4 Lewis Blood Group System

• Lewis system is the only antigen system that is not produced by red blood cells
• Lewis system is produced by tissue cells and secreted into bodily fluids (antigens are produced in secretions and plasma)
• Le gene is the most potent; produces lewis enzyme
• If Lewis enzyme acted on type 1 precursor substance, the product will no longer be susceptible to the action of enzymes produced by the Secretor and ABO
• Lewis gene is found in chromosome 19

  • It is distantly linked to Se and H gene
  • Codes of L-fucosyltransferase that adds L-fucose to type 1 precursor substance
  • Enzyme competes with Se and ABO gene by attaching L-fucose to C4 of N-acetylglucosamine of type 1 precursor chain
• Type 1 precursor substance

  
• H soluble substance

  
• Le9 antigen

  
• A and B soluble substances can serve as substrates for ABO and Se enzymes
• Le (a+ b-) phenotype are non-secretor

  • Lewis genotype: Lele or Lele
  • Lea is produced regardless of Secretor status
• Le (a- b+) phenotype are secretor; means you have a dominant Lewis enzyme at the same time Secretor

  • Lewis genotype: LeLe or Lele
  • Leb is produced from H soluble substance
  • Lea is still formed but only Leb is adsorbed onto RBC membrane
• Le (a- b-) phenotype are recessive for Lewis gene; due to a mutation rather than a lack in the Le gene

  • Lewis genotype: lele
  • Non-functional or partially active transferase enzyme
• Lewis antibodies are frequently detected in antibody screening; considered naturally occurring and are generally produced by Le (a-b-) individuals

  • occur frequently in pregnant women
• IgM can cause occasional in vivo and in vitro hemolysis; has increased reaction with enzyme-treated cells
• Lewis antibodies can be neutralized by Lewis antigens in plasma or saliva
• Anti-Lea is the commonly encountered antibody or Lewis system

  • It binds complement and can cause in vitro hemolysis
  • Rarely causes hemolytic transfusion reaction
• Anti-Leb have IgM that binds complement (to a lesser extent than anti-Lea); it is produced by the Le(a-b-) and Le(a+b-)