Background: We previously reported that immunosuppression occurs from the early phase in patients with severe acute pancreatitis and that peripheral lymphocyte reduction due to apoptosis is linked to the development of subsequent infectious complications in patients with severe acute pancreatitis. We also demonstrated that Th1 (T helper cell type 1)/Th2 (T helper cell type 2) balance tends to Th1 suppression in experimental severe acute pancreatitis and that serum levels of IL-18, one of Th1 cytokines, are significantly elevated and are correlated with the severity in patients with acute pancreatitis. On the other hand, IL-15, one of Th1 cytokines, is a novel cytokine that shares many biological properties with IL-2 and stimulates T cell proliferation. However, serum IL-15 levels have not been determined yet in patients with acute pancreatitis, and it is unclear whether IL-15 is implicated in acute pancreatitis.
Methods: Serum IL-15 concentrations were determined in 5 healthy volunteers, 5 patients with mild acute pancreatitis, and 54 patients with severe acute pancreatitis at the time of admission (within the initial 72 hours after the onset of disease) by an ELISA. In patients with severe acute pancreatitis, relationships of their serum IL-15 levels on admission with pancreatic necrosis, severity indexes, organ dysfunction and infection during the clinical course, and prognosis were analyzed.
Results: Serum IL-15 levels in patients with severe acute pancreatitis (5.8 ± 0.5 pg/ml) were significantly higher than those in healthy volunteers (1.0 ± 0.1 pg/ml) and patients with mild acute pancreatitis (2.8 ± 0.5 pg/ml). In severe acute pancreatitis, serum IL-15 levels in patients with pancreatic necrosis (6.6 ± 0.6 pg/ml) were significantly higher than those in patients without pancreatic necrosis (4.2 ± 0.7 pg/ml). Serum IL-15 levels were significantly positively correlated with Ranson score (R=0.541), APACHE II score (R=0.646), and Japanese severity score (R=0.655). Serum IL-15 levels in patients with organ dysfunction (7.8 ± 0.7 pg/ml) were significantly higher than those without organ dysfunction (3.3 ± 0.3 pg/ml). Serum IL-15 levels in patients with infection (8.4 ± 1.3 pg/ml) were significantly higher than those without infection (5.2 ± 0.5 pg/ml). Serum IL-15 levels in the non-survivors (8.8 ± 1.3 pg/ml) were significantly higher than those in the survivors (4.7 ± 0.4 pg/ml).
Conclusions: Serum IL-15 levels are significantly elevated in patients with severe acute pancreatitis. IL-15 may be closely related to the severity, organ dysfunction, infection, and prognosis in this disease.