Identification of Tyrosine Phosphatase 2(256–760) Construct as a New, Sensitive Marker for the Detection of Islet Autoimmunity in Type 2 Diabetic Patients

Abstract

OBJECTIVE—The presence of autoantibodies to islet antigens GAD and/or tyrosine phosphatase 2 (IA-2) in type 2 diabetic patients (latent autoimmune diabetes in adults [LADA]) identifies subjects at high risk to develop insulin dependency. The aim of this study was to dissect humoral anti–IA-2 immune response in Caucasian LADA patients, identifying the most sensitive construct to evaluate IA-2 immunoreactivity and comparing LADA IA-2 epitope specificities to those found in type 1 diabetes. RESEARCH DESIGN AND METHODS—We analyzed 177 LADA and 978 type 2 diabetic patients with different disease duration, collected in a nationwide Italian survey, the Non–Insulin Requiring Autoimmune Diabetes (NIRAD) study aimed at assessing prevalence and characteristics of autoimmune diabetes in type 2 diabetic patients and 106 newly diagnosed type 1 diabetic patients (53 children, 53 adults). By radioimmunoassay, we analyzed humoral immunoreactivity to seven IA-2 constructs: IA-2PTP (687–979), IA-2(761–964), IA-2(256–760), IA-2JM (601–630), IA-2IC (605–979), IA-2BDC (256–556:630–979), and IA-2FL (1–979). RESULTS—IA-2(256–760) fragment was identified as the marker with the highest sensitivity for detection of humoral IA-2 immunoreactivity in LADA patients, identifying IA-2 autoantibodies in ∼30% of GAD antibody (GADA)-positive LADA patients and in 3.4% of GADA-negative type 2 diabetic patients. LADA IA-2(256–760)A positivity was associated with an increased frequency of autoimmune diabetes HLA-susceptible genotypes and with a higher risk for developing thyroid autoimmunity compared with autoantibody-negative type 2 diabetic patients. At disease diagnosis, adult-onset type 1 diabetic and LADA patients showed a lower IA-2 COOH-terminal immunoreactivity compared with childhood-onset type 1 diabetic patients. CONCLUSIONS—IA-2 immunoreactivity in LADA patients has thus far been underestimated, and IA-2(256–760) autoantibody detection may represent a novel diagnostic tool for the identification of islet autoimmunity in these patients.

Humoral Autoimmunity against the Extracellular Domain of the Neuroendocrine Autoantigen IA-2 Heightens the Risk of Type 1 Diabetes

“…These studies, which for the most part were conducted in patients affected by T1DM and latent autoimmune diabetes of the adulthood (26), have demonstrated that IA-2 antibody responses appear to be primarily directed against the IA-2ic (amino acids 601-979) of the molecule (20, 26 -30). Currently two of these constructs, namely ICA512bdc (amino acids 256 -556; 630 -979) and IA-2ic (amino acids 601-979) in combination with other islet autoantibodies, have been widely used in large scale RIAs in epidemiological studies to classify T1DM patients and identify their at-risk relatives and enroll them in intervention studies aimed at preventing overt disease (16 -18).…”

GADA Titer-Related Risk for Organ-Specific Autoimmunity in LADA Subjects Subdivided according to Gender (NIRAD Study 6)

“…IA-2 IC , IA-2 256 -760 , ZnT8, and tTG antibodies were measured by previously described radioimmunoprecipitation assays (15,16). TPO and APC antibodies were measured using RIA (Medipan, Berlin, Germany) and ELISA (Axa Diagnostics, Pomezia Italy) commercially available kits, respectively.…”

Distinct clinical and laboratory characteristics of latent autoimmune diabetes in adults in relation to type 1 and type 2 diabetes mellitus

“…In contrast to IAA and ICA, anti-IA-2 AAbs show no variation with age and thus, when anti-GAD65 autoantibodies are also evaluated, an autoimmune signature of the diabetes can be defined [23] . Recently, antibodies against the IA-2 (256-760) fragment were shown to be a reliable marker in LADA patients and they were positively correlated with higher frequency of autoimmunity and susceptible HLA haplotypes [48] . Patients with autoimmune diabetes are likely to be presented with an additional autoimmune condition of endocrine (thyroid and adrenal glands) or non-endocrine organs (thyroid and adrenal glands) [23] .…”