Complement-fixing islet cell antibodies in the spontaneously diabetic BB rat.

Fourteen rats of the spontaneously diabetic BB line were bled from the retroorbital sinus approximately every 10 days. Sera taken from an early age up to 20 days after the onset of overt diabetes were assayed for complement-fixing antibodies against antigens of the surface of islet cells (CFA). Dispersed islet cells from normal Wistar rats prelabeled with 3H-leucine were used as targets. Target cells in suspension were incubated with heat-inactivated rat sera and then, after washing, exposed to guinea pig complement. Cytolytic "injury" was measured by the percentage of labeled cellular proteins released into the medium. Sera from sequential bleedings from eight normal Wistar rats and three rats from a nondiabetic BB subline were assayed to establish basal control cytolytic activity. The mean response +/- SD obtained with all control sera was 7.7 +/- 1.7%. A response exceeding the mean + 3 SD (12.8%) was considered significantly different from the basal value. Thirteen of the fourteen BB rats developed strongly positive sera. The cytolytic activity preceded the onset of overt diabetes. In several rats CFA appeared 4-8 wk preceding diabetes while in other rats CFA appeared 1-2 wk preceding the manifestation of the disease. These results indicate that CFA may contribute to the destruction of pancreatic islets directly or by attracting mononuclear cells.