Immobilization of proteins on intact red blood cells (RBCs) can be valuable for several different reasons. In vivo, RBCs carrying specific ligands can be targeted to cells exposing specific antigens, eventually for the delivery of drugs encapsulated in the same RBC (1 ). Alternatively, RBCs carrying antigens or enzymes on the extracellular surface of their membrane can perform as antigen delivery systems (2 ) or as bioreactors for the degradation of toxic metabolites (3 ). In vitro, RBCs carrying proteins can be used as diagnostic reagents in agglutination or hemolytic assays (4 ).
