Characterization of Zinc Transporter 8 antibodies in autoimmune diabetic patients from Argentinian population using monomeric, homodimeric and heterodimeric ZnT8 antigen variants.

FACCINETTI, NATALIA I.; GUERRA, LUCIANO L.; PENAS, ALBERTO; IACONO, RUBÉN F.; FRECHTEL, G.; TRIFONE, L.; POSKUS, EDGARDO; TRABUCCHI, ALDANA; VALDEZ, SILVINA N.

EUROPEAN JOURNAL OF ENDOCRINOLOGY

BIOSCIENTIFICA LTD

Lugar: Bristol; Año: 2015 vol. 174 p. 157 - 175

0804-4643

Objective: In order to gain further knowledge of the structure of zinc transporter 8 (ZnT8) epitopes, we studied the role ofthe amino acid at position 325 in the antigen and its dimeric conformation for autoantibodies to ZnT8 (ZnT8A) recognition.Methods: For this purpose, several ZnT8 C-terminal domain variants were designed: monomer carrying Arg325 or Trp325,homo-dimers ZnT8-Arg?Arg325 and ZnT8-Trp?Trp325, and hetero-dimer ZnT8-Arg?Trp325. Two groups of Argentiniandiabetic patients were subjected to analysis using [35S]-ZnT8 variants by radioligand binding assay (RBA): i) 100 new-onset,insulin-dependent, type 1 diabetic patients and ii) 282 slowly progressing to insulin requirement, non-obese adult-onsetdiabetic patients. In addition, 50 type 1 diabetic patients and 100 normal control sera provided by the American DiabetesAssociation (ADA) were evaluated in order to calculate the sensitivity and specificity of ZnT8A assays for each antigenicvariant. Other routine b-cell autoantibodies were also tested by RBA.Results: Of the 100 Argentinian type 1 diabetic patients, 65 were ZnT8AC. Out of them, 8 patients recognized allrecombinant forms of ZnT8 and most patients (56) reacted against the heterodimer. Additionally, out of 282 non-obese adultonsetdiabetic patients 46 were ZnT8AC, whereas 29 patients recognized only dimers. Besides, exclusive reactivity againstZnT8A was found in 9.0% for type 1 diabetes mellitus and 10.3% for non-obese adult-onset diabetic patients.Conclusions: Significantly higher signal values in RBA were obtained with the heterodimeric variant. An increased detectionof humoral autoimmunity was found in both groups when ZnT8A was employed in combination with the other b-cellautoantibodies. The inclusion of homodimeric immunoreactive peptides revealed the existence of quaternary structuredefinedepitopes probably resembling the actual state of the autoantigen in vivo. Finally, the differential profiles of ZnT8Aexhibited by type 1 and non-obese adult-onset diabetic patients suggest the different nature of autoimmune processesunderlying both pathologies.