Jk(a) antigen
The Jk(a) antigen belongs to the Kidd antigen system. Anti-Jk(a) antibodies are usually formed in response to previous transfusions and may result in acute or delayed hemolytic transfusion reactions or hemolytic disease of the fetus and newborn (HDFN). The antibody tends to disappear quickly and is therefore a common cause of delayed hemolytic transfusion reactions.