Low-affinity allergen-specific IgE in cord blood and affinity maturation after birth

To the Editor: Newborn blood and cord blood (CB) often contain allergen-specific IgE when the mother has a history of allergy and/or allergic inflammation during pregnancy.1,2 Such finding indicates intrauterine allergen-sensitization by maternofetal interactions.2,3 To our knowledge, there are no published data on fetal atopy and allergic disease despite the evidence of maternofetal passage of allergens across the placenta.3 The limited allergic responses in young infants and fetuses are considered to be due to immunological immaturity.4 Using an animal model, a recent study described 2 sequential immunological maturation class switching pathways that generate high- and low-affinity IgE.5 The high-affinity IgE is generated through sequential class switching (->γ->[straight epsilon]), in which an intermediary IgG phase is necessary for the affinity maturation by somatic hypermutation.