Quantitative variation of the A antigen at birth: its significance in ABO hemolytic diseases and in the infant's development.

ABO hemolytic disease of the newborn poses certain prognostic problems because maternal antibody titer is poorly related to severity of the ensuing hemolytic process. Heterogeneity of anti-A antibodies, as recently discussed by Polley e t al. [lo], may be one of the factors responsible for this poor association, Another factor may be the quantitative behavior of the A antigen. Infants with ABO hemolytic disease are predominantly of subtype A, and not A, L5, 151, and the A antigen is “stronger” in the A, than the A, subtype. Furthermore, the A antigen of erythrocytes undergoes marked quantitative change during life; for example, in embryonic erythrocytes i t is initially weak but increases slowly during fetal life [8 ] . After birth, the strength of the A antigen increases rapidly during the first few months of life and then a t a slower rate until adult values are reached a t about 3 years of age or shortly thereafter [4]. Among adults there is still considerable variation within thc A subtypes, which is partly