In vitro stimulation by islet antigen facilitates the detectability of beta-cell reactive cells in diabetes-prone BB/OK rats.

It has been supposed that beta-cell destruction in man and animals is due to autoreactive T-cells. We used the [51Cr]-release assay to identify the presence of beta-cell reactive cells in the spleen of diabetes-prone BB/OK rats before and after diabetes manifestation as well as in long-term normoglycaemic rats with a reduced diabetes risk of 3%. Splenic mononuclear cells (MNCs) obtained from diabetes-resistant LEW.1W and the majority of long-term normoglycaemic BB/OK rats (86.4%) showed no reactivity to pancreatic islets in vitro. In contrast, beta-cell reactive cells were identified in dependence on age in 30.4-65.0% of 75-120 days old normoglycaemic rats and in relation to diabetes duration (1 and 20 days) in 75.0% and 16.0% of diabetic BB/OK rats. Islet antigen-specific stimulation of splenic MNCs, that showed no spontaneous islet-directed reactivity, resulted in a concentration-dependent activation of cytolytically reactive cells in BB/OK but not in LEW.1W rats. Splenic MNCs derived from all diabetic, from 82.4% of young normoglycaemic and from 46.2% of long-term normoglycaemic BB/OK rats developed an islet-directed reactivity in vitro. Phenotyping of MNCs showed a significant increase of activated IL2R+ T-lymphocytes in diabetic BB/OK rats, but without any correlation to their cytolytic potential in the [51Cr]-release assay. Despite this fact, IL2R+ cells enriched from the pool of MNCs mediated an enhanced [51Cr]-release from islets, indicating their relevance in the beta-cell destruction. These data suggest, that functional reactivity rather than phenotypic characterization of MNCs is useful to identify the existence of beta-cell reactive cells. Furthermore, for screening diabetes risk in young normoglycaemic BB/OK rats besides the detection of beta-cell reactive cells the occurrence of regulatory cells seems to be decisive.