A clinically significant anti-N in a patient whose red cells were negative for N and U antigens

A patient with sickle cell anemia had M+N-S-s-U-phenotype and developed anti-E, anti-U, and anti-N after multiple transfusions. The anti-N was IgG, showed positive red cell mononuclear phagocyte assay, caused shortened survival of 51Cr-labeled N+ red cells, and incited a delayed hemolytic transfusion reaction. The anti-U also caused decreased survival of U+ cells. The serological findings indicated that the anti-N recognized both N and 'N' antigens.