The increasing success of liver transplantation in recent years has provided an experimental model to study and document the hepatic synthesis of many plasma proteins. 1-5 The normal hepatobiliary tract has not been regarded as a major source of antibody,6 , 7 aside from the enteric IgA secreted from plasma into the biliary tree. 8 Liver transplantation affords the opportunity to study the production of antibody to red cells. Recipient ABO incompatibility to the donor (a mismatched transplant, e.g., a group A liver transplanted into a group B recipient), although not absolutely contraindicated in liver transplantation, is avoided when possible. However, ABO-unmatched transplants (defined as a group O liver transplanted into a non-group O recipient or a group A or B liver to an AB recipient) are used frequently. We report the short-term occurrence of anti-recipient ABO antibody after eight unmatched transplants. In five cases there was evidence of hemolysis. No such antibodies have been seen in over 180 ABO-matched transplants at our center. These antibodies were most probably produced by donor lymphocytes transplanted in or with the livers. METHODS Serologic studies were performed according to standard methods. 9 Serum isohemagglutinins were tested without intubation, after 37°C incubation for 30 minutes, and with broad-spectrum antiglobulin reagents. Six patients with ABO-unmatched liver transplants and confirmed anti-recipient antibody production were studied prospectively. Blood samples were drawn at least weekly for direct and indirect antiglobulin testing, crossmatching, and elutions. The hematocrit, serum bilirubin, clinical status, and transfusions were closely monitored. Two other confirmed cases (in Patients 5 and 7) were found on review of all ABO-unmatched liver transplantations performed at our center. Confirmed cases of isohemagglutinin production were defined as those in which passive transfer of antibody could be ruled out-i.e., either no unmatched plasma-containing blood products were given at surgery (five cases) or, if they were, immediate postoperative specimens were negative for antibody (Patients 1A, 1B, and 6)-and there was serologic or clinical confirmation of the antibody's presence by repeat testing or signs of hemolysis. Cases were designated as possible if the antibody was first detected after the second postoperative day but the above criteria were not met in full. Liver transplantation was performed according to established techniques, including cyclosporine immunosuppression. 10,11 Little or no plasma was transferred in the grafts because the livers were copiously perfused with preservative solution and then, just before anastomosis, with saline. 12 Our transfusion practices have been described elsewhere.

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