Electron microscopy of thrombocytes in the orthotopic porcine liver homograft during the late rejection. (Phagocytosis of thrombocytes by Kupffer cells)

Role of the donor liver in the origin of platelet disorders and hyperfibrinolysis in liver transplantation

We investigated the role of the donor liver in the origin of platelet disorders and hemostatic defects in liver transplantation. Eighteen pigs received an orthotopic or a heterotopic, auxiliary liver graft. Liver biopsies were taken for electron microscopic studies 5-10 min after reperfusion in nine animals. Blood samples were taken from the first hepatic outflow and from the systemic circulation before and 5 min after graft recirculation. Electron microscopy did not show any evidence of microthrombi or platelet aggregation in the graft, either after orthotopic liver transplantation or after heterotopic liver transplantation. Most blood platelets, which were lying free in the sinusoids, showed cell processes and many seemed to have lost their granulae, suggesting a degree of platelet activation. There were also signs of phagocytosis of platelets by the Kupffer cells. In the hepatic outflow, platelet count was significantly lower (p < 0.05) and fibrinolytic activity significantly higher (p < 0.01), than systemic post-reperfusion values. There were no important changes in the coagulation parameters. No significant changes were found between the effects on hemostasis of orthotopic and auxiliary graft reperfusion. In the second part of the study evidence for platelet activation was found after graft reperfusion in human liver transplantation. Plasma levels of platelet factor-4 and beta-thromboglobulin increased significantly after graft reperfusion. These studies suggest that platelet disorders and increased fibrinolytic activity are the major components of the hemostatic defect after graft recirculation in liver transplantation. Sequestration of platelets in the graft is probably due to the accumulation of (activated and degranulated) platelets in the sinusoids and phagocytosis by Kupffer cells.

Electron microscopy of Kupffer cells in the orthotopic porcine liver homograft during the late stage after transplantation (phagocytosis of host cells by Kupffer cells)

Electron microscopical observations of macrophages (Kupffer cells) in the orthotopic porcine liver homograft in later stages after transplantation are described and demonstrated. The findings show close topographical relations between the Kupffer cells and hepatocyte debris, erythrocytes, thrombocytes, lymphocytes and granulocytes. Besides an uptake of hepatocyte debris, a phagocytosis and degradation of apparently unaltered erythrocytes, thrombocytes and probably also lymphocytes by the macrophages were observed. The possible significance of these findings is discussed with regard to the immunological interactions between macrophages and lymphocytes, to the course of the rejection in the liver homograft, to the effect on the blood cells and platelets of the host organism, and thus to the long-term prognosis of liver transplantation.