Role of insulin autoantibody affinity as a predictive marker for type 1 diabetes in young children with HLA-conferred disease susceptibility.

Background: Insulin autoantibodies (IAA) are early markers of prediabetic autoimmunity. As transient and fluctuating IAA positivity are common among young children, distinguishing non-progressive IAA from destruction-related IAA is essential when preventive measures are considered. We tested whether children progressing rapidly to type 1 diabetes (progressors) are characterized by a higher prediabetic IAA affinity than IAA-positive children remaining unaffected or progressing more slowly to diabetes (non-progressors), and whether IAA affinity increases towards diagnosis.

Methods: Finnish children with HLA-conferred diabetes susceptibility were observed from birth for diabetes-associated autoantibodies and progression to overt type 1 diabetes. IAA levels and affinities of the first IAA-positive prediabetic samples and samples obtained closest to the diagnosis in 64 progressors were compared with corresponding values in 64 matched IAA-positive non-progressors.

Results: The median age at diagnosis was 3.9 years in progressors and the median follow-up time 7.6 years among unaffected subjects. In the first samples the median IAA affinity was 1.4 x 10(10) L/mol in both groups (p = 0.33), while at the second sampling it was 1.1 x 10(10) L/mol in progressors and 1.2 x 10(10) L/mol in unaffected subjects (p = 0.46). No changes in affinity levels were observed (p = 0.33 and p = 0.84, respectively). IAA titers increased towards diagnosis among progressors (from a median of 13.6 to 20.1 relative units; p = 0.02).

Conclusions: Among young IAA-positive children with HLA-conferred disease susceptibility IAA affinity failed to distinguish rapid progressors from slowly or non-progressing subjects. In relation to IAA affinity, no maturation of the humoral immune response was observed over time from seroconversion to diagnosis.