Demonstration of A antigen and A allele of ABO histo-blood group in nail in a case with the absence of A antigen and anti-A antibody in blood.

We report a case with the inconsistency that the red blood cells lacked both A- and B-antigens while the serum showed reactivity with control B-red cells but not with A-red cells. A- and B-antigens were examined by serological blood typing and immunohistochemical staining, and DNA analyses were performed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), DNA sequencing, and hot-stop PCR. A-antigens were demonstrable in the nail of the subject by serological study and immunostaining. DNA analyses showed that the nail retained a small amount of A-allele comparing to that of O-allele. Those genomic analyses of ABO genes were useful for demonstration of A allele in the nail of an individual with the absence of A antigen on red blood cells and the corresponding antibody in serum.