The expression of Lewis blood group antigens depends on the alleles inherited at two independent loci, FUT2 (Secretor [SE ] gene) and FUT3 (Lewis [LE ] gene). The Se and Le alleles encode separate fucosyltransferases that interact to form Lewis antigens in secretions and fluids. The Lewis antigens on RBCs are not integral to the membrane but are passively adsorbed from the plasma. The antigens are widely distributed in human tissue and fluids and are receptors for some pathogenic bacteria. Lewis antibodies are rarely clinically significant, although there are rare reports of hemolytic transfusion reactions, hemolytic disease of the fetus and newborn, and renal transplant rejection. This review provides a general overview of the Lewis blood group system. An extensive overview by Daniels1 contains additional detailed information on the Lewis blood group system and related antigens.
