Novel considerations on the antibody/autoantigen system in type I (insulin-dependent) diabetes mellitus

Insulin dependent diabetes (IDDM) has an autoimmune pathogenesis. Included is the presence of antibodies to pancreatic islet cells. The first identified were islet cell antibodies (ICA), detected by indirect immunofluorescence, and which react with all cells within islets. Importantly, the autoantibodies are found several years prior to disease and although a pathogenic role for the autoantibodies is unclear, they have become useful markers of prediabetes. A number of studies of twins discordant for IDDM and of first degree relatives of IDDM patients have established that there is an increased risk for disease in individuals who have ICA, especially when ICA levels are high. This high predictive value of ICA decreases in the general population where the incidence of IDDM is lower than in first degree relatives, and both ICA and the disease risk associated with ICA, appear to be influenced by a genetic susceptibility. This has been substantiated in a study of patients with endocrine autoimmunity and ICA (Polyendocrine Study) where the predictive value of very high levels of ICA is less than 50 in patients without a first degree relative with IDDM. Hence, there remain a substantial number of patients with ICA who do not develop disease. From these patients, it was demonstrated that ICA include at least two distinct specificities, one of which is beta cell specific and is not associated with a high risk for IDDM. These data, and an increasing list of new autoantibodies in IDDM, have increased the search for the relevant autoantigens. That of classic ICA is suggested to be a sialoganglioside, and a number of protein autoantigens have been suggested as other potential autoantigens. Of particular importance has been the identification of glutamic acid decarboxylase (GAD), the biosynthesizing enzyme of the neurotransmitter gamma amino butyric acid, as the autoantigen corresponding to the 64K autoantibodies found in the majority of newly diagnosed IDDM patients. Despite the identification of GAD, specific assays developed so far have not detected anti GAD antibodies at high frequencies in newly diagnosed patients. Like ICA, it appears that there may be distinct specificities of autoantibodies to GAD and associated products. Enzyme digestion of the autoantigen yields 50K, 40K and 37K fragments which appear to be derived from distinct polypeptide chains. Patients may have autoantibodies to either the 50K fragment or the 40/37K fragment or all fragments. Importantly, studies in twins and in the polyendocrine patients indicate that autoantibodies to the 37K fragment are more strongly associated with the progression to disease. In addition to these autoantigens, autoantibodies are detected against the hormone insulin and its precursor proinsulin in up to 40 of newly diagnosed patients. Heat shock protein 65, carboxypeptidase H and glucose transporter have also been reported as autoantigens relevant to IDDM. It is now clear that the autoimmune response associated with IDDM is heterogeneous and against several islet antigens. The search will continue to determine which of these is important in the pathogenesis and which will provide effective markers for prediction which will eventually allow safe intervention therapy for the prevention of IDDM. © 1991 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.</p

Novel considerations on the antibody/autoantigen system in type I (insulin-dependent) diabetes mellitus

Insulin dependent diabetes (IDDM) has an autoimmune pathogenesis. Included is the presence of antibodies to pancreatic islet cells. The first identified were islet cell antibodies (ICA), detected by indirect immunofluorescence, and which react with all cells within islets. Importantly, the autoantibodies are found several years prior to disease and although a pathogenic role for the autoantibodies is unclear, they have become useful markers of prediabetes. A number of studies of twins discordant for IDDM and of first degree relatives of IDDM patients have established that there is an increased risk for disease in individuals who have ICA, especially when ICA levels are high. This high predictive value of ICA decreases in the general population where the incidence of IDDM is lower than in first degree relatives, and both ICA and the disease risk associated with ICA, appear to be influenced by a genetic susceptibility. This has been substantiated in a study of patients with endocrine autoimmunity and ICA (Polyendocrine Study) where the predictive value of very high levels of ICA is less than 50 in patients without a first degree relative with IDDM. Hence, there remain a substantial number of patients with ICA who do not develop disease. From these patients, it was demonstrated that ICA include at least two distinct specificities, one of which is beta cell specific and is not associated with a high risk for IDDM. These data, and an increasing list of new autoantibodies in IDDM, have increased the search for the relevant autoantigens. That of classic ICA is suggested to be a sialoganglioside, and a number of protein autoantigens have been suggested as other potential autoantigens. Of particular importance has been the identification of glutamic acid decarboxylase (GAD), the biosynthesizing enzyme of the neurotransmitter gamma amino butyric acid, as the autoantigen corresponding to the 64K autoantibodies found in the majority of newly diagnosed IDDM patients. Despite the identification of GAD, specific assays developed so far have not detected anti GAD antibodies at high frequencies in newly diagnosed patients. Like ICA, it appears that there may be distinct specificities of autoantibodies to GAD and associated products. Enzyme digestion of the autoantigen yields 50K, 40K and 37K fragments which appear to be derived from distinct polypeptide chains. Patients may have autoantibodies to either the 50K fragment or the 40/37K fragment or all fragments. Importantly, studies in twins and in the polyendocrine patients indicate that autoantibodies to the 37K fragment are more strongly associated with the progression to disease. In addition to these autoantigens, autoantibodies are detected against the hormone insulin and its precursor proinsulin in up to 40 of newly diagnosed patients. Heat shock protein 65, carboxypeptidase H and glucose transporter have also been reported as autoantigens relevant to IDDM. It is now clear that the autoimmune response associated with IDDM is heterogeneous and against several islet antigens. The search will continue to determine which of these is important in the pathogenesis and which will provide effective markers for prediction which will eventually allow safe intervention therapy for the prevention of IDDM. © 1991 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.</p

Antibodies to islet 37k antigen, but not to glutamate decarboxylase, discriminate rapid progression to IDDM in endocrine autoimmunity

Apart from islet cell antibodies (ICAs), antibodies to glutamate decarboxylase (GAD), insulin autoantibodies (IAAs), and a novel islet antigen (37k antigen) are potential markers for insulin-dependent diabetes mellitus (IDDM). GAD is also an antigen in stiff-man syndrome (SMS), and both SMS and IDDM are associated with ICAs and autoimmunity to other endocrine organs. We investigated possible links between antibody responses to islet antigens with autoimmunity to other endocrine organs and determined which specific antibodies can identify individuals who progress to IDDM. Antibodies to GAD were detected in â?¥90 of both diabetic and nondiabetic patients with ICAs and other endocrine autoimmunity, in 59 of ICA-positive IDDM patients without endocrine autoimmunity, in all patients with SMS, but in only 1-3 of healthy (nondiabetic) and autoimmune disease control subjects. GAD antibody levels were increased in ICA-positive IDDM patients with polyendocrine autoimmunity compared with those without. In contrast, antibodies to 37k antigen were only detected in patients who developed acute-onset IDDM. IAAs were also associated with IDDM. Thus, certain factors enhance antibody responses to GAD in polyendocrine autoimmunity, but this does not necessarily lead to development of IDDM or SMS. Antibodies to 37k antigen are strongly associated with acute-onset IDDM and are useful serological markers for disease.</p

Antibodies to islet 37k antigen, but not to glutamate decarboxylase, discriminate rapid progression to IDDM in endocrine autoimmunity

Apart from islet cell antibodies (ICAs), antibodies to glutamate decarboxylase (GAD), insulin autoantibodies (IAAs), and a novel islet antigen (37k antigen) are potential markers for insulin-dependent diabetes mellitus (IDDM). GAD is also an antigen in stiff-man syndrome (SMS), and both SMS and IDDM are associated with ICAs and autoimmunity to other endocrine organs. We investigated possible links between antibody responses to islet antigens with autoimmunity to other endocrine organs and determined which specific antibodies can identify individuals who progress to IDDM. Antibodies to GAD were detected in â?¥90 of both diabetic and nondiabetic patients with ICAs and other endocrine autoimmunity, in 59 of ICA-positive IDDM patients without endocrine autoimmunity, in all patients with SMS, but in only 1-3 of healthy (nondiabetic) and autoimmune disease control subjects. GAD antibody levels were increased in ICA-positive IDDM patients with polyendocrine autoimmunity compared with those without. In contrast, antibodies to 37k antigen were only detected in patients who developed acute-onset IDDM. IAAs were also associated with IDDM. Thus, certain factors enhance antibody responses to GAD in polyendocrine autoimmunity, but this does not necessarily lead to development of IDDM or SMS. Antibodies to 37k antigen are strongly associated with acute-onset IDDM and are useful serological markers for disease.</p

Lack of immunohistological changes in the islets of nondiabetic, autoimmune, polyendocrine patients with ?-Selective GAD-specific islet cell antibodies

We examined the pancreases from three nondiabetic, autoimmune, polyendocrine patients with islet cell antibodies (ICAs) and glutamic acid decarboxylase (GAD) antibodies who died without developing insulin-dependent diabetes mellitus (IDDM). All three patients had the β-selective GAD- specific ICA subtype and antibodies to the GAD-derived 50 kD tryptic fragment. None had whole islet ICA or antibodies to the non-GAD-derived 37k islet antigen, which appear to be more closely associated with IDDM than antibodies to GAD. The three patients also were negative for insulin autoantibodies. Islets within pancreas from patients 1 and 2 appeared well preserved as assessed by hematoxylin and eosin staining. In these two patients, insulin content, as assessed by indirect immunofluorescence on cryostat sections, was normal. Patient 3 had a prolonged postmortem time, and the islet insulin content was reduced slightly. In all three pancreases, no evidence was found of increased human leukocyte antigen class I or de novo class II molecule expression on islet cells, and islet infiltration by T- or B-cells or macrophages was not detected. Islet capillary endothelial cells did not show signs of hypertrophy. No immunoglobulin or complement deposition within or around islets was found. These data indicate that humoral GAD autoimmunity does not necessarily associate with visible β-cell damage.</p

Antibodies to GAD and tryptic fragments of islet 64K antigen as distinct markers for development of IDDM: studies with identical twins

Insulin-dependent diabetes mellitus (IDDM) is associated with antibodies to a 64,000-M(r) islet cell protein, at least part of which is identified as glutamic acid decarboxylase (GAD). These antibodies are detected as two distinct antibody specificities to 50,000-M(r) and 37,000/40,000-M(r) tryptic fragments of the autoantigen (50K and 37K antibodies, respectively). We determined the frequencies of antibodies to intact GAD, tryptic fragments of islet 64,000-M(r) antigen, islet cell antibodies (ICAs), and insulin autoantibodies (IAAs) in sera from 58 nondiabetic identical twins of patients with IDDM, of whom 12 subsequently developed diabetes. ICA, antibodies to intact GAD, and those to tryptic fragments were detected at similar frequencies in prediabetic twins (67-75), but only 25 had IAA. Of 46 twins who remain nondiabetic, GAD antibodies, 50K antibodies, and ICA were detected in 6 (13), 7 (15), and 5 (11), respectively, whereas only 1 (2) possessed 37K antibodies and 2 (4) had IAA. Eight of 9 twins with 37K antibodies and all 6 twins with ICA > 20 Juvenile Diabetes Foundation U have developed diabetes. Antibodies to GAD are sensitive markers for diabetes development but may also be present in genetically susceptible individuals who are unlikely to develop disease. Antibodies to 37,000/40,000-M(r) fragments of the 64,000-M(r) antigen or high-titer ICA were the best markers for diabetes development in these twins.</p

Antibodies to GAD and tryptic fragments of islet 64K antigen as distinct markers for development of IDDM: studies with identical twins

Insulin-dependent diabetes mellitus (IDDM) is associated with antibodies to a 64,000-M(r) islet cell protein, at least part of which is identified as glutamic acid decarboxylase (GAD). These antibodies are detected as two distinct antibody specificities to 50,000-M(r) and 37,000/40,000-M(r) tryptic fragments of the autoantigen (50K and 37K antibodies, respectively). We determined the frequencies of antibodies to intact GAD, tryptic fragments of islet 64,000-M(r) antigen, islet cell antibodies (ICAs), and insulin autoantibodies (IAAs) in sera from 58 nondiabetic identical twins of patients with IDDM, of whom 12 subsequently developed diabetes. ICA, antibodies to intact GAD, and those to tryptic fragments were detected at similar frequencies in prediabetic twins (67-75), but only 25 had IAA. Of 46 twins who remain nondiabetic, GAD antibodies, 50K antibodies, and ICA were detected in 6 (13), 7 (15), and 5 (11), respectively, whereas only 1 (2) possessed 37K antibodies and 2 (4) had IAA. Eight of 9 twins with 37K antibodies and all 6 twins with ICA > 20 Juvenile Diabetes Foundation U have developed diabetes. Antibodies to GAD are sensitive markers for diabetes development but may also be present in genetically susceptible individuals who are unlikely to develop disease. Antibodies to 37,000/40,000-M(r) fragments of the 64,000-M(r) antigen or high-titer ICA were the best markers for diabetes development in these twins.</p

Slow metabolic deterioration towards diabetes in islet cell antibody positive patients with autoimmune polyendocrine disease

We studied metabolic progression to IDDM in a cohort of adults who are ICA-positive and have associated autoimmune endocrine disease or circulating organ-specific autoantibodies (the Polyendocrine Study). Of the 186 individuals recruited 27 developed overt diabetes after a median follow-up of 4.5 years (range 0.4-12). Of these, eight patients did not require insulin treatment until at least 6 months after clinical diagnosis, with an interval of 1.8 years (1.2-5.7). An IVGTT was performed in 38 subjects and 23 had sequential studies. Of the initial 38 subjects six developed diabetes and only three showed a loss of FPIR to glucose (below the first percentile of a normal control group) before clinical onset of the disease. An additional three subjects showed a loss of the FPIR, and all still have normal glucose tolerance after median follow-up of 28 months (22-95). A whole or mixed pattern of islet cell staining was found in five of the six patients who developed diabetes and antibodies against an islet 37 k-antigen were detectable in four patients, all of whom required insulin soon after diagnosis. A beta-cell selective ICA staining pattern was seen in 14 of 17 subjects who did not develop diabetes and the mixed pattern in only three. None of this group had detectable 37k-antibodies. We conclude that metabolic deterioration is slow in polyendocrine patients, and that the IVGTT has less prognostic significance in this group than in first degree relatives of patients with IDDM. In contrast, the presence of the whole or mixed ICA staining pattern or of 37k-antibodies can identify a high risk of progression to IDDM within this polyendocrine population and may indicate the rate of metabolic deterioration. © 1994 Springer-Verlag.</p

Slow metabolic deterioration towards diabetes in islet cell antibody positive patients with autoimmune polyendocrine disease

We studied metabolic progression to IDDM in a cohort of adults who are ICA-positive and have associated autoimmune endocrine disease or circulating organ-specific autoantibodies (the Polyendocrine Study). Of the 186 individuals recruited 27 developed overt diabetes after a median follow-up of 4.5 years (range 0.4-12). Of these, eight patients did not require insulin treatment until at least 6 months after clinical diagnosis, with an interval of 1.8 years (1.2-5.7). An IVGTT was performed in 38 subjects and 23 had sequential studies. Of the initial 38 subjects six developed diabetes and only three showed a loss of FPIR to glucose (below the first percentile of a normal control group) before clinical onset of the disease. An additional three subjects showed a loss of the FPIR, and all still have normal glucose tolerance after median follow-up of 28 months (22-95). A whole or mixed pattern of islet cell staining was found in five of the six patients who developed diabetes and antibodies against an islet 37 k-antigen were detectable in four patients, all of whom required insulin soon after diagnosis. A beta-cell selective ICA staining pattern was seen in 14 of 17 subjects who did not develop diabetes and the mixed pattern in only three. None of this group had detectable 37k-antibodies. We conclude that metabolic deterioration is slow in polyendocrine patients, and that the IVGTT has less prognostic significance in this group than in first degree relatives of patients with IDDM. In contrast, the presence of the whole or mixed ICA staining pattern or of 37k-antibodies can identify a high risk of progression to IDDM within this polyendocrine population and may indicate the rate of metabolic deterioration. © 1994 Springer-Verlag.</p

Lack of immunohistological changes in the islets of nondiabetic, autoimmune, polyendocrine patients with ?-Selective GAD-specific islet cell antibodies

We examined the pancreases from three nondiabetic, autoimmune, polyendocrine patients with islet cell antibodies (ICAs) and glutamic acid decarboxylase (GAD) antibodies who died without developing insulin-dependent diabetes mellitus (IDDM). All three patients had the β-selective GAD- specific ICA subtype and antibodies to the GAD-derived 50 kD tryptic fragment. None had whole islet ICA or antibodies to the non-GAD-derived 37k islet antigen, which appear to be more closely associated with IDDM than antibodies to GAD. The three patients also were negative for insulin autoantibodies. Islets within pancreas from patients 1 and 2 appeared well preserved as assessed by hematoxylin and eosin staining. In these two patients, insulin content, as assessed by indirect immunofluorescence on cryostat sections, was normal. Patient 3 had a prolonged postmortem time, and the islet insulin content was reduced slightly. In all three pancreases, no evidence was found of increased human leukocyte antigen class I or de novo class II molecule expression on islet cells, and islet infiltration by T- or B-cells or macrophages was not detected. Islet capillary endothelial cells did not show signs of hypertrophy. No immunoglobulin or complement deposition within or around islets was found. These data indicate that humoral GAD autoimmunity does not necessarily associate with visible β-cell damage.</p