The presence of preformed HLA DSA in transplanted patients with a negative cytotoxicity crossmatch is associated with a lower allograft survival. The detection of anti-HLA with no DSA has no influence in the graft outcome. Finally, there were no demonstrable effects of mean fluorescence intensity (MFI) values >1500 on graft survival.

OBJECTIVEThe characterization of diverse subtypes of diabetes is a dynamic field of clinical research and an active area of discussion. The objective of this study was to identify new antigenic determinants in the neuroendocrine autoantigen IA-2 (ICA512) and assess whether circulating autoantibodies directed to new IA-2 epitopes identify autoimmune diabetes in young and adult populations with diabetes.RESEARCH DESIGN AND METHODSClinically diagnosed patients with type 2 diabetes (n = 258; diabetes duration: 0.01–31 years) were evaluated using a new biomarker detecting autoantibodies directed to the extracellular domain of the neuroendocrine autoantigen IA-2 (IA-2ec). The proportion of IA-2ec autoantibodies was also evaluated in newly diagnosed patients with type 1 diabetes (n = 150; diabetes duration: 0.04–0.49 years). In addition, IA-2 (intracellular domain), GAD65, and zinc transporter 8 autoantibodies were assayed.RESULTSIA-2ec autoantibodies were detected in patients with type 1 diabetes and, surprisingly, in 5% of patients with type 2 diabetes without serologic responses to other IA-2 antigenic epitopes or other islet autoantigens. We also assessed the ability of IA-2ec–derived peptides to elicit CD4+ T-cell responses by stimulating peripheral blood mononuclear cells from patients with type 1 diabetes (n = 18) and HLA-matched healthy subjects (n = 13) with peptides and staining with the peptide/DQ8-specific tetramers, observing disease-associated responses to previously unreported epitopes within IA-2ec.CONCLUSIONSWe developed a new antibody biomarker identifying novel antigenic determinants within the N terminus of IA-2. IA-2ec autoantibodies can be detected in patients with type 1 diabetes and in a subgroup of adult autoimmune patients with type 2 diabetes phenotype negative for conventional islet autoantibody testing. These observations suggest that islet autoimmunity may be more common in clinically diagnosed type 2 diabetes than previously observed.

Autoantibodies directed against tyrosine phosphatase IA-2 antibody (IA-2 Ab) are diagnostic for autoimmune type 1 diabetes. Conventional assays target the intracellular domain of IA-2. Among patients with ketosis-prone diabetes (KPD), characterized by presentation with diabetic ketoacidosis (DKA), >60% of adults lack three classic islet autoantibodiesdIA-2, GAD65, and ZnT8 Absdassociated with type 1 diabetes. We aimed to determine whether apparently autoantibodynegative ("A2") KPD patients possess occult IA-2 Ab directed against fulllength IA-2 (IA-2FL) or its extracellular domain (IA-2EC). RESEARCH DESIGN AND METHODS We developed an assay that targets IA-2FL and IA-2EC and used it to analyze 288 subjects with A2 KPD. RESULTS Ten A2 KPD patients were positive for IA-2EC Ab (3.5%), and three were also positive for IA-2FL Ab (1.0%), similar to frequencies in type 1 and type 2 diabetes. CONCLUSIONS Measurement of IA-2FL Ab and IA-2EC Ab improves the accuracy of the Ab classification of KPD patients. Ketosis-prone diabetes (KPD) is a heterogenous syndrome characterized by presentation with diabetic ketoacidosis (DKA) and classified by the presence or absence of islet autoantibodies ("A+" or "A2") and presence or absence of b-cell functional reserve ("b+" or "b2") (1,2). Distinct from patients with type 1 diabetes, patients with KPD often present when older, have fewer recurrences of DKA, and can often discontinue insulin treatment while maintaining glycemic control (3). More than 60% of KPD adult patients lack evidence of islet autoimmunity (i.e., are A2) by testing for the presence of autoantibodies against the 65-kDa isoform of glutamate decarboxylase (GAD65), zinc transporter T8 (ZnT8), and the neuroendocrine autoantigen IA-2 (or ICA512) (1,2,4). Constructs used in conventional IA-2 autoantibody assays include intracellular fragments, but not the extracellular domain (IA-2EC), which has recently been investigated as a target for IA-2-specific autoantibodies (5). We reported that 1% of patients with autoimmune type 1 diabetes are positive only for the IA-2EC antibody (Ab), as were 4.7% of 258 patients with type 2 diabetes (5,6). Furthermore, we reported that full-length IA-2 (IA-2FL

We identified autoantibodies (AAb) reacting with a variant IA-2 molecule (IA-2var) that has three amino acid substitutions (Cys 27 , Gly 608 , and Pro 671) within the full-length molecule. We examined IA-2var AAb in first-degree relatives of type 1 diabetes (T1D) probands from the TrialNet Pathway to Prevention Study. The presence of IA-2varspecific AAb in relatives was associated with accelerated progression to T1D in those positive for AAb to GAD65 and/or insulin but negative in the standard test for IA-2 AAb. Furthermore, relatives with single islet AAb (by traditional assays) and carrying both IA-2var AAb and the high-risk HLA-DRB1*04-DQB1*03:02 haplotype progress rapidly to onset of T1D. Molecular modeling of IA-2var predicts that the genomic variation that alters the three amino acids induces changes in the threedimensional structure of the molecule, which may lead to epitope unmasking in the IA-2 extracellular domain. Our observations suggest that the presence of AAb to IA-2var would identify high-risk subjects who would benefit from participation in prevention trials who have one islet antibody by traditional testing and otherwise would be misclassified as "low risk" relatives. Type 1 diabetes (T1D) is an autoimmune disease that results from the targeted destruction of pancreatic b-cells by autoreactive T cells (1,2). The development of T1D is associated with the occurrence of autoantibodies (AAb) to pancreatic islet antigens that can be used as predictive biomarkers of disease progression (3). AAb associated with T1D are mainly directed against proteins that are involved in the secretory pathway of insulin, including insulin, glutamic acid decarboxylase (GAD65), islet tyrosine phosphatase-like protein (IA-2), and zinc transporter 8 SLC30A8 (ZnT8). The presence of AAb to IA-2 is associated with a high risk of T1D development (4-7). Screening for T1D-associated AAb allows for identification of asymptomatic, high-risk individuals (8) and for natural history studies of disease in cadaveric donors (9). The neuroendocrine molecule IA-2 is a transmembrane glycoprotein of the tyrosine phosphatase-like protein family that is localized to the insulin-secretory granules of the pancreatic b-cell (10). IA-2 (PTPRN) encodes a 979-amino acid protein containing three domains: the N-terminal extracellular (or luminal) domain (amino acids 1-556), the transmembrane domain (amino acids 557-600), and the COOH-terminal intracellular (or cytoplasmic) domain (amino acids 601-979) containing a juxtamembrane (JM) domain (amino acids 601-686) and a protein tyrosine phosphatase