunization. The suppression of a DTH reaction by CD8⁺ AC-SPL cells in WT mice was blocked by the local inclusion of antibodies to TGF-β when WT splenic CD8⁺ AC-SPL cells were injected into the DTH reaction site. Moreover, the DTH reaction in immunized dnTGFβRII and Cbl-b^−/− mice was not suppressed by the transfer of WT CD8⁺ AC-SPL cells to the site challenged with antigen. In aggregate, these observations suggest that T cell sensitivity to TGF-β is not an obligate requirement for the in vivo induction of CD8⁺ AC-SPL T cells but the suppression of an in vivo DTH reaction by CD8⁺ AC-SPL cells is dependent on TGF-β.

The suppression of hypersensitivity by ocular-induced CD8(+) T cells requires compatibility in the Qa-1 haplotype

The injection of antigen into the anterior chamber (AC, intracameral injection)2 of a murine eye induces the generation of splenic CD8⁺ regulatory T cells (AC-SPL cells) that effect the antigen-specific suppression of a Delayed-Type Hypersensitivity (DTH) reaction. Here we show (i) for the first time that the local antigen-specific suppression of DTH-induced swelling in immunized mice by either an intracameral injection of antigen or by the direct injection of CD8⁺ AC-SPL cells into an antigen-challenged site is associated with an absence of infiltrated mononuclear cells, (ii) the local antigen-specific suppression of the DTH reaction by CD8⁺ AC-SPL cells requires compatibility between the Qa-1 but not H2 antigen haplotype of the immunized recipient and the injected AC-SPL regulatory T cells, (iii) The suppression of the DTH reaction by CD8⁺ AC-SPL cells requires the expression of Qa-1 but not H2 antigens and is not due to bystander suppression.

Implication for the CD94/NKG2A-Qa-1 system in the generation and function of ocular-induced splenic CD8+ regulatory T cells

The injection of antigen into the anterior chamber (AC) induces the production of antigen-specific splenic CD8+ regulatory T cells (Tregs) /suppressor T cells that perform the local suppression of delayed-type hypersensitivity (DTH) responses. Because CD94/NKG2A-Qa-1-dependent interactions have been implicated in CD8+ Treg-mediated immune suppression and DBA/2J mice are deficient in CD94/NKG2R, we have utilized these mice to test the hypothesis that the CD94/NKG2A-Qa-1 system is essential to the induction and immunosuppressive function of CD8+ Tregs in anterior chamber-associated immune deviation (ACAID). We show that: (i) neither ACAID-mediated suppression of DTH to ovalbumin nor splenic Tregs/suppressor T cells was induced in DBA/2J mice that received an injection of antigen into the AC; (ii) splenic CD8+ Tregs from ACAID-induced DBA/2NCr mice suppressed the initiation of DTH when transferred to DBA/2J mice; (iii) following injection of antigen into the AC, intravenous administration of splenocytes or Peripheral Blood Mononuclear Cells (PBMC) isolated from DBA/2NCr but not from DBA/2J mice transferred suppression of DTH to DBA/2NCr mice; (iv) antibodies to CD94/NKG2A reduced the ACAID CD8+ T cell-mediated suppression of DTH and (v) The deficiency of such immune regulation in DBA/2J mice also correlated with a decreased number of Qa-1(b+) B cells, F4/80+ cells, a deficient number of CD94/NKG2AR and Qa-1 tetramer binding by CD8+ T cells. These results demonstrate that defective ACAID in DBA/2J mice involves multiple regulatory lesions resulting in a lack of induction of a CD8+ Treg response and possibly defective CD94/NKG2A-dependent suppression of peripheral cell-mediated immunity.

Mechanisms of immune privilege in the anterior segment of the eye: what we learn from corneal transplantation

The eye, like the brain and reproductive organs, possesses inherent immune privilege, and inflammation is self-regulated so as to preserve the organ functions. Studies over the past 30 years have provided insights of the multiple mechanisms of immune privilege. At present, three major lines of thought prevail regarding the molecular mechanisms of immune privilege in the eye: there are (1) anatomical, cellular, and molecular barriers in the eye; (2) eye-derived immunological tolerance, the so-called anterior chamber-associated immune deviation; and (3) immune suppressive intraocular microenvironment. In this review, the mechanisms of immune privilege that have been learned from ocular inflammation animal models, especially corneal transplantation, are described. Roles of new B7 family molecules on local immune regulation within the cornea are also introduced.

Emerging concepts in CD8(+) T regulatory cells

CD8(+) T regulatory cells (T regs) are elicited by unique antigen presenting cells during viral infections, by manipulation of co-stimulatory molecules, or in the development of tumors. CD8(+) T regs display antigen-specificity, which is most exquisitely manifested by the HLA-E-restricted cytolytic CD8(+) T regs in MS. There is evidence that some CD8(+) T regs also express organ specificity. In many cases, IFN-gamma is required for either the induction or expression of CD8(+) T regs. CD8(+) T regs can produce suppression directly by killing immune cells or indirectly by co-opting other cells to elaborate end-stage suppressive molecules such as TGF-beta, IL-10, and indoleamine dioxygenase (IDO).

A penetrating ocular injury can affect the induction of anterior chamber-associated immune deviation

PURPOSE

To determine the effect of penetrating ocular injury on the induction of anterior chamber-associated immune deviation (ACAID).

METHODS

An injection of 5 mul ovalbumin (OVA, 20 mg/ml) into the anterior chamber (AC) of female BALB/c mice was performed to induce ACAID. A penetrating ocular injury was induced via the limbus on OVA-inoculated eyes at 24 h, 48 h, 72 h, and 120 h following AC injection. The mice receiving an OVA inoculation without the ocular injury served as the AC-injection group. Delayed type hypersensitivity (DTH) was examined to evaluate the induction of ACAID. The levels of transforming growth factor (TGF)-beta1, interleukin (IL)-10, and interferon (IFN)-gamma produced by splenocytes were detected by enzyme-linked immunosorbent assays (ELISA). The frequency of CD4(+)CD25(+)Foxp3(+)T cells in the splenocytes was detected by flow cytometry.

RESULTS

A significantly decreased DTH response was observed in the AC-injection group as well as in mice that received a penetrating injury at 72 h and 120 h following AC-injection of OVA. The levels of TGF-beta1 and IL-10 produced by splenocytes of mice in the AC-injection group and in the 72-h and 120-h group were significant higher than those in the 24-h and 48-h group. However, the levels of IFN-gamma produced by splenocytes of the AC-injection group and the 72-h and 120-h group were significantly lower than those in the 24-h and 48-h group. An increased frequency of CD4(+)CD25(+)Foxp3(+)T cells was found in the AC-injection group and the 72-h and 120-h group.

CONCLUSIONS

Penetrating ocular injury preformed shortly (24 h-48 h) after an AC injection of an antigen was able to abrogate ACAID and was associated with a decreased production of TGF-beta1 and IL-10, an increased production of IFN-gamma, and a decreased expression of CD4(+)CD25(+)Foxp3(+)T cells.

Dose dependence of oral tolerance to nickel

The dose dependence of oral nickel tolerance was analyzed by comparing three different subsets of C57BL/6 mice: Ni(very low) mice were reared in a nickel-reduced environment, Ni(low) and Ni(high) mice were reared in a stainless steel-containing environment and the latter received oral NiCl(2) (10 mM). In spleen and feces, Ni(very low) mice exhibit significantly lower nickel concentrations than Ni(low) and Ni(high) mice. In contrast to Ni(very low) mice that can be sensitized with a single intradermal administration of NiCl(2) alone, Ni(low) mice can only be sensitized in the presence of an adjuvant and Ni(high) mice cannot be sensitized at all. This dose-dependent resistance to nickel sensitization (i.e. Ni(high) > Ni(low) > Ni(very low)) correlates with differences in the number and type of nickel-specific T regulatory (Treg) cells. Adoptive transfer studies into Ni(very low) recipients showed that Ni(very low) mice completely lack specific Treg cells whereas Ni(low) and Ni(high) mice harbor them, albeit their numbers and/or suppressive strength are much higher in Ni(high) than Ni(low) mice. The principal Treg subset in Ni(low) mice consists of CD4(+)CD25(+) cells, among which CD4(+)CD25(+)alpha(E)beta(7)(+) cells are the most effective. In Ni(high) mice, CD4(+)CD25(+) Treg cells co-exist with an ensemble of CD8(+) Treg and CD4(+)CD25(-) suppressor-inducer cells.

Transforming growth factor beta-producing Foxp3(+)CD8(+)CD25(+) T cells induced by iris pigment epithelial cells display regulatory phenotype and acquire regulatory functions

The ocular pigment epithelial (PE) cells convert T cells into T regulators (Tregs) in vitro. The PE-induced Tregs fully suppress activation of bystander responder T cells. Iris PE (IPE) cells from anterior segment in the eye produce costimulatory molecules and transforming growth factor beta (TGFbeta) that is delivered to CD8(+) Tregs. We have now examined whether T cells exposed to cultured IPE express CD25 and Foxp3, and to determine if the CD25(+) IPE-exposed T cells display regulatory functions in vitro. We have found that cultured B7-2(+) IPE converted CTLA-4(+) T cells into CD25(+) Tregs that suppress the activation of bystander T cells. The CD8(+) IPE-induced Tregs constitutively expressed CD25. Through TGFbeta-TGFbeta receptor interactions, the IPE converted these T cells into CD25(+) Tregs that express Foxp3 transcripts. The CD8(+) IPE-induced Tregs produced immunoregulatory cytokines, e.g., interleukin-10 and TGFbeta. In addition, IPE-exposed T cells that downregulated Foxp3 mRNA failed to acquire the regulatory function. In conclusion, ocular pigment epithelial cells convert CD8(+) T cells into CD25(+) Tregs by inducing the transcription factor Foxp3. Thus, T cells that encounter ocular parenchymal cells participate in the T-cell suppression.

Expansion of B cells is necessary for the induction of T-cell tolerance elicited through the anterior chamber of the eye

Antigens injected into the anterior chamber (AC) of the eye induce a form of peripheral immune tolerance termed anterior chamber-associated immune deviation (ACAID). ACAID is initiated by F4/80+ ocular antigen-presenting cells (APC) which capture ocular antigens and migrate to the spleen where they transfer antigenic peptides to B cells, which act as ancillary APC for the induction of T-regulatory cells (T(reg)) that inhibit delayed-type hypersensitivity (DTH) responses. Here we show that ocular-like APC induce the expansion of tolerogenic splenic B cells. Furthermore, we show that inhibiting B-cell proliferation with either mitomycin-c or gamma-irradiation abolishes the ability of B cells to induce T(reg). To our knowledge, this is the first study to report that B-cell proliferation is needed for B-cell-induced T-cell tolerance.

CD4+CD25+Tregs express an increased LAG-3 and CTLA-4 in anterior chamber-associated immune deviation

BACKGROUND

Regulatory CD4(+)CD25(+) T cells have been proven to be essential for maintenance of peripheral tolerance and autoimmune diseases. ACAID is a model of immune privilege in the eye. Relatively little is known about the role and phenotype of these regulatory CD4(+)CD25(+) T cells in ACAID.

METHODS

Injection of OVA into the anterior chamber of BALB/C mice was performed to induce ACAID. The frequencies of splenic CD4(+)CD25(+) Tregs and the expression of CTLA-4 and LAG-3 on these cells were determined by flow cytometry. Magnetic cell sorting was used to isolate CD4(+)CD25(+) and CD4(+)CD25(-)T cells. The function of CD4(+)CD25(+) T cells was detected by in vitro immunosuppression assays and in vivo adoptive transfer.

RESULTS

ACAID was successfully induced following an i.c. injection of OVA. Frequencies of CD4(+)CD25(+) and Tregs were significantly increased in ACAID mice as compared to those in controls. The CD4(+)CD25(+) T cells stimulated with OVA in ACAID mice showed a stronger suppressive ability in vitro than those seen in non-ACAID mice. CD4(+)CD25(+) T cells from ACAID mice, but not from non-ACAID mice, were able to suppress DTH responses in an antigen-specific manner following adoptive transfer. The frequencies of CTLA-4 or LAG-3 on Tregs in ACAID mice were higher as compared with those in naive mice.

CONCLUSION

Splenic CD4(+)CD25(+)Foxp3(+)T cells expressing CTLA4 and LAG3 play an important role in the induction of ACAID.

Gammadelta T cells promote anterior chamber-associated immune deviation and immune privilege through their production of IL-10

Anterior chamber-associated immune deviation (ACAID) is a form of peripheral tolerance that is induced by introducing Ags into the anterior chamber (AC) of the eye, and is maintained by Ag-specific regulatory T cells (Tregs). ACAID regulates harmful immune responses that can lead to irreparable injury to innocent bystander cells that are incapable of regeneration. This form of immune privilege in the eye is mediated through Tregs and is a product of complex cellular interactions. These involve F4/80+ ocular APCs, B cells, NKT cells, CD4+CD25+ Tregs, and CD8+ Tregs. gammadelta T cells are crucial for the generation of ACAID and for corneal allograft survival. However, the functions of gammadelta T cells in ACAID are unknown. Several hypotheses were proposed for determining the functions of gammadelta T cells in ACAID. The results indicate that gammadelta T cells do not cause direct suppression of delayed-type hypersensitivity nor do they act as tolerogenic APCs. In contrast, gammadelta T cells were shown to secrete IL-10 and facilitate the generation of ACAID Tregs. Moreover, the contribution of gammadelta T cells ACAID generation could be replaced by adding exogenous recombinant mouse IL-10 to ACAID spleen cell cultures lacking gammadelta T cells.

Immune privilege induced by regulatory T cells in transplantation tolerance

Immune privilege was originally believed to be associated with particular organs, such as the testes, brain, the anterior chamber of the eye, and the placenta, which need to be protected from any excessive inflammatory activity. It is now becoming clear, however, that immune privilege can be acquired locally in many different tissues in response to inflammation, but particularly due to the action of regulatory T cells (Tregs) induced by the deliberate therapeutic manipulation of the immune system toward tolerance. In this review, we consider the interplay between Tregs, dendritic cells, and the graft itself and the resulting local protective mechanisms that are coordinated to maintain the tolerant state. We discuss how both anti-inflammatory cytokines and negative costimulatory interactions can elicit a number of interrelated mechanisms to regulate both T-cell and antigen-presenting cell activity, for example, by catabolism of the amino acids tryptophan and arginine and the induction of hemoxygenase and carbon monoxide. The induction of local immune privilege has implications for the design of therapeutic regimens and the monitoring of the tolerant status of patients being weaned off immunosuppression.

Indoleamine 2,3-dioxygenase (IDO) is involved in promoting the development of anterior chamber-associated immune deviation

Indoleamine 2,3-dioxygenase (IDO), a rate-limiting enzyme in the tryptophan catabolism, has been shown to play an important role in various forms of immune tolerance. Since anterior chamber associated immune deviation (ACAID) is a systemic immune tolerance elicited by introducing exogenous antigens into the anterior chamber of the eye, we investigated the expression and function of IDO in the development of this ocular tolerance. ACAID was induced in BALB/c mice by an intracameral injection of 50mug ovalbumin (OVA). The IDO expression in the splenocytes during ACAID was determined by fluorescent quantitative real-time PCR, Western blot analysis and immunohistochemistry. The development of ACAID was evaluated by the delayed-type hypersensitivity (DTH) response after intraperitoneal injection of an IDO inhibitor 1-methyl-dl-tryptophan (1-MT). Secretion of IFN-gamma and IL-4 by splenocytes and lymph node cells from the mice treated with or without 1-MT were also evaluated using intracellular cytokine staining. Our results showed that the IDO expression was significantly increased at both mRNA and protein levels following OVA intracameral injection. Inhibition of IDO with 1-MT prevented the development of ACAID, which was indicated by the re-appearance of the OVA-specific DTH response. IL-4 was significantly reduced and IFN-gamma was partially recovered after the treatment of 1-MT. Our study reveal that IDO is up-regulated during ACAID and IDO inhibitor prevents ACAID generation, suggesting that IDO is involved in the development of this immune tolerance.

Peripheral tolerance via the anterior chamber of the eye: role of B cells in MHC class I and II antigen presentation

Ags introduced into the anterior chamber (AC) of the eye induce a form of peripheral immune tolerance termed AC-associated immune deviation (ACAID). ACAID mitigates ocular autoimmune diseases and promotes corneal allograft survival. Ags injected into the AC are processed by F4/80(+) APCs, which migrate to the thymus and spleen. In the spleen, ocular APCs induce the development of Ag-specific B cells that act as ancillary APCs and are required for ACAID induction. In this study, we show that ocular-like APCs elicit the generation of Ag-specific splenic B cells that induce ACAID. However, direct cell contact between ocular-like APCs and splenic B cells is not necessary for the induction of ACAID B cells. Peripheral tolerance produced by ACAID requires the participation of ACAID B cells, which induce the generation of both CD4(+) regulatory T cells (Tregs) and CD8(+) Tregs. Using in vitro and in vivo models of ACAID, we demonstrate that ACAID B cells must express both MHC class I and II molecules for the generation of Tregs. These results suggest that peripheral tolerance induced through the eye requires Ag-presenting B cells that simultaneously present Ags on both MHC class I and II molecules.

Inhibition of lymphokine-activated killer cells generation in vitro by soluble factors released from mixed human tumor and peripheral blood mononuclear adherent cells culture

BACKGROUND

A variety of molecules produced by both tumor cells and normal cells reduce the activity of lymphokine-activated killer (LAK) cells. We tested the possible cross-regulation of mel-624 melanoma cells and adherent peripheral blood mononuclear cells (PBMCs) in affecting LAK cell activity.

METHODS

PBMC adherent cells were cultured together with mel-624 melanoma cells. Supernatant was transferred to a 4-day LAK cells generation culture consisted of PBMC nonadherent cells and interleukin-2. LAK cytotoxic activity was tested in a 4-hour assay against Daudi tumor cells prelabeled with sodium (51)chromate.

RESULTS

The supernatant produced within the first 48 hours of mixed mel-624 melanoma cell and adherent PBMC culture substantially (by 69 percent) reduced the generation of LAK cells, whereas the supernatant from either tumor culture or adherent PBMC culture had no effect. The inhibitory effect was manifested on the generation of LAK cells when autologous nonadherent cells were cultured with 1,000 units/ml IL-2, but there was no effect on mature LAK cell cytotoxic activity. Inhibition of LAK cell generation was partially dependent on protein synthesis and was not mediated by transforming growth factor ss (TGF-ss).

CONCLUSION

Our results point toward the production of soluble, yet unidentified proteins, in mixed tumor-adherent PBMC cultures, which substantially reduced the induction of LAK cells in culture.

Differential roles of CD8+ and CD8- T lymphocytes in corneal allograft rejection in 'high-risk' hosts

We examined the role of perforin and FasL in corneal allograft rejection mediated by CD8+ and CD8 T cells. BALB/c corneas were transplanted orthotopically into vascularized, 'high-risk' graft beds in C57BL/6 mice, perforin knockout mice and FasL-defective gld/gld mice. CD8+ and CD8 T cells were collected following graft rejection and adoptively transferred to SCID mice, which were then challenged with BALB/c corneal allografts. In every case, CD8 T cells could mediate graft rejection when adoptively transferred to SCID mice that received BALB/c corneal allografts. Although CD8+ T cells also mediated graft rejection, the tempo was slower. Moreover, CD8+ T cells collected FasL-defective donors that had rejected corneal allografts, mediated corneal allograft rejection in only 50% of the SCID mice that received the adoptively transferred cells. In some cases, CD8+ T-cell-mediated rejection occurred in the absence of delayed-type hypersensitivity and cytotoxic T-lymphocyte activity, but was associated with CD8+ T-cell-mediated apoptosis of BALB/c corneal cells in vitro. The results demonstrate the redundancy in immune mechanisms of corneal allograft rejection. Either CD8+ or CD8 T cells can produce corneal allograft rejection, however functional FasL is necessary for optimal rejection, even in a high-risk setting.

See no evil, hear no evil, do no evil: the lessons of immune privilege

Immune-mediated inflammation and allograft rejection are greatly reduced in certain organs, a phenomenon called 'immune privilege'. Immune privilege is well developed in three regions of the body: the eye, the brain and the pregnant uterus. Immune-mediated inflammation has devastating consequences in the eye and brain, which have limited capacity for regeneration. Likewise, loss of immune privilege at the maternal-fetal interface culminates in abortion in rodents. However, all three regions share many adaptations that restrict the induction and expression of immune-mediated inflammation. A growing body of evidence from rodent studies suggests that a breakdown in immune privilege contributes to multiple sclerosis, uveitis, corneal allograft rejection and possibly even immune abortion.

Desiccating Stress Induces T Cell-Mediated Sjögren’s Syndrome-Like Lacrimal Keratoconjunctivitis

Chronic dry eye syndrome affects over 10 million people in the United States; it is associated with inflammation of the lacrimal gland (LG) and in some cases involves T cell infiltration of the conjunctiva. We demonstrate that environmental desiccating stress (DS) elicits T cell-mediated inflammation of the cornea, conjunctiva, and LG, but not other organs in mice. The lacrimal keratoconjunctivitis (LKC) was mediated by CD4(+) T cells, which, when adoptively transferred to T cell-deficient nude mice, produced inflammation in the LG, cornea, and conjunctiva, but not in any other organ. Adoptively transferred CD4(+) T cells produced LKC even though recipients were not exposed to DS. LKC was exacerbated in euthymic mice depleted of CD4(+)CD25(+)forkhead/winged helix transcription factor(+) regulatory T cells. The results suggest that DS exposes shared epitopes in the cornea, conjunctiva, and LG that induce pathogenic CD4(+) T cells that produce LKC, which under normal circumstances is restrained by CD4(+)CD25(+)forkhead/winged helix transcription factor(+) regulatory T cells.

Abnormal anterior chamber associated immune deviation (ACAID) in 129-strain mice

PURPOSE

To characterize anterior chamber immune deviation (ACAID) in 129-strain and mixed 129-strain mice.

METHODS

ACAID was assayed using standard protocols with herpes simplex-1 (HSV-1) and trinitrophenol-hapten-spleen cells (TNP-spleen) in C57B1/6, 129P2, 129X1, and intercrossed strains. Systemic tolerance induction was assayed using an ultraviolet light skin tolerance protocol to 2,-4,6-trinitro-l-chlorobenzene (TNCB).

RESULTS

129X1 and C57Bl/6xl29Xl Fl mice did not show ACAID to HSV-1. C57Bl/6xl29P2 mice did not show ACAID to TNP-spleen. C57Bl/6xl29P2 mice did show normal peripheral immune deviation to TNCB. (C57Bl/6xl29Xl) x C57B1/6 N2 backcrossed mice showed a bimodal ACAID response to HSV-1 suggesting a single dominant allele in the 129X1 background responsible for suppressing ACAID.

CONCLUSION

ACAID to multiple antigens is significantly reduced in 129-strain mice and their outcrossed progeny. Since 129-strain embryonic stem cells are widely used to generate knockout and transgenic mice, care must be taken to extensively backcross resultant strains in order to assess the effect of particular genes on ACAID.

Peripheral generation and function of CD4+CD25+ regulatory T cells

The balance between immunity and tolerance is important to maintain immune homeostasis. Several mechanisms are in place to ensure that the immune response is controlled, such as T cell anergy, apoptosis and immune ignorance. A fourth mechanism of peripheral tolerance is the active suppression by regulatory or suppressor T cells. The existence of suppressor T cells was first described in the early 1970s, but these cells became discredited in the 1980s. The work of Shimon Sakaguchi and others, however, has brought these cells back into the limelight and nowadays research into regulatory/suppressor T cells is a very active field of immunology. Different types of regulatory T cells have been described, including CD4+CD25+ T cells that constitutively express CTLA-4, GITR and Foxp3, TGF-beta producing Th3 cells, IL-10 producing Tr1 cells, and CD8+CD28- T cells. This review will focus on the generation and function of CD4+CD25+ regulatory T cells. CD4+CD25+ regulatory cells were originally described as thymus-derived anergic/suppressive T cells. Recent papers, however, indicate that these cells might also be generated in the periphery. CD4+CD25+ regulatory T cells can be activated by self-antigens and non-self-antigens, and once activated can suppress T cells in an antigen nonspecific manner. Interestingly, the suppressive effects of these cells are not restricted to the adaptive immune system (T and B cells) but can also affect the activation and function of innate immune cells (monocytes, macrophages, dendritic cells). These features make the CD4+CD25+ regulatory T cell subset an interesting target for immunotherapy of chronic inflammatory or autoimmune diseases.