Peripheral lymphocyte reduction in severe acute pancreatitis is caused by apoptotic cell death.

To investigate impairment of cellular immunity in severe acute pancreatitis, alterations of peripheral lymphocytes in acute pancreatitis were examined. In 48 patients with severe acute pancreatitis, the mean peripheral lymphocyte count on admission was 959 + 105/mm3, and it was significantly decreased in the patients with subsequent infection (623 +/- 90/mm3 ) in comparison to those without infection (1084 +/- 135/mm(3)). According to an analysis of lymphocyte subsets, although both B and T lymphocytes were decreased in peripheral circulation in the patients with infection, it was primarily CD8-positive lymphocytes that decreased in these subsets. Cell cycle analysis of lymphocytes collected from these patients indicated that apoptotic changes occurred after 24 hours' incubation in lymphocytes from patients with severe pancreatitis but not in lymphocytes from healthy control subjects. In a rat model of experimental necrotizing pancreatitis, total peripheral lymphocytes and T lymphocytes were significantly decreased 5 hours after induction of pancreatitis. In severe pancreatitis, peripheral lymphocytes are eliminated from systemic circulation possibly as a result of apoptosis. It has been suggested that impairment of cellular immunity due to peripheral lymphocyte apoptosis is linked to the development of subsequent infectious complications in acute pancreatitis.