Thymic atrophy caused by thymocyte apoptosis in experimental severe acute pancreatitis

Although a reduction in peripheral lymphocytes has been reported in clinical cases of acute pancreatitis, the thymic change remains still unknown. To investigate impairment of cellular immunity in acute pancreatitis, alterations of the thymus in rats with acute pancreatitis were examined experimentally. Male Wistar rats were used. Two groups with pancreatitis of different severity and a control group for each were established. The thymus was weighed and the number of thymocytes counted. Apoptosis in the thymus was examined by in situ nick-end labeling, DNA agarose gel electrophoresis, and cell cycle analysis using propidium iodide. Both thymus weight and number of thymocytes decreased significantly in the rats with necrotizing pancreatitis 20 h after induction of pancreatitis (P <0.02 vs sham operation). Neither thymus atrophy nor thymocyte reduction was observed in rats with edematous pancreatitis. In thymuses from rats with necrotizing pancreatitis, in situ nick-end labeling showed a significant increase in apoptotic changes of thymocytes, which was also confirmed by the stepladder pattern on agarose gel electrophoresis of the extracted DNA and by cell cycle analysis. It is concluded that thymus atrophy associated with apoptosis occurs in rats with necrotizing pancreatitis.