The Lewis System
The Lewis system is unique among blood group systems in that the antigens are not manufactured within the erythrocyte, nor do they form an integral part of the cytoskeletal membrane. Rather, they are synthesized by tissues, secreted into blood and body fluids, and adsorb onto the red blood cell. While antibodies against antigens in this system are fairly commonly encountered, they are generally not considered to be clinically significant in transfusion. In vitro and in vivo hemolysis are rare but have been reported. Because Lewis phenotype expression is based upon the interaction of several genes, and because the phenotype expression can be transient, the Lewis system is a fascinating system to learn about.
