Acute HCV infection detected in a blood donor by NAT

Anti-K (anti-KEL1) of the Kell blood group system is a relatively infrequent cause of HDN. Anemia in Kell HDN may be severe and appears to be due to suppression of erythropoiesis rather than immune destruction of fetal RBCs.1 Kell antigens appear on erythroid progenitor cells early in erythropoiesis, after glycophorin C, but before glycophorin A and band 3, and much earlier than the Rh proteins.2,3 Vaughan et al.4 found that culturing K+ erythroid progenitors in the presence of anti-K inhibited cell proliferation. They suggested that the Kell glycoprotein plays an important role in erythropoiesis by enzymatically modulating peptide growth factors on the cell surface, a function inhibited by binding of anti-K. However, the rare Kell-null phenotype (K0), in which Kell glycoprotein is absent, is not associated with anemia or any apparent defect in erythropoiesis. We have therefore used an in vitro functional assay to test the possibility that anti-K, in contrast to anti-D, might cause fetal anemia by promoting phagocytosis of early erythroid progenitors. We isolated CD34+ cells from K+ D+ umbilical cord blood by an immunomagnetic separation technique, which involves the use of anti-CD34 conjugated to magnetic particles (Miltenyi Biotec, Bergisch Gladbach, Germany). The isolated cells were cultured, under serum-free conditions at a concentration of 105 cells per mL, in medium containing stem cell factor (100 ng/mL), IL-3 (10 ng/mL), and erythropoietin (3 U/mL).3 Cell surface antigens were detected on the cells by flow cytometry with either human alloantibodies, purified by adsorption and elution on RBCs; or MoAbs, and FITCconjugated F(ab )2 fragments of antihuman IgG or anti-mouse immunoglobulins (Dako, Glostrup, Denmark). After 7 days in culture, the progenitor cells expressed K antigen, but not Rh antigens (Fig. 1); they also expressed the erythroid markers Rh-associated glycoprotein and glycophorin A, but not band 3. These cultured Day 7 erythroid progenitors and cord RBCs derived from the same K+ D+ cord sample were incubated with anti-K (n = 3) or anti-D from sera of pregnant women. The antibodies were affinity isolated by adsorption and elution from RBCs in order to remove HLA antibodies. Sensitized target cells were then incubated with monocytes for 40 min.5 Figure 2 shows the chemiluminescent responses of monocytes to sensitized cells as a ratio of their