Expression of the adhesion molecules Mac-1 and L-selectin on neutrophils in acute pancreatitis is protease- and complement-dependent

Objective To examine the effect of pancreatic proteases on the expression o f the adhesion molecules Mac-1 and L-selectin on neutrophils, and the role of complement activation in this process. Summary Background Data Sequestration of neutrophils in the pancreatic and pulmonary microvasculature characterizes acute pancreatitis. Methods Serum was collected from inbred rats after induction of necrotizing pancreatitis; trypsinogen activation peptide was measured to quantify tryp sin activation. Normal rat serum was also collected and subjected to limite d trypsin digestion with and without the addition of complement inhibitor. Both groups of sera were incubated in vitro with healthy leukocytes. Expres sion of Mac-1 and L-selectin on neutrophils was measured quantitatively by flow cyometry. To assess the consequences of these events in vivo, trypsina ted serum with or without complement inhibition or control serum was infuse d intravenous into rats. Soybean trypsin inhibitor was added to serum befor e injections to block residual trypsin activity. Pancreatic and pulmonary i njury was quantitiated by histology, measurement of edema, and myeloperoxid ase activity. Results Mac-1 expression on neutrophils incubated with pancreatitis serum w as increased compared with controls, whereas L-selectin was decreased. Neut rophils incubated with trypsinated serum also showed upregulation of Mac-1 and downregulation of L-selectin, particularly with trypsin at 10(-4) mol/L . Addition of soluble complement receptor 1 abrogated both Mac-1 upregulati on and L-selectin downregulation. Lungs of animals injected with trypsinate d serum showed increased edema and myeloperoxidase activity, which were red uced by soluble complement receptor 1. Conclusions Trypsin-generated complement activation participates in the upr egulation of Mac-1 and shedding of L-selectin on neutrophils in acute pancr eatitis. Protease or complement inhibition may be effective in preventing l eukocyte migration and subsequent local and remote organ injury.