Intravital microscopic investigation of xenogeneic microcirculation and impact of complement depletion by cobra venom factor

Discordant xenografts are hyperacutly rejected within minutes. Disturbances in the microcirculation are considered to be the central mechanisms of hyp eracute xenogeneic rejection (HXR). In this study intravital fluorescence m icroscopy was applied to investigate the dynamics of microcirculatory alter ations in a setting in which HXR was inhibited by complement (C) depletion. Blood flow was measured as rat livers were perfused with isogeneic rat or xenogeneic human blood to assess the pattern of either physiological isogen eic hemoperfusion or in the course of HXR. Next, the complement system of t he perfusate was inactivated by cobra venom factor (CVF) in order to inhibi t HXR. Liver sinusoids of the isogeneic group were homogeneously perfused ( sinusoidal perfusion rate 93.6 +/- 0.3%), whereas in the xenogeneic group t he sinusoidal perfusion rate dropped to 67.1 +/- 3%. The perfusion in the p eriportal zone of an acinus was significantly lower (59.0 +/- 3.3%) than in the pericentral zone (76.2 +/- 3.1%). Treatment with CVF improved the sinu soidal perfusion to a value of 85.6 +/- 2.3%, physiological perfusion, howe ver could not be reached. In contrast to the isogeneic group, massive white blood cell (WBC) and platelet accumulation was found in the xenogeneic gro up, especially in the terminal portal vessels and in the periportal zone of liver acini. WBC and platelet counts show that the adherence of these cell s appears rapidly in the first 5 min after reperfusion as firm adherence. C VF was not able to inhibit WBC and platelet accumulation, indicating that W BC endothelial interactions do not require an intact complement system. Bil e flow,a parameter of liver function, decreased only slightly during isogen eic perfusion. The addition of CVF to the rat blood reduced the bile flow t o one half of the untreated isogeneic flow, indicating a hepatotoxic side-e ffect of CVF. In xenogeneic perfusion the bile flow dropped to 62.6% and wi th the addition of CVF to 37.5% in the first 15 min after reperfusion. The bile flow of the CVF treated groups recovered during the perfusion but coul d not reach isogeneic values.