Marcella Li

Natural history of antibodies to deamidated gliadin peptides and transglutaminase in early childhood celiac disease.

Introduction: Gliadin proteins play a key role in the pathogenesis of celiac disease; however, as a screen for celiac disease, anti-gliadin antibody testing has been replaced by the more sensitive and specific serological assays for transglutaminase autoantibodies (TGAA). A new generation of anti-gliadin antibody assays has been developed to detect synthetic, deamidated homologous gliadin peptides (DGP) with high sensitivity and specificity. Methods: Sera were collected prospectively from children with an increased risk for celiac disease as part of an ongoing study at Denver, and studied for the development of celiac autoimmunity. We investigated the high-performance DGP antibody assay in 50 TGAA-positive children both before the development of celiac autoimmunity and following the institution of a gluten-free diet to determine the relationship of DGP antibodies to TGAA. TGAA were measured by an in-house radioassay. Results: DGP antibodies and TGAA parallel each other over the period of years children were studied. DGP antibodies resolved sooner than TGAA in subjects on a gluten-free diet. DGP antibodies appeared earlier than TGAA in 9 children. Conclusions: Measuring DGP antibodies may be more useful than TGAA in monitoring children on a gluten-free diet. DGP antibodies can precede the appearance of TGAA in some at-risk children.

Transgenic Insulin (B:9-23) T-Cell Receptor Mice Develop Autoimmune Diabetes Dependent Upon RAG Genotype, H-2g7 Homozygosity, and Insulin 2 Gene Knockout

A series of recent studies in humans and the NOD mouse model have highlighted the central role that autoimmunity directed against insulin, in particular the insulin B chain 9-23 peptide, may play in the pathogenesis of type 1 diabetes. Both pathogenic and protective T-cell clones recognizing the B:9-23 peptide have been produced. This report describes the successful creation of BDC12-4.1 T-cell receptor (TCR) transgenic mice with spontaneous insulitis in F1 mice (FVB × NOD) and spontaneous diabetes in NOD.RAG−/− (backcross 1 generation). Disease progression is heterogeneous and is modified by a series of genetic factors including heterozygosity (H-2g7/H-2q) versus homozygosity for H-2g7, the presence of additional T-/B-cell receptor–rearranged genes (RAG+ versus RAG−/−), and the insulin 2 gene knockout (the insulin gene expressed in the NOD thymus). Despite lymphopenia, 40% of H-2g7/g7 BDC12-4.1 TCR+ RAG−/− Ins2−/− mice are diabetic by 10 weeks of age. As few as 13,500 transgenic T-cells from a diabetic TCR+ RAG−/− mouse can transfer diabetes to an NOD.scid mouse. The current study demonstrates that the BDC12-4.1 TCR is sufficient to cause diabetes at NOD backcross 1, bypassing polygenic inhibition of insulitis and diabetogenesis.

Conserved T cell receptor α-chain induces insulin autoantibodies

A fundamental question is what are the molecular determinants that lead to spontaneous preferential targeting of specific autoantigens in autoimmune diseases, such as the insulin B:9–23 peptide sequence in type 1 diabetes. Anti-insulin B:9–23 T cell clones isolated from prediabetic NOD islets have a conserved Vα-segment/Jα-segment, but no conservation of the α-chain N region and no conservation of the Vβ-chain. Here, we show that the conserved T cell receptor α-chain generates insulin autoantibodies when transgenically or retrogenically introduced into mice without its corresponding Vβ. We suggest that a major part of the mystery as to why islet autoimmunity develops relates to recognition of a primary insulin peptide by a conserved α chain T cell receptor.

Murine High Specificity/Sensitivity Competitive Europium Insulin Autoantibody Assay

BACKGROUND Most insulin autoantibody assays for both human and animal models are in a radioassay format utilizing (125)I-insulin, but despite the radioassay format international workshops have documented difficulty in standardization between laboratories. There is thus a need for simpler assay formats that do not utilize radioactivity, yet retain the high specificity and sensitivity of radioassays. METHODS To establish an easier enzyme-linked immunosorbent assay (ELISA) for insulin autoantibodies of non-obese diabetic (NOD) mice, we used an ELISA format, competition with unlabeled insulin, europium-avidin, and time-resolved fluorescence detection (competitive europium insulin autoantibody assay). RESULTS The competitive europium assay of insulin autoantibodies when applied to sera from NOD mice had high sensitivity and specificity (92% sensitivity, 100% specificity) compared to our standard insulin autoantibody radioassay (72% sensitivity, 100% specificity) in analyzing blind workshop sera. It is noteworthy that though the assay has extremely high sensitivity for murine insulin autoantibodies and utilizes human insulin as target autoantigen, human sera with high levels of insulin autoantibodies are not detected. CONCLUSIONS Our results clearly indicate that low levels of insulin autoantibodies can be detected in an ELISA-like format. Combining a europium-based ELISA with competition with fluid-phase autoantigen can be applicable to many autoantigens to achieve high specificity and sensitivity in an ELISA format.

Establishment of Native Insulin‐Negative NOD Mice and the Methodology to Distinguish Specific Insulin Knockout Genotypes and a B:16 Alanine Preproinsulin Transgene

Abstract: We hypothesize that NOD mice without native insulin, but with an altered insulin B:9‐23 sequence, will be completely protected from diabetes/insulitis if insulin B:9‐23 is an essential T cell epitope. To investigate this hypothesis, we have established initial insulin 1‐ and 2‐negative NOD mice with a transgene directing production of preproinsulin with alanine at position B:16 rather than the native tyrosine of both insulin 1 and insulin 2. Sets of primers for PCR‐based assays have been created and validated. They are able to distinguish the presence or absence of the insulin gene knockouts and of both native insulin 1 and insulin 2 (and thus distinguish heterozygous versus homozygous knockouts), as well as the presence of the altered insulin transgene, B:16 alanine preproinsulin. Four B:16 alanine transgenic founders were produced directly in NOD mice and, by intercrossing, initial live native insulin‐negative B:16 alanine transgenic mice have been generated.

Deleting islet autoimmunity

Even though there are numerous autoantigens for type 1 diabetes, current evidence suggests that a single autoantigen, namely insulin, is responsible for the key initiating event in autoimmunity. If a single autoantigen is necessary for triggering the autoimmune process, then antigen-specific therapy to block or delete the immune response against that autoantigen before epitope spreading occurs, may become a larger focus of future immunotherapeutic strategies. In this article, we review current literature regarding insulin as an autoantigen and potential approaches to deleting insulin-reactive T cells through the use of peptide vaccines and targeted T cell receptor immunizations.