Transfusion reactions are mediated by Type II hypersensitivity reactions. These occur due to preformed antibodies that bind to the foreign antigen (AB group on RBC) and lead to hemolysis by NK cells. This is a form of Antibody dependent cellular cytotoxicity.
AB is the only blood group that does not have preformed IgM antibodies in the plasma.
Blood group A has anti-B IgM
Blood group B has ani-A IgM
Blood group AB "NADA"
Blood group O has both anti-A & anti-B IgM
FA 2017 page 390
O type patients have preform IgG anti A anti B. Not IgM antibodies
"Shortly after transfusion" raise up suspicion for anaphylaxis.
no sign of hemolysis-> favor anaphylaxis due to IgA deficiency=> effector cell is Mast cells