Mature high-affinity immune responses to (pro)insulin anticipate the autoimmune cascade that leads to type 1 diabetes
Peter Achenbach, … , Anette-G. Ziegler, Ezio Bonifacio
Peter Achenbach, … , Anette-G. Ziegler, Ezio Bonifacio
Published August 16, 2004
Citation Information: J Clin Invest. 2004;114(4):589-597. https://doi.org/10.1172/JCI21307.
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Article Metabolism

Mature high-affinity immune responses to (pro)insulin anticipate the autoimmune cascade that leads to type 1 diabetes

Abstract

Children at risk for type 1 diabetes can develop early insulin autoantibodies (IAAs). Many, but not all, of these children subsequently develop multiple islet autoantibodies and diabetes. To determine whether disease progression is reflected by autoantibody maturity, IAA affinity was measured by competitive radiobinding assay in first and subsequent IAA-positive samples from children followed from birth in the BABYDIAB cohort. IAA affinity in first positive samples ranged from less than 106 l/mol to more than 1011 l/mol. High affinity was associated with HLA DRB1*04, young age of IAA appearance, and subsequent progression to multiple islet autoantibodies or type 1 diabetes. IAA affinity in multiple antibody–positive children was on average 100-fold higher than in children who remained single IAA positive or became autoantibody negative. All high-affinity IAAs required conservation of human insulin A chain residues 8–13 and were reactive with proinsulin. In contrast, most lower-affinity IAAs were dependent on COOH-terminal B chain residues and did not bind proinsulin. These data are consistent with the concept that type 1 diabetes is associated with sustained early exposure to (pro)insulin in the context of HLA DR4 and show that high-affinity proinsulin-reactive IAAs identify children with the highest diabetes risk.

Authors

Peter Achenbach, Kerstin Koczwara, Annette Knopff, Heike Naserke, Anette-G. Ziegler, Ezio Bonifacio

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Figure 1

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Competitive insulin binding curves of IAAs. (A) Competition of an IAA-po...
Competitive insulin binding curves of IAAs. (A) Competition of an IAA-positive serum against [125I] insulin labeled at Tyr14A (circles), Tyr19A (triangles), and Tyr16B (diamonds) with increasing concentrations of unlabeled human insulin. Binding curves were similar with the [125I] insulin labeled at residues Tyr14A, Tyr19A, or Tyr16B, and calculated IAA affinities did not significantly differ among Tyr14A [125I] insulin (2.1 × 1011 l/mol), Tyr19A [125I] insulin (2.3 × 1011 l/mol), and Tyr16B [125I] insulin (5.7 × 1011 l/mol). Insulin labeled at position Tyr16B was associated with considerably higher nonspecific binding than insulin labeled at Tyr14A or Tyr19A. (B) Scatchard analysis performed for the competition curve obtained against Tyr14A radiolabeled insulin. (C) Binding curves of a serum mix containing a serum with high-affinity IAAs (1.7 × 1011 l/mol) and a serum with low-affinity IAAs (2 × 105 l/mol) (squares) and a serum mix containing a serum with high-affinity IAAs (1.7 × 1011 l/mol) and a serum with moderate-affinity IAAs (6.3 × 107 l/mol) (circles). Both curves fit a 2-site binding model. (D) Binding curves obtained for the first IAA-positive serum from 56 children in the BABYDIAB study. IAA binding in 1 serum conforms to a 2-site binding model (dotted line), whereas the remaining sera conform to a 1-site binding model. Curves that are shifted to the right indicate lower-affinity IAAs.