Red cell antibody formation in the newborn

Abstract

Because the placenta efficiently transfers IgG from mother to fetus, the serologic immune repertoire of a term newborn closely mimics that of the mother. Although the common isohemagglutinins directed against the A and B antigens are IgM and thus not placentally transferred, many individuals will have anti-erythrocyte IgG antibodies that result from direct exposure to nonself erythrocytes (eg, from transfusion or pregnancy) or that arise as cross-reactive antibodies. If the newborn's erythrocytes express the target antigen, hemolysis may occur; if the target antigen is not present, then the transferred antibody should be of no consequence unless the infant should require red cell transfusion, in which case alloreactive antibodies might cause hemolysis of the transfused cells. In this volume of the Journal, Reeves et al describe an 11-week-old infant who presented with nonhemolytic anemia in the context of a viral infection, and who, upon testing, demonstrated anti-PP1Pk antibodies. These can arise in the rare individual whosered cells lack the P, P1, and Pk antigens (<1:100 000 in the general population), and may cause hemolytic disease of the newborn if placentally transferred to a fetus whose red cells are PP1Pk positive. However, in this case, the infant's red cells were PP1Pk negative (consistent with the absence of hemolysis), both parents were PP1Pk positive, and maternal serum lacked any anti-PP1Pk antibodies. Thus, the anti-PP1Pk antibody was almost certainly being produced by the infant himself rather than being maternally derived, and although it had no direct clinical effect, it did complicate subsequent transfusion management. Because of limited capacity to generate anti-erythrocyte antibodies prior to approximately 4 months of age, current transfusion practice allows for relatively limited pretransfusion crossmatching for young infants, and, in some situations, antibody determination from maternal samples can be substituted for direct testing of infant sera. Even though generally safe, the current report serves as an important reminder that formation of red cell antibodies during early infancy, although rare, is not impossible even in the absence of prior sensitizing transfusions, and it is incumbent on clinicians to keep this possibility in mind. Article page 302 ▶ Unexpected Non-Maternally Derived Anti-PP1Pk in an 11-Week-Old PatientThe Journal of PediatricsVol. 181PreviewAlloantibody formation at less than 4 months of age is rare. Most antibodies identified in these patients are maternally derived. Anti-PP1Pk was detected in an 11-week-old infant that was not maternally derived. A multidisciplinary team approach led to appropriate testing, diagnosis, and transfusion management in this critically ill infant. Full-Text PDF