Patricia R. Hutchings

Role of MHC class I expression and CD8+ T cells in the evolution of iodine-induced thyroiditis in NOD-H2h4 and NOD mice

Dietary iodine has long been known to influence the development of human autoimmune thyroid disease. In nonobese diabetic (NOD) and NOD‐H2h4 mice elevated dietary iodine has been shown to induce autoimmune thyroid disease. Immune responses to thyroid antigens can be detected in these mouse strains, including T cell responses in the NOD‐H2h4 mouse to thyroid peroxidase. Cell transfer studies and antibody depletion experiments reveal a requirement for both CD4+ T cells and CD8+ T cells in the development of thyroid autoimmunity. Histological analyses of the thyroids show that following 1 week of iodine administration MHC class I expression is elevated on thyroid follicular cells and CD4+ and CD8+ T cells have begun to infiltrate the gland. Although MHC class II expression on thyroid epithelial cells was also elevated, the tempo of expression was slower and the extent of expression was far less than that for MHC class I. Depletion of CD8+ T cells at early stages of disease induction inhibited not only thyroid infiltration and autoantibody production but also reduced the levels of MHC expression in the thyroid, suggesting that cytokine production by infiltrating lymphocytes was responsible for the increased MHC expression.

An islet-homing NOD CD8+cytotoxic T cell clone recognizes GAD65and causes insulitis

T cells play a central role in the development of diabetes both in man and in the non-obese diabetic (NOD) mouse. Both the CD4(+) and CD8(+) subsets of T cells are required for the normal development of IDDM in NOD mice. Islet reactive CD4(+) T cells play a clear pathogenic role as evidenced from the isolation of diabetogenic CD4(+) T cell clones. CD8(+) T cells seem to be involved in the initiation of diabetes as lack of these cells leads to protection from diabetes. We have isolated a GAD(65) reactive, cytotoxic CD8(+) T cell clone R1 that produces large quantities of IFNgamma and accelerates the onset of insulitis. This clone proliferates and produces IFNgamma in response to GAD(65) presenting APCs and kills GAD(65) presenting targets. Furthermore, it expresses TNFalpha, CD25, CD28, CD44, CD45 and LFA1, but not CD95L This is the first example of a GAD(65)specific CD8(+) T cell clone that accelerates the onset of the insulitis, although it does not appear to accelerate the onset of diabetes.

Comparative Study of the Protective Effect Afforded by Intravenous Administration of Bovine or Ovine Insulin to Young NOD Mice

Soluble bovine or ovine insulin given intravenously to female NOD mice shortly after weaning had a downregulating effect on several autoimmune parameters associated with insulin-dependent diabetes. The titer of spontaneous anti-insulin antibodies was reduced, insulitis was delayed and less severe, and only 25% of treated mice were diabetic at 30 weeks compared with 70% of untreated mice. An interesting paradox occurred in that bovine insulin, although poorly immunogenic in NOD mice and ineffective as a tolerogen for complete Freunds adjuvant–induced cellular and humoral responses to ovine insulin, was nearly as effective as immunogenic ovine insulin in protecting against diabetes and better than ovine insulin at downregulating spontaneous autoantibodies to insulin. Bovine and ovine insulins differ by only one amino acid on the A-chain loop, but whereas modulation of the induced response to ovine insulin appeared to be sheep-specific, modulation of the induced and spontaneous autoimmunity was achieved almost equally well by bovine or ovine insulin. We suggest therefore that modulation of the induced and spontaneous responses are dependent on different T-cell epitopes and that modulation of spontaneous autoimmunity appears to be governed by an epitope common to both insulins.

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.

Effect of MHC Transgene Expression on Spontaneous Insulin Autoantibody Class Switch in Nonobese Diabetic Mice

A study of spontaneous anti-insulin autoantibodies in nonobese diabetic (NOD) mice revealed that when first detected, the antibodies are immunoglobulin M (IgM), but by age 10 weeks, immunoglobulin G (IgG) autoantibodies have appeared in many of these animals. When NOD strains, partially or completely protected from IDDM by the insertion of transgenes in the class II region, were compared, it was found that the switch to IgG autoantibodies was inhibited and the autoantibodies remained IgM indefinitely. We speculate that the switch to IgG may be a marker of events leading to IDDM in NOD mice and an indication that T-cell help has been generated for responses to β-cell antigens. Such help not only directs the development of IgG autoantibodies, but more importantly, allows the emergence of potentially pathogenic T-cell clones that are capable of infiltrating the pancreas and mediating β-cell damage.

Effect of the synthetic immunomodulator, Linomide, on experimental models of thyroiditis

The drug Linomide is an immunomodulator showing marked down‐regulation of several experimental autoimmune diseases. In this study, its effect on three different experimental models of thyroid disease and on spontaneous infiltration of salivary glands (sialoadenitis), was investigated. Although very effective at preventing thyroid infiltrates in mice immunized with mouse thyroglobulin and complete Freund’s adjuvant and in spontaneous models of thyroiditis and sialoadenitis, it completely failed to modify experimental autoimmune thyroiditis (EAT) induced in mice immunized with mouse thyroglobulin and lipopolysaccharide. There was no significant shift in the observed isotypes of anti‐mouse thyroglobulin antibodies and only anti‐mouse thyroglobulin antibodies in the spontaneous model were completely down‐modulated by the drug. One surprising fact to emerge was that Linomide‐treated donor mice, although protected from thyroid lesions themselves, were still able to transfer EAT showing that they must have been effectively primed while being treated with Linomide. It is possible that the drug down modulated EAT by interfering with the trafficking of primed effector cells.

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.