Modulating autoimmune responses to GAD inhibits disease progression and prolongs islet graft survival in diabetes-prone mice

Involvement of OSP/claudin-11 in oligodendrocyte membrane interactions: role in biology and disease

Oligodendrocyte-specific protein (OSP/claudin-11) is a four transmembrane protein concentrated in central nervous system myelin. Recent evidence has emerged suggesting that OSP/claudin-11 is involved in membrane interactions at tight junctions and with the extracellular matrix. OSP/claudin-11 seems to modulate proliferation and migration of oligodendrocytes presumably through these interactions. Furthermore, evidence is presented implicating OSP/claudin-11 as an autoantigen in the development of autoimmune demyelinating disease.

Prevention of diabetes in the NOD mouse by a Th1 clone specific for a hsp60 peptide

Peptide-based therapies have been shown to be effective in the prevention of diabetes in the NOD mouse. We have been interested in the T cell response elicited by such therapies and have been studying a T cell clone (C3.5) specific for hsp60 AA 437-460, generated following immunization with the hsp60 437-460 peptide. The C3.5 clone was CD4(+), Vbeta8.3 TCR(+), I-A(g7)restricted and of the Th1 type. The injection of this clone into prediabetic NOD mice prevented the adoptive transfer of the disease and suppressed the development of spontaneous diabetes. This effect was reflected in a reduction in the degree and severity of insulitis in mice injected with this clone. In addition, an antibody response was elicited to the C3.5 clone in mice given multiple injections of the clone. The epitope recognized by C3.5 is located in the N-terminus of the hsp60 AA 437-460 peptide, and this clone was unable to recognize the native hsp60 molecule. These data raise questions concerning the mechanism by which peptide-based therapies prevent autoimmune disease.

Stimulation of the developing immune system can prevent autoimmunity

Both genetic and environmental factors contribute to the development of autoimmunity. Animals and humans exposed to natural infections have a reduced rate of autoimmune diseases. There is increasing evidence that immune stimulation prevents autoimmune diseases. Our hypothesis is that the process of the development of pathogenic cells involved in autoimmunity can be modulated by early stimulation of the immune system in autoimmunity prone individuals This allows for the upregulation of cytokines and growth factors that influence the generation of regulatory cells involved in autoimmunity. As we live in a 'cleaner environment' the decreasing chances of natural infection in the general population may contribute to the induction of autoimmunity because the developing immune system is not exposed to stimulation that may be necessary to generate regulatory cells involved in the modulation and prevention of autoimmunity. Immunization with certain vaccines may provide an alternative approach to stimulate the immune system to modulate or prevent the generation of pathogenic cells involved in autoimmunity by induction of regulatory cells.

Mast cell and neuroendocrine cytoplasmic autoantigen(s) detected by monoclonal pANCA antibodies

pANCA is a marker antibody expressed in most patients with ulcerative colitis, and its cognate antigen is potentially an immunologic target in this disease. This study evaluates whether pANCA detects an autoantigen that is expressed in the colonic mucosa. Immunohistochemistry of colon specimens with human pANCA monoclonal antibodies (Fab 5-2 and 5-3) revealed a minor population of immunoreactive mucosal cells bearing a cytoplasmic vesicle antigen. By distribution, morphology, and tryptase expression, these were identified as mast cells. Immunofluorescent analysis revealed similar immunoreactivity of mouse mast cell lines and human KU812. Western analysis of mouse mast cell lines revealed immunoreactive proteins, and these were distinct from previously proposed pANCA antigens (histone H1, HMG 1 and 2, and neutrophil vesicle antigens). Cognate antigen for Fab 5-2 and 5-3 was also expressed in other tissue mast cells, cerebellar neurons, and pancreatic islet cells. These findings identify a novel cytoplasmic autoantigen(s) associated with UC by its presence in colonic mucosa and recognition by a disease-associated marker antibody.

Prevention of autoimmune diabetes by oral administration of syngeneic pancreatic extract to young NOD mice

Oral administration of relevant autoantigens is being considered as a realistic approach for the prevention of several autoimmune diseases. In this study we administered, orally, to young female NOD/Ak mice (diabetes incidence, 40%) and NOD/LtJ mice (diabetes incidence, 70%) whole pancreatic extract on days 19, 20, 21, 22, 23, 26, and 27 and studied its effects on the development of diabetes until day 250. The cumulative incidence of diabetes in both the colonies after pancreatic extract treatment was compared with the incidence after oral administration of syngeneic liver extract or in untreated mice. In the NOD/Ak mice, the incidence of diabetes in the pancreatic extract group was significantly lower (6%; n = 34, p = 0.004) and was delayed compared with 33% in the liver group (n = 34) and 44% in the untreated group (n = 18). Significant protection from diabetes and a delay in its onset also were observed in the NOD/LtJ mice treated with pancreatic extract (16%; n = 19, p = 0.002) compared with those liver extract treated (72%; n = 18) and in untreated mice (60%; n = 22). Pancreatic histology at day 90 from all the study groups showed that the protection from diabetes in the pancreatic-extract group was not associated with reduced insulitis. We speculate that the marked disease protection observed in this study with orally administered pancreatic extract may be associated with the presence of immunoregulatory cells with a predominant Th2 cytokine bias. Our studies may have implications for the prevention of insulin-dependent diabetes mellitus (IDDM) in humans.

Insulin-dependent diabetes mellitus and its animal models

Major questions are still unanswered in the understanding of the pathogenesis of type 1 diabetes, including the important question of the nature of the autoantigen(s) recognised in the development of disease. In the nonobese diabetic mouse model, there is new evidence that insulin plays an important role: not only is it an antigen for pathogenic CD4+ T cells but also it is recognised by highly diabetogenic CD8+ T cells. Further studies using transgenic mice have also highlighted the role of glutamic acid decarboxylase as an autoantigen. It remains to be seen whether one or both of these autoantigens can be used in strategies to prevent human diabetes.

Human insulin B chain but not A chain decreases the rate of diabetes in BB rats

The autoimmune response seen in insulin-dependent diabetes mellitus (IDDM) includes a humoral immune response against human insulin. Early insulin treatment has been used to prevent IDDM in the rodent models of IDDM, and a prevention trial is underway in humans. The metabolic effects of insulin may not be involved in this prevention since, in NOD mice, the use of metabolically inert human insulin B chain was effective. We wished to ascertain whether immunization of diabetes-prone BB/W rats with insulin B chain, A chain, or both could alter the incidence of diabetes. Immunizations began by 30 days of age and the rats were followed until 120 days of age. Only immunization with insulin B chain plus adjuvant was effective in reducing the rate of diabetes. All immunization frequencies were effective, but a significantly lower rate of diabetes was achieved with injections every week. All of the doses tested resulted in significantly lower rates of diabetes. These data confirm in the BB rat model that immunization with insulin B chain in the presence of adjuvant can reduce diabetes incidence. The absence of any metabolic effect of B chain and the requirement for adjuvant suggest that this effect is mediated via modulation of the autoimmune response.

The role of MHC class II molecules in susceptibility to type I diabetes: identification of peptide epitopes and characterization of the T cell repertoire

Susceptibility to type I diabetes is linked to class II MHC alleles in both mouse and man. However, the molecular mechanisms by which MHC molecules mediate disease susceptibility are unknown. To analyze how I-A alleles predispose to, or prevent, the development of type I diabetes, we have chosen, as the first step, to investigate the immune response to an important islet cell protein in diabetes-susceptible and diabetes-resistant mice. MHC class II alleles conferring susceptibility and resistance to diabetes select completely different sets of immunogenic epitopes from the beta islet cell autoantigen glutamic acid decarboxylase 65. Peptide-binding studies, analysis of MHC restriction, and immunization with these peptide epitopes indicate that the two amino acid substitutions within the I-A(beta) chain that distinguish a diabetes-susceptibility from a diabetes-resistance allele are sufficient to alter peptide binding and MHC restriction and may also influence antigen presentation and the selection of the T cell repertoire. The data indicate that the molecular mechanisms for class II-mediated selection of immunodominant epitopes are complex and differ for each individual peptide epitope. Further study of the functional characteristics of the response to these epitopes should provide insight into mechanisms of MHC-mediated diabetes susceptibility.

Pancreatic IL-4 Expression Results in Islet-Reactive Th2 Cells That Inhibit Diabetogenic Lymphocytes in the Nonobese Diabetic Mouse

When immunological tolerance breaks down, autoimmune destruction of insulin-producing β cells in the pancreas can cause insulin-dependent diabetes mellitus. We previously showed that transgenic nonobese diabetic (NOD) mice expressing IL-4 in the pancreas (NOD-IL-4 mice) were protected from insulitis and diabetes. Here we have characterized the avoidance of pathological autoimmunity in these mice. The absence of disease did not result from a lack of T cell priming, because T cells responding to dominant islet Ags were present. These islet Ag-specific T cells displayed a Th2 phenotype, indicating that Th2 responses could account for the observed tolerance. Interestingly, islet Ag-specific Th1 T cells were present and found to be functional, because neutralization of the Th2 effector cytokines IL-4 and IL-10 resulted in diabetes. Histological examination revealed that NOD-IL-4 splenocytes inhibited diabetogenic T cells in cotransfer experiments by limiting insulitis and delaying diabetes. Neutralization of IL-4 in this system abrogated the ability of NOD-IL-4 splenocytes to delay the onset of diabetes. These results indicate that IL-4 expressed in the islets does not prevent the generation of pathogenic islet responses but induces islet Ag-specific Th2 T cells that block the action of diabetogenic T cells in the pancreas.

Synthesis and kinetics of cyclization of MHC class II-derived cyclic peptide vaccine for diabetes

Conformationally constrained cyclic peptides are known to be better vaccines because of their ability to mimic the native structure of a protein against which an immune response is sought. To test the hypothesis of using conformationally constrained, disease-associated, MHC-derived peptides as vaccines for the prevention of type I diabetes, a 22 amino acid nonobese diabetic(NOD) mouse MHC class II-derived synthetic peptide was cyclized by the formation of end-to-end disulfide bonds and used to prevent diabetes and insulitis in NOD mice. The peptide was synthesized by Fmoc chemistry and cyclized using two methods: a commercially available cyclizing resin (Ekathiox) and air oxidation. When a 10 m excess of resin was used, the Ekathiox yielded a substantial amount of cyclic peptide with few or no side reactions. The kinetics of cyclization by air oxidation at different temperatures indicated that increasing both temperature and pH decreased the cyclization time significantly. Air oxidation at pH 10 at 37-55 degrees C yielded the desired product within 2 h.

Type 1 Diabetes

Type 1 (insulin-dependent) diabetes occurs worldwide and can appear at any age. The genetic susceptibility is strongly associated with HLA-DQ and DR on chromosome 6, but genetic factors on other chromosomes such as the insulin gene on chromosome 11 and the cytotoxic T-lymphocyte antigen gene on chromosome 2 may modulate disease risk. Numerous studies further support the view that environmental factors are important. Gestational infections may contribute to initiation, whereas later infections may accelerate islet β-cell autoimmunity. The pathogenesis is strongly related to autoimmunity against the islet β cells. Markers of autoimmunity include autoantibodies against glutamic acid decarboxylase, insulin, and islet cell antigen-2, a tyrosine phosphatase-like protein. Molecular techniques are used to establish reproducible and precise autoantibody assays, which have been subject to worldwide standardization. The diagnostic sensitivity (40–80%) and specificity (99%) of all three autoantibodies for type 1 diabetes are high, and double or triple positivity among first-degree relatives predicts disease. Combined genetic and antibody testing improved prediction in the general population despite the transient nature of these autoantibodies. Classification of diabetes has also been improved by autoantibody testing and may be used in type 2 diabetes to predict secondary failure and insulin requirement. Islet autoantibodies do not seem to be related to late complications but rather to metabolic control, perhaps because the presence of islet cell autoantibodies marks different residual β-cell function. Combined genetic and autoantibody screening permit rational approaches to identify subjects for secondary and tertiary intervention trials.

Induction of Glutamic Acid Decarboxylase 65-Specific Th2 Cells and Suppression of Autoimmune Diabetes at Late Stages of Disease Is Epitope Dependent

Peptide-based immunotherapy is one strategy by which to selectively suppress the T cell-mediated destruction of β cells and treat insulin-dependent diabetes mellitus (IDDM). Here, we investigated whether a panel of T cell epitopes derived from the β cell autoantigen glutamic acid decarboxylase 65 (GAD65) differ in their capacity to induce Th2 cell function in nonobese diabetic (NOD) mice and in turn prevent overt IDDM at different preclinical stages of disease development. The panel consists of GAD65-specific peptides spanning aa 217–236 (p217), 247–265 (p247), 290–309 (p290), and 524–543 (p524). Our studies revealed that all of the peptides effectively prevented insulitis and diabetes when administered to NOD mice before the onset of insulitis. In contrast, only a mixture of p217 and p290 prevented progression of insulitis and overt IDDM in NOD mice exhibiting extensive β cell autoimmunity. Immunization with the GAD65-specific peptides did not block IDDM development in NOD mice deficient in IL-4 expression. These findings demonstrate that GAD65-specific peptide immunotherapy effectively suppresses progression to overt IDDM, requires the production of IL-4, and is dependent on the epitope targeted and the extent of preexisting β cell autoimmunity in the recipient.

Cure of progressive murine leishmaniasis: interleukin 4 dominance is abolished by transient CD4(+) T cell depletion and T helper cell type 1-selective cytokine therapy

Progressive infection with Leishmania major in susceptible BALB/c mice is mediated by interleukin (IL)-4-producing T helper cell type 2 (Th2) CD4(+) T cells that, once established, become resistant to Th1-deviating therapies with recombinant (r)IL-12 and/or neutralizing anti-IL-4 antibodies. We sought to restore protective immunity in advanced leishmaniasis by depletion of Th2-biased CD4(+) populations and by cytokine-directed reconstitution of Th1 cellular responses during lymphocyte recovery. Treatment with cytolytic GK1.5 anti-CD4 mAb alone did not reverse disease in 3 wk-infected BALB/c mice, but GK1.5 combined with anti-IL-4 antibody and intralesional rIL-12 cured cutaneous lesions in 80% of mice and established a Th1-polarized cytokine response to L. major antigen protective against reinfection. The curative effects of GK1.5 were not replaced by cytotoxic anti-CD8 monoclonal antibody 2.43 or nondepleting anti-CD4 mAb YTS177, confirming that depletion of CD4(+) cells was specific and essential for therapeutic effect. Finally, combined CD4(+) depletion and IL-4 neutralization were curative, indicating that neither increased parasite burden nor altered accessory cell function independently biased towards Th2 reconstitution in advanced leishmaniasis. Advanced leishmaniasis can be cured by T cell depletion and cytokine-directed recovery of Th1 cellular responses, suggesting novel interventions for other immune-mediated diseases and identifying distinct roles for CD4(+) T cell and non-T cell in the maintenance of Th2 and Th1 phenotypes.

Transgenes and knockout mutations in animal models of type 1 diabetes and multiple sclerosis

In this article, we will examine the roles of transgenic and knockout animals that aid us in understanding two autoimmune diseases-type 1 (insulin-dependent) diabetes and multiple sclerosis. The first sections will focus on studies in type 1 diabetes to show how genetically altered animals have given insight into the role of various immune cell types, autoantigens, co-stimulatory molecules, cytokines and, finally, the role of various effector pathways in the pathogenesis of diabetes. The second section concentrating on the animal model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), will show how animals that express a T-cell receptor derived from a clone able to cause disease have given insight into the pathogenesis of EAE.

Absence of significant Th2 response in diabetes-prone non-obese diabetic (NOD) mice

Accumulating evidence suggests that Th1 T cells play a pivotal role in the development of autoimmune diabetes. Conversely, promoting a Th2 response inhibits disease progression. However, it has not been determined whether Th2 cells are regulatory T cells that fail at the time of diabetes development in naive non-diabetic NOD mice. Therefore, in order to evaluate cytokine secretion by spleen and islet infiltrating T cells in NOD mice at different stages of the autoimmune process, we developed an ELISPOT assay that detects IL-2, IL-4, and interferon-gamma (IFN-gamma) secretion in vitro at the single-cell level. We showed that, whatever the age considered, IFN-gamma is predominantly secreted, and that no IL-4-secreting cells are detected in the islets of male and female NOD mice. Spleen cells from 8-week-old female NOD mice, which include regulatory suppressor T cells, do not secrete IL-4, either upon presentation of islet cell antigens in vitro, or after transfer in vivo, but do secrete IFN-gamma. IFN-gamma secretion by T cells from diabetic mice results from CD4 but not CD8 T cells in transfer experiments into NOD/severe combined immunodeficient (SCID) recipients. These results suggest that (i) detection of regulatory CD4 T cells in NOD mice is not paralleled by a Th2 response; (ii) beta cell destruction does not depend on a switch from a Th2 to a Th1-type response; and (iii) CD8 T cells do not participate in induction of diabetes by secreting IFN-gamma.

Antigen-based immunotherapy for autoimmune disease: from animal models to humans?

Insights into tolerance and autoimmune processes have led to novel immunotherapeutics for inhibiting autoimmune disease in animal models. However, recent studies question the immune basis of some of these therapeutic strategies and raise concerns about their efficacy and safety. Here, we discuss the feasibility of extending the success of antigen-based immunotherapeutics for T-cell-mediated autoimmune diseases from animal models to humans.

Formiminotransferase cyclodeaminase is an organ-specific autoantigen recognized by sera of patients with autoimmune hepatitis

BACKGROUND & AIMS

Anti-liver cytosol type 1 autoantibodies have been reported in association with anti-liver-kidney microsome type 1 autoantibodies in 30% of patients with autoimmune hepatitis type II. In 10% of cases, anti-liver cytosol type 1 antibodies are the only liver-related circulating autoantibodies. The liver cytosol antigen is a liver-specific 62-kilodalton protein present in the cell as an oligomer of approximately 240 kilodaltons. The aim of this study was to identify the antigen recognized by anti-liver cytosol antibody.

METHODS

To identify the liver cytosol antigen, an anti-liver cytosol type 1-positive serum was used for the screening of a complementary DNA library from HepG2 cells. Double immunodiffusion method was used to show the identity between the cytosolic and the cloned protein.

RESULTS

The sequence of two isolated clones showed 85.2% homology with the formiminotransferase cyclodeaminase (FTCD) enzyme from pig liver. Antibodies purified by affinity with the recombinant protein and sera from mice immunized with FTCD recognized a 62-kilodalton human cytosolic protein when tested by immunoblot. The identity of precipitation lines was found between the cytosolic antigen and FTCD.

CONCLUSIONS

This enzyme is a liver-specific antigen recognized by the sera of patients with autoimmune hepatitis.

Systemic levels of cytokines and GAD-specific autoantibodies isotypes in Chinese IDDM patients

It is not clear if a Th1/Th2 imbalance in Type 1 diabetes (insulin-dependent diabetes mellitus, IDDM) would lead to a particular antigen-specific IgG subclass dominant as had been shown in the mouse model. In new-onset Type 1 diabetics, an autoantibody response to glutamate decarboxylase (GADab) is frequently observed but the GADab subclass repertoire is not well-established. We determined the systemic levels of representative Th1 and Th2 cytokines and the GADab IgG subclass distribution in 41 Chinese IDDM patients of whom 26 were recently diagnosed (< or = 1 year) and 32 had GADab, to ascertain a likely association of antigen-specific antibody isotype and the Th1/Th2 dichotomy. With high-sensitivity ELISA systems that measure sub-picogram cytokine concentrations, 26 of the 41 patients (63.4%) had at least one of the pro-inflammatory Th1 cytokines (TNF-alpha, IFN-gamma and IL-12) detected. Fewer patients (4/41) had the anti-inflammatory Th2 cytokine IL-4 detected. For IL-10, all subjects had measurable quantities but only three diabetics had levels above the upper limit for healthy subjects (n = 20). Grouped according to the profile of detectable cytokines, there were 24 Th1, 2 Th2 and 2 Th0 patterns. GAD-specific IgG1 antibody was more frequently expressed; 22 of 32 GADab[+] patients. The rank order for the GADab subclasses was IgG1 > 4 > 3 > 2; IgG2 was found in 11 GADab[+] patients. Recent-onset diabetics have a similar ranking of the GAD-specific IgG subclasses. In human Type 1 diabetes, a predominance of GAD-specific IgG1 antibody response is observed together with a dominant Th1 cytokine pattern.

Regulatory T cells in the control of autoimmunity: the essential role of transforming growth factor beta and interleukin 4 in the prevention of autoimmune thyroiditis in rats by peripheral CD4(+)CD45RC- cells and CD4(+)CD8(-) thymocytes

Previous studies have shown that induction of autoimmune diabetes by adult thymectomy and split dose irradiation of PVG.RT1(u) rats can be prevented by their reconstitution with peripheral CD4(+)CD45RC-TCR-alpha/beta+RT6(+) cells and CD4(+)CD8(-) thymocytes from normal syngeneic donors. These data provide evidence for the role of regulatory T cells in the prevention of a tissue-specific autoimmune disease but the mode of action of these cells has not been reported previously. In this study, autoimmune thyroiditis was induced in PVG.RT1(c) rats using a similar protocol of thymectomy and irradiation. Although a cell-mediated mechanism has been implicated in the pathogenesis of diabetes in PVG.RT1(u) rats, development of thyroiditis is independent of CD8(+) T cells and is characterized by high titers of immunoglobulin (Ig)G1 antithyroglobulin antibodies, indicating a major humoral component in the pathogenesis of disease. As with autoimmune diabetes in PVG. RT1(u) rats, development of thyroiditis was prevented by the transfer of CD4(+)CD45RC- and CD4(+)CD8(-) thymocytes from normal donors but not by CD4(+)CD45RC+ peripheral T cells. We now show that transforming growth factor (TGF)-beta and interleukin (IL)-4 both play essential roles in the mechanism of this protection since administration of monoclonal antibodies that block the biological activity of either of these cytokines abrogates the protective effect of the donor cells in the recipient rats. The prevention of both diabetes and thyroiditis by CD4(+)CD45RC- peripheral cells and CD4(+)CD8(-) thymocytes therefore does not support the view that the mechanism of regulation involves a switch from a T helper cell type 1 (Th1) to a Th2-like response, but rather relies upon a specific suppression of the autoimmune responses involving TGF-beta and IL-4. The observation that the same two cytokines were implicated in the protective mechanism, whether thymocytes or peripheral cells were used to prevent autoimmunity, strongly suggests that the regulatory cells from both sources act in the same way and that the thymocytes are programmed in the periphery for their protective role. The implications of this result with respect to immunological homeostasis are discussed.

The effect of local production of cytokines in the pathogenesis of insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease mediated by self-reactive T cells that induce inflammation and destruction of pancreatic islet beta cells. A widely held belief is that T helper lymphocytes carrying a type 1 inflammatory phenotype are the major players in generating IDDM. However, recent evidence shows that cytokines belonging to the Th2 pathway can also induce autoimmune diabetes. The expression of cytokines directly within the pancreatic islets of transgenic mice helped to characterize the modulatory effects that Th1 or Th2 cytokines play on T cell-mediated autoimmune responses and diabetogenesis. This review describes the new information that these transgenic models have provided in understanding the exceedingly complex cytokine network and its role in the pathogenesis of IDDM.

Lentivirus-mediated transduction of islet grafts with interleukin 4 results in sustained gene expression and protection from insulitis

Autoimmune destruction of islets in the pancreas leads to the development of insulin-dependent diabetes mellitus (IDDM). Replacement of insulin-producing tissue by transplantation of islets provides a cure to disease but requires immunosuppression or a means of controlling anti-graft immune responses. To promote islet survival we have utilized a local approach by expressing immunoregulatory molecules in islet grafts. The results presented here show that the human immunodeficiency virus (HIV)-based lentiviral vector is capable of stably transducing whole islets. Foreign reporter gene expression was observed both in vitro and in vivo 30 days after transplantation. Grafts containing insulin-positive beta-islet cells expressing foreign protein indicate that transduction does not interfere with glucose regulation. The absence of inflammatory infiltrates in grafts suggests that transduction does not activate the immune system. When islets transduced with an HIV vector expressing IL-4 were transplanted into diabetes-prone mice, animals were protected from autoimmune insulitis and islet destruction. As demonstrated by proliferative and cytokine analysis, protection was consistent with a switching of islet-antigen-specific T cell responses toward a Th2 phenotype. These results suggest that HIV-based lentivirus vectors can efficiently transduce islet cells with genes encoding potentially therapeutic molecules, for possibly managing diabetes.

Deaggregated homologous immunoglobulin-peptide conjugates induce peptide-specific T cell nonresponsiveness in vivo

Previous studies have proven the efficacy of intravenous injection of deaggregated protein as a means of inducing tolerance. In the present study, the immunodominant peptide 70-86 of myelin basic protein (MBP) was covalently linked to either mouse Ig or Lewis rat IgG. Lewis rats immunized with MBP in complete Freund's adjuvant were completely protected from development of experimental allergic encephalomyelitis (EAE) by their injection with as little as 40 microg of peptide conjugate on days 0 and 10 after immunization. Peptide-specific proliferative and cytokine responses by T cells from treated rats in vitro were severely depressed compared with controls, while responses to whole MBP were unaffected. Significantly, injections of 100 microg of peptide conjugate on days 0 and 4 after adoptive transfer of peptide-specific T lines protected rats from passive EAE while a single injection of 100 microg of conjugate at the onset of active EAE prevented any further disease progression. Both results suggest that primed effector cells as well as naive T cells are prone to tolerance induction by this means. The ability to intervene in ongoing immune responses with such specificity may be useful therapeutically in control of autoimmunity or allergic responses to environmental antigens.

Endogenous immune response to glutamic acid decarboxylase (GAD67) in NOD mice is modulated by adjuvant immunotherapy

We have shown that immunization of non-obese diabetic (NOD) mice with adjuvants (CFA or BCG) prevents the onset of diabetes by induction of regulatory cells. Since autoimmune responses to glutamic acid decarboxylase (GAD) are up-regulated in insulin-dependent diabetes mellitus (IDDM), in this study GAD67-specific antibody, T cell proliferation and lymphokine production patterns were analysed in the adjuvant-treated mice to characterize the regulatory mechanisms underlying the protection. We used both spontaneous diabetes and syngeneic islet transplantation models in NOD mice. Protection against spontaneous diabetes and prevention of syngeneic islet graft rejection by CFA or BCG treatment was found to be accompanied by the production of long lasting and high titre anti-GAD67 antibody of IgG1 isotype in the sera. Upon in vitro stimulation with GAD67, draining lymph node and spleen cells from CFA-immunized NOD mice or syngeneic islet-grafted and BCG-protected NOD mice produced much more IL-4, whereas there was no significant change in IFN-gamma production. The strong early T cell proliferative response to GAD67 in CFA or BCG-immunized NOD mice was followed by a low or unresponsiveness state. Taken together, these results suggest a shift in Th1/Th2 balance in the GAD67-specific endogenous immune response to a change in Th2 levels after adjuvant treatment. We postulate that the protective effect of CFA or BCG is due to the diversion of GAD-specific endogenous cellular immune response to a non-pathogenic humoral response.

Attenuation of Inducible Th2 Immunity with Autoimmune Disease Progression

Autoantigen-based immunotherapeutics have been shown to activate regulatory responses capable of inhibiting T cell-mediated autoimmune disease in animal models. However, their efficacy generally declines, as treatment occurs later in the disease process, and their mechanism of action is a matter of intense debate. Here, we report that the early administration of β cell autoantigens (βCAAs) to nonobese diabetic (NOD) mice broadly diverts the natural development of potentially pathogenic Th1-biased autoimmune responses toward the Th2 phenotype through Th2 spreading. With disease progression, there was a steady decline in the ability of βCAA treatment to promote Th2-type cellular and humoral autoimmunity. Late in the disease process, some βCAAs were still able to induce Th2 responses and Th2 spreading (although to a much lesser extent), while other autoantigens were not. This attenuation of inducible Th2 immunity with disease progression is likely to reflect a reduction in the availability of uncommitted autoantigen-reactive precursor T cells. These findings suggest that there are inherent differences in the frequency of βCAA-reactive T cells and that, in advanced stages of autoimmune disease, regulatory responses may be best elicited with target tissue Ags against which large uncommitted T cell pools are still available. Since individuals presenting the first signs of autoimmune disease are likely to already have an advanced disease process, these findings may be useful for the rational design of Ag-based immunotherapeutics.

Widespread expression of an autoantigen-GAD65 transgene does not tolerize non-obese diabetic mice and can exacerbate disease

Glutamic acid decarboxylase (GAD)65 is a pancreatic beta cell autoantigen implicated as a target of T cells that initiate and sustain insulin-dependent diabetes mellitus (IDDM) in humans and in non-obese diabetic (NOD) mice. In an attempt to establish immunological tolerance toward GAD65 in NOD mice, and thereby to test the importance of GAD in IDDM, we generated three lines transgenic for murine GAD65 driven by a major histocompatibility complex class I promoter. However, despite widespread transgene expression in both newborn and adult mice, T cell tolerance was not induced. Mononuclear cell infiltration of the islets (insulitis) and diabetes were at least as bad in transgenic mice as in nontransgenic NOD mice, and in mice with the highest level of GAD65 expression, disease was exacerbated. In contrast, the same transgene introduced into mouse strain, FvB, induced neither insulitis nor diabetes, and T cells were tolerant to GAD. Thus, the failure of NOD mice to develop tolerance toward GAD65 reflects at minimum a basic defect in central tolerance, not seen in animals not predisposed to IDDM. Hence, it may not be possible experimentally to induce full tolerance toward GAD65 in prediabetic individuals. Additionally, the fact that autoimmune infiltration in GAD65 transgenic NOD mice remained largely restricted to the pancreas, indicates that the organ-specificity of autoimmune disease is dictated by tissue-specific factors in addition to those directing autoantigen expression.

Infectious Th1 and Th2 autoimmunity in diabetes-prone mice

In the non-obese diabetic (NOD) mouse, a Th1-biased autoimmune response arises spontaneously against glutamic acid decarboxylase, concurrent with the onset of insulitis. Subsequently, Th1-type autoreactivity spreads intra- and intermolecularly to other beta-cell autoantigens (beta CAAs), suggesting that a spontaneous Th1 cascade underlies disease progression. Induction of Th2 immunity to a single beta CAA results in the spreading of Th2-type T-cell and humoral responses to other beta CAAs in an infectious manner. Thus, both Th1 and Th2 autoimmunity can evolve in amplificatory cascades defined by site-specific, but not antigen-specific, positive feedback circuits. Despite the continued presence of Th1 autoimmunity, the induction of Th2 spreading is associated with active tolerance to beta CAAs and reduced disease incidence. With disease progression there is an attenuation of beta CAA-inducible Th2 spreading, presumably because of a reduced availability of uncommitted beta CAA-reactive precursor T cells. We discuss the implications of these findings for the rational design of antigen-based immunotherapeutics.

Protection from insulin dependent diabetes mellitus afforded by insulin antigens in incomplete Freund's adjuvant depends on route of administration

Several islet antigens have been shown to modify the time of onset and severity of spontaneous insulin dependent diabetes mellitus (IDDM) in NOD (non-obese diabetic) mice. Oral, intravenous and intra-nasal administration of insulin and glutamic acid decarboxylase (GAD) or their derived peptides have all been shown to be effective to differing degrees in reducing the incidence and delaying the onset of diabetes in this mouse model of the disease. Incomplete Freund's Adjuvant (IFA) has also played a key role in tolerance when co-administered with insulin peptides subcutaneously. We show that route of administration may be of crucial importance, since although insulin B chain and the B9-23 peptide given in IFA subcutaneously protected (either partially or completely) from IDDM, when given intraperitoneally they completely failed to modify the disease.

Th1 unresponsiveness can be infectious for unrelated antigens

CD4+ T cells may be assigned a functional status (Th1 or Th2) according to the cytokines they produce including IL-2, IFN-gamma and IL-4. Th1 and Th2 CD4+ T cells deliver different isotype-switching signals to antigen-specific B cells which bias the serum Ig isotypes. The stimulation of Th1 or Th2 responses is influenced by adjuvants and administration of antigen in IFA results in Th1 unresponsiveness as evidenced by: (i) reduced T cell proliferation to antigen; (ii) reduced IFN-gamma production in response to antigen; and (iii) reduced IgG2a isotype antigen-specific antibodies following antigen/CFA challenge. The impact of established human gamma globulin (HGG) specific Th1 unresponsiveness on subsequent immunization with an unrelated antigen, human serum albumin (HSA) in Th1-inducing CFA was then examined. When subsequently challenged with a mixture of HSA and HGG in CFA the HGG-specific Th1 unresponsiveness was infectious and dominant, preventing the induction of a Th1 response to HSA. Reduced T cell proliferation, IFN-gamma production and IgG2a antibody were consequently observed in response to HSA. The HGG-specific Th1 unresponsiveness was not infectious when HGG/CFA and HSA/CFA were administered at separate sites. This demonstrates that antigen-specific Th1 unresponsiveness can be infectious for new, molecularly unrelated antigens and supports studies showing that Th1-mediated autoimmune diseases such as experimental allergic encephalomyelitis (EAE) and diabetes can be ameliorated using antigens molecularly distinct from the disease-inducing immunogen.

Primary γδ Cell Clones Can Be Defined Phenotypically and Functionally as Th1/Th2 Cells and Illustrate the Association of CD4 with Th2 Differentiation

The division of CD4+ αβ T cells into Th1 and Th2 subsets has become an established and important paradigm. The respective activities of these subsets appear to have profound effects on the course of infectious and autoimmune diseases. It is believed that specific programs of differentiation induce the commitment of an uncommitted Th0 precursor cell to Th1 or Th2. A component of these programs is hypothesized to be the nature of MHC-peptide antigen presentation to the αβ T cell. It has heretofore remained uncertain whether a Th1/Th2 classification likewise defines, at the clonal level, γδ T cells. Such cells do not, as a general rule, express either CD4 or CD8αβ, and they do not commonly recognize peptide-MHC. In this report, γδ cell clones are described that conform strikingly to the Th1/Th2 classification, both by cytokine expression and by functional activities of the clones in vitro and in vivo. Provocatively, both the γδ cell clones and primary γδ cells in vivo showed a strong association of the Th2 phenotype with CD4 expression. These results are discussed with regard to the immunoregulatory role that is increasingly emerging for γδ cells.

GAD-reactive CD4+ Th1 cells induce diabetes in NOD/SCID mice

Although glutamic acid decarboxylase (GAD) has been implicated in IDDM, there is no direct evidence showing GAD-reactive T cells are diabetogenic in vivo. To address this issue, 3-wk-old NOD mice received two injections of purified rat brain GAD; one mouse rapidly developed diabetes 3 wk later. Splenocytes from this mouse showed a proliferative response to purified GAD, and were used to generate a CD4+ T cell line, designated 5A, that expresses TCRs encoding Vbeta2 and Vbeta12. 5A T cells exhibit a MHC restricted proliferative response to purified GAD, as well as GAD65 peptide 524-543. After antigen-specific stimulation, 5A T cells secrete IFNgamma and TNFalpha/beta, but not IL-4. They are also cytotoxic against NOD-derived hybridoma cells (expressing I-Ag7) that were transfected with rat GAD65, but not nontransfected hybridoma cells. Adoptive transfer of 5A cells into NOD/SCID mice produced insulitis in all mice. Diabetes occurred in 83% of the mice. We conclude that GAD injection in young NOD mice may, in some cases, provoke diabetes due to the activation of diabetogenic T cells reactive to GAD65 peptides. Our data provide direct evidence that GAD65 autoimmunity may be a critical event in the pathogenesis of IDDM.

Determinant spreading of T helper cell 2 (Th2) responses to pancreatic islet autoantigens

The nature (Th1 versus Th2) and dynamics of the autoimmune response during the development of insulin-dependent diabetes mellitus (IDDM) and after immunotherapy are unclear. Here, we show in nonobese diabetic (NOD) mice that the autoreactive T cell response starts and spreads as a pure Th1 type autoimmunity, suggesting that a spontaneous Th1 cascade underlies disease progression. Surprisingly, induction of antiinflammatory Th2 responses to a single beta cell antigen (betaCA) resulted in the spreading of Th2 cellular and humoral immunity to unrelated betaCAs in an infectious manner and protection from IDDM. The data suggest that both Th1 and Th2 autoimmunity evolve in amplificatory cascades by generating site-specific, but not antigen-specific, positive feedback circuits. Determinant spreading of Th2 responses may be a fundamental mechanism underlying antigen-based immunotherapeutics, explaining observations of infectious tolerance and providing a new theoretical framework for therapeutic intervention.

Oral somatic transgene vaccination using attenuated S. typhimurium

An attenuated strain of S. typhimurium has been used as a vehicle for oral genetic immunization. Eukaryotic expression vectors containing truncated genes of ActA and listeriolysin--two virulence factors of Listeria monocytogenes--have been used to transform S. typhimurium aroA. Multiple or even single oral immunizations with such transformants induced excellent cellular and humoral responses. In addition, protective immunity was induced with listeriolysin transformants. The quality of the responses suggested a transfer of plasmid DNA from the bacterial carrier to the host. Such transfer was unequivocally shown in vitro with primary peritoneal macrophages. We describe a highly versatile system for antigen delivery, identification of protective antigens for vaccination, and efficient generation of antibodies against the product of open reading frames present on virtually any DNA segment.

Systemic antigen in the treatment of T-cell-mediated autoimmune diseases

Systemic injection of antigen is one of the approaches that reproducibly induces effective antigen-specific hyporesponsiveness. Here, Roland Liblau and colleagues discuss the cellular and molecular bases of such tolerance, review the current use of this therapeutic strategy in experimental organ-specific autoimmune diseases and analyse what steps are necessary to make this approach suitable for clinical use.

Treatment of NOD diabetes with a novel peptide of the hsp60 molecule induces Th2-type antibodies

A peptide from the sequence of hsp60 molecule, designated p277, has been shown to be functionally involved in modulating the development of auto-immune diabetes in the NOD mouse: administration of p277 to NOD mice can arrest the diabetogenic autoimmune process, even when far advanced. Is p277 the only hsp60 peptide able to modulate the disease? We mapped T cell responses to peptides spanning the mouse hsp60 molecule and identified an immunogenic peptide, designated p12, that is also functional in arresting NOD diabetes. Although no spontaneous T cell reactivity to p12 could be detected in NOD mice, subcutaneous administration of 100 microg of p12 in mineral oil to 10-week-old female NOD mice, similar to treatment with p277, significantly prevented progression of the disease. Administration of other immunogenic peptides was not effective. A peptide from the glutamic acid decarboxylase (GAD65) sequence, GADp35, and a peptide from the myco-bacterial hsp60 molecule did not influence the development of diabetes. The effectiveness of hsp60 peptides p12 and p277 was associated with the induction of antibodies to the peptides of the IgG1 and IgG2b isotypes, antibodies which appear to be regulated by anti-inflammatory cytokines. There was a negative correlation between the amounts of antibodies induced by the hsp60 peptides and the level of blood glucose. Thus, more than one peptide of the hsp60 molecule can be used to inhibit the development of NOD diabetes, and the effect of peptide therapy appears to be associated with the induction of specific antibody isotypes.

Identification of immunodominant T cell epitopes of human glutamic acid decarboxylase 65 by using HLA-DR(alpha1*0101,beta1*0401) transgenic mice

Glutamic acid decarboxylase isoform 2 (GAD65; EC 4.1.1.15) has been identified as a key target autoantigen of insulin-dependent diabetes mellitus (IDDM). IDDM is genetically associated with the major histocompatibility complex (MHC), and particular alleles from the HLA-DQ and HLA-DR loci contribute to disease. Among DR4 subtypes, HLA-DRB1*0401, HLA-DRB1*0402, and HLA-DRB1*0405 alleles lend susceptibility, while HLA-DRB1*0403 confers protection. We have utilized HLA-DR(alpha1*0101,beta1*0401) (hereafter referred to as DR0401), human CD4, murine class II null triple transgenic mice and recombinant GAD65 to generate T cell hybridomas, and we have used overlapping sets of peptides to map the immunodominant epitopes of this autoantigen. We have identified 10 immunogenic regions for GAD65, of which 6 are recognized by multiple hybridomas. These epitopes are also generated by human antigen-presenting cells and their presentation is DR0401 restricted, as shown by the use of typed human lymphoblastoid cell lines and antibody blocking experiments. Immunodominant GAD65 epitopes defined in transgenic mice correspond to GAD65 regions previously shown to elicit T cell responses specifically in DR0401 IDDM patients, underscoring the validity of this approach. Interestingly, although the major epitopes contain DR0401 binding motifs, one of the epitopes contains a DR0405 motif.

Transgenic plants expressing autoantigens fed to mice to induce oral immune tolerance

Oral administration of protein can induce antigen-specific immune hyporesponsiveness. However, the utility of oral tolerance to autoantigens in the treatment of autoimmune diseases may be limited when candidate autoantigens cannot be produced by conventional systems in quantities sufficient for clinical studies. Plants may be ideally suited for this purpose, as they can synthesize, glycosylate and assemble mammalian proteins to provide huge quantities of relatively low cost soluble proteins. Furthermore, edible transgenic plants could provide a simple and direct method of autoantigen delivery for oral tolerance. Therefore, the aim of this study was to determine whether a transgenic plant expression system was capable of synthesizing the diabetes-associated autoantigen, glutamic acid decarboxylase (GAD) in an immunogenic form and whether the oral administration of an autoantigen expressed by a plant could directly induce protective immune responses in a mouse model of diabetes. We show that a GAD-expressing transgenic plant, given as a dietary supplement, inhibits the development of diabetes in the non-obese diabetic (NOD) mouse.