Altered immune response to insulin in newly diagnosed compared to insulin-treated diabetic patients and healthy control subjects

Insulin-dependent diabetes mellitus (IDDM) is the result of a T-cell mediated autoimmune beta-cell destruction,which is accompanied by autoantibodies. We analysed the cellular and humoral immune response to insulin and insulin peptides in patients with recent-onset IDDM, IDDM patients treated with insulin, non-diabetic first degree relatives and unrelated control subjects. There were no differences in T-cell reactivity to whole insulin or insulin peptides in general between age-matched groups of IDDM patients, relatives or healthy control subjects. In contrast to investigations in NOD mice, no immunodominant or disease-specific insulin peptide could be identified. Surprisingly, a positive correlation of T-cell responses to insulin with age was noted (p < 0.005). This resulted in an inverse relation of insulin autoantibodies (IAA) and insulin reactive T-cells (p < 0.001) together with the well-described negative correlation of IAA with age. Interestingly, insulin-treated patients differed from age-matched recent-onset IDDM patients: first, simultaneous immune recognition of insulin with T-cells and IAA was only seen in patients treated for 6 months with insulin; second, insulin-treated patients rarely responded to whole insulin; third, they displayed less determinant spreading, and finally, recognition of multiple insulin peptides was not accompanied by crossreactivity to whole insulin. These distinct observations in insulin-treated IDDM patients, together with the inverse correlation between humoral and cellular responses to insulin, may result from activation or modulation of different T-cell subsets, and may be of relevance to insulin therapy trials, in which selective activation of non-destructive T-cell subsets may be a key to successful intervention.