Anti-K is produced in response to which antigen?

• A. Cellano
• B. Kell
• C. Kpa
• D. Kpb

Answer: (C)

Anti-K is formed when someone who lacks the Kell K antigen is exposed to it on donor red cells, such as during transfusion or pregnancy. In the Kell system, the K antigen (often called K1) is the primary target of this alloantibody, so anti-K most commonly reflects an immune response to that specific Kell epitope. The Kell system also includes other antigens like Kpa and Kpb, which can provoke their own antibodies (anti-Kpa, anti-Kpb) if a person lacks them and is exposed to cells that carry them. The Cellano antigen (often referred to as k) is a different Kell antigen and is not the usual trigger for anti-K. Thus, the antibody most characteristically produced in response to Kell antigen exposure is directed against the K antigen itself, with clinical implications for transfusion safety and hemolytic disease of the fetus and newborn.