An Islet-Cell Protein Tyrosine Phosphatase Is a Likely Precursor to the 37-kDa Autoantigen in Type 1 Diabetes: Human and Macaque Sequences, Tissue Distribution, Unique and Shared Epitopes, and Predictive Autoantibodies

Early childhood infections and the risk of islet autoimmunity: the Diabetes Autoimmunity Study in the Young (DAISY)

OBJECTIVE

Type 1 diabetes is a common chronic childhood disease, and the incidence is increasing globally. Childhood infections are considered a potential environmental trigger of type 1 diabetes. Alternatively, improved hygiene and reduced childhood infections could explain the increase in type 1 diabetes in developed countries. The association of reported illnesses during infancy and later development of islet autoimmunity (IA) were examined in the Diabetes Autoimmunity Study in the Young.

RESEARCH DESIGN AND METHODS

Complete illness interviews through 9 months of age were collected for 1,729 children-1,174 without a family history of type 1 diabetes and 555 with a first-degree relative with type 1 diabetes. Persistent IA was defined as positive antibodies to insulin, glutamic acid decarboxylase, or tyrosine phosphatase on at least two consecutive study visits.

RESULTS

There were 109 children with persistent IA among the 1,729 children with illness records. A greater number of gastrointestinal illnesses were associated with an increased risk of IA, but only among children who were exposed to gluten-containing grains (wheat or barley) either <4 months of age (hazard ratio 1.37 [95% CI 1.22-1.55]; P < 0.0001) or ≥7 months of age (1.12 [1.05-1.19]; P = 0.0005) compared with 4-6 months of age (P for interaction = 0.02). There were no associations of upper respiratory symptoms, respiratory illnesses, or fevers with IA.

CONCLUSIONS

Specific pathogens such as enteroviruses or rotavirus may increase the risk of IA in the presence of existing inflammation induced by diet.

Homing of GAD65 specific autoimmunity and development of insulitis requires expression of both DQ8 and human GAD65 in transgenic mice

MHC-class II genes determine susceptibility in human type-1 diabetes. In their context, presentation of target antigen(s) results in autoimmunity and beta-cell destruction. An animal model, in which human beta-cell autoantigen(s) are presented to effector cells in the context of human MHC-class II diabetes-susceptibility genes, would be desirable for studying molecular mechanisms of disease and developing antigen-specific immune-interventions. We report the development of antigen-specific insulitis in double-transgenic mice carrying the HLA-DQ8 diabetes-susceptibility haplotype and expressing the human autoantigen GAD65 in pancreatic beta-cells. Immunization with human GAD65 cDNA resulted in severe insulitis and low antibody levels in double-transgenic mice while control mice were mostly insulitis free. CFA/protein immunization resulted in high antibody levels and modest insulitis. Pancreatic lymphocytic infiltration progressed through stages (exocrine pancreas followed by peri- and intra-insulitis). Adoptive transfer of splenocytes from DNA-immunized mice resulted in development of insulitis in recipient transgenics. Our results show that immunization with a clinically relevant, type-1 diabetes human autoantigen, in a humanized genetic setting, results in the development of an immune response that homes to islets of Langerhans. This animal model will facilitate studies of autoimmunity to GAD65 in the context of HLA-DQ8, and development of methods to induce tolerance and prevent insulitis.

A novel high-throughput method for accurate, rapid, and economical measurement of multiple type 1 diabetes autoantibodies

Prediction of Type 1 diabetes for study of preventive therapies requires screening the general population, where 85% of new cases occur. Even with HLA-based prescreening, nearly 20% of all children will need multiple serum autoantibody testings. High-throughput, economical, and accurate methods are therefore essential. We have developed such a radiobinding method, using 96-well microtiter plates and a novel immune complex capture method via membrane-bound Protein A. Each microtiter plate contained a standard negative control serum, and low-, medium-, and high-level positive control sera. All sera were evaluated in triplicate. This readily allowed quality control criteria both for triplicates of individual sera and for each 96-well plate. Inter-assay coefficients of variation (CVs) were all </=16%, while intra-assay CVs were all </=10%. The assay was found to be sensitive (to detect autoantibodies in patients) and specific (low reactivity in thousands of healthy volunteers). The format worked well using diverse antigens such as 35S-met-GAD65, 35S-met-ICA512/IA2, 35S-met-Phogrin, and 125I-insulin, and could be used for simultaneous screening of reactivity to both GAD65 and ICA512/IA2 in the same well. Diagnostic accuracy compared favorably with microcentrifuge tube-based Protein A-agarose GAD65 and IA2 autoantibody radiobinding assays and with acid-charcoal-polyethylene glycol (PEG) based competitive insulin autoantibody assays. In the case of 125I-insulin, comparing signal in the absence versus presence of cold insulin competitor was not necessary. Total serum volumes required were only 6 microl for GAD and ICA512, and only 15 microl for IAA. The method costs less than all other commonly used formats, and should be useful for population screening.

Characterization and chromosomal localization of PTP-NP-2, a new isoform of protein tyrosine phosphatase-like receptor, expressed on synaptic boutons

Recently, there have been several reports describing the cloning and characterization of the novel family of protein tyrosine phosphatase-like receptor molecules (known as IA-2 and PTP-NP/PTP-IAR/IA-2beta/phogrin), which may act as autoantigens in diabetes. Here, we report the molecular characterization and chromosomal localization of a new isoform of this family in brain termed PTP-NP-2 (for PTP-NP tyrosine phosphatase isoform), and its function in rat primary hippocampal neurons. PTP-NP-2 has 48% identity to IA-2. The principal difference between PTP-NP-2 and PTP-NP is a 17-amino-acid insert near the N-terminus of PTP-NP that is absent in PTP-NP-2. Genomic DNA analysis indicates that the 17-amino-acid insert is coded by a separate exon, suggesting that both IA-2beta and PTP-NP-2 are isoforms arising by alternate splicing of the same gene. Reverse transcriptase-PCR revealed that both isoforms are present in human SH-SY5Y neuroblastoma cells. PTP-NP-2 mRNA expression is highly restricted, with a 5.5-kb specific transcript in human fetal and adult brain and 5.5 and 3. 8 kb in human adult pancreas. SH-SY5Y neuroblastoma and U87-MG glioblastoma cells showed specific transcripts of 5.5 and 3.8<HSP SP = "0.25">kb, respectively, indicating the existence of several isoforms of this molecule in the nervous system. The human gene encoding PTP-NP-2 was assigned to human chromosome 7q22-qter using Southern blot analysis of genomic DNAs from rodent/human somatic hybrid cell lines. Confocal microscopy analyses of rat primary hippocampal neurons revealed that PTP-NP-2 is abundantly expressed on synaptic boutons in primary neurons. Wild-type PTP-NP-2 showed no measurable tyrosine phosphatase activity using an in-vitro pNPP assay. Examination of the PTP-NP-2 catalytic consensus sequence revealed that this sequence differed from the typical tyrosine phosphatase-domain consensus sequence by an alanine to aspartate change (amino acid 930). Mutation of aspartate 930 to alanine produced a catalytically active enzyme, suggesting that native PTP-NP and its isoform PTP-NP-2 are catalytically inactive receptor protein tyrosine phosphatase homologues. Taken together, these results indicate that the tyrosine phosphatase PTP-NP-2 is a new isoform of PTP-NP tyrosine phosphatase, is expressed on synaptic boutons and may participate in the regulation of synaptic bouton endocytosis.