Delayed hyperacute xenograft rejection in porcine to canine fetal liver transplantation

Fetal tissues are generally considered to express weaker antigenic cell-surface molecules than adult tissues. We have reported that transplantation of porcine fetal liver tissue (fragments) is useful for acute and chronic hepatic failure in rats. We further investigated, in the present study, whether transplantation of a porcine fetal liver has the advantage of delayed hyperacute xenograft rejection (HAR) in comparison with that of an adult liver. Porcine fetal liver heterotopically transplanted into dogs was compared. Haematoxylin-eosin (HE) and immunohistochemical studies using IgM, C3, IgG antibodies were performed in serial biopsies of the liver grafts. Lectin binding to target antigen epitopes on pig and dog tissues was studied by flow cytometry. Carbohydrate expression on the liver was also studied by immunohistochemistry. The macroscopic and HE section findings indicate that HAR started 15 min postgraft in fetal and adult liver grafts. Thereafter, vascular changes and parenchymal damage progressed more rapidly in the adult grafts. The final HAR time in adult liver transplantation was determined to be 60 min, while it was determined to be 180 min in fetal liver transplantation. IgM, C3 and IgG were deposited more strongly in the adult grafts than in the fetal grafts up until 60 min after xenografting. Phaseolus vulgaris erythroagglutinin lectin competitively blocked dog sera binding to porcine PBLs. The fetal liver expressed oligosaccharide at a significantly lower level than the adult liver. We conclude that porcine fetal liver xenografts had a significantly delayed HAR.