Some observations on the Inb antigen and evidence that anti-Inb causes accelerated destruction of radiolabeled red cells

This report describes an example of anti-Inb, a red cell alloantibody directed against a high-frequency antigen, detected in a prenatal sample obtained from a Canadian woman of Asian Indian extraction. Although the antibody is IgG1, it could not be detected in the serum or on the red cells (RBCs) of her In(b+) infant. Evidence is provided that the Inb antigen is denatured by papain, ficin, trypsin, bromelin, cystein-activated papain/dithiothreitol, 6 percent aminoethylisothiouronium, and 50 mM dithiothreitol, but not by neuraminidase. Inb antigen strength appears reduced on the In(Lu) type but not on the LuLu type of Lu(a-b-) RBCs. RBCs from a patient with paroxysmal nocturnal hemoglobinuria showed normal Inb antigen strength as did Ko, Ge:-2,3, Ge:-2,-3, and Yt(a-) RBCs. A RBC survival study using 51Cr-labeled In(b+) RBCs showed 97 percent survival 90 minutes after injection but reduced survivals of 62 and 14 percent at 24 and 96 hours, respectively. These results indicate that this example of anti-Inb is unlikely to be implicated in an immediate hemolytic transfusion reaction, but that delayed extravascular hemolysis might occur