Intragraft expression of recipient‐type ABO blood group antigens: Long‐term follow‐up and histological features after liver transplantation

Several reports have shown detection of recipient‐type ABO histo‐blood group antigens (r‐ABOAg) in the liver allograft, which may represent either true intragraft chimerism or other events such as cell injury. Little is known about factors that affect the timing and extent of r‐ABOAg expression in the graft. We examined 65 recipients who underwent ABO nonidentical living donor liver transplantation (61 compatible, 4 incompatible). Ninety‐seven postoperative specimens (71 episode biopsies, 16 protocol biopsies, and 10 explanted allografts) were available for evaluation with immunohistochemistry of ABH blood type antigens. The expression of r‐ABOAg was assessed in relation to histological and clinical factors. Capillaries in the portal tracts were the primary sites of r‐ABOAg expression. The percentage of specimens showing r‐ABOAg expression increased with lengthening of the post‐transplantation period. Only 1 (4%) of 28 specimens showed endothelium with r‐ABOAg within 1 year after the procedure, but 10 (29%) of 35 did between 1 and 5 years after transplantation and 21 (62%) of 34 after more than 5 years. Proportional analysis found that chronic rejection was a significant factor (P = 0.006) for any r‐ABOAg expression in the capillaries, and allograft portal fibrosis was a significant predictive factor for extensive r‐ABOAg expression (seen in more than one third of the portal tracts) in the capillaries (P = 0.017). Sex mismatch, age of recipients, age of donors, graft/recipient body weight ratio, and histology other than chronic rejection and fibrosis did not correlate with the expression of r‐ABOAg. In conclusion, these observations suggest that portal capillaries with r‐ABOAg are the results of graft injury and repair, and some of them may be neovessels of recipient origin. (Liver Transpl 2005;11:547–554.)