Dynamic changes of GAD65 autoantibody epitope specificities in individuals at risk of developing type 1 diabetes

Schlosser, Michael; Banga, J. Paul; Madec, Anne-Marie; Binder, Katherine A.; Strebelow, M.; Rjasanowski, I; Waßmuth, Ralf; Gilliam, Lisa K.; Luo, Dong; Hampe, Christiane S.

doi:10.1007/s00125-005-1719-1

Cited by 59 publications

(48 citation statements)

References 54 publications

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“…Evidence for epitope spreading has previously been based mainly on the findings related to the occurrence of GAD65-C-Ab together with GAD65-M-Ab, while spreading as such has been seen only in single individuals (12). The immune response was not observed to spread to the N-terminal region to such an extent as described previously (12,22), possibly due to the younger age of the children in the present study or the HLA selection criteria used. As a whole, the response to GAD65 was confirmed to be predominantly composed of IgG1 antibodies and antibodies targeting the middle region of GAD65.…”

Section: Discussionsupporting

confidence: 44%

Early epitope- and isotype-specific humoral immune responses to GAD65 in young children with genetic susceptibility to type 1 diabetes

Ronkainen

Hoppu²,

Korhonen³

et al. 2006

eur j endocrinol

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Objective: The pattern of the humoral immunity to disease-associated autoantigens may reflect the severity of the autoimmune disease process. The purpose of this study was to delineate the maturation of the humoral immunity to one of the main autoantigens in type 1 diabetes (T1D), glutamic acid decarboxylase (GAD65). Design and methods: Serum samples were obtained for the detection of epitope-and isotype-specific antibodies sequentially with short intervals from 36 young children with HLA-conferred genetic susceptibility to T1D starting from the first appearance of GAD65Ab. During prospective observation, ten children developed T1D. Antibodies were analyzed using biotinylated anti-human immunoglobulin (Ig) antibodies and chimeric GAD molecules in radio-binding assays. Results: The immune response to GAD65 started as reactivity to the middle region and spread rapidly to the C-terminal region. IgG1 antibodies dominated among the isotypes from the first appearance of GAD65Ab, while other IgG subclasses were observed to a lesser extent. IgG4 antibodies emerged clearly as the last IgG subclass. A broad initial response comprising three to four IgG subclasses and the lack of an emerging IgG4 response during follow-up was associated with increased risk for progression to clinical diabetes (P!0.05). Conclusions:The humoral response to GAD65 epitope clusters is relatively uniform in young children, whereas there is conspicuous individual variation in IgG subclass responses except for IgG1. A narrow initial IgG subclass response to GAD65 and the emergence of IgG4 antibodies were characteristic of those who remained non-diabetic over the first few years of GAD65 autoimmunity.European Journal of Endocrinology 155 633-642

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Section: Discussionsupporting

confidence: 44%

Early epitope- and isotype-specific humoral immune responses to GAD65 in young children with genetic susceptibility to type 1 diabetes

Ronkainen

Hoppu²,

Korhonen³

et al. 2006

eur j endocrinol

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“…In light of recent evidence that autoantibodies may play a role in modulating the T cell response (11), it is notable that antibody specificity, rather than antibody titer, is associated with T1D and disease progression (13,34,35). The GAD65Ab response in T1D patients is characterized by GAD65Ab specificities similar to that of mAb b96.11 (13), whereas GAD65Ab in patients with SPS often recognize GAD65Ab epitopes similar to that bound by b78 (14).…”

Section: Discussionmentioning

confidence: 99%

The lack of anti-idiotypic antibodies, not the presence of the corresponding autoantibodies to glutamate decarboxylase, defines type 1 diabetes

Oak

Gilliam

Landin‐Olsson

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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Autoantibodies to glutamate decarboxylase 65 (GAD65Ab) are commonly believed to be a major characteristic for type 1 diabetes (T1D). We investigated the presence of GAD65Ab in healthy individuals (n ‫؍‬ 238) and first-degree relatives (FDRs) of T1D patients (n ‫؍‬ 27) who tested negative for GAD65Ab in conventional RIAs. Sera were applied to affinity columns coated with GAD65-specific mAbs to absorb anti-idiotypic antibodies (anti-Ids). The absorbed sera were analyzed for binding to GAD65 by RIAs. Both healthy individuals and FDRs present GAD65Ab that are inhibited by anti-Id, masking them in conventional detection methods. The presence of GAD65Ab-specific anti-Ids was confirmed by competitive ELISA. Remarkably, T1D patients (n ‫؍‬ 54) and Stiff Person Syndrome patients (n ‫؍‬ 8) show a specific lack of anti-Ids to disease-associated GAD65Ab epitopes. Purified anti-Ids from healthy individuals and FDRs inhibited the binding of GAD65Ab from T1D patients to GAD65. We conclude that masked GAD65Ab are present in the healthy population and that a lack of particular anti-Ids, rather than GAD65Ab per se, is a characteristic of T1D. The lack of these inhibitory antibodies may contribute to T cell activation by GAD65Ab.T ype 1 diabetes (T1D) is an autoimmune disease characterized by the presence of serologically detectable autoantibodies to multiple islet cell autoantigens. Autoantibodies to glutamate decarboxylase 65 (GAD65Ab) can be detected in the majority of new-onset T1D patients (1), in patients with latent autoimmune diabetes in adults (for review see ref.2), diabetes-related polyendocrine diseases (for review see ref.3), and in some rare neurologic diseases, notably Stiff Person Syndrome (SPS) (4), but rarely in the general population. GAD65Ab often herald the onset of T1D by months or years and are used to predict disease together with other islet cell autoantibodies (5, 6). The function of these autoantibodies and their B cells in the pathogenesis of T1D is not clear, especially as a patient with severe B cell deficiency and diabetes was reported (7). Although GAD65Ab are often considered to be an epiphenomenon resulting from the autoimmune destruction of the pancreatic ␤ cells, some studies suggest that they may be involved in antigen processing and presentation and thus modulate the immune response (8-10). This hypothesis is supported by a recent study demonstrating a pathogenic role of autoantibodies by enhancing islet cell antigen presentation to autoreactive T cells (11). Harbers et al. (11) showed that both antigen-specific CD8 ϩ T cells and antigenspecific antibodies were necessary for the development of autoimmune diabetes in transgenic mice that express a membranebound form of ovalbumin in pancreatic ␤ cells.To investigate the possible role of GAD65Ab in T1D pathogenesis, we previously injected young nonobese diabetic (NOD) mice with the GAD65-specific mAb b96.11 (12). This antibody specificity was shown earlier to be predictive of the development of T1D in humans (13). We found that this treatment i...

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“…Affinity maturation of an ongoing antibody response is associated with both "epitope focusing" to provide for selection of higher affinity antibodies and also "epitope spreading" to enable the immune response to encompass wider regions of the antigenic molecule. In type 1 diabetes specifically, there is evidence that the autoantibody response may first involve the COOH-terminal domain, with later spreading to the PLP and NH 2 -terminal domains (3,26). Notably, four of five major T-cell epitopes restricted by the high-risk HLA allele DRB1*0401 could be localized on the structure of GAD65 within the same region as the immunodominant B-cell epitope regions ctc1 and ctc2, and the fifth epitope was close to E264, which defines the M6 epitope in the PLP domain.…”

Section: Discussionmentioning

confidence: 99%

COOH-Terminal Clustering of Autoantibody and T-Cell Determinants on the Structure of GAD65 Provide Insights Into the Molecular Basis of Autoreactivity

et al. 2008

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OBJECTIVE-To gain structural insights into the autoantigenic properties of GAD65 in type 1 diabetes, we analyzed experimental epitope mapping data in the context of the recently determined crystal structures of GAD65 and GAD67, to allow "molecular positioning" of epitope sites for B-and T-cell reactivity. RESEARCH DESIGN AND METHODS-Datawere assembled from analysis of reported effects of mutagenesis of GAD65 on its reactivity with a panel of 11 human monoclonal antibodies (mAbs), supplemented by use of recombinant Fab to crossinhibit reactivity with GAD65 by radioimmunoprecipitation of the same mAbs. RESULTS-The COOH-terminal region on GAD65 was the major autoantigenic site. B-cell epitopes were distributed within two separate clusters around different faces of the COOHterminal domain. Inclusion of epitope sites in the pyridoxal phosphate-and NH 2 -terminal domains was attributed to the juxtaposition of all three domains in the crystal structure. Epitope preferences of different mAbs to GAD65 aligned with different clinical expressions of type 1 diabetes. Epitopes for four of five known reactive T-cell sequences restricted by HLA DRB1*0401 were aligned to solvent-exposed regions of the GAD65 structure and colocalized within the two B-cell epitope clusters. The continuous COOH-terminal epitope region of GAD65 was structurally highly flexible and therefore differed markedly from the equivalent region of GAD67.CONCLUSIONS-Structural features could explain the differing antigenicity, and perhaps immunogenicity, of GAD65 versus GAD67. The proximity of B-and T-cell epitopes within the GAD65 structure suggests that antigen-antibody complexes may influence antigen processing by accessory cells and thereby T-cell reactivity. Diabetes 57:1293-1301, 2008 T ype 1 diabetes is characterized by autoimmune reactivity to islet cell antigens that include the 65-kDa isoform of GAD (GAD65). Of the two isoforms of GAD, GAD67 and GAD65, only GAD65 is autoantigenic, in diseases that include particularly type 1 diabetes (1,2). Importantly, the specificity of antibodies for particular epitopes on GAD65 rather than their actual levels may be a better indicator of impending or actual destruction of islet ␤-cells. Thus in genetically prone individuals, changes in the focus of autoantibody responses to epitopes of GAD65, i.e., intramolecular epitope shifts during the period of pre-diabetic insulitis, herald the onset of overt type 1 diabetes (3).B-cell/autoantibody epitopes on GAD65 engage conformational determinants that are widely distributed over the linear sequence of the three domains, NH 2 -terminal (amino acids 1-234), pyridoxal phosphate (PLP)-binding (235-442), and COOH-terminal (443-585) domains (4). Presently, unanswered questions include the precise location of epitope sites and critical binding residues for autoantibody recognition, the differing immune reactivity of the GAD65 versus the GAD67 isoform, and the failure of natural immune tolerance to GAD65 in the first place. These questions prompted the recent crystallographic s...

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Dynamic changes of GAD65 autoantibody epitope specificities in individuals at risk of developing type 1 diabetes

Cited by 59 publications

References 54 publications

Early epitope- and isotype-specific humoral immune responses to GAD65 in young children with genetic susceptibility to type 1 diabetes

Early epitope- and isotype-specific humoral immune responses to GAD65 in young children with genetic susceptibility to type 1 diabetes

The lack of anti-idiotypic antibodies, not the presence of the corresponding autoantibodies to glutamate decarboxylase, defines type 1 diabetes

COOH-Terminal Clustering of Autoantibody and T-Cell Determinants on the Structure of GAD65 Provide Insights Into the Molecular Basis of Autoreactivity

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