A Coculture Model of Intrahepatic Islet Transplantation: Activation of Kupffer Cells by Islets and Acinar Tissue

Clinical and experimental studies of intrahepatic islet transplantation have allowed histological and systemic observations to be made, but the location of the transplanted islets makes it difficult to assess direct effects on the cells of the liver. An in vitro coculture model of Kupffer cells with islets or pancreatic acinar tissue is described, using porcine tissue and measuring the secretion of thromboxane B₂, prostaglandin E₂, 6-keto-prostaglandin F_1α, and prostaglandin F_2α as an indicator of Kupffer cell stimulation. The results have demonstrated activation of Kupffer cells in the presence of acinar or islet tissue, both when the cells were in direct contact and when separated by a membrane. This indicated that the stimulation was due to a soluble factor or factors, and was confirmed by the culture of Kupffer cells with acinar conditioned medium. The degree of stimulation was much greater with acinar tissue than with islets. In subsequent experiments, aprotinin, an enzyme activation inhibitor, was added to the cocultures in an attempt to reduce Kupffer cell activation. This had no effect, possibly due to the fact that the endogenous pancreatic enzymes may already be activated during digestion of the pancreas. Aprotinin alone caused an increase in secretion of eicosanoids from Kupffer cells. The high response to acinar tissue is of particular relevance to islet autotransplantation in which unpurified pancreatic digest is often transplanted. The clinical effectiveness of aprotinin in the light of these results is discussed. In conclusion, although unable to mimic the complex situation following intrahepatic islet transplantation, the coculture model described here allows the opportunity to assess the events relating to specific cell types, and will provide the scope to undertake more detailed studies on the mechanisms involved. The same model could be applied to the coculture of pancreatic tissue with hepatocytes to determine any effects on the normal function of hepatocytes.