New approach for in vivo detection of insulitis in type I diabetes: activated lymphocyte targeting with 123I-labelled interleukin 2.

Insulitis is considered the histopathological hallmark of type I (insulin-dependent) diabetes. In the non-obese diabetic (NOD) mouse, diabetes has never been observed in the absence of insulitis. The in vivo detection of insulitis could be of relevance for early prediction of diabetes. As approximately 15% of islet-infiltrating lymphocytes express interleukin 2 receptors, we have labelled recombinant interleukin 2 with 123I and used this radiopharmaceutical to detect insulitis by gamma camera imaging. We studied 71 prediabetic NOD and 27 normal Balb/c mice. Labelled alpha-lactalbumin was used as the control protein. In the first set of experiments we studied the tissue distribution of radiolabelled interleukin 2 in isolated organs from animals sacrificed at different time points. Higher radioactivity was detected in the pancreas of NOD mice injected with labelled interleukin 2, as compared to NOD mice receiving labelled alpha-lactalbumin (p < 0.003 at 20 min: p < 0.001 at 40 min; p < 0.001 at 60 min) or Balb/c mice injected with labelled interleukin 2 (p < 0.05 at 40 min; p < 0.001 at 60 min). In another set of experiments, gamma camera images have been acquired after injection of 123I-labelled interleukin 2. Radioactivity in the pancreatic region of prediabetic NOD and Balb/c mice showed similar kinetics to those observed by single organ counting, with higher accumulation in the pancreatic region of NOD mice (p < 0.04 after 22-45 min in NOD mice vs Balb/c mice).(ABSTRACT TRUNCATED AT 250 WORDS)