Carbohydrate Blood Groups

Resolution of an unexpected ABO typing discrepancy in a 9‐month‐old patient with juvenile myelomonocytic leukemia

“…In addition to their representation on RBCs, they are readily identified in other tissues, the gut epithelium being a particularly rich site of expression 3 . In general, carbohydrate antigens engender an IgM immune response with greatest reactivity at colder temperatures (eg, 4°C); however, anti‐A and anti‐B are potent agglutinins at 37°C, which serves as the basis for the requirement to transfuse ABO‐compatible units of blood 4 . In addition to their expression on human tissues, including RBCs, the A, B, and H antigens are present in nature 3 .…”

“…However, the A 2 antigen is structurally different than the A 1 antigen (it is less complex) 2 . In addition, there are fewer copies of the A 2 antigen on RBCs in comparison with the A 1 antigen 4 . Thus, there are both qualitative and quantitative differences between A 2 and A 1 .…”

“…3 In general, carbohydrate antigens engender an IgM immune response with greatest reactivity at colder temperatures (eg, 4°C); however, anti-A and anti-B are potent agglutinins at 37°C, which serves as the basis for the requirement to transfuse ABOcompatible units of blood. 4 In addition to their expression on human tissues, including RBCs, the A, B, and H antigens are present in nature. 3 This exposure is the basis for the production of "naturally occurring" antibodies as an expected accompaniment of an individual's RBC antigen type (eg, anti-B in those of the A blood group).…”

“…2 In addition, there are fewer copies of the A 2 antigen on RBCs in comparison with the A 1 antigen. 4 Thus, there are both qualitative and quantitative differences between A 2 and A 1 . Interestingly, individuals of the A 2 phenotype can generate antibodies with specificity for the A 1 antigen.…”