Heterogeneous IgG subclass distribution of islet cell antibodies

IA-2 antibody epitopes and isotypes during the prediabetic process in siblings of children with type 1 diabetes

To characterize the humoral immune response to the protein tyrosine phosphatase (PTP)-like autoantigen (IA-2) in preclinical type 1 diabetes (T1D), and to assess the utility of epitope and isotype-specific IA-2 antibody responses as surrogate markers for disease development, we analyzed these antibodies in 34 initially non-diabetic siblings of affected children derived from the "Childhood Diabetes in Finland" (DiMe) Study. Half of them presented with T1D during an average observation period of 8.7 years. Radiobinding assays were used to determine IA-2/IA-2 beta epitope-specific (the juxtamembrane region, JM; the PTP-like and the beta PTP-like domain) antibodies and isotype-specific (IgG1-4, IgA, IgE and IgM) IA-2 antibodies. Initially, 30 of the 34 siblings tested positive for epitope-specific antibodies. The siblings who progressed to clinical diabetes had IA-2 JM antibodies more often (P<0.05) but IgE-IA-2 antibodies less frequently (P<0.05) than the siblings who did not progress to T1D. During the identical follow-up time, the non-progressors had higher integrated titers of IgE-IA-2 antibodies (P=0.05). The occurrence of IgE-IA-2 antibodies was protective, since despite IA-2 JM antibodies, children with IgE-IA-2 antibodies did rarely progress to T1D. This study demonstrates that JM-reactive IA-2 antibodies are associated with an increased risk of progression to overt T1D, whereas an IgE response to IA-2 confers relative protection against clinical disease.

Insulin autoantibody isotypes during the prediabetic process in young children with increased genetic risk of type 1 diabetes

This work aimed to assess the maturation of the humoral immune response to insulin in preclinical type 1 diabetes by observing the emergence of various isotypes of insulin autoantibodies (IAA) in children with HLA-DQB1-conferred disease susceptibility. The series was derived from the Finnish Type 1 Diabetes Prediction and Prevention Study and comprised 15 IAA-positive children who presented with type 1 diabetes during prospective observation (progressors) and 30 children who remained nondiabetic (nonprogressors). An isotype-specific radiobinding assay was used to determine isotype-specific IAA (IgG1-4 and IgA) from samples obtained with an interval of 3-12 mo. The progressors had IAA of subclass IgG3 in their first IAA-positive sample more often than did the nonprogressors (13 of 15 versus 12 of 30; p = 0.003). Nine progressors had a dominant IgG1-IAA response initially, and six had a dominant IgG3-IAA response. The corresponding distribution among the nonprogressors was that 20 had a dominant IgG1-IAA response, none had an IgG3-IAA response, and three had a dominant response other than IgG1- or IgG3-IAA (chi(2)(df = 2) = 12.02; p = 0.002). The progressors had higher integrated levels (area under the curve) of IgG1-IAA (p = 0.05) and IgG3-IAA (p = 0.002). Nine progressors had a dominant integrated IgG1-IAA response and six had a dominant IgG3-IAA response over the observation period, whereas 22 nonprogressors had a dominant IgG1-IAA response, six had a dominant IgG2-IAA response, and one an IgG3-IAA response (chi(2)(df = 2) = 11.23; p = 0.004). Genetically susceptible young children who progress rapidly to clinical type 1 diabetes are characterized by strong IgG1 and IgG3 responses to insulin, whereas a weak or absent IgG3 response is associated with relative protection from disease.

Restricted IgG1 subclass of anti-Yo antibodies in paraneoplastic cerebellar degeneration

Paraneoplastic cerebellar degeneration (PCD) occurs as a non-metastatic manifestation of cancer in a small proportion of patients with certain breast or gynaecological tumours, and is characterised by widespread Purkinje cell loss. Antibodies against a Purkinje cell cytoplasmic antigen, called Yo, that is expressed by the tumours, are present in the majority of these patients, but the pathogenic role of the antibodies is not clear. To characterise further the immune response in these cases, 13 anti-Yo positive sera were tested for IgG subclasses by immunohistochemistry and western blotting and, in four cases, PHA-stimulated cytokine secretion by peripheral blood lymphocytes was measured. Surprisingly, anti-Yo antibodies were entirely restricted to the IgG1 subclass, whereas antibodies against the small cell cancer-associated antigen, Hu, were found in all four IgG subclasses. There was a trend towards raised IgG1 levels in the total IgG of the anti-Yo positive patients and, in two, PHA-stimulated peripheral blood lymphocytes secreted raised levels of IFN-gamma. By contrast, in the other two cases tested, raised levels of IL-4 were secreted. Patients with PCD associated with anti-Yo antibodies appear to have strong immune responses that are polarised with respect to the IgG subclass and Th cytokine profiles.

Early Autoantibody Responses in Prediabetes Are IgG1 Dominated and Suggest Antigen-Specific Regulation

The islet autoimmunity of preclinical type 1 diabetes remains poorly characterized in humans. In this paper, the IgG subclass response to the islet autoantigens insulin, glutamic acid decarboxylase, and IA-2 was studied sequentially from birth to diabetes onset or current follow-up in 26 autoantibody positive offspring of parents with diabetes. Islet autoantibody appearance was characterized by an early IgG1 peak response to one or more Ags, most commonly to insulin, at a median age of 2.2 yr (interquartile range, 2–2.9 yr). In five offspring, an acute fulminant β-cell destruction and diabetes onset occurred during this initial Ab response. In the remainder, early Ab levels declined markedly, and Ab peaks against other β cell Ags arose sequentially over several years suggesting regulation and spreading of autoimmunity. Second peak Ab responses to the same Ag were observed in only two offspring, both developing diabetes at this time. Two others developed diabetes with declining Ab levels. Abs of IgG1 subclass dominated against each Ag, and other subclasses, were usually only detected during peak IgG1 responses. The IgG4 response to insulin was exceptional, being dominant over IgG1 in four offspring and in five others appeared and/or persisted after IgG1 levels declined. These Th2-associated IgG4 responses were not correlated with protection from diabetes. The presence of IgG1-restricted responses to DA2 were associated with diabetes development. These findings suggest that type 1 diabetes has an early acute destructive phase of β cell autoimmunity, which may be regulated and which spreads chronically until diabetes onset.

Progression to type 1 diabetes is associated with a change in the immunoglobulin isotype profile of autoantibodies to glutamic acid decarboxylase (GAD65). Childhood Diabetes in Finland Study Group

To investigate whether type 1 diabetes in man is associated with a preferential Th1/Th2 response, and whether autoantibodies to one of the main autoantigens would reflect such a response, we characterized the immunoglobulin isotype profile to the 65-kDa isoform of glutamic acid decarboxylase (GAD65) in siblings to IDDM patients. Samples obtained from affected subjects before and at clinical onset of IDDM, from unaffected individuals at high risk and at low risk and from healthy controls were studied. The immunoglobulin isotype profile in the siblings at low risk reflected a more immature, i.e., IgM and Th2 like, i.e., IgE response compared to the progressors and siblings at high risk, with significantly higher median levels of IgM and IgE. The rank order of anti-GAD65 immunoglobulin isotypes was similar in the siblings before and at clinical onset of IDDM, IgG1 > IgG4 > IgM > IgE > IgA > IgG3 > IgG2, but markedly different in the individuals at low risk, IgG1 > IgM > IgE > IgG4 > IgG3 > IgA > IgG2. Based on these observations, we suggest that progression to clinical onset of IDDM is associated with a maturation and a decrease in the Th2 immune response against GAD65; findings which could have implications for future intervention and prediction strategies.

IgG subclass antibodies to glutamic acid decarboxylase and risk for progression to clinical insulin-dependent diabetes

Pancreatic islet beta cell destruction leading to insulin-dependent diabetes mellitus (IDDM) is believed to be mediated by a T-helper 1 (T(H)1) lymphocyte response to islet antigens. In the mouse, T(H)1 (IL-2, IFN-gamma) and T(H)2 (IL-4, -5, -6, -10) responses are associated with the generation of IgG2a and IgG1 subclasses, respectively. The equivalent human subclasses have not been defined. Because the IgG subclass response to an antigen may be a potentially useful marker of T(H)1/T(H)2 immune balance we measured IgG subclass antibodies to glutamic acid decarboxylase (GAD), a major islet autoantigen in IDDM, in 34 newly-diagnosed IDDM patients and in 28 at-risk, first-degree relatives of people with IDDM. In the newly-diagnosed patients, total IgG antibodies to GAD were detected in 74% (25/34); IgG1 and/or IgG3 were significantly more frequent than IgG4 or IgG4/IgG2 (14/34 versus 5/34, p = 0.01). GAD antibody-negative patients were significantly younger (p = 0.01). In 15 at-risk relatives who had not progressed to clinical diabetes after a median of 4.5 years, 10 had IgG2 and/or IgG4 antibodies compared to only 3/13 progressors (p = 0.02). Total IgG and IgG2 antibodies were higher in non-progressors. Non-progressors were older than progressors (p = 0.01), and relatives with IgG2 and/or IgG4 responses were also older (p = 0.01). These results suggest that IgG subclass antibodies to GAD may contribute to diabetes risk assessment in islet antibody relatives.

Islet cell antigens in the prediction and prevention of insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM) is associated with both antibody and T-cell autoimmunity to pancreatic islet cell components. In recent years, considerable progress has been made in the identification of the molecular components of the pancreatic islets to which these immune responses are directed. These advances have led to the development of a number of immune markers for use in screening for individuals at risk for disease, and there is promise of antigen-specific immune intervention therapies to prevent diabetes in those identified as at risk. In this article, we review our current knowledge of autoantigens associated with IDDM and the implications this has on the prediction and prevention of the disease.