Rejection of Discordant (tilapia-to-rat) Hepatocyte Xenotransplantation

BACKGROUND: Presently, most of the xenotransplantation researches involved two different mammalian species, but for the hepatocyte transplantation between two different Classes is rarely reported. OBJECTIVE: To observe rejection and pathway among various Classes (tilapia/rat) hepatocyte transplantation. DESIGN, TIME AND SETTING: A controlled observational study was performed at the Medical College, Tongji University from September 2007 to September 2008. MATERIALS: Adult healthy tilapia and 20 adult healthy Sprague-Dawley rats weighing 200-250 g were used in this study. The rats were randomly assigned to a transplantation group and a control group. METHODS: Tilapia hepatocytes were digested by collagenase for isolation and resuspended by saline. Cells concentration was adjusted to 2×10^10/L. Cell suspensions (2 ×10^7) were injected into the spleen for transplantation group and the saline was injected into the spleen for control group. MAIN OUTCOME MEASURES: Histological changes in grafts at various time points, IgM and IgG surrounding the grafts were measured respectively using hematoxylin-eosin staining and immunohistochemical method. RESULTS: In the transplantation group, the clustered and pieced of hepatocytes were found disseminated at 2 hour post-transplantation, and the hepatocytes showed round in shape with clear boundary. Nucleus was found either round or elliptical shape, and cytoplasm was stained lightly. At 4 hour post-transplantation, the boundary of the partial hepatocytes was become unclear. Pyknosis and karyorrhexis occurred, living hepatocytes were obviously decreased and the graft was infiltrated with leukocytes. At 8 hour post-transplantation, living hepatocytes were hardly found. Complete hepatocytes were not observed at 24 hours after transplantation. Massive infiltration with monocyte and lymphocyte and granuloma-like-region were presented at 3 day post-transplantation. In the control group, small bleeding region occurred in the early stage following operation with the weak inflammation reaction. Few IgM was observed surrounding the graft at 1 hour post-transplantation. However, IgM was more congregated surrounding the graft at 4 hours post-transplantation, but decreased until day 3 in the transplantation group. IgM and IgG were not detected in the rat spleen in the control group. CONCLUSION: Tilapia hepatocyte transplantation in rats may develop hyperacute rejection, which may affect tilapia hepatocytes by complement dependent cytotoxicity and antibody dependent cell-mediated cytotoxicity following reaction between rat normal antibody and heteroantigen on tilapia hepatocyte surface.