Studies on the Role of the Plasma Protease Inhibitors on in Vitro C3 Activation and in Acute Pancreatitis

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Abstract
Plasma samples from 32 patients with severe acute pancreatitis contained cleavage products of C3, and the C3 levels were significantly lower than those of control subjects. Peritoneal exudate from all patients showed complete degradation of C3 on crossed immunoelectrophoresis. α1-Antitrypsin and α2-macroglobulin showed no signs of complex formation in plasma. However, in the peritoneal exudate, 5%–25% of the α1-antitrypsin and 45%–100% of the α2-macroglobulin were in complex. Trypsin-α1-antitrypsin complexes were demonstrated in all peritoneal exudates. All patients showed significantly decreased levels of α2-macroglobulin in their plasma. α1-Antitrypsin levels varied greatly, but the mean value was not significantly increased compared with those of normal controls. Orosomucoid, another acute-phase reactant, was present in increased concentration in the plasma of all patients. The addition of increasing amounts of human trypsin to serum in vitro resulted in the appearance of cleavage products of C3 upon saturation of α2-macroglobulin, when the α1-antitrypsin was found to be only about 40% saturated. Taken together, these data are evidence of complement catabolism in acute pancreatitis and suggest that this process takes place mainly in the abdominal cavity as a result of a protease-antiprotease imbalance. α2-Macroglobulin, but not α1-antitrypsin, can protect against C3 degradation caused by trypsin in vitro.

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