Persistent anti-Dr^a in two pregnancies

The Drori (Dr^a) antigen is one of the ten high-prevalence antigens of the Cromer blood system, which are carried on decay-accelerating factor (DAF, CD55). The Dr(a-) phenotype was first described in a 48-year-old Jewish woman from Bukhara. Her serum contained an antibody to a high-prevalence antigen named anti-Dr^a. Most known individuals with the Dr(a-) phenotype are Jews from the geographic area of Bukhara, but individuals from Japan have also been described. Antibodies in the Cromer blood group system, including anti-Dr^a, have never been reported to cause HDN. In most of the cases with anti-Dr^a examined in Israel, the antibodies have been subtyped as IgG2 and IgG4. This report is of a woman with Dr(a-) phenotype and an anti-Dr^a titer of 256 to 512 in her serum, observed during two successive pregnancies. At birth, the RBCs of the first- and second-born child were negative and positive in the DAT, respectively, and neither manifested clinical signs of HDN. The disappearance of Cromer system antibodies, including anti-Dr^a in midpregnancy, has been described in a previous study. In that study, it was theorized that the antibodies in the serum of the women were adsorbed onto placental DAF. The finding of a high anti-Dr^a titer in two successive pregnancies in this patient, with a positive DAT for the RBCs of one of the two babies at term, differs from published reports, suggesting that a different mechanism might be involved.