Anti-BI antibodys which recognizes both B and I antigen of red blood cells is very rare and its characteristics are not well known. In this study, we report an anti-BI antibody which was detected in a patient with B-cell type acute lymphocytic leukemia (B-ALL). The patient was diagnosed as having A1B antigen on red cell membranes and an antibody reacted with B cells. However, no unexpected antibody reacting with O cells was found in the patient's serum. The antibody detected in the serum which caused the discrepancy in the diagnosis of ABO typing did not react with Bi-cord or Bi-adult cells but rather with BI cells only. On the basis of this evidence, we determined the specificity of the antibody to be the anti-BI antibody.
The mechanisms of the development of this antibody are unclear. However, because the antibody paralleled the progression of the disease in the patient, the possibility of antigenic change of the red cell membrane, secretion of the antibody from the B-ALL cells, and immunologic abnormalities associated with the ALL were considerd. Clinical significance of this antibody was not evaluated because the patient did not receive blood trnasfusion.
