Nicole M. Parish

Cutting Edge: Interactions Through the IL-10 Receptor Regulate Autoimmune Diabetes

BDC2.5/nonobese diabetic (NOD) transgenic mice express a TCR from a diabetogenic T cell clone yet do not spontaneously develop diabetes at high incidence. Evidence exists showing that in the absence of endogenous TCR α-chain rearrangements this transgenic mouse spontaneously develops diabetes and that CTLA-4 negatively regulates diabetes onset. This strongly suggests that onset of diabetes in BDC2.5/NOD mice is governed by T cell regulation. We addressed the mechanism of immune regulation in BDC2.5/NOD mice. We find that activated spleen cells from young, but not old, BDC2.5/NOD mice are able to transfer diabetes to NOD-scid recipients. We have used anti-IL-10R to show that the failure of splenocytes from older mice to transfer diabetes is due to dominant regulation. We furthermore found that diabetes developed following anti-IL-10R treatment of 6-wk old BDC2.5/NOD mice indicating that endogenous IL-10 plays a key role in the regulation of diabetes onset in this transgenic mouse.

Tolerogenic strategies to halt or prevent type 1 diabetes

A variety of therapeutic strategies have been developed to tolerize autoreactive T cells and prevent autoimmune pathology. In terms of type 1 diabetes, prevention strategies can inhibit the priming and expansion of autoreactive T cells; however, a cure for diabetes would require tolerance to be established in the presence of primed effector cells together with replacement of the destroyed β cell mass. Replacement of β cells could be accomplished by transplantation of islets or stem cells or through islet regeneration. We will focus here on tolerogenic strategies that have been used to prevent onset of type 1 diabetes and discuss the potential for a cure.

Nondepleting Anti-CD4 Has an Immediate Action on Diabetogenic Effector Cells, Halting Their Destruction of Pancreatic β Cells

The induction of tolerance in a primed immune system is a major aim for therapy in autoimmunity and transplant rejection. In this paper, we investigate the action of the nondepleting anti-CD4 Ab, YTS 177. Although this Ab is nondepleting, we have demonstrated a direct action in vivo on activated effector cells. We show that the Ab inhibits transfer of insulin-dependent diabetes mellitus by the CD4+ Th1 clone BDC2.5 to nonobese diabetic mice. Furthermore, we show that this Ab acts directly on diabetogenic effector cells because it prevented BDC2.5-induced insulin-dependent diabetes mellitus in nonobese diabetic-scid recipients in the absence of other T cells. The Ab halts the diabetic process even when it is administered after the BDC2.5 cells have infiltrated the pancreas and destruction of islets is already underway. This is accompanied by an immediate decrease in proinflammatory cytokine production with cessation of β cell destruction and disappearance of infiltrating cells from the pancreas, leaving any remaining β cells intact. These data suggest that Abs such as this may be effective not only because they induce regulatory T cells but also because they are able to directly prevent effector cell function.

Tolerance to IDDM Induced by CD4 Antibodies in Nonobese Diabetic Mice is Reversed by Cyclophosphamide

IDDM can be induced in nonobese diabetic (NOD) mice in several ways, including high doses of cyclophosphamide and transfer of diabetic spleen cells to sublethally irradiated recipients. It has previously been established that transferred diabetes can be prevented by treatment with a nondepleting CD4 monoclonal antibody; however, we report herein that cyclophosphamide-induced diabetes also can be prevented using this antibody. The protection induced by CD4 monoclonal antibody to transferred diabetes is maintained for a long period after cessation of antibody treatment. However, cyclophosphamide can abrogate this induced tolerance and we report that this abrogation does not require new T-cells. During the course of the experimental work described, we observed that the thymus had a suppressive effect on the expression of transferred disease. Mice that were depleted of their peripheral T-cells showed a doubling of the time for disease expression if they were euthymic, compared with thymectomized mice.

The regulation of autoimmunity through CD4+ T cells.

Our experiments imply that it is possible to use monoclonal antibody therapy to reestablish self tolerance to self antigens. This can be achieved by using a short course of an nd anti-CD4 antibody thus avoiding the problem of long term immunosuppression. The mechanism by which such a state of self tolerance is achieved remains to be clarified but possible mechanisms include deletion or anergy of autoreactive T cells or some form of suppression mediated through local cytokine production. As this antibody induced state of tolerance can be reversed in the NOD mouse by cyclophospamide deletion cannot be the method by which autoreactivity is prevented. The mixing experiments which have been described in the thyroiditis experiments strongly suggest that anery is not the mechanism. It therefore remains most likely that tolerance induced following administration of nd anti-CD4 is an active process maintained through the production of an inhibitory cytokine. This ability to reprogram the immune system using monoclonal antibodies makes it not beyond the realms of possibility that individuals suffering from IDDM may become tolerant of their beta cell antigens and thus be able to regenerate their own beta cell mass. If this could indeed occur it might mean that a lifetime of insulin injections and the development of the life threatening complications that may accompany a disease like IDDM may be avoided.

Thymus-dependent monoclonal antibody-induced protection from transferred diabetes

It is well established that long‐term protection from insulin‐dependent diabetes mellitus (IDDM) can be afforded to non‐obese diabetic (NOD) mice by a short course of non‐depleting (nd) anti‐CD4 monoclonal antibodies (mAb). Since it is increasingly apparent that the CD8+ T cell plays a prominent role in the development of IDDM, we have investigated the effect of an anti‐CD8 mAb (YTS 105) of the same isotype in both spontaneous and induced IDDM in NOD mice. Treatment with YTS 105 for 3 weeks was able to prevent the transfer of IDDM for a long period, and also substantially reduced spontaneous IDDM in female NOD mice. The role of the thymus in tolerance induction by these antibodies was studied. In the adult transfer model, thymectomized NOD mice, unlike their euthymic counterparts, were not protected long‐term by treatment with YTS 105, and began to become overtly diabetic shortly after treatment. This was also true when the nd anti‐CD4 mAb was used. Protection from spontaneous disease was not affected in the same way by thymectomy. The reasons for the observed effect of the thymus in the transfer model, and the differences between the two models that may explain the contrasting results are discussed.

Both central and peripheral tolerance mechanisms play roles in diabetes prevention in NOD-E transgenic mice

The non-obese diabetic (NOD) mouse spontaneously develops diabetes and is a widely used model of Type 1 Diabetes in humans. The major histocompatibility complex class II plays an important role in governing disease susceptibility in NOD mice. NOD mice express a rare I-A allele, I-Ag7, and do not express I-E molecules. Interestingly, transgenic NOD mice which express I-E (NOD-E) fail to develop diabetes although, the protective mechanism(s) are incompletely understood. Initially, we explored whether diabetes prevention was due to deletion of autoreactive T cells. Through adoptive transfer with depletion of CD25+T cells, we demonstrated that autoreactive T cells were present in the periphery of NOD-E mice. Although, BDC2.5NOD T cells proliferated less in the pancreatic lymph nodes of NOD-E mice, we found that they transferred disease with a similar kinetic in NOD.scid and NOD-E.scid recipients suggesting that there was little difference in peripheral antigen presentation in NOD-E mice. We also found that there were no proportional or functional differences between NOD and NOD-E T regs. Our studies indicate that autoreactive T cells are present within the periphery of NOD-E mice but that these cells are present in low numbers suggesting that peripheral tolerogenic mechanisms are able to prevent them from inducing diabetes.

Characterisation of CD8 monoclonal antibody-induced protection from diabetes in NOD mice

NOD mice can be protected from transferred diabetes for long periods by short-term treatment with CD8 mabs. This protection has previously been shown to be thymus-dependent as thymectomised mice do not show the long-term protection observed in intact mice. In this study we show that the thymus is required only during antibody treatment as its removal thereafter does not affect protection. Recent thymic emigrants (RTEs) are not necessary for long-term tolerance induction and irradiation plays no part as anti-CD8 treatment cannot protect NOD.scid recipients from diabetes development. IL-10 is also shown to play an important role in the anti-CD8 induced protection in intact mice as it is reversed by IL-10R blockade.

Animal models of autoimmune endocrine disease and their uses in developing new methods of intervention.

This review provides basic information concerning the major animal models in use for the study of autoimmune endocrine diseases (AEDs). Although several other models exist which parallel human AEDs such as autoimmune orchitis, most research in this area has centred on animal models of insulin-dependent diabetes mellitus (IDDM) and thyroiditis. These models, between them, appear to exhibit most of the disease manifestations of their human counterparts and thereby permit the study of possible methods of intervention in the disease process. While no one model represents a perfect correlation with the human disease it represents, common characteristics are recognizable between them. For instance, the central role of activated T cells in controlling the disease process. The chapter continues by examining the various ways in which models of autoimmunity, specifically IDDM and experimental allergic thyroiditis (EAT), have been used to investigate the possibility of preventing or arresting autoimmune destruction. Several different approaches are described that illustrate the variety of techniques that have proven both potentially, or in reality, effective and those that have proven less efficacious than first hoped.

Effect of MHC Class II Encoding Transgenes on Autoimmunity in Nonobese Diabetic Mice

Publisher Summary The introduction of major histocompatibility complex (MHC) class II-encoding transgenes into non-obese diabetic (NOD) mice influences the spontaneous development of insulitis and, in some cases, insulin-dependent diabetes mellitus (IDDM). Expression of these transgenes not only affects the immune response to self-antigens but also modifies the responses to exogenous antigens. The mechanism by which H-2A and H-2E transgenes mediate these effects remains to be elucidated and might not be the same for every situation. The availability of T cell lines and clones that cause IDDM when transferred into neonatal NOD mice would enable each mouse line to be analyzed for the in vivo effects of competition between the transgenically encoded H-2 molecule and the endogenous NOD H-2A. This chapter discusses the question of the ability of the transgenic H-2 molecules to induce antigen-specific anergy. The availability of a panel of transfectants expressing the mutated H-2 transgenes facilitates the analysis to be undertaken in vitro.