T cell autoreactivity to proinsulin epitopes in diabetic patients and healthy subjects

We investigated the immune response to proinsulin, a potential autoantigen in IDDM secreted exclusively by pancreatic beta-cells. A total of 2,142 sho rt-term cell lines were generated from 19 individuals; seven IDDM patients at the disease onset and 12 control subjects. No increase in the frequency of proinsulin reactive cells was observed in the IDDM group. To define proi nsulin epitopes, proliferative responses of proinsulin-specific lines were examined against 10 overlapping 15 amino acid peptides encompassing the hum an proinsulin sequence. The predominant immune response was directed agains t the proinsulin p35-50 peptide located in the (C) connecting peptide betwe en the alpha- and beta-chain of insulin. Recognition of the proinsulin p35- 50 peptide could be shown by generating specific T cell clones against the peptide. However, unlike responses to other tissue-specific autoantigens th ere were only low proliferative responses to proinsulin as measured by H-3- thymidine incorporation. This low reactivity may be partially explained by the location of the p35-50 peptide in the C-peptide which is released into the circulation and therefore, may induce a clonal anergy of T reactive cel ls. However, the significantly higher H-3-thymidine incorporation after CD3 -D28 triggering showed that peptide specific T cells were capable of a sign ificant response with a stronger TCR signal. (C) 1999 Academic Press.