We describe the case of a 44-year-old woman with a delayed hemolytic transfusion reaction (DHTR). She had a history of two pregnancies and a blood transfusion, the details of which were unknown. At the time of her first vascular surgery on November 15, 1989, she received 1200 ml of crossmatch-compatible concentrated red blood cells (CRC). Before the first operation, screening for anti-RBC antibodies (Ab) was negative. At the time of the second admission on Feburary 15, 1996, anti-E Abs were detected by indirect antiglobulin test. She received 560 ml of E-antigen-negative, crossmatch-compatible, CRC for treatment of anemia on March 1 and 2, 1996. After this transfusion, total bilirubin (1.6 mg/dl) and lactate dehydrogenase (1355 IU/ml) were elevated on March 12, 1996. She had no evidence of clinical hemolysis. We suspected DHTR from these data, and therefore screened for anti-RBC Abs. Anti-E, Jka, Dia, Fyb, and S Abs were detected in blood samples obtained from the patient on March 12, 1996. Anti-E, Jka Dia, and S Abs were present more than 1 month and anti-Fyb Ab was disappeared at 18 days after transfusion.

We have reported a rare case of auto anti-E antibody with specificity mimicking alloantibody with E specificity. A patient whose red cells typed as R1R1 and who had a positive direct antiglobulin test was admitted to our hospital. After standard serologic testing was performed, flow cytometry, Western blot analysis and differential allogenic adsorption test were used to verify whether antibody binds to the patient's red cells and normal red cells. A high titer anti-E antibody was detected transiently from the patient's serum and eluate. An indirect antiglobulin test using red cells treated by cysteine-activated papain and dithiothreitol (ZZAP) and chloroquine showed that both the patient's serum and eluate bound an apparent anti-E antibody to E negative patient's red cells. Fluorescence activated cells sorter (FACS) and Western blot analysis verified that the patient's red cells lacked E antigen. Further, it was clarified that the antibody does not bind to any E negative normal red cells by differential allogenic adsorption test. These results provide evidence that an antibody mimicking an E alloantibody can bind to patient's own E negative red cells but not to allogenic E negative red cells.

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