Activation of the complement cascade by trypsin.

In twenty-three patients with acute pancreatitis, the plasma levels of immunoreactive trypsin were determined with a RIA method. The patients were divided into groups according to the severity of the disease. Ranson's criteria and the development of multisystem organ failure were used for the classification. Elevated plasma levels of immunoreactive trypsin were found in all groups after admittance. Incubation of fresh human serum and plasma with bovine trypsin in concentrations between 10(-6) and 10(-4) M at 20 degrees C activated the complement cascade. The anaphylatoxins C3a and C5a were determined with a RIA and the terminal complement complex (TCC) with an ELISA method. C3a and C5a were released and TCC was formed. The effect of trypsin on leukocyte activation was determined with a chemiluminescence technique. Trypsin dissolved in saline did not activate the leukocytes. However, serum digested by trypsin-activated leukocytes in a dose-dependent manner. The present study supports the theory that trypsin can activate complement components and results in formation of split products which have potent vascular, and leukocyte activating effects.