The nonobese diabetic (NOD) mouse, a model of human type I diabetes, develops insulitis beginning at 4–6 wk of age. By 30 wk of age, 72% of females and 39% of males develop spontaneous diabetes, apparently because of an overwhelming autoimmune response to the insulin-producing β-cells within the islets. To identify the immune mechanism responsible for destruction of β-cells in the NOD mouse, we developed an adoptive transfer protocol that induces diabetes in NOD mice at an age when spontaneous diabetes is rarely observed.

Splenocytes from overtly diabetic NOD mice were unable to transfer diabetes to very young (≤6 wk) irradiated NOD mice but effectively transferred diabetes to irradiated NOD mice 6 wk of age. In such transfers, overt diabetes was induced within 12–22 days in >95% (79/82) of the recipients. Thus, transfer of splenocytes to young mice induces them to become diabetic at a higher frequency and at a younger age than their untreated littermates. Equally successful transfers with as few as 5 × 106 spleen cells have been performed in male and female NOD mice, even though males display a lower spontaneous incidence of diabetes than females. Splenocytes obtained from diabetic mice maintained on insulin for up to 2 mo also transferred diabetes.

Because NOD mice display increasing levels of insulitis with age, spleen cells obtained from nondiabetic NOD mice of different ages were tested for their ability to transfer diabetes. Spleen cells obtained from 7-wk-old nondiabetic donors were unable to transfer disease, suggesting that high numbers of effector cells are not yet present in the spleens of young NOD mice. In contrast, spleen cells obtained from most nondiabetic NOD mice >15 wk of age were able to transfer diabetes, indicating that the donor need not be overtly diabetic at the time of transfer.

Our study provides direct demonstration of the immunological nature of the diabetic disease process in the NOD mouse and provides a method to determine which cells are the effectors of β-cell destruction.

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