What are transfusion reactons?

➢ Transfusion of allogeneic erythrocytes into an individual who already has antibodies against them may produce an immediate reaction; erythrocyte destruction and symptoms of a 'transfusion reaction'. ➢ Thus, if mismatched blood is transfused, it will cause blood agglutination, complement activation and intravascular hemolysis in the recipient ➢ The large pentameric structure of IgM allows for building of bridges between encountered epitopes on molecules that are too distant as to be connected by smaller IgG ➢ The first component of complement C1q consists of six subunits and reacts with the Fc via its globular heads. ➢ The activation of this component requires the binding of two globular heads for activation ➢ One molecule of IgM with its pentameric conformation can easily activate C1q, while the ability of IgG, which has only two sites to activate C1q, is low.