Which antibody is neutralized by Lewis substance?

• A. anti-K
• B. anti-Lu^a
• C. anti-D
• D. anti-Le^a

Answer: (D)

Neutralization by soluble Lewis substances occurs because Lea and Leb antigens are present in secretions and can act as free antigens that bind antibodies in serum. When the corresponding Lewis substance is added, antibodies directed against Lea or Leb are soaked up by the soluble antigen and can no longer react with the antigen on red cells. Anti-Lea is specifically neutralized by the Lewis substance Lea, so it will disappear in tests that include Lea in solution. The other antibodies—anti-K, anti-D, and anti-Lu^a—target different antigen systems and are not neutralized by Lewis substances in this way, so they would not be adsorbed by Lea-containing solution.