Spontaneous diabetes in rats: destruction of islets is prevented by immunological tolerance

T Cell-Mediated Beta Cell Destruction: Autoimmunity and Alloimmunity in the Context of Type 1 Diabetes

Type 1 diabetes (T1D) results from destruction of pancreatic beta cells by T cells of the immune system. Despite improvements in insulin analogs and continuous blood glucose level monitoring, there is no cure for T1D, and some individuals develop life-threatening complications. Pancreas and islet transplantation have been attractive therapeutic approaches; however, transplants containing insulin-producing cells are vulnerable to both recurrent autoimmunity and conventional allograft rejection. Current immune suppression treatments subdue the immune system, but not without complications. Ideally a successful approach would target only the destructive immune cells and leave the remaining immune system intact to fight foreign pathogens. This review discusses the autoimmune diabetes disease process, diabetic complications that warrant a transplant, and alloimmunity. First, we describe the current understanding of autoimmune destruction of beta cells including the roles of CD4 and CD8 T cells and several possibilities for antigen-specific tolerance induction. Second, we outline diabetic complications necessitating beta cell replacement. Third, we discuss transplant recognition, potential sources for beta cell replacement, and tolerance-promoting therapies under development. We hypothesize that a better understanding of autoreactive T cell targets during disease pathogenesis and alloimmunity following transplant destruction could enhance attempts to re-establish tolerance to beta cells.

Immunogenetics of type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is an autoimmune disease arising through a complex interaction of both genetic and immunologic factors. Similar to the majority of autoimmune diseases, T1DM usually has a relapsing remitting disease course with autoantibody and T cellular responses to islet autoantigens, which precede the clinical onset of the disease process. The immunological diagnosis of autoimmune diseases relies primarily on the detection of autoantibodies in the serum of T1DM patients. Although their pathogenic significance remains uncertain, they have the practical advantage of serving as surrogate biomarkers for predicting the clinical onset of T1DM. Type 1 diabetes is a polygenic disease with a small number of genes having large effects (i.e. HLA), and a large number of genes having small effects. Risk of T1DM progression is conferred by specific HLA DR/DQ alleles [e.g., DRB1*03-DQB1*0201 (DR3) or DRB1*04-DQB1*0302 (DR4)]. In addition, HLA alleles such as DQB1*0602 are associated with dominant protection from T1DM in multiple populations. A discordance rate of greater than 50% between monozygotic twins indicates a potential involvement of environmental factors on disease development. Viral infections may play a role in the chain of events leading to disease, albeit conclusive evidence linking infections with T1DM remains to be firmly established. Two syndromes have been described in which an immune-mediated form of diabetes occurs as the result of a single gene defect. These syndromes are termed autoimmune polyglandular syndrome type I (APS-I) or autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED), and X-linked poyendocrinopathy, immune dysfunction and diarrhea (XPID). These two syndromes are unique models to understand the mechanisms involved in the loss of tolerance to self-antigens in autoimmune diabetes and its associated organ-specific autoimmune disorders. A growing number of animal models of these diseases have greatly helped elucidate the immunologic mechanisms leading to autoimmune diabetes.

Genomic biomarkers correlate with HLA-identical renal transplant tolerance

The ability to achieve immunologic tolerance after transplantation is a therapeutic goal. Here, we report interim results from an ongoing trial of tolerance in HLA-identical sibling renal transplantation. The immunosuppressive regimen included alemtuzumab induction, donor hematopoietic stem cells, tacrolimus/mycophenolate immunosuppression converted to sirolimus, and complete drug withdrawal by 24 months post-transplantation. Recipients were considered tolerant if they had normal biopsies and renal function after an additional 12 months without immunosuppression. Of the 20 recipients enrolled, 10 had at least 36 months of follow-up after transplantation. Five of these 10 recipients had immunosuppression successfully withdrawn for 16-36 months (tolerant), 2 had disease recurrence, and 3 had subclinical rejection in protocol biopsies (nontolerant). Microchimerism disappeared after 1 year, and CD4(+)CD25(high)CD127(-)FOXP3(+) regulatory T cells and CD19(+)IgD/M(+)CD27(-) B cells were increased through 5 years post-transplantation in both tolerant and nontolerant recipients. Immune/inflammatory gene expression pathways in the peripheral blood and urine, however, were differentially downregulated between tolerant and nontolerant recipients. In summary, interim results from this trial of tolerance in HLA-identical renal transplantation suggest that predictive genomic biomarkers, but not immunoregulatory phenotyping, may be able to discriminate tolerant from nontolerant patients.

Potent induction immunotherapy promotes long-term insulin independence after islet transplantation in type 1 diabetes

The seemingly inexorable decline in insulin independence after islet transplant alone (ITA) has raised concern about its clinical utility. We hypothesized that induction immunosuppression therapy determines durability of insulin independence. We analyzed the proportion of insulin-independent patients following final islet infusion in four groups of ITA recipients according to induction immunotherapy: University of Minnesota recipients given FcR nonbinding anti-CD3 antibody alone or T cell depleting antibodies (TCDAb) and TNF-α inhibition (TNF-α-i) (group 1; n = 29); recipients reported to the Collaborative Islet Transplant Registry (CITR) given TCDAb+TNF-α-i (group 2; n = 20); CITR recipients given TCDAb without TNF-α-i (group 3; n = 43); and CITR recipients given IL-2 receptor antibodies (IL-2RAb) alone (group 4; n = 177). Results were compared with outcomes in pancreas transplant alone (PTA) recipients reported to the Scientific Registry of Transplant Recipients (group 5; n = 677). The 5-year insulin independence rates in group 1 (50%) and group 2 (50%) were comparable to outcomes in PTA (group 5: 52%; p>>0.05) but significantly higher than in group 3 (0%; p = 0.001) and group 4 (20%; p = 0.02). Induction immunosuppression was significantly associated with 5-year insulin independence (p = 0.03), regardless of maintenance immunosuppression or other factors. These findings support potential for long-term insulin independence after ITA using potent induction therapy, with anti-CD3 Ab or TCDAb+TNF-α-i.

Bone marrow and pancreatic islets: an old story with new perspectives

In the past years, in the field of β-cell replacement for diabetes therapy, the easy availability of bone marrow (BM) and the widely consolidated clinical experience in the field of hematology have contributed to the development of strategy to achieve donor-specific transplantation tolerance. Recently, the potential role of BM in diabetes therapy has been reassessed from a different point of view. Diverse groups investigated the contribution of BM cells to β-cell replacement as direct differentiation into insulin-producing cells. More importantly, while direct differentiation is highly unlikely, a wide array of experimental evidences indicates that cells of BM origin are capable of facilitating the survival or the endogenous regeneration of β-cells through an as yet well-defined regeneration process. These new experimental in vitro and in vivo data will expand in the near future the clinical trials involving BM or BM-derived cells to cure both type 1 and type 2 diabetes in humans. In this review we recapitulate the history of use of BM in diabetes therapy and we provide clinically relevant actual information about the participation of BM and BM-derived stem cells in islet cell regeneration processes. Furthermore, new aspects such as employing BM as "feeder tissue" for pancreatic islets and new clinical use of BM in diabetes therapy are discussed.

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.

Prevention of type 1 diabetes by gene therapy

The autoimmune disease type 1 diabetes in humans and NOD mice is determined by multiple genetic factors, among the strongest of which is the inheritance of diabetes-permissive MHC class II alleles associated with susceptibility to disease. Here we examined whether expression of MHC class II alleles associated with resistance to disease could be used to prevent the occurrence of diabetes. Expression of diabetes-resistant MHC class II I-Abeta chain molecules in NOD mice following retroviral transduction of autologous bone marrow hematopoietic stem cells prevented the development of autoreactive T cells by intrathymic deletion and protected the mice from the development of insulitis and diabetes. These data suggest that type 1 diabetes could be prevented in individuals expressing MHC alleles associated with susceptibility to disease by restoration of protective MHC class II expression through genetic engineering of hematopoietic stem cells.

Mixed hematopoietic chimerism allows cure of autoimmune diabetes through allogeneic tolerance and reversal of autoimmunity

Bone marrow transplantation from diabetes-resistant strains with complete replacement of the recipient immune system by the allogeneic donor has led to tolerance to donor islets and cure of diabetes in a mouse model of type 1 diabetes. However, the ability to tolerize host T-cells of diabetic NOD mice is unknown. We demonstrate that nonmyeloablative conditioning achieves mixed hematopoietic chimerism across major histocompatibility complex (MHC) barriers in spontaneously diabetic NOD mice. This conditioning preserves alloreactive and autoreactive diabetogenic host NOD T-cells, but when mixed chimerism was established, diabetic NOD mice accepted donor-type allogeneic islet grafts and were cured of diabetes, despite a significant recipient T-cell contribution. Furthermore, induction of mixed chimerism permitted acceptance of NOD islet grafts, demonstrating reversal of autoimmunity. Allogeneic bone marrow transplantation was critical for tolerization of diabetogenic and alloreactive host T-cells. Thus, mixed hematopoietic chimerism induces tolerance to donor islets and reverses established autoimmunity in diabetic NOD mice.

Factors influencing Islet of Langerhans graft function and monitoring

Transplantation of islet of Langerhans represents a viable therapeutic option for insulin-dependent diabetes mellitus. Dramatic progress has been recently reported with the introduction of a glucocorticoid-free immunosuppressive regimen that improved success rate, namely, insulin independence for 1 year or more, from 8% to 100%. The fate of islet grafts is determined by many concurrent phenomena, some of which are common to organ grafts (i.e. rejection), while others are unique to nonvascularized cell transplants, including transplant cell mass and viability, as well as nonspecific inflammation at the site of implant. Moreover, islet grafts lack clinical markers of early rejection, making it difficult to recognize imminent rejection and to implement intervention with graft-saving immunosuppressive regimens. In the present review, we will address the problems influencing islet graft success and the monitoring of islet cell graft function.

Cellular and molecular mechanism for Kilham rat virus-induced autoimmune diabetes in DR-BB rats

Kilham rat virus (KRV) causes autoimmune diabetes in diabetes-resistant BioBreeding (DR-BB) rats; however, the mechanism by which KRV induces autoimmune diabetes without the direct infection of beta cells is not well understood. We first asked whether molecular mimicry, such as a common epitope between a KRV-specific peptide and a beta cell autoantigen, is involved in the initiation of KRV-induced autoimmune diabetes in DR-BB rats. We found that KRV peptide-specific T cells generated in DR-BB rats infected with recombinant vaccinia virus expressing KRV-specific structural and nonstructural proteins could not induce diabetes, indicating that molecular mimicry is not the mechanism by which KRV induces autoimmune diabetes. Alternatively, we asked whether KRV infection of DR-BB rats could disrupt the finely tuned immune balance and activate autoreactive T cells that are cytotoxic to beta cells, resulting in T cell-mediated autoimmune diabetes. We found that both Th1-like CD45RC+CD4+ and cytotoxic CD8+ T cells were up-regulated, whereas Th2-like CD45RC-CD4+ T cells were down-regulated, and that isolated and activated CD45RC+CD4+ and CD8+ T cells from KRV-infected DR-BB rats induced autoimmune diabetes in young diabetes-prone BioBreeding (DP-BB) rats. We conclude that KRV-induced autoimmune diabetes in DR-BB rats is not due to molecular mimicry, but is due to a breakdown of the finely tuned immune balance of Th1-like CD45RC+CD4+ and Th2-like CD45RC-CD4+ T cells, resulting in the selective activation of beta cell-cytotoxic effector T cells.

Glucose control and long-term survival in biobreeding/Worcester rats after intraperitoneal implantation of hydrophilic macrobeads containing porcine islets without immunosuppression

BACKGROUND

We investigated the effectiveness of implanted macrobeads containing porcine islets as long-term therapy for type I diabetes mellitus in Biobreeding/Worcester (BB/Wor) rats, an animal model of spontaneous type I human diabetes. End points included acute control of glucose, weight gain, survival time, and the renal changes associated with diabetes.

MATERIALS AND METHODS

Eighteen chronic spontaneously diabetic BB/Wor rats were each implanted with 56-150 porcine islet macrobeads secreting 1.3-5.2 U of insulin/24 hr in culture medium at 37 degrees C. Their clinical courses and selective histological observations were compared with those of animals maintained on Linplant insulin-release implants (6 rats) or protamine zinc insulin alone (10 rats).

RESULTS

The rats that underwent porcine islet macrobead implantation (PIMI) survived for a mean of 171 days (range, 79-288) after implantation without exogenous insulin, immunosuppressive treatment, or lactated Ringer's therapy. All appeared healthy and maintained their body weights (mean 356+/-21 g) throughout this period, even though their nonfasting blood glucose levels fluctuated significantly, with the mean for the group being 245+/-102 mg/dl (range, 157-320 mg/dl). There was mild glucosuria in some animals. In comparison, the 10 BB/Wor rats maintained on exogenous protamine zinc insulin had a mean survival time of 53 days (range, 10-217), a "last entry" mean body weight of 283+/-23 g, and a mean nonfasting glucose level of 340+/-90 mg/dl. The six Linplant implant animals had a mean survival time of 164 days (range, 1-264 days), a "last entry" mean body weight of 374+/-21 g, and a mean nonfasting glucose level of 189+/-91 mg/dl (range, 135-219). Episodes of ketonuria, abrupt loss of body weight, dehydration, and symptomatic hypoglycemia were more common in both these groups than in the PIMI animals. Glucose tolerance tests comparing diabetic animals treated with porcine islet macrobead implants, exogenous insulin-treated diabetic BB/Wor rats, and normal nondiabetic Wistar-Furth rats showed that the responses of those with the macrobead implants were similar to those of the normal rats, while the exogenous insulin-treated diabetic BB/Wor rats had the expected abnormal responses. Light microscopic examination of the PIMI and Linplant animals' kidney sections appeared normal, whereas those of the exogenous insulin-injected BB rats showed moderate focal tubular atrophy and an increased mesangial matrix. Macrobeads retrieved from the peritoneal cavity at necropsy were found to secrete insulin, C-peptide, and glucagon, indicating that they were still functional after 199 or more days in the peritoneal cavity.

CONCLUSIONS

Our results indicate that macrobeads containing porcine islets implanted intraperitoneally in natural insulin-dependent diabetic BB/Wor rats are capable of normalizing glucose control, permitting a normal life span, and preventing the renal changes normally associated with diabetes. Therefore, further short- and long-term studies of porcine islet macrobead implantation in chemically induced and naturally occurring diabetes in rodents, as well as larger animals including dogs, monkeys and possibly humans, are merited.

Prolongation of porcine islet xenograft survival in mice after therapy with immunosuppressive peptides

BACKGROUND

Recently, peptides derived from the heavy chain of HLA-B2702 have been shown to modulate immune responses. In this study, we examined the use of these peptides for immunosuppression in a pig to mouse islet xenograft model.

METHODS

Purified porcine islets were transplanted in autoimmune (non-obese diabetic) and non-autoimmune (streptozotocin-injected CBA or C57/Bl6) diabetic mice. Various dosing regimens of HLA-derived peptides with and without antilymphocyte therapy were administered to recipient mice. Graft rejection was determined by daily serum glucose determinations, and, at selected time points, grafts were removed to demonstrate function and provide immunohistochemical examination.

RESULTS

HLA-derived peptides were demonstrated to prolong graft survival in both pretransplant and posttransplant treatment regimens. This effect was increased with concomitant antilymphocyte therapy.

CONCLUSIONS

Further elucidation of the mechanism of action of these immunomodulatory peptides may help in the development of novel immunosuppressive protocols.

Lack of recurrence of insulin-dependent diabetes mellitus in syngeneic and allogeneic islet-transplanted diabetic biobreeding rats

BACKGROUND

Previous reports on experimental islet transplantation in animal models of human insulin-dependent diabetes mellitus show that islet grafts are susceptible to autoimmune destruction similar to that seen in native pancreatic islets. In this study, we demonstrated a lack of disease recurrence in diabetic BioBreeding (BB) rats after syngeneic and allogeneic islet transplantation.

METHODS

Four hundred to 1200 islets from BB (RT1u) and Lewis (RT1(1)) donors, isolated with stationary collagenase digestion and Ficoll density purification, were intraportally transplanted into spontaneously diabetic BB rats. The recipients received no immunologic manipulations before or after islet transplantation.

RESULTS

When more than 900 syngeneic islets or when more than 600 allogeneic islets were transplanted, BB recipients remained normoglycemic for over 280 days, irrespective of age at onset, duration of exogenous insulin treatment, or age at transplantation. When at least 500 islets were transplanted, the recipients survived for a long period with normoglycemia or in a noninsulin-dependent diabetic state. Upon histological examination, mononuclear cell infiltration was observed in every islet graft examined, but the severity of infiltration in most of the grafts was mild to moderate. These results indicate that the islet grafts in the BB recipients were destroyed extremely slowly.

CONCLUSIONS

It is conceivable that in our BB colony, a state of immunologically low responsiveness that allows diabetic animals to accept syngeneic or allogeneic islet grafts, occurs around the onset period and becomes more pronounced with aging. Our BB rat colony can be considered to be a novel substrain with unique immunological characteristics.

Islet cell antibodies and glutamic acid decarboxylase antibodies in patients with insulin-dependent diabetes mellitus undergoing kidney and islet-after-kidney transplantation

The humoral immune response to islet autoantigens, here defined by the presence of islet cell antibodies (ICA) and glutamic acid decarboxylase (GAD 65) antibodies, was studied in patients with long-term insulin-dependent diabetes mellitus (IDDM) receiving immunosuppressive therapy following kidney and islet-after-kidney transplantation. In a cross-sectional study of 30 kidney-grafted, long-term IDDM patients and 30 matched, nontransplanted IDDM controls, we observed a significant (P<0.05) decrease in ICA positivity by standard immunosuppressive therapy, but not in frequency or index levels of GAD 65 antibodies. Because of this intriguing finding, we investigated, in a pilot study on seven islet-after-kidney transplant recipients, the time course of frequency and levels of ICAs and GAD 65 antibodies relative to islet graft function. Stable islet graft function was seen in the patients with low GAD 65 antibody index levels, whereas rapid islet graft failure occurred in a patient with high GAD 65 antibody index levels prior to transplantation. In addition, GAD 65 autoimmunity reoccurred in one pretransplant antibody-negative patient 2 months after graft failure was noted. In conclusion, these observations suggest that beta-cell autoimmunity directed to GAD 65 can persist despite immunosuppressive therapy and may adversely affect islet graft function, possibly indicating disease recurrence as a major threat to successful clinical islet transplantation.

Prevention of autoimmunity in nonobese diabetic (NOD) mice by neonatal transfer of allogeneic thymic macrophages

Nonobese diabetic (NOD) mice spontaneously develop insulin dependent diabetes mellitus. The disease results from an autoimmune process which involves mononuclear cells surrounding and eventually infiltrating the pancreatic islets of Langerhans. Macrophages are thought to be the first cells to infiltrate the islets and are actively involved in the disease process because diabetes is prevented if host macrophages are depleted or inactivated. Several lines of evidence also suggest that NOD macrophages are phenotypically and functionally abnormal. In this study, allogeneic (CBA) macrophages derived from the thymus were inoculated into newborn NOD mice and these were followed for more than 250 days. Spontaneous diabetes was significantly reduced in female NOD mice (6% diabetic versus 45% of controls). Insulitis was also significantly reduced in both male and female mice compared to their control counterparts, and in most cases there were virtually no inflammatory cells in the pancreas. Allogeneic skin grafting and mixed leukocyte cultures indicated that the recipients were not tolerant of donor antigens, and donor-derived cells were not detected in the lymphoid tissues by either flow cytometry or immunohistochemistry. The results show that macrophages from diabetes-resistant donors will prevent insulitis and diabetes in most recipients, however, the mechanism for the protection is unclear, but does not appear to be due to long-term tolerance induction.

Direct assessment of the role of NK cells in autoimmune diabetes

Considerable indirect evidence implicates participation of natural killer cells (NK) in the pathogenesis of diabetes in BB rats. The most convincing evidence derives from studies showing that anti-CD8 antibody effectively prevents both primary disease onset and autoimmune damage to transplanted islets. However, anti-CD8 treatment depletes both NK and cytotoxic T cells (CTL) since both cell types express the CD8 marker. To study directly the role of NK in diabetic BB rats we used MCA 3.2.3, a monoclonal antibody which selectively depletes normal Lewis rats of NK cells but not CTL. A regimen of ip injected antibody achieved rapid reduction of NK cells in diabetic and nondiabetic BB rats by FACS analysis. NK cell activity remained low in rats treated weekly as evidenced by YAC tumor cell killing. We next studied the effect of NK depletion on disease incidence in diabetes-prone BB rats of which about one half are expected to develop diabetes. Onset and incidence of diabetes in 3.2.3-treated and control antibody-treated aged matched litter mates were equal. These studies suggest that NK cells are not necessary for autoimmune islet destruction in spontaneously diabetic BB rats and support a role for CTL in pathogenesis of the disease.

Prevention of autoimmune diabetes in the BB rat by intrathymic islet transplantation at birth

Spontaneous diabetes in the BioBreeding (BB) rat, like human type I diabetes, results from the destruction of pancreatic islets by autoreactive T lymphocytes recognizing beta cell-specific antigens. T cell tolerance is in part mediated by interactions of maturing thymocytes with antigens expressed in the thymic microenvironment; islets were therefore implanted into the thymus of neonatal diabetes-prone BB rats to determine whether exposure of T cell precursors to beta cell antigens could influence the development of diabetes. This treatment completely prevented diabetes and insulitis in the native pancreas. The effect may be the result of specific modulation of diabetogenic T cells maturing in an islet-bearing thymus.

The spontaneously diabetic BB rat: sites of the defects leading to autoimmunity and diabetes mellitus. A review

In summary, our bone marrow chimeras studies suggest that there are two defects in the BB rat associated with diabetes and/or lymphopenia, one residing at the level of the bone marrow lymphoid stem cell and the other within the T-cell differentiative environment, apparently postthymic. Our neonatal thymus transplantation studies and the adult thymus transplantation studies of others suggest a third defect in the BB rat, within the thymus itself, but this defect appears not to be responsible for the development of either the diabetes or the T lymphocytopenia. Rather, the thymic defect appears to control, at least in part, the lymphocyte hyporesponsiveness characteristic of the diabetes-prone BB rat. The role of the RT6 T-cell differentiation antigen in the etiopathogenesis of diabetes in this animal model remains unclear.

The role of class II major histocompatibility complex antigens in autoimmune diabetes: animal models

Like human insulin-dependent diabetes, autoimmune diabetes in BB rats and NOD mice is under control of Class II genes of the major histocompatibility complex. The mechanisms of expression of these genes is still unclear. No aberrant expression of Class II antigens was found in BB rats at the onset of diabetes. The putative role of inadequate Class II-linked suppressor control is suggested, however, by the observation that in vivo treatment with anti-Class II monoclonal antibody prevents the onset of diabetes in NOD mice, and that this protection can be transfer by CD4+ T cells.

Neonatal induction of allogeneic tolerance prevents T cell-mediated autoimmunity in NOD mice

Diabetes in the NOD mouse strain is a genetically programmed T cell-mediated autoimmune process that is directed against an as yet unknown antigen target(s) on pancreatic beta cells. To investigate whether the course of the autoimmune disease could be altered by immune manipulations of the T cell repertoire, we have induced allogeneic tolerance by injecting F1 semiallogeneic spleen cells into NOD neonates. This procedure resulted in a significant protection against both insulitis and diabetes. However, although it requires the induction of tolerance, as shown by the failure of non-tolerizing irradiated cells to prevent autoimmunity, protection appeared to be independent of the major histocompatibility complex haplotypes of the F1 spleen cells injected at birth, e.g. (C57BL/6 x NOD)F1, (CBA/Ca x NOD)F1 or (BALB/c x NOD)F1 cells. In addition, a similar degree of protection was induced, whether the tolerant state, as assessed by mixed lymphocyte reaction studies in vitro, was of short duration, approximately 6 weeks, or lasted for more than 12 weeks. Putative veto or suppressor functions of chimeric T cells were ruled out, since mice tolerized with T cell-depleted F1 spleen cells were equally protected. We conclude that the expression of spontaneous T cell-mediated autoimmunity can be modulated by immune manipulations at birth. Whether the protection observed in the present experiments resulted from the production of one or several specific holes in the autoimmune T cell repertoire, i.e. cross-tolerance, or whether it resulted from nonspecific disturbances of the emerging T cell repertoire remains to be elucidated.

The pathophysiology of diabetes mellitus: an update (continuing education credit)

Both IDDM and NIDDM are multifaceted diseases whose pathophysiologies share two important characteristics. When not clinically treated, both involve chronic hyperglycemia. Further, all individuals with diabetes are at risk for developing the complications of the disease. These complications include neuropathies, retinopathies, and nephropathies. Other complications less often cited include sympathetic nervous sensitivity (at least in NIDDM), as well as neurobehavioral sequelae, especially in very young children whose IDDM treatment/response leads to two or more profound hypoglycemic episodes before age five. The future is bright--improved and appropriate insulinization, effective second-generation oral hypoglycemic agents, pancreatic transplantation, and immunosuppression offer hope in the management of diabetes.

Immunological aspects of diabetes mellitus: prospects for pharmacological modification

It is now well known that insulin-dependent diabetes is a chronic progressive autoimmune disease. The prolonged prediabetic phase of progressive beta-cell dysfunction is associated with immunological abnormalities. A prediabetic period is suggested by the appearance of islet cell antibodies, anti-insulin antibodies, and anti-insulin receptor antibodies. The existence of activated T lymphocytes and abnormal T cell subsets are also other markers. There is still no concensus about the use of the immunosuppression superimposed upon conventional insulin therapy in early diagnosed IDDM and the follow-up of the relatives of IDDM patients who share the genetic predisposition and serological markers for the risk of future onset of IDDM. Treatment in the prodromal period cannot be justified because a link between the disease and early markers such as ICA has not been established with certainty (Diabetes Research Program NIH, 1983). Many immunopharmacological manipulations were reported to be effective in animal models. However, most of them are not readily applied to human subjects. Moreover, IDDM patients are now believed to be heterogeneous, with a complex genetic background. HLA-DR, and more recently DQ, are closely related to the genetic predisposition to IDDM but those genes are not themselves diabetogenic. The contribution of autoimmunity does not appear to be uniform, and in some cases, the contribution of virus is considered more important. There is a lack of a marker for the future onset of IDDM. ICA and ICSA were found after mumps infection, but the existence of those autoantibodies and even the co-existence of HLA-DR3 do not always indicate the future trend to insulin dependency. More precise markers will be disclosed through the biochemical analysis of the target antigens on pancreatic beta-cell for islet antibodies and effector T cells. Much safer and more effective immunopharmacological treatment will be developed through animal experimentation using rat and mouse models. The recent development and interest in this field will further facilitate the attainment of the goal for the complete prevention of IDDM.

Protection from autoimmune disease as the third function of the major histocompatibility gene complex

The collection of genes known as the major histocompatibility gene complex (MHC) appears to subserve three functions. Firstly, its class I genes, coding for antigens on all nucleated cells, assist clones of cytotoxic T cells to kill virus-infected cells quickly, without being muffled by the myriad numbers of free virus particles. Secondly, the absence of autoimmunity to both class I and class II MHC antigens shows that they impose unbreakable tolerances on the immune repertoire. The class II antigens, which are confined to B lymphocytes (if their apparent occurrence on other dividing cells is a cross-reaction), may have the sole function of tolerance induction, supplementing this activity of the class I antigens. Both sets of MHC antigens serve to diversify immunity-repertoire gaps among individuals of a population, thus hampering epidemic spread of infection and providing a diversity of immunoreactivity that favours survival of at least some members of a population in the face of pestilence. Thirdly, the permanence of the MHC tolerance inductions affords a powerful, adaptable mechanism for curtailment of reproductively disadvantageous autoimmune disease liable to arise through somatic mutations in lymphocytes multiplying under drive from a microbial antigenic stimulus.

Prevention of diabetes in BioBreeding/Worcester rats with monoclonal antibodies that recognize T lymphocytes or natural killer cells

Diabetes-prone BioBreeding/Worcester (BB/Wor) rats received thrice weekly injections of mAb against antigens expressed on the surface of all T cells (OX19), cytotoxic/suppressor, and NK cells (OX8), helper/inducer cells (W3/25, OX35, OX38), and Ia+ cells (OX6, 3JP, OX17). Treatment with OX8 or OX19 achieved stable reductions of splenic and peripheral blood NK cells and helper/inducer T lymphocytes, respectively, and protected against diabetes. OX19 injections also prevented lymphocytic insulitis, thyroiditis, and the synthesis of autoantibodies to thyroid colloid and smooth muscle antigens. OX8 injections reduced splenic NK-mediated YAC-1 cell lysis, but did not prevent insulitis, thyroiditis, or autoantibody synthesis. Injections of mAb specific for antigens on the surface of helper/inducer cells, and for cells expressing IaE antigens provided marginal protection against diabetes without reductions of phenotypic subsets. These findings suggest that pancreatic beta cell destruction in the spontaneously diabetic BB/Wor rat is mediated by the combined action of NK and helper/inducer cells.

Effect of antiserum to monoclonal anti-islet cell surface antibody on pancreatic insulitis in non-obese diabetic mice

Immunotherapeutic intervention has been studied in non-obese diabetic (NOD) mice. Twenty-five male NOD mice aged 6 weeks were treated with anti-mouse T lymphocyte serum (ATS), N-(2-carboxyphenyl)-4-chloroanthranilic acid disodium salt (CCA); a non-specific immunostimulant which seems to potentiate the suppressor T cell activity, and antiserum raised against previously reported monoclonal antibody 3A4 to the surface of islet cells. Pancreatic islets from NOD mice sacrificed at 12 weeks of age were scored morphologically for the severity and the frequency of insulitis. Both the severity of insulitis in each islet and the frequency of insulitis-positive islets in each pancreas were reduced in the groups treated with ATS (group B), antiserum to 3A4 (group D) and a combination of antiserum plus CCA (group E) in comparison with other groups (control: group A and CCA: group C). At 8 weeks of age, the binding capacities of sera to insulinoma cells measured by protein A radioligand assay were significantly decreased in the groups treated with antiserum to 3A4 (groups D and E) as compared with those in the other groups. These results suggest that both ATS and antiserum to 3A4 prevent the occurrence and the progress of insulitis in NOD mice, but the immunosuppressive mechanisms differ from each other; therefore, combination therapy with these suppressants may be more effective in the prevention of Type 1 diabetes mellitus.

Type I diabetes mellitus: a chronic autoimmune disease?

Currently defined categories of diabetes mellitus reflect our growing knowledge of the biochemical and immunologic basis of several disorders resulting in hyperglycemia. The authors discuss the autoimmune phenomenon and autoimmune diseases associated with Type I diabetes mellitus. Special focus is placed on the impact of immunologic assays on the current and future clinical care of patients with Type I diabetes and their genetically susceptible relatives.

Two genes required for diabetes in BB rats. Evidence from cyclical intercrosses and backcrosses

The BB rat develops a syndrome of autoimmune diabetes similar to Type I diabetes of man. It also has a severe T cell lymphopenia. As part of an ongoing breeding program to transfer the diabetogenic genes of the BB rat onto inbred rat strain backgrounds, diabetic animals were used in a backcross (BC)- intercross (IC)-backcross breeding scheme with Brown Norway (BN), Lewis (L), and Wistar-Furth (WF) inbred rats. We have used monoclonal antibodies to analyze both lymphopenia and major histocompatibility (MHC) antigens (the RT1 locus in the rat) in relation to the development of diabetes. To examine T cell subsets we used a panel of monoclonal antibodies, in particular W3/25 and OX19 , which discriminate the abnormal phenotype better than W3/13. In our breeding program, at least two independent genes or gene complexes are required for the expression of diabetes. One gene determines the lymphopenia, is inherited by simple autosomal recessive genetics and is not linked to the MHC. The second gene is linked to the MHC. Both genes are necessary, but neither gene is sufficient by itself for the development of diabetes.

Islet cell surface and lymphocyte antibodies often precede the spontaneous diabetes in the BB rat

The diabetic syndrome of the BB rat shows many homologies with that of human insulin-dependent diabetes and evidence that the onset of the disease is associated with the presence of autoantibodies, including islet cell surface antibodies. In this study, sera were sampled serially from weaning to 157 days of age from 26 BB rats in two low-incidence litters, and 22 rats of three high-incidence litters. Clinical and metabolic variables were monitored concurrently with blood lymphocyte counts. Islet morphology was correlated at sacrifice. In the high-incidence litters, eight rats developed insulin-dependent diabetes, five impaired glucose tolerance, and the remaining nine all showed insulitis. In the low-incidence litters, only one animal showed impaired glucose tolerance and another insulitis. In the high-incidence litters 16 rats (73%) had islet cell surface antibodies compared with 4 out of 26 (15%) low-incidence controls (p less than 0.002). Antibodies reactive with Wistar rat spleen lymphocytes were present in all high-incidence rats compared with 19% (5 out of 26) among the control litters (p less than 0.002). Time courses of islet cell surface and lymphocyte antibody appearance and their peak values varied, but already at weaning the levels of both antibodies were increased among the high-incidence litter rats (p less than 0.001). Islet cell surface and/or lymphocyte antibodies were therefore present in the majority of animals at an age where neither morphological nor metabolic evidence of the diabetic syndrome were yet detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetes mellitus: relationships of nonhuman primates and other animal models to human forms of diabetes

Results from studies with M. nigra allow some conclusions and predictions about the etiology and development of diabetes relative to the islet lesion in monkeys and human beings. Some factor or factors must initiate the lesion; whether this is genetic, environmental, or a combination of both is not known. Amyloid is not the initiating factor to the islet lesion, but appears later as there is deterioration of cells. Sufficient evidence does not yet exist to choose from among the alternatives regarding the source of amyloid. With gradual deterioration of cells and replacement by amyloid, secretion of insulin is impaired and concentrations of glucagon increase. Sufficient circulating insulin is probably chronically available to the cells in this moderately impaired state, so that an acute decrease in delta IRI in response to glucose in an iv-administered GTT does not cause significant impairment in glucose clearance. The increase in circulating glucagon is probably due to a loss of controls on alpha-cell secretion or synthesis of glucagon. Fasting glucose levels increase but remain within the nondiabetic range. Eventually there is sufficient accretion of amyloid, usually greater than 50%, so that substantial beta-cell loss occurs and the monkey can no longer maintain fasting normoglycemia. The monkey then is hyperglycemic and hypoinsulinemic. Only at this time are the impairments detectable by the usual diagnostic clinical criterion of hyperglycemia. The ICAs arise in response to secretory cell deterioration and are present until there no longer are sufficient cells to elicit an immune response. Results from M. nigra can give insight into a similar condition that probably exists in a subpopulation of older diabetic humans. Humans probably pass through stages similar to those discerned in monkeys. Nondiabetic humans with sufficient beta cells to sustain adequate secretion of insulin, but with moderate amyloid infiltration, probably would be in a category equivalent to BD monkeys; since these people are not overtly hyperglycemic, they are not clinically recognizable as diabetic and would be classified retrospectively as nondiabetic. Continued loss of cells with concomitant amyloid deposition would eventually lead to hyperglycemia; if examined at autopsy, these people would have visible islet amyloid as well as a retrospective diagnosis of diabetes. Older type II diabetic humans with ICA usually proceed to insulin therapy more rapidly than do those who are ICA negative (Irvine et al., 1977; Del Prete et al., 1977; Gray et al., 1980).(ABSTRACT TRUNCATED AT 400 WORDS)

Passive transfer of insulitis and lymphopenia in the BB rat

The BB rat spontaneously develops insulitis followed by impaired glucose tolerance (IGT) or an insulin-dependent diabetic (IDDM) syndrome. Passive transfer of insulitis from newly detected diabetic BB rats to nude mice has been achieved by intraperitoneal or intravenous injection(s) of blood and spleen lymphocytes. After a single injection of cells, 37% of the mice (n = 72) showed insulitis with a mean intensity of 1.9 +/- 0.3 (on a scale of 0 to 3). After three successive injections, 58% of the recipient mice (n = 12) showed insulitis with a mean intensity of 2.5 +/- 0.3. Only one of the control mice (n = 45) demonstrated mild insulitis. The small number of affected islets (13% after a single injection, 17% after three injections) probably explains the absence of random or post IP glucose hyperglycemia in the recipient mice. During this study the yield of lymphocytes in diabetic BB rats was found to be consistently lower than in control normal Wistar rats. This lymphopenia was found not only in the blood and the spleen but also in the thymus and the lymph nodes. Peripheral blood lymphopenia antedated glucoregulatory disturbances. All rats showing either insulitis alone or with IGT or IDDM were lymphopenic. None with normal lymphocyte counts developed any abnormality. Diabetics showed a marked decrease in the proportions of T+ lymphocytes in all tissues whereas the proportion of B(Ia+) lymphocytes was normal in blood, spleen, and thymus but increased in lymph nodes. However, in absolute terms both T+ and Ia+ lymphocytes were decreased. The subset decreased by the greatest proportion in all tissues, except in the thymus was the one that includes helper T lymphocytes. This lymphopenia could be related to the presence of circulating antilymphocyte antibodies. These results strongly support a role for altered immunity in the etiology of the syndrome. If the observed anomalies of lymphocyte numbers and subsets are responsible, then a novel mechanism different from most other "autoimmune" disorders must be implicated.

Influence of islet and bone marrow transplantation on the diabetes and immunodeficiency of BB rats

The results of islet transplantation in spontaneous autoimmune diabetes of BB rats were studied to determine whether this disease process might damage the transplanted islet tissue. Since BB rats are not genetically uniform, syngenetic grafts could not be used; therefore, allograft rejection was prevented by rendering BB rats immunologically tolerant of WF transplantation antigens by neonatal inoculation with bone marrow cells. Despite the resultant tolerant state, which permitted successful engraftment of WF skin allografts, the transplanted islets ameliorated the spontaneous diabetes of BB rats only briefly before they were destroyed by immune insulitis. BB rats from the diabetic stock were found to suffer from abnormalities in T lymphocytes and their subsets as well as defective immune response patterns. When analyzed with monoclonal antibodies specific for rat lymphocyte markers, BB rats of the diabetic stock were found to be lymphocytopenic. There was a reduction in helper T cells and a more severe deficit in the suppressor/cytotoxic subset. BB rats that were inoculated neonatally with bone marrow from normal donors were found to have a strikingly reduced incidence of diabetes. Moreover, the T cell functional, numerical, and microenvironmental defects that were present in noninoculated BB rats were restored in marrow-inoculated BB rats, findings possibly related to the decreased incidence of diabetes.

Humoral immunity in the spontaneously diabetic BB rat

Litters of BB rats with an expected high and low incidence of insulin-dependent diabetes were followed from weaning until the age of about 140 days. Islet cell surface antibodies (ICSA) and lymphocyte antibodies (LA) were determined in a radioligand assay with fixed rat insulinoma (RIN 5F) cells, an insulin-secreting cell line, or spleen lymphocytes. In the low-incidence litter, 2 out of 14 rats had ICSA and LA; one showed insulitis at the end of the study. In the high-incidence litter, 3 out of 7 developed diabetes; all 3 showed ICSA at weaning. The remaining 4 showed insulitis. All 7 diabetes-susceptible rats had ICSA and LA at some time during the study. It is concluded that there is a high incidence of circulating ICSA and LA in the spontaneously diabetic BB rat. The antibodies can often be detected before the onset of diabetes, and may be implicated in the beta-cell destructive process and in the lymphocytopenia characteristic of the syndrome.

Autoimmune diatheses and T lymphocyte immunoincompetences in BB rats

BB rats were found to have autoantibodies to gastric parietal cells, thyroid colloid antigens, smooth muscle, and thymocytes. No autoantibodies reactive with pancreatic islet cells (cytoplasmic), thyroid epithelial cells, adrenal cortex, testes, or anterior pituitary sections were identified. BB rats with gastric parietal autoantibodies had modest degrees of lymphocytic gastritis, but none developed iron or vitamin B12 deficiencies. These results suggest that BB rats have an underlying autoimmune diathesis. In addition, reports of peripheral T lymphopenia in such rats were confirmed, and markedly reduced helper T cell and cytotoxic-suppressor T cell subsets were demonstrated. Histological studies also revealed depletions of the T cell areas of spleen and lymph nodes. Furthermore, BB rats exhibited a profound inability to reject skin grafts across major and minor histocompatibility barriers. This was confirmed by mixed lymphocyte culture studies in vitro. BB-rat lymphocytes from either spleen or peripheral blood also showed profoundly reduced responses to T cell mitogens. Although BB-rat lymphocytes could produce normal levels of interleukin-2, they were unable to respond to this T cell growth factor. However, examination of thymuses from BB rats showed largely normal histologies, normal numbers of thymocyte subsets, and good mitogenic responses to con A. Thus, it appears that BB rats may have a thymic or post thymic defect in T lymphocyte maturation. The relevance of the immunologic lesion to the etiology of IDD in BB rats remains to be shown.