Anti-Uz found in mother's serum and child's eluate

A saline-reactive antibody, anti-Uz, that reacted stronger with S+ than with S- red blood cells (RBCs) and failed to react with U- or ficin-treated RBCs has been previously reported. We describe an antibody of similar specificity in the postpartum serum of an untransfused woman and the eluate from her fourth child's cord RBCs. The mother's RBCs typed S-s+U+, He+(weak), and appeared to have normal glycophorin A and B content, as deter- mined by immunoblotting. The direct antiglobulin test (DAT) and the autocontrol were negative. Her serum reacted stronger with S + RBCs only in the antiglobulin phase, and failed to react with U- or ficin-treated RBCs. The antibody was adsorbed completely by S-s+U+ RBCs, proving that anti-S was not present. Monocyte monolayer assay results with S+s-U+ and S-s+U+ RBCs indicated that transfusion of incompatible blood would not result in significant hemolysis. The child's cord RBCs typed S-s+. The DAT was 3+ with anti-IgG, and an eluate prepared from these RBCs had the same reactivity as the maternal serum. The child showed no clinical signs of hemolytic disease of the newborn. In contrast to previous reports, these results suggest an immune form of anti-Uz.