Early appearance of complement-dependent antibody mediated cytotoxicity (C'AMC) to islet cells in serum of diabetes-prone BB/OK rats

: The present study examines the ability of serum from BB rats below the age of 33 days to mediate cytotoxicity to islet cells in vitro. Serum activities of complement-dependent antibody mediated cytotoxicity (C'AMC) were cross-sectionally analyzed in diabetes-prone BB/OK rats at 10 (n = 14), 20 (n = 14) and 30 (n = 10) days of age and were compared with those in non-diabetic, diabetes-prone BB/OK rats studied at 50 (n = 10) and 100 (n = 10) days of age. Exposure of 51Cr-labeled neonatal rat islet cells to sera from diabetes-prone BB/OK rats and rabbit complement revealed C'AMC activities above the mean + 2 SD of that of control Wistar rats in only two (14%) cases at day 10. This percentage increased to 79% at day 20 with all animals being C'AMC-positive at day 30. The means of the specific 51Cr-release were 3.6 +/- 1.7% at day 10, 10.4 +/- 2.2% at day 20, and 16.1 +/- 1.8% at day 30. Also, 90% of BB/OK rats investigated at 50 or 100 days of age were C'AMC-positive. In contrast, when 51Cr-labeled splenic lymphocytes were substituted for islet cells, isotope release did not exceed spontaneous release with any of the serum samples tested. Taken together, the present findings indicate that anti-islet but not anti-lymphocyte serum C'AMC activity usually appears in diabetes-prone BB/OK rats after day 10 with all animals being affected at day 30. The absence of cytolytic activity in 86% of BB/OK rats studied at 10 days of age strongly suggests, however, that anti-islet C'AMC is neither an inborn abnormality of humoral immunity in the BB rat nor does it seem to be passively acquired by transplacental passage.