The Jra antigen of JR blood group systems is located on ABCG2 and Jr(a–) subjects whose red blood cells (RBCs) lack ABCG2 have been identified mostly among the Japanese. Although anti-Jra can cause fetal anemia, little is known regarding its mechanism.STUDY DESIGN AND METHODS:
We reviewed clinical courses of all reported cases with fetal anemia due to anti-Jra. We analyzed the ABCG2 expressions of cord RBCs at various gestational ages. We examined the effects of sera containing anti-Jra from three pregnancies with fetal anemia or monoclonal anti-Jra on erythropoiesis and phagocytosis. We also examined epitopes of anti-Jra.RESULTS:
Case series suggested that the majority of fetal anemia with anti-Jra may not be progressive in the later gestational ages. ABCG2 expression levels of cord RBCs were significantly higher than those of adults and neonates with high individual variation and gradually decreased with advancing gestational ages. Anti-Jra did not significantly impact erythroid colony formation, although we detected a tendency toward the suppression of erythroid burst-forming unit formation by anti-Jra using feline marrow cells. Anti-Jra did not induce phagocytosis of sensitized RBCs by monocytes. While many anti-Jra recognized the same regions as a monoclonal anti-ABCG2, 5D3, epitopes of anti-Jra did not correlate with the incidence of fetal anemia.CONCLUSION:
ABCG2 expression levels in cord RBCs are higher than those of adults, and the change of ABCG2 expression in erythroid lineage cells may influence the clinical course of fetal anemia with anti-Jra, although we could not detect significant effects of anti-Jra on erythroid colony formation or phagocytosis.