Fluorescence videomicroscopic assessment of xenogeneic microcirculation and impact of antibody removal by...

Alterations in microcirculation are considered central to the pathogenesis of hyperacute xenogeneic rejection (HXR) of vascularized xenografts, but currently there exist no data describing these microhemodynamic alterations.

Rat livers were perfused in situ with either isogeneic rat blood or xenogeneic human blood. The microcirculation of these xenoperfused livers was investigated directly using intravital fluorescence microscopy, and compared with that of isogeneic hemoperfused livers. In addition, the impact of antibody depletion by immunoadsorption was investigated.

Although a homogenous microcirculation was found during isogeneic liver perfusion (index of acinar perfusion 90.4%/sinusoidal perfusion rate 93.6%), xenoperfusion resulted in a rapid breakdown of the microcirculation (47.5%/67.1%, respectively). Perfusion deficits were found predominantly in the periportal areas. Immunoadsorption reduced the total amount of IgM and IgG by 75.2% and 96.2%, respectively, and caused a significantly improved liver perfusion (80.2%/84.4%) and liver function, as indicated by bile production. In contrast, the massive hepatic leukocyte and platelet accumulation observed during perfusion with untreated xenogeneic blood was not altered by antibody depletion.

Thus, the combination of isolated rat liver perfusion and intravital fluorescence microscopy enables the observation and quantification of the early phase of HXR. This is an important step forward for sensitive characterization of the rejection process and will enable the mechanisms involved in HXR to be elucidated. Antibody depletion was shown to improve liver function and perfusion, but did not reconstitute liver viability to the level of the isogeneic perfusion. These findings highlight the need for additional therapeutic regimens in xenografting.