Prevention of diabetes in BB/Wor rats by intrathymic islet injection

Anti-malarial drugs: possible mechanisms of action in autoimmune disease and prospects for drug development

A wide variety of mechanisms of anti-rheumatic action have been proposed for antimalarial agents. The molecular actions of chloroquine have been most thoroughly studied in vitro and in vivo, but it is likely that hydroxychloroquine works by a similar mechanism. Both agents are weak diprotic bases that can pass through the lipid cell membrane and preferentially concentrate in acidic cyto-plasmic vesicles. The resulting slight elevation of pH within these vesicles in macrophages or other antigen-presenting cells may influence the immune response to autoantigens. We hypothesize that anti-malarial agents influence the association of autoantigenic peptides with class II MHC molecules in the compartment for peptide loading and/or the subsequent processing and transport of the peptide-MHC complex to the cell membrane. This model of anti-malarial action provides a method to test additional drugs for their ability to modulate the immune response.

Survival and Function of Syngeneic Rat Islet Grafts Placed within the Thymus versus under the Kidney Capsule

The role of the thymus in the ongoing acquisition of tolerance to self antigens has made it an attractive site for islet transplantation. Several studies have reported survival of rodent islet allografts in the thymus without requiring the long-term use of immunosuppressive agents; however, the degree of glucose homeostasis in the intrathymic islet transplant recipients has not been examined. We transplanted 500, 1000, or 2000 syngeneic islets into the thymus of streptozotocin-induced diabetic Wistar-Furth rats, and compared the metabolic response of these recipients with animals receiving 2000 syngeneic islets under the kidney capsule. Three of four recipients which received 2000 islets under the kidney capsule achieved normoglycemia (≤8.4 mmol/L) within 1 wk and all animals became normoglycemic within 2 wk posttransplantation. In contrast, intrathymic implantation of 2000 islets induced normoglycemia in only one of six recipients during the same time interval, and when this number was reduced to 1000 or 500 islets, none of the recipients (n = 6) normalized within 1 wk posttransplantation. Animals that received an intrathymic transplant were glucose intolerant compared to normal controls and animals with subcapsular islet transplant. Removal of the graft-bearing organs resulted in hyperglycemia in all cases, and examination of the grafts revealed the presence of numerous well-granulated insulin-containing cells in both sites. The cellular insulin content of the subcapsular grafts (67.4 ± 12.1 μg; n = 4) was significantly higher (p ≥0.05) than what was extracted from intrathymic grafts (9.5 ± 1.2 μg from 1000 islets; n = 3 and 20.0 ± 4.6 μg from 2000 islets; n = 3). We conclude that 2000 syngeneic islets implanted either in the thymus or beneath the kidney capsule can normalize hyperglycemia in streptozotocin-diabetic rats; however, normal glucose tolerance was not established in intrathymic islet recipients, suggesting that a higher number of islets may be necessary to achieve normal glucose homeostasis.

Development of the Nonobese Diabetic Mouse and Contribution of Animal Models for Understanding Type 1 Diabetes

In 1974, the discovery of a mouse and a rat that spontaneously developed hyperglycemia led to the development of 2 autoimmune diabetes models: nonobese diabetic (NOD) mouse and Bio-Breeding rat. These models have contributed to our understanding of autoimmune diabetes, provided tools to dissect autoimmune islet damage, and facilitated development of early detection, prevention, and treatment of type 1 diabetes. The genetic characterization, monoclonal antibodies, and congenic strains have made NOD mice especially useful.Although the establishment of the inbred NOD mouse strain was documented by Makino et al (Jikken Dobutsu. 1980;29:1-13), this review will focus on the not-as-well-known history leading to the discovery of a glycosuric female mouse by Yoshihiro Tochino. This discovery was spearheaded by years of effort by Japanese scientists from different disciplines and dedicated animal care personnel and by the support of the Shionogi Pharmaceutical Company, Osaka, Japan. The history is based on the early literature, mostly written in Japanese, and personal communications especially with Dr Tochino, who was involved in diabetes animal model development and who contributed to the release of NOD mice to the international scientific community. This article also reviews the scientific contributions made by the Bio-Breeding rat to autoimmune diabetes.

Resolving the conundrum of islet transplantation by linking metabolic dysregulation, inflammation, and immune regulation

Although type 1 diabetes cannot be prevented or reversed, replacement of insulin production by transplantation of the pancreas or pancreatic islets represents a definitive solution. At present, transplantation can restore euglycemia, but this restoration is short-lived, requires islets from multiple donors, and necessitates lifelong immunosuppression. An emerging paradigm in transplantation and autoimmunity indicates that systemic inflammation contributes to tissue injury while disrupting immune tolerance. We identify multiple barriers to successful islet transplantation, each of which either contributes to the inflammatory state or is augmented by it. To optimize islet transplantation for diabetes reversal, we suggest that targeting these interacting barriers and the accompanying inflammation may represent an improved approach to achieve successful clinical islet transplantation by enhancing islet survival, regeneration or neogenesis potential, and tolerance induction. Overall, we consider the proinflammatory effects of important technical, immunological, and metabolic barriers including: 1) islet isolation and transplantation, including selection of implantation site; 2) recurrent autoimmunity, alloimmune rejection, and unique features of the autoimmune-prone immune system; and 3) the deranged metabolism of the islet transplant recipient. Consideration of these themes reveals that each is interrelated to and exacerbated by the other and that this connection is mediated by a systemic inflammatory state. This inflammatory state may form the central barrier to successful islet transplantation. Overall, there remains substantial promise in islet transplantation with several avenues of ongoing promising research. This review focuses on interactions between the technical, immunological, and metabolic barriers that must be overcome to optimize the success of this important therapeutic approach.

Achieving antigen-specific tolerance in diabetes: regulating specifically

Autoreactive T cells that escape negative selection in the thymus do not normally cause productive immune responses to self-antigens because of a number of regulatory mechanisms. Studies with anti-CD3 monoclonal antibodies (mAbs) have suggested that immune regulatory mechanisms are induced by drug treatments that are able to stop on-going unwanted immune responses, such as type 1 diabetes, involving induction of regulatory T cells. TGF-beta dependent and independent mechanisms have been described involving CD4(+) as well as CD8(+) T cells. The challenge is now to apply these mechanisms in an antigen-specific manner and so that lasting tolerance to the autoimmune responses can be maintained. We discuss recent data concerning the mechanisms of anti-CD3 mAb treatment and the ways in which our understanding of these mechanisms can be used to develop adoptive immune therapy with regulatory T cells to treat patients with type 1 diabetes or other autoimmune diseases.

Gene and cell therapies for diabetes mellitus: strategies and clinical potential

The last 5 years have witnessed an explosion in the use of genes and cells as biomedicines. While primarily aimed at cancer, gene engineering and cell therapy strategies have additionally been used for Mendelian, neurodegenerative and metabolic disorders. The main focus of gene and cell therapy strategies in metabolism has been diabetes mellitus. This disease is a disorder of glucose homeostasis, either due to the immune-mediated eradication of pancreatic beta cells in the islets of Langerhans (type 1 diabetes) or resulting from insulin resistance and obesity syndromes where the insulin-producing capability of the beta cell is ultimately exhausted in the face of insensitivity to the effects of insulin in the peripheral glucose-utilising tissues (type 2 diabetes). A significant number of animal studies have demonstrated the potential in restoring normoglycaemia by islet transplantation in the context of immunoregulation achieved by gene transfer of immunoregulatory genes to allo- and xenogeneic islets ex vivo. Additionally, gene and cell therapy has also been used to induce tolerance to auto- and alloantigens and to generate the tolerant state in autoimmune rodent animal models of type 1 diabetes or rodent recipients of allogeneic/xenogeneic islet transplants. The achievements of gene and cell therapy in type 2 diabetes are less evident, but seminal studies promise that this modality can be relevant to treat and perhaps prevent the underlying causes of the disease. Here we present an overview of the current status of gene and cell therapy for type 1 and 2 diabetes and we propose potential therapeutic options that could be clinically useful. For type 1 diabetes, transplantation of islets engineered to evade or suppress the recipient immune response is the most readily-available technology today. A number of gene delivery vectors encoding proteins that impair a variety of immune cells have already been examined and proven versatile. More challenging but, nonetheless, just over the horizon are attempts to promote tolerance to islet allografts. Type 2 diabetes will likely require a better understanding of the processes that determine insulin sensitivity in the periphery. Targeting tissues such as muscle and fat with vectors encoding genes whose products promote insulin sensitivity and glucose uptake is an approach that does not carry with it the side-effects often associated with pharmacologic agents currently in use. In the end, progress in vector design, elucidation of antigen-specific immunity and insulin sensitivity will provide the framework for gene drug use in the treatment of type 1 and type 2 diabetes.

Role of T cells in development of chronic pancreatitis in male Wistar Bonn/Kobori rats: effects of tacrolimus

We assessed T cell association with acinar cell apoptosis and a preventive effect of tacrolimus, a T cell suppressant, on the development of chronic pancreatitis in male Wistar Bonn/Kobori rats. At 15 wk, cellular infiltrates composed of F4/80-positive cells (monocytes/macrophages), CD4-positive cells, and CD8-positive cells were extensive in the interlobular connective tissue and parenchyma. In particular, CD8-positive cells invaded pancreatic lobules and formed close associations with acinar cells, some of which demonstrated features of apoptosis. At 20 wk, CD8-positive cells were still abundant in the fibrotic tissue formed with loss of acinar cells. Repeated subcutaneous injection of 0.1 mg x kg(-1) x day(-1) but not 0.025 mg x kg(-1) x day(-1) of tacrolimus for 10 wk completely prevented the occurrence of acinar cell apoptosis, infiltration of CD4- and CD8-positive cells, and development of pancreatitis at the age of 20 wk, but these maneuvers did not recover the decreased plasma corticosterone levels, which may be responsible for the development of disease. We demonstrated that T cells, possibly CD8-positive cells, are involved in inducing apoptosis of acinar cells, raising the possibility that tacrolimus might find clinical application in the treatment of autoimmune chronic pancreatitis.

Pathophysiology of immune-mediated (type 1) diabetes mellitus: potential for immunotherapy

Type 1 diabetes mellitus is a chronic T cell-mediated disease resulting from autoimmune destruction of pancreatic beta-cells. This process leads to progressive and irreversible failure of insulin secretion. Development of the disease involves both genetic and environmental factors. Genetic predisposition is mainly connected with the human leucocyte antigen (HLA) region, which encodes structures responsible for antigen presentation. A comprehensive molecular understanding of the pathogenesis of the disease is essential for the design of rational and well tolerated means of prevention. This paper describes recent experimental and clinical findings and elucidates the current possibilities for immunotherapy of type 1 diabetes. The nature of breakdown of self-tolerance and the mechanisms involved in its recovery are discussed.

Tolerance to islet autoantigens in type 1 diabetes

Tolerance to beta cell autoantigens represents a fragile equilibrium. Autoreactive T cells specific to these autoantigens are present in most normal individuals but are kept under control by a number of peripheral tolerance mechanisms, among which CD4(+) CD25(+) CD62L(+) T cell-mediated regulation probably plays a central role. The equilibrium may be disrupted by inappropriate activation of autoantigen-specific T cells, notably following to local inflammation that enhances the expression of the various molecules contributing to antigen recognition by T cells. Even when T cell activation finally overrides regulation, stimulation of regulatory cells by CD3 antibodies may reset the control of autoimmunity. Other procedures may also lead to disease prevention. These procedures are essentially focused on Th2 cytokines, whether used systemically or produced by Th2 cells after specific stimulation by autoantigens. Protection can also be obtained by NK T cell stimulation. Administration of beta cell antigens or CD3 antibodies is now being tested in clinical trials in prediabetics and/or recently diagnosed diabetes.

BB rat thymocytes cultured in the presence of islets lose their ability to transfer autoimmune diabetes

Thymocytes from adult BB rats can adoptively transfer autoimmune diabetes to athymic recipients. It is also known that the development of BB rat T-cells is recapitulated in adult thymus organ cultures (ATOCs). Based on these observations, we tested the hypothesis that cells capable of the adoptive transfer of diabetes would be present in long-term ATOCs but could be rendered nondiabetogenic by co-culture with appropriate antigens. We observed that cells recovered from adult diabetes-resistant BB (BBDR) rat thymi cultured for up to 14 days can adoptively transfer disease to athymic WAG-rnu/rnu rats treated with polyinosinic: polycytidylic acid and a monoclonal antibody to preclude development of ART2a+ regulatory T-cells. Co-culture of adult BBDR thymi in the presence of BBDR thyrocytes had no effect on the ability of recovered cells to induce diabetes in 70-80% of adoptive recipients. In contrast, co-culture in the presence of islets prevented transfer of diabetes, on average, in >90% of recipients. Fresh islets, frozen islets, and islets pretreated with streptozotocin to deplete insulin were equally effective in preventing diabetes, but none prevented insulitis in nondiabetic recipients. Co-culture in the presence of islets was not associated with detectable alterations in phenotype or in the secretion of gamma-interferon or interleukin-4, either in cultures or in cells recovered from adoptive recipients. We conclude that islet antigens involved in the initiation of autoimmune diabetes in BB rats may be absent or deficient in BB rat thymi. Exposure of ATOCs to exogenous islets may lead to deletion or anergy of diabetogenic T-cells or to the positive selection of regulatory T-cells.

Mechanisms of tolerance induction after intrathymic islet injection: determination of the fate of alloreactive thymocytes

BACKGROUND

Intrathymic (IT) administration of antigen when combined with peripheral T-cell depletion has been shown to induce operational tolerance in a wide range of experimental protocols. IT injection of pancreatic islets has been demonstrated not only to induce tolerance to alloantigen but also to prevent the development of autoimmune beta-cell destruction in models of type I diabetes. However, little is known about the mechanisms involved in tolerance induction after IT islet injection.

METHODS AND RESULTS

A protocol for the induction of tolerance to fully allogeneic (C57BL/10; H2b) peripheral islet allografts was developed in CBA/Ca (H2k) recipients by the IT injection of allogeneic islets combined with depletion of peripheral CD4+ T cells. This protocol was based upon our own data and those of others showing that CD4+ T cells play a critical role in islet allograft rejection. Using this regimen, donor-type peripheral islet allografts survived indefinitely whereas third-party grafts were rejected. To determine the fate of alloreactive thymocytes that recognize donor major histocompatibility complex antigens via the direct pathway, T-cell receptor transgenic mice specific for the major histocompatibility complex class I molecule Kb (BM3 and DES) were used as recipients. IT injection of islets expressing the specific alloantigen Kb resulted in clonal deletion of alloreactive thymocytes in T-cell receptor transgenic recipients. No evidence of clonal inactivation in the residual peripheral alloreactive population was observed in this system.

CONCLUSIONS

IT injection of allogeneic islets and concomitant CD4+ T-cell depletion is able to induce donor-specific unresponsiveness. One mechanism responsible for this unresponsiveness is the clonal deletion of thymocytes that recognize alloantigen via the direct pathway.

Acquired Thymic Tolerance: Role of CTLA4 in the Initiation and Maintenance of Tolerance in a Clinically Relevant Autoimmune Disease Model

Injection of Ag into the thymus of adult animals induces specific systemic tolerance. The mechanisms of acquired thymic tolerance include anergy and the deletion of Ag-specific T cells. Here, we report that anergy to nominal Ag induced via acquired thymic tolerance requires CTL-associated Ag 4 (CTLA4) engagement. The role of CTLA4 in the induction and maintenance of tolerance was then investigated in the murine experimental autoimmune encephalomyelitis model. CTLA4 blockade abrogated the induction but not the maintenance phase of acquired thymic tolerance induced by intrathymic injection of myelin Ags. In addition, CTLA4 blockade had a restricted window of action after priming with Ag, which is consistent with the expression patterns of CTLA4 in vivo. We conclude that: 1) the induction of acquired thymic tolerance requires signaling through CTLA4 and 2) CTLA4 does not appear to be required for the maintenance of acquired thymic tolerance. This is the first report documenting the role of a CTLA4 negative signaling pathway in the induction of tolerance in an autoimmune disease model.

Experimental Goodpasture's syndrome in Wistar-Kyoto rats immunized with alpha3 chain of type IV collagen

BACKGROUND

Glomerulonephritis and lung hemorrhage of autoimmune Goodpasture syndrome develop due to immune reactions against epitope(s) of the non-collagenous (NC1) domain of alpha3-chain of type IV collagen [alpha3(IV) NC1]. Whether thymic mechanisms have a role in the loss of tolerance to the Goodpasture epitope has not been established. We studied the renal and pulmonary effects of immunization with different forms (monomer, dimer, or hexamer) of alpha3(IV) NC1 collagen in Wistar-Kyoto (WKY) rats, and assessed whether the intrathymic inoculation of the antigen may protect against anti-GBM disease.

METHODS

WKY rats were immunized with bovine alpha3(IV) monomer, dimer, or hexamer, or with alpha3(IV) NC1 synthetic peptide. Renal function, kidney and lung immunohistology, and circulating and tissue bound antibodies to type IV collagen chains were analyzed. Effects of intrathymic inoculation of antigen on subsequent disease induction were analyzed in WKY rats given alpha3(IV) NC1 dimer or GBM preparation intrathymically 48 hours before immunization.

RESULTS

Proteinuria, linear IgG deposition in GBM, and crescentic glomerulonephritis developed in WKY rats immunized with alpha3(IV) NC1 dimer or hexamer. Lesions were dose-dependent upon injections of 10 to 100 microgram dimer. The alpha3(IV) NC1 monomer induced less severe proteinuria and no crescents. Pulmonary hemorrhage was detectable in 35% of rats immunized with 25 to 100 microgram alpha3(IV) NC1 dimer; alpha3(IV) synthetic peptide (36 carboxyl terminal) did not induce disease. Rats injected intrathymically with up to 100 microgram alpha3(IV) NC1 dimer or with GBM 48 hours before immunization were not protected against subsequent development of proteinuria and glomerulonephritis.

CONCLUSIONS

These findings document that glomerulonephritis and lung hemorrhage can be elicited in WKY rats by immunization with alpha3(IV) NC1. Failure of the intrathymic inoculation of antigen to prevent disease suggests that immunological tolerance cannot be achieved by this intervention, in contrast to other autoimmune conditions, and may imply independent roles for cellular and humoral nephritogenic pathways in anti-GBM nephritis.

Effect of intrathymic administration of mycobacterial heat shock protein 65 and peptide p277 on the development of diabetes in NOD mice: caution required in vaccination studies

Heat shock protein 65 (hsp65) and a derived peptide, p277, are autoantigens reported in IDDM. I.p. injection of hsp65 reduced diabetes incidence in NOD mice and administration of p277 cured already diabetic mice. Also, intrathymic (i.t.) administration of whole islets or GAD65 prevented diabetes in NOD mice. The aim of this study was to evaluate whether i.t. injection of mycobacterial hsp65 or p277 can prevent diabetes in NOD mice. Three-week-old NOD female mice were injected intrathymically with 50 microg of hsp65 (n=30), 5 microg of p277 (n=30), and PBS (n=29). Diabetes incidence was observed for the following 300 days. Pancreas was then used for histological and immunohistological evaluation. No significant differences in diabetes incidence were observed among the three groups of mice. Interestingly, hsp65-treated mice developed diabetes slightly faster at 177+/-6 days compared to 202+/-8 days (p=0.015) for the p277-treated group and 197+/-7 days (p=0.033) for controls. The insulitis score and average islet size did not differ significantly among the three groups of diabetic mice. Scattered TCR-gamma/delta positive cells were found in the pancreas of all groups of mice. In contrast, a huge infiltrate of TCR-gamma/delta positive cells was detected in four out of eight (50%) p277-diabetic NOD mice. Thus, our data show an earlier onset of diabetes in hsp65-treated mice and no improvement in the incidence with either hsp65 or p277, suggesting that hsp65 acts in a different way from what was reported with GAD65. Caution is advised in future vaccination studies as hsp65 poses a potential danger.

Acquired thymic tolerance and experimental allergic encephalomyelitis in the rat. I. Parameters and analysis of possible mechanisms

Intrathymic injection of guinea pig myelin basic protein (MBP) or the immunodominant, encephalitogenic fragment of MPB, 68-86, without otherwise compromising the peripheral lymphocyte pool in adult LEW rats, dramatically inhibits onset of experimental allergic encephalomyelitis (EAE) caused by the usual peripheral inoculation with MBP in complete Freund's adjuvant. This surprising finding demonstrates that interaction of antigen and one or more components of an intact thymus can down-regulate systemic responses by mature T cells already existing in the peripheral lymphocyte pool. How this happens is not known. In studies designed to explore possible mechanisms: (a) adult thymectomized animals remain susceptible to active EAE, thus EAE cannot be attributed solely to recent thymic emigrants that might be inactivated by antigen deposited in the thymus; (b) heterotopic isografts of injected thymic lobes transfer thymic tolerance to secondary recipients, thus the tolerance effect is dominant over an intact, non-treated thymus; (c) T cells from made thymic tolerant but not immunized donors are less effective in causing EAE following adoptive transfer into, and active immunization of, secondary, irradiated recipients; and (d) animals resistant to active EAE as a consequence of thymic tolerance are fully vulnerable to adoptive EAE caused by already activated MBP-specific T cell subpopulations. These results rule out a possible mechanism previously proposed for acquired thymic tolerance, i. e., that potentially pathogenic T cells traffic to the antigen-injected thymus where they are inactivated or eliminated.

Mechanisms of Acquired Thymic Tolerance In Vivo: Intrathymic Injection of Antigen Induces Apoptosis of Thymocytes and Peripheral T Cell Anergy

Intrathymic injection of Ag induces Ag-specific tolerance in several clinically relevant experimental autoimmune and transplantation models. However, the exact mechanisms of acquired thymic tolerance in vivo remain unclear. We investigated the mechanisms of acquired thymic tolerance in mice that are transgenic for the TCR specific for peptide 323-339 of OVA. Intrathymic injection of OVA leads to apoptosis of thymocytes starting as early as 3 h after injection and persisting up to 7 days. Double positive thymocytes undergo apoptosis earlier than single positive thymocytes, and significantly higher percentages of double positive thymocytes ultimately die as compared with single positive cells. Apoptotic cells show decreased surface expression of CD4. In the periphery, T cells from intrathymically injected animals had suppressed proliferation and IL-2 production to OVA compared with T cells from control Ag-injected mice. We conclude that intrathymic injection of Ag induces apoptosis of immature thymocytes and a subpopulation of mature thymocytes and induces prolonged anergy in peripheral T cells in vivo. Understanding the mechanisms of acquired thymic tolerance may lead to development of novel clinical strategies to prevent autoimmune disease and transplant rejection.

Prevention of experimental autoimmune uveoretinitis by intrathymic S-antigen injection

The objective of this paper was to determine whether intrathymic injection of retinal S-antigen (S-Ag) can prevent experimental autoimmune uveoretinitis (EAU) in Lewis rats. Lewis rats were injected intrathymically with 25-100 micrograms of S-Ag in 100 microliters split between thymic lobes. Controls received vehicle alone (PBS) or 100 micrograms of BSA. Animals were immunized two weeks later with 100 micrograms of S-Ag in CFA with or without pertussis toxin (0.5 micrograms/rat). Clinical ocular disease was confirmed by histopathology. Splenocytes and lymph node cells were assayed, in vitro, for their ability to proliferate in response to various concentrations of S-Ag. Furthermore, attempts were made to adoptively transfer protection to naive rats using spleen cells from intrathymically injected animals and to adoptively transfer EAU to protected rats using Con A activated cells from affected animals. Intrathymic injection of S-Ag reduced the incidence of EAU in animals subsequently immunized with S-Ag and pertussis, and prevented it entirely in rats immunized in the absence of pertussis. Splenic and lymph node cells from intrathymically injected animals showed reduced reactivity to S-Ag compared to controls, suggesting that intrathymic S-Ag injection may have rendered them tolerant to this antigen. We were unable to adoptively transfer protection to naive rats, nor were intrathymically injected rats protected from EAU induced by the adoptive transfer of primed lymph node cells. These data demonstrate that intrathymic S-Ag injection can be an effective method for protection from EAU, apparently through the induction of immunological tolerance and not active suppression. The tolerance was not absolute and could be overcome by increasing the intensity of the antigenic challenge.

In vivo mechanisms of acquired thymic tolerance

Injection of antigen into the thymus of adult animals induces specific systemic tolerance, but the mechanisms of acquired thymic tolerance are not well understood. To investigate these mechanisms we used a model of intrathymic injection of ovalbumin (OVA) in BALB/c mice. We show an antigen-specific decrease in proliferative responses to OVA, as well as a significant decrease in antigen-specific IL-2 secretion and IFN-gamma production by splenocytes and lymph node cells of tolerant mice. Addition of recombinant IL-2 in vitro reversed the defect in IFN-gamma production by cells from OVA-tolerized animals, but did not reverse the proliferation or IL-2 production defects. By using an adoptive transfer system, where a small population of OVA peptide-specific CD4+ TCR transgenic T cells are transferred into syngeneic normal recipients, we show an absence of peripheral antigen-dependent clonal expansion of transferred CD4+ TCR transgenic cells in tolerant mice in vivo. There was an increase in clonotype-positive T cells in the thymus after immunization, confirming that activated T cells circulate through the thymus. Furthermore, thymectomy after intrathymic injection abrogates the effect of acquired thymic tolerance and restores antigen-dependent clonal expansion in vivo. We conclude that intrathymic injection of antigen induces Th1 cell unresponsiveness and prevents the peripheral expansion of antigen-specific CD4(+) T cells in vivo. This is the first demonstration that in acquired thymic tolerance antigen-specific T cells circulate to the thymus where they may be anergized or ultimately deleted.

Expression and immune response to islet antigens following treatment with low doses of streptozotocin in H-2d mice

Insulin dependent diabetes mellitus (IDDM) is likely to be due to the immunologic destruction of the islets of Langerhans. However, the relative importance of expression of a unique set of islet antigens or of differences in immune responses to those antigens in determining susceptibility to auto-immune diabetes is unknown. To a large extent, the reason for this uncertainty is the difficulty in directly identifying islet antigens expressed in vivo. We have studied the relationship between islet antigen expression, immune responsiveness to islet antigens, and the development of diabetes in diabetes induced by multiple low-doses of streptozotocin (STZ) in mice of the H-2d haplotype. We identified the expression of relevant islet antigens by testing the ability of STZ treated islets to induce tolerance to diabetes in C57BL/KsJ mice after intrathymic transplantation. C57BL/KsJ but not BALB/cByJ mice developed hyperglycaemia and insulitis following STZ treatment. Interferon-gamma transcription was detected in intrapancreatic lymphocytes from C57BL/KsJ mice but at lower levels in cell from BALB/cByJ. IL-4 levels were higher in BALB/cByJ than C57BL/KsJ. Intrathymic STZ-treated islets from syngeneic mice induced tolerance to diabetes in C57BL/KsJ mice following transient depletion of mature peripheral T cells, but islets from resistant BALB/cByJ mice did not induce tolerance to disease in C57BL/KsJ mice even though they did cause tolerance to the alloantigens. (C57BL/KsJ x BALB/cByJ)F1 mice developed hyperglycaemia like the susceptible parent following STZ treatment, and islets from these mice induced tolerance to MDSDM when treated with STZ and transplanted intrathymically into C57BL/KsJ. We conclude the expression of islet antigens and the intrapancreatic responses to STZ treated islets differs between mice that are susceptible and resistant to multi-dose streptozotocin induced diabetes mellitus.

Mouse models of autoimmune disease suggest that self-tolerance is maintained by unresponsive autoreactive T cells

Multiple organ-localized autoimmune diseases, such as thyroiditis and gastritis, spontaneously develop in BALB/c nu/nu (nude) mice receiving embryonic rat thymus grafts (TG) under their renal capsules (TG nude mice). When thyroid was grafted into the rat thymus of TG nude mice, development of autoimmune thyroiditis, but not other diseases, was completely prevented. However, when such mice received thyroid antigen plus complete Freund's adjuvant (CFA), severe autoimmune thyroiditis developed, suggesting that some thyroid-specific autoreactive T cells migrate into the periphery, but remain unresponsive. Development of autoimmune diseases, including thyroiditis, in TG nude mice was prevented by a single intraperitoneal injection of splenic CD4+ cells from normal BALB/c mice and also from mice with intrathymic thyroid grafts, indicating that thyroid-specific suppressor T cells are present in normal mice and that such T cells are neither deleted nor inactivated by the intrathymic thyroid grafts, in contrast to autoreactive T cells. Thus clonal deletion in the thymus, and clonal anergy and/or ignorance in the periphery, of autoreactive cells is important to maintain immune tolerance to organ-specific antigen, but CD4 suppressor T cells may play a more important role in tolerance, and the failure of education of this population may cause autoimmune diseases in the TG nude mouse model.

Diabetic animal models

Insulin-dependent (type 1) diabetes is a frequent disease with an incidence of up to about 1%. It requires daily treatment and serious late complications are observed. Good animal models exist for studying diabetes. These can be categorized as animals with spontaneously developing diabetes (BB rats, NOD mice) and as animals with induced diabetes (e.g. by virus). Immunodeficient nude mice have also been widely used. None of the models is perfect, but each has contributed to our present knowledge of the disease. Studies on the pathogenesis of type 1 diabetes are given as an example. Recently, experience with prophylactic treatment of animals in order to prevent diabetes has been applied to humans with promising results.

'Split tolerance' induction by intrathymic injection of acetylcholine receptor in a rat model of autoimmune myasthenia gravis; implications for the design of specific immunotherapies

Experimental autoimmune myasthenia gravis (EAMG) in the Lewis rat, induced by a single injection of acetylcholine receptor (AChR) protein, is a model used to study human myasthenia gravis (MG). The production of anti-AChR antibodies in the animal model and human MG is T cell-dependent, and AChR-specific T cells have been considered as a potential target for specific immunotherapy. Intrathymic injection of antigens induces antigen-specific tolerance in several T cell-mediated autoimmune models. We examined the effect of intrathymic injection of AChR on T cell responses and the production of antibodies to AChR in EAMG rats. Primed lymph node cells from rats receiving intrathymic injection of AChR exhibited reduced proliferation to AChR with marked suppression of interferon-gamma (IFN-gamma) secretion in the antigen-stimulated culture, compared with those of rats injected with PBS. However, neither anti-Narke AChR nor anti-rat AChR antibody production was suppressed or enhanced in intrathymically AChR-injected animals compared with that of animals injected intrathymically with PBS or perithymically with AChR. This 'split tolerance' may be attributable to the suppression of type-1 T helper cells (Th1). Our results suggest that the suppression of Th1 function alone may not be sufficient for the prevention of antibody-mediated autoimmune diseases.

Mechanisms of acquired thymic tolerance in experimental autoimmune encephalomyelitis: thymic dendritic-enriched cells induce specific peripheral T cell unresponsiveness in vivo

Experimental autoimmune encephalomyelitis (EAE), an experimental model for the study of multiple sclerosis, is an autoimmune disease of the central nervous system that can be induced in a number of species by immunization with myelin basic protein (MBP). MBP-reactive CD4+ T cells, predominantly expressing the V beta 8.2 T cell receptor (TCR), migrate from the peripheral lymphoid organs and initiate the inflammatory response in the brain. We have previously shown that a single intrathymic injection of MBP or its major encephalitogenic peptide (p71-90), but not a nonencephalitogenic peptide (p21-40), induces antigen-specific systemic tolerance and inhibits the induction of EAE in Lewis rats. In this study, we investigated the mechanisms of induction and maintenance of acquired thymic tolerance in this model. First, we investigated which thymic cell is responsible for "induction" of systemic tolerance. Thymic dendritic-enriched cells, isolated by plastic adherence, when incubated in vitro with p71-90 and injected intravenously into Lewis rats, were capable of preventing the development of EAE, but his protection was lost in thymectomized recipients. In addition, intravenous injection of thymic dendritic cells isolated from animals that had been previously injected intrathymically with p71-90 but not p21-40 also prevented the development of EAE. Second, to determine the "effector" mechanisms involved in acquired thymic tolerance, we compared TCR expression in the brains of animals with actively induced EAE with TCR expression in animals that received intrathymic injection of p71-90 or p21-40. Using a semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) technique, we found increased expression of CD4 and V beta 8.2 message in brains of immunized animals compared with those of naive animals. In animals intrathymically injected with p71-90 but not p21-40, CD4 and V beta 8.2 transcript levels were significantly reduced compared with immunized controls. Immunohistologic studies of brain tissue and spleens with specific V beta 8.2 and control V beta 10 monoclonal antibodies confirmed these observations in vivo. These findings, taken together with recent data demonstrating that activated T cells circulate through the thymus, suggest that interaction of thymic dendritic cells with specific TCR of activated peripheral T cells can lead to inactivation of these antigen-specific cells and confirm the role of V beta 8.2-expressing T cells in EAE.

Breakdown of self-tolerance by intrathymic injection of a T-cell line inducing autoimmune gastritis in mice

Autoimmune gastritis (AIG) develops spontaneously in BALB/c mice thymectomized 3 days after birth (3d-Tx). We first confirmed our previous observations that CD4+ splenic T cells in AIG mice induced AIG in nu/nu mice, while those in normal mice suppressed the development of the disease. In addition, we found that a quantitative balance between these effector (Te) and suppressor (Ts) T cells determined either onset or prevention of the disease. Peripheralization of Ts seemed to begin around 3 days after birth, since the incidence of AIG in mice that underwent Tx 6 days after birth (6d-Tx) decreased markedly, compared with that of 3d-Tx mice; 12% in the former, while 79% in the latter. Notably, Ts existed in the 6d-Tx mice that escaped AIG. We next examined the target specificity of such Ts using syngeneic parietal cells known as autoantigens and two kinds of T-cell lines established from an AIG mouse; one is gastritis inducible in vivo, termed A-II, while another is not, named AC-II. Intrathymic injection of parietal cells into mice 3 days after birth followed by 6d-Tx completely prevented the development of AIG. In contrast, injection of irradiated A-II, but not AC-II cells resulted in AIG in 67% of the mice. No autoimmune oophoritis (AIO) was induced in female mice, implying that the breakdown of tolerance is organ specific. Taken together, peripheral tolerance for organ-specific autoantigens seems to be maintained by CD4+ Ts responding to Te, which induces the disease.

Thymic epithelial defects and predisposition to autoimmune disease in BB rats

We report an association between thymic epithelial defects and predisposition to autoimmunity. Diabetes-prone (DP) BB rats develop spontaneous hyperglycemia and are deficient in T cell subsets expressing the RT6 alloantigen. Diabetes resistant (DR) BB rats become diabetic if depleted of RT6+ T cells. The inciting immune system defects are unknown. We made the following observations: 1) Regions of thymic cortex and medulla devoid of thymic epithelium exist in DP-BB, DR-BB, and Lewis rats, all of which are susceptible to autoimmune disorders. Such defects were absent in eight normal rat strains. 2) Thymic epithelial defects are absent at birth, but present in BB rats at 4 weeks of age. 3) The genetic predisposition to thymic epithelial defects is an autosomal dominant trait. 4) The observation of thymic defects in (DP x WF)F1 rats led to the prediction that such animals, which never develop spontaneous autoimmunity, might be susceptible to its induction. Following depletion of RT6+ T cells we observed diabetes in 91%, and thyroiditis in 43%, of treated F1 animals (n = 23). Pancreatic insulitis was uniformly present. Because thymic epithelium participates in the positive and negative selection of developing thymocytes, we propose that thymic epithelial defects may play an important role in the predisposition of BB rats to autoimmunity.

Immunotherapy of autoimmune disease

T-cell recognition of autoantigens stands as the primary target for immune intervention in autoimmune disease. Experiments in animal models, in combination with a number of clinical trials completed in the last year, have helped to clarify the pathogenesis of various autoimmune diseases and indicate future strategies for immunotherapy.

Acquired tolerance to experimental autoimmune encephalomyelitis by intrathymic injection of myelin basic protein or its major encephalitogenic peptide

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory disease of the central nervous system that can be induced in a number of species by immunization with myelin basic protein (MBP) in adjuvant, and serves as an experimental model for the study of multiple sclerosis. The role of the thymus in acquired tolerance in autoimmune models has not been thoroughly investigated. In this study, we examined the effects of intrathymic injection of MBP or its major encephalitogenic peptide on the course of EAE in Lewis rats. A single intrathymic injection of MBP 48 h pre- but not postimmunization protects animals from actively induced EAE. An intact MBP-primed thymus was required up to 10 d postimmunization, as thymectomy on days 1, 2, and 7 postimmunization abrogated the protective effect, whereas thymectomy on day 10 did not. The proliferative response of primed lymphocytes was significantly reduced in animals that were intrathymically injected with MBP. Protection against clinical EAE was induced by thymic injection of the major encephalitogenic region (residues 71-90) but not a nonencephalitogenic (21-40) MBP epitope. Immunohistologic examination of the brain from rats intrathymically injected with encephalitogenic peptide showed markedly reduced cellular infiltrate and virtual absence of activation and inflammatory cytokines as compared with rats intrathymically injected with the nonencephalitogenic peptide. These results indicate that the thymus may play an active role in acquired systemic immunologic tolerance in T cell-mediated experimental autoimmune diseases. This effect may be mediated by a process of clonal inactivation of autoreactive T cell clones circulating through the thymus.

Effects of intrathymic injection of organ-specific autoantigens, parietal cells, at the neonatal stage on autoreactive effector and suppressor T cell precursors

Thymectomy on day 3 after birth (3d-Tx) induces autoimmune gastritis (AIG) in 81%, and oophoritis (AIO) in 25% of BALB/c mice at the age of 2 to 3 months. Intrathymic, but not intraperitoneal injection of syngeneic parietal cells into sex-matched BALB/c mice within 24 h of birth resulted in almost complete prevention of the development of AIG in these mice in which 3d-Tx was performed. The prevention induced was parietal cell specific, since the development of AIO was not inhibited in female mice. Moreover, the injection of BALB/c liver cells, Mls-matched (BALB/c) and -disparate (DBA/2) B blasts which resulted in V beta 6 T cell deletion, as well as the injection of staphylococcal enterotoxin B failed to prevent the diseases. These findings suggested that recognition of an autoantigen in the thymus is necessary for the induction of tolerance, and that involvement of Mls-1 antigens in the pathogenesis of AIG, as has been suggested previously (Schwartz, R. H., Cell 1989. 57: 1073), was unlikely. T cells that suppress the development of organ-specific autoimmune diseases in 3d-Tx mice seem to maintain the unresponsiveness of autoreactive T cells at the periphery in normal mice. In agreement with our previous observations, we found that intraperitoneal (i.p.) injection of spleen cells from 3-month-old normal mice into 3d-Tx mice on day 10 after birth prevented the development of AIG, whereas spleen cells from age-matched AIG+ (mice with AIG) or AIG- (mice without AIG) 3d-Tx mice failed to do this. This implies that the suppressor cells probably affect the differentiation of effector-precursor to effector. In fact, these suppressor cells did not inhibit the adoptive transfer of AIG to nu/nu BALB/c mice by spleen cells from 3d-Tx mice manifesting AIG. By negative selection using monoclonal antibody and complement, it was confirmed that the phenotype of the suppressor cell was CD4. In contrast to 3d-Tx, 10d-Tx did not induce AIG, indicating the peripheralization of the suppressor cell by that time. On the other hand, intrathymic injection of parietal cells immediately after birth did not affect suppressor cell generation, implying that some T cells, including suppressor cells, escape thymus selection. We postulate that these cells correspond to the precursors of the autoreactive effector T cells and suppressor T cells that are present in normal mice.

Induction of tolerance to autoimmune diabetes with islet antigens

The development of T cell tolerance to self-antigens is imparted principally through negative selection events during thymic ontogeny. However, this tolerance may be limited to antigens that are expressed in the thymus, and additional mechanisms are probably required to regulate autoimmune responses to tissue-specific antigens. Autoimmune diabetes can be induced experimentally by treating susceptible stains of mice with multiple low doses of streptozotocin (STZ). In this report we show that transplantation of isolated islets of Langerhans into the thymuses of adult C57BL/KsJ mice will induce tolerance to the subsequent induction of autoimmune diabetes. This tolerance is tissue specific and thymus dependent. It was not induced by thymic transfer of adrenal tissue or by kidney transfer of islets. Furthermore, depletion of mature T cells was required and the tolerant state was abrogated by the adoptive transfer of normal splenocytes. It is interesting that pretreatment of the islets with STZ enhanced their ability to induce tolerance, and suggests that antigen shedding induced by tissue damage may facilitate transfer of islet antigens to tolerizing cells in the thymus. These findings indicate that thymic tolerance specific for tissue can be stimulated to occur in the presence of atopic tissue-specific intrathymic antigens. Elimination of disease-related T cells in the absence of global immunosuppression represents a novel approach for the prevention of autoimmune disease.