Toll-like receptor 4 detected in exocrine pancreas and the change of expression in cerulein-induced pancreatitis

Objectives: To detect Toll-like receptor 4 (TLR4) expression and distribution in rat pancreas and the change of TLR4 expression in cerulein-induced pancreatitis (CIP). Methods: Acute pancreatitis was induced by subcutaneous injections of cerulein at a total dose of 20 mg/kg. Immunohistochemistry (IHC) was used to detect and localize TLR4 in rat pancreas, and real-time reverse transcription-polymerase chain reaction (RT-PCR) was used to quantitatively determine the expression of TLR4 mRNA in CIP. Results: IHC showed the presence of TLR4 in rat pancreas, and its distribution was specifically localized to pancreatic ductal epithelium, vascular endothelium, and islet. No TLR4 staining was detected in exocrine acinar cells. Real-time RT-PCR results revealed low-level TLR4 mRNA expression in the rat pancreas, and the change of TLR4 in CIP only developed within the first 4 hours, which is a rapid upregulation process that peaks at the first hour. TLR4 mRNA was sustained at baseline level from 4 to 24 hours. Conclusions: TLR4 protein was expressed in pancreas and localized to epithelial ( pancreatic duct) or endothelial ( vessels) tissues; TLR4 responded favorably to the inflammatory process, and the change of expression was characterized as a rapid up-regulation in the early stage of CIP.