Poster Presentation The 13th International Congress of the Immunology of Diabetes Society 2013

Non-synonymous Single Nucleotide Polymorphisms (SNPs) in the IA-2 Gene and Novel Epitopes within the IA-2 Extracellular Domain (#107)

Michael P Morran 1 , Eddied James 2 , Santiago Schnell 1 , Ying-Jian Zhang 1 , Howard Davidson 3 , Dorothy J. Becker 4 , Massimo Pietropaolo 1
  1. University of Michigan Medical School, Ann Arbor, MI, United States
  2. Benaroya Research Institute, University of Washington, Seattle, Washington, United States
  3. Pediatrics, University of Colorado Denver, Denver, Colorado, United States
  4. Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States

The neuroendocrine tyrosine phosphatase-like protein IA-2 is a transmembrane glycoprotein localized in the secretory granules of β-cells and a major autoantigen in type 1 diabetes (T1D). We previously reported that a subgroup of subjects with Ab directed to full length IA-2 exhibited a very high risk as well as rapid progression to T1D onset. Kaplan and Meier analysis revealed that a subgroup subjects with no detectable Ab against the conventional constructs (IA-2ic or ICA512bdc) exhibited Ab responses toward IA-2 (Log rank, P = 0.008) as well as the IA-2 extracellular domain (amino acid residues: 26-577).
We demonstrated that the full length IA-2 nucleotide sequence contains three validated non-synonymous SNPs (listed in SNP Consortium and Celera databases) (SNP-IA-2 construct: aa residues 27, 608, and 671) and identified SNP-IA-2 Ab reactivity in individuals who lack serologic responses against other conventional antigenic determinants of IA-2. The prevalence of Ab to SNP-IA-2 was 60% in new onset T1D and 36.2% in prediabetics respectively.
Protein sequence and folding analysis indicates that the IA-2 variants influence the overall folding of SNP-IA-2 and create potential new Ab-protein interaction sites compared to native IA-2. Three dimensional models of the native IA-2 (Locus: NM_002846.3) and SNP-IA-2 display distinctly different structural morphology within the extracellular domain, likely due to the amino acid variants found within the juxtamembrane domain of IA-2. Correspondingly, while previous studies have focused on T cell epitopes within the C-terminal region of IA-2, we identified CD4+ T cells in T1D patients that respond to novel epitopes within the extracellular domain (n=8).
In sum, the ability to identify at risk individuals due to SNP-IA-2 Ab reactivity may aid in improving T1D prediction. Furthermore, the identification of T cell responses against the extracellular domain of IA-2 may lead to advances in peptide-based immunotherapies targeted to prevent T1D.