Assays were developed to detect cell-mediated immune destruction of pancreatic islet beta cells by lymphoid cells isolated from diabetic BioBreeding/Worcester (BB/W) rats. Splenic lymphoid cells from diabetic (D), diabetes-prone (DP), and diabetes-resistant (DR) BB/W rats were incubated for 2 days with monolayer cultures of major histocompatibility complex (MHC)-compatible Wistar-Furth (WF) rat islet cells or a rat islet cell line (RIN), and islet beta cell survival was determined by measuring insulin content in the cultures. D splenic lymphoid cells significantly decreased insulin content in WF rat islet (−32%) and RIN cultures (−77%). DP cells also significantly reduced the insulin content in WF rat islet (−20%) and RIN cultures (−63%), whereas DR cells had no significant effect. Islet-directed cytotoxicity was detected also by the release of 51Cr from RIN cells incubated for 8 h with BB/W spleen cells. Cytotoxicity was linearly related to the number of effector spleen cells. At a target:effector of 1:20, lysis (mean ± SEM) of RIN target cells by spleen cells from D rats (21.6 ± 2.0%) and DP rats (16.5 ± 4.1%) was significantly greater than the effect of DR spleen cells (5.4 ± 1.0%). D and DP splenic lymphoid cells activated in vitro for 2 days with concanavalin A exhibited a doubling of cytotoxicity to RIN islet cells. These results provide direct evidence for lymphoid cell-mediated immune damage to islet beta cells in diabetic BB rats.

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