Anti-A₁Le^b: a mind boggler

The Lewis blood group system is unique because antigens are neither alleles of the same gene nor are they synthesized by red blood cells (RBCs); rather, they are adsorbed onto the RBC membrane from plasma as glycolipids. Antibodies against Lewis antigens are predominantly naturally occurring immunoglobulin (Ig)M type that sometimes react at 37°C and the antihuman globulin phase. Lewis compound antigens, ALe^b and BLe^b, have been described that were confirmed because of the presence of antibodies against them. These compound antigens are the result of an interaction between ABO, H, SE, and LE genes.