Which of the following is NOT true of anti-Le^a?

• A. OccurS in Le(a-b-) individuals
• B. Composed mostly of IgM
• C. Neutralized by Lewis substance
• D. Causes hemolytic disease of the newborn (HDN)

Answer: (D)

Anti-Le^a antibodies are a Lewis system antibody that typically targets the Le^a antigen found on some RBCs and in secretions. They are usually naturally occurring and seen in individuals who lack Le^a on their RBCs (Le(a− b−) or Le(a−) phenotypes) because they have been sensitized to Le^a in the environment. These antibodies are predominantly IgM, meaning they react best at cooler temperatures and generally do not react at body temperature or in the antiglobulin phase, limiting their clinical impact. A key diagnostic clue is that anti-Le^a activity can be neutralized by soluble Lewis substance (Le^a) in saliva or other secretions, which confirms the specificity of the antibody. Because most anti-Le^a are IgM and because fetal RBCs express Le^a poorly and the antibodies do not readily cross the placenta, anti-Le^a is not a cause of hemolytic disease of the newborn. In practice, anti-Le^a is usually considered clinically insignificant for transfusion or pregnancy outcomes, which is why the statement about HDN is not true.