T cell responses to type 1 diabetes related peptides sharing homologous regions

Glutamic acid decarboxylase (GAD) 65 is a major autoantigen in type 1 diabe tes. Regions of homology exist between GAD65 (residues 250-273) and the Cox sackie P2-C protein (residues 28-50) and between GAD65 (residues 506-518) a nd proinsulin (residues 24-36), and each of these has been reported to be a diabetes-associated T cell target. The aim of this study was to determine whether the homologous regions are shared targets of T lymphocyte reactivit y in individual patients with type 1 diabetes. T cell proliferation against the corresponding peptide pairs, GAD(254-276) and Coxsackie P2-C32-54 and GAD(506-518) and proinsulin(24-36), were measured in peripheral blood monon uclear cells from 26 patients with newly diagnosed type 1 diabetes and 24 c ontrol subjects. Responses with stimulation indices higher than 3 were foun d against each of the antigens tested in both patients and control subjects , and no differences were observed between groups. A strong positive correl ation was found between responses to the corresponding peptide pairs GAD(25 4-276) and Coxsackie P2-C32-54 (r=0.77, P<0.0001), and between responses to the corresponding peptide pairs GAD(506-518) and proinsulin(24-36) (r=0.66 , P<0.0001). However, a similar correlation was also observed between respo nses to the noncorresponding pairs Coxsackie P2-C32-54 and proinsulin(24-36 ) (r=0.82, P<0.0001), Coxsackie P2-C32-54 and GAD(506-518) (r=0.82, P<0.000 1), and GAD(254-276) and proinsulin(24-36) (r=0.83, P<0.0001). Strikingly, increased responses to peptides were found almost exclusively in subjects w ith high stimulation indices against the recall antigen tetanus toroid, fur ther suggesting that peripheral blood T cell responses are related to a gen eral subject hyperreactivity. These data suggest that proliferative T cell responses to peptides containing putative autoreactive epitopes of GAD65 an d proinsulin are not specific for type 1 diabetes, that correlation between T cell reactivity to peptides is not restricted to those containing homolo gous regions, and that non-antigen-specific factors are important determina nts of in vitro measurements of T cell reactivity.