Islet-specific immune mechanisms

Environmental factors in the development of Type 1 diabetes

Environmental factors appear to play an important role in the pathogenesis of childhood-onset type 1 diabetes (T1D). The most important factors are thought to be infectious, dietary, perinatal, and psychosocial. Enteroviruses (especially Coxsackie B virus), breastfeeding, the early presence or lack of certain foods, birth weight, childhood over-nutrition, maternal islet autoimmunity, and negative stress events have been shown to be related to the prevalence of T1D. However, clear conclusions to date are limited because most studies lacked power to detect exposure/disease associations, were not prospective or long-term, did not start in infancy, had imprecise or infrequent exposure estimates, had confounding exposures, and failed to account for genetic susceptibility. In addition to the identification of specific antigenic triggers, several more general hypotheses, including the accelerator and hygiene hypotheses, are testable approaches worth pursuing.

Islet-cell antibodies and endogenous insulin secretion in Sudanese diabetic children

Cytoplasmic islet-cell antibodies (ICA) and endogenous insulin secretion were studied in 46 Sudanese children (mean age 11.6 years) with newly diagnosed insulin-dependent diabetes mellitus (IDDM). Islet-cell antibodies were detected both by the indirect immunofluorescence (IF) and complement fixation (CF) methods. Endogenous insulin levels were measured as C-peptide concentration using radio-immunoassays. The degree of metabolic control of diabetics was judged by the presence of diabetic ketoacidosis (DKA) at onset, glycated haemoglobin (HbA1c) level and insulin requirement, expressed as dose per kg body weight per day, at the time of presentation. Twenty-nine patients (63%) had either IF-ICA or CF-ICA or both in their sera. These figures are significantly higher than those reported for African populations. Islet-cell antibody positive patients had significantly lower C-peptide concentration, higher HbA1c level, higher insulin requirement and higher prevalence of ketoacidosis at presentation. Furthermore, the C-peptide levels were higher in CF-ICA positive patients than in subjects who showed only IF-ICA positivity. Our findings show a clear association between ICA and severity of diabetes at clinical onset and also suggest that the presence of CF-ICA at or shortly after diagnosis of IDDM is indicative of preservation of some functioning beta-cell mass.

Quantitative analysis of islet glutamic acid decarboxylase p64 autoantibodies in insulin-dependent diabetes mellitus

Autoantibodies against the beta-cell M(r) 64,000 protein (p64), recently identified as an isoform of glutamic acid decarboxylase (GAD), are prevalent in patients with insulin-dependent diabetes mellitus (IDDM). Dog islets were found to represent an abundant source of native p64 allowing the study of antigen-antibody interactions in IDDM. A quantitative, standardized assay for p64 antibodies based on dog islets was developed and evaluated. Utilizing dog and human islets the p64 antibodies were detected in 17/19 (89%) new onset 15-32-year-old patients, compared to 15/19 (79%) in a rat islet assay. ICA were detected in 15/19 (79%) patients and correlated with the presence of p64 antibodies (rs = 0.59, P < 0.004) but not with age at onset, sex, or C-peptide levels. Sensitivity therefore is improved with the dog islet p64 antibody assay which will allow future studies requiring native p64 antigen in larger quantities are possible based on our findings.

Coxsackievirus B4-induced development of antibodies to 64,000-Mr islet autoantigen and hyperglycemia in mice

Diabetogenic Coxsackievirus B4 infection produces a diabetes syndrome in susceptible mice resembling insulin-dependent diabetes mellitus. We reported a two- to threefold increased expression of a 64,000-Mr (64 K) islet autoantigen in the infected mice preceding the development of hyperglycemia, suggesting a possible role of the virus in autoimmunity. To assess if the virus could be a trigger of autoimmunity, 64 K autoantibody development was correlated with hyperglycemia and virus replication in islets during early and late infection. Additionally, the effects of blood removal from these mice on the incidence of hyperglycemia and antibody production were evaluated. Noninfected control mice were essentially 64 K antibody negative, the infected consistently positive. Approximately 30% of the animals developed antibodies by 72 h postinfection (p.i.) and 90% by 4-6 wk p.i. Virus-induced hyperglycemia appeared bimodal: hyperglycemia in 50% of the mice by 1 wk p.i., which decreased to 30% by 3 wk and then increased to 80-100% by 6 wk p.i. Infectious virus was abundant in the islets at 72 h but undetectable later. Hyperglycemia seen at 6 wk decreased dramatically (67-73%) if the mice were bled once between 72 h and 2 wk p.i. Only 50-60% of the mice bled once were 64 K positive compared to 90% positive nonbled mice. Coxsackievirus may initiate or enhance the autoimmune response.

HLA heterozygosity in insulin-dependent diabetes is most frequent at the DQ locus

Restriction fragment length polymorphism using an HLA-DQ beta-chain genomic probe showed that 63 children with insulin-dependent (type 1) diabetes mellitus (IDDM) were all (100%) positive for the BamH1 fragments 12 kb and/or 4 kb compared to 98% (62/63) for HLA-DR3 and/or 4 and 75% (47/63) for HLA-B8 and/or 15. The 36 (56%) DR3-positive children were all 4-kb-positive; however, a total of 44 (70%) children were 4-kb-positive (P less than 0.02). The 55 (87%) DR4-positive children were all 12-kb-positive, but a total of 56 (89%) were 12-kb-positive (NS). The heterozygosity at the HLA region increased from 11/63 (18%) for HLA-B8/15 to 29/63 (46%) for HLA-DR3/4 (P less than 0.0004) and to 37/63 (59%) for the HLA-DQ 4 kb/12 kb fragments (P less than 0.02). The test of an equal probability of a positive result under the adjacent pair of tests indicates that the increased risk of developing IDDM in association with HLA-DQ is to a great extent due to heterozygosity at this locus. There were no differences between the 4 kb/12 kb and the DR3/4-positive IDDM children with respect to fasting or meal-stimulated C peptide, insulin requirement, or levels of insulin antibodies formed during the first 12 months of insulin therapy. Our results support the hypothesis that HLA-DQ is closely associated with an increased risk of childhood IDDM, and when typed for at this locus parameters of the clinical course were homogeneous, suggesting that factors other than HLA-DQ may determine previously observed differences between IDDM children in clinical or functional parameters.

Lessons from the NOD mouse for the pathogenesis and immunotherapy of human type 1 (insulin-dependent) diabetes mellitus

Suitable animal models of human Type 1 (insulin-dependent) diabetes mellitus have long been sought, in particular a model that would permit detailed histological and immunological investigation of changes in the islet preceding the metabolic disorder. This would allow hypotheses as to pathogenesis of the condition to be examined and interventions such as immunotherapy to be tested. The most widely studied models include the low-dose streptozotocin induced diabetic mouse and the BB rat, but both differ in important respects from the human disease. In this review we describe one highly successful model, the non obese diabetic mouse. Selected aspects of pathogenesis and immunotherapy are presented and analogies with human Type 1 diabetes discussed.

Transgenic mice with I-A on islet cells are normoglycemic but immunologically intolerant

Insulin-dependent diabetes mellitus (IDDM) is caused by a specific loss of the insulin-producing beta cells from pancreatic Langerhans islets. It has been proposed that aberrant expression of major histocompatibility complex (MHC) class II molecules on these cells could be a triggering factor for their autoimmune destruction. This proposal was tested in transgenic mice that express allogeneic or syngeneic class II molecules on the surface of islet cells at a level comparable with that normally found on resting B lymphocytes. These animals do not develop diabetes, nor is lymphocyte infiltration of the islets observed. This immunological inactivity does not result from tolerance to the "foreign" class II molecules.

Islet cell and other organ-specific autoantibodies in all children developing type 1 (insulin-dependent) diabetes mellitus in Sweden during one year and in matched control children

The majority (about 90%) of children developing Type 1 (insulin-dependent) diabetes mellitus do not have a first-degree relative with the disease. Nearly all (389/405, 96%) children (0-14 years) in Sweden, who developed diabetes during one year, were therefore studied to compare islet cell, thyroid peroxidase, thyroglobulin, and gastric H+, K+-ATPase antibodies with 321 age, sex, and geographically matched, but non-related, control children. Islet cell (cytoplasmic) antibodies were found in 81% (316/389) of the patients and in 3% (9/321) of the control children (p less than 0.001). The median islet cell antibody levels were 70 (range 3-8200) Juvenile Diabetes Foundation (JDF) Units in the islet cell antibody positive patients, and 27 (range 17-1200) JDF Units in the control children (NS). Autoantibodies against thyroid peroxidase (8%), thyroglobulin (6%), and gastric H+, K+-ATPase (3%) were all increased in the patients compared with the control children, being 2% (p less than 0.001), 2% (p less than 0.01), and 0.3% (p less than 0.01), respectively. During an observation time of 20-34 months, two of the nine islet cell antibody positive control children developed Type 1 diabetes, after 8 and 25 months respectively, while the others remained healthy and became islet cell antibody negative. None of the islet cell antibody negative control children developed diabetes during the same time of observation. This first investigation of an unselected population of diabetic children and matched control children shows: that islet cell antibodies are strongly associated with newly diagnosed childhood diabetes, that other autoantibodies are more frequent among diabetic children than control children, and that the frequency of islet cell antibodies in the background population of children is higher than previously documented, and could also be transient, underlining that factors additional to islet cell antibodies are necessary for the later development of Type 1 diabetes.

Effect of probucol on development of diabetes mellitus in BB rats

Insulin-dependent diabetes mellitus (IDDM) results from an inflammatory process leading to destruction of the insulin-producing beta cells of the pancreas. Genetically mediated autoimmune processes are considered the most likely explanation for IDDM in humans, while viral infections, toxic agents, nutritional alterations and stress are also considered possibilities. The precise mechanisms by which autoimmunity, infections, toxins or other agents produce beta cell damage are not known. Toxin-induced diabetes in animals can be prevented by antioxidant therapy, while an agent that inhibits hydroxyl radical formation, desferrioxamine, extends the survival time of free allotypic islets in nonobese diabetic mice. The BB/W rat develops IDDM secondary to a pervasive autoimmune defect. This well-studied animal model develops IDDM with a highly predictable frequency and timing. This study describes the effects of the potent antioxidant, probucol, on the development of diabetes in BB rats by introducing it into standard rat chow at a 1% concentration at the time of weaning, and continuing this feeding schedule through 160 days of life. Control rats from split litters received standard chow only. Diabetes developed in 86.2% of the control rats at a mean age of 90.4 days. Probucol administration was associated with a reduction to 62% and a delay in diabetes diagnosis to 99.6 days. These very preliminary results suggest that probucol may be altering the inflammatory process, resulting in beta cell destruction in these genetically diabetes-prone rats.

Diabetes and tolerance in transgenic mice expressing class II MHC molecules in pancreatic beta cells

Insulin-dependent diabetes is caused by the loss of insulin-producing beta cells in pancreatic islets. It has been proposed that aberrant expression of Class II Major Histocompatibility Complex (MHC) molecules on beta cells stimulates an autoimmune attack against beta cell antigens. To test this hypothesis, we generated transgenic mice that express Class II MHC molecules (E alpha d/E beta b, or I-Eb) on beta cells. Diabetes was found in 100% of transgenic progeny from three expressing transgenic mouse lines, but without evidence for lymphocytic infiltrates. Furthermore, T lymphocytes appeared to be tolerant to the transgene I-Eb molecule, despite the absence of expression of I-Eb in the thymus or any other lymphoid tissue. The results suggest that novel expression of Class II MHC molecules on nonlymphoid cells is by itself insufficient to initiate autoimmune responses against tissue-specific antigens.