Preproinsulin is a target T cell autoantigen in human Type 1 diabetes. This study analyses the phenotype and epitope recognition of preproinsulin reactive T cells in subjects with a high genetic risk of diabetes [HLA-DRB1*04, DQ8 with Ab+ (autoantibody-positive) or without islet autoantibodies (control subjects)], and in HLA-matched diabetic patients.

A preproinsulin peptide library approach was used to screen for cytokine profiles and epitope specificities in human peripheral blood lymphocytes, and CD4⁺CD45RA⁻ and CD4⁺CD45RA⁺ T cell subfractions, representing memory and naive and recently primed T cells respectively.

In CD4⁺ T cell subsets we identified immunodominant epitopes and cytokine production patterns that differed profoundly between patients, Ab+ subjects and non-diabetic HLA-matched control subjects. In Ab+ subjects, a C-peptide epitope C13–29 and insulin B-chain epitope B11–27 were preferentially recognised, whereas insulin-treated Type 1 diabetic patients reacted to native insulin and B-chain epitope B1–16. In peripheral blood lymphocytes of Ab+ subjects, an increase in T helper (Th) 1 (IFNγ, IL-2) and Th2 (IL-4) cytokines was detectable, wheras in CD45RA⁺ and CD45RA⁻ subsets, IL-4 and IL-10 phenotypes dominated, compatible with the contribution of non-CD4 cells to IFNγ content. In insulin-treated Type 1 diabetic patients, naive and recently primed CD4⁺ cells were characterised by increasd IFNγ, TNFα, and IL-5.

Our data show that T cell reactivity to preproinsulin in CD45RA subsets is Th2-dominant in Ab+ subjects, challenging the Th1 paradigm in Type 1 diabetes. Characteristic immunodominant epitopes and cytokine patterns distinguish diabetic patients and Ab+ subjects from HLA-matched healthy individuals. This could prove useful in monitoring of T-cell immunity in clinical diabetes intervention trials.