Pancreatic elastase is proven to be a mannose-binding protein--implications for the systemic response to pancreatitis

Mannose-binding proteins (MBPs) have been isolated from serum, liver, lung, and kidney and are believed to play an important role in first-line host defense during acute phase inflammatory response. Because of the inflammatory nature of pancreatitis, we postulate that the pancreas produces endogenous MBP.

Pancreatic juice, from both human and rat, was collected by pancreatic duct cannulation and subjected to mannose-Sepharose affinity chromatography to isolate pancreatic MBP (pMBP). Protein eluates from the mannose-Sepharose column were analyzed using reverse-phase high-performance liquid chromatography, sodium dodeclysulfate-polyacrylamide gel electrophoresis, and, subsequently, by N-terminal protein sequencing. Western blot analysis was used to identify the pMBP, and reverse transcriptionase-polymerase chain reaction was used to examine its mRNA expression. Complement lysis was measured using red blood cells coated with yeast mannan. Tumor necrosis factor (TNF)-alpha mRNA expression in macrophages was measured using RNase protection assay.

A 30-kd MBP was isolated from both human and rat pancreatic juice and a rat acinar cell line. Genetic analysis (using RT-PCR with known MBP primers) and protein analysis (using Western blot with a known anti-MBP antibody) suggest that the pMBP is different from any previously described MBP. Protein sequencing analysis of pMBP generated an N-terminus sequence of 12 residues, indicating that pMBP is human pancreatic elastase III. Western blot analysis using an anti-elastase antibody confirms that the pMBP is a pancreatic elastase. Exposure of macrophages to pancreatic elastase resulted in an increased mRNA level of TNF-alpha, a potent proinflammatory cytokine in acute-phase response. Addition of mannan to pancreatic elastase further upregulated the TNF-alpha response.

We isolated an MBP from the pancreas and identified it as pancreatic elastase. We characterized it as having properties different from that of any previously known MBP. We showed that pMBP or pancreatic elastase is involved in the activation of macrophages, and that this activation is potentiated by mannan. We postulate that the mannose-binding properties of pancreatic elastase identify this enzyme as a candidate catalyst for both pancreatic and systemic inflammation.