Abstract: Objective To explore a newly discovered T cell antigen [the group-specific antigen(Gag)of endogenous retrovirus (ERV)] associated with type 1 diabetes (T1D) and the pathogenesis of T1D. Methods First, to analyze the amino acid sequence of an islet-expressing Gag antigen, Gag 194 and identified one peptide[P193-P210(VSRLRGRRDPPAVDSTTS)], for production of Gag-specific monoclonal antibodies (mAbs). Second, ELISA and Western blot methods were performed to evaluate antigen specificity of the mAbs. Third, the expression of Gag antigen in pancreatic islets of T1D-susceptible non-obese diabetic (NOD) mice and T1D-resistant C57BL/6 mice was examined by immunohistochemical experiments. Results Five mAbs, namely 1F4C8,2D4C6,3C3B9,4D6B3 and 5F9E4 were obtained, and all of them were IgG2b subtype. Their antigen specificity and titer varied slightly. Three mAbs (1F4C8, 2D4C6 and 5F9E4) specifically recognize the ERV Gag antigen expressed in the pancreatic islets of NOD mice and at the age of 3 weeks, the antigen was detectable. Within the islets, the Gag antigen located near β-cells rather than the area infiltrated by lympho- cytes.In contrast, the T1D-resistant C57BL/6 mice do not express the Gag antigen as detected using the same mAb. Conclusions The expression of ERV Gag antigen in pancreatic islets of NOD mice occurs at very young age, suggesting that genetic factors of this diabetes-prone mouse strain may contribute to the expression.

Key words: type 1 diabetes, non-obese diabetic (NOD) mice, endogenous retrovirus, monoclonal antibody, group-specific antigen Gag