In a transfusion, what triggers an immune transfusion reaction when donor red blood cells are incompatible with the recipient?

• A. Recipient antibodies attacking donor antigens
• B. Donor antibodies attacking recipient antigens
• C. Donor antigens attacking recipient antibodies
• D. Recipient antibodies attacking donor platelets

Answer: (A)

When donor red blood cells are not compatible, the recipient’s immune system recognizes the donor’s red cell antigens as foreign. The recipient’s antibodies then bind to those donor antigens on the transfused cells and activate processes that destroy the donor red cells (hemolysis). This antibody-mediated attack on donor antigens is what drives an acute hemolytic transfusion reaction.

So, the best description is that the recipient’s antibodies attack donor antigens. The idea that donor antibodies would attack recipient antigens is not the typical mechanism for a standard RBC transfusion reaction, and antibodies attacking recipient platelets would relate to a different situation altogether (platelet-focused problems rather than red cell hemolysis).